Introduction to OOP Chapter 19: Container Classes : next previous audio real text

An Example, Java Window Events

A good example is the way that window events are handled in Java. Each window maintains a list of listeners, each listener must implement a fixed interface (WindowListener).
public class CloseQuit extends WindowAdapter {
		// execute when the user clicks in the close box
	public void windowClosing (WindowEvent e) {
		System.exit(0); // halt the program
When an event occurs the window simply runs down the list of listener, invoking the appropriate method in each. No downcasting required.
Intro OOP, Chapter 19, Slide 10