3.Factory Method 工厂方法模式（创建型模式)

1.定义：

定义一个用于创建对象的接口，让子类决定实例化哪一个类。Factory Method使得一个类的实例化延迟到子类。

2.实现代码如下：

 /// <summary>
    /// 工厂方法
    /// </summary>
    public abstract class Factory
    {
        public abstract Compute GetCompute();
    }

    public class AddFactory : Factory
    {
        public override Compute GetCompute()
        {
            return new AddCompute();
        }
    }
    public class JianFaFactory : Factory
    {
        public override Compute GetCompute()
        {
            return new SubCompute();
        }
    }
    public class ChengFaFactory : Factory
    {
        public override Compute GetCompute()
        {
            return new ChengFaCompute();
        }
    }
    public class ChuFaFactory : Factory
    {
        public override Compute GetCompute()
        {
            return new ChuFaCompute();
        }
    }

    /// <summary>
    /// 计算类
    /// </summary>
    public abstract class Compute
    {
        protected int number1;

        public int Number1
        {
            get { return number1; }
            set { number1 = value; }
        }
        protected int number2;

        public int Number2
        {
            get { return number2; }
            set { number2 = value; }
        }

        public abstract int GetResult();

    }

    /// <summary>
    /// 加法
    /// </summary>
    public class AddCompute : Compute
    {
        public override int GetResult()
        {
            return number1 + number2;
        }
    }
    /// <summary>
    /// 减法
    /// </summary>
    public class SubCompute : Compute
    {
        public override int GetResult()
        {
            return number1 - number2;
        }
    }
    /// <summary>
    /// 乘法
    /// </summary>
    public class ChengFaCompute : Compute
    {
        public override int GetResult()
        {
            return number1 * number2;
        }
    }

    /// <summary>
    /// 除法
    /// </summary>
    public class ChuFaCompute : Compute
    {
        public override int GetResult()
        {
            return number1 / number2;
        }
    }    

 static void Main(string[] args)
        {
            int number1 = ;
            int number2 = ;

            Factory factory = null;
            string operate = "+";
            switch (operate)
            {
                case "+":
                   factory = new AddFactory();
                    break;
                case "-":
                     factory = new JianFaFactory();
                    break;
                case "*":
                     factory = new ChengFaFactory();
                    break;
                case "/":
                     factory = new ChuFaFactory();
                    break;
                default:
                    break;
            }
            Compute compute = factory.GetCompute();

            compute.Number1 = number1;
            compute.Number2 = number2;
            Console.WriteLine(compute.GetResult());
            Console.ReadKey();
        }

3.和简单工厂不同的地方是

(1)简单工厂是由switch直接创建具体的产品对象，而工厂方法是swith延迟创建具体的产品对象，先创建相应的工厂，在延迟创建具体的产品对象

(2)简单工厂只能创建一个工厂，工厂方法可以创建多个工厂

4.工厂方法的好处：

(1)用工厂方法在一个类的内部创建对象通常比直接创建对象更灵活。

(2)Factory Method模式通过面向对象的手法，将所要创建的具体对象的创建工作延迟到了子类，从而提供了一种扩展的策略，较好的解决了这种紧耦合的关系。