protected void fireChangeListeners() {
        if (this.changeListeners == null) {
            return;
        }
        for (int a = 0; a < this.changeListeners.size(); a++) {
            ChangeListener l = this.changeListeners.get(a);
            try {
                l.stateChanged(new ChangeEvent(this));
            } catch (RuntimeException e) {
                e.printStackTrace();
            }
        }
    }