Java Calendar 日历类的时间操作，这也许是 Java 环境下创建和管理日历及操作时间最简单的一个方案了，示范代码也很简单。

演示了获取时间，日期时间的累加和累减，以及日期时间的比较。

原文地址：blog.csdn.net/joyous/article/details/9630893

注意事项：

Calendar 的 month 从 0 开始，也就是全年 12 个月由 0 ~ 11 进行表示。

而 Calendar.DAY_OF_WEEK 定义值如下，每周从 SUNDAY 开始，从 1 ~ 7：

Calendar.SUNDAY = 1

Calendar.MONDAY = 2

Calendar.TUESDAY = 3

Calendar.WEDNESDAY = 4

Calendar.THURSDAY = 5

Calendar.FRIDAY = 6

Calendar.SATURDAY = 7

SimpleDateFormat 的格式定义

 

Letter
			
Date or Time Component
			
Presentation
			
Examples
		
G
			
Era designator
			
Text
			
AD
		
y
			
Year
			
Year
			
1996; 96
		
Y
			
Week year
			
Year
			
2009; 09
		
M
			
Month in year (context sensitive)
			
Month
			
July; Jul; 07
		
L
			
Month in year (standalone form)
			
Month
			
July; Jul; 07
		
w
			
Week in year
			
Number
			
27
		
W
			
Week in month
			
Number
			
2
		
D
			
Day in year
			
Number
			
189
		
d
			
Day in month
			
Number
			
10
		
F
			
Day of week in month
			
Number
			
2
		
E
			
Day name in week
			
Text
			
Tuesday; Tue
		
u
			
Day number of week (1 = Monday, ..., 7 = Sunday)
			
Number
			
1
		
a
			
Am/pm marker
			
Text
			
PM
		
H
			
Hour in day (0-23)
			
Number
			
0
		
k
			
Hour in day (1-24)
			
Number
			
24
		
K
			
Hour in am/pm (0-11)
			
Number
			
0
		
h
			
Hour in am/pm (1-12)
			
Number
			
12
		
m
			
Minute in hour
			
Number
			
30
		
s
			
Second in minute
			
Number
			
55
		
S
			
Millisecond
			
Number
			
978
		
z
			
Time zone
			
General time zone
			
Pacific Standard Time; PST; GMT-08:00
		
Z
			
Time zone
			
RFC 822 time zone
			
-0800
		
X
			
Time zone
			
ISO 8601 time zone
			
-08; -0800; -08:00
		
 

Java Calendar 演示代码如下：

 

package demo;

import java.util.Date;
import java.text.SimpleDateFormat;
import java.text.DateFormat;
import java.text.ParseException;
import java.util.Calendar;

public class Test
{
  public Test()
  {
  }

  public static void main(String[] args)
  {
    // 字符串转换日期格式
    // DateFormat fmtDateTime = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    // 接收传入参数
    // String strDate = args[1];
    // 得到日期格式对象
    // Date date = fmtDateTime.parse(strDate);

    // 完整显示今天日期时间
    String str = (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SSS")).format(new Date());
    System.out.println(str);

    // 创建 Calendar 对象
    Calendar calendar = Calendar.getInstance();

    try
    {
      // 对 calendar 设置时间的方法
      // 设置传入的时间格式
      SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-M-d H:m:s");
      // 指定一个日期
      Date date = dateFormat.parse("2013-6-1 13:24:16");
      // 对 calendar 设置为 date 所定的日期
      calendar.setTime(date);

      // 按特定格式显示刚设置的时间
      str = (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SSS")).format(calendar.getTime());
      System.out.println(str);
    }
    catch (ParseException e)
    {
      e.printStackTrace();
    }

    // 或者另一種設置 calendar 方式
    // 分別爲 year, month, date, hourOfDay, minute, second
    calendar = Calendar.getInstance();
    calendar.set(2013, 1, 2, 17, 35, 44);
    str = (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SSS")).format(calendar.getTime());
    System.out.println(str);

