简单工厂模式的本质是利用多态性，将实例化的过程交给工厂去完成，减少耦合度
实现加减乘除功能的计算器：
//操作类基类
public class Operation
{
public double NumberA { get; set; }
public double NumberB { get; set; }
public virtual double GetResult()
{
double result = 0;
return result;
}
}
//具体的操作类，实现各自的计算逻辑
public class OperationAdd : Operation
{
public override double GetResult()
{
return NumberA + NumberB;
}
}
public class OperationSub : Operation
{
public override double GetResult()
{
return NumberA - NumberB;
}
}
public class OperationMul : Operation
{
public override double GetResult()
{
return NumberA * NumberB;
}
}
public class OperationDiv : Operation
{
public override double GetResult()
{
if (NumberB==0)
{
throw new Exception("除数不能为0");
}
return NumberA / NumberB;
}
}
然后构造工厂类，根据客户端传入的参数，实例化不同的操作类，返回给调用者
public class OperationFactory
{
public static Operation CreateOperation(string operation)
{
Operation oper = null;
switch (operation)
{
case "+": oper = new OperationAdd();
break;
case "-": oper = new OperationSub();
break;
case "*": oper = new OperationMul();
break;
case "/": oper = new OperationDiv();
break;
default:
oper = new Operation();
break;
}
return oper;
}
}
客户端调用时，不需要认识所有的操作类，而只需要认识操作类的基类和工厂类即可：
//乘法
Operation operMutil = OperationFactory.CreateOperation("*");
operMutil .NumberA = 3;
operMutil .NumberB = 5;
double mutilResult = operMutil .GetResult();
//加法
Operation operAdd = OperationFactory.CreateOperation("+");
operAdd .NumberA = 3;
operAdd .NumberB = 5;
double addResult = operAdd .GetResult();
原文：http://www.cnblogs.com/angela217/p/5345649.html