享元模式

      享元模式（Flyweight）：运用共享技术有效地支持大量细粒度的对象。享元模式分为内部模式（不会随着环境改变而改变共享内容，下例）和外部模式（会随着环境改变而改变共享内容）。

类图：

代码：

publicabstractclass Flyweight {

    publicabstractvoid operation();

}

publicclass ConcreteFlyweightAextends Flyweight {

    @Override

    publicvoid operation() {

       System.out.println("共享的类型A操作");

    }

}

publicclass ConcreteFlyweightBextends Flyweight{

    @Override

    publicvoid operation() {

       System.out.println("共享的类型B操作");

    }

}

publicclass UnshareConcreteFlyweightextends Flyweight{

    @Override

    publicvoid operation() {

       System.out.println("不共享的类型操作");

    }

}

publicclass FlyweightFactory {

    private Map<String, Flyweight>flyweights=new HashMap<String, Flyweight>();

    public FlyweightFactory(){

       flyweights.put("A",new ConcreteFlyweightA());

       flyweights.put("B",new ConcreteFlyweightB());

    }

    public Flyweight getFlyweight(String key){

       returnflyweights.get(key);

    }

}

publicstaticvoid main(String[] args) {

       FlyweightFactory ff=new FlyweightFactory();

       ff.getFlyweight("B").operation();

       ff.getFlyweight("A").operation();

       ff.getFlyweight("A").operation();

    }

优点：可以减少对象的数量，节约内存。

缺点：只适合处理粒度小的对象。

      享元模式看上去像是对对象的个数限制，本人认为享元模式和创造型的工厂，单例比较相似。