Java中的 Calendar roll() 方法及示例

Calendar 类中的roll(int calndr_field , boolean up_down )方法用于通过将传递的字段向上或向下移动单个时间单位来对传递的日历字段进行操作。这涉及在不更改较大字段的情况下添加或减去时间字段。

句法：

public abstract void roll(int calndr_field, boolean up_down)

参数：该方法有两个参数：

• calndr_field ：这是日历类型，是指要操作的日历的字段。
• up_down ：这是布尔类型，用于指示是向上或向下移动 calndr_field 还是增加或减少。 true 表示增加一个时间单位，false 表示减去相同的时间单位。

返回值：该方法不返回任何值。

下面的程序说明了 Calendar 类的 roll() 方法的工作：
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
        // 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));
    }
}

输出：

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

示例 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
        // 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));
    }
}

输出：

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

参考： https: Java/util/Calendar.html#roll-int-boolean-