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Write a program to input a date in ddmmyyyy 8 digit format and print it in 1) dd / mm / yyyy format 2) dd, month name , yyyy format. 

import java.util.*;

public class DateFormat {
    int[] d = new int[3];
    private final int[] DAY_COUNT = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
    private final String[] MONTH_NAME = {
            "January", "February", "March", "April", "May", "June", "July", "August", "September", "October",
            "November", "December"
    };

    void input() {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter date as 'ddmmyyyy': ");
        String date = sc.next();
        if (date.length() != 8) {
            System.out.println("Invalid Input Format");
            System.exit(-1);
        }
        d[0] = Integer.parseInt(date.substring(0, 2));
        d[1] = Integer.parseInt(date.substring(2, 4));
        d[2] = Integer.parseInt(date.substring(4, 8));
        sc.close();
    }

    boolean validate() {
        if (d[0] < 1 || d[2] < 1 || d[1] < 1 || d[1] > 12)
            return false;
        if (d[1] == 2 && d[2] % 4 == 0 && d[0] == 29) // leap yaer condition
            return true;
        else if (d[0] > DAY_COUNT[d[1] - 1])
            return false;
        return true;
    }

    void show() {
        if (!validate()) {
            System.out.println("Invalid Date");
            return;
        }
        System.out.printf("%d/%d/%d\n", d[0], d[1], d[2]);
        System.out.printf("%d %s, %d\n", d[0], MONTH_NAME[d[1] - 1], d[2]);
    }

    public static void main(String[] args) {
        DateFormat a = new DateFormat();
        a.input();
        a.show();
    }
}

Algorithm

boolean validate()

  1. if day, month or year is smaller than 1 or month is greater than 12 return false
  2. If month is february and is a leap yaer and days are 29 return true
  3. if daya > DAY_COUNT[d[1] - 1] then return false
  4. return true

void show()

  1. if 'validate()' evaluates false then print "Invalid Date" and eeturn
  2. Print the date in the required format.

void input()

  1. Initialize Scanner object to take input.
  2. Take date input into the string value 'date'.
  3. If length of date is not equal to 8 then print "Invalid Input Format" and return.
  4. Store d[0] as parsed Integer of date.substring(0, 2)
  5. Store d[1] as parsed Integer of date.substring(2, 4)
  6. Store d[2] as parsed Integer of date.substring(4, 8)

void main()

  1. Initialize the object of class DateFormat to invoke methods.
  2. Invoke the functions input and show

Variable Description

Name Type Uses
global
d int[] Integer array of size 3 to store date
DAY_COUNT int[] Stores the number of days of 12 months of the year
MONTH_NAME String[] Name of the 12 months of the year
void main()
a DateFormat Object to call its methods
void input()
sc Scanner to take user input
date String to store enetered date