通俗易懂的java设计模式之享元模式

这种模式没有什么好说的，只作为一个记录。代码如下：

public class Flyweight {
    public static void main(String[] args) {
        IFlyweight flyweight1 = FlyweightFactory.getFlyweight("aa");
        IFlyweight flyweight2 = FlyweightFactory.getFlyweight("bb");
        flyweight1.operation("a");
        flyweight2.operation("b");
    }
}
// 抽象享元角色
interface IFlyweight {
    void operation(String extrinsicState);
}
// 具体享元角色
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
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);
    }
}

优点： 大大减少对象的创建，降低系统的内存，使效率提高。

缺点： 提高了系统的复杂度，需要分离出外部状态和内部状态，而且外部状态具有固有化的性质，不应该随着内部状态的变化而变化，否则会造成系统的混乱。

使用场景：  1、系统有大量相似对象。 2、需要缓冲池的场景。