Java根据年、月判断月中有多少天

LocalDateTime startTime;
int year = startTime.getYear();
int month = startTime.getMonth().getValue();

    
	public int days(int year, int month) {
		int days = 0;
		switch(month) {
			case 1:
			case 3:
			case 5:
			case 7:
			case 8:
			case 10:
			case 12:
				days = 31;
				return days;
			case 4:
			case 6:
			case 9:
			case 11:
				days = 30;
				return days;

		}
		if((year %100!=0&& year %4==0)|| year %400==0) {
			if(month ==2) {
				days = 29;
				return days;
			}
		}else {
			if(month ==2) {
				days = 28;
				return days;
			}
		}
		return days;
	}