public void propertyChange(PropertyChangeEvent event) {
 if(event.getProperty().equals("field_editor_value")){
   //field for which validation is required
   if(event.getSource()==fieldName){
     //validation is successful
     if(doValidation(...)){
	setValid(true);
	setErrorMessage(null);						super.performApply();
	super.propertyChange(event);
     }
     //validation fails
     else{
	setValid(false);
	setErrorMessage("Error message");
     }
   }
 }
}