Calculate Dates in Java

package nilpointer.net;

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class Demo {

	public static void main(String[] args) {

		try {
			SimpleDateFormat simpleDateFormat = new SimpleDateFormat("dd/MM/yyyy");

			Date today = new Date();
			System.out.println("Today: " + simpleDateFormat.format(today));

			Calendar calendar = Calendar.getInstance();
			calendar.setTime(today);

			// Add 20 days
			calendar.add(Calendar.DATE, 20);
			System.out.println("Add 20 days: " + simpleDateFormat.format(calendar.getTime()));

			// Subtract 10 days
			calendar.add(Calendar.DATE, -10);
			System.out.println("Subtract 10 days: " + simpleDateFormat.format(calendar.getTime()));

			// Add 3 months
			calendar.add(Calendar.MONTH, 3);
			System.out.println("Add 3 months: " + simpleDateFormat.format(calendar.getTime()));

			// Subtract 2 months
			calendar.add(Calendar.MONTH, -2);
			System.out.println("Subtract 2 months: " + simpleDateFormat.format(calendar.getTime()));

			// Add 3 years
			calendar.add(Calendar.YEAR, 3);
			System.out.println("Add 3 years: " + simpleDateFormat.format(calendar.getTime()));

			// Subtract 2 years
			calendar.add(Calendar.YEAR, -2);
			System.out.println("Subtract 2 years: " + simpleDateFormat.format(calendar.getTime()));

		} catch (Exception e) {
			System.err.println(e.getMessage());
		}

	}

}

Output

Today: 14/11/2021
Add 20 days: 04/12/2021
Subtract 10 days: 24/11/2021
Add 3 months: 24/02/2022
Subtract 2 months: 24/12/2021
Add 3 years: 24/12/2024
Subtract 2 years: 24/12/2022