设计模式 - 享元模式

• 简介
  运用共享技术有效的支持大量细粒度的对象

• 应用：当一个应用使用了大量的对象，而大量的这些对象造成了很大的存储开销的时候就应该使用，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，此时可以考虑使用享元模式。

• 代码

//享元类的接口或者超累
abstract class Flyweight
{
    public abstract void Operation(int extrinsicstate);
}
//具体的实现子类
class ConcreteFlyweight :Flyweight
{
    private string name ="";
    public ConcreteFlyweight(string name){
        this.name = name;
    }

    public override void Operation(int extrinsicstate)
    {
        Console.WriteLine("具体 Flyweight:"+extrinsicstate);
    }
}
//不共享的子类,不共享类的存在是因为有些数据是不需要共享的。
class UnsharedConcreteFlyweight :Flyweight
{
    public override void Operation(int extrinsicstate)
    {
        Console.WriteLine("不共享的具体 Flyweight:"+extrinsicstate);
    }
}
//享元工厂类，创建并管理 Flyweight 对象
class FlyweightFactory
{
    private Hashtable flyweights = new Hashtable();

    public Flyweight GetFlyweight(string key)
    {
        if(!flyweights.ContainsKey(key))
            flyweights.Add(key,new ConcreteFlyweight(key))
        }
        return (Flyweight)flyweights(key);
    }
}
//客户端调用
static void Main(string[] args){
    int num =  22;
    FlyweightFactory  f = new FlyweightFactory();
    Flyweight fx = f.GetFlyweight("X");
    fx.Operation(--num);
    Flyweight fy = f.GetFlyweight("Y");
    fy.Operation(--num);
    Flyweight uf = new UnsharedConcreteFlyweight();
    uf.Operation(--num);
    Console.Read();
}