Introduction to Java for Beginners

1. Introduction: Java is one of the easiest programming languages to learn, making it perfect for beginners. In this course, I'm going to walk you through programming and Java step-by-step. By the end of this course, you will create to a real programs using Java. And you'll have a solid understanding of programming basics and fundamentals. Oven programming in Java since 2011. And I even use Java to create my own game servers startup into this and 14, I made a full-time income from his project for a few years before selling it. So I have a lot of experience using Java and I'm looking forward to sharing my knowledge with you throughout this course. 2. Installing IntelliJ: Before we can learn Java, we need a place where we can actually write and run our code. This is known as an IDE, which stands for Integrated Development Environment. That's a super fancy way of saying it is a text editor that will also convert your code into an actual program. Now the industry standard for IDEs and Java is going to be called intelligence. So you can simply just Google intelligent download. This is a free software. Go ahead and click on the top link right here, and make sure that you select Community Edition. And they also select the correct operating system that you're on. I'm on Windows, which is the default. So I'm going to stay here on the Windows tab. I can then click on Download. And your download should start. And on most browsers who will have to agree that you wanted to download this file. Once it's done downloading, you can click on it right here. Here we have the actual installer. This is a pretty standard installer. Well, you just click Next around 800 times and then you should be good to go. I'm just going to go through and keep everything here, the default. And then I'm going to go ahead and pause the recording while the installation is happening. After us uninstalling, we can go ahead and click on this checkbox right here, and then finally click on Finish. Once you open it, you should be sent to a page similar to this one. You're going to want to click on New Project. Now on this page you want to make sure you selected Java at the top. That should be the default. And for the project SDK, we can go ahead and select whatever the default is. But if you don't see a default, you can download a JDK. So we can click on this and you can select the version you want. Any version should do. We're not going to be doing anything. That's very version dependent process course. Just simply click on download. Now assuming you already have an SDK, we can just simply click on next and then next again. And then finally we can give a path to our project and a name. We can click on the three dots here to browse. I'm going to select my Java folder right here, and I'm going to create a new folder. This one will be called a workspace. Within here. I'm just going to select it and then click on Okay. Now the project name by default is workspace. That's fine. I'm going to go ahead and click on Finish. Now intelligent is finally open. On the left here we have this project which we can toggle by clicking. This is going to show all the files and folders within our workspace. Now, everywhere else in this giant panel right here is where our code will be shown. But we don't have any code open right now. But now that intelligence is successfully installed, we're good to go and start writing some code with the next video. 3. Hello World: We're now ready to finally work on our very first Java program. And it is a common practice to simply print the text hello world to the screen as your very first program, no matter which language or learning will continue that here, navigate over to the source folder. And here we need to make a new folder inside of it. You can right-click, go to New and select package. A package is basically just a folder. And a Java programmer uses packages, a way to organize all of your code files. You can have multiple code files inside of packages and you could have multiple packages within your project. For now, we're just going to work with in one package. So go ahead and left-click here. We now need to enter in a package name, and this needs to be unique. Now a common practice is to use a reversed domain. For example, com.google.com.YouTube. But obviously, this shouldn't be one of the popular domains, but rather your own domain. And if we don't own a domain, don't worry, you don't need to. You can technically enter anything you want. But for example, to follow with the standard naming conventions, Let's do something like com dot alex dot Flores or something else like that. Obviously this has my name and you could use your own name if you want or something completely made-up. I'm going to name this package the exact domain that I own. So for example, com dot worn off keys. Now if I press Enter, we see this folder has been created right here. Now within here I can create my own file, so I can right-click, go to a new Java class. And here we have a couple of different options. We're going to stick with a standard class. I'll explain the difference between all of these in future videos. The class name I'm going to call this Hello World with a capital H and a capital W and no spaces. It's very important that none of these files have spaces in their names. Once you press Enter, you'll have a few pieces of code written right here. If you expand this folder, you now see the hello world-class right here. Now the details of what each of these things do will be covered in a future video. For now, we're just going to add onto this existing code. Now if you click onto this opening curly brace right here, you can press Enter and you can tell that we're automatically tabbed. And once now tabbing, it's very important within any programming language because it makes your code much easier to read. And the benefit of that becomes much more apparent later on once we have much larger files. But for now, we don't have to worry about large files. Our goal right now is just to print the text hello world to the screen. I'm now gonna write some code. Go ahead and follow along with me and throw those course. We're going to understand what each part of this code does. But most of this is not going to be explained right now. To start off, I can say public, static, void, main, and then parentheses and ending parentheses should automatically be generated. And then afterwards we can put a space and then a curly brace, and similar to the parentheses and ending curly brace will automatically be generated. Now in-between the two curly braces, if you press Enter or C, There were also tabbed end once more. We need to go back into the parentheses and type string with a capital S space. Then a square bracket and an ending square bracket will be added. And then we can type in arcs. Now we just wrote a lot of code and most of it looks very confusing to you. Don't worry about that at all. As long as your code looks like this and there's not any red squiggly lines anywhere, then you're good to go. And my red squiggly lines, I made something like this. Here we see this red squiggly line right here. This is intelligence for letting us know that there is an error in our code. We hover over it. It's going to say that a ending parenthesis as expected. So I can add one in here, and then that error goes away. Again if you're confused right now, don't worry, everything will be explained as we continue throughout the course. The next step will be explained her right now though, our goal is to print something to the console. We can do this by typing system with a capital S, dot out, dot print LN. We can add an a parenthesis and an ending parentheses will automatically be added. Within here we can add in a double quote and similar to everything else, and ending double quote will be added. Now we have an error at the end here. If I hover over this, we see a semicolon is expected. I can add one and here, similar to a period with an English sentence is semicolon ends a statement or a Java sentence. At the end of most lines, you're going to add in a semicolon. And you might have noticed that we don't have a semicolon right here on line six or seven. The reason for that will be explained later on. But generally, most of the lines of code you're gonna write should have a semicolon at the end. Now within these double-quotes here, we can add in whatever text we want. And as we printed to the console, for example, I can add in Helloworld. Then from here I can go to Run at the top, because then click on Run right here. Alternatively, you can use a shortcut displayed here. We get this pop up right here. We wanted to click on Hello world. And now we see that it's building. Now we can just pop up right here. I'm going to go ahead and lower this height just so I have more room to work with the code. But we do see the text Hello world, and that the process finished with an exit code of 0. An executive's 0 basically means that everything went well and there were no problems. Now if we wanted to, we can add in different exclamation points within the string. And instead of going through all these drop-downs here, we can actually just click on this green arrow near the top right. Or you can press Shift plus F2, whichever one you prefer. If I click on this, we now see it's going to rebuild our project. And we now see Hello World with exclamation points. Afterwards. You've now completed your very first Java program. I know a lot of this code looks very confusing right now, but everything will be explained as we go on further course. 4. Comments: When programming, we can't just write anything we want because this isn't valid Java code. And so if I hover over these, these are going to say that there's going to be errors related with this code. But sometimes you may want to add in different notes or was properly known as comments into your code. This will help you or co-workers better understand what is happening within the code. For example, I can do two forward slashes here, and then I can say print hello world to the console. Now in this exact example, we probably do not want to add an a comment for this line because the line is fairly self-explanatory anyway. But this is how you properly add in a comment. This wouldn't have any effect on the program or what's printed to the console. It is just there as a note for other programmers and yourself. Now as we move forward through this course, you're going to see what should and shouldn't have a comment attached to it. Again, a line like this is very self-explanatory, so we do not need to add in any comments. Now, alternatively, we can add in multi-line comments by doing forward slash star. And then an ending star forward slash and intelligent actually does the ending for us. Within here I can say this is a comment. All of this text here is grayed out because it is not technically code, but rather it is a comment. 5. Variables: We're now going to talk about arguably one of the most important concepts when it comes to programming. And that is the concept of variables. Like you think of a variable as basically a container that holds some kind of value. Your computer's RAM or memory is basically a bunch of shelves that hold these containers. Now, each container is going to have a name and the value inside can be read or changed at any time. So for example, let's create an integer which is basically just a whole number. I can say int space. And now we have to name our variable. This should be something that is descriptive. We should not have variables named a or X or things like that that aren't very descriptive. So in this case, I want this to hold my current age. So I'm going to type age. So I'm naming this variable age. You can name it basically anything you want. But there are some rules which I'll go over later in this video. Afterwards we're going to add an equal sign. And then after the equals sign, we can add in any number. In this case it will be 28. And then finally, we have to add in a semicolon what is actually happening here? Well, the int is basically going to tell Java that we want to create a variable, and this is going to hold an integer type of value. There are different values of variables can hold and we'll cover those later on in the video. Now, every variable needs his own name. In this case, we give it the name of age. Afterwards we have an equal sign, which is technically known as an assignment operator. This will take the value on the right and assign it to the variable on the left. And then of course we have the age and you can add in whatever number you want here. It could be 999, it could be 0, it could be negative 5 thousand. Any whole number will work. But for simplicity, I'm just going to add in my current age, which is 28. So what can we actually do with this variable? Well, the most basic thing we can do is probably to print it out to the console. Instead of writing out system.out.print line each time, intelligence actually gives us a shortcut because that is a rather long line of code to write. So I can type in S0 UT for system out. If I press Enter, it will automatically generate this line of code for us. Now it does not generate the double-quotes and that's intentional. If I were to add in the double-quotes and then age at which we run this program, we simply see the word age and our console. But that's not what we want. We want to see the value inside the age variable. We have to remove these double-quotes, so it will not display what's known as a string. A string is basically like a sentence or a collection of characters, something that makes up some actual texts. Now without the quotes, it's going to try and reference the value inside of the age variable. In this case, it will reach into that container I mentioned before, and it'll pull out the value of 28 and then send that to the costumer. Far bind us again. We should now see 28 in the console like we do right here. That's one example of what we can do with variables. We can also reassign a value. For example, let's say I have a birthday, I could say age equals 29 with a semicolon. Notice how I do not use the int right here. When I do that, there's an error. If I hover over it, it says variable age has already been defined. So basically the int is only there when we're creating the variable. But after it's created, we can still change this value by reassigning a value just like this. Now to prove this, I can print this to the console. So OUT, I could print out age. And if I run this, we now see 28 and also 29300. So an integer is just a whole number, but there are various other types of variables. For example, if I delete all of this, I can now say string with a capital S name equals Alex. And notice how I'm rapidness inside of double quotes. If I were to just say Alex here, it would think that we're looking for a variable with that name, but there are none. So to tell Java that we're working with a string of characters such as a sentence or a message, some type of text. Then we're going to add in our double-quotes. Java will not look for a variable named Alex, but rather we'll treat this as a string of text. Now of course we can put this to the console. I can print out name. And if I run this, we will see Alex in the console. But there are many other variable types. For example, we have a Boolean. Boolean Jeff represents either a true or false value. That's all it does. So for example here, I can say is programming equals true. Now true is not in quotes because that is technically not a string. True or false, which is the only other option for a boolean, are technically keywords in Java. We're able to just write them within our code. For example, if this is true, I can now print is programming. Now if I run this, we should see true in the console. Of course, just like integers, we can reassign value studies. So I can say is programming equals false. And if I run this, we're now going to see False within the console. Now I'm going to delete this line here. And you might notice how I named his programming. I have a lowercase I and a capital P. Within variable names, we cannot have spaces. So whenever we have multiple words, it is a common practice to use something known as CamelCase notation. Camel case notation is when a word is written with the very first capital letter being lowercase instead. But then every word after that has an uppercase letter at the start. This makes it very easy to read without any spaces. Compare that to camel case notation. This is obviously a lot harder to read, especially for other people who are just reading your code and didn't write it. So they don't know exactly what it is. Other rules involved that variables cannot have a name that's hard for the number. Typically, you shouldn't do this anyway, so that's not very descriptive. But if for some reason you absolutely want to, you can add it in an underscore to start. It then becomes a valid variable name. As we move forward throughout the course, you'll see more examples of variable names so we can get a better idea of what is a good naming convention. Now let's move onto other variable types. Next we have a char, which is similar to a string, but it represents only one single character. For example, I can say letter equals a. And these use single quotes, not double-quotes. If I was to add in multiple characters here, it's not going to like it and it's going to complain. So again, these only use a single characters. We also have a double, which is similar to an integer, but of course this is going to be any number. It doesn't just have to be a whole number. For example, age equals 28.5. This would be a valid double, but I'm using the same name as an existing variable. So I'm going to say age as double. That is another rule for naming is that every name has to be unique. Otherwise it wouldn't know which variable you were exactly referencing. 6. User Input: So far we've just printed things to the console. But what if we wanted to receive input from the users who are using your program? In this case, it would just be us. But what if we want to enter certain numbers or names or other things like that and have it actually be understood within our DAW program. Now in order to do this, this is going to be a couple of concepts. There'll be slightly confusing and very much out of the scope of this video here. These are concepts that will be explained later on in the course, but they're far too complicated to explain right now. So go ahead and code along with me and be aware that these will be explained later on. So let's start off by making something known as a scanner. This is what is used to receive input within our console. So I can say scanner with a capital S, I press Enter. We're now going to import scanner. This is something that comes built-in with Java, but in order to use it within this file, we have to import all of that code into this file. That's what this line right here does. Now that we've created a scanner similar to the variables we looked at in the last video. We have to give this a name. I'm going to call this input. Then we can use an assignment operator or an equal sign to assign a new value to this. Now, this is going to be something that will be explained in much more detail later on in the course. But for now, just go ahead and code along. Here. I'm gonna say new space scanner with a capital S and then parentheses afterwards. Now I get this error here. When I hover over this, it says cannot resolve constructor Scanner. Again, the concept of a constructor and why this error is occurring, it will be covered in a future video. But for now, let's let go inside the parentheses unless add in a system with a capital S dot n. This should get rid of the error. Now we're ready to start receiving input from the console. Let's start off with a simple string. For example, I can say string name equals input dot next. And this is going to return a string by default. Then I can print out the names of the console. So OUT and name. And let's make sure the user knows what to do. I can say S OUT, then I can enter in. Please enter your name. Now if I run this, we're going to see please anterior name, but it doesn't immediately close like a data and other situations here is actually waiting for us to enter our name. In this case, I'll add an Alex, and if I press enter, it will then print Alex. And here's where it says a process finished. The green texts will be the texts that I entered and the white text will be coming from a Java program itself. Now if I run this again, I added my full name. For example, Alexander space Flores. If I run this, we now just see Alexander. That's because the next function here is going to count every single character up until a certain whitespace. So if there's a space or a tab or a new line and things like that are going to make it. So it'll just stop looking for new characters and just return what his found so far. If we wanted to get the full line, we can say next line. Similar to variables, this is going to use CamelCase notation, meaning that we have a lowercase n because it's the first letter of the first word. But the first letter of every other word. For example, L, is going to be uppercase. If I run this, I can now enter my full name with a space, so Alexander space for us. And if I press Enter, we see the full string has been printed back to us. Now we don't just have to do strings. For example, I can say please enter your age. Then here I can say int age equals input dot next. And here we see a bunch of other options. In this case, we want next int because that's our variable type, which is an int. Then I can use S0 UT. I could print out age without any quotes. And if I run this, it's then going to ask us for our age. In this case, I'll enter 28. Then it'll print 28 back to us. 7. Arithmetic Operators: Oftentimes when we have numbers, we don't just want to print them out to the console. We might want to add, subtract, multiply, or divide with those numbers. For example, I can say int number equals 50. Let's go ahead and start off by printing this to the console. Just we can always see what's happening. Now I'm not going to run this because it's very obvious what would happen. But let's say we want to add one to this number. A couple of different ways to do it. One example will be number equals number plus one. Now if I run this, you're probably going to know what's going to be printed. In this case it'll be 51. We can add ten or a 100 or any other type of value. What we want to this intruder. Now there is a shorter way to do this. So I'm going to use control forward slash to go ahead and comment out the current line. And then I'm going to say number plus equal to 100. This is basically the same exact thing as what we have right here, is just a shorter way to add a number onto a variable. So if I run this, we're going to see 150 in the console. We can do the same exact concept when it comes to subtraction. Instead of plus, I have minus. And if I run this, we're going to see negative 50 in the console. Of course we have multiplication. So if I run this, here we see 5 thousand and division, which has a forward slash. If I run this, we're going to see 0. Now the 0 here is because we're using integers which are whole numbers. If I were to change this int to a double, which allows decimal points, and I were to run this. We now see 0.5. And of course all these symbols can be used on this original syntax. For example, we can say divide it by 100 times 100. Anything like that will still work. Now you might be wondering, why would anyone who uses this type of syntax if this is just shorter? The main reason for using this type of syntax here is because if you have multiple variables, then this was the only way to do things. For example, I can say int number two equals ten. Then I can say number equals number two times 100. We cannot do that with this type of syntax here, because this type of syntax is going to only modify the variable mentioned in this case, that will be number. Now I'm going to delete most of the stuff and I'm going to create another integer called number equal to five. Now let's say we want to add or subtract one from this variable with what we just saw, we could do number plus equal to one. If I ran this, of course it's sort of work. We would see six in the console. But increasing and decreasing a number by one is so common that most programming languages, including Java, have a way to do this, an even shorter syntax. This is known as incrementing and decrementing a value. So I can say number plus, plus. If I save this, we're still going to see six in the console. This is going to increase the number by one. We could also do number minus minus. If I run this, we're going to see four in the console because we're subtracting from the original number, which in this case is five. Now the pluses and minuses can go on either assigned to the variable, and they do a slightly different things. In this use case, if I were to run it, we're going to see no actual change. And we're still going to see six in the console. But that's only because of how our code is written here. Having the pluses before or after will be much more clear on the difference. If I add the pluses directly on the variable right here, if I run this brush still going to see six in the console. That's because the pluses before the variable name, first going to increment the variable and then use it. Using, in this case, we passing it in to the print line function, basically printing it to the console. But if I were to add pluses afterwards, that means we're first going to use the variable and then increase it. If I were to run this, we're going to see five in the console. But technically in the memory of our program, number still holds the value six. We just didn't print it. To prove this, I can print this out again. Check our print out number. And if I run this, we're then going to see 56. The same exact concept applies when it comes to minus, minus. If I go to run this, we're going to see five and then four. Now of course, if I do minus, minus before, we're then going to see 44. That's because we are first decrease in the number and then using it. Then of course we're just printing out the results again. As we move forward to the course, you're going to see a number of different ways and instances where this is going to be useful to use. Especially when it comes to our first project, which will be around halfway through the course. 