Void in Java

You confuse screen output with return value.

void hello(){
System.out.println("hello world");
}

it returns nothing. it prints to the screen but it's not a return.
A return is this:

int returnMe(int i){
return i;
}

you can write

int i = returnMe(i);
but not
int i = hello();

returning means providing a value that can be stored for the rest of the program.
output is NOT a return.

Well, let's make it even simpler, and I hope this time it will be clear.

You want to display "hello world": 2 solutions:


You just do the display without return:

void helloworld() {
system.out.println("hello world");
}

You call a function that returns the string via a function that doesn't need to return anything

void displayHelloWorld(String text) {
system.out.println(text);
}

String helloworld() {
return displayHelloWorld("Hello World");
}


Is that clearer?

If you need to include it.
A method MUST have a return type. A JVM is stubborn and a compiler even more so. No return type, no compilation.
void is used when your method shouldn't return anything. Let's take a concrete example: if you're making a car, you wouldn't add a periscope "just in case," would you? So you wouldn't add a return type "just in case" either (and if so, which one??)

Remember this:
You need a return type.
If you don't return anything with your method, you indicate it simply with void (which means "I return nothing")
Of course, you could put something else (nothing stops you), but then your method would make no sense.
Put a type when you need one.

It has nothing to do with memory, it's the type of return of your function!

If you don't need to return anything because your function is only supposed to do something on its own and that's it, then you use void. If it needs to calculate the sum of all your employees and return the number, then you will declare it as int instead of void and you'll be required to put your "return" at the end.