工厂方法模式

简单工厂模式有一个缺点，就是增加子类的时候，需要修改工厂类里的switch。工厂方法模式可以优化简单工厂模式的这个缺点。

UML图：

示例代码：

    public interface ICar
    {
        string GuaDang();
    } 

    public class ShouDong:ICar
    {
        public string GuaDang()
        {
            return "我是手动挡";
        }
    }

    public class ZiDong:ICar
    {
        public string GuaDang()
        {
            return "我是自动挡";
        }
    }

    public interface ICarFactory
    {
        ICar GetCar();
    }

    class ShouDongFactory:ICarFactory
    {
        public ICar GetCar()
        {
            return new ShouDong();
        }
    }

    public class ZiDongFactory:ICarFactory
    {
        public ICar GetCar()
        {
            return new ZiDong();
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            ICarFactory fac = new ShouDongFactory();
            Console.WriteLine(fac.GetCar().GuaDang());

            ICarFactory facA = new ZiDongFactory();
            Console.WriteLine(facA.GetCar().GuaDang());
        }
    }