A low-level event that indicates that a window has changed its status. This low-level event is generated by a Window object when it is opened, closed, activated, deactivated, iconified, or deiconified, or when focus is transfered into or out of the Window.
 The event is passed to every WindowListener
 or WindowAdapter object which registered to receive such
 events using the window's addWindowListener method.
 (WindowAdapter objects implement the
 WindowListener interface.) Each such listener object
 gets this WindowEvent when the event occurs.
 
 An unspecified behavior will be caused if the  id parameter
 of any particular  WindowEvent instance is not
 in the range from  WINDOW_FIRST to  WINDOW_LAST.
extends 
WindowAdapter, WindowListener,  Tutorial: Writing a Window Listener