8. If Else If Else: We're now about to dive into a very important concept known as control flow. Control flow is basically where we get to control the flow of the program who would've guessed. And this is most commonly done with something known as IF statements. Basically, if something equals something, then we're going to run a certain piece of code. Otherwise, we might not think of a favorite shooting game. If you press the Reload button, it's going to check if you have a full Magdalena. Not If you do is not go into reload. But if you don't have a full magazine, it will then reload. Let's start off by creating some user input, striking create a scanner. I'm going to call this input. I'm going to assign the value of new scanner passing in system dot n. Now that we have access to this input object, we can actually read input from the user. So I'm going to say int number equals input dot next int. Now I'm going to just simply print this out to make sure everything is working. All right, Mike, and run this with shift and FTN. Here it's expecting me to enter a number. I'm going to enter 50 and then we get 50 printed back. Everything is working fine. But instead of just printing out the number, I'm going to use an if statement. The syntax for an if statement would be if parenthesis, and then a curly brace and an ending curly brace on the next line. Now inside the parentheses is where our condition goes. And this condition is going to be typically comparing the two. Thanks. For example, I can say number two equals signs, 52 equals signs is very important because a single equal sign, as I mentioned before, is an assignment operator. This will take the value on the right and assign it to the variable on the left. But two equal signs is a comparison. This is going to see if the value on the left, he calls the value on the right. I'm going to add in a comment here it says comparison. Now, what happens if these two things are equal? Well, this will basically become a Boolean expression. And if you remember before, a Boolean equals either true or false, there's no other values of Boolean can use an IF statements and inhabit conditional like this is basically going to look for a Boolean value. Hypothetically, let me comment this out and let me just enter in the number 50. Now in this case, our text editor gives us this yellow warning by hover over it. It says condition number equals 50 is always true. Now, obviously that's the case because our value right here is 50 and that's never changing. Now, the important part here is that it is always true, which is a Boolean value. So this is basically the same thing as saying if true. Now if this is the case, then the code inside these curly braces will always be ran. If this was false and the code inside the curly braces will never be ran. The condition inside the parentheses must be a true condition. I'm going to use Control Z to backspace up until here where we're actually receiving user input. And within here I'm going to simply print to the console saying the number is 50. Now I'm gonna get rid of some of these comments here, just to make our code a little cleaner. I'm gonna try running us with shift and F2. And here it's expected me to enter a number. If I enter 50, going to say the numbers 50. And if I run this again, I enter anything else. For example, 99. It's not going to print anything because this condition is false. Therefore, the code inside will not run. But what if we wanted to check other numbers? Will in theory, we could just add a bunch of if statements. For example, a number exactly equal to 51. But what if we only want one thing to be printed to the console? Now every time we create an if statement, this is going to create something known as an if statement chain. An if statement chain. This is going to contain up to three different types of statements. We have our if statements, we have our else-if statements, and we have our else-if statements. Let's take a look at else-if statements. If I get rid of this if statement here, I could then say else, if number is exactly equal to 51, I can then print out the number is 51. Now an else-if statement has to be directly after an if statement. These will basically look at all previous if and else-if statements. And if they're all false, then it will go ahead and try and compare these two values. In this case, IF statement online 16, it's going to compare number 50. If that is true, we're then going to run this code. And then we're going to jump down to right here. We're not going to actually even try and compare the number of 251 because the else-if statement sees that the if statement was true. It sees that there is no point to even check the two values. But if we entered a different number, for example 51, this condition is now false. The else-if statement, we'll see that will then try and compare these two values. In this case, the two values are the same. So this code we ran, but if I enter 52, nothing here will be ramp. To prove this, I can run our program. I can enter 50. Here we see the numbers 50, foreign run it again. I can enter a 51, and here we see the number is 51. Finally, I can run it and I can enter 52 and nothing happens. Now for each IF statement chain, for example, this right here, we can have only one if statement, but as many else-if statements as we want. For example, I can say else if number is exactly equal to 52, I could then print out the number is 52. And to make things a little more interesting, I can say else f-number is exactly equal to 52. Again, I couldn't print out test just to make sure that this print statement is very different than the others. So if I run this, I enter 52 in the console. We now see the number is for the two, but we do not see text. That's because this condition here was true. Therefore, this else-if statement is not going to even bother comparing these two values and will certainly not print out anything within the curly braces. Now of course, our IDE is complaining because these two things should not actually be here. This statement here will actually never be ran no matter what. Because if the number is 52, then this code right here on line 21, we ran instead, because our condition online 20 will be true. I'm going to remove this. And the final thing I wanted to show you is the else statement. This has to be at the very end of an if statement chain. This is basically just a catch-all. If nothing else in the if statement chain was true, for example, I can print out unknown number and I can run this. And if I enter 5352, we know what's going to happen. But what happens if I enter 53? It says unknown number because all three of these if statements right here or false, therefore the else statement we ran. But if I were to run this and I want to enter 52, then it says the number is for the two. And the else statement is not ran because it sees or one of the previous f or else-if statements were true. Basically the program is going to go through all of these and try and find the first true statements and ignore all the rest. 9. Switch Statements: In the last video, we had a look at if statements, but that is just one example of control-flow. Another example is going to be something known as a switch statement. Now this is less commonly used as if statements, but you will see it from time to time. So it's important to understand how it works. I can simply say switch parentheses and then curly braces afterwards. Now antibodies parentheses is going to be a value, not necessarily a condition, but any type of value. For example, in this case a number. Now inside, we're basically going to have something known as case statements, which are kind of like if statements. I can say case 50 with a colon. If I press Enter, I could then add in the number is 50. Then I have to add in something known as a break statement. I'm gonna go ahead and run this with Shift F2. Within here, I can enter the number 50, that's going to say the numbers 50. Now if I run this again, I enter anything else. For example, 51. Nothing's actually going to happen because obviously we're not handling 51 anywhere. This is different than an if statement and it had its own use cases. It actually most commonly used for my experience when comparing strings, but you can use it instead of if statements if we really wanted to. But there's more to this. For example, I can add in more cases. So case 51, I can add in. The number is 51 and I can break. Now of course, if I run this and add in 51, it will just say that. But what happens if I want to check for two different numbers? Well, I can also say case of 52. And then the print statement will say the number is 51 or 52. Now if I run this, I can then go ahead and enter in 52. It says the number is 51 or 52. Of course we'll get the same output if I enter the number to one. Now the ability to check two different values with an if statement will be explained in a few videos in the course. It's much easier to explain that with switch statements. So that's why I'm covering it here. One thing to keep in mind, it has basically if any of the cases are true, the code will continue to run until a break statement is found. For example, I can change this to the number is 52. Then I can print out the number is 51 right here. Notice how we do not have a break statement after this print statement right here. This right here is the only breaks him when we have four hundred fifty one and fifty two. So if I run this and I inherit 51, what's going to happen is it will continue to run the code until it finds a break statement. We see the number is 51. It doesn't care if there's a case here. It's just going to ignore that. And it's going to run this line right here, the number for the two, and then we're gonna break. Now one last thing for switch statements is going to be default, which is something that typically goes at the very end. And this is kind of like the else statement for if statements. Here I can print out unknown number. And technically you don't need a break statement even though a lot will argue it is proper syntax. But the code work just fine even without a break statement, because of course, the default should be the very last case that your check within your switch statement. If I go ahead and run this and I enter any other number, for example, negative 500. We then see unknown number. Switch statements are fairly simple and they can be used instead of if statements and some use cases. But typically you're just going to be using if statements. 10. Comparison Operators: We're now going to jump back to if statements and take a look at comparison operators. These are different ways that we can compare two values. Previously, we had to look at double equal sign, which will just simply check the value on the left and compare it to the value on the right. But there are many more operators we can use within Java or pretty much any programming language. For example, we have a greater than sign. There were less than sign. We have greater than or equal to and we have less than or equal to. And we also have a not equal to. Now most of these are very self-explanatory. But let's take a look at some examples. Like I say, if number is not equal to 50, I can then print out the number his not 50. And if I run this and I enter 50, of course we're not going to see anything because the number does equal 50. Therefore, this condition right here is false. But if I run this again and I enter anything else, For example, one, we see that the number is not 50 because of course, one is the same thing as 50. Now let's try some other things. For example, I can say number is greater than 50. I can also the number is greater than 50. And if I run this, I can now enter whatever number I want, for example, 900. And it'll say that the number is greater than 50. But if I enter anything less than or equal to 50, then nothing's going to happen. The equal to part is important because 50 is not greater than 50. It's equal to it. If I enter 50, nothing's gonna be printed. If I wanted that functionality, I can say greater than or equal to 50. If I run this and I enter 50, of course, we're now going to see the number is greater than 50. But that's just because I did not update this text. But the important part here is that number is now a greater than or equal to 50. And of course, the less sign operators will work the exact same way. I'm sure you can imagine how those will work and we can use these to have more complicated expressions within our if statements to then have a more complex and more meaningful programs. 11. Logical Operator: Let's have a look at logical operators. These are other ways to add in more complicated checks within our if statements. So a few examples of this will be the NOT operator. This will also be the logical AND operator. And the logical OR operator, which is by holding Shift and pressing the key above, enter. The NOT operator is going to basically just reverse a value. The AND operator will basically make sure that thing to the left and the things on the right are true. The or operator will make sure that thing to the left or to the right or both are true. Let's take a look at all of these with examples. I can say if number exactly equal to 50, number is exactly equal to 55, I can then print out 50 or 55. And if I run this, I can now enter 50 and we see 50 or 55 running this again, entering 55, we see the same thing. And of course, if I run this and I enter anything else, for example, 70, we don't see anything in the console. Basically, this wants to see that the left side of the or operator, or the right side, or both are true. And it might be obvious because this is the logical OR operator. Let me go ahead and add in what these stand for. The logical OR operator is going to be this or that, either one. Now the AND operator will make too much sense in this use case, because the number variable cannot hold a 5055 at the same time. Better example of the AND operator is when using greater than and less than. So for example, I could say number is greater than or equal to 50 and number is less than or equal to 55. So anything from 50 to 55 should be included. I'm going to change this to 5255. And if I run this, I can now enter 52. And we see that this is true. Essentially if the number is greater than or 50 and the number is less than or 55 than the entire if statement will be true. If either of these two expressions are false, then the if statement will be false. For example, if I run this one more time and I enter 56, nothing's going to actually happen. While this part right here is true, because 56 is greater than or equal to 50. It is false right here, because for the six is not less than or equal to 55. And the and operator requires both a left and the right to be true. Now let's take a look at a NOT operator, which is basically just going to reverse a Boolean expression with an if statements, we can actually pair certain conditions together. For example, I can wrap a parentheses around this entire thing. And if I were to run this, the same thing would happen. But now we can use a NOT operator or beforehand. This entire expression will be either true or false depending on whether the value of number is the NOT operator is simply going to reverse that. So I'm going to say not 5255. If I run this, I could then enter 52. Nothing happens. But if I run this again and I enter anything that is not between 5055, for example, all 34, we see not 5255. The NOT operator is going to simply just reverse a Boolean expression. And throughout the course we're gonna see more use cases of the not operator and the other two operators as well. And how useful they can be. 12. While Loops: We're now going to look at the most simple example of a loop. And this is a way to make certain pieces of code continue to run again and again as long as we want them to run. So there's a few different types of loops. But in this video we're gonna take a look at the while loop. So we can say While parenthesis and then curly braces. And inside this condition is going to be a Boolean expression. This is going to be either true or false for if this loop should continue to run. For example, I can make an integer called counter and set this equal to 0. I could then say, while the counter is less than ten, I can then go inside of the while loop and everything inside the curly braces will be ran as long as this condition right here is true. Now currently this would be known as an infinite loop because counter is never changing. It's always 0. So counter lift and tin is always true. We want to make sure that we actually changed the state of counter, where it being ten or greater is a possibility. That way we don't get stuck in a sleep forever. Do that. I'm going to first print out what counter is, like. I say counter, colon space. And then outside of the string, I could do plus counter. This will add on the contents of the counter variable onto the overall string that has been passed in to the print line function. Now afterwards I can say counter plus plus. Or if I really wanted to, I could put this right here. As we learned before, putting the plus, plus to the left of the variable name will first increase it and then you use it. Using, in this case, we printing it to the console. So before run this, let's go over what I just did. I created an integer variable with a value of 0. And we're saying while that variable is less than ten, we're going to run all the code inside of these curly braces. Now this code simply just prints out counter. But before we actually print out counter, we're going to increase it by one. This means that our loop is no longer infinite because they first time this runs, it'll print one, then two, then three, and so on until it gets to ten, where counter less than tin would no longer be true. So we can then break out of our loop and continue with the rest of our program. Let's see this in action. I can do Shift F2. It should run our program. And if I expand this window, we now see counter one all the way through ten. This is a very simple example of a loop. Basically, while this is true, we're going to run all the code inside of the curly braces. 13. Do While Loops: Let's now take a look at the do while loop. This is similar to the while loop, but it's slightly less commonly used. The syntax with us will be due, then curly braces. And then at the ending curly brace we would say while with our parentheses and a semicolon. Now the condition is going to be put inside of this right here. Basically the concept here is we are going to run this block of code immediately, no matter what. Then afterwards it's basically just going to become a normal while loop. We're going to continue to run that block of code while this condition is true. But no matter what this block of code we ran at least once, that is different than a while loop, where this block hook code is only ran even the first time, only if the condition is true. Now a practical use case for this is receiving user input and making sure we get the correct type of input or a correct number. For example, I can say scanner input equals new scanner. I can pass in system dot n. And then here I'm going to say int number. I'm not going to assign a value to it. And that's something we can do with variables. We can create them, but you don't have to assign a value to them immediately. Now inside the do block of code right here, I'm going to say number equals input dot next int. Then I'm going to say while number is less than ten. So essentially what this code is going to do is we're first going to receive some input from the user. We're going to create a number which we're going to use later on. And then we're going to run this code. No matter what the walk condition is, it always runs once. So essentially we are going to receive input from the user, ideally a number. And then we're going to continue to run this as long as this condition right here is true. Therefore, we have to provide a number that is ten or more in order for it to actually receive valid input. Now, afterwards I'm going to print out the number. I'm going to run this with shift and FTN. Now inside of here, I can enter whatever I want. For example, five or seven. Anything less than ten will be completely ignored because the while loop will continue to make this block of code right here run over and over again until this condition is false. I can even enter negative 5 thousand, for example, and it's still going to continue to work. But as soon as I enter anything ten or greater, for example, 84, it's going to break out of that loop, and it's going to print 84 right here. 14. For Loops: Let's take a look at the most powerful loop, which is known as the for-loop. This is the best way to count things or to iterate over a list of certain elements. That might sound confusing, but over the course you'll see examples of that. For now, let's just simply try counting something. In previous example, I created a counter and then he used a while loop to go ahead and count over that. We can use a for-loop to achieve this and a much cleaner way. For example, I can say for parentheses, curly braces. And inside the parentheses there's going to be three different elements that are going to be separated by semicolons. The first one is going to be the initialization. This is where we can actually create variables that can be used with our loop. So I can say int counter equals 0. The second one is going to be a condition similar to a while or a do-while loop. This will be if the loop should continue to run. In this case, I'm going to say counter less than ten. Then afterwards, this last section is going to be code that we ran every single time the loop completes. In this case, we want to say plus plus counter. So each time we're going to increase counter by one. Now within here I'm simply just going to print counter to the console. And if I run this with shift and F2, we should see a count from 0 to nine, as we see right here. Still in the loop. First starts, it creates this variable only once. Then seats if this condition is true, if so, it didn't runs all the code within our curly braces here, simply just print 0 to the console as we see there. Then once it gets to the end, it realizes there's nothing left to do. So it goes to loop back. As it's doing that it increases counter here. That gnosis, that counter is now 11 is less than ten. So cute repeating the process until this condition is false, which we see right here. Because once it's nine and it increases to ten, the condition is no longer true. Therefore, we break out of the loop. 15. Break and Continue: Let's take a look at the break and the continue keywords with how to look at break within switch statements. And it works in a similar way here. But these are two key words that can be used within any of the loop types. For example, I can say int counter equals 0, while counter is less than ten. Now in here I'm first going to increase counter and then I'm going to print it to the console. But let's say that I went to skip the number five after I increase it. But before I print to the console, like I said, if counter is exactly equal to five, I can now continue and continuing or basically just skip everything else in a loop and just go back to the start of the loop. It will still check the condition. But everything passed this continuous statement here, well, basically be ignored in this case is just this line here. Essentially, once we hit this, we're just going to jump back up to the start and they continue looping normally from there, I'm going to press Shift and F2 to run the code. And here we see one through ten, but five is missing. We see 46 immediately afterwards. That is the continue keyword. It will automatically jump back to the start of the loop. Now let's take a look at the break keyword. Some of you might already guess what this is going to do. Essentially, instead of just jumping back to the start, if he's going to break out of the loop entirely. If I run this, we see one through four because once five is reached, it's immediately going to break and start running the code outside of the while loop. You can use these two keywords to have better control over your loops and what is executed and when to break out of them. And both these keywords here work on every loop in Java, including the three types we've seen so far. 16. Calculator Project: Let's put all the skills we've learned so far into US. Let's make our very first project. We're just going to be a simple calculator. Now, most of the things you've learned so far will be directly applied inside this project. What this project is designed to still be difficult if you're brand new to programming when you first started this course. If you run into any problems or you're struggling with this project that is expected and don't worry, There's three main things I wanted to do when it comes to this video. The first one is going to be going over a plan. When designing any program, even just a simple calculator, it's important to have a plan and an overall idea of what you want to do before you start writing code. The second thing is I want you to try on your own. So I'm going to show you step-by-step how I would make us. But before I do that, I want you to pause this video and try making it on your own after we go over a plan. While courses like this one help, the best way to get better at programming is right code. I highly encourage you to get as far as you possibly can on your own before you watch how I would implement this. Now the third thing is going to be, I will show you how I made this program. After we've designed our plan together and after you've tried to make this on your own, I'm going to show you how I would make this program. Let's start off with step one, going over a plan. What should this project do? And what do we need to do in order to achieve that? Well, the first thing is it should ask for two numbers. Then it should ask, or a math operation. This will be a plus, minus multiplication or division. So it'd be one of these four characters. Afterwards, we need to display the result and then loop back to the start of the program where we ask for numbers. This is a very, very basic plan when it comes to this project. Some of these things should be simple. Other things will require you to think, perhaps even going back to previous lessons. Again, try and pause this video right now and get as far as you possibly can on your own and then come back once you've completed a project or once your 100% stuck and you can't get any further. And I'll show you step-by-step how I would make this program. Hopefully you've already tried on your own. Now, let's go ahead and implement each one of these steps. But our plan here shows an important use of reading all the instructions. For example, here we see, we will loop back to the start of the program. That means that this entire program could be inside of a while loop. I can say while true. Now this will be an infinite loop that will run forever, which is fine for this use case. Now it's gonna say it should ask for two numbers. So I'm going to just start off by making a scanner calling inputs, setting this equal to a new scanner passing in system dot n. Then I'm going to print out enter the first number. Then I'm going to say int number one equals input dot next int. So far we've asked for one number. Let's basically do the same exact thing for the second number. I just print out enter the second number. And then we're going to have another integer, int number two equals input dot next int. So far at the very first step is done. We now have the two numbers. Now we should get a math operation. So plus minus star or four slash will be addition, subtraction, multiplication, or division. Next, let's tell the user what to do. I can say enter an operation. Then we're going to say what options there are. Plus, minus star and slash. Like I say, String Operation equals input dot next. So now we have access to both the numbers and the operation we want. Now using if statements for comparing two strings does not work correctly with everything I've taught you so far. With that said, we're going to be using switch statements here. I can say switch operation. I could then say case with a plus. I'm going to add in break and then I'm going to say case minus break. I'm just gonna go ahead and add in all four of these. We have case, star, break, case, forward slash break. Now in order to get a result in all of these, I need to create it outside of this curly brace. The details of why that is will be explained in a future video. So I'm going to create an integer called results. I won't assign a value yet. We're going to do that inside of our switch statement. So if they entered a plus, I'm then going to say results equals number one plus number two. Also make sure you spell a number of correctly. Then from minus, I'm going to say result equals number one minus number two. For multiplication, I can say result equals number one times number two. And then for division I can say result equals number one divided by number two. Now, outside of the switch statement, I can then print out the result, like I say, results space. And I can add on the results right here. Now here we're actually getting an error and our IDE by hover over this, it says variable results might not have been initialized. We can go ahead and click on initialize a variable. It's simply going to assign 0 right here. Even though we're going to override that value, it's still likes to see that we're going to have a default value because it doesn't know for sure if one of these four cases will be ran. Let's go ahead and run this and let's see what happens. If I press Shift and F2, it's going to say enter the first number. I'm going to enter five, enter the second number, three, and turn operation. I'm going to enter multiplication. The result is 15, and now it looks back into the first number. So for example, I could do 105 and then subtraction. And here we get five. So it's going to keep looping over and over again and keep asking for the first second number. And we can then do any type of operationally we want with those numbers. Now keep in mind that we are using integers here. So if you try to vision it is only going to give you a whole number of results. If you wanted a more accurate results, you can use double and instead of integer for the result variable. Now if you can put it this program on your own, then congratulations and good work. But if he needed to watch some of the extra video in order to do it, don't worry, that's perfectly fine, especially if you're new to programming, because this is a brand new skill. As he move on through the course, more things become more apparent to you and easier for you. It just takes time to learn all of these things. 