An abstract class in Java need not implement any methods from its implementing interface. Why?

Question

Let\'s look at the following simple code snippet in Java.

interface Sum
{
    abstract public void showSum();
}

interface Mul
{
    abstract public void showMul         


        

Answer 1

This ought to be comment to JB Nizet's answer, but I cant post comments yet :( Note that you could provide the implementation for the showSum() method in your abstract class, and still have that class remain abstract without any problems. An abstract class could have all methods implemented and still be abstract!