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July 09, 2005

Heavy Java interfaces

There's one thing I never realized about Java until recently: You are allowed to go crazy with nesting. Say you have a simple interface:

public interface Interface {
    public void foo();
}

You could now nest an implementation of that inside the interface and make that implementation available in a singleton-ish fashion, all in the same file:

public interface Interface {

    public void foo();

    public class InterfaceImpl implements Interface {
        public void foo() { }
    }

    public static Interface INSTANCE = new InterfaceImpl();

}

You may now write Interface i = Interface.INSTANCE. Let's make this look even more wrong and implement Interface on the fly:

public interface Interface {

    public void foo();

    public static Interface INSTANCE = new Interface() {
        public void foo() { }
    };
	
}

By now you should feel an urgent need to wash your hands.

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