17. Methods: This is where things start to get a little more complicated but also more fun. This next topic is about methods. Methods are basically just a block of code that are ran and their goal is to do one specific thing. In fact, we've been working in a Methodist entire time. This main method right here is ran by default whenever we run our own program. But we can create our own methods outside of the curly braces for the main function, I can say public, static, void, example, parentheses, and then curly braces. And in here we can write whatever code you want. For example, I can just simply print out hello world. Then in our main method, I can say example. And it'll automatically know we're trying to run this function. If I press Shift and F2, it should run our program. And here we see HelloWorld in the console. So a lot is happening here. And I also have mentioned methods, and it also have mentioned functions. And functions are practically the same thing, although there is a slight difference. Function is basically what we see right here. This is technically a function and so is this. But whenever a function is inside of a class, which I'll explain in a future video. These are now called methods, but in most cases it won't matter. They're interchangeable for the most part. But technically a function is outside of a class and a method is inside. Now again, we'll cover classes in more detail in the future for now, just think of them as a container will all of your methods can sit in. Adding these parentheses here will invoke or run or fire this function. These are all interchangeable terms basically of a way to run the function. Those are also common terminologies that are used when we're actually trying to run a function. Now you might be wondering why called the example method when we can just print Hello World in the main method. Well, that's because this is obviously an oversimplified example. In a real program, you may not want to just use this example function once. You might want to use this example function multiple times throughout your class or have been throughout your entire project. Having the ability to abstract certain pieces of functionality into their own methods makes it much easier to reuse that functionality. We'll see this in real examples as we move forward to the course. But now let's explain what these parentheses are and also what this void means right here. Basically a function can receive input and it can also return input. I'm going to get rid of these comments. And if I click on the example name and I press Shift and F6, I can now refactor or rename this entire function. I can say add. Now if I press Enter, it renames the function as well as the function invocation. Now inside of the parentheses, we can add in something known as parameters. For example, I can say int num one and int num2. These are separated by a comma. We can even have multiple types of variables. For example, string example. But in this case we're just adding two numbers. So there's no need to have a string here. Now, automatically intelligent gives us this red arrow here, saying that we cannot call it without any parameters. So we can pass in some information here, for example, 510, and now we no longer have any errors, but this code does not work as we expect it to. That's because we're still just simply printing Hello World. But what we wanted to do is we want to return the sum between num1 and num2. I can say return num1 plus num2. Now it gives us error here. If I hover over it, it says cannot return a value from a method with a void result type. This avoids right here, means nothing is going to be returned. We have to be very clear what type of data will be returned from each function. In this case, we're returning an integer because we're adding to introduce together. So we could change a void to int and the error goes away. Now over here I can say int sum equals add 510, and I can print out some. Now if I run this with Shift F ten, this'll print 15th to the console. Now if we wanted to, we could also just pass in this function call inside of the print line function. And in fact, print line has been its own built-in function that we've been using this entire time. It has its own parentheses and we're passing in information to it just like we are with this add function. And here's a perfect example of why we want to make functions. Because I can copy and paste this a couple of times. And I can now add in different values of I wanted to. This now gives us three different results of 1520 and negative three. And it's all because we have a simple add function right here. Now obviously this is a very simple function. But if we had more complicated functions with more code inside of them, you can see the benefits of having to only write the code once and then a running that from different places as many times as you want it. Now one last note is that these here are technically called parameters, but when they're passed in, such as right here, or these numbers directly, these are known as arguments. You have parameters and arguments. Just like functions or methods, these are often used interchangeably, but technically, what you write in the function itself is known as parameters. And what you pass into the function is known as arguments. But again, just like functions versus methods, they're often used interchangeably. 18. Method Overloading: In the previous video, we created a simple add function that returns the sum between two numbers. But what if we want to add strings together to create a sentence? For example, I can print out add hello and world. And obviously this doesn't work. But of course I could print out add 55 and this would work. Now, typically, you can only have one method with the same name, similar to variables, but we can do something known as method overloading. This basically means having multiple methods with the same name, but different parameters and different return types. For example, I can say public static string with a capital S, String s1 and S2. Now within here I can return s1 plus a space plus S2. Basically putting the two words together. Now we have a two methods that have the same name, but we have overloaded them where Java is now going to know which one to call depending on the parameters passed in. Online, five are passing and strings. So what's going to call a method here? Lines stick for passing an integers. So what's gonna call the method here? I can go ahead and run this holster the output. Here we see HelloWorld and ten. Method overloading is often useful in situations like this, where you have similar functionalities, but you want to pass in different types of variables. You can overload those methods, basically coning them and having different parameters and possibly a different return type if it makes sense to you. 19. Scope: Every time we create an opening curly brace, such as this one right here, It's creating something known as a scope. And the scope is going to limit what can and can't use certain variables. For example, I can say int counter equals 0. And then I'm going to create a while loop to increment this counter. While counter is less than ten. I can then say counter plus plus. Now we can access as counter perfectly fine, so I can print it right here and everything works as expected. But what happens if I create a second variable inside? For example, I say int example equals 15. And I were to print this out for whatever reason. Obviously it doesn't make too much sense, but this is just an example. Everything works so far. But what happens if I try and access example outside of the while loop scope? So I could try printing this out. I can add an example and we get an error here. If I hover over this, it says cannot resolve symbol example and it even has a solution here. Or I can click to bring the int example into the current scope. Note that example is created online 14 right here. But if I go to click on the solution, we are now creating the variable on line nine, which is inside the main function scope. This means everything inside the main function can use it, including the while loops own scope, because I is also inside of the main function. So it has changed our code to simply just reassigned example with the value of 15. But we're creating it outside of the while loop. Now, even with all this said, it's not a good idea to just simply blindly put all of your variables at the top of your function. For example, let's say that I am not printing out this variable here on line 20. In this case, the example variable has no need to be defined in the main scope. And instead, it could be just simply defined in the while loop scope. I could say int example. And then I can get rid of the variable creation right here. Typically, unless you have a good reason to, you should always define your variables as locally as possible. By that, I mean, right here, this is locally as possible because we are using the variable online 16. So it is going to your local to the scope right here. There's no need to define it outside in the main scope, because right now with this code, we're not using an anti, the main scope at all. We're just using it inside the while loop scope. 20. Ternary Operator: Sometimes you might want to write an if statement, but in a more condensed way, this is often the case whenever you want to have a single value or that you're assigning to a variable depending on a true or false statement, we can achieve this was something known as a ternary operator. This is basically going to be some type of condition followed by a question mark, then a true value, colon, and then a false value. Now this might seem confusing. So let's take a look at a real example. I'm going to create a Boolean called is member until this equal to true. This might be if you're paying for a membership somewhere and they offer a single onetime payment, they might give you a discount on that purchase. So for example, here I can say int price equals is member. Now again, this is our condition. A condition is just a Boolean expression. So a simple Boolean statement will work just fine. So question mark, and then we have our true value. In this case the price might be $10. But what's say that we want to charge a higher price for people who are not already members. So I can add any colon and then the price here could be at $40. Now I can go ahead and print out the price here. And I can run this with shift and FTN. Here we see ten in the console. But if I change is member to false and I run this, we are then going to see 40 in the console. The reason for this is now this condition here is false. So what's going to use this code here which was partly false value, anything after the colon is going to be used. If the condition is false, anything before the colon is going to be used if It's true. Now obviously we could do something similar to this. If I say int price equals 0, then I can say if is, remember, I can now say price equals ten, else price equals 40. And this will work in the exact same way. But a ternary operator really shines here whenever you're using very simple if statements where you want this to be on a single line of code. Because obviously writing this one line of code is much easier than writing all of these. 21. Arrays: Let's now talk about arrays, which are basically just a collection of variables. As an example, let's say I have a number of different student test scores. I can say int student one equals 96, int student two equals 49, student three equals 76, and so on and so on. Unless I have a bunch of these, well, I don't want to necessarily create a bunch of different variables. Instead, I can create one variable which is known as an array. This is basically going to be a collection or a list of a bunch of different variables. I have to first specify of variable that array is going to hold. Each array can only hold one, a single type. You cannot mix and match them. For example, you cannot have an integer with a string that all have to be the same exact type. So I can say int, opening and closing square brackets. This represents an array. I couldn't say student scores equals a new int width, the square brackets as well. This is going to create our own array. But whenever we're creating array without initial values, which I'll show you an example of here in a moment, we do have to specify how many different types of elements we want to make room for. In this case, I wanted to make room for three. And so now I have created in array that can hold up to the three integers to assign a specific value. I can say students scores, square brackets. And in here is where we specify something known as an index. This is basically just a counter for which exact slot we're going to use out of the three we are given. This starts counting at 0. So I can say students scores index of 0 equals 96. Students scores index of one equals 49. Students scores index of two equals 76. Now I'm going to go ahead and get rid of these three integers right up here. And now I want to print out each one of these to the console. So to do that, we can use a very similar syntax to this. So I can print out students scores index of 0. I'm going to go ahead and copy and paste this using Control C and Control V, or Command C, command V on a Mac. And now I can change these indexes to 12. Now I can run this with shift and FTN. Here we see all three numbers. But what happens if I try and access index three, which doesn't actually exist. In fact, we get this little warning right here. If I hover over this, it says array index is out of balance. If I go to run this, we're actually going to get an error in our console. And this is known as an exception. An exception is something will take a further look at in the future. But for now, just think of it as an error. The reason why we got this is because we're trying to access something that the array does not have room for. We only assigned space for three integers in this array, and we have used all three. Again, remember, it starts counting at 0. So the three spots we have our 012. Therefore, index three cannot exist. And it says trying to access something outside of the boundaries of this array. One more example I want to show you is how to create an integer by setting specific values when creating it. So instead of specifying three, we can delete this. And then after the square brackets, we're going to create our own curly braces. In here. We can add in any number of elements. We want Example ninety six, forty nine, and seventy six. And now we have these warnings here. If I hover over it, it says a variable is already assigned to this value. So essentially these three lines of code here are not necessarily whatsoever. By delete them and I run the program again, we're going to get the same exact output as you see right here. Now we can have arrays for any type of variables. For example, we can create an array of strings or an array of booleans, but this is a very simple example with integers. And one last thing I wanted to show you is how to access the length or the number of elements within an array. And one last thing I wanted to show you is how to access how many elements are, how many items are inside of an array? I can print this out. I'm going to access students scores dot here. We can access length. This is going to be an integer, and it's going to say how many elements are inside of this array. So I can go ahead and run this. Here we see the number three because there are three elements. If I added an extra one here, I can then run this one more time and we should see four as we do right here. Now of course we don't see the 100 printed to the console because we're not printing index three, which now exists thanks to this 100 right here. But we are only printing the initial zeros or to the 100 is on display to the console. 22. For Each Loops: In the previous video, we had a look at how to create arrays and also how to access each individual element. But what if we had a larger number of integers and we don't want to mainly print out each one. We can use a standard loop or something known as a for each loop to go ahead and loop through each element. Here, I will show you two examples. Here we have a standard for-loop. I'll also show you a new concept which is a for each loop. But first we have a standard for-loop, like I say, for parentheses, curly braces. And inside I'm first going to create my own integer int counter equals 0. While the counter is less than students scores dot length. We can then increase counter. And then in here I can certainly print out students scores index of counter. We can pass in variables as an index here. And this will access index 0, then 12, and so on until we loop through every single element of this array. To prove this, I can run this with shift and F11. Here we see all four numbers in our console. Now looping through arrays is so common that they made a shorter syntax. I'm going to comment out these three lines. Here. I'm going to use something known as a for-each loop. I can say for int number, colon, then the name of our array. In this case a student scores. Within here the number of variable is going to hold each individual element as it loops through them. So the first iteration of this loop, the number variable will hold the value 96. The next time it loops through, it'll hold 49 and so on. To prove this, I can print out number and I can run this with shift and FTN. And here we see the same exact output. Now, typically a foreach loop will work, but in some use cases you might need access to the index that you're using. For example, this counter variable right here. This situations, you can simply just use a standard for-loop. But again, in most situations the for each loop will be just fine. 23. Multi Dimensional Arrays: In previous videos we've had a look at simple arrays, but now let's take a look at multidimensional arrays. Basically a Raisa have arrays as values. Here I'm going to create an array that has an array of scores. For example, I can say int two brackets here, scores equals curly braces. And within here is going to expect another array of values. But to define these arrays, we're just going to be using the curly braces. For example, we have our curly braces with ninety, six, forty, five, and eighty. Now to make this easier to understand listed at now, to make this easier to understand what this is going to be for Test1. We then have test2, which has different scores, let's say 8666 and then 90. How do we want to loop through each individual element? We first have to loop through each individual array, where the value then becomes each individual array here. So we can use a standard for-loop as well as a for each loop. I'll show you an example of both. For the standard for-loop, I guess it for int counter equals 0, while counter is less than scores dot length, I can then increase counter. Now within here, we need something known as a nested for-loop. Where does, where we have a loop inside of a loop? I can say for int counter to equal 0, while counter two is less than scores, index of counter dot length plus plus counter to what is happening here. Basically, we're doing a standard for-loop, which I'm sure you understand already. But then we have a nested for-loop. I'm creating a second counter variable and I'm using it everywhere aside from right here. Basically what's going to happen is we're looping through each individual array. And this is what we're going to have access to on the first for-loop. Index 0 of the first for-loop will be this entire array index one, or the second iteration as it loops through again, will be this entire array. But now we're going to access each individual element inside scores index of counter at first is going to access to this array right here. We're accessing the length property from the first array. And then as the initial for-loop loop's again, we're going to get access to the second array because counter with an equal one. Again, remember this is index 0. Index one. The indexes start counting at 0. So to access each individual value I can print out. First, I will print out test plus, I'll add in parentheses and I can say counter plus one. The reason for this is because counter starts at 0 and we want to say test1, test2 and not test 0, test one. We're simply going to add one to the counter. But this has not going to modify the counter-variable at all because we're essentially taking the value of counter and then adding one. But we're not assigning that to the counter-variable. Afterwards, we're going to add in each individual score. For example, scores index of counter, and then a second bracket, index of counter to stop. I run this with shift and F2. We now see test1 is 9825 and test two is eighty six, sixty six and ninety. Just to simplify things a little bit, if I get rid of these parentheses and I run this, we basically get the same exact thing except this counter here is going to show index 0 as we're looping through the very first array, and index1 as we're looping through the second array. The only reason why I added plus one here is to make it more human-readable. Now, as you can tell, this code is a little confusing. And typically you're not going to working with multi-dimensional arrays that often, Ideally there are better solutions to handle your data, especially if your data needs three or more dimensions of arrays, there's usually always going to be a better solution than using that many nested arrays. But just to be complete here, I'm gonna go ahead and show you how to loop through a nested array or a multi-dimensional array rather, with a, for each loop, I say for int array, I can call this array one colon scores. This is going to loop through each individual array. Now within here we have access to each array. So for the first iteration of that, for each loop, we're going to gain access to this value. And then the next iteration we're going to get access to this value. We can use a standard for each loop on this array. For number, colon array one. Now within here we can print out number. Now I can run this with shift and F2. And here we see all six individual numbers. This is a good example, like I mentioned in the last video, that for each loops do not have access to the index. Here we're saying that test number because we're essentially using the index right here. Both for each loops. We don't necessarily have access to that. If you wanted access to the index to print out the test number, and then you'd have to use a standard for-loop. 24. Varargs: Now that we have a better understanding of arrays, we can tackle a concept known as varargs, which is a different way to pass in as many different parameters as you want into a function. So I'm going to make a very simple add function. I can say public, static int add. And here I can have int num1, int num2 within here. It's very simple. We just simply return num1 plus num2. Now to make sure everything works, I can print out add passing in 1015, and I can run this with shift and F11. Here we see the sum as 25, so everything seems to be working. But what if I want to add on another number here, or multiple different numbers as many as I want. The problem here is I have to now add in an individual parameter for every single input and a number of inputs could possibly change. Well, the concept of varargs solves this. We essentially can pass in any number of integers into our parameters. For example, I can say int three dots and then nymphs or numbers, whichever one you prefer. Numbers is essentially going to be an array. With that said, we no longer have access to num1, num2. Instead, we now need to loop through each individual element of this array, like I say, int sum equals 0. And then I can return some. But before we return, we need to actually add on every single number to the sum. I can use a standard for-loop or it can use a for each loop. So for int number, colon numbers. And then I can say sum is plus equal to number. So now I can run this and we should see the sum of all these numbers right here, which at 53. We can even lower this to as many or as few arguments as we want. For example, I can just have tin and it's going to print out ten. Now one thing to keep in mind is that varargs need to be the very last argument. Because if we had additional things here, for whatever reason we, let's say we have a student integer here. It doesn't know where the start and where they stop. If we have additional arguments that we'll need to add them before the varargs. Varargs should always be at the very end. So it knows where they start, and it knows that every further parameter passed in, it's going to be accessed as that varargs. For example, ten here is going to be students, and it actually identifies that right here, but any additional numbers here. So just 515 are now going to be part of the varargs parameter. 