public void addPropertyChangeListener(PropertyChangeListener listener){
  if (propertyChangeSupport == null) {
    propertyChangeSupport=new PropertyChangeSupport(this);
  }
  propertyChangeSupport.addPropertyChangeListener(listener);
}

public void addPropertyChangeListener ( PropertyChangeListener listener ) { if ( propertyChangeSupport == null ) { propertyChangeSupport = new PropertyChangeSupport ( this ) ; } propertyChangeSupport . addPropertyChangeListener ( listener ) ; }
add a propertychangelistener to the listener list .
