模式设计（一）Simple Factory（完整）

工厂模式专门负责将大量有共同接口的类实例化。工厂模式可以动态决定将哪一个类实例化，不必事先知道每次要实例化哪一个类。工厂模式有以下几种形态：
·       简单工厂（Simple Factory）模式
·       工厂方法（Factory Method）模式
·       抽象工厂（Abstract Factory）模式

    Simple Factory模式根据提供给它的数据，返回几个可能类中的一个类的实例。通常它返回的类都有一个公共的父类和公共的方法。

Simple Factory模式实际上不是GoF 23个设计模式中的一员。
下面我们来看看一个Simple Factory的例子:

以上为整个类结构的UML图。
工厂类角色Creator (PersonSimFactory)：工厂类在客户端的直接控制下（GetPerson方法）创建产品对象。

抽象产品角色Product (Person)：定义简单工厂创建的对象的父类或它们共同拥有的接口。可以是一个类、抽象类或接口（我们这里使用了类为例）当然你也可以把下面的Person类改为abstract类，把GetInfo()变为abstract函数来运行或者可以将Person变为Interface，将实现延迟到子类中也没有问题。

具体产品角色CreatedProduct (WritePerson, YellowPerson,BlackPerson)：定义工厂具体加工出的对象。

具体代码(C#)：

using  System;

namespace  SimFactory
{
    /**//// <summary>
    ///============== Program Description==============
    ///Name:SimFactory.cs
    ///Objective:SimFactory 
    ///Date:2006-02-09 
    ///Written By coffee.liu
    ///================================================
    /// </summary>
    public  class Person
    {
        protected string sex,race;
        public string GetSex(){
        return sex;
        }
        public string GetRace(){
        return race;
        }
        public virtual void GetInfo(){
        }
    }

    public class YellowPerson:Person
    {
        public YellowPerson()
        {
            sex="Man";
            race="Yellow";
        }
        public YellowPerson(string Ysex)
        {
           sex=Ysex;
           race="Yellow";
        }
        public override void GetInfo(){
          Console.WriteLine("the "+race+" Person Info:"+sex); 
        }
    }

    public class BlackPerson:Person
    {
        public BlackPerson()
        {
            sex="Man";
            race="Black";
        }
        public BlackPerson(string Bsex)
        {
            sex=Bsex;
            race="Black";
        }
        public override void GetInfo()
        {
            Console.WriteLine("the "+race+" Person Info:"+sex); 
        }
    }

    public class WritePerson:Person
    {
        public WritePerson()
        {
            sex="Man";
            race="Write";
        }
        public WritePerson(string Wsex)
        {
            sex=Wsex;
            race="Write";
        }
        public override void GetInfo()
        {
            Console.WriteLine("the "+race+" Person Info:"+sex); 
        }
    }
    public class PersonSimFactory{
        public PersonSimFactory(){}
        public Person GetPerson(string RaceType){
            if (RaceType=="Yellow")
               return new YellowPerson();
            else
            if (RaceType=="Black")
                return new BlackPerson();
            else
            if (RaceType=="Write")
                return new WritePerson();
            else
                return new YellowPerson();
            
        }
    }
}
/**/ ////////
///////
///////
using  System;

namespace  SimFactory
{
    /**//// <summary>
    ///============== Program Description==============
    ///Name:SimFactory.cs
    ///Objective:SimFactory 
    ///Date:2006-02-09 
    ///Written By coffee.liu
    ///================================================
    /// </summary>
    class Class1
    {
        /**//// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main(string[] args)
        {
            PersonSimFactory PSF=new PersonSimFactory();
            Person PP=PSF.GetPerson("Yellow");
            PP.GetInfo();
            Console.WriteLine(".");
            PP=PSF.GetPerson("Black");
            PP.GetInfo();
            Console.WriteLine(".");
             PP=PSF.GetPerson("Write");
            PP.GetInfo();
        }
    }
}

具体代码（Pascal）:

program SimFactory;
      //==============  Program Description ==============
     // Name:SimFactory.dpr
     // Objective:SimFactory
     // Date : 2006 - 04 - 23
     // Written By coffee.liu
     //================================================
{$APPTYPE CONSOLE}

uses
  SysUtils;
  type Person = Class protected class
       protected
        sex:string;
        race:string;
        public Function GetSex()function GetSex():string;
        public Function GetRace()function GetRace():string;
        public procedure GetInfo;virtual;abstract;

   end;
   type YellowPerson=Class (class(Person)
       constructor YellowPerson();
        public procedure GetInfo;override;
     end;
    type BlackPerson=Class (class(Person)
       constructor BlackPerson();
        public procedure GetInfo;override;
     end;
    type WritePerson=Class (class(Person)
       constructor WritePerson();
        public procedure GetInfo;override;
     end;
    type PersonSimFactory=Class constructorclass
        constructor PersonSimFactory();
        public Function GetPerson()function  GetPerson(RaceType:string):Person;
         end;
{ Person }

Function Person()function Person.GetRace: string;
begin
 result:=race;
end;

Function Person()function Person.GetSex: string;
begin
  result:=sex;
end;