25. Constants and Casting: Sometimes you might not want your variables to change the values, and also sometimes might want to change the type of variables that your variables are. Let's start off by taking a look at something known as constants. And this basically means that a variable value cannot change. If I say string name equals Alex, I can print this out to the console. And of course before I do so, I can actually change this to my full name, which is Alexander. But let's say hypothetically, I don't want this value to change. I can add the final keyword before we create our variable. And now I get an error right here. If I hover over this, it's going to say that you cannot assign a value to a final variable. Name might be wondering, why would you want to do this? Why not just simply not change the value of the variable? That might be the obvious solution when it comes to a simple programs such as this one. But in a real programs where you have hundreds of files on hundreds of thousands of lines of code potentially, and potentially even other coworkers. You might not remember everything your code does. And you also might not remember that certain variables might have side effects if you change the values. If you're going to have a variable whose values should not change, then you should make it a final variable with this keyword here. Now next, I'm going to show you something known as casting, which is basically where you can take a variable and assign it to a different variable of a different type. For example, I could say int amount equals ten. And I can then create a double which holds a decimal value. So therefore, we can have non whole numbers. And I can say new amount equals amount. Now if I go ahead and print out new amount and run this with shift and FTN. We now see ten points 0. And in this case we don't actually need to cast anything because all doubles can technically still be integers. But once we create a double, it's going to add on the decimal of 0, but let's assume that this was going to be reversed. I can say double amount equals 10.5. I could then say int new amount equals amount. And we get an error here. If I hover over this, it says the required type is an integer, but provided type as a double. Well, we can do something known as casting this integer except the double value as an integer value. And to do that, we can add in parentheses and the variable type, in this case int right before the target variable name, which in this case is amount. Now if I run this, we now say ten in the console and not 10.5, because integers can only be whole numbers. So anything that is not acceptable, for example, this 0.5 is just going to be ignored. The whole number that is leftover in this case, tin is going to be assigned into our new amount variable right here. Now this is how you cast primitive values. And I'm going to discuss the difference between primitive and reference types of values in a future video. Let's take a quick example of how to convert an integer into a string. So for example, we have an integer ten, but we want the string ten, something like this. Well, I can say int number equals ten. Then I can say string, string equals string with a capital S dot value of. Here we can see all the different possible parameters we can pass in. We can pass in an integer, a char along afloat and so many others. In this case, we just want to pass in a number. And then I can print out string to the console. And if I run this, we're going to see ten as a string. Now if I wanted to do the reverse here, I can say string, string equals ten in quotes. I could then say int number. I could then say integer with a capital I dot parse int. And here we see we can pass in a string. And this top function is going to also return an integer. I can pass in the string arguments. Then I can print out number to the console. If I run this, we should still see ten. But now this is an actual numerical value. So I wanted to, I could increase this by one before printing it. Now with C11, beforehand, we were converting a number to a string, so we could not increase that once it was already in string form. 26. Common String Methods: At this point, you should already know how a basic if Stephen works. But if you ever tried comparing strings with an if statement, you might notice that it doesn't work correctly. For example, let us start off by asking the user for some input. I could say enter your name. Then afterwards I'm gonna create a scanner. I'll call this input. I'm going to make this equal to a new scanner passing in system dot n. This is all pretty similar stuff that we've seen before. I could say stream, user name equals input dot next line. This will retrieve the entire line that the user has entered. Now let's say that if I enter my name as Alex, it will then say hi Alex. Of course, in a real program, we could just use the variable value. But I want to specifically do this in an if statement to demonstrate something. I can say if username is exactly equal to Alex, I couldn't print out Hello Alex. I can run this with Shift and left him. I could then enter my name and I'm going to enter the exact string we're looking for in the if statement. So Alex, with a capital a, if I go ahead and enter that and then I press Enter, we don't see anything printed to the console. That's because strengths cannot be compared by using a double equals sign. If I hover over this, it says string values are compared using double equals and not equals as a method. In order to compare strings. Instead of using dough equals, we can take the string, we can press dot. And here we have access to a bunch of different functions. We'll look at a couple of these towards the end of this video. But the one I want to show you is called equals as well as equals ignore case. So we'll start off with equals. Here we can pass in another string, for example, Alex and I can run this. And I can now enter Alex with a capital a. And it will then say Hello Alex. If I run this again, I can enter Alex with a lowercase a. And nothing we printed. If I wanted to ignore the capitalization of either string, then I can say equals ignore case and then pass on Alex. So if I run this, I can now enter Alex with a lowercase a. And it'll print out Hello Alex, because it is not going to care about the capitalization of either string. This is how we compare two strings within an if statement. But now let's take a look at a couple of other examples of commonly used string methods. I'm going to go ahead and delete all this code. And I'm simply just going to say string name equals Alex. And then within here I'm not going to print theme, adopt to lowercase. I couldn't run this and we're going to see Alex that has a capital a. Now we display them all lowercase in the console. In a similar way, we also have to uppercase. And of course if I run this, we see Alex in all uppercase and the console. There's a couple of other functions we have, such as length. If I run this, we're going to see how many individual characters are inside the string. In this case it's for. And we can actually just press a period at the end of name and we see a bunch of other methods we can use. For example, here we can get a character at a specific index. Here I can get index one, which should be a lowercase l. If I run this, we can confirm that in our console. Here we see a lowercase l went back. We have a bunch of other options. For example, we can concat, which means concatenate, basically adding on an extra part of a string. So I can add all my last name here. And if I run this, we now see Alex Flores. And the space that has added in the console is because of the space I added right here. By default, it won't add any spaces. It'll only do exactly what you tell it to. Feel free to mess around with some other string functions here, there are a number of useful ones that you can actually use to change the string or to use the string in different ways. 27. Escape Sequences: Let's now dive into another string concept known as escape sequences. This is basically going to be individual characters that have specific meanings within restraints. For example, I can say string, string equals hello space, world. I'm gonna go ahead and print this to the console. And of course this would just print out hello world. But what if I wanted hello and world to be on different lines? Well, I can use a forward slash n. Now this becomes an orange color. That's because this has known as an escape sequence for slash n is going to be a newline. To prove this, I can run it swift shift and FTN. Here we see Hello World on the next line. Another one is forward slash n, which is going to be a tab. For example, after adding a new line, I can now add on a new tab. And I can run this again. Here we see Hello world, but the world is now indented once by a tab character. We can also do two forward slashes, which just becomes a single forward slash. Because of hours we add on a single forward slash. It's going to assume that this was going to be an escape character or an escape sequence. But if I wanted an actual forward slash and the string, I didn't have to escape that forward slash by basically just adding 200 words office. I can then run this. Here. We now see a forward slash in the string. Whereas beforehand it's going to assume we're going to try and escape with a capital W, which doesn't actually mean anything. So it's now going to give us an error. We can also escape double-quotes. So this will just become a normal double quote. And the reason for this is because a double-quotes represents the start or the end of a string. If I were to simply just add a double quote here, it's not going to know that this has going to be part of the string. Rather a thinks we're trying to in the current string as a variable. If I went world to be in quotes, I can add in the double-quotes, but I have to escape them by adding a forethought beforehand. Now this is looking a little confusing. So I'm going to replace all the previous escape sequences with just a simple space. So now I can run this and we should see Hello World, but world is wrapped inside double-quotes. Now there are a number of other escape sequence characters that you can use, but these are by far the most common ones. You're going to see. 28. The Math Class and Random Numbers: Let's take a look at the math class. And this has a couple of different things that we can do when it comes to basic math operations. The first example is going to be getting the absolute value of a number, which is basically just going to convert a negative number to a positive number. But more technically, this is going to count the distance from that number to 0. I'm going to print out math with a capital M dot abs, which stands for absolute value. And here we can see we can pass in a number of different numeric values. In this case, we can pass in positive ten. I went to copy and paste this and pass in negative ten. And then I can run this with shift and FTN. And here we see tin in both cases. So in basic terms, this will just convert a negative number to a positive number. I'm going to go ahead and comment this out. Moving forward, I can print out math dot minimum. And this is going to take in at two numbers of the same type, and this will return the minimum value between them. For example, I can pass in 107, also going to print out math.max, which is a similar concept, but we will return the maximum value between them. I can also return 107 here as well. So if I run this the first time, we're going to get seven because that is the minimum value. But the second time we're going to get ten because that is he maximum value. Now if we say math dot and we'd go through all of these, there's a number of different math operations. So you might be familiar with depending on how experienced you are with math in school. But some more basic examples will be floor, which will basically just rounded number down. And it also seal, which will run a number up. For example, I can pass in 0.2. I can wrap this inside of printing this out here. Then I can also print out Math.floor and I can pass in 0.9. Now if I run this within our console, we're going to see one and also 0. This is going to round up, no matter what, it doesn't matter if it's lower than five. And it's going to round down, no matter what, it doesn't matter if it's higher than or equal to five. Now one more thing I wanted to show you is how to generate a random number. There are two ways to do this. There is an older way which you're most likely going to see her behind a time within working with other code are following other tutorials. And there is a newer way. The older way, I can say int random equals new random with a capital R parentheses here at the press Alt and Enter to import this, I could then say nextInt. I can then print out random to the console. So if I run this, we're going to get a random number. Obviously this is going to generate any random number, but we don't necessarily want that. Lot of times we want something between 010 are just 0100, things like that. So we can pass in an integer here. For example, ten, run us. It's now going to generate a random number between 09. But if we wanted one through ten, we can just simply add one to the end of this. So if I run this again, here we see two. I don't know if I keep running this, we're going to get your random number between 110. This is the old way of doing this. There is a new way. So random number knew, I could say int random equals thread, local random dot, current dot next int. And this works in the same exact way as before. And also with both the old and the new way of doing this weekend generate other random values, for example, Booleans. If we wanted a random true or false value, which will come up from time to time. You can use next Boolean. You can get ram next, doubles and other things like that. But for example, here we can pass an int and then the boundary will be ten, and we'll add one to the end of it. And I can then print out random to the console. So these are the two different ways to generate random numbers within your Java program. 29. Primitive vs Reference Type Variables: This video is going to be a little more advanced than previous videos. We're going to learn about primitive versus reference type variables and how certain variables are stored in memory. So I'm going to minimize my project right here. So we have more room for these diagrams. Here we have the stack and here we have the heap. These are two different places where information can be stored in your computer's memory. We'll start off by talking about primitive type values. For example, I could say int number equals ten. This is known as a primitive type evalue typically store basic pieces of information. All primitive type values are stored directly on the stack, and this goes from the bottom up. Other examples would be Boolean. I can say is programming equals true? I can then have char letter equals a. I can have a double, I can call this pi. And so that equal to 3.14159. And these are the main primitive type values that you're going to see. Let me go back. Let me delete a couple of these and let's go back to our number. But what happens if I were to assign a number to equal to the value of number one. For example, number two equals number boldest will actually still create an entirely new value on the stack. Now number two equals the value of number. What would happen if I were to modify the value of number one that affects number two, I'm going to print out number. And then on the next line I'm going to print out number two. Before this, I'm going to say number equals 15. What's going to happen here is because these are two separate values. Number two is not going to be affected at all. So this will print 15 and then ten. To prove this, I can run it with Shift and FTN. Here we see 1510. So primitive types will have their own individual value on the stack, even if we're assigning it to an existing variable. This will simply just create another variable in your computer's memory and assign that value to it. This means line eight is going to create a separate integer that has no correlation at all with that line number seven, aside from the fact that they happen to share the same value. That's nice, but what is a reference type? And whereas the heap used. So I'm going to leave all this code here and I'm gonna create an integer array. I can say int numbers equals 51015. And this is going to create something on both the stack and the heap. But the values 51015 are stored on the heap. And the variable numbers is going to be stored on the stack. But this is only going to be storing something known as a pointer. Not the exact details of how pointers work behind the scenes aren't too important when working with Java, because Java handles a lot of this for us. But this will basically just, it points to the actual value which has stored on the heap. For example, I can create another array here. I can call this example. I can set this equal to numbers. What happens here is our array values 51015. It's still only exist once in our computer's memory. And those three values are stored in the heap as an array. But the variables, numbers and example are stored on the stack, but they are now pointers pointing to the array of integers. That means if we modify 510 or 15, we will actually see that change no matter which variable we're trying to access, whether it is numbers or example. To prove this, I can say numbers, index one, which is going to be the ten here, equals 11. I can then print out numbers index1. And then I can print out example index one. I can run this with shift and FTN. Here we see 11 on both cases. That's because these three values here are stored on the heap just once. And then the numbers array and the example of Ray are just going to point to that value. Meaning we have two separate variables that we see here when running your code, but the values are stored only once inside of the heap. And this is a difference between primitive and reference types. Reference types are going to have their values only once in the heap with a pointer on the stack. But primitive types are so simple that we can just simply store the values on the stack. So I can say int num1 equals five, int num2 equals ten. And then I'm going to call an add function, which will make here in a second, and I'll pass in 510. Going outside of our main function, I can say public, static int add, int num1, int num2. Within here I can return num1 plus num2. What's going to happen here is when we pass in 510, it's actually going to create two more variables on the stack called num1 and num2 assign the same exact values as the arguments that we're passing in right here. To prove this, after our add function, I'm going to print out num one with a comma and then num2. But within our add function, I'm going to say num1 equals ten. Now if I run this, we now see 510. But we actually changed num one equal to ten. And in fact the sum of the add function. If I were to put this inside of a print statement, this is going to print out 20. So if I run this warmer time with the 20 in the console and then 510, only break this down line by line just in case it's a confusing for you. Were first creating two variables that are stored on the stack, 510. We're thinking went to print out the sum, passing in 510. Notice how we're not changing num1, num2 at any point at all. That's important to note when we reach line ten, when we were passing in num1 and num2 to the console. These two variables are not changing at all. Once we actually invoke the add function, we're passing in 510, which are going to create two more variables stored on a stack. And we happen to just modify the first number or the first argument right here, to the value of ten. Essentially meaning that we are adding ten to whatever the second argument is, which in this case it's ten, and that's why we get 20 right here. Now the important part here is that we are modifying the very first argument that's passed in, but this has a brand new integer. Primitive types are just going to pass in their value. And it's going to basically just be a copy of that value. Any modifications to that within the function will not actually affect it in the function that originally called it. Basically we're modifying our first argument here. But it's not actually modifying anything from our main function. That's because these are primitive types and just the value is passed in. But what happens if we pass in an array of integers? For example, we have an array with just two values. Instead of num1 and num2, I can say int numbers equals 510. I could then pass in numbers. And then I'm going to log numbers index 0 and numbers index one. Now we have a problem with our function as she cuts were expecting two different integers. But instead, I just want to add two numbers together from a number array, like I say int, brackets, numbers. Then I can return numbers, index 0 plus numbers and X1. ******* run this with shift and F11. Here we should see both the some printed out and each individual number as we see right here. But what would happen if I change numbers index 0 to ten, which originally is five in this array, keep in mind that this array is not being changed at all. And we're passing in the first element of the array into this console log right here. So if I run this, we now say 20 printed out as a sum Kf are changing the first index which has index 0, which is five, to the value of tan right here. Meaning we're basically printing out ten plus ten. But then numbers index 0 printed to the console is now changed. That's because the reference or the pointer to that array is passed in as an argument, not the actual values themselves. So when we go to Modify numbers index 0, it's actually modifying the same exact array that we created online five, because we're just passing in that pointer that is on a stack which just points to the actual values which are stored on the heap. And this is an important difference between primitive and reference types whenever you're working with functions, is important to know that when you modify something as an argument, for example, int numbers right here, that it might or might not actually modify that with the rest of your program depending on if it's a primitive or a reference type. Now a lot of these concepts are new and I know that this is probably one of the more confusing concepts when it comes to programming. If you're new to programming. So if you're having any problems, I suggest watching this lesson over again and really try and focus on the stack and the heap at visual representations as an explaining everything. 30. Object Oriented Programming Basics: We're now going to dive into a concept known as object oriented programming. And a short form way of saying this is hoop or OOP. And this is definitely where Java gets a lot more interesting and we can actually build some real-world programs with it. But first, let's talk about what is object oriented programming? Well, this is a concept that is not exclusive to Java. Other programming languages have this constant as well. This is basically where we can represent real-world objects within our code. And in these upcoming videos, I'm going to be explaining what further keywords meant, such as class and static, and other keywords that I mentioned I'll be explaining later on. Let's quickly take a look at what a class is versus an object. Class is basically going to be the actual code that represents the blueprint of a certain type of functionality or certain type of object. Now when I say blueprint, I want you to think of a Houses blueprint. For example, if you ever see a bunch of houses that looks similar to each other, there's only one, a single blueprint that they basically copy and pasted. And each house is going to be its own object. A house is going to be an object or the blueprint is going to be the class. So we can have a mini instances of each individual class and those are known as objects. What's actually used this house example in a real programming example within our main package here, I can right-click. I can go to New, and then Java class within here. I'm going to name this house, but I'm going to be using a Pascal case notation, basically meaning that we capitalize the very first letter of every word. If I had house example, both the H and the E would be capitalized. But in this case I just want to credit class called house. Go ahead and press Enter and it should automatically open. And now within this class or within this blueprint, we can add in various properties. Now what is a property? These are basically variables and methods that are specifically defined within this house class. And it helps us access different values or work with different functionality within the context of a house. Diving into a lot more detail of what would actually go into a house class over the next few videos. But first, let's take a quick look at how this house class can actually be used within our main class here. I'm gonna go ahead and delete some of these comments. I can now say house with a capital H. And here we see it's going to try and import from our local file system. I can go ahead and press Enter, and then here we can go ahead and name our variable. In this case, I'll say house with a lowercase h, I'm going to assign us equal to a new house. Now the new keyword is part of object-oriented programming and classes, but the details of that will be explained later on. For now, we can think of this as basically just having a new house, a house class right here. This is going to be the blueprint, but now we've actually created a real instance of our house. Let's take a very simple example by having the house print helloworld. I can say public void. And notice how we do not have static here. I'll explain the difference between static and non-static methods in a few videos. But for now, do not include static in this example. So public, void, print. And then I'm going to have no parameters. I'm simply just going to print out hello world to the console. Now if I hover over this, we see that the method prints is never used. Let's go ahead and try using it. Going back into our main class here we have access to this house. I can say House press a period. This is going to have a drop-down with all available properties and methods that we can access. In this case, we have access to our print function. I can go ahead and press Enter, and I'm going to run this. And here we see Hello World in the console. I'm going to go ahead and rename this variable. I can click anywhere inside the variable name, and I can hold Shift and press F6 at the same time. Now we can go ahead and change this. I'm going to change this name to my house with a capital H and lowercase m. Now, I'm going to create a brand new variable. Like I say, house. Your house equals a new house. And these two variables have nothing in common aside from the fact that they were created with the same class. Basically they are neighbors to each other, but they're not the same house. If your neighbor has a similar house to yours, doesn't mean that it is your house. If just a similar house based off the same blueprint. For example, I can say your house dot print. And I can go ahead and run this. And now we're going to see two instances of HelloWorld and our console, as we see right here. This is the very basics of classes and how to create objects around those classes. And over the next few videos, we're going to be diving much further into object oriented programming, where we can create a functional house object that really represents an actual house within our programs. 31. Constructors: We're now going to talk about a concept called constructors, which is basically just going to be a built-in method into every class that is ran or invoked whenever a new instance of that class is created. There's actually a default constructor in every single class. Whether we create one ourselves or not, it's going to automatically have one. So a constructor, we'll look at something like a method, but slightly different because it was not going to have a return type, such as the void right here. And also the constructor name has to be the exact name of the class. So I can say public house with a capital H. This is now known as our constructor. To prove this, I'm going to print out a new house was made. And I'm going to run this in our console. Here we see a new house was made because we created a new instance of our house class right here as the variable my house. And so that made the constructor be ran within our printing out hello world. But then we're creating another house, which means the other constructor is ramp. And then of course we're printing out hello world again. Now a constructor cannot return anything, but it can't take in different parameters. For example, I can have string owner name. Then I can say a new house was made. The owner is like an add on owner name. Now we get two related problems right here. That's because back in our main class, we're not passing in any arguments. So for example here it can pass an Alex. Of course you can add in your own name. And here I'm going to pass in Bob. Of course you can add in any other name you want. So if I run this, we can now take a look at our console. And here we see a new house was made. The owner is Alex. And that's because we created a new instance of a house class right here. And we passed an ALEKS as a string to our constructor. And then of course, when we create a Bob's house, we see the owner is Bob and the console. Now, similar to methods, constructors can be overridden, so we can pass in different types of values into the parameters. Like I say, public house. I couldn't say floors. Here, I could print out new house was made. It has I can add on floors and that can add on the string floors. And I'm also going to put parentheses around the S because we might pass in a single story house. So now we have two different constructors, and these are going to be ran at different times. For example, backup Bob's house. Instead of passing in Bob, I'm going to make this a two-story house. You might notice that automatically IntelliJ IS going to notice that this is now going to be the floors parameter. This is not going to be owner named like it says right here. That's because it understands that we're overriding the constructor to pass in two different types of variables. And here we're passing an integer. So that means we are going to be using this constructor right here. So now if I run this and if we look into our console, we now see the first instance of our house is going to print out. The owner is Alex. But the second instance of our house is going to print out a has two floors. That's because we are using the different type of constructor that passes on integers only. Now in this example, we've just printed out some text, but in real use cases, which we'll take a look out in a few videos. We're going to basically use these as set-up functions to make sure everything else is set up and going to work correctly for our house to function. 