// Java code for maintaining lists of events for different sensors.
        // The lists are maintained in a hash map where the key is the sensor id.
	// Note that this code is not thread safe (we discuss this issue
	// in assignment 4)
	
	private static Map<Integer,List<Event>> events = 
			new HashMap<Integer,List<Event>>();

	private static void addEvent(Event event) {
		int id = event.getSensorid();
		List<Event> eventList = events.get(id);
		if (eventList == null) {
			eventList = new ArrayList<Event>();
			events.put(id, eventList);
		}
		eventList.add(event);
	}

	private static List<Event> getEventList(int id) {
		List<Event> eventList = events.get(id);
		if (eventList == null) {
			eventList = new ArrayList<Event>();
		}
		return eventList;
	}