public Bill findBillByDate(Household household, Calendar calendar)
			throws InstanceNotFoundException {
		Set<Bill> bills = household.getBills();
		for (Bill bill : bills) {
			if (((bill.getDate().get(Calendar.MONTH)) == (calendar
					.get(Calendar.MONTH)))
					&& ((bill.getDate().get(Calendar.YEAR)) == (calendar
							.get(Calendar.YEAR)))) {
				return bill;
			}
		}
		throw new InstanceNotFoundException(null, "Bill");

	}