简单工厂模式

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();