GregorianCalendar的奇怪行为 [英] Strange behaviour with GregorianCalendar

问题描述

我在GregorianCalendar类中遇到了一个奇怪的行为，我想知道我是否真的做得不好。

I just encountered a strange behaviour with the GregorianCalendar class, and I was wondering if I really was doing something bad.

这仅在初始化日期的月份为实际的最大值大于我要设置日历的月份。

This only appends when the initialization date's month has an actualMaximum bigger than the month I'm going to set the calendar to.

下面是示例代码：

    // today is 2010/05/31  
    GregorianCalendar cal = new GregorianCalendar();

    cal.set(Calendar.YEAR, 2010);
    cal.set(Calendar.MONTH, 1); // FEBRUARY

    cal.set(Calendar.DAY_OF_MONTH, cal.getActualMaximum(Calendar.DAY_OF_MONTH));
    cal.set(Calendar.HOUR_OF_DAY, cal.getActualMaximum(Calendar.HOUR_OF_DAY));
    cal.set(Calendar.MINUTE, cal.getActualMaximum(Calendar.MINUTE));
    cal.set(Calendar.SECOND, cal.getActualMaximum(Calendar.SECOND));
    cal.set(Calendar.MILLISECOND, cal.getActualMaximum(Calendar.MILLISECOND));

    return cal.getTime(); // => 2010/03/03, wtf

我知道问题是由日历初始化日期引起的是31天（五月），与设置为2月（28天）的月份相混淆。修复很容易（只需在设置年和月之前将day_of_month设置为1），但是我想知道这确实是想要的行为。有什么想法吗？

I know the problem is caused by the fact that the calendar initialization date is a 31 day month ( may ), which mess with the month set to february (28 days). The fix is easy ( just set day_of_month to 1 before setting year and month ), but I was wondering is this really was the wanted behaviour. Any thoughts ?

推荐答案

它正在获取当前日期/时间的实际最大值。 5月有31天，比2月28日晚3天，因此将转移到3月3日。

It is getting the actual maximums of the current date/time. May has 31 days which is 3 more than 28 February and it will thus shift to 3 March.

您需要致电 Calendar＃clear（） 在获得/创建后：

You need to call Calendar#clear() after obtaining/creating it:

GregorianCalendar cal = new GregorianCalendar();
cal.clear();
// ...

结果为：

Sun Feb 28 23:59:59 GMT-04:00 2010

（根据我的时区是正确的）

(which is correct as per my timezone)

正如答案之一所说， java。 util.Calendar 和 Date 是史诗般的失败。在进行密集的日期/时间操作时，请考虑 JodaTime 。

As said in one of the answers, the java.util.Calendar and Date are epic failures. Consider JodaTime when doing intensive date/time operations.

这篇关于GregorianCalendar的奇怪行为的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！