使用 Calendar 计算时间

一. 类型转换

1.1 Date → Calendar

public Calendar date2Calendar(Date date){
    
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);
    return calendar;
}

1.2 Calendar → Date

public Date calendar2Date(Calendar calendar){
    
    return calendar.getTime();
}

二. 时间计算

2.1 ?毫秒

/* * 计算两个日期之间的差值： * 日期1：2019-12-31 12:30:12 * 日期2：2020-01-01 13:31:13 */
Calendar startCalendar = Calendar.getInstance();
Calendar endCalendar = Calendar.getInstance();

// 手动设置时间
startCalendar.set(2019, Calendar.DECEMBER, 31, 12, 30, 12);
endCalendar.set(2020, Calendar.JANUARY, 1, 13, 31, 13);
startCalendar.set(Calendar.MILLISECOND, 0);
endCalendar.set(Calendar.MILLISECOND, 0);

long startCalendarTimeInMills = startCalendar.getTimeInMillis();
long endCalendarTimeInMills = endCalendar.getTimeInMillis();

long differenceInMills = endCalendarTimeInMills - startCalendarTimeInMills;
System.out.println("相差：" + differenceInMills + "（毫秒）");

代码执行结果：

相差： 90061000（毫秒）

Process finished with exit code 0

2.2 ?秒

/* * 计算两个日期之间的差值： * 日期1：2019-12-31 12:30:12 * 日期2：2020-01-01 13:31:13 */
Calendar startCalendar = Calendar.getInstance();
Calendar endCalendar = Calendar.getInstance();

// 手动设置时间
startCalendar.set(2019, Calendar.DECEMBER, 31, 12, 30, 12);
endCalendar.set(2020, Calendar.JANUARY, 1, 13, 31, 13);
startCalendar.set(Calendar.MILLISECOND, 0);
endCalendar.set(Calendar.MILLISECOND, 0);

long startCalendarTimeInMills = startCalendar.getTimeInMillis();
long endCalendarTimeInMills = endCalendar.getTimeInMillis();
long differenceInMills = endCalendarTimeInMills - startCalendarTimeInMills;

//1秒 = 1000毫秒
long differenceInSecond = differenceInMills / 1000;
System.out.println("相差： " + differenceInSecond + "（秒）");

代码执行结果：

相差： 90061（秒）

Process finished with exit code 0

2.3 ?分钟

/* * 计算两个日期之间的差值： * 日期1：2019-12-31 12:30:12 * 日期2：2020-01-01 13:31:13 */
Calendar startCalendar = Calendar.getInstance();
Calendar endCalendar = Calendar.getInstance();

// 手动设置时间
startCalendar.set(2019, Calendar.DECEMBER, 31, 12, 30, 12);
endCalendar.set(2020, Calendar.JANUARY, 1, 13, 31, 13);
startCalendar.set(Calendar.MILLISECOND, 0);
endCalendar.set(Calendar.MILLISECOND, 0);

// 计算毫秒差值
long startCalendarTimeInMills = startCalendar.getTimeInMillis();
long endCalendarTimeInMills = endCalendar.getTimeInMillis();
long differenceInMills = endCalendarTimeInMills - startCalendarTimeInMills;

// 1秒 = 1000毫秒
long differenceInSecond = differenceInMills / 1000;

// 1分钟 = 60秒
long differenceInMinute = differenceInSecond / 60;
System.out.println("相差： " + differenceInMinute + "（分钟）");

代码执行结果：

相差： 1501（分钟）

Process finished with exit code 0

2.4 ?小时

/* * 计算两个日期之间的差值： * 日期1：2019-12-31 12:30:12 * 日期2：2020-01-01 13:31:13 */
Calendar startCalendar = Calendar.getInstance();
Calendar endCalendar = Calendar.getInstance();

// 手动设置时间
startCalendar.set(2019, Calendar.DECEMBER, 31, 12, 30, 12);
endCalendar.set(2020, Calendar.JANUARY, 1, 13, 31, 13);
startCalendar.set(Calendar.MILLISECOND, 0);
endCalendar.set(Calendar.MILLISECOND, 0);

