code: public boolean add(SimulatorEvent event) {
      if (lastEvent != null && event.getTimeStamp() < lastEvent.getTimeStamp())
        throw new IllegalArgumentException("Event happens in the past: "
            + event.getClass());
  
      event.setInternalCount(eventCount++);
      return events.add(event);
    }
docs: Add a single {@link SimulatorEvent} to the {@link SimulatorEventQueue}.
  
  @param event
  the {@link SimulatorEvent}
  @return true if the event is added to the queue (to follow the same
  convention as Collection.add()).