if (changeSupport == null) changeSupport = new SwingPropertyChangeSupport(this); changeSupport.addPropertyChangeListener(listener);
listenerList.add(PropertyChangeListener.class, listener);
  public void addPropertyChangeListener(PropertyChangeListener listener)  {    if (changeSupport == null)      changeSupport = new SwingPropertyChangeSupport(this);    changeSupport.addPropertyChangeListener(listener);  }