一句话总结

共享对象

内容

本质是通过缓存来达到对象的共享,从而降低内存的消耗。类似于线程池,主要解决同一个对象频繁的创建和销毁。

场景

房源共享等

类图

代码示例

// 抽象享元角色
public interface IFlyweight {
    void operation(String extrinsicState);
}
// 具体享元角色
public class ConcreteFlyweight implements IFlyweight {
    private String intrinsicState;
    public ConcreteFlyweight(String intrinsicState) {
        this.intrinsicState = intrinsicState;
    }
    public void operation(String extrinsicState) {
        System.out.println("Object address: " + System.identityHashCode(this));
        System.out.println("IntrinsicState: " + this.intrinsicState);
        System.out.println("ExtrinsicState: " + extrinsicState);
    }
}
// 享元工厂
public class FlyweightFactory {
    private static Map<String, IFlyweight> pool = new HashMap<String, IFlyweight>();
    // 因为内部状态具备不变性，因此作为缓存的键
    public static IFlyweight getFlyweight(String intrinsicState) {
        if (!pool.containsKey(intrinsicState)) {
            IFlyweight flyweight = new ConcreteFlyweight(intrinsicState);
            pool.put(intrinsicState, flyweight);
        }
        return pool.get(intrinsicState);
    }
}
public class Test {
    public static void main(String[] args) {
        IFlyweight flyweight1 = FlyweightFactory.getFlyweight("aa");
        IFlyweight flyweight2 = FlyweightFactory.getFlyweight("bb");
        flyweight1.operation("a");
        flyweight2.operation("b");
    }
}

在源码时的应用

Integer类中

    public static Integer valueOf(int i) {
        if (i >= IntegerCache.low && i <= IntegerCache.high)
            return IntegerCache.cache[i + (-IntegerCache.low)];
        return new Integer(i);
    }