## Problem Description :

Write a program in Java that adds number of years, months, weeks and days in 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 addition 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 Addition in given Date
*
*/

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 add? : ");
int years = input.nextInt();
System.out.println("Enter how many months you want to add? : ");
int months = input.nextInt();
System.out.println("Enter how many weeks you want to add? : ");
int weeks = input.nextInt();
System.out.println("Enter how many days you want to add? : ");
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 add years, months, week and days to given date ?

Note : You can validate your result using date calculator.

## References :

https://en.wikipedia.org/wiki/Regular_expression

https://docs.oracle.com/javase/7/docs/api/java/util/Calendar.html

https://docs.oracle.com/javase/7/docs/api/java/util/Date.html

https://docs.oracle.com/javase/7/docs/api/java/lang/String.html

Thank you friends, I hope you have clearly understood the solution of this problem. If you have any doubt, suggestion or query please feel free to comment below. You can also discuss this solution in our forum.

Tags : Date and Time problems, Date addition in Java, Solution in Java, String, DateFormat, SimpleDateFormat, Regular expressions, if else statement, Calendar.