乔达时间-不一致的结果 [英] Joda Time - inconsistent result

问题描述

我对Joda-Time库中的daysBetween函数进行了快速测试，结果不一致.还有其他人有同样的问题吗?

I ran a quick test on daysBetween function in Joda-Time library and I am getting inconsistent result. Does anyone else have the same problem?

下面是我用于测试的代码.

Below is the code I use for testing.

public static int elapsedDaysJoda() {
    DateTime dt1 = new DateTime(new Date());        
    Calendar cal = Calendar.getInstance();
    cal.set(2011, 0, 1); 
    DateTime dt2 = new DateTime(cal.getTime());
    Days days = Days.daysBetween(dt2, dt1);
    return days.getDays();
}

public static void main(String[] args) {
    for(int i=0; i < 10; i++) {
        System.out.println(elapsedDaysJoda());
    }
}

推荐答案

首先，也是主要问题:您正在Java中两次在new Date()和Calendar.getInstance()中向Java请求当前日期时间"，因此不能确定这两个调用将返回完全相同的时刻，或者如果它们可以在几毫秒内有所不同，则返回.

First, and main problem: you are asking Java for the "current datetime" twice, in new Date() and in Calendar.getInstance(), and you cannot be sure that this two calls will return exactly the same instant or if they can differ in a few milliseconds.

此外，因为您使用的是DateTime而不是LocalDate，所以几毫秒的差异可能会改变经过时间的计算.如果您(从概念上)正在处理几天之间的差异，并且您不关心时间(h:m:s.ssss)，那么您最好使用LocalDate.

Besides, because you are using DateTime instead of LocalDate, that difference of a few milliseconds can alter the calculation of the elapsed days. If you are (conceptually) dealing with difference between days and you do not care about times (h:m:s.sss) perhaps you should better use LocalDate.

第一个问题可以通过只请求Java当前时间来解决:

The first problem could be solved by asking for Java current datime only once:

public static int elapsedDaysJoda() {
    Calendar cal = Calendar.getInstance();
    DateTime dt1 = new DateTime(cal);
    cal.set(2011, 0, 1); 
    DateTime dt2 = new DateTime(cal.getTime());
    Days days = Days.daysBetween(dt2, dt1);
    return days.getDays();
}

此外(或替代；这也可以修复不一致的结果)，您可以使用LocalDate代替DateTime.

In addition (or alternatively; this also fixes the inconsistent results), you could use LocalDate instead of DateTime.

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