32. The "this" Keyword and Properties: We're now going to look at the, this keyword, as well as how to create different properties which are going to basically just be variables inside of our class. I'm gonna get rid of these comments here. And I'm also going to get rid of these print statements within our two constructors. Now inside of our class, but outside of the functions, I'm going to create a couple of different variables. For example, I could say private string with a capital S, owner name. I couldn't say private int floors. And the private part of this, as well as the public on some of these methods are going to be explained in a future video. Now I've already demonstrated how we can overload constructors. But in this case, we just want a single constructor with both pieces of information being passed in. Here I can say int floors. And now inside of this, I'm going to want to assign the new owner name and the new floors from the parameters to our local variables. Because these two variables here are different variables then our parameters right here. But before I do that, we have two related problems because if I go back, We are now using incorrect syntax for a constructor. Here, let's say my house has two stories, unless say that this is still a Bob's house, which of course you can use any string you want on these, but it is also two stories. So going back into the house class, we no longer have any problems. But how are we going to set the owner name online for equal to the parameter that's being passed in. Because of course, they're the same exact name. Saying owner name equals owner name doesn't really do anything. It doesn't actually modify line for whatsoever, because this is going to reference the most local variable in the scope, which in this case is just going to be the parameter under name right here. Now technically, we could change the names of these variables, so they're not exactly the same, but that's not the most correct solution. The most correct solution would just say this dot owner name equals owner name and this dot floors equals force. What is actually happening here? Well, this represents the current object. Whenever this constructor is ran for my house, which has the owner name of Alex and two floors. The, this keyword right here is going to reference the my house object right here. When we're creating Bob's house, that this object right here is going to be referencing the your house object right here. The, this keyword right here is going to represent the current object that is being used for this class. To prove this within our print function, I can say this house is owned by. I could then print out this dot owner name. And it has plus this dot floors force. Of course, I'll put parentheses around the S just in case you want to pass in a single story house. Now we're still using this print function, as you can see right here. I'm going to go ahead and run this program. And here we see in this house is owned by Alex and it has two floors. We also see this house was owned by Bob and it has two floors. The names and the number of floors are going to be saved locally. Right here. We're not accessing the parameters that we added in right here, because these are bounced who only be accessed within the constructor's scope. So basically we have our own parameters or our own variables within this class. We're assigning those whenever we're creating the object from the constructor. And then we can access these variables anywhere within this class. For example, within this print function by saying this dot owner name and that stuff wars. Now, technically in this use case for the print function, the, this keyword is optional because by default it will assume that we're going to use the current instance of the class. So I can go ahead and delete these. And if I run this again, it's going to work the same exact way. Now, technically this is not good practice because saying this.name and desktop floors makes it very clear that we're trying to access variables stored in the class, but it is technically optional in this case of the printf function. But our constructor has these to be required because they have the same exact variable names as our parameter. To be very clear, which values we're assigning to, what variables. We can say this dot on her name to reference our local private string here. And this dot floors WHO reference our local private integer here. And then assign those to the owner name at perimeter. And the floors parameter. 33. Encapsulation, Abstraction, Getters and Setters: Diving further into object oriented programming, we're now going to introduce two more concepts which are going to get slightly more confusing, but hopefully I can explain them well enough for you to fully understand. These two concepts are going to be known as encapsulation as well as obstraction. But also we're taking a look at getters and setters, which are kind of an example of abstraction. Encapsulation is basically going to be a concept of object oriented programming where we want all of our functionality to be encapsulated into one single place. And even a class itself is kind of an example of encapsulation. For example, here we have a house class. So any functionality we're going to have regarding a house, such as how many doors that has, how many floors it has, different windows and rooms and other things like that. Basically, anything to do with a house should be enclosed or encapsulated inside of this house class. Now another concept is something like some medicine or a pill where you have all the functionality encapsulated inside of a single pill. That means that the users of this class or the people taking the medicine, don't necessarily have to know the inner workings, everything. They just have to see the outside object and know that everything is encapsulated inside. That's more of a concept that can't really be demonstrated to clearly, but it's something that is important to understand that when writing your own Java code, you want everything to be capsulated inside of its own class. Now the next concept is abstraction, which is slightly similar to encapsulation. But basically this means that you only want the user who is using the class to gain access to things that they actually need. For example, I'm going to change these private properties right here to public. And I'll explain what private versus public in this video. But for now, just follow along and change these to public. And now inside of our main file, after I create the first house, but before I print it, I can say my house dot. Now here we have access to all the properties and methods within this class. And we can see the owner name and the floors. I can change the owner name to Bob. Let's say Bob just hijack my house, for example. And if I run this, we now see Bob twice in the causal, as we see right here. Now this is technically a bad practice. And I'm going to change these variables back to private by using Control Z or Command Z on a Mac. And now we see one related problem. If I hover over this right here, it says owner name has a private access inside of com dot worn off keys dot house. So I'm going to remove this line of code right here. And now we cannot directly access who owns the house without actually being inside of the house. For example, I could say this dot name equals Bob, and this would work just fine. And that's because the private property right here is something known as an access modifier. This is going to restrict the access that certain things have when it comes to different properties and methods. A private method or private property in this case, is going to mean that the only thing that can access this is things within the same exact class. That's why we're able to access it right here, as well as right here. Even though it's private, we're still inside of the class. That's also why we had the error right here. What I'm trying to access it because we're not inside of the house class. We are inside of the Warnock keys course class or whichever you named your class. Now, public, as you can probably guess, means that anything can access it by accessing its own object. For example, we have a public void print. This method is public, which means if we have an object for this class, for example, my house or your house, we can then access the print method on it. Now you might be wondering why not just directly access anything we want. Why restrict certain access? Well, that's the whole concept behind abstraction is basically going to take all the inner functionality and how the house works and only give you access to what's necessary for the House to perform its job. Now in some situations, you can give inner access to certain things using getters and setters, which we'll take a look at here in a moment. But typically as a good rule of thumb, you should only give access to what's absolutely necessary. And you should never give direct access to variables directly like this. Instead, you should always use getters and setters. Let's take a quick look at how that works. I can say public, string get. Now here it's going to auto populates the concept of get owner name, which is actually what I'm going to use here. The reason why I knew this is because it's going to return a string. And whenever I type Git, it's going to assume are creating something known as a getter method. Basically, this is just a method that returns a private property. In this case, I can return owner name. Now I can actually access owner name which is private from this getter method. We also have setter methods, which is a similar concept, but obviously we're not getting the value. Instead we're studying the value, like I say, public void because we're not returning anything. Set owner name within here. It's going to have one parameter. I can say string owner name. And then within this I can say this dot owner name equals owner name. Now if I wanted to, I can actually go over to my house, Like I say, my house dot set owner name. I can pass in Joe. And if I run this, we're then going to see Joe and Bob in the console. And actually we see Bob twice because of mistake I made here in the print function. As an example, I said we can use this here. I'm going to go ahead and delete this and then run the program one more time. And now we see Joe and Bob in the console. This is an example of a getter method and a setter method. Now you might be wondering why bother with any of these getters and setters. Why not just completely remove these functions here and just make our properties public? When I was first learning object oriented programming, I would have the same exact question and I was very confused. Why do all this extra work and just for the same exact results. But as I wrote more and more code over the years, I realized that using getters and setters is much more convenient and it makes things much more organized. For example, imagine that we have a very large project with dozens of houses. Oliver, our project, and we want to change all the owners names to, let's say uppercase. Or we want to log all the owners names whenever they're changed or anything like that. I want to perform some type of functionality whenever the owner name has changed. For example, here we can say this owner name equals owner name dot toUpperCase. And to make things even more convenient, we can change a line ten right here of this owner name equals name to set owner name. Passing in owner name. This will make it to the default constructor will also have it be an uppercase. If I run this, we should see both on our names and uppercase. And if we had everything set to public without any getters or setters, and we had dozens of houses in a larger project, we'd have to go through and manually change all of our names to uppercase, which sounds very tedious and very annoying. But because we use the correct rules of abstraction and we use getters and setters with private properties right up here. We now have the ability to easily change certain aspects of our program from one single change right here. 34. Inheritance: Let's take a look at something known as inheritance. This is basically where we can add on or extend another class to give it more functionality. For example, I can make a new Java class and I'm going to call this hotel. And I'm going to extend house. Like I say extends house. What this means is it's going to inherit all of the functionality within the house class. But then we can add on more functionality and side. For example, we can now specify a lobbyist square footage, or the number of staff, things like that, that it hotel has a house doesn't have, but a house is still going to have an owner and a certain number of floors which a hotel also has. Instead of making a hotel class, which would have these properties inside, we're just going to extend house which already has these properties. That way we don't have to actually make them again. But we're getting this error here. If I hover over it, it says there is no default constructor available. If we go over to the house, we see that there is no default constructor, meaning that there was no constructor that has 0 parameters. So we have these two parameters right here, the owner name and floors. And that means that our hotel, which extends house, also has to have a similar constructor. So I can say public, hotel, string, owner name, and then int floors. Now we get another error. If I hover over this, it says there's no default constructor available. This means that we have to use something known as the super method. So if I call superheroes, I could then pass in owner name and floors. And the super function is only going to be used within classes that extend another class. This will basically just call the constructor of the class we're extending in this case house. So now we've created a hotel constructor. This is going to call a constructor of the house constructor. Therefore, we are going to set the private properties of owner name and floors equal to the properties we're passing in. In this case, we're simply just going to pass those and from the hotel constructor. Now if this seems confusing, don't worry, let's go ahead and make a new hotel instance, and it'll make a lot more sense after that. Here in our main class, I'm going to say hotel. My hotel equals a new hotel. We can then pass in the owner. And then the amount of floors, let's say ten. I can now print out my hotel dot gets owner name. But inside of the hotel class, we don't have an owner name at all. That's because we are still extending the house class, inherits all the previous functionality inside of this class. For example, get owner name. So of course if I were to run this, it'll just simply print Alex to the console. I'm not going to bore you with that simple concept. I'm sure you understand that. But let's dive further into how these constructors work and how the super method works. Basically, I'm passing in ALEKS and tin as parameters into the hotel constructor. Therefore, the owner name and floors will be Alex and ten were then calling super, which is going to call the constructor of the extended class. In this case, that is house. Essentially we're going to call this function right here, which will set these to private properties equal to Alex and ten. Now we can access these within hotel if they are public or something that is known as protected. So, so far we've seen private and public. There was also another one which is protected. For example, inside the constructor. I cannot print out this owner name. We see in the drop-down here, there is no option. And also if I just leave it like this, we're going to get an error. If I hover over this, it says owner name has private access. That's because the private access means the only things directly in this class can access it. Not necessarily things that extend this class. If we wanted the extending classes to access it, we can change private to protect it. Now the error goes away and protect it basically means that anything inside the class can use it as well as any classes that extend this class can use it. 35. Polymorphism: Let's now talk about a concept known as polymorphism. This is basically something that means many forms because poly means many and morphism means forms. To take a look at the problem that polymorphism solves. Here we have the my hotel object as well as your house object and my house object. These two are using the print function. And because the hotel extends the house, we now have access to the print function. I can say my hotel dot print. Now if I run this, we see that the houses owned by each person and it has so many floors. The hotel is still says the houses owned. We want to basically override the exact functionality for the print function within the hotel class. To do this, let's take a look at the house class real quick. Our print functions as public void print. Our hotel class needs to have the same exact function. I can say public, void, print. And now for simplicity, I'm simply just going to copy and paste the previous line here. I can use Control C on Windows or Command C on Mac. And then I can go ahead and use control V on Windows or Command V on Mac. Now we get an error because these two properties are private and they're not protected. So I need to use their corresponding getters. So I could say Get owner name. We don't have a gift for his method yet. So if I say git floors, it doesn't actually exist. Plus go ahead and make one. There should be pretty simple, I guess a public int get Flores within here, I can simply just return false. So now we have a getter that we can use. Within hotel. We no longer have an error here. We can change. The house is owned by two, the hotel is unbiased. Now if I run this and we look at our console, here we see the hotel is owned by Alex and it has ten floors, or the previous house objects still say house. This is what polymorphism is, that we have many forms of the same exact function. So here we have a print function in our house, and here we have a printf function in our hotel. Whenever we're trying to access a print function, we're always going to use the closest one to the exact class. For example, now that we have this printf function, it'll use this. But beforehand it didn't have it. So it would look to the house class which we are extending. And of course, house did have a printf function. So it would then use that. Now, this is also known as a concept of method overwriting. Now this is not meant to be confused with method overloading. This is where we have two methods of the same exact name, but perhaps different parameters. For example, I can say public, void, print, and as an argument I can say int times. Here I'm going to loop through a certain amount of times depending on how many times is passed in. I can say for int a equals 0, while a is less than times plus plus a. Now within here I could just copy and paste this line right here, or I can just simply call the print function. So now going back to our main class, we're simply printing this, but we also can say my hotel dot print and pass in five. And now I can run this. And here we see it is printed out five different times. Now of course, we see five times right here. But we also have this sixth time at the top. And that's because right here we're saying my hotel dot print without any actual arguments. So therefore it's going to use the normal printf function that we created. Now we've already gone over method overloading. This isn't really a refresher. This is just to clarify that method overriding is different than method overloading. Obviously, they can get confused because there's similar words, but they are different concepts as you can see here. 36. The "static" Keyword: So far we have different properties within our classes, for example, owner name and floors. And these are going to be tied to each individual object that we create. For example, my house, your house, and my hotel. I'm not going to introduce a new keyword, which is the static keyword, which you might see right here. This basically is not going to tie the properties to the individual objects, but rather ties of properties to the class itself. Now every single house is different, so it's hard for me to describe a static example when it comes to houses. So we're going to use birds instead. I can right-click new Java class. And I'm going to name this a bird. Now let's say that each bird is going to have its own name. So I can say private string type. And then here I can say public bird at a constructor, we can have a string in here called type. And then within the constructor we can assign the local variable type equal to the parameters passed in from the constructor. Here I can say this dot type equals type. Everything seems pretty basic so far, Let's go into my main class and I'm going to comment these out. We will uncomment them in future videos when we go back to the house example. But again, static is much easier to understand and for me to explain without using houses. Here I can say bird, bird equals new bird. I have access to a bird, but now I have the pass in a certain type. For example, I can pass in a crow, and now we have access to a bird. Everything seems pretty standard so far. Now, static properties such as variables and methods come in once you want to bounce something to the class itself. Like I mentioned, the house has the owner name and floors that are bound to each individual object created from this house class. So in our main file here we have my house, which is going to have it on properties of owner name and floors. And then your house will have different properties, also called older name and floors. And my hotel had the same thing because this is extending the house class. But if I go into bird here, I can create something known as a static variable. Like I say, public, static, int wings equals two. Now if I go back into my main file here, when I go to access bird wings, we see it doesn't actually exist. That's because again, the static variables are not tied to the objects bird itself. The object being this object that we created right here. Instead, they are tied to the actual class. So bird wings. So now if I run this, we're going to see the amount of wings at this bird house. In this case it is two. But why use static here instead of just making a normal variable? Let's because this is only created one single time. And otherwise, for example, with string type, this variable here is created each time we make a new instance of our Bird class. Going back to the house example, we have three different instances of owner name and floors because we haven't three different objects that are going to use them. But if I had three different birds, we would still only have one integer called wings. So static variables like this one here are going to be used whenever you have a class that has a shared piece of information. So for example here birds have two wings and that's never going to change. Having it as a local variables such as private int wings equals two. It doesn't make too much sense because this is never going to change. So therefore, we don't need to have a wings variable tied to each individual object we create. Instead we can just tie it directly to the class. Now we can also have static methods. I can say public, static, int, get wings for example. Here we can just simply return wings. Now typically static methods are only going to be used whenever you're trying to access or use a static variables or some type of functionality or to return things such as a simple getter right here. Now in my main class, I cannot print out bird dot get wings. And of course this will have the same result because we're just simply returning the same variable, but similar to the variable bird dot get wings doesn't actually exist. Because again, static properties and static methods are tied to the class, not tied to the object created from the class. 37. Abstract Classes: So far we've had a look at normal classes, such as our house, our bird, and our hotel classes. But now we're going to take a look at something known as abstract classes. This is a different type of class which we cannot directly use. For example, if I go to my bird class and I make this a public abstract class, nothing directly happens here. Everything looks normal. But if we go back to our main file, here we have an error because we cannot directly use abstract classes. These are classes that are designed to only be used with classes that extend them. For example, here I can make a new class and I'm going to call this a crow. This is going to extend the bird class. Extends Bird. And now we have to create our own constructor because we have a non-default constructor here. So I can say public grow the parameter being the same exact one as bird. So string type, as we can see right here, going back into our CHRO class, we can call this super function passing in type. Now all the arrows should go away. If we go back into our main class. And instead of using bird directly, I am now going to say cro, gro equals a new CRO. Now we have access to this and we'd had that still pass in a string. In this case, we'll pass in Crow name. And this technically is a bird because cro extends Bird. But why would you want to have an abstract class that needs to be extended? We cannot use this directly. Well, that's where the concept of abstract functions come in. So for example, here I can say public abstract, void. I can call this Singh. And I'm not going to include any function body. If I were to do that, we have an error. If I hover over this and now it says abstract methods cannot have a potty. So here I am just going to create the declaration of a function, but there is no body attached to it. Now every class had extends, the bird class is forced to extend this sinc function. If I go back to a crow, here we have an error. If I hover over it, it says the class Crow must be either declared abstract or implement the abstract methods. Seeing in bert here I can say public, void, sing. I can then print out a sound that a crow might make. For example, this. Now if I go back into my main file, I can now say Crow dot sin. And if I run this, we're then going to see that this we printed to the console. Now let's say I have another class here. I'm going to call this a Robin. I can have this extend bird. So we can create our own constructor. So public Robin, string type. Then we can pass in this two are super method which we'll call the constructor of bird. Now we still have to override the toString method. Public void, sing. Here I'm going to print out tweet, tweet. And now I can make a robin instance by saying Robin, Robin equals new robin, passing in Robin here. And then I can now say Robin dot sin. If I run this, we're going to see the two different sounds that birds will make. And this is useful because the bird class is an abstract class, meaning it has a lot of setup, but it's not meant to directly be used. It's meant to be used with other classes that are going to have a specific functionality. For example, each bird might make a slightly different noise. And so we want to force each type of bird to implement that functionality directly. 