An adapter class provides an empty implementation of all 
methods in an event listener interface.Adapter classes are 
useful when you want to receive and process only some of 
the events that are handled by a particular event listener 
interface.you can define a new class to act lisener by 
extending one of the adapter classes and implementing onlu 
those events in which you are interested.
   For ex: the MouseMotionListenerAdapter class has two 
methods,mouseDragged() and mouseMoved(). The signatures of 
these empty are exactly as defined in the 
MouseMotionListener interface. If you are interested in 
onlu mouse drag events,that you could simply extend 
MouseMotionAdapter and implement mouseDragged().

adapter class provides empty implementation for
eventlistener interface