Java GregorianCalendar - roll() Method

The java.util.GregorianCalendar.roll() method is used to add a signed amount to the specified calendar field without changing larger fields. A negative roll amount means to subtract from field without changing larger fields. If the specified amount is 0, this method performs nothing.

Example: Consider a GregorianCalendar originally set to November 30, 1999. Calling roll(Calendar.MONTH, 2) sets the calendar to January 30, 1999. The YEAR field is unchanged because it is a larger field than MONTH.

Syntax

public void roll(int field, int amount)

Parameters

Return Value

void type.

Exception

Throws IllegalArgumentException, if field is ZONE_OFFSET, DST_OFFSET, or unknown, or if any calendar fields have out-of-range values in non-lenient mode.

Example:

In the example below, the java.util.GregorianCalendar.roll() method is used to add the specified unit of time on the given time field of the GregorianCalendar object.

import java.util.*;

public class MyClass {
  public static void main(String[] args) {
    //creating a Calendar object with specified date
    GregorianCalendar Cal = new GregorianCalendar(2015, 10, 30);

    //printing the Calendar
    System.out.println("The Calendar is: " + Cal.getTime());

    //rolling the month up by 2
    Cal.roll(GregorianCalendar.MONTH, 2);

    //printing the Calendar
    System.out.println("Modified Calendar is: " + Cal.getTime());    
  }
}

The output of the above code will be:

The Calendar is: Mon Nov 30 00:00:00 UTC 2015
Modified Calendar is: Fri Jan 30 00:00:00 UTC 2015