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

Concrete classes must always implement all of the methods of an interface. If you weren't already extending JFrame you could extend KeyAdapter. It implements empty methods for KeyListener to avoid writing them out. You could use an anonymous class with that inside of your Foo class like this:

addKeyListener(new KeyAdapter() {
    public void keyTyped(KeyEvent e) {
        // handle typed key here
    }
});