Java设计模式之享元模式

享元模式（Flyweight）：运用共享技术有效地支持大量细粒度对象。

所有具体享元类的超类，接受并作用于外部状态：

public abstract class FlyWeight {//所有具体享元类的超类，接受并作用于外部状态    public abstract void operation(int extrinsicState);}class ConcreteFlyWeight extends FlyWeight {    @Override    public void operation(int extrinsicState) {        System.out.println("具体FlyWeight：" + extrinsicState);    }}class UnsharedConcreteFlyWeight extends FlyWeight {    @Override    public void operation(int extrinsicState) {        System.out.println("不共享的具体FlyWeight：" + extrinsicState);    }}

享元工厂：

public class FlyWeightFactory {//享元工厂    private HashMap<String, FlyWeight> flyWeights = new HashMap<String, FlyWeight>();    public FlyWeight getFlyWeight(String key) {        if (!flyWeights.containsKey(key)) {            flyWeights.put(key, new ConcreteFlyWeight());        }        return flyWeights.get(key);    }}

客户端：

public class FlyWeightClient {//客户端    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");        fy.operation(--extrinsicState);        FlyWeight fz = f.getFlyWeight("Z");        fz.operation(--extrinsicState);        FlyWeight uf = new UnsharedConcreteFlyWeight();        uf.operation(--extrinsicState);    }}

运行结果：

具体FlyWeight：21具体FlyWeight：20具体FlyWeight：19不共享的具体FlyWeight：18

享元模式的应用场景：

如果一个应用程序使用了大量的对象，而大量的这些对象造成了很大的存储开销时就应该考虑使用；还有就是对象的大多数状态可以外部状态，如果删除对象的外部状态，那么可以用相对较少的共享对象取代很多组对象时，可以考虑使用享元模式。