14.15. Adapter Classes

Many event-listener interfaces, such as MouseListener and MouseMotionListener, contain multiple methods. It’s not always desirable to declare every method in an event-listener interface. For instance, an application may need only the mouseClicked handler from MouseListener or the mouseDragged handler from MouseMotionListener. Interface WindowListener specifies seven window event-handling methods. For many of the listener interfaces that have multiple methods, packages java.awt.event and javax.swing.event provide event-listener adapter classes. An adapter class implements an interface and provides a default implementation (with an empty method body) of each method in the interface. Figure 14.30 shows several java.awt.event adapter classes and the interfaces they implement. You can extend an adapter class to inherit the default implementation of every method and subsequently override only the method(s) you need for event handling.

Fig. 14.30. Event-adapter classes and the interfaces they implement in package java.awt.event.

Event-adapter class in java.awt.event	Implements interface
ComponentAdapter	ComponentListener
ContainerAdapter	ContainerListener
FocusAdapter	FocusListener
KeyAdapter	KeyListener
MouseAdapter	MouseListener
MouseMotionAdapter	MouseMotionListener
WindowAdapter	WindowListener