简单工厂模式：就是店---很多糕点，你需要通过工厂来生成。目的是为了减少代码，先写一个父类，然后让子类继承这个父类，然后在写一个工厂类，根据switch来调用不同的子类。

测试的时候，直接调用工厂类即可。

直接上代码：

下面的算法是一个 计算器的实现：

  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4. using System.Text;
  5.  
  6. namespace DesignDemo
  7. {
  8.     class Operation2
  9.     {
  10.         private
    double _numberA;
  11.         private
    double _numberB;
  12.  
  13.         public
    double numberA
  14.         {
  15.             get {return _numberA;}
  16.             set { _numberA = value; }
  17.         }
  18.  
  19.         public
    double numberB
  20.         {
  21.             get { return _numberB; }
  22.             set { _numberB = value; }
  23.         }
  24.  
  25.         public
    virtual
    double GetResult()
  26.         {
  27.             double result = 0d;
  28.             return result;
  29.         }
  30.     }
  31.  
  32.     class OperationAdd : Operation2
  33.     {
  34.         public
    override
    double GetResult()
  35.         {
  36.             double result = 0;
  37.             result = numberA + numberB;
  38.             return result;
  39.         }
  40.     }
  41.  
  42.     class OperationSub : Operation2
  43.     {
  44.         public
    override
    double GetResult()
  45.         {
  46.             double result = 0;
  47.             result = numberA - numberB;
  48.             return result;
  49.         }
  50.     }
  51.  
  52.     class OperationMul : Operation2
  53.     {
  54.         public
    override
    double GetResult()
  55.         {
  56.             double result = 0;
  57.             result = numberA * numberB;
  58.             return result;
  59.         }
  60.     }
  61.  
  62.     class OperationDiv : Operation2
  63.     {
  64.         public
    override
    double GetResult()
  65.         {
  66.             double result = 0;
  67.             if (numberB == 0)
  68.             {
  69.                 throw
    new Exception("除数不能为0");
  70.             }
  71.             result = numberA / numberB;
  72.             return result;
  73.         }
  74.     }
  75.  
  76.  
  77.     /************************************************************************/
  78.     /* 建立简单工厂模式：减少耦合，把变化的东西封装成类 */
  79.     /************************************************************************/
  80.  
  81.     class OperationFactory
  82.     {
  83.         public
    static Operation2 createOperate(string operate)
  84.         {
  85.             Operation2 per = null;
  86.             switch (operate)
  87.             {
  88.                 case "+":
  89.                     per = new OperationAdd();
  90.                     break;
  91.                 case "-":
  92.                     per = new OperationSub();
  93.                     break;
  94.                 case "*":
  95.                     per = new OperationMul();
  96.                     break;
  97.                 case "/":
  98.                     per = new OperationDiv();
  99.                     break;
  100.             }
  101.             return per;
  102.         }
  103.     }
  104. }