设计模式のFactoryPattern（工厂模式）----创建模式

 public class Operation
    {
        private double _leftOP = 0;
        private double _rightOP = 0;

        public double LeftOP
        {
            get { return _leftOP; }
            set { _leftOP = value; }
        }

        public double RightOP
        {
            get { return _rightOP; }
            set { _rightOP = value; }
        }

        public virtual double GetResult()
        {
            double result=0;
            return result;
        }
    }

    public class OperationAdd : Operation   //加法计算  
    {
        public override double GetResult()
        {

            double result = 0;
            result = LeftOP + RightOP;
            return result;
        }
    }
    public class OperationSub : Operation    //减法计算  
    {
        public override double GetResult()
        {
            double result = 0;
            result = LeftOP - RightOP;
            return result;
        }
    }
    public class OperationMul : Operation     //乘法计算  
    {
        public override double GetResult()
        {
            double result = 0;
            result = LeftOP * RightOP;
            return result;
        }
    }
    public class OperationDiv : Operation    //除法计算  
    {
        public override double GetResult()
        {
            double result = 0;
            if (RightOP == 0)               //考虑除法的除数为0时没有意义  
                throw new Exception("除法不能为0");
            result = LeftOP / RightOP;
            return result;
        }
    }

    public class OperationFactory            //定义OperationFactory（运算符工厂）  
    {
        public static Operation createOperate(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;
        }
    }