Actionscript 3: Can someone explain to me the concept of static variables and methods?

Question

Hi, I'm learning AS3, and am a bit confused as to what a static variable or method does, or how it differs from a method or variable without this keyword. This should be simple enough to answer, I think.

Answer 1

A static variable or method is shared by all instances of a class. That's a pretty decent definition, but may not actually make it as clear as an example...

So in a class Foo maybe you'd want to have a static variable fooCounter to keep track of how many Foo's have been instantiated. (We'll just ignore thread safety for now).

public class Foo {
    private static var fooCounter:int = 0;

    public function Foo() {
        super();
        fooCounter++;
    }

    public static function howManyFoos():int {
        return fooCounter;
    }
}

So each time that you make a new Foo() in the above example, the counter gets incremented. So at any time if we want to know how many Foo's there are, we don't ask an instance for the value of the counter, we ask the Foo class since that information is "static" and applies to the entireFoo class.

var one:Foo = new Foo();
var two:Foo = new Foo();
trace("we have this many Foos: " + Foo.howManyFoos());  // should return 2