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Write a program to accept 2 dates in the string format dd/mm/yyyy and find the difference in days between the 2 dates. 

import java.util.*;

public class DateDiff {
    int d, m, y;

    DateDiff(String date) {
        int[] ind = { date.indexOf('/'), date.lastIndexOf('/') };
        d = Integer.parseInt(date.substring(0, ind[0]));
        m = Integer.parseInt(date.substring(ind[0] + 1, ind[1]));
        y = Integer.parseInt(date.substring(ind[1] + 1));
    }

    int getDaysofMonth() {
        int res = 0;
        int[] DAY_COUNT = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
        if (y % 4 == 0)
            DAY_COUNT[1]++;
        for (int x = 1; x < m; x++)
            res += DAY_COUNT[x - 1];
        return res;
    }

    int subtract(DateDiff b) {
        int d = b.getDaysofMonth() + b.d - (this.getDaysofMonth() + this.d);
        if (b.y - this.y != 0) {
            int bg = Math.max(b.y, this.y);
            int sm = Math.min(b.y, this.y);
            for (int x = sm; x < bg; x++)
                if (x % 4 == 0)
                    d += 366;
                else
                    d += 365;
        }
        return d;
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Date 1: ");
        DateDiff d1 = new DateDiff(sc.next());
        System.out.print("Date 2: ");
        DateDiff d2 = new DateDiff(sc.next());
        System.out.printf("Difference: %d days", d1.subtract(d2));
        sc.close();
    }
}

Algorithm

public DateDiff(String date)

  1. Initialize int[] ind = { date.indexOf('/'), date.lastIndexOf('/') }
  2. Store d as parsed int of substring of date from 0 to ind[0]
  3. Store m as parsed int of substring of date from ind[0]+1 to ind[1]
  4. Store y as parsed int of substring of date from ind[1] to end

int getDaysofMonth()

  1. Intialize r=0
  2. Initialize DAY_COUNT and store the number of days of each month as an inteer array.
  3. if a leap year then DAY_COUNT[1]=DAY_COUNT[1]+1
  4. Start for loop with x = 1 and condition x < m and x=x+1
  5. res = res + DAY_COUNT[x - 1]
  6. End for loop
  7. return res

int subtract(DateDiff b)

  1. Intialize d = b.getDaysofMonth() + b.d - (getDaysofMonth() + d), this stores the differnce in dates and months
  2. Start if with condtion b.y - y != 0
  3. Stores the maximum between b.y and y in int bg
  4. Stores the minimum between b.y and y in int sm
  5. Start for loop with x=sm and condition x<bg and x=x+1
  6. if it's a laep year the d=d+366 else d=d+365
  7. End for loop
  8. End if
  9. return d

void main()

  1. Intialize Scanner object to take input.
  2. Intialize object named d1 of class DateDiff to store first entered date.
  3. Take input pass it to d1.input()
  4. Intialize object named d2 of class DateDiff to store second entered date.
  5. Take input pass it to d2.input()
  6. Calculate the day differnece using 'd1.subtract(d2)' method and print thr result

Variable Description

Name Type Use
global
d int to store date
m int to store month
y int to store year
int getDaysofMonth()
res int Resultant value which will be returned later on in the function
DAY_COUNT in[] Integer array storing the number of days of the 12 months
int subtract()
b DateDiff the object of the date from which the current date has to be
subtracted
d int stores the difference in number of days between the dates
bg int store the year of gretater numerical value
sm int store the year of smaller numerical value
void main
sc Scanner to take user input
d1 DateDiff Objecr to store first date
d2 DateDiff Objecr to store second date