/// <summary>    /// 操作基类    /// </summary>    public class Operation    {        private double _numberA = 0;        private double _numberB = 0;        public double NumberA        {            get { return _numberA; }            set { _numberA = value; }        }        public double NumberB        {            get { return _numberB; }            set { _numberB = value; }        }        public virtual double GetResult()        {            return 0;        }    }    /// <summary>    /// 具体操作类    /// </summary>    public class OperationAdd : Operation    {        public override double GetResult()        {            double result = 0;            result = NumberA + NumberB;            return result;        }    }    public class OperationSub : Operation    {        public override double GetResult()        {            double result = 0;            result = NumberA - NumberB;            return result;        }    }    /// <summary>    /// 工厂根据需求生产某一类型的事物    /// </summary>    public class Student    {        private Operation func = null;        public void ApplyOperation(string operate)        {            switch(operate)            {                case "+":                    this.func = new OperationAdd();                    break;                case "-":                    this.func = new OperationSub();;                    break;            }        }        public double GetResult(double numberA, double numberB)        {            func.NumberA = numberA;            func.NumberB = numberB;            return func.GetResult();        }    }    class Program    {        static void Main(string[] args)        {            var XiaoMing = new Student();            XiaoMing.ApplyOperation("+");            var add_result = XiaoMing.GetResult(1, 2);            Console.WriteLine("result is:" + add_result);            XiaoMing.ApplyOperation("-");            var sub_result = XiaoMing.GetResult(7, 2);            Console.WriteLine("result is:" + sub_result);            Console.Read();        }    }