public void setButtonAlpha(final double BUTTON_ALPHA) {
        double alpha = BUTTON_ALPHA < 0 ? 0 : (BUTTON_ALPHA > 1 ? 1.0 : BUTTON_ALPHA);
        if (null == buttonAlpha) {
            _buttonAlpha = alpha;
        } else {
            buttonAlpha.set(alpha);
        }
    }