策略模式

    /// <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();
        }
    }