Handling a Property Change Event
Property change events are fired when a bound property is changed. 

 bean.addPropertyChangeListener(
   new MyPropertyChangeListener());
     
 class MyPropertyChangeListener implements 
   PropertyChangeListener {
     public void propertyChange(PropertyChangeEvent evt) {
       Object oldValue = evt.getOldValue();
       Object newValue = evt.getNewValue();
       process(oldValue, newValue);
     }
 }