code: private void fireTangoUserEvent(TangoUser tangoUser, EventData eventData) {
          TangoUserEvent tangoUserEvent = new TangoUserEvent(tangoUser, eventData);
          // Notifying those that are interested in this event
          ArrayList<EventListener> listeners = event_listeners.getListeners(ITangoUserListener.class);
          for (EventListener eventListener : listeners) {
              ((ITangoUserListener) eventListener).user(tangoUserEvent);
          }
      }
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