The listener interface for receiving hierarchy changed events.
The class that is interested in processing a hierarchy changed event
should implement this interface.
The listener object created from that class is then registered with a
Component using the Component's addHierarchyListener
method. When the hierarchy to which the Component belongs changes, the
hierarchyChanged method in the listener object is invoked,
and the HierarchyEvent is passed to it.
Hierarchy events are provided for notification purposes ONLY;
The AWT will automatically handle changes to the hierarchy internally so
that GUI layout, displayability, and visibility work properly regardless
of whether a program registers a HierarchyListener or not.