// 计算毫秒差值
long startCalendarTimeInMills = startCalendar.getTimeInMillis();
long endCalendarTimeInMills = endCalendar.getTimeInMillis();
long differenceInMills = endCalendarTimeInMills - startCalendarTimeInMills;

// 1秒 = 1000毫秒
long differenceInSecond = differenceInMills / 1000;

// 1分钟 = 60秒
long differenceInMinute = differenceInSecond / 60;

// 1小时 = 60分钟 = 3600秒
long differenceInHour = differenceInSecond / 3600;
System.out.println("相差： " + differenceInHour + "（小时）");

代码执行结果：

相差： 25（小时）

Process finished with exit code 0

2.5 ? 时?分?秒?毫秒

/* * 计算两个日期之间的差值： * 日期1：2019-12-31 12:30:12 * 日期2：2020-01-01 13:31:13 */
Calendar startCalendar = Calendar.getInstance();
Calendar endCalendar = Calendar.getInstance();

// 手动设置时间
startCalendar.set(2019, Calendar.DECEMBER, 31, 12, 30, 12);
endCalendar.set(2020, Calendar.JANUARY, 1, 13, 31, 13);
startCalendar.set(Calendar.MILLISECOND, 0);
endCalendar.set(Calendar.MILLISECOND, 0);

// 计算毫秒差值
long startCalendarTimeInMills = startCalendar.getTimeInMillis();
long endCalendarTimeInMills = endCalendar.getTimeInMillis();
long differenceInMills = endCalendarTimeInMills - startCalendarTimeInMills;

// 1秒 = 1000毫秒
long differenceInSecond = differenceInMills / 1000;

// 1分钟 = 60秒
long differenceInMinute = differenceInSecond / 60;

// 1小时 = 60分钟 = 3600秒
long differenceInHour = differenceInSecond / 3600;

System.out.println("相差： " +
        (differenceInSecond / 3600) + "小时" +
        (differenceInSecond % 3600) / 60 + "分钟" +
        (differenceInSecond % 3600 % 60) + "秒" +
        (differenceInMills % 1000) + "毫秒");

代码执行结果：

相差： 25小时1分钟1秒0毫秒

Process finished with exit code 0

三、时间比较

3.1 两个日期相差几天？

public static void main(String[] args) {
    

    /* * 计算两个日期之间的差值： * 日期1：2019-12-31 12:30:12 * 日期2：2020-01-01 13:31:13 */
    Calendar calendar1 = Calendar.getInstance();
    Calendar calendar2 = Calendar.getInstance();

    calendar1.set(2019, Calendar.DECEMBER, 31, 12, 30, 12);
    calendar2.set(2020, Calendar.JANUARY, 1, 13, 31, 13);
    calendar1.set(Calendar.MILLISECOND, 0);
    calendar2.set(Calendar.MILLISECOND, 0);

    // 1.获取日期毫秒数
    long timeInMills1 = calendar1.getTimeInMillis();
    long timeInMills2 = calendar2.getTimeInMillis();

    // 2.计算：本日期是自1900年以来的第几天？
    long days1 = timeInMills1 / 1000 / 3600 / 24;
    long days2 = timeInMills2 / 1000 / 3600 / 24;
    System.out.println("日期 " + calendar1.getTime() + 
                       " 是1900年以来的第" + days1 + "天");
    System.out.println("日期 " + calendar2.getTime() + 
                       " 是1900年以来的第" + days2 + "天");

    // 3.计算日期相差的天数
    long differenceDays = days2 - days1;
    System.out.println("两个日期相差：" + differenceDays + "天");
}

代码执行结果：

日期 Tue Dec 31 12:30:12 CST 2019 是1900年以来的第18261天
日期 Wed Jan 01 13:31:13 CST 2020 是1900年以来的第18262天
两个日期相差：1天

Process finished with exit code 0