Java日期和时间:如何使plus()和直到()彼此相反 [英] Java Date and Time: How do I make plus() and until() to be each others inverse

问题描述

在大多数情况下，这两种方法彼此相反:

Most of the time, these 2 methods are each others inverse:

• Temporal Temporal.plus(long, TemporalUnit)
• long Temporal.until(Temporal, TemporalUnit)

• Temporal Temporal.plus(long, TemporalUnit)
• long Temporal.until(Temporal, TemporalUnit)

例如，从1月1日开始

System.out.println("1-JAN plus 1 month: " +
    LocalDate.of(2017, 1, 1).plus(1, ChronoUnit.MONTHS));
System.out.println("1-JAN until 1-FEB in months: " +
    LocalDate.of(2017, 1, 1).until(LocalDate.of(2017, 2, 1), ChronoUnit.MONTHS));

它们彼此相反:

1月1日加上1个月:2017-02-1
1月1日至1月2日:1//良好

1-JAN plus 1 month: 2017-02-01
1-JAN until 1-FEB in months: 1 // GOOD

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但是，在此示例中，从1月31日开始:

---

However, in this example starting from 31-JAN:

System.out.println("31-JAN plus 1 month: " +
    LocalDate.of(2017, 1, 31).plus(1, ChronoUnit.MONTHS));
System.out.println("31-JAN until 28-FEB in months: " +
    LocalDate.of(2017, 1, 31).until(LocalDate.of(2017, 2, 28), ChronoUnit.MONTHS));

它们彼此不相反:

31年1月31日加上1个月:2017年2月28日//不好?应该到3月1日吗?
1月31日至2月28日2月:0//还是不好?应该是1?

31-JAN plus 1 month: 2017-02-28 // Bad? Should ceil to 1 March?
31-JAN until 28-FEB in months: 0 // Or is this bad? Should be 1?

---

如何使它们彼此相反?

---

How can I make them to be each others inverse?

推荐答案

这些日期之间只有28天，因此整月数为0.但是，如果您希望少于1个月，可以使用一些舍入被认为是一个月.例如

There is only 28 days between those dates so the number of whole months is 0. However you could use a bit of rounding if you want less than 1 month be be considered a month. e.g.

// compare the months after rounding to the next month
LocalDate a = LocalDate.of(2017, 1, 31);
LocalDate b = LocalDate.of(2017, 2, 28);
long months = a.plus(1, ChronoUnit.MONTHS)
        .until(b.plus(1, ChronoUnit.MONTHS), ChronoUnit.MONTHS);
System.out.println(a + " until " + b + " in months: " + months);

打印

2017-01-31 until 2017-02-28 in months: 1

和

// compare the months after rounding to the next month
LocalDate a = LocalDate.of(2017, 1, 31);
LocalDate b = LocalDate.of(2017, 3, 30);
long months = a.plus(1, ChronoUnit.MONTHS)
        .until(b.plus(1, ChronoUnit.MONTHS), ChronoUnit.MONTHS);
System.out.println(a + " until " + b + " in months: " + months);

打印

2017-01-31 until 2017-03-30 in months: 2

我可能希望加号不加限制

I probably want the plus to ceil instead of to floor

根据您的要求，您可能希望将整个月视为30天.

You might want to treat all months as notionally 30 days depending on your requirements.

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