设计模式-工厂方法模式

public interface IYunSuan
    {
        double getResult(int num1, int num2);        
    }
    public class jia : IYunSuan
    {
        public double getResult(int num1, int num2)
        {
            return num1 + num2;
        }
    }
    public class jian : IYunSuan
    {
        public double getResult(int num1, int num2)
        {
            return num1-num2;
        }
    }
    public class cheng : IYunSuan
    {
        public double getResult(int num1, int num2)
        {
            return num1*num2;
        }
    }
    public class chu : IYunSuan
    {
        public double getResult(int num1, int num2)
        {
            if (num2 == 0) return 0;
            return num1/num2;
        }
    }

    //////////////
     //简单工厂，专门生产对象
        public static IYunSuan createYunSuanObj(string type)
        {
            switch (type)
            {
                case "+":return new jia();
                case "-": return new jian();
                case "*": return new cheng();
                case "/": return new chu();
            }
            return null;
        }
    //工厂方法模式,把简单工厂分解
    public interface IFactory
    {
        IYunSuan createYunSuanObj();
    }
    public class jiaFactory : IFactory
    {
        public IYunSuan createYunSuanObj()
        {
            return new jia();
        }
    }
    public class jianFactory : IFactory
    {
        public IYunSuan createYunSuanObj()
        {
            return new jian();
        }
    }
    public class chengFactory : IFactory
    {
        public IYunSuan createYunSuanObj()
        {
            return new cheng();
        }
    }
    public class chuFactory : IFactory
    {
        public IYunSuan createYunSuanObj()
        {
            return new chu();
        }
    }

        前端：
        static void Main(string[] args)
        {
            //简单工厂模式
            //var jia=simpleFactory.createYunSuanObj("+");
            //var result=jia.getResult(1,2);
            //Console.WriteLine(result);
            //Console.ReadLine();
                        //工厂方法模式
            IFactory factory = new jiaFactory();
            var jia=factory.createYunSuanObj();
            var result=jia.getResult(1, 2);
            Console.WriteLine(result);
            Console.ReadLine();
        }

总结：定义一个创建对象的接口，让子类决定实例化哪个类，工厂模式使得一个类的实例化延迟到其子类。是基于简单工厂的扩展模式，解耦了简单工厂的工厂类，符合了几大原则
优点：解耦
缺点：代码量增加N多，让人蛋疼。