code: public synchronized void fireVolumeChangeEvent(Object source, int volume) {
          VolumeChangeEvent vce = new VolumeChangeEvent(source, volume);
  
          for (VolumeChangeListener vcl : volListeners) {
              vcl.volumeChanged(vce);
          }
      }
docs: Sends the appropriate {@link VolumeChangeEvent} to all registered
  {@link VolumeChangeListener}.
  
  @param source source of event
  @param volume the new volume