hierarchyListener = AWTEventMulticaster.add(hierarchyListener, l);
hierarchyListener = AWTEventMulticaster.add(hierarchyListener, listener);
  public synchronized void addHierarchyListener(HierarchyListener l)  {		hierarchyListener = AWTEventMulticaster.add(hierarchyListener, l);		if (hierarchyListener != null)			enableEvents(AWTEvent.HIERARCHY_EVENT_MASK);	}