/**
  * Invalides the current value so that the next invocation of <code>createValue</code> will ask
  * for the property again.
  */
 public void invalidate() {
   if (pcl != null) {
     toolkit.removePropertyChangeListener(getKey(), pcl);
     toolkit = null;
     pcl = null;
     value = null;
   }
 }
 void dispose() {
   kit.removePropertyChangeListener(key, this);
 }