How can we use listener interface to handle events? Compare listener interface with adapter class

 To handle events we must implement event listener interfaces. It has two major requirements. First, it must have been registered with one or more sources to receive notifications about specific types of events. Second, it must implement methods to receive and process these notifications.

2nd part

Any class which handles events must implement a listener interface for the event type it wishes to handle. A class can implement any number of listener interfaces. To implement a listener interface the class must implement every method in the interface.

Sometimes we may want to implement only one or two of the methods in an interface. We can avoid having to write our own implementation of all the methods in an interface by using an adapter class. An adapter class is a class that already implements all the methods in the corresponding interface. Our class must extend the adapter class by inheritance so we can extend only one adapter class in our class because Java does not support multiple inheritances. Here are the Java adapter classes and the listener interfaces they implement. We can notice that adapters exist for only listener interfaces with more than one method.

Adapter Class

ComponentAdapter

Container Adapter

FocusAdapter

Key Adapter

MouseMotionAdapter

MouseAdapter

Window Adapter

Listener Interface

ComponentListener

ContainerListener

FocusListener

KeyListener

MouseListener

MouseMotionListener

Window Listener