java 源码 设计模式案例 - Calendar类， 单例实现运用

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;
    }

    简单工厂模式(一个抽象接口, 不同的实现,再到工厂里面根据不同的参数,创建对应的对象)
    适配器模式

    枚举式单例

    public enum EnumSingleton {
        INSTANCE;


        public  static  EnumSingleton getInstance(){
            return INSTANCE;
        }
    }


    public class Runtime {
        private static final Runtime currentRuntime = new Runtime();

        private static Version version;

        /**
         * Returns the runtime object associated with the current Java application.
         * Most of the methods of class {@code Runtime} are instance
         * methods and must be invoked with respect to the current runtime object.
         *
         * @return  the {@code Runtime} object associated with the current
         *          Java application.
         */
        public static Runtime getRuntime() {
            return currentRuntime;
        }
    }