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Given a date, check if it is valid or not. It may be assumed that the given date is in range from 01/01/1800 to 31/12/9999. 

import java.util.*;

public class DateVerify {
    final int[] MIN_DATE = { 1, 1, 1800 };
    final int[] MAX_DATE = { 31, 12, 9999 };
    final int[] DAY_COUNT = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
    public int[] d = new int[3];

    void input() {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter day as dd: ");
        d[0] = sc.nextInt();
        System.out.print("Enter month as mm: ");
        d[1] = sc.nextInt();
        System.out.print("Enter year as yyyy: ");
        d[2] = sc.nextInt();
        sc.close();
    }

    boolean verify() {
        if (!(d[2] >= MIN_DATE[2] && d[2] <= MAX_DATE[2]))
            return false;
        if (d[0] < 1 || d[1] < 1 || d[1] > 12)
            return false;
        boolean isLeap = d[2] % 4 == 0;
        if (d[1] == 2 && isLeap && d[0] == 29)
            return true;
        else if (d[0] > DAY_COUNT[d[1] - 1])
            return false;
        // checking for strict range
        if (d[2] == MIN_DATE[2] && d[1] == MIN_DATE[1] && d[0] < MIN_DATE[0])
            return false;
        else if (d[2] == MAX_DATE[2] && d[1] == MAX_DATE[1] && d[0] > MAX_DATE[0])
            return false;
        return true;
    }

    public static void main(String[] args) {
        DateVerify a = new DateVerify();
        a.input();
        System.out.printf("The given date %d/%d/%d is %s Date\n", a.d[0], a.d[1], a.d[2],
                (a.verify() ? "a Valid" : "an Invalid"));
    }
}

Algorithm

void main()

  1. Initialize Object of the class DateVerify to call its method.
  2. Take input of the date by calling the input() method.
  3. Check if the date entered is valid by calling verify() and then print the message accordingly.

void input()

  1. Initialize Scanner object to take input.
  2. Store thr entered date at index 0 of array d.
  3. Store thr entered month at index 1 of array d.
  4. Store thr entered year at index 2 of array d.

boolean verify()

  1. If the entered year is smaller than the MIN_DATE[2] or entered year is greater than MAX_DATE[2] then return false.
  2. if days are smaller than 1 or month is smaller than 1 or month is greater than 1 then return false
  3. Initialize a boolean value isLeap which is the status if the current is a leap year.
  4. If month is February and it a leap year and days are 29 then retuen true
  5. If days is greater than DAY_COUNT[month-1] then return false
  6. If year == MIN_DATE[2] and month == MIN_DATE[1] && days < MIN_DATE[0] return false
  7. If year == MAX_DATE[2] and month == MAX_DATE[1] and days > MAX_DATE[0] return false

Variable Description

Name Type Uses
global
d int[] integer array of size 3 to store date
MIN_DATE int[] integer array storing minimum possible date
MAX_DATE int[] integer array storing maximum possible date
DAY_COUNT int[] this stores the day count for 12 months of the year
void main()
a DateVerify object to call method
void input()
sc Scanner to take user Input