38. Interfaces: Let's now take a look at interfaces, which has some similar concepts to abstract classes, which would just have to look at. But they have some key differences. For example, here we have an abstract class of bird. And abstract classes will typically have just normal things within classes, for example, different methods and variables. However, we also are usually going to have an abstract function which any class that extends the bird class is forced to implement. We've had a look at this in the last video with our CRO and Robin class, where we need to now override the sing method. Now one thing to keep in mind is that each class in Java can only extend one other class, but we can use as many interfaces as we want. For example, here in my project, I'm going to make a new Java class. And I'm going to change this to an interface right here. And I'm going to name this animal. Now within this animal, we cannot have a constructor, for example, public animal. This is going to cause an error. The only methods we can have in here are abstract methods. Let's say I want my Robin and Cro class to implement this animal interface. This will also mean that every animal I make in the future, whether it be cows, dogs, snakes, anything will have to implement this. So this should only contain things that are specific to any single animal, let's say public int, average lifespan. And again, these are going to be abstract methods. So I cannot write an actual function body here because again, this is an interface. We can only have functions themselves. But if I go into micro class, for example, I can make this implements animal. Now we get an error. If I hover over this, it says class Crow must either be declared abstract or implement the abstract method average lifespan in animal. Here I can say public int average lifespan. And this is going to return eight. Now we no longer get an error anywhere. I go to my Robin, I can now say implements animal. We'd have to do the same exact thing. Public int, average lifespan. Here I can return to. Now I can go back into my main file and I can print out grow dot average lifespan, and I can print out robin dot average lifespan. By run this we're going to see 82 respectively. And you might be thinking we can achieve this same exact concept with just adding in the function has an abstract method to our Bird class. And that's true. And after classes are similar to interfaces in some ways. But the main difference here is you would typically will want to use an interface whenever you only have abstract functions and you don't have any other type of functions. And one key difference here, like I previously mentioned, is that we can implement as many different interfaces as we want. For example, if I had another interface called animal to, I could implement it here. These are separated by commas, but in Java we can only extend one single class. So that is one advantage that interfaces have is that you can use as many of them as possible. So you typically want to use interfaces unless it makes sense to actually use a class. For example, you have default functionality that should be inherited or technically extended by every single child class. But otherwise, if you just have these functions here, that each individual child class, such as Robin and Cro, should actually override and implement themselves, then you should use an interface. 39. Instance Of: What if you wanted to check certain types of classes against other types of classes? For example, I'm going to start off with the code I left off with in the last video, but I'm going to get rid of all the print statements right here. We just now have a crow and a robin. I cannot have an if statement saying if a crow is an instance of a bird, I can print out Crow is a bird. And here we get this warning. If I hover over it, it says conditioned grow incidence of bird is always true. That's because this row right here is just a variable that we created, but we're never changing it at all. It knows for sure that this is an instance of a bird because cro extends Bird as we see right here. Now of course, if I run this, it's co-invest, say a crow is a bird, as we see right here. But this also can be done with interfaces. So a crow is an instance of an animal. Now if I run this, we're going to get the same exact response as we see right here. Of course, technically we should change the sentence to say a crow is an animal. But you get the idea. Instance of can be useful if we wanted to check if a certain object is an instance of another class or an interface. And this is one more use case for interfaces because technically you don't necessarily have to have anything inside of your interface and it will still work. For example, a robin is still implementing animal, and the CRO is still implementing animal average lifespan now just becomes a normal method that is attached to the crow class and attached to the robin class respectively. And has nothing to do with the animal interface. But now that a robin and CRO are both animals because we're still implementing the interface. We can still use them and checks like this. 40. Enums: We're now going to be moving away from object oriented programming and moving into other aspects of Java. For example, in this video, we're going to learn about enums, which stands for enumerations. Basically, these are specific types of values that are kind of like variables, but they cannot change and they can be used in very specific ways. So let's go ahead and make a new file here. So we can select Java class. Then here we can select enum. I'm going to call this days of week. You can have enums to have whatever values you want. But typically these are going to be things that should never change. So they're not technically like a variable where you could have input from a user or some type of random number. These are things that are going to be concrete and always use in the exact same way. A good example of this is the days of the week, which will not change. Here, I'm going to add in a Sunday comma. I noticed how I'm typing in all uppercase. This is a common convention when actually using enums. So then we can have Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday. Obviously you spell correctly. Now we have these seven different values within our enum, but how do we actually use them and how are they useful? So going back into our main file, here, I can say days of week dots. And then I can access each individual value if I wanted to. Or I can get all of them as an array. Here we see the values method is built into enums and it returns days of week as an array. But for example, if I wanted to print out days of week Friday, I can then run this. Here we see Friday in the console. We can also use these with an if statements. Now, each individual enum value also has a set of different methods. For example, we can compare it to another instance of days a week. We can get the name, we can get the ordinal unless to hit quick look at these two things. So I went to print out the name. Then I'm going to copy and paste this line. And I'm going to print out the ordinal. Now if I run this here, we see Friday again, and then 55 is going to be the actual index that this is used. For example, Sunday is 0. Now you don't have to add in these comments, I'm just doing this to make it easier for us to actually read this. So here we have 012345, and of course Saturday would be six, but this is why we see five and our console. I'm going to get rid of all these. And now let's expand on this enum. For example, let's say I don't want Friday to be an all uppercase, but rather I want to rewrite a specific string as a name of that day. So similar to classes, enums can actually have their own constructor. I'm gonna put a semicolon at the very end of all my values in this case had a Saturday. And then here I can say days of week. Now you might notice I don't have public or private or anything like that here. That's because if I hover over this error, it says public modifier not allowed here. The reason for that is this constructor function right here can only be ran within the enum itself. For example, within Sunday parenthesis. Here we would pass in at different arguments into the constructor. We cannot access this constructor outside of this eNode file. But why would we need a constructor in the first place? Well, we can actually store at different values for each individual enum value. Similar to private properties of a class, I guess say private string name, I guess a private boolean, Workday. And then within the constructor, I can require these two properties. So string name, Boolean, Workday. Then I can say this.name equals name and this dot workday equals workday. Now we get some errors on each of our values. And that's because by default it's going to call a constructor with no built-in arguments. But of course, if I hover over this, it's going to expect a string and a Boolean. Here. I can pass on Sunday and then I can say false for it being a workday. I'm going to do the same thing for all of these. So for example, Monday and true, like I say Tuesday and true, Wednesday and a true. I can then pass in Thursday. And true. Here we have a Friday and true, and then finally, Saturday and false. Now we have no more errors unless trying to use one of these within our actual file here. Instead of days a week dot Theta dot name, can I access the actual values such as weekday? And we can't, we actually have to make our own public getters in order to do that. Here I can say public, string getName. I can now return name. Then I can say public boolean is Workday, and I can now return workday. Getname is not a really good name for the method. The reason for that is this can be easily mixed up with name. For example, we have name and getName. It's very unclear which one does we will want. One thing we can do is we can rename this to get Display Name. Now a display name as something that typically is going to be shown to users. So something with a uppercase F and lowercase, everything else would be a better display name that everything being an uppercase, everything being an uppercase, it looks a weird to the user. And so a capital F with everything lowercase, it's actually how you'd say this. Normally, this would be a proper display name. Going back instead of getName, I can now say kids display name. Then of course here I'm going to say Friday dot is workday. I think go ahead and run this. We should see the display name as well as if it's a workday, which in this case S has Friday and true. Now you can actually use enums as a variable types. For example, I can say days of week, day equals days of week, Monday. I can then say if day is workday, I can print out going to work today. Otherwise, I can print out it's a weekend. Now if I run this, we're going to see going to work today because we were accessing the value Day, which equals Monday. But of course, if I change this to Saturday and I run this, we now see it's a weekend. Now there's just one more thing I wanted to show you with enums, and that is the ability to loop through all of them, like I say, four days of week, day. Here I can pass in days a week dot values. If I hover over this, we see that this returns an array of days a week. This will be an array of each individual value as its own element. Within here I can print out day dot, get us by name, then a colon. Then I can add on day is Workday. If I run this, it's going to loop through every single day. It's going to print their name as well as a Boolean if it's a workday or not. Obviously with an enums, we're not receiving any external input from other parts of the program. Everything with an enum or self-enclosed, meaning that the arguments passed into the constructor or just static values that are not actually variables. As you can see, I'm just passing it a string and a passing in a Boolean value. I'm not passing in any variables. Enums are useful whenever you have something like the days of the week where they are concrete and never going to change. Not even the variables passing the constructor, they are not going to change. This has very useful if you ever have things that are very concrete like this, because then you can easily access them and reference certain values without worrying about them ever-changing. 41. Try Catch Finally: In a previous video, when we use scanners, we saw what an error looks like. Let's go ahead and recreate that. I can create a scanner. I call it input and I sine is equal to the value of new Scanner. Here I can pass in System.in. This should all be pretty familiar to you from earlier in the course. Now here I'm simply just going to print out input dot next int. And if I run this, it's going to expect me to enter an integer. For example, if I enter five, everything works well and the process finished with a successful exit code, which is 0. But if I run this again and I enter a string such as test, we now get an exception. This is basically just an error. And at first glance this might look really confusing, but it's actually very simple. Basically we have an exception in the thread main and it's going to have a list of where all the errors came from. This is known as a stack trace. And this is basically tracking down exactly where the error came from. Now these are all actually clickable, and in fact we see the name of the error right here as input mismatch exception. That happens when we enter something that is not the proper type. I can actually click on one of these, for example, scanner dot Java. And this is going to open the skin or class, which has a bunch of stuff that we actually don't have to worry about. I'm going to close out of that. But what's more important is we can click on our own code. We can actually see this in blue. If I close out of all my files, I can then click on this right here, is going to open it and put me on the same exact line where the error is. Nice, but how do we actually fix this? We can use something known as try-catch. I'm going to add an a comment here. We have try-catch and also we have another option known as finally, the syntax for this would be try curly braces, and then afterwards you have to add in a catch. This is going to have an exception. I will call this an exception here. And there are different types of exceptions. Typically, you do not want to have a generic exception here, but rather you want to use the exact type of exception that you're expecting to catch. In this case, it is an input mismatch exception, as we can see from the stack trace right here. So instead of just saying exception, I'm going to say input mismatch exception. Now within here I can say e dot print stack trace. And this is basically just going to do the same exact thing that we see in our console right here. To prove this, I can take this print line statements. I can put it inside the try-catch. If I run this, we're going to get the same exact results. If I enter in something that is not an integer, for example, this string. Here we see the exact error. So what exactly is happening here? Well, basically we're going to try this code right here. If something doesn't work, then it's going to throw an error. Now by default, if we do not catch an error, the program is going to crash. To prove this, I can bring this line back right here. And I'm going to comment out our try-catch for now. And to do this with multiple lines, you can just select all of them and then do control forward slash or Command forward slash on a Mac. Now within here I'm going to print out worked. This is after we were receiving the next int input. If I run this, it's going to ask me for a number. I'm going to enter five and it has worked. But if I run this again and I entered test, it is not going to say worked. That's because the program actually crashed. And so everything past this is not gonna be ramp. This is the main reason why you want to use try-catch. Because if I print out worked after this and I run the program here, I can enter in test. And it's going to still throw the error because we're printing it because of line 14, edit, print stack trace. But it's not going to crash the program. And we see that because we're printing out worked directly afterwards. Whenever you have some code that might throw an exception, you wanted to make sure you catch that exception and then handle it accordingly. In some cases, this could be printing out. You did not enter a number and we don't necessarily need to print out a stack trace. So I'm going to remove that. Now if I run this and I enter intestine, we're not going to see the error. Instead, we're just going to see it. You did not enter a number. Now I mentioned this finally thing. What exactly is that? Well, that always comes after. Try and catch. Here I can add. And finally, this is something that will be ran no matter what happens. So try we ran one line at a time. So it'll run this line and this line and this line. If there's ever an exception, it will immediately stop trying to run this code here. And it will immediately jump to the catch statement, basically running whatever is inside these curly braces right here. And obviously with that said, this highlighted code here will only be ran if there's an exception. If everything works well within the try-block right here, then the catch code will never be ran. But finally is going through ran no matter what, no matter if everything worked perfectly fine or if there is an exception, I can print out. Finally ran. And I'm going to run this within here. I can enter a number, let's say ten. And here we see finally it was ran. If I run this again, I can enter a string. We see you did not enter a number, but we still see finally RAN. Now, this is useful in a lot of use cases, but a very specific one is outside the scope of this entire course. That's basically when it comes to database connections. Essentially with our try statement, we would try to connect to the database. Within a catch, we would handle any errors and example being invalid login details. And then finally is going to close any open connections. Now at some use cases, you will see connections like this, and this is a good example in theory of wind finally can be used. 42. Throwing Errors: In the last video, we had a look at how to handle different errors. But whatever we want to create our own errors. For example, I'm going to delete all of this and I'm going to change this comment here to throwing an error. And that is what we're going to call it whenever we want to create our own error. For example, here I can say a string. Next string equals input dot next line. Now within here I'm going to say if next string dot equals ignore case error, I didn't want to throw my own error. To do this, I can say throw new exception and I can pass in a string. And this will be the message that is printed to the console. For example, an error was given from the user because the user enter the string right here as error. But we get an error right now. The solution here is to add the exception to method's signature. If I click on this, our main method now says throws exception. This will basically tell Java that within this function, we're going to be throwing our own exception. Now, outside of our if statement, I can print out whatever the next string is from the user. I'm going to go ahead and run this. And within here I'm going to enter HelloWorld and it should print out hello world and everything works just as expected. But if I run this one more time, I cannot print out error. And this will then make this if statement true. So if I press Enter, we're now going to get our own exception. Here we have the string. It says an error was given from the user, and we can click on this to then see where the exception was thrown. Now you might be wondering, why would we ever want to do this? Why not just tell the user to not enter the string error? Well, one reason you want to do this is so programmers who are using your code or yourself with other parts of your project are then forced to catch certain errors and interact correctly. For example, if you're creating your own program that other developers will be downloading and importing. You can then throw different errors so that developers are then forced to catch them and handle it according to how they want to. Depending on the type of error it is. The same concept goes for your own projects. You can throw certain errors whenever certain things are happening. In other parts of your program, you can use the try-catch system in order to actually solve that problem. 43. Lists and Array Lists: New the start of the course, we had to look at arrays, but now we're gonna take a look at lists and ArrayLists. These are basically going to be more advanced ways of using arrays. And in a lot of situations that are going to be more user-friendly and more powerful. So let's say I want to have an array of integers, like I say int numbers equals brackets. And here I can add in my list of numbers, for example, 123. Now let's say I want to go ahead and add on a fourth element. Well, if I say numbers index three equals four, we're now going to have an error. If I hover over this, it says array index out of bounds. Basically meaning that any array cannot have new things added to it. You'd have to create an entirely different array. For example, I could say numbers equals a new integer array with 1234 in it. And this will work. But obviously I don't want to have to do this. I want the ability to just simply add something to this array. But by default, arrays do not have this functionality. That's why we have array lists. These are much easier ways to use arrays where we can easily remove things, add things, of course, access, things similar to existing erase. I'm going to go ahead and comment this line out here. And I'm going to make a new ArrayList. Now the first step is to create a generic list. This is going to be from Java util. This is going to be an interface, as we can see from the green icon right here. Now within here we have to pass in what type of data we're looking at a store and we cannot pass an int because this has a primitive type, we need to pass in a certain class. Within Java, we have access to integer, which is a class. And this is going to allow us to use integers within this list. So I'm going to call this list numbers. So we can assign this equal to a new ArrayList. Now here we have just less than and greater than sign. And then these parentheses, the less than and greater than sign, could hold what HEPA value you want, for example, an integer. But in modern Java, we don't need to do this. It's going to basically just access what type of value we need from the integer we passed in right here. What exactly just happened? Well, if I hover over list here, we see that this is an interface, as we see right here, public interface. And this gives us a number of different built-in functionalities that most different lists are gonna have. Now after saying that, I should've mentioned that ArrayList is not the only type of list, but it is the easiest one to understand and the easiest one to demonstrate. We're going to use it for this tutorial. Now, ArrayList is its own class that is going to implement the list interface. So it's going to get all the functionality that list offers, but also build onto it. This is cool and all, but how do I actually use the numbers list? Well, here I can say numbers dot. The first option is at all where we can pass in a different collection, such as another list and add all the elements to it. Or we can add an individual elements such as an integer. For example, one. Now if I had numbers dot here, we can add a certain element into a certain index. We also can clear the list. We can see if it's empty, There's a bunch of other options such as removing certain elements, getting the current size or the amount of elements in the list, and many, many more. Let's go ahead and add all three numbers we wanted to this list. Numbers, don't add two numbers, dot add three. Now the numbers ArrayList is very similar to the numbers array which has commented out. Now obviously in such a simple example, it won't matter. But if we really want to add, let's say, ten or 100 numbers, we can easily loop through those numbers and then pass them into the add function right here. Or if we wanted to, we can pass in an array into the new array list constructor right here. Now we can't just pass in a generic array. We have to say arrays with a capital a dot as list. Now within here, we're gonna have a varargs with any number of integers. So I can say 123. Now if I delete this, we're still going to have the same exact result. So if you have an existing array, you can easily pass it in, similar to syntax like this. But typically you're not going to do this. Most of the time. You're going to just create an ArrayList and then add things onto it as you need. So let's go ahead and print out everything here. I can print out numbers. And if I run this, we now see 123. Let's go ahead and try or moving some elements from here. I can say numbers dot remove. Here we can pass in a specific object or a specific integer. An integer is not going to remove that specific element. This actually going to remove the index. I kind of move index one, which is going to be the value two. I run this, we now see just 13 in our array, like we do right here. But what happens if I want to actually just remove the number two? Well, like I say, integer value of and pass into. Now if I run this, we're going to see 13 as we do right here. Now this might seem a little weird. Why do we actually have to do this? Well, if I say numbers dot remove here, we see that this is an overloaded method. We can pass in an index or a capacitor, an object for passing in just the number two or the number one or any type of basic integer. It's going to treat that as a primitive type of int. It'll uses topic sample right here. But if we pass in a specific class or an object that represents something, then it's going to use the second option right here. This is exactly what we're doing with this line of code right here. This is going to pass in an object and not just a primitive integer. It will then go through the ArrayList and trying to remove any elements that match this value here, which in this case it does, as we see, we do not see the number two. Now let's print out how many elements there are in the surrealist. So I could say numbers dot size. If I run this here, we're gonna see two in the console. And we can also clear this. So let's go ahead and say numbers. Dot clear. Now if I run this, it's going to actually clear this after we print out the two numbers as we see right here. But our size is now at 0 because we've actually cleared the ArrayList. Now an ArrayList and listen general is known as a collection. It's basically a custom class that allows us to add certain things on and remove certain things. And there's a bunch of different examples of them. In this video and the next video we're going to go over two examples. But honestly covering every example would warrant its own course just on that. So we're just going to stick to some of the more basic, more commonly used collections, such as ArrayList and HashMaps, which we'll take a look at in the next video. 