public class Date { public static boolean isLeapYear(int year) { return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0); } public static boolean isValidDate(int date, int month, int year) { if (year < 1) { return false; } if (month < 1 || month > 12) { return false; } int[] daysInMonth = {31, isLeapYear(year) ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; return date > 0 && date <= daysInMonth[month - 1]; } public static String getDayOfWeek(int date, int month, int year) { if (month == 1 || month == 2) { month += 12; ...