## Problem Description :

Write a program in Java that subtracts years, months, weeks and days from given date.

## Concept :

We are using add() method of Calendar class that is present in java.util.* package and accepts Calendar constants YEAR, MONTH, DAY_OF_WEEK_IN_MONTH and DAY_OF_MONTH for the subtraction of years, month, weeks and days respectively.

## Java program :

```package com.javamultiplex.datetime;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Scanner;

/**
*
* @author Rohit Agarwal
* @category Date and Time
* @problem How to do subtraction from given date?
*
*/
public class SubtractionInDate {

public static final String NEW_DATE_PATTERN = "MMM. dd yyyy, EEEE";

public static void main(String[] args) {

Scanner input = null;
try {
input = new Scanner(System.in);
System.out.println("Enter date in dd/MM/yyyy format :");
String date = input.next();
// If Date is valid, converting String to date.
Date mydate = getValidDate(date);
if (mydate != null) {

System.out.println("Enter how many years you want to subtract? : ");
int years = input.nextInt();
System.out.println("Enter how many months you want to subtract? : ");
int months = input.nextInt();
System.out.println("Enter how many weeks you want to subtract? : ");
int weeks = input.nextInt();
System.out.println("Enter how many days you want to subtract? : ");
int days = input.nextInt();

// Creating Calendar class instance.
Calendar calendar = Calendar.getInstance();
// Converting Date to Calendar
calendar.setTime(mydate);

// Adding years to Calendar date.
// Adding months to Calendar date.
// Adding weeks to Calendar date.
// Adding days to Calendar date.

// Converting Calendar to Date.
Date newDate = calendar.getTime();
DateFormat format = new SimpleDateFormat(NEW_DATE_PATTERN);
String myNewDate = format.format(newDate);
System.out.println("New Date : " + myNewDate);

} else {
System.out.println("Dates are invalid.");
}
} finally {
if (input != null) {
input.close();
}
}

}

private static Date getValidDate(String date) {

Date mydate = null;
if (isValidDateFormat(date)) {
/**
* d -> Day of month
* M -> Month of year
* y -> Year
*/
DateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy");
/**
* By default setLenient() is true. We should make it false for
* strict date validations.
*
* If setLenient() is true - It accepts all dates. If setLenient()
* is false - It accepts only valid dates.
*/
dateFormat.setLenient(false);
try {
mydate = dateFormat.parse(date);
} catch (ParseException e) {
mydate = null;
}
}
return mydate;
}

private static boolean isValidDateFormat(String date) {

/**
* Regular Expression that matches String with format dd/MM/yyyy.
* dd -> 01-31
* MM -> 01-12
* yyyy -> 4 digit number
*/
String pattern = "(0?[1-9]|[12][0-9]|3[01])\\/(0?[1-9]|1[0-2])\\/([0-9]{4})";
boolean result = false;
if (date.matches(pattern)) {
result = true;
}
return result;
}

}

```

## Output :

 Output - How to subtract years, months, weeks and days from given date?

Note : You can validate your result using date calculator.