11.3 Listeners and Adapters

Listeners are used by the AWT to handle various GUI events. A listener object can be associated with a GUI object, when the GUI object receives an event it will check if it has a listener object to handle the event. If it finds a listener object it will pass the event to the listener for handling.

Listeners are normally interfaces. To use a listener you must create a class that implements the interface for the type of listener you need. The class must provide code for the methods declared in the interface. Then you create an instance of your listener class and associate it with the GUI object.

Examples of listeners are:

WindowListener - Listener that handles window events such as opening and closing
MouseListener - Listener that handle mouse events such as button clicks
MouseMotionListener - Listener that handles mouse events for mouse movement
KeyListener - Listener for handling keyboard events
ActionListener - Listener for handling actions like buttons being pressed and menus being selected

Adapters are classes that implement listener interfaces but only provide dummy methods that do nothing. Using an adapter provides a shortcut for creating listeners since you only have to override the methods on the adapter that you want to use, the rest have dummy implementations.