@Override
public String toString() {
	switch (this) {
	case SUNDAY: return "Su";
	case MONDAY: return "M";
	case TUESDAY: return "T";
	case WEDNESDAY: return "W";
	case THURSDAY: return "R";
	case FRIDAY: return "F";
	case SATURDAY: return "Sa";
	case ANY: return " ";
	default: throw new IllegalArgumentException();
	}
}