Calendar roll() Method in Java with Examples

The roll(int calndr_field, boolean up_down) method in Calendar class is used to operate on the passed calendar field by moving the passed field, up or down by a single unit of time. This involves addition or subtraction of the time field without changing the larger fields.

Syntax:

public abstract void roll(int calndr_field, boolean up_down)

Parameters: The method takes two parameters:

• calndr_field: This is of Calendar type and refers to the field of the calendar that is to be operated upon.
• up_down: This is of the boolean type that is used to indicate whether to move calndr_field up or down or to increase or decrease. The true indicates adding a unit of time and false subtracts the same.

Return Value: The method does not return any value.

Below programs illustrate the working of roll() Method of Calendar class:
Example 1:

// Java code to illustrate
// isSet() method

import java.util.*;
public class Calendar_Demo {
    public static void main(String args[])
    {

        // Creating a calendar
        Calendar calndr = Calendar.getInstance();

        // Displaying the year
        System.out.println("The Current Year"
                           + " is: "
                           + calndr.get(
                                 Calendar.YEAR));

        // Decrementing the year
        // false indicates subtraction
        calndr.roll(Calendar.YEAR, false);

        // Displaying the result after operation
        System.out.println("The New Year is: "
                           + calndr.get(
                                 Calendar.YEAR));

        // Incrementing the year
        // true indicates addition
        calndr.roll(Calendar.YEAR, true);

        // Displaying the result after operation
        System.out.println("The new year is: "
                           + calndr.get(
                                 Calendar.YEAR));
    }
}

Output:

The Current Year is: 2019
The New Year is: 2018
The new year is: 2019

Example 2:

// Java code to illustrate
// isSet() method

import java.util.*;
public class Calendar_Demo {
    public static void main(String args[])
    {

        // Creating a calendar
        Calendar calndr = Calendar.getInstance();

        // Displaying the month
        System.out.println("The Current Month"
                           + " is: "
                           + calndr.get(
                                 Calendar.MONTH));

        // Incrementing the month
        // true indicates addition
        calndr.roll(Calendar.MONTH, true);

        // Displaying the result after operation
        System.out.println("The New Month is: "
                           + calndr.get(
                                 Calendar.MONTH));

        // Decrementing the month
        // false indicates subtraction
        calndr.roll(Calendar.MONTH, false);

        // Displaying the result after operation
        System.out.println("The new month is: "
                           + calndr.get(
                                 Calendar.MONTH));
    }
}

Output:

The Current Month is: 1
The New Month is: 2
The new month is: 1

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/Calendar.html#roll-int-boolean-