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Java has so many built in functions.

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In this lesson, you're going to look at some examples of built in functions.

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First thing I'll need you to do is create a new class by yourself inside the section for a project,

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create a new file name built in functions Java, and make sure the built in functions class has the

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main method.

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So what is a built in function?

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A built in function is one that Java already made for you.

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Built in functions are general to every application.

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For example, every application needs to call the print line function.

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Oh, yes.

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Every time you go to print line, what you were doing was calling a function named print line and passing

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in a string as an argument.

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And after you call the function somewhere, somehow you're running an actual function called print line.

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That print line function, it receives your string as a parameter, and then somehow print line performs

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the magical task of printing your message to the console.

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And notice that the print line function is void.

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It doesn't need to calculate or return anything.

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It only performs the task of printing your message to the console.

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How do I know this?

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Well, if you hover over the function call, it will tell you that you're calling a void function.

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Also, why do we have to write system out before calling the function?

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The short answer is the function Print line isn't local to your class, it's in some other class somewhere

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else attached to system out.

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In any case, inside the built in functions class print.

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Hello, Java.

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And run your code.

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I know it seems silly of me to ask you to print Hello Java, but I hope that you can really appreciate

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what's going on behind the scenes.

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You're calling the print line function and passing in one argument.

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Hello Java.

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The print line function existing somewhere it runs and it receives your argument as a parameter.

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Then it performs the magical task of printing your message to the console.

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Java defines many math functions for you, like log sign or COS.

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These functions are part of the math class that Java made for you.

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Here's an example of me using the log function to take the natural logarithm of 101.53.

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Now, usually these math functions expect a double parameter and return a double value.

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Let's say I want to take the log of 119.6.

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I would call the log function and pass in 119.6 as an argument.

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The log function would run, compute the log and return the value.

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Your call now holds the return value which you can store in a variable.

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So in Maine, we're going to calculate the sine of 1.2.

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And I'm going to store their result in a variable called sign.

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Then I'm going to print.

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The son of 1.2 is.

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The return value that we stored in the variable sign.

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I'm going to run my code.

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And the sign of 1.2 is indeed 0.93.

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But wait, Rianne, how did you know the result would be a double?

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Just hover over the call and it tells you the sine function that Java made for you.

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It expects a double parameter, and accordingly we pass the A double value.

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If you hover back over the call, it also returns a double.

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And since the function returns a double, I know to store the return value in a double variable.

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Okay.

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Now there are math functions that expect more than one parameter.

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For example, if I want to calculate two to the power of four, I would need to pass in two arguments

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the base and the exponent.

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So inside, man, I'm going to calculate two to the power of four.

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Double power is equal to math power.

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And I'm going to calculate to raise to the power of four.

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Then I'm going to print the result.

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Two to the power of four is.

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The return value from the math power function.

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Rerunning this code.

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And as I expect to, to the power of four equals 16.

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That being said, there are thousands of built in functions when you install the Java development kit.

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It comes with thousands of built in functions that you can use.

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If you're thinking of memorizing all of them, please stop.

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A good developer doesn't memorize code.

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A good developer learns to use the internet, read documentation and find resources.

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For example, this is how I do things.

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Oh, I need to take the square root of a number in Java.

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How do I do it?

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Is there a built in function that I can call?

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Well, I'm assuming it would be a math function, so I would look up math functions.

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Java on Google.

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The first two links look good, but I always prefer going over to the Oracle documentation.

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Then I would do a control f search.

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Square root.

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And there you go.

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It shows me the function that I need, the parameter it expects and the value it returns.

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Now I have all the information I need to use this function in my code.

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So when you're in doubt about something, go on the Internet and look it up.

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I need to emphasize the best Developers know how to use the internet to read documentation and find

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resources.

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In this lesson, you saw that Java provides thousands of general functions that they think could be

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useful to you.

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If you're thinking of memorizing all of them, please stop.

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A good developer doesn't memorize code.

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A good developer learns to use the Internet, read documentation and find resources.

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In other words, go on Google and look it up.