What's the difference between BaseButton<E> and BaseButton<E extends BaseButton<E>>?

Question

I have two formats of a class BaseButton :

public abstract class BaseButton<E extends BaseButton<E>> extends JXButton implements Initializer {

    private static final long serialVersionUID = 11L;

    public BaseButton() {
        LibraryLogger.initMessage(ClassUtils.getInstance().getResolvedClassName(this.getClass()));  
        initialize();
    }

    public abstract void initialize();
}

And:

public abstract class BaseButton<E> extends JXButton implements Initializer {

    private static final long serialVersionUID = 11L;

    public BaseButton() {
        LibraryLogger.initMessage(ClassUtils.getInstance().getResolvedClassName(this.getClass()));  
        initialize();
    }

    public abstract void initialize();
}

And I am creating child classes as:

public class GreenButton extends BaseButton<GreenButton> {

}

My question is what is the difference between these two types of generic notation?

Which one is better and why?

Any information will be very helpful to me.

Thanks.

Answer 1

With the code you provided, it makes no difference.

However, when you start using the generic type E , that's when you'll start seeing a difference. In the first example, E will have all the methods and members of BaseButton . So, if BaseButton has a method int foo(String s) , you will be able to say:

int bar(E arg) {
    arg.foo("test");
}

If you try the same thing with the second example, the compiler will report an error, because E implicitly extends Object and Object does not have a foo method.