public static int daysInMonth(int month, int year) {
      return switch (month) {
        case 2 -> isLeapYear(year) ? 29 : 28;
        case 4, 6, 9, 11 -> 30;
        default -> 31;
      }
    }

private static boolean isLeapYear(int year) {
   return year % 400 == 0 || (year % 4 == 0  && year % 100 != 0);
}