44. Maps and Hash Maps: We're now gonna take a look at HashMaps, which are a way to store something known as a key value pair. Basically meaning that for every single key, there is a corresponding value. Let's take an actual look at some examples. Here. I'm going to have a map, and this has going to store a key and value, which can be two different types of variables. For example, the key can be a string and the value can be an integer. Similar to ArrayLists, these have to be the actual class types. So we cannot say int here. We'd have to specify integer with a capital I. Within here, I can add in different types of scores. And I'm going to assign a equal to a new HashMap. Now similar to an ArrayList, we can add in a string and integer if we want to. But in modern Java is not necessary, so I'm not going to. Now, what exactly is a key value pair listed at these scores are for a certain video game. I can say scores dot. And here we can see we're passing in a string, which is what we have from this string right here. And we're also passing in an integer from this integer right here. This is a key value pair. For example, let's say that I have 77 points in this game. I can say scores dot put. Bob has PD points in the game and scores dot put here, joe has 30 points in the game. Let's go ahead and print this out to the console. So I can print out scores and I can run this. And here we see Alex equals 77, Joe equals 30, and Bob equals 80. But what other options do we have when it comes to this? I can say scores dot here. I can get an, a certain thing. And this was where we would pass in the string. For example, I can pass an Alex. And I'm going to cut this entire line here with Control X or Command X on Mac. And then I can print this out. I can paste it in with Control V or Command V on a Mac. And if I run this, we're going to get the scores for the string Alex, in this case is 77. If I say scores dot, we could then clear it similar to an ArrayList. This will just remove all the entries. We can get an entry set or a key sets. We can also get the values and we'll take a look at what those three things do here in a moment. We can see if it's empty. We can replace certain things. We can get the size. Here's where we can get the values. We also can see if it contains a key, horrific attains a value. And there's a bunch of other options, such as removing them. Most of these are self-explanatory, other ones you might have to experiment with or look up the documentation. Let's go ahead and try looping through all of the keys or all the values or both. I'm going to get rid of these print statements here. I'm going to say for string key. And then here we're going to use a for-each loop. So we have our colon here. I can now say scores dot key set. And this returns a set which is similar in concept to a list which we saw in the last video. Now within here I can just simply print out key. If I run this, it's going to print Alex, Bob, and Joe, as we see right here. But now what happens if we wanted to get access to the values? I can say scores dot v, and here we have values. Now we'd have to change this to an int, I guess I int value. And then I can print out value. If I run this, we can now see all three of the values from this exact map. But what if I wanted to gain access to both? Well, I can say for entry with a capital E, we're going to use this from Java util map. Here we have to specify what types of variables we need. So in this case a string and an integer. I'm going to call this variable entry. Then with a colon, I can now say scores dot entrySet. Now if I hover over entry sets, this is going to return a set of an entry which has a K and V, which stands for key and value. So essentially, I can say entry dot fgetc key or entry dot get value to gain access to it. For example, string key equals entry, talk KCI, and then int value equals entry dot get value. I can then print out key which has the username, has plus value points. Now if I run this, it's going to print out what each user has and their corresponding points, as we see right here. 45. Building a Jar File: We're about to approach the final project for the course, which is going to be remaking the game Battleship within Java. But before we do that, we need to make sure we understand how to actually convert our Java code into an executable file. You might be familiar with dot EXE files where you can double-click them and it'll open up a program. In Java, we have a dot jar files, which you probably have seen before. How do we exactly convert all of our source code into a dot jar file that we can actually run. Well, the first step is to click on the gear at the top-right and then go to project structure. Or you can use this confusing shortcut right here. Once you're here, you want to go to the left and click on artifacts, and then click on the plus hover over jar and then go to from modules with dependencies. From there, we need to specify a main class. This is basically the class where our main function is. If I click on an Open Folder, it'll automatically select all the different files that have a main function in them. So we only have one. We can simply click on Okay, and then click on Okay again. Now from here, I can click on Okay. Then I can click on Build, build artifacts. And from here we can simply press Enter or you can also click on Build. We see that it is building something near the bottom. And now that is done, we can expand our OUT directory, go into Artifacts. And here we see our workspace dot jar. I'm going to right-click on this. I could then click on Copy path slash reference. And then from here I'm going to click on absolute path. If I paste this in, this is going to be a file path to this exact jar file. Now to run this, we can't simply just open it up. We need to actually run it through a terminal. The reason for that if this is a console application, meaning that we are working within our console like we've seen throughout this entire program. So therefore, we don't have a custom window with buttons and images and all that stuff that is outside the scope of this course. We haven't covered any of that within this course. So how exactly do we run this? We have to open up our own terminal. If you're on Windows, you can go ahead and do a search or command, and then go ahead and press Enter. Now if you're on a Mac because I don't own a Mac, I'm not sure how to do that, but you can simply just google how to open terminal on Mac and it should have a bunch of results. So I'll help you out. Now, either way, once you have your command prompt or your terminal open, you could type in Java space, dash jar space, and then you want to paste in your path. But be aware if you have spaces in your path, you need to rapidly entire thing and double-quotes. I'll add into double codes here. And then inside I can right-click to paste in the path. Here we see the Warnock keys folder has spaces in it. So I have to add in double-quotes on either side. If I press Enter, we see that nothing actually happens. That's because our code doesn't actually do anything. Let's go ahead and print out the text, Hello World. And then I'm going to go to Build, build artifacts and press Enter. Here we see it's building one more time. Going back to the terminal, I can press the up arrow to go to the previous command. If I press Enter, it's now going to say helloworld. The actual code is now ran through this jar file. 46. Battleship Project Intro: We're now going to be diving into the final project for the course that is going to be making a single-player Battleship game. Here we see this board and we have five different types of ships, and they're all randomly positioned around the board. We can then enter coordinate, for example, a 0, which is actually empty as we can see right here. And it will then say miss. But I can select H for this coordinate right here. And it will then say hit. And this is now replaced with an x. If I do I, then j 0 is then going to say, use sank their battleship and this entire ship right here is sink. Now, unlike previous videos in the course where we wrote code together, during this project, we're going to be working on the plans for each individual feature together. And then I wanted to try and make that feature on your own. Now once you've completed that feature, or once you feel like you've done as much as you can and you still need additional help. You could then go to the next section of the video where we will actually be building it together. But I highly encourage you to try each individual part of this project alone before watching the step-by-step tutorial. This is how actual software developers work. So it's a great habit to get into that way. You can build a skill of problem-solving using programming. 47. Files and Coordinates: To start the project, I would delete all the files you have in your project as safe home, the file that has your main function I was in creates these five different files here. And keep in mind that battleship Maine file. This contains my main function right here. Now there's a lot of pieces within that project that rely on each other. For example, if I hover over my main function here, I'm creating a player object, and I'm creating a board object. In order to make things step-by-step, we want to start with the smallest possible piece that is going to not depend on anything else. And it's also going to be used and various other places in this project here that is going to be a coordinate. Now I mentioned that you should write everything yourself before actually following along. But this file is very simple. So I'm just going to run over this file real quick with you. And in future videos with this project, you're going to want to try things on your own before you follow along step-by-step with my own explanations. Here we have a chord class which stands for coordinate. This is going to represent an x and y-value on the board itself. Also going to have a Boolean property, which is going to represent if this has been hit. Therefore meaning that if a ship is there and we actually guessed that coordinate. Now, when we create a coordinate, we're simply passing in x and y through the constructor and we're assigning it to the local variables here. We then have a getter and setter for all three private properties, the x, the y, and the is hit Boolean. So essentially we're able to get the x, get the y, C If this coordinate is hit, as well as those individual values as well. Now here we have a toString function. Whenever we print an object to the console, it's actually going to run the toString function behind the scenes. So essentially if we were to print out a coordinate, it's going to print out x comma y. Now, just for clarification, if case you don't know what a quarter is. Each individual cell here is going to be its own coordinate. For example, this has be 0, this is a one, and so on. We are eventually going to create our own board here. We're different ships are randomly placed and the board columns are represented from the letters a through J. And the board rows are represented from the numbers 0 through nine. Now this x and y value is going to represent where they are depending on the columns and rows. And the hip value is going to represent if this has been an actual hit. So therefore, we've guessed where a ship is. Here we have a C5, for example, for this cell right here. If I say C5, then going to change to an x. So therefore, this coordinate and my program has the value changes to true. 48. Ships: Let's now create our very own ship. And before you actually write any of the code yourself, I highly suggest that we actually look over the plan for this class and exactly the tips that I've given here. What exactly is a ship? Well, obviously within our program here, if I open it up, this is going to represent an actual ship where here we have four different coordinates. And the situation we have five different coordinates. This one's a smaller ship, was just two of them in total, five different chips. So if we look at this class, the first thing we see is a private list that's going to hold a number of different coordinates. Of course, this is the class that we wrote in the last video. As we see right here, each ship requires its own list of coordinates, so we know exactly where they are. Now we also see all possible ship sizes right here. And keep in mind that every comment I add in, such as this one right here, this block of comments right here is designed to help you as much as possible and give some useful information of what's inside these functions. But here we have a static method that returns an integer array. This is basically just going to return 54332. And if I go over to my program and I run it again, here we see a ship that is five long. Here we see a four long ship, but it's just a vertical. Here we see a too long a three and then another three. So if I were to add in a six long ship, and then I run that program again. We now see it right here. This is going to determine how many different ships there are in the sizes of each ship. So keep that in mind moving forward by default, I have 54332. Now next we have the constructor. And because this has only one line long, I can't really hide the functionality from you, but obviously it's very simple. We're just receiving a list of coordinates and we're assigning that to the local coordinates list right here. Then we also have a getter for both the coordinates and the amount of coordinates we have. Basically get size is going to get the size of the ship as it kind of describes by the name. Meaning that right here, this three will return three lists to overturn two and so on. Now these are probably self-explanatory, but the next few ones might not be. And again, I highly encourage you to take a look at the different comments I added in. For example, this is GET index returns an integer and it takes in a quarter in it. And if you remember correctly, an index is where a certain element is within an array or a list starts at 0. Here the description is, this returns the index in the coordinates list where the perineum cord was found. This is the perimeter coordinate and we're referring to the coordinates list right up here. Now scrolling down further, we see that this returns the index of its present or your returns negative one. If it is not present. If you cannot find the index, then you want to return negative one. Now next here we're going to see if this is already in use. Here it checks to see if a coordinate is within the ship. Here's a tip. Use the GET index method. Essentially get index should return negative one if it is not in use or it should return something else if it isn't US. And then here we have a more complicated function, which is it checks to see if a given coordinate would be a hit. Now the complexity from this function comes from a, returning a Boolean array. This array is going to hold two different values. The first one is going to be a Boolean, true or false if it was a hit. In the second one is going to be a Boolean, true or false if it's sank the ship. So for example, if I guess something and it's a miss, we will have false and false. Here we'll say mes equals false and false. If it's a hit, but it does not sink the ship, there'll be true and false. If it doesn't sink the ship, then it's going to be true and true. These are the possible return values when it comes to the functionality. This has all the functionality that a ship has. So go ahead and pause this video and try and add in as much as you can, try and get as far as possible. And once you've completed everything or you've tried your best and you really just need extra help. Then go ahead and resume the rest of this video and I'll go over my solution for how I made the ship. Alright, so starting at the top, here we have a GET index. This is the first hidden method that I did not go over yet. So let's review what this is trying to do. Here. We have a coordinate arguments and we're trying to see where exactly this is within our coordinates array, which has stored locally on his class at the top right here. Essentially it'll return index or it will return negative one if it cannot find it. So we're going to start off by looping through each individual coordinate within our list. We're saying int a equals 0, while a is less than the coronet list size, we're going to increase a pretty standard for-loop. Within here. We're going to get our target quarter in it. And this will change depending on each iteration of the for loop. Whereas then simply just going to check if the x value equals the target x-value and the y-value equals a target y-value. If both of these are true, then that means this is the same exact coordinate. And we wanted to return to the current index, basically just returning a. Now if this statement is never true, then we're eventually going to break out of this entire loop. And therefore we're going to start just returning negative one, meaning we could not find it. This would be the GET index function. Now let's move on to the end-use function, which basically just use the index method. Here. We're creating a Boolean called is in use and assignment equal to get index passing and coordinates is not equal to negative one. So negative one means that nothing was found. And if something was found, that that means something between 0 and the total number of coordinates would be returned. So basically, if the index is not negative one, that means it is news. Now we can actually simplify this code. I wrote it in two separate lines just so I can minimize this, because single line functions cannot be minimized as we see right here. If I minimize this function, we still actually see the code. So going back down to simplify this code, I can just simply return, get index, passing and coordinate is not equal to negative one. This will return true or false depending on if this coordinate isn't used for the ship. Then here we have the more complicated function which is did hit. And again, this returns a Boolean array where the first Boolean value is going to be if it was a hit and a second Boolean value is going to be if its think that ship. If I expand this here, we're first going to get the index from our GET index method. And if the index is negative one, that means that this was a miss. So therefore, a miss should return a Boolean array with false and false, as we see right here. Here we see this negative one, which is going to be the same exact negative one that is returned if we can't find anything. Now, after that, once we get to this code here, we know that we actually hit something. Now what he says, see if we actually sank that ship or if it's just normal hit. First, we're going to get the coordinate at that certain index and we're going to set its hip value to true. If you remember in the coordinate class here we have this Boolean hit. And so we're now assigning this to true because we did actually hit that part of the ship. Now going back into ship here, I'm going to create a Boolean called sank and set this equal to true. Essentially meaning that by default we're going to assume the ship sank. And then here we're going to loop through every single coordinate of the ship. If it is not hit, then what's to say that sank equals false and we're going to break out of this loop. So essentially, all this code does right here. It's a seat if the ship has any coordinates left that are not hit. If every single coordinate of the ship is hit, then the ship will then sink. Then finally, we can return our Boolean array. At this point of the code right here, we know that there was an actual hit. The first Boolean is always true, but the second boolean is going to be true or false depending of it actually sank ownership depending on his logic right here. This is going to be the dead hit function. And this is probably the most complicated function in the ship class. But hopefully all this explanation made sense to you and hopefully you got most of those functionality down. Now, of course, in programming there are many, many different ways to write this same type of code. So if your code achieves something similar to what mine does, and if it works, then don't worry, if it looks slightly different, that's perfectly fine as long as it's still does the same thing. 49. Player: Let's take a look at the player class. This is basically just going to handle all the ships for a specific player. Now in this project we only have one player. So basically, this is just where we handle all of the ships. So I'll show you a few pieces of basic setup code. But when it comes to the actual functionality of how everything works, I highly encourage you to try using my examples here and go ahead and write the functionality yourself, and then come back to the video. One has showed you my own examples. To start off, here we have a list of ships, the ship class, That's something we made in the previous video. We also have a constructor here, which is going to receive the board size. If we go to my main file, here we see we are making a new player and we're passing in the board size. Now, going back, we also can return all the ships, just a very simple getter. Now, moving forward here we have a random function. The goal of this is to randomly assign a starting point for a ship depending on the board size and the boat size. It also should make sure that the boat can actually fit on the board. For example, here we have this five long boat. And if this starting point was, let's say J4, where to actually ends here. Then there'll be four characters, there'll be off the board. We can't have that. So we want to make sure we can actually the boat on the Akron board. Now this returns an integer and the return statement says the starting position for the ship to fit on the board. For example, if this starting position was right here, this would be six because G is equivalent of six, I'm just displaying letters here, so it's easy to distinguish if its rows or columns. But let's say it's starting right here. This would be six and this would not fit the entire board because this is a five long ship. We have ten total columns and ten rows. Six plus five equals 11. So we would go off by one. It's going to return five instead. Basically meaning we're going to adjust for that change to make sure that the board can fit the boat. Now moving forward, Here, we're going to have a guitar coordinates with a starting coordinate and an ending coordinate. This is going to create a list of coordinates from a starting ending point. An example is a start of zeros 0 and an end of 03. But let's return would be 00010 to the goal for this is to pass in a starting coordinate here and an ending coordinate here. And it will then return all coordinates needed in order to fill the entire ship. Moving forward here we have is in use or basically going to check a coordinate and see if any ships are going to actually be using that. Then here we have placed ships, which is actually the most complicated function within this class. We're going to run the ship, it gets sizes. If I go over here and this is going to return a new integer array. In my case, I have five different ship sizes. I have a five long, uh, for long. Two instances of a three-level ship, and finally A2 long ship with them player. Here I'm going to run ship dot get sizes to get all ships and randomly assign if each ship should be vertical or not. If I go into my board here, we see that five is horizontal. But this three right here is vertical. But this three right here is horizontal. Twitter going to randomly assign a vertical Boolean to each individual ship that we're gonna try and create. We're also going to randomly assign a starting coordinate and add the ship size to get the ending coordinate. For example, here, this RNA coordinate will be five for, but we're going to add the ship size to get the ending coordinate right here. This is going to be 94. Keep in mind that a is basically 0, which is why J is nine. Next it says a mixture that all coordinates allow the ship to fit on the board and are not being used by other ships. You can use previous methods we've made in this class for that. Basically making sure that is a unique coordinate that will actually work. Then finally, add the resulting ship to the ships list, which is declared right here at the top. Now here's a tip. The starting coordinates x and y values should be randomized. So for example, this right here, this 54 coordinate, this will be randomly generated. But the ending coordinates x and y values, will simply be the ship size added to the starting coordinate. For example, here we have a five long ship. So we're going to take this and add five to it. Obviously will count that starting one as one and not 0. So we're basically just going to end with a five lordship. Also, you should only add to either the x or the y, depending on if it's vertical or not. Never both. So basically here, this has a horizontal ship, which means we are only adding to the y. We see that the x is four. The entire time for this entire ship is only the y-values that are changing. For example, f through j. If we were to add to both of them, we would have a five-by-five grid here with a giant platform, but we want an actual representation of a ship. This is going to be slightly more complicated, especially on a place ships function than the last class. But try and get as many of these things done as you can. And then once you feel like you've gone as far as you can, or once you've completed everything, go ahead and play the rest of this video so you can take a look at what I did for the solutions. Let's start at the top for the random function. If I expand this here, I'm going to start off by making a random integer. With a maximum value of the board size. In this case between 09 because the board size is ten. Then I'm going to say, while the random number plus the boat size is greater than the board size, I'm then going to subtract the random number. So let's take a look at this five long ship right here. If our random number started right here, which is six, we now know that six plus five, because randomness six boats heisst five in this case, that is greater than the board size of ten. We're going to continue to subtract it until it actually fits. In this case, we're just subtracting once, giving us this position. And then we're going to return the new starting position. This is one solution in order to randomly select a starting point and making sure that the starting point will actually work when it comes to the boat size and the board size. Now next here we have get all coordinates. At the start, we're going to make a list of coordinates, and we're also going to return that list at the end. Then we have to actually mutate or modify that coordinate list in order to have all the values that we want. Now we're going to be adding to the x or the y, depending if it's vertical or horizontal. Here, I'm first starting off by checking to see if the x values are the same between the start and the y-coordinate. If we take a look at the boat, for example, this right here, the x-values are always the same. They are always four. Therefore, this has a horizontal boat. So with that said, I need to continuously increase the y-values. Now in here I'm going to get the minimum and the maximum y-value. And we see right here I am only using Git. Why? Because again, the x-values are always the same. I'm then going to loop through all the y-values. I'm going to add a new coordinate to the coordinates list that we made right here. I'm going to always use the same exact x-value, but I'm going to pass in the y-value from a for-loop. That way the exit always the same as it should be for this boat, but the y-value is voice changing. Now in this else statement, this is the exact same concept, but instead of the y-value is for the x-value. Then after either these are ran, then going to return the list of coordinates. Moving forward, we now have the easiest function in here which is going to pass in a coordinate and see if any of our ships are going to be using it. So basically we're looping through all the ships. If it's unused, we're returning true. Otherwise we're going to return false. Now, moving forward here we have the most complicated function, which is to place all the ships. We're going to start off by looping through all the possible ships that we want. Then we're going to randomly assign a Boolean if this should be vertical or not. We're then going to create a list of coordinates, but we're not going to assign anything to it just yet. Now you might see a keyword or to hear that you're not too familiar with. For example, what is this main colon or before this while loop? And what are we doing exactly right here? Basically because we have our main loop and we have a loop inside of it. With this for-loop, I need to make sure that I label each loop