How do I add or subtract a date?

The java.util.Calendar allows us to do a date arithmetic function such as add or subtract a unit of time to the specified date field.

The method that done this process is the Calendar.add(int field, int amount). Where the value of the field can be Calendar.DATE, Calendar.MONTH, Calendar.YEAR. So this mean if you want to subtract in days, months or years use Calendar.DATE, Calendar.MONTH or Calendar.YEAR respectively.

package org.kodejava.util;

import java.util.Calendar;

public class CalendarAddExample {
    public static void main(String[] args) {
        Calendar cal = Calendar.getInstance();

        System.out.println("Today : " + cal.getTime());

        // Subtract 30 days from the calendar
        cal.add(Calendar.DATE, -30);
        System.out.println("30 days ago: " + cal.getTime());

        // Add 10 months to the calendar
        cal.add(Calendar.MONTH, 10);
        System.out.println("10 months later: " + cal.getTime());

        // Subtract 1 year from the calendar
        cal.add(Calendar.YEAR, -1);
        System.out.println("1 year ago: " + cal.getTime());

In the code above we want to know what is the date back to 30 days ago. The sample result of the code is shown below:

Today : Wed Sep 15 17:58:49 CST 2021
30 days ago: Mon Aug 16 17:58:49 CST 2021
10 months later: Thu Jun 16 17:58:49 CST 2022
1 year ago: Wed Jun 16 17:58:49 CST 2021


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