code: protected final void fireVetoableChange(String propertyName,
              Object oldValue,
              Object newValue)
              throws PropertyVetoException {
          VetoableChangeSupport aVetoSupport = this.vetoSupport;
          if (aVetoSupport == null) {
              return;
          }
          aVetoSupport.fireVetoableChange(propertyName, oldValue, newValue);
      }
docs: Support for reporting changes for constrained Object properties. This method can be called
  before a constrained property will be changed and it will send the appropriate
  PropertyChangeEvent to any registered VetoableChangeListeners.
  
  @param propertyName the property whose value has changed
  @param oldValue the property's previous value
  @param newValue the property's new value
  @throws PropertyVetoException if a constrained property change is rejected