@Override
    public void reactToChanges(ObservationEvent ev) {
        if(ev instanceof ValidateButtonEvent){
            ValidateButtonEvent event = (ValidateButtonEvent)ev;
            String label = ((ValidateButton)event.getSource()).getText();
            switch(label){
                case OK_label:
                    validate = true;
                    break;
                case CANCEL_label:
                    validate = false;
            }
            this.notifyObserver();
        }
    }