结构型设计模式之享元模式(Flyweight)

结构
意图	运用共享技术有效地支持大量细粒度的对象。
适用性	一个应用程序使用了大量的对象。 完全由于使用大量的对象，造成很大的存储开销。 对象的大多数状态都可变为外部状态。 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。 应用程序不依赖于对象标识。由于F l y w e i g h t 对象可以被共享，对于概念上明显有别的对象，标识测试将返回真值。

  using System;
     using System.Collections;

     class FlyweightFactory
     {
         private ArrayList pool = new ArrayList();

         // the flyweightfactory can crete all entries in the pool at startup
         // (if the pool is small, and it is likely all will be used), or as
         // needed, if the pool si large and it is likely some will never be used
         public FlyweightFactory()
         {
             pool.Add(new ConcreteEvenFlyweight());
             pool.Add(new ConcreteUnevenFlyweight());
         }

         public Flyweight GetFlyweight(int key)
         {
             // here we would determine if the flyweight identified by key
             // exists, and if so return it. If not, we would create it.
             // As in this demo we have implementation all the possible
             // flyweights we wish to use, we retrun the suitable one.
             int i = key % ;
             return((Flyweight)pool[i]);
         }
     }

     abstract class Flyweight
     {
         abstract public void DoOperation(int extrinsicState);
     }

     class UnsharedConcreteFlyweight : Flyweight
     {
         override public void DoOperation(int extrinsicState)
         {

         }
     }

     class ConcreteEvenFlyweight : Flyweight
     {
         override public void DoOperation(int extrinsicState)
         {
             Console.WriteLine("In ConcreteEvenFlyweight.DoOperation: {0}", extrinsicState);
         }
     }

     class ConcreteUnevenFlyweight : Flyweight
     {
         override public void DoOperation(int extrinsicState)
         {
             Console.WriteLine("In ConcreteUnevenFlyweight.DoOperation: {0}", extrinsicState);
         }
     }

     /// <summary>
     ///    Summary description for Client.
     /// </summary>
     public class Client
     {
         public static int Main(string[] args)
         {
             int[] data = {,,,,,,,};

             FlyweightFactory f = new FlyweightFactory();

             int extrinsicState = ;
             foreach (int i in data)
             {
                 Flyweight flyweight = f.GetFlyweight(i);
                   flyweight.DoOperation(extrinsicState);
             }

             return ;
         }
     }

享元模式