correctly. For example, if this is true, I want to continue on our while loop. But because I'm inside the for-loop, it will assume I'm continuing on the for-loop itself. With that said, I have to add a label to the while loop. And then I can continue on that specific while-loop and not in the for-loop. Let's take a look at what the for loop is doing. First of all, this is an infinite loop, basically meaning we're going to continuously run all this code until we eventually reach this break statement here. So as I start, I'm going to get this starting x and y-values. I'm then going to use those to create a starting coordinates. Then I'm going to get the ending coordinates, but I'm not going to randomize these. Instead I'm going to say index and end y are going to equal to the start x or y plus the boat size. If it is a vertical boats, we're going to take the starting x, and that's all. But if it is not a vertical boat, we're then going to take the starting x and add on the both sides. Then it is the reverse for the end. Why? If it's a vertical boat, we're going to take the starting y and add on the both sides. Otherwise, we're just going to use a starting Y. And then we'll use these two values to create an ending coordinate. Then we're going to assign a new value to this coordinates list right here. That value is going to be the results of guitar coordinates from the start and the end. This will take the start and the end coordinates and everything in-between and add them to a list. And this is the function we previously made. Now afterwards I'm going to loop through all the new coordinates that we just got, and I'm going to make sure that they're not in use. If they aren't used, we're going to jump back to the start of the while loop and basically just keep trying again and again and again until you find a bunch of boats that have not been used before. Now if all the boats we found our exclusive, meaning that they are not overlapping over each other. In this for-loop is going to just run through itself and going to continue on into this break statement. Now this break statement will break out of this entire while loop. And then here we're going to create a new ship passing in the coordinates we just got, and then pass the entire ship into the ships list right here. So this is definitely one of the more complicated functions. I don't believe we even covered these labels here, but there are definitely other solutions that don't require these labels that he might have been able to find. But if you weren't able to get the place ships or anything else in the player class. Don't worry, the place ships functions specifically was more complicated than most of the stuff we've covered so far. 50. Finishing the Game: This will be the last video on the battleship project. Within this video, we're going to create our board class and our battleship class. So let's start with support class, which we are making a New England sub within our main function. And here we are passing in the board size as well as the player which we have already created. Now in the board class, I'm going to go over some basic functionality, and then I'll go over the concepts behind these different functions here. So you can go ahead and try to make them on your own. And once you get stuck or once you complete the functionality, you can then see how my solutions look. So starting off, we have an integer for the board size. This just simply comes from the actual parameter. Then we also have a multi-dimensional character array. This is going to be the actual board itself. For example, this is index 0, index one, index 10, and so on. Then we have a letters list which has all the different letters for the column identifiers. So basically all the letters we see right up here. That way we don't have a 00 as a coordinate or 10 as a coordinate where it's unclear which one is the columns and which one is the rows using letters makes this very clear. Which one is the columns and rows. Then we have access to a player here, which also we are just getting from the perimeters. And so we're just assigning it right here. We are first creating a game board, which we'll take a look at here in a moment. And then we're going to place the ships for creating the game board. This is going to fill each coordinate with the board with a certain space character. So for example, board index zeros, 0 equals space. Now of course, you shouldn't manually assign each one of these. This should be done through a for-loop. Now moving forward, here we have placed ships. This is going to loop through player dot get ships. And to review that real quick, under gets ships right here. This just simply returns a list of all the ships attached to this player. So we're going to get all the ships with a player, and then we're going to get the ships coordinates in order to get the x and y-values. If we go into the ship class, here we see get coordinates. And this just simply returns a list of all the coordinates associated with that ship. We're then going to assign the ship size as the character in board X and board. Why? For example, here this five long character, each individual board index, for example, this one, this one and so on are called five because this is the five long ship over here. This is the four long ship. Here we have the three long ship. So the characters are going to be how big that boat is. That way it's very clear where the boat starts and stops. And here's a tip. An integer will count as a character, but not in the way that you want. You need to convert ship dot get size into a string with string dot value of and then access the first character of the results. The reason for this is because every single individual character is going to have a number associated with it when it comes to its ascii value, which is going to basically just be a table of what each individual character on your keyboard represents in a numeric value. You can go ahead and Google ascii value or ascii table to get a better understanding of what I'm talking about. But with this said, you need to make sure that you're actually converting the ship size into the real number you want, because by default it will not represent the real number. But basically this means that ship dot get size is going to return a number that you're not expecting. And so you need to convert it into a string first with string dot value of. Here we're going to get a letter index. And you can actually see this function here because it is only one line long. But let's go over it real quick. Here we're going to return into America value for each letter in the letters array. So we're passing in a certain letter here. And this is the literacy could be index of, and we're going to return the index of this letter from the letter array that would define a fraud appear. For example, a would be 0, and so on. Now next we're going to attempt to hit a certain coordinates. This would see if a coordinate would be a hit or not. We're going to pass in the x and y value of the coordinate, and it's going to return a string. If we missed, it will return mess right here. If we hit, it will return hit right here. If it is a hit, that would sink a ship, it would instead return, you sank their battleship. Now, finally here we have two string. Whenever we're printing an object to the console, IF function is going to be called. So we can override this method to make it. So whenever we're printing the board to the console that we're going to print exactly what we want, which is going to be the full board, as we see right here. This is printed because our pal ship class, whenever we're running the game loop, we're going to print out the actual board, but we'll cover that here in a moment. This is going to loop through all the board coordinates and prints the correct characters where they should be. And a tip here is to print the column labels first, which is the letters, as you can see right here. Then print each row one at a time, starting with the row number, and then each coordinate for that row, we're going to just print out the row number. And then we're going to go through and add an each individual coordinates. And keep in mind that these lines right here, also known as pipes, are by holding Shift and pressing the backslash button, which is right above Enter. Then I have a space. Then I have the actual content for the individual coordinate, then another space followed by more lines. So this function here is going to return a string that represents this entire board right here. This is going to be the entire board class. Go ahead and try and make as much progress on this as possible, and then come back and see my solutions. And then afterwards, we'll go over the concepts behind the battleship class, which just has two main functions. But for now, go over the board functionality and try make as much as possible. Alright, so hopefully you were able to add the functionality for the board class, or you were able to get as far as you possibly can. Let's now go over my solution for how I implemented these functionalities. So here we have create gameboard. If I expand this, we're going to loop through each individual array of the board. So each individual row is going to be a nested array within the multi-dimensional array right here. I'm then going to fill this entire row with a space. And if you created a nested loop to go ahead and do this, that's perfectly fine as well. Like I've mentioned before, there are multiple different ways to solve each problem when it comes to software development. If you wrote this code, that's fine. If you wrote code similar to it, that still works. That's fine as well. Next we're going to look at place ships. If I expand this, we're going to loop through every single ship that the player has. Then we're going to loop through each coordinate of that ship. We're going to get the x and y value from that coordinates. And we can then assign board index XX and XY equal to this expression right here. This goes back to what I was mentioning of using the ship size passed into string dot value of dust because we are looking for a specific character and each individual character has his own integer value. Because this is a character array, we cannot simply just assign an integer to it because each individual character on your keyboard is represented by a specific integer. And it will assume that that is going to actually be the case. For example, the character 0 as represented by numeric 48, the character one represented by numeric 49, and so on. What we want to do is make sure that we were actually using the correct string. We're going to take the ship size and pass it into a string. But of course, this gives us a string variable when we want a character variable. So we can simply just access the char at index 0, which there's only one index because this has only a single digit value. But basically, this will convert the ship size of five into the character five and then assign that to the correct board position right here. So this will go through all the ships and basically just placed the 5's where the five long ship is. The threes are, the three long ship is and so on. Now moving forward here we have get Letter index which was covered earlier on FSS single line of code. Moving forward again, he, we're going to attempt to hit a certain coordinates. So first we're gonna create a coordinate with the x and y-value. And then we're going to loop through every single ship for this exact player. If you remember from the ship class, we have a did hit function by go over to that. Here this is going to return a Boolean array where the first value will be if it was a hit and the second value is going to be if it's sink the ship, false. False means it was a mess. True false means it was a hit, but it did not sink that ship. And true, true means that it did hit and it did sink that ship. So going back to my board here, I'm going to get access to all the hit data. And then I can create two separate Booleans. Or did hit is index 0 and sink is going to be index1 with zinc went to see if he is true. If so, we're going to X out that specific coordinate. So for example, if I run the program here, I can select B1 to represent this right here. I can enter B1 and it changes that three to an x because that was an actual hit. And it also returns the string hit right here. So in order to do that, here, we're going to return if a sink using a ternary operator, we're going to return us think they're battleship, but otherwise we're going to return hit. And this is actually where the strength comes from that we see in our console right here. Now after this for-loop, if nothing actually matched, that means that it missed. So we're simply just going to return the string miss. Moving forward here we have a toString function. This is basically just going to print the entire board to the screen. We're going to use a StringBuilder class. And there's nothing wrong with using a normal string and just adding onto it. They're basically going to do the same thing. But I'm using a StringBuilder, which basically just allows me to add more things to the string in a cleaner way. But behind the scenes it's basically just adding onto a string. Here I'm starting off with these extra spaces. Because if I go to my program, that's what we see right here with us highlighted text. This is the starting spaces to make sure that the column labels are lined up with each individual column. Then I'm credit something known as a delimiter, which you can kind of think of as a separator. And this will be a space followed by a pipe, followed by another space. And that's what we see right here in-between each individual character for the exact coordinate. Then I'm going to add an a comment. I'm going to say that this is going to be adding on the columns. So I'm going to loop through the board size because boards are always a perfect square. I can loop through the board size two different times. One for adding the columns, one for adding the rows and the individual content. Here I'm going to append the letters dot get a, which will start at 0 and loop through the entire board size, which is why we see this right here. I can now loop through this entire thing. Next, we're going to append the delimiter to the actual string, basically adding on the space, the pipe and the extra space. But we do not want to do this when it comes to the very last element here, as we see, j does not have an extra line at the end of it. To check this, we can say if a is less than border size minus one, if I were to change this, and I will run this one more time, we're going to see an extra line on the edge of j. Which I don't really like, but that is up to you if we want to have that. So I'm going to change this back to what it was. Now moving forward. After we've added on all the columns, we're going to add on a new line using the four slash n escape character. From here. It's then going to go to the next line right down here. Now here we're going to add on each individual row and the actual content for the board. So essentially we're going to have a nested for-loop, looping through it, basically twice, one for the x values and one for the y values. Inside of this nested for-loop. We're then going to have a and B, which basically can represent x and y. In fact, to make things easier, I'm going to click near a, and I'm going to press Shift and F6 and rename this to x. Then I'm going to do the same thing like be shift and F6 and I can change this to y. Now this makes us more clear when we're accessing the board values are basically just looping through the entire x and y coordinates for the possible values. Now one thing I want to do is when y is 0, that means we're at the very start right here. And so we want to add on the row number, for example, 012 and so on. So we're going to add onto that right here, and then we're going to append the delimiter, that being a space, pipe space, which we see right here. Now afterwards we're going to add each individual character. We're going to add on the board at index X and index y. Here is 00, here is 01, is 0, to here is 10, and so on. Now, most of these are gonna be spaces, but of course, when the ships were created, they were placed specific random characters with where the boats should actually be. Afterwards, we're just simply appending the delimiter that way after we print out this space here, we'd have another space with a pipe and another space to create some whitespace to make it easier to read everything. And then afterwards we're going to append a new line. This is going to what's taking this line right here and wrapping it down to the next row. Then at the very end of the function, we're going to return results at ToString, basically just returning the string that we just created. So this is everything when it comes to the actual board and printing things out. If this was a complicated for you, don't worry, that's completely normal. This project here is assigned to have some easy aspects and some challenging aspects. If he gets stuck in these parts, don't worry, this perfectly normal. But now that we have our board class created, Let's go over to our battleship class, and let's take a look at the final two functions we need in order to make everything work. So, so far we've created a player and created a board. And now we're going to run, run game loop passing in our board. There are two functions similar to the rest of this project. I'm going to explain the concepts behind it and then you can go ahead and see what you can do with those concepts and then afterwards check my solution compared to yours. So here's a description of how this game loop is going to work. We're gonna create an infinite loop that will do six different things. The first is to draw the current game board, basically just printing out this board object to the screen because we created a toString function down here. Whenever we print a port object, it's going to run this function. Next, we're going to print the last action. So this was either a miss, a hit, or sank their battleship. We're going to actually want to create this string that's mentioned here before our wild loop. Then we're going to ask the user for a coordinates, or they can input the string quit. As we can see right here at the bottom, enter coordinate. Here's an example, or quit to stop playing. If I enter quit, it's actually going to close the program. Basically meeting, we're gonna return from this function. Notice that four is what I've just described. Quit the game. If quit was entered, that five. Now this is where most of the logic is. Step five is to check if they coordinate is valid. Basically meaning it's going to have to individual characters. The first one is a valid letter that is part of this array right here. And the second one is a valid number between 09 if either of those are false or it is not a character long string, it's going to continue to ask them for the correct coordinates. For example, if I run this and I enter or simply just a, it's gonna ask me again, if I enter Z 0, it's going to ask me again, if I enter a 0, it's going to actually work. It has to be a valid coordinate. And this is actually what we're going to do in this next function right here. But I'll describe that once we get there, we're going to first check if a coordinate was valid. If so, we're going to attempt to hit that coordinates. Then we're going to store the last action string to print it out after the board is displayed on the next loop iteration. That's why I mentioned right here. Basically we're going to have a string before a while loop, but we're going to assess value once we actually had determined if it's a valid coordinate. And after we've tried to hit that coordinate, that way when we loop back to the start, we're going to draw the current gameboard. We're going to print the last action. That way the game board does not cover it up and then we're going to continue on afterwards. If the coordinate is not valid, then we're going to jump back to step three, which is right here. Ask the user for a coordinate input or to enter quit. This right here is what we're going to do to loop again and again and again, if they do not enter a valid coordinate. And this is where all the parts of the game come together. Now, this function here is going to use this next function which is valid coordinate. We're going to pass in a string, which will be the actual user input. When I enter b5 right here, the string B5 is going to be entered within this parameter right here. We're also going to have a board. And if we look at the exact description here, this is going to check if the user input is valid. Now there are two requirements. The first one is it must be a two character long string. The next one is it must be a letter. It a through J only, followed immediately by a number which is 0 through nine only. Now here the tip input is received and strings. So getting an int value of the second character, which should be 0 through nine, will not act like 0 through nine. Instead, it's going to act like it's ascii chart values, which I mentioned earlier in this video. This means the character 0 would equal the integer 48 and the character one would equal the integer 49, and so on up until the character nine equals the integer 57. To check if the string input of the second character is 0 through nine. You actually said check to see if it's integer value is greater than or equal to 48 and less than or equal to 57, basically meaning 0 equals 489 equals 57. So we want to be within these two values right here. Go ahead and write the functionality for this. I would suggest starting with the is valid coordinate function because it required for the game loop. And then once you have this done, go ahead and try and tackle the game loop. And then afterwards you can compare your solutions to mine. Let's start off with the is valid coordinate. If I expand this, here are first going to see if the length of the string is not equal to two. If that is correct, then we're going to return false because this has to be a two character long string. For example, if I enter B5, which is three characters long, It's then going to ask me again, if I entered test, which is not two characters long. It's going to ask me again, and it will continue to ask him again until I enter a valid coordinates such as J nine. Now obviously this is a mess, but it actually worked. Now afterwards I'm going to create a character array to separate the exact coordinates into the individual characters. The first thing to do with that information is to check if the letter actually exists. Board app.get Letter index, as we see right here, it's going to return the index from all of our letters right here. Meaning that if it does not exist, It's going to return negative one. This will basically make sure that a through J was used. Now if it's not, we're simply going to return false. But if it is used, we're gonna continue and move on and check the next values, which will be checking 0 through nine. Here we're creating an integer and a string is equal to a character. Remember, array is a character array, meaning that they're going to be individual characters which have numbers that represent them. For example, the character 0, represented by integer 48. Character one is represented by integer 49, and so on. We're going to actually make sure that this is nine by seeing if the value is greater than or equal to 48 anion. If the value is less than or equal to 57. If this condition right here is true, that means that everything is correct when it comes to the valid user input. So now let's scroll up and let's make the very final function for this entire project, which is run game loop. I'll take all the functionality and put it together to actually be usable. If I expand this, we're going to start off by making a scanner. And we're going to create a string, which is called last action. And we're assigning this equal to null. We're going to assign this later on. This will be either the mess or the hit, or the US sank their battleship string. And we're going to go ahead and make this first because we're wanting to print out the board. And then immediately afterwards we're going to print out the last action. That way it is not automatically replaced by the board. For example, if I were to print this out beforehand, an hour to run us. If I enter a 0, for example, the board covers it up. If I scroll up here, we see the mess. So this is why we need to create a string outside of the while loop. So it's not going to be reset each time, and we can then print it out if it actually exists. Next, we're gonna create a string called coordinates, and this is going to receive the user input. Here we have a do-while loop, which if you remember, basically this is going to run this exact code at least once, no matter what. Then afterwards, it will continue to run this code as long as this expression right here is true. So let's take a look at what this code inside is. Here we're printing out inner coordinates, example a 0 or quit to stop playing. We're then going to get the next word that the user enters. And we're going to convert this to uppercase. So anything like lowercase a 0 would become uppercase Israel. And this makes it easier for us to compare things. Afterwards, we're simply going to see if the input was quit. If so, we're going to return from the main function, which would in turn return back here and then just exit the main program. But assuming they did not enter quit, we're then going to see if it is a valid coordinate. We're also going to use a NOT operator right here. Basically meaning if this is not a valid coordinate with the cord ended board given, then we're going to continue to live through until the user enters a valid coordinate. But if they do enter a valid coordinates, we're going to continue on and run all this code right here, starting off by getting a character array. And this is a similar concept to what we had before with the is valid coordinate function, we're going to get a character array with index 0 is going to be the letter and index one is going to be the number. So scrolling back up here we're going to get the column which is board dot get Letter index, array index 0. Now getting the index of this is basically going to convert a through J into a 0 through nine. The user sees a through J, but the program does not actually use a through J. We use different numbers for the actual columns. So to 0 through nine. And this is actually the index of each individual character. If we go to our board, this has index 0, index one, all the way up to index nine. Getting the index from this list is going to give us the correct y-coordinate, therefore giving us the column. Now for the row, we're simply going to take that exact character and we're going to subtract 48 for the same exact reasons as we see down here with all the ascii examples. Basically character 0 equals 48. So if we subtract 48, that means that any number we have is going to be a valid integer. It's going back up here. The last action is going to equal board to attempt hit, passing in the row and the column. And this is going to call the attempt hit function, which would then loop through and see if a ship was actually there. And then return a string, depending on if I actually hit or if it missed or if a saint that ship. And this is how this entire program works. If I run this one more time, now that we see how everything works, I can now enter B3, for example. And it's going to excess out. If I enter b2, which is above it, It's going to say Miss. And I can keep on entering B4, B5. Finally be six. And now it says, do you think they're battleship? Because all coordinates are now x out for that ship. And now we have a completely working single-player Battleship game, which we built together using Java. 51. Conclusion: This concludes my entire Java course for beginners. I want to thank you for taking the course. And if we want to learn more about software development from my tutorials, then checkout my YouTube channel, worn off keys.