Implement an interface and override methods in Java?

Question

Why do you have to override all methods of an interface?

For instance if I have

public class Foo extend JFrame implements ActionListener, KeyListener {
          


        

Answer 1

This is exactly what the KeyAdapter class is for: it implements all methods of the interface (but none of the implementations do anything). Since you cannot extend two classes, you should use an inner class for your listener (which is a cleaner design anyway):

public class Foo extend JFrame {
      foo(){
          ...
          component.addKeyListener(new MyKeyListener());
          ...
      }

    private class MyKeyListener extends KeyAdapter{
        @Override
        public void keyPressed(KeyEvent arg) {          
        }
    }
}