Component.java 文件源码

/**
 * Adds the specified listener to this component. This is harmless if the
 * listener is null, but if the listener has already been registered, it
 * will now be registered twice.
 *
 * @param listener the new listener to add
 * @see HierarchyEvent
 * @see #removeHierarchyListener(HierarchyListener)
 * @see #getHierarchyListeners()
 * @since 1.3
 */
public synchronized void addHierarchyListener(HierarchyListener listener)
{
  if (listener != null)
    {
      hierarchyListener = AWTEventMulticaster.add(hierarchyListener,
                                                  listener);
      newEventsOnly = true;
      // Need to lock the tree, otherwise we might end up inconsistent.
      synchronized (getTreeLock())
      {
        numHierarchyListeners++;
        if (parent != null)
          parent.updateHierarchyListenerCount(AWTEvent.HIERARCHY_EVENT_MASK,
                                              1);
      }
    }
}