简单工厂模式：本着高内聚低耦合的原则，将系统的逻辑部分和功能分开
例如简易计算器的实现代码
1 using System; 2 using System.Collections.Generic; 3 using System.Text; 4 5 namespace Operation 6 { 7 /// <summary> 8 /// 运算类 9 /// </summary> 10 public class Operation 11 { 12 private double _numberA = 0; 13 private double _numberB = 0; 14 15 /// <summary> 16 /// 数字A 17 /// </summary> 18 public double NumberA 19 { 20 get 21 { 22 return _numberA; 23 } 24 set 25 { 26 _numberA = value; 27 } 28 } 29 30 /// <summary> 31 /// 数字B 32 /// </summary> 33 public double NumberB 34 { 35 get 36 { 37 return _numberB; 38 } 39 set 40 { 41 _numberB = value; 42 } 43 } 44 45 /// <summary> 46 /// 得到运算结果 47 /// </summary> 48 /// <returns></returns> 49 public virtual double getResult() 50 { 51 double result = 0; 52 return result; 53 } 54 55 56 } 57 58 /// <summary> 59 /// 加法类 60 /// </summary> 61 class OperationAdd : Operation 62 { 63 public override double getResult() 64 { 65 double result = 0; 66 result = NumberA + NumberB; 67 return result; 68 } 69 } 70 71 /// <summary> 72 /// 减法类 73 /// </summary> 74 class OperationSub : Operation 75 { 76 public override double getResult() 77 { 78 double result = 0; 79 result = NumberA - NumberB; 80 return result; 81 } 82 } 83 84 /// <summary> 85 /// 乘法类 86 /// </summary> 87 class OperationMul : Operation 88 { 89 public override double getResult() 90 { 91 double result = 0; 92 result = NumberA * NumberB; 93 return result; 94 } 95 } 96 97 /// <summary> 98 /// 除法类 99 /// </summary> 100 class OperationDiv : Operation 101 { 102 public override double getResult() 103 { 104 double result = 0; 105 if (NumberB==0) 106 throw new Exception("除数不能为0。"); 107 result = NumberA / NumberB; 108 return result; 109 } 110 } 111 112 /// <summary> 113 /// 平方类 114 /// </summary> 115 class OperationSqr : Operation 116 { 117 public override double getResult() 118 { 119 double result = 0; 120 result = NumberB * NumberB; 121 return result; 122 } 123 } 124 125 /// <summary> 126 /// 平方根类 127 /// </summary> 128 class OperationSqrt : Operation 129 { 130 public override double getResult() 131 { 132 double result = 0; 133 if (NumberB < 0) 134 throw new Exception("负数不能开平方根。"); 135 result = Math.Sqrt(NumberB); 136 return result; 137 } 138 } 139 140 /// <summary> 141 /// 相反数类 142 /// </summary> 143 class OperationReverse : Operation 144 { 145 public override double getResult() 146 { 147 double result = 0; 148 result = -NumberB; 149 return result; 150 } 151 } 152 153 /// <summary> 154 /// 运算类工厂 155 /// </summary> 156 class OperationFactory 157 { 158 public static Operation createOperate(string operate) 159 { 160 Operation oper = null; 161 switch (operate) 162 { 163 case "+": 164 { 165 oper = new OperationAdd(); 166 break; 167 } 168 case "-": 169 { 170 oper = new OperationSub(); 171 break; 172 } 173 case "*": 174 { 175 oper = new OperationMul(); 176 break; 177 } 178 case "/": 179 { 180 oper = new OperationDiv(); 181 break; 182 } 183 case "sqr": 184 { 185 oper = new OperationSqr(); 186 break; 187 } 188 case "sqrt": 189 { 190 oper = new OperationSqrt(); 191 break; 192 } 193 case "+/-": 194 { 195 oper = new OperationReverse(); 196 break; 197 } 198 } 199 200 return oper; 201 } 202 } 203 204 }
工厂方法模式：和工厂方法不同的地方是加入了“开放-封闭原则”（软件实体类、模块或者函数等等，应该可以扩展，但是不可以修改）规则，将简单工厂的内部判断逻辑移动到了客户端代码来进行，在扩展新功能的时候，简单工厂模式要修改工厂类，工厂方法模式是修改客户端。
计算器实现代码：
1 using System; 2 using System.Collections.Generic; 3 using System.Text; 4 5 namespace 工厂方法_计算器 6 { 7 8 /// <summary> 9 /// 运算类 10 /// </summary> 11 class Operation 12 { 13 private double _numberA = 0; 14 private double _numberB = 0; 15 16 public double NumberA 17 { 18 get { return _numberA; } 19 set { _numberA = value; } 20 } 21 22 public double NumberB 23 { 24 get { return _numberB; } 25 set { _numberB = value; } 26 } 27 28 /// <summary> 29 /// 得到运算结果 30 /// </summary> 31 /// <returns></returns> 32 public virtual double GetResult() 33 { 34 double result = 0; 35 return result; 36 } 37 } 38 39 /// <summary> 40 /// 加法类 41 /// </summary> 42 class OperationAdd : Operation 43 { 44 public override double GetResult() 45 { 46 double result = 0; 47 result = NumberA + NumberB; 48 return result; 49 } 50 } 51 52 /// <summary> 53 /// 减法类 54 /// </summary> 55 class OperationSub : Operation 56 { 57 public override double GetResult() 58 { 59 double result = 0; 60 result = NumberA - NumberB; 61 return result; 62 } 63 } 64 /// <summary> 65 /// 乘法类 66 /// </summary> 67 class OperationMul : Operation 68 { 69 public override double GetResult() 70 { 71 double result = 0; 72 result = NumberA * NumberB; 73 return result; 74 } 75 } 76 /// <summary> 77 /// 除法类 78 /// </summary> 79 class OperationDiv : Operation 80 { 81 public override double GetResult() 82 { 83 double result = 0; 84 if (NumberB == 0) 85 throw new Exception("除数不能为0。"); 86 result = NumberA / NumberB; 87 return result; 88 } 89 } 90 91 /// <summary> 92 /// 工厂方法 93 /// </summary> 94 interface IFactory 95 { 96 Operation CreateOperation(); 97 } 98 99 /// <summary> 100 /// 专门负责生产“+”的工厂 101 /// </summary> 102 class AddFactory : IFactory 103 { 104 public Operation CreateOperation() 105 { 106 return new OperationAdd(); 107 } 108 } 109 110 /// <summary> 111 /// 专门负责生产“-”的工厂 112 /// </summary> 113 class SubFactory : IFactory 114 { 115 public Operation CreateOperation() 116 { 117 return new OperationSub(); 118 } 119 } 120 121 /// <summary> 122 /// 专门负责生产“*”的工厂 123 /// </summary> 124 class MulFactory : IFactory 125 { 126 public Operation CreateOperation() 127 { 128 return new OperationMul(); 129 } 130 } 131 132 /// <summary> 133 /// 专门负责生产“/”的工厂 134 /// </summary> 135 class DivFactory : IFactory 136 { 137 public Operation CreateOperation() 138 { 139 return new OperationDiv(); 140 } 141 } 142 143 }
参考资料：程杰《大话设计模式》