The listener interface for receiving hierarchy changed events.

  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.