java – Calendar.UNDECIMBER做什么？

虽然没有实现13个月的日历扩展java.util.Calendar,但在Java 8的新API中有一些.随着new java.time API的推出,它还创建了ThreeTen Extra project,其中包含an implementation for that.

该类是org.threeten.extra.chrono.CopticChronology,它扩展了本机java.time.chrono.Chronology.我刚刚制作了一个示例代码,用于在此日历中创建日期并循环显示其日期：

// Coptic calendar
CopticChronology cal = CopticChronology.INSTANCE;
// range for month of year (from 1 to 13)
System.out.println("month range: " + cal.range(ChronoField.MONTH_OF_YEAR)); // 1 - 13

// getting a date in Coptic calendar and loop through the months
DateTimeFormatter fmt = DateTimeFormatter.ofPattern("dd/MM/yyyy");
// September 11th is equivalent to 01/01 in Coptic calendar
CopticDate d = cal.date(LocalDate.of(2017,9,11));
for (int i = 0; i < 14; i++) {
    System.out.println(fmt.format(d));
    d = d.plus(1,ChronoUnit.MONTHS);
}

输出是：

month range: 1 - 13
01/01/1734
01/02/1734
01/03/1734
01/04/1734
01/05/1734
01/06/1734
01/07/1734
01/08/1734
01/09/1734
01/10/1734
01/11/1734
01/12/1734
01/13/1734
01/01/1735

请注意,这一年在第13个月之后发生了变化.

对于Ethiopian calendar,ThreeTen Extra项目也有an implementation,也有13个月.

而且,作为一个14个月的日历的例子,有PaxChronology class,它实现了Pax Calendar：一个拟议的改革日历系统,但据我所知,目前尚未使用.

引用维基百科：

The common year is divided into 13 months of 28 days each,whose names are the same as in the Gregorian calendar,except that a month called Columbus occurs between November and December. The first day of every week,month and year would be Sunday.

In leap years,a one-week month called Pax would be inserted after Columbus.

并根据javadoc：

Leap years occur in every year whose last two digits are divisible by 6,are 99,or are 00 and the year is not divisible by 400.

例：

PaxChronology paxCal = PaxChronology.INSTANCE;
System.out.println("month range: " + paxCal.range(ChronoField.MONTH_OF_YEAR));

PaxDate pd = paxCal.date(1930,1,1);
for (int i = 0; i < 15; i++) {
    // fmt is the same DateTimeFormatter from previous example
    System.out.println(fmt.format(pd));
    // adjusting for first day of next month - using TemporalAdjuster because
    // adding 1 ChronoUnit.MONTHS throws an exception for 14th month (not sure why)
    pd = pd.plus(30,ChronoUnit.DAYS).with(TemporalAdjusters.firstDayOfMonth());
}

输出：

month range: 1 - 13/14
01/01/1930
01/02/1930
01/03/1930
01/04/1930
01/05/1930
01/06/1930
01/07/1930
01/08/1930
01/09/1930
01/10/1930
01/11/1930
01/12/1930
01/13/1930
01/14/1930
01/01/1931

您可以注意到,第14个月后年份发生了变化.范围是1 – 13/14,因为几年可以有13或14个月,这取决于它是否是闰年.