question: protected final void fireVetoableChange ( String propertyName , Object oldValue , Object newValue ) throws PropertyVetoException { vcs . fireVetoableChange ( propertyName , oldValue , newValue ) ; }
target:  Report a vetoable property update to any registered listeners.  If anyone vetos the change, then fire a new event reverting everyone to  the old value and then rethrow the PropertyVetoException. <p> No event is fired if old and new are equal and non-null.