Handling a Vetoable Property Change Event
Vetoable property change events are fired when a constrained property is changed. A listener can veto the change by throwing PropertyVetoException. 

 bean.addVetoableChangeListener(
   new MyVetoableChangeListener());
     
 class MyVetoableChangeListener implements 
   VetoableChangeListener {
     public void vetoableChange(PropertyChangeEvent evt) 
       throws PropertyVetoException {
         Object oldValue = evt.getOldValue();
         Object newValue = evt.getNewValue();
         if (!process(oldValue, newValue)) {
           throw new PropertyVetoException(
             "message", evt);
         }
     }
 }