    // Calendar 取得当前时间的方法
    // 初始化 (重置) Calendar 对象
    calendar = Calendar.getInstance();
    // 或者用 Date 来初始化 Calendar 对象
    calendar.setTime(new Date());

    // setTime 类似上面一行
    // Date date = new Date();
    // calendar.setTime(date);

    str = (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SSS")).format(calendar.getTime());
    System.out.println(str);

    // 显示年份
    int year = calendar.get(Calendar.YEAR);
    System.out.println("year is = " + String.valueOf(year));

    // 显示月份 (从0开始, 实际显示要加一)
    int month = calendar.get(Calendar.MONTH);
    System.out.println("nth is = " + (month + 1));

    // 本周几
    int week = calendar.get(Calendar.DAY_OF_WEEK);
    System.out.println("week is = " + week);

    // 今年的第 N 天
    int DAY_OF_YEAR = calendar.get(Calendar.DAY_OF_YEAR);
    System.out.println("DAY_OF_YEAR is = " + DAY_OF_YEAR);

    // 本月第 N 天
    int DAY_OF_MONTH = calendar.get(Calendar.DAY_OF_MONTH);
    System.out.println("DAY_OF_MONTH = " + String.valueOf(DAY_OF_MONTH));

    // 3小时以后
    calendar.add(Calendar.HOUR_OF_DAY, 3);
    int HOUR_OF_DAY = calendar.get(Calendar.HOUR_OF_DAY);
    System.out.println("HOUR_OF_DAY + 3 = " + HOUR_OF_DAY);

    // 当前分钟数
    int MINUTE = calendar.get(Calendar.MINUTE);
    System.out.println("MINUTE = " + MINUTE);

    // 15 分钟以后
    calendar.add(Calendar.MINUTE, 15);
    MINUTE = calendar.get(Calendar.MINUTE);
    System.out.println("MINUTE + 15 = " + MINUTE);

    // 30分钟前
    calendar.add(Calendar.MINUTE, -30);
    MINUTE = calendar.get(Calendar.MINUTE);
    System.out.println("MINUTE - 30 = " + MINUTE);

    // 7天前
    calendar.add(Calendar.DAY_OF_YEAR, -7);
    // 显示当月 x 号
    int day_of_month = calendar.get(Calendar.DAY_OF_MONTH);
    System.out.println("day_of_month -7 = " + day_of_month);

    // 格式化显示
    str = (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SS")).format(calendar.getTime());
    System.out.println(str);

    // 重置 Calendar 显示当前时间
    calendar.setTime(new Date());
    str = (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss:SS")).format(calendar.getTime());
    System.out.println(str);

    // 创建一个 Calendar 用于比较时间
    Calendar calendarNew = Calendar.getInstance();

    // 设定为 5 小时以前，后者大，显示 -1
    calendarNew.add(Calendar.HOUR, -5);
    System.out.println("时间比较：" + calendarNew.compareTo(calendar));

    // 设定7小时以后，前者大，显示 1
    calendarNew.add(Calendar.HOUR, +7);
    System.out.println("时间比较：" + calendarNew.compareTo(calendar));

    // 退回 2 小时，时间相同，显示 0
    calendarNew.add(Calendar.HOUR, -2);
    System.out.println("时间比较：" + calendarNew.compareTo(calendar));
  }
}

运行结果

2013-06-07 23:27:34:195
2013-06-01 13:24:16:000
2013-02-02 17:35:44:197
2013-06-07 23:27:34:197
year is = 2013
nth is = 6
week is = 6
DAY_OF_YEAR is = 158
DAY_OF_MONTH = 7
HOUR_OF_DAY + 3 = 2
MINUTE = 27
MINUTE + 15 = 42
MINUTE - 30 = 12
2013-06-08 02:12:34:197
2013-06-07 23:27:34:199
时间比较：-1
时间比较：1
时间比较：0

