java - Calendar.getInstance()和GregorianCalendar.getInstance()之间的区别

自从首次引入替换日期以来，我一直在使用静态方法 Calendar.getInstance()来获取新的日历对象。我从来没有遇到过问题，但是我只是出于某种原因而想知道使用 GregorianCalendar.getInstance()方法是否更好。

我的程序是否可以在某些语言环境或某些父类(super class)版本将返回我不期望的对象类的JVM中运行？除了 GregorianCalendar 以外，是否有实现过日历的实现？

正如我说的那样，目前我没有问题，但我一直在寻求改进自己的做法。

最佳答案

是的，日历可以返回特定于语言环境的日历。从源头上。

/**
 * Gets a calendar using the default time zone and locale. The
 * <code>Calendar</code> returned is based on the current time
 * in the default time zone with the default
 * {@link Locale.Category#FORMAT FORMAT} locale.
 *
 * @return a Calendar.
 */
public static Calendar getInstance()
{
    return createCalendar(TimeZone.getDefault(), Locale.getDefault(Locale.Category.FORMAT));
}

private static Calendar createCalendar(TimeZone zone,
                                       Locale aLocale)
{
    CalendarProvider provider =
        LocaleProviderAdapter.getAdapter(CalendarProvider.class, aLocale)
                             .getCalendarProvider();
    if (provider != null) {
        try {
            return provider.getInstance(zone, aLocale);
        } catch (IllegalArgumentException iae) {
            // fall back to the default instantiation
        }
    }

    Calendar cal = null;

    if (aLocale.hasExtensions()) {
        String caltype = aLocale.getUnicodeLocaleType("ca");
        if (caltype != null) {
            switch (caltype) {
            case "buddhist":
            cal = new BuddhistCalendar(zone, aLocale);
                break;
            case "japanese":
                cal = new JapaneseImperialCalendar(zone, aLocale);
                break;
            case "gregory":
                cal = new GregorianCalendar(zone, aLocale);
                break;
            }
        }
    }
    if (cal == null) {
        // If no known calendar type is explicitly specified,
        // perform the traditional way to create a Calendar:
        // create a BuddhistCalendar for th_TH locale,
        // a JapaneseImperialCalendar for ja_JP_JP locale, or
        // a GregorianCalendar for any other locales.
        // NOTE: The language, country and variant strings are interned.
        if (aLocale.getLanguage() == "th" && aLocale.getCountry() == "TH") {
            cal = new BuddhistCalendar(zone, aLocale);
        } else if (aLocale.getVariant() == "JP" && aLocale.getLanguage() == "ja"
                   && aLocale.getCountry() == "JP") {
            cal = new JapaneseImperialCalendar(zone, aLocale);
        } else {
            cal = new GregorianCalendar(zone, aLocale);
        }
    }
    return cal;
}

关于java - Calendar.getInstance()和GregorianCalendar.getInstance()之间的区别，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/25593768/