学步园

假想场景：hp和apple是全球知名的电脑生产厂家，他们各自的电脑操作系统分别是windows和macintosh，microsoft是软件行业的龙头。为了吸引更多客户购买电脑，hp和apple请ms为他们开发两款最常用的软件，办公软件和及时通讯工具。ms结了订单后，分别为hp和apple开发了office和msn。

上面的场景其实蕴含着我们常见的设计模式思维方式，code is cheap，代码来了。

一：简单工厂

using System;<br /> //ms的产品<br /> public class Software<br /> {<br /> private string softwareName;</p> <p> public virtual string SoftwareName<br /> {<br /> get { return softwareName; }<br /> set { softwareName = value; }<br /> }<br /> public string GetSoftwareName()<br /> {<br /> return softwareName;<br /> }<br /> }<br /> //ms的产品：office<br /> public class Office:Software<br /> {<br /> public override string GetSoftwareName()<br /> {<br /> this.SoftwareName = "Office";<br /> return “Office”;<br /> }<br /> }<br /> //ms的产品：msn<br /> public class Msn : Software<br /> {<br /> public override string GetSoftwareName()<br /> {<br /> this.SoftwareName = "Msn";<br /> return “Msn”;<br /> }<br /> }<br /> /// <summary><br /> /// 简单工厂<br /> /// </summary><br /> public class MsSoftwareFactory<br /> {<br /> public static Software CreateSoftware(string softwareName)<br /> {<br /> Software msSoftware = null;<br /> switch (softwareName)<br /> {<br /> default:<br /> break;<br /> case "office":<br /> msSoftware = new Office();<br /> break;<br /> case "msn":<br /> msSoftware = new Msn();<br /> break;<br /> }<br /> return msSoftware;<br /> }<br /> }</p> <p>/// <summary><br /> /// 客户端调用<br /> /// </summary><br /> public class Client {<br /> static void Main(string[] args)<br /> {<br /> Software msSoftware = MsSoftwareFactory.CreateSoftware("office");<br /> Console.WriteLine(msSoftware.GetSoftwareName());<br /> }<br /> }

上面的简单工厂在一个方法体中有个switch...case，违背了“对扩展开放，对修改封闭”的原则，即“开放-封闭原则”。下面的工厂方法就克服了简单工厂的缺点，降低了客户端程序和产品对象的耦合。

二：工厂方法
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。工厂方法使一个类的实例化延迟到其子类。
using System;<br /> //ms的产品<br /> public class Software<br /> {<br /> private string softwareName;</p> <p> public string SoftwareName<br /> {<br /> get { return softwareName; }<br /> set { softwareName = value; }<br /> }<br /> public virtual string GetSoftwareName()<br /> {<br /> return softwareName;<br /> }<br /> }<br /> //ms的产品：office<br /> public class Office:Software<br /> {<br /> public override string GetSoftwareName()<br /> {<br /> this.SoftwareName = "Office";<br /> return "Office";<br /> }<br /> }<br /> //ms的产品：msn<br /> public class Msn : Software<br /> {<br /> public override string GetSoftwareName()<br /> {<br /> this.SoftwareName = "Msn";<br /> return "Msn";<br /> }<br /> }</p> <p>interface ISoftwareFactory<br /> {<br /> Software CreateSoftware();<br /> }</p> <p>/// <summary><br /> /// office工厂<br /> /// </summary><br /> public class OfficeFactory:ISoftwareFactory<br /> {<br /> public Software CreateSoftware()<br /> {<br /> return new Office();<br /> }<br /> }</p> <p>/// <summary><br /> /// msn工厂<br /> /// </summary><br /> public class MsnFactory : ISoftwareFactory<br /> {<br /> public Software CreateSoftware()<br /> {<br /> return new Msn();<br /> }<br /> }</p> <p>/// <summary><br /> /// 客户端调用<br /> /// </summary><br /> public class Client {<br /> static void Main(string[] args)<br /> {<br /> ISoftwareFactory factory = new OfficeFactory();<br /> Software msSoftware = factory.CreateSoftware();<br /> Console.WriteLine(msSoftware.GetSoftwareName());<br /> }<br /> }

工厂方法的缺点是每加一个产品，就要创建一个对应的产品工厂类，增加了额外的开发量。

三、抽象工厂

提供一个创建一系列相关或者相互依赖对象的接口，而无需指定它们具体的类。
抽象工厂最经典的应用莫过于数据库访问程序。网上有很多这方面的讨论。不多说了。这里我继续用开篇讲的场景来描述。
我们知道office和msn根据操作系统的不同可以分为windows版本的和mac版本的，也许还有linux，unix版本的，归根结底，这里的产品涉及到产品系列的问题，抽象工厂可以解决这个问题：
using System;</p> <p>//ms的产品：office<br /> public class Office<br /> {<br /> private string softwareName;</p> <p> public string SoftwareName<br /> {<br /> get { return softwareName; }<br /> set { softwareName = value; }<br /> }<br /> }</p> <p>public interface IOffice<br /> {<br /> Office GetOffice();<br /> }</p> <p>//ms的windows版本Office<br /> public class WinOffice : IOffice<br /> {<br /> public Office GetOffice()<br /> {<br /> return new Office();<br /> }<br /> }</p> <p>//ms的macintosh版本Office<br /> public class MacOffice : IOffice<br /> {<br /> public Office GetOffice()<br /> {<br /> return new Office();<br /> }<br /> }</p> <p>//ms的产品：msn<br /> public class Msn<br /> {<br /> private string softwareName;</p> <p> public string SoftwareName<br /> {<br /> get { return softwareName; }<br /> set { softwareName = value; }<br /> }<br /> }</p> <p>public interface IMsn<br /> {<br /> Msn GetMsn();<br /> }</p> <p>//ms的windows版本msn<br /> public class WinMsn:IMsn<br /> {<br /> public Msn GetMsn()<br /> {<br /> return new Msn();<br /> }<br /> }</p> <p>//ms的macintosh版本msn<br /> public class MacMsn : IMsn<br /> {<br /> public Msn GetMsn()<br /> {<br /> return new Msn();<br /> }<br /> }</p> <p>interface ISoftwareFactory<br /> {<br /> IOffice CreateOffice();<br /> IMsn CreateMsn();<br /> }</p> <p>/// <summary><br /> /// windows版本的工厂<br /> /// </summary><br /> public class WindowsFactory:ISoftwareFactory<br /> {<br /> public IOffice CreateOffice()<br /> {<br /> return new WinOffice();<br /> }<br /> public IMsn CreateMsn()<br /> {<br /> return new WinMsn();<br /> }<br /> }</p> <p>/// <summary><br /> /// macintosh版本的工厂<br /> /// </summary><br /> public class MacFactory : ISoftwareFactory<br /> {<br /> public IOffice CreateOffice()<br /> {<br /> return new MacOffice();<br /> }<br /> public IMsn CreateMsn()<br /> {<br /> return new MacMsn();<br /> }<br /> }</p> <p>/// <summary><br /> /// 客户端调用<br /> /// </summary><br /> public class Client {<br /> static void Main(string[] args)<br /> {<br /> ISoftwareFactory factory = new WindowsFactory();<br /> IOffice office = factory.CreateOffice();<br /> IMsn msn = factory.CreateMsn();<br /> }<br /> }