要计算时间差，可用 Calendar.getTimeInMillis() 取得两个时间的微秒级的时间差，再加以换算即可，比如获得相差天数，代码如下：

    // 得微秒级时间差
    long val = calendarEnd.getTimeInMillis() - calendarBegin.getTimeInMillis();
    // 换算后得到天数
    long day = val / (1000 * 60 * 60 * 24);


其他与 date 相关的类型转换代码如下。

Timestamp 类型转换为 Date 类型：

Timestamp stamp = new Timestamp(System.currentTimeMillis());
Date date = new Date(stamp.getTime());
System.out.println(date);

Timestamp 类型转换为 Calendar 类型：

// 获取 Timestamp 类型时间
Timestamp timestamp = new Timestamp(System.currentTimeMillis());

// 转换为 Calendar 类型，SUN 也推荐用 Calendar 处理时间信息
Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(timestamp.getTime());

Date 类型转换为 Calendar 类型：

// Date 向 Calendar 赋值
calendar.setTime(date);

Calendar 类型转换为 Timestamp 类型：

// 创建 Calendar 对象，也同时获取了当前时间
Calendar calendar = Calendar.getInstance();

// 转换为 Timestamp 类型对象
Timestamp timestamp = new Timestamp(calendar.getTimeInMillis());
System.out.println(timestamp);

Calendar 类型转换为 Date 类型：

// Calendar 对象类型转换为 Date 对象类型
Calendar calendar = Calendar.getInstance();
java.util.Date date = calendar.getTime();
System.out.println(date);

StringDate 转换为 Date 或者 Timestamp

/* 将字符串日期或者日期时间转换为 timestamp 格式 */
try
  {
    // 一个字符串日期
    String strDate = "2020-01-31";

    // 设置传入格式
    // yyyy-MM-dd 或者完整的 yyyy-MM-dd HH:mm:ss
    DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
    Date date = dateFormat.parse(strDate);

    // 创建 Calendar 用于处理 date 对象
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);

    // 由 calendar 对象生成 timestamp
    Timestamp timestamp = new Timestamp(calendar.getTimeInMillis());
    System.out.printf(timestamp);
  }
  catch (Exception e)
  {
    e.printStackTrace();
  }

原文地址：blog.csdn.net/joyous/article/details/9630893

https://blog.inull.net

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import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class CalendarDemo {
    public static void main(String[] args) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        System.out.println("1 - 当前日期: " + sdf.format(new Date()));

        Calendar calendar = Calendar.getInstance();
        System.out.println("2 - 当前年份: " + calendar.get(Calendar.YEAR));
        int currentMonth = calendar.get(Calendar.MONTH)+1; // 月份是从0开始,0表示1月
        System.out.println("3 - 当前月份(1位数): " + currentMonth);
        System.out.println("4 - 当前日: " + calendar.get(Calendar.DATE));

        System.out.println("==========================================");
        System.out.println("5 - 当前小时(12小时制): " + calendar.get(Calendar.HOUR));
        System.out.println("6 - 当前小时(24小时制): " + calendar.get(Calendar.HOUR_OF_DAY));
        System.out.println("7 - 当前分钟: " + calendar.get(Calendar.MINUTE));
        System.out.println("8 - 当前秒: " + calendar.get(Calendar.SECOND));

        System.out.println("==========================================");
        System.out.println("9 - 当前上下午(0-上午;1-下午): " + calendar.get(Calendar.AM_PM));

        System.out.println("==========================================");
        System.out.println("10 - 今天是今年的第 " + calendar.get(Calendar.DAY_OF_YEAR) + " 天");
        System.out.println("11 - 今天是这个月的第 " + calendar.get(Calendar.DAY_OF_MONTH) + " 天");
        System.out.println("12 - 今天是这个月的第 " + calendar.get(Calendar.DAY_OF_WEEK) + " 周");
        System.out.println("13 - 今天是这个月本周的第 " + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH) + " 天");

        calendar.setTime(new Date());
        calendar.add(Calendar.MONTH, 2); // 1月从0开始的
        System.out.println("14 - 下个月月份(1位数): " + calendar.get(Calendar.MONTH));

