Java GregorianCalendar - roll() Method

The java.util.GregorianCalendar.roll() method is used to add or subtract (up/down) a single unit of time on the given time field without changing larger fields.

Example: Consider a GregorianCalendar originally set to December 31, 1999. Calling roll(Calendar.MONTH, true) sets the calendar to January 31, 1999. The YEAR field is unchanged because it is a larger field than MONTH.

Syntax

public void roll(int field, boolean up)

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 a single 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, 11, 25);

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

    //rolling the month up by 1
    Cal.roll(GregorianCalendar.MONTH, true);

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

The output of the above code will be:

The Calendar is: Fri Dec 25 00:00:00 UTC 2015
Modified Calendar is: Sun Jan 25 00:00:00 UTC 2015