/**
  * Notifies this <tt>AbstractCallToggleButton</tt> that its associated action has been performed
  * and that it should execute its very logic.
  */
 @Override
 public void buttonPressed() {
   if (!sliderMenuIsVisible) toggleMute();
 }
 /**
  * Event fired when volume has changed.
  *
  * @param volumeChangeEvent the volume change event.
  */
 public void volumeChange(VolumeChangeEvent volumeChangeEvent) {
   if (volumeChangeEvent.getLevel() == 0) toggleMute();
   else if (mute) toggleMute();
 }