        calendar.set(Calendar.DATE, 0);
        System.out.println("15 - 下个月最后一天日期: " + sdf.format(calendar.getTime()));
    }
}
输出结果:
1 - 当前日期: 2017-07-27
2 - 当前年份: 2017
3 - 当前月份(1位数): 7
4 - 当前日: 27
==========================================
5 - 当前小时(12小时制): 5
6 - 当前小时(24小时制): 17
7 - 当前分钟: 40
8 - 当前秒: 1
==========================================
9 - 当前上下午(0-上午;1-下午): 1
==========================================
10 - 今天是今年的第 208 天
11 - 今天是这个月的第 27 天
12 - 今天是这个月的第 5 周
13 - 今天是这个月本周的第 4 天
14 - 下个月月份(1位数): 8
15 - 下个月最后一天日期: 2017-08-31

from head first java 
import java.util.Calendar;

public class XCalendar {
	public static void main(String[] args){
		Calendar c = Calendar.getInstance();
		c.set(2004, 0 , 7 , 15 ,40 );  //设置时间
		System.out.println("now date:" + c.getTime());
		long day1 = c.getTimeInMillis();
		day1 += 1000 * 60 * 60;
		c.setTimeInMillis(day1);  //以mills set time
		System.out.println("now date:" + c.getTime());
		System.out.println("new Hour:" + c.get(Calendar.HOUR_OF_DAY));
		c.add(Calendar.DATE, 35);  //增加天数，会改变月份
		System.out.println("add 35 days:" + c.getTime());
		c.roll(Calendar.DATE, 35); //不改变月份情况下来增加天数。
		System.out.println("roll 35 days:" + c.getTime());
		c.set(Calendar.DATE, 1);  //手动设置日期
		System.out.println("after set 1：" + c.getTime());
	}
}

java calendar
 Calendar类after()方法 (Calendar Class after() method)
after() method is available in java.util package.
 after()方法在java.util包中可用。 
after() method is used to check whether this calendar time is after the time denoted by the given Object's time or not.
 after()方法用于检查此日历时间是否在给定Object的时间所表示的时间之后。 
after() method is a non-static method, it is accessible with the class object and if we try to access the method with the class name then we will get an error.
 after()方法是一种非静态方法，可通过类对象访问，如果尝试使用类名称访问该方法，则会收到错误消息。 
after() method does not throw an exception at the checking this calendar time with the given time.
 after()方法在检查给定时间的日历时间时不会引发异常。 
Syntax:
 句法： 
    public boolean after(Object time);

Parameter(s):
 参数： 
Object time – represents the time to be compared with this calendar time.
 对象时间 –表示要与此日历时间进行比较的时间。 
Return value:
 返回值： 
The return type of the method is boolean, it returns true when the given time is before this calendar time otherwise it returns false.
 方法的返回类型为boolean ，如果给定时间早于日历时间，则返回true ，否则返回false 。 
Example:
 例： 
// Java Program to demonstrate the example of
// boolean after(Object) method of Calendar

import java.util.*;

public class AfterOfCalendar {
    public static void main(String[] args) {
        // Instantiating two Calendar object
        Calendar curr_ca = Calendar.getInstance();
        Calendar after_ca = Calendar.getInstance();

        // By using add() method is to add the 
        // 10 months to the current calendar
        after_ca.add(Calendar.MONTH, 10);

        // Display current and after calendar
        System.out.println("curr_ca.getTime(): " + curr_ca.getTime());
        System.out.println("after_ca.getTime(): " + after_ca.getTime());

        // By using after() method is to check
        // the after_ca time is after the curr_ca
        boolean status = after_ca.after(curr_ca);

        //Display Result
        System.out.println("after_ca.after(curr_ca): " + status);
    }
}

Output
 输出量 
curr_ca.getTime(): Thu Jan 23 11:12:36 GMT 2020
after_ca.getTime(): Mon Nov 23 11:12:36 GMT 2020
after_ca.after(curr_ca): true


翻译自: https://www.includehelp.com/java/calendar-after-method-with-example.aspx
java calendar