Java Calendar.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY)，它会向后滚动，向前滚动还是未知？

Question

假设以下代码在 2009 年 8 月 22 日(星期六)执行

   Calendar c = Calendar.getInstance();
   c.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);

c.get(Calendar.DAY_OF_MONTH) 将返回 23。我感兴趣的条件是返回 14(上周日，而不是下周日)。

当设置 DAY_OF_WEEK 时，是否有任何与日历滚动 DAY_OF_MONTH/YEAR 的方向相关的规则？如果有，它们是什么？

Answer 1

它应该始终保持相同的 WEEK_OF_MONTH (http://java.sun.com/j2se/1.4.2/docs/api/java/util/Calendar.html#WEEK_OF_MONTH)。来自文档:

When setting or getting the WEEK_OF_MONTH or WEEK_OF_YEAR fields, Calendar must determine the first week of the month or year as a reference point. The first week of a month or year is defined as the earliest seven day period beginning on getFirstDayOfWeek() and containing at least getMinimalDaysInFirstWeek() days of that month or year. Weeks numbered ..., -1, 0 precede the first week; weeks numbered 2, 3,... follow it. Note that the normalized numbering returned by get() may be different. For example, a specific Calendar subclass may designate the week before week 1 of a year as week n of the previous year.