Question

I ran across a class that was set up like this:

public class MyClass {    private static boolean started = false;    private MyClass(){   }    public static void doSomething(){     if(started){       return;     }     started = true;     //code below that is only supposed to run     //run if not started   } } 

My understanding with static methods is that you should not use class variables in them unless they are constant, and do not change. Instead you should use parameters. My question is why is this not breaking when called multiple times by doing MyClass.doSomething(). It seems to me like it should not work but does. It will only go pass the if statement once.

So could anyone explain to me why this does not break?

Answer 1

The method doSomething() and the variable started are both static, so there is only one copy of the variable and it is accessible from doSomething(). The first time doSomething() is called, started is false, so it sets started to true and then does… well, something. The second and subsequent times it’s called, started is true, so it returns without doing anything.