简单工厂模式

class Operation {
    private double num1;
    private double num2;

    public double Num1
    {
        get
        {
            return num1;
        }

        set
        {
            num1 = value;
        }
    }
    public double Num2
    {
        set
        {
            num2=value;
        }
        get
        {            
            return num2;
        }
    }
    public virtual double GetResult()
    {
        double result = 0;
        return result;
    }
}
class OperationAdd : Operation
{
    public override double GetResult()
    {
        double result = 0;
        result = Num1 + Num2;
        return result;
    }
}
class OperationSub : Operation
{
    public override double GetResult()
    {
        double result = 0;
        result = Num1 - Num2;
        return result;
    }
}
class OperationMul : Operation
{
    public override double GetResult()
    {
        double result = 0;
        result = Num1 * Num2;
        return result;
    }
}
class OperationDiv : Operation
{
    public override double GetResult()
    {
        double result = 0;
        result = Num1 / Num2;
        return result;
    }
}
class OperationFactory
{
    public static Operation creatOperate( string operate)
    {
        Operation oper = null;
        switch (operate)
        {
            case "+":
                oper = new OperationAdd();
                break;
            case "-":
                oper = new OperationSub();
                break;
            case "*":
                oper = new OperationMul();
                break;
            case "/":
                oper = new OperationDiv();
                break;
        }
        return oper;
    }
}

　　

客户端代码：

Operation oper;
oper = OperationFactory.createOperate("+");
oper.Num1 = 1;
oper.Num2 = 2;
double result = oper.GetResult();