The listener interface for receiving keyboard events (keystrokes).
The class that is interested in processing a keyboard event
either implements this interface (and all the methods it
contains) or extends the abstract
KeyAdapter
class
(overriding only the methods of interest).
The listener object created from that class is then registered with a
component using the component's addKeyListener
method. A keyboard event is generated when a key is pressed, released,
or typed. The relevant method in the listener
object is then invoked, and the KeyEvent
is passed to it.