结构型设计模式之享元模式

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。

 1  using System;
 2     using System.Collections;
 3
 4     class FlyweightFactory
 5     {
 6         private ArrayList pool = new ArrayList();
 7
 8         // the flyweightfactory can crete all entries in the pool at startup
 9         // (if the pool is small, and it is likely all will be used), or as
10         // needed, if the pool si large and it is likely some will never be used
11         public FlyweightFactory()
12         {
13             pool.Add(new ConcreteEvenFlyweight());
14             pool.Add(new ConcreteUnevenFlyweight());
15         }
16
17         public Flyweight GetFlyweight(int key)
18         {
19             // here we would determine if the flyweight identified by key
20             // exists, and if so return it. If not, we would create it.
21             // As in this demo we have implementation all the possible
22             // flyweights we wish to use, we retrun the suitable one.
23             int i = key % 2;
24             return((Flyweight)pool[i]);
25         }
26     }
27
28     abstract class Flyweight
29     {
30         abstract public void DoOperation(int extrinsicState);
31     }
32
33     class UnsharedConcreteFlyweight : Flyweight
34     {
35         override public void DoOperation(int extrinsicState)
36         {
37
38         }
39     }
40
41     class ConcreteEvenFlyweight : Flyweight
42     {
43         override public void DoOperation(int extrinsicState)
44         {
45             Console.WriteLine("In ConcreteEvenFlyweight.DoOperation: {0}", extrinsicState);
46         }
47     }
48
49     class ConcreteUnevenFlyweight : Flyweight
50     {
51         override public void DoOperation(int extrinsicState)
52         {
53             Console.WriteLine("In ConcreteUnevenFlyweight.DoOperation: {0}", extrinsicState);
54         }
55     }
56
57     /// <summary>
58     ///    Summary description for Client.
59     /// </summary>
60     public class Client
61     {
62         public static int Main(string[] args)
63         {
64             int[] data = {1,2,3,4,5,6,7,8};
65
66             FlyweightFactory f = new FlyweightFactory();
67
68             int extrinsicState = 3;
69             foreach (int i in data)
70             {
71                 Flyweight flyweight = f.GetFlyweight(i);
72                   flyweight.DoOperation(extrinsicState);
73             }
74
75             return 0;
76         }
77     }

享元模式