Calendar中使用的设计模式

工厂方法

我主要是列出主要的代码，还是需要大家去查看源码

 public static Calendar getInstance()
    {
        return createCalendar(TimeZone.getDefault(), Locale.getDefault(Locale.Category.FORMAT));
    }

public static Calendar getInstance(TimeZone zone)
    {
        return createCalendar(zone, Locale.getDefault(Locale.Category.FORMAT));
    }

private static Calendar createCalendar(TimeZone zone,
                                           Locale aLocale)
 {
  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;
                }
            }
        }
}

建造者模式

处了上面我们可以根据工厂创建对象，它也给我买提供了建造者创建对象，也就是创建你想要的的Calendar

有很多set方法，你可以指定你要想的。

     public Builder setWeekDate(int weekYear, int weekOfYear, int dayOfWeek) {
            allocateFields();
            internalSet(WEEK_YEAR, weekYear);
            internalSet(WEEK_OF_YEAR, weekOfYear);
            internalSet(DAY_OF_WEEK, dayOfWeek);
            return this;
        }

 public Calendar build() {
            if (locale == null) {
                locale = Locale.getDefault();
            }
            if (zone == null) {
                zone = TimeZone.getDefault();
            }
            Calendar cal;
            if (type == null) {
                type = locale.getUnicodeLocaleType("ca");
            }
            if (type == null) {
                if (locale.getCountry() == "TH"
                    && locale.getLanguage() == "th") {
                    type = "buddhist";
                } else {
                    type = "gregory";
                }
            }
            switch (type) {
            case "gregory":
                cal = new GregorianCalendar(zone, locale, true);
                break;
            case "iso8601":
                GregorianCalendar gcal = new GregorianCalendar(zone, locale, true);
                // make gcal a proleptic Gregorian
                gcal.setGregorianChange(new Date(Long.MIN_VALUE));
                // and week definition to be compatible with ISO 8601
                setWeekDefinition(MONDAY, 4);
                cal = gcal;
                break;
            case "buddhist":
                cal = new BuddhistCalendar(zone, locale);
                cal.clear();
                break;
            case "japanese":
                cal = new JapaneseImperialCalendar(zone, locale, true);
                break;
            default:
                throw new IllegalArgumentException("unknown calendar type: " + type);
            }

        /**
         * Constructs a {@code Calendar.Builder}.
         */
        public Builder() {
        }

总结

当设计模式和源码结合起来看，你会发现新的。