享元模式（Flyweight），运用共享技术有效地支持大量细粒度的对象。[DP]

解决对象的开销问题，像围棋，一盘棋理论上有361个空位可以放棋子，那如果用常规的面向对象方式编程，每盘棋都可能有两三百个棋子对象产生，一台服务器就很难支持更多的玩家玩围棋游戏了，毕竟内存空间还是有限的。如果用了享元模式来处理棋子，那么棋子对象可以减少到只有两个实例。

 

import java.util.HashMap;
import java.util.Map;

// 享元接口
interface Flyweight {
    void operation(String extrinsicState);
}

// 具体享元类
class ConcreteFlyweight implements Flyweight {
    private String intrinsicState;

    public ConcreteFlyweight(String state) {
        this.intrinsicState = state;
    }

    @Override
    public void operation(String extrinsicState) {
        System.out.println("Intrinsic state: " + intrinsicState + ", Extrinsic state: " + extrinsicState);
    }
}

// 享元工厂类
class FlyweightFactory {
    private Map<String, Flyweight> flyweightPool = new HashMap<>();

    public Flyweight getFlyweight(String state) {
        Flyweight flyweight = flyweightPool.get(state);
        if (flyweight == null) {
            flyweight = new ConcreteFlyweight(state);
            flyweightPool.put(state, flyweight);
        }
        return flyweight;
    }
}

// 客户端代码
public class Client {
    public static void main(String[] args) {
        FlyweightFactory factory = new FlyweightFactory();

        Flyweight flyweight1 = factory.getFlyweight("state1");
        Flyweight flyweight2 = factory.getFlyweight("state2");
        Flyweight flyweight3 = factory.getFlyweight("state1");

        flyweight1.operation("extrinsicStateA");
        flyweight2.operation("extrinsicStateB");
        flyweight3.operation("extrinsicStateA");

        // 输出将显示flyweight1和flyweight3是同一个对象，因为它们共享相同的内在状态"state1"
    }
}