Java Keywords and Expressions

English In this video we're going to talk more about keywords, and also just elaborate a little bit on expressions, which we've already covered to a degree previously. Firstly with the keywords. Now Java has actually got 50 reserved words that are used for keywords in your applications. And you have seen some of those in operation already. For example on the screen you can see some of the keywords that are showing in blue. IntelliJ will actually highlight keywords in blue to show you that they actually are a keyword. So, what I'm going to do is just go to a browser, and I'm gonna paste in this link. And the link will be in the resources section of this video. And here is a list of Java keywords, and you can see in the Java programming language a keyword is one of 53 reserved words that have a predefined meaning in the language and as we scroll down in the list you will see some of this you already use boolean is one double is another And also float but don't worry you don't need to memorize any of these because we are going to go through each and every one of this in the course but the thing is they are reserved and lets swing back to IntelliJ and I'm going to talk further about that And incidentally, if you pull this video, I've created a new project called KeywordsAndExpressions. So anything in blue, that's showing IntelliJ editor is confirming to you that this is a reserved word. So for example, we can't go in here, And create a variable called. Say int, So if we type int int=5; unexpected token. And that's because as far as IntelliJs concerned, int is a reserved word. It's actually a data type. We could use int2, that would be quite valid because that's only using part of the word, but you can't use an exact word. So anytime you get into weird errors, just make sure that you're not using a reserved keyword, and you can refer back to that list. And some of the other keywords that you've already seen that you can't use are false, you saw false before, we've used that in a previous video, true, and null. But we'll be talking about those as we progress through the course. So as I mentioned, by the time you've finished with this course you will have gone through all 50 of those keywords. We will have a good understanding of what they actually are. Okay, now lets talk now about expressions. We have talked a little bit in the past about those and you have seen some of those in operations, but lets just expand that a little bit more just so we have a specific understanding of what expressions are. I am just going to delete this and make a bit more space. Expressions are essentially building blocks of all Java programs. You'll be using expressions a lot, and expressions are built with values, variables, and operators, which you've seen previously. But also with method calls, which we'll be discussing in a future set of videos later in the course. For example, if we wanted to create an expression to convert miles into kilometers, you'd need to know firstly that a mile was equal to- To 1.609344 kilometers. So if we wanted to figure out what a 100 miles were converted to kilometers, double kilometers equals 100 times 1.609344. So that would be a valid statement. For that line, the actual expression is this component of the entire line. The data type does not form part of an expression, but everything else on the line typically forms or is part of the expression. So the expression component is variables, values, and operators. All of those used in this case. We've got a variable kilometers. We've got values, like a 101.609344. And of course, operators, equals, and multiplications. So that's an expression this component of the line. By adding the datatype, we're creating a valid java statement. The combination of that And also the semi colon at the end of the line as well. Some more examples of expressions. We've got something like if highscore equals 50. As we've done before. We're getting an error because I haven't defined the variable. So I'll just define that. So, this component is the expression. Within the brackets as you can see there. So, the keyword for if in the brackets, and the braces as well do not form part of the expression as this component in here. And incidentally there's another expression, and the expression is quite valid as well. With a literal value as it's got there with the number 50. And finally, another valid expression. Is this component here. So the component within the brackets is also an expression. And that's actually calling a method. And we'll be talking about methods in a future section of the course as well. The main idea is just to get your head around what components of the entire line is an expression from what an expression actually is. Just a confirmation when you're defining a variable the entire line minus the semi colon at the end and the datatype is the expression, so that's that component there. Or with the literal value that's the component there minus the data type at the start and also the semi colon. If you've got a control statement, control flow statement, and we'll be talking more about those also in future videos, the component in brackets is the expression. And if you're using a method, and again, methods, we're going to be covering later, but anything in the brackets, essentially, that is also an expression as well. And now that you know that I'm going to clear this off, now that that's off the screen. And my challenge for you is as follows. Have a look at the code that you can see on the screen. Write down what components of the lines I've entered there are expressions. And come back and check your results after you've had a go at it. So, how did you get on? Did you figure it out? Let's go through and talk this through. So the components that are expressions, firstly on the first line. The score equals a hundred component is the expression. Remembering that a data type and also the semicolon to the end the line are not part of the expression. In the second example, the if score greater than 99. Well the part in brackets is also an expression. So the if, the braces, and the brackets do not form part of an expression. In the next case we’ll be printing out to the console. The component that’s in between the brackets and the double quotes is the expression. The final example here, score = 0 that is also a valid expression as well. So did you figure all this out, congratulations if you got them all. So that's expressions and you'll be seeing expressions and keywords in use a lot more in future videos. But speaking of future videos, in the next video we're gonna be discussing statements which we touch on briefly here. Also, what whitespace is and the use of indenting, So, I'll see you on that video.