code: private void fireTangoChangeEvent(TangoChange tangoChange, EventData eventData) {
          TangoChangeEvent change_event = new TangoChangeEvent(tangoChange, eventData);
          ArrayList<EventListener>    listeners = event_listeners.getListeners(ITangoChangeListener.class);
          for (EventListener eventListener : listeners) {
              ((ITangoChangeListener) eventListener).change(change_event);
          }
      }
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