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前面讲到的简单工厂如下面这段代码，后续需要拓展功能时，需要在简单工厂里面添加 case ，这依旧违反了开放-封闭中的对修改关闭的原则。

// 工厂生成对象类public class OperationFactory{    public static OperationClass GetOperation(string operationType)    {        OperationClass opera = null;        switch (operationType)        {            case "+":                opera = new AddOperation();                break;            case "-":                opera = new SubOperation();                break;            case "*":                opera = new MulOperation();                break;            case "/":                opera = new DivOperation();                break;            case "sqrt":                opera = new SqrtOperation();                break;            case "squa":                opera = new SquareOperation();                break;            default:                 break;        }        return opera;    }}

一、将一个雷锋的简单工厂修改成工厂模式

1. 简单工厂实现代码

public class LeiFeng{    public void Sweep()    {        Console.WriteLine("扫地");    }    public void Wash()    {        Console.WriteLine("洗衣");    }    public void BuyRice()    {        Console.WriteLine("买米");    }}public class Undergraduate : LeiFeng { }public class Volunteer : LeiFeng { }public class SimpleFactory{    public static LeiFeng CreateLeiFeng(string type)    {        LeiFeng result = null;        switch (type)        {            case "big student":                result = new Undergraduate();                break;            case "volunteer":                result = new Volunteer();                break;            default:                break;        }        return result;    }}LeiFeng studentA = SimpleFactory.CreateLeiFeng("big student");studentA.Sweep();LeiFeng studentB = SimpleFactory.CreateLeiFeng("big student");studentB.Wash();LeiFeng studentC = SimpleFactory.CreateLeiFeng("big student");studentC.BuyRice();

2. 工厂模式实现代码

结构是这样的

public interface IFactory{    LeiFeng CreateLeiFeng();}public class UndergraduateFactory : IFactory{    public LeiFeng CreateLeiFeng()    {        return new Undergraduate();       }}public class VolunteerFactory : IFactory{    public LeiFeng CreateLeiFeng()    {        return new Volunteer();    }}    IFactory factory = new UndergraduateFactory();LeiFeng lf = factory.CreateLeiFeng();lf.Sweep();lf.Wash();lf.BuyRice();

后面要改只需要改第一行：IFactory factory = new UndergraduateFactory();

3. 你可能会说，那工厂其实没什么作用，直接一句不就可以了：

LeiFeng lf = new Undergraduate();

结构如下

这不够规范，而且工厂模式可以结合单例模式。