简单工厂模式学习

   在设计模式中,用到最多的就是工厂模式了,工厂模式又分为:简单工厂模式、抽象工厂模式、工厂方法模式，而在工厂中，我用到最多就是简单工厂模式，简单工厂模式的优点在我看来就是：

   扩展性比较好，因为各具体实现类都继承自父类，如果再增加一个类似操作方法类，那就让此类再次继承自父类，在工厂类中添加一个判断就行了，而不用修改原来的实现类。

   其它的还未体会到，先贴一段具体代表性的代码吧，从《大话设计模式》中摘抄。

class Program    {        static void Main(string[] args)        {            Operation m_Operation = OperationFactory.createOperation("+");            m_Operation.NumberA = 10;            m_Operation.NumberB = 8;            Console.Write("结果是：{0}",m_Operation.GetResult().ToString());            Console.Read();        }    }    /// <summary>    /// 操作基类    /// </summary>    public class Operation    {        private double m_NumberA = 0;        public double NumberA        {            get { return m_NumberA; }            set { m_NumberA = value; }        }        private double m_NumberB = 0;        public double NumberB        {            get { return m_NumberB; }            set { m_NumberB = value; }        }        public virtual double GetResult()        {            double result = 0;            return result;        }    }    /// <summary>    /// 加法类    /// </summary>    class OperationAdd : Operation    {        public override double GetResult()        {            double result = 0;            result = this.NumberA + this.NumberB;            return result;        }    }    /// <summary>    /// 减法    /// </summary>    class OperationSub : Operation    {        public override double GetResult()        {            double result = 0;            result = this.NumberA - this.NumberB;            return result;        }    }    /// <summary>    /// 乘法    /// </summary>    class OperationMul : Operation    {        public override double GetResult()        {            double result = 0;            result = this.NumberA * this.NumberB;            return result;        }    }    /// <summary>    /// 除法    /// </summary>    class OperationDiv : Operation    {        public override double GetResult()        {            double result = 0;            if (NumberB == 0)            {                throw new Exception("除数不能为0！");            }            result = this.NumberA / this.NumberB;            return result;        }    }    public class OperationFactory    {        public static Operation createOperation(string p_Operation)        {            Operation m_Operation = null;            switch (p_Operation)            {                case "+":                    m_Operation = new OperationAdd();                    break;                case "-":                    m_Operation = new OperationSub();                    break;                case "*":                    m_Operation = new OperationMul();                    break;                case "/":                    m_Operation = new OperationDiv();                    break;            }            return m_Operation;        }    }