public synchronized static LinkedList<Theater> getAllTheaters(int zone){
		if(theaters.size() == 0)
			return null;
		LinkedList<Theater> result = new LinkedList<Theater>();
		for(Theater t : theaters)
			if(t.getZone() == zone)
				result.add(t);
		if(result.size() == 0)
			return null;
		return result;
	}