年号が変わったらJavaのCalendarの和暦変換はどうなるのか

2016/08/24

と仕事中にふと思った。

コードを探してみたらあった。

http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/util/JapaneseImperialCalendar.java#JapaneseImperialCalendar

クラスについて

JapaneseImperialCalendar implements a Japanese calendar system in which the imperial era-based year numbering is supported from the Meiji era. The following are the eras supported by this calendar system.

年号ベースで番号付けしてる日本のカレンダーを実装してますって書いてありますね。明治より前は登録されていないようです。生年月日での用途が主だからということでしょうかね。

年代(Era)クラス

public final class More Era {
     private final String name;
     private final String abbr;
     private final long since;
     private final CalendarDate sinceDate;
     private final boolean localTime;
}

public final class More Era {

private final String name;

private final String abbr;

private final long since;

private final CalendarDate sinceDate;

private final boolean localTime;

}

日本以外にも国独自の表記ってあるんだなー。

The class Era represents a calendar era that defines a period of time in which the same year numbering is used. For example, Gregorian year 2004 is Heisei 16 in the Japanese calendar system. An era starts at any point of time (Gregorian) that is represented by CalendarDate.

Eras that are applicable to a particular calendar system can be obtained by calling CalendarSystem.getEras() one of which can be used to specify a date in CalendarDate.

The following era names are defined in this release.

<tt> Calendar system Era name Since (in Gregorian) ----------------------------------------------------------------------- Japanese calendar Meiji 1868-01-01 midnight local time Taisho 1912-07-30 midnight local time Showa 1926-12-26 midnight local time Heisei 1989-01-08 midnight local time Julian calendar BeforeCommonEra -292275055-05-16T16:47:04.192Z CommonEra 0000-12-30 midnight local time Taiwanese calendar MinGuo 1911-01-01 midnight local time Thai Buddhist calendar BuddhistEra -543-01-01 midnight local time -----------------------------------------------------------------------</tt>

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<tt>
   Calendar system         Era name         Since (in Gregorian)
   -----------------------------------------------------------------------
   Japanese calendar       Meiji            1868-01-01 midnight local time
                           Taisho           1912-07-30 midnight local time
                           Showa            1926-12-26 midnight local time
                           Heisei           1989-01-08 midnight local time
   Julian calendar         BeforeCommonEra  -292275055-05-16T16:47:04.192Z
                           CommonEra        0000-12-30 midnight local time
   Taiwanese calendar      MinGuo           1911-01-01 midnight local time
   Thai Buddhist calendar  BuddhistEra      -543-01-01 midnight local time
   -----------------------------------------------------------------------</tt>