Java 日历 roll(int calndr_field, int amt)方法及示例

Calendar类中的 roll(int calndr_field , int amt ) 方法用于对传递的日历字段进行操作，将传递的金额添加到特定的日历字段中，而不改变大字段的值。

注意： 正数必须添加，负数必须减去。

语法

public void roll(int calndr_field , int amt )

参数： 该方法需要两个参数。
1. calndr_field。 这是一个日历类型的参数，指的是要操作的日历字段。
2. amt: 这是一个整数类型的参数，根据数值的符号进行加减。

返回值： 该方法不返回任何值。

下面的程序说明了日历类的roll()方法的工作原理：

示例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
        // by 5
        calndr.roll(Calendar.YEAR, -5);
  
        // Displaying the result after the operation
        System.out.println("The New Year is: "
                           + calndr.get(
                                 Calendar.YEAR));
  
        // Incrementing the year
        // by 2
        calndr.roll(Calendar.YEAR, 2);
  
        // Displaying the result after operation
        System.out.println("The new year is: "
                           + calndr.get(
                                 Calendar.YEAR));
    }
}

输出:

The Current Year is: 2019
The New Year is: 2014
The new year is: 2016

例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
        // by 3
        calndr.roll(Calendar.MONTH, 3);
  
        // Displaying the result after operation
        System.out.println("The New Month is: "
                           + calndr.get(
                                 Calendar.MONTH));
  
        // Decrementing the month
        // by 1
        calndr.roll(Calendar.MONTH, -1);
  
        // Displaying the result after operation
        System.out.println("The new month is: "
                           + calndr.get(
                                 Calendar.MONTH));
    }
}

输出:

The Current Month is: 2
The New Month is: 5
The new month is: 4

参考： https://docs.oracle.com/javase/7/docs/api/java/util/Calendar.html#roll(int, %20int)