設計模式：結構型 - 享元模式

享元模式：運用共享技術有效地支持大量細粒度的對象

如果一個應用程序使用了大量的對象，而大量的這些對象造成了很大的存儲開銷時就應該考慮使用；還有對象的大多數狀態可以外部狀態，如果刪除對象的外部狀態，那麼可以用相對較少的共享對象取代很多組對象。

 

UML：

 

JAVA：

public class FlyWeightTest {
    public static void main(String[] args) {
        int extrinsicstate = 22;
        FlyweightFactory f = new FlyweightFactory();
        Flyweight fx = f.getFlyweight("X");
        fx.operation(--extrinsicstate);

        Flyweight fy = f.getFlyweight("Y");
        fx.operation(--extrinsicstate);

        UnsharedConcreteFlyweight uf = new UnsharedConcreteFlyweight();
        uf.operation(--extrinsicstate);
    }
}

class FlyweightFactory{
    private Hashtable flyweights = new Hashtable();

    public FlyweightFactory(){
        flyweights.put("X",new ConcreteFlyweight());
        flyweights.put("Y",new ConcreteFlyweight());
        flyweights.put("Z",new ConcreteFlyweight());
    }

    public Flyweight getFlyweight(String key){
        return (Flyweight) flyweights.get(key);
    }
}

abstract class Flyweight{
    public abstract void operation(int extrinsicstate);
}
class ConcreteFlyweight extends Flyweight{
    @Override
    public void operation(int extrinsicstate) {
        System.out.println("具體實現Flyweight:"+extrinsicstate);
    }
}

//不需要共享的子類
class UnsharedConcreteFlyweight extends Flyweight{
    @Override
    public void operation(int extrinsicstate) {
        System.out.println("不共享的 具體實現Flyweight:"+extrinsicstate);
    }
}