{ YellowPerson }

constructor YellowPerson.YellowPerson;
begin
            sex:='Man';
            race:='Yellow';
end;
procedure YellowPerson.GetInfo;
   begin
    inherited;
      WriteLn('the '+race+' Person Info:'+sex);
   end;
{ WritePerson }

procedure WritePerson.GetInfo;
begin
  inherited;
     WriteLn('the '+race+' Person Info:'+sex);
end;

constructor WritePerson.WritePerson;
begin
            sex:='Man';
            race:='Write';
end;

{ BlackPerson }

constructor BlackPerson.BlackPerson;
begin
            sex:='Man';
            race:='Black';
end;

procedure BlackPerson.GetInfo;
begin
  inherited;
      WriteLn('the '+race+' Person Info:'+sex);
end;

{ PersonSimFactory }

Function PersonSimFactory()function PersonSimFactory.GetPerson(RaceType: string): Person;
begin

            if RaceType='Yellow' then
               result:=YellowPerson.YellowPerson
            else
            if RaceType='Black' then
                result:=BlackPerson.BlackPerson
            else
            if RaceType='Write' then
                 result:=WritePerson.WritePerson
            else
                 result:=YellowPerson.YellowPerson;

end;

constructor PersonSimFactory.PersonSimFactory;
begin
      inherited;
end;
var
PSF:PersonSimFactory;
PP:Person;
begin
   PSF:=PersonSimFactory.PersonSimFactory;
   PP:=PSF.GetPerson('Yellow');
   PP.GetInfo;
   WriteLn('..');
   PP:=PSF.GetPerson('Black');
   PP.GetInfo;
   WriteLn('..');
   PP:=PSF.GetPerson('Write');
   PP.GetInfo;
   WriteLn('..error.');
   PP:=PSF.GetPerson('Write11');
   PP.GetInfo;
end.

我们甚至可以将抽象产品类作为子类的工厂：


程序代码(C#)：
 

using  System;

namespace  SimFactoryPlus1
{
    /**//// <summary>
    ///============== Program Description==============
    ///Name:SimFactory.cs
    ///Objective:SimFactory 
    ///Date:2006-02-09 
    ///Written By coffee.liu
    ///================================================
    /// </summary>
    class Class1
    {
        /**//// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main(string[] args)
        {
            
            Person PP=Person.GetPerson("Yellow");
            PP.GetInfo();
            Console.WriteLine(".");
            PP=Person.GetPerson("Black");
            PP.GetInfo();
            Console.WriteLine(".");
            PP=Person.GetPerson("Write");
            PP.GetInfo();
        }
    }
    public  class Person
    {
        protected string sex,race;
        public string GetSex()
        {
            return sex;
        }
        public string GetRace()
        {
            return race;
        }
        public virtual void GetInfo()
        {
        }
        public static Person GetPerson(string RaceType)
        {
            if (RaceType=="Yellow")
                return new YellowPerson();
            else
                if (RaceType=="Black")
                return new BlackPerson();
            else
                if (RaceType=="Write")
                return new WritePerson();
            else
                return new YellowPerson();
            
        }
    }

    public class YellowPerson:Person
    {
        public YellowPerson()
        {
            sex="Man";
            race="Yellow";
        }
        public YellowPerson(string Ysex)
        {
            sex=Ysex;
            race="Yellow";
        }
        public override void GetInfo()
        {
            Console.WriteLine("the "+race+" Person Info:"+sex); 
        }
    }

    public class BlackPerson:Person
    {
        public BlackPerson()
        {
            sex="Man";
            race="Black";
        }
        public BlackPerson(string Bsex)
        {
            sex=Bsex;
            race="Black";
        }
        public override void GetInfo()
        {
            Console.WriteLine("the "+race+" Person Info:"+sex); 
        }
    }

    public class WritePerson:Person
    {
        public WritePerson()
        {
            sex="Man";
            race="Write";
        }
        public WritePerson(string Wsex)
        {
            sex=Wsex;
            race="Write";
        }
        public override void GetInfo()
        {
            Console.WriteLine("the "+race+" Person Info:"+sex); 
        }
    }

}

程序代码（Pascal）

program SimFactory;
      //==============  Program Description ==============
     // Name:SimFactory.dpr
     // Objective:SimFactory
     // Date : 2006 - 04 - 23
     // Written By coffee.liu
     //================================================
{$APPTYPE CONSOLE}

uses
  SysUtils;
  type Person = Class protected class
       protected
        sex:string;
        race:string;
        public Function GetSex()function GetSex():string;
        public Function GetRace()function GetRace():string;
        public procedure GetInfo;virtual;abstract;
        Class functionclass Function GetPerson()function  GetPerson(RaceType:string):Person;
   end;
   type YellowPerson=Class (class(Person)
       constructor YellowPerson();
        public procedure GetInfo;override;
     end;
    type BlackPerson=Class (class(Person)
       constructor BlackPerson();
        public procedure GetInfo;override;
     end;
    type WritePerson=Class (class(Person)
       constructor WritePerson();
        public procedure GetInfo;override;
     end;
{ Person }

Class functionclass Function Person()function Person.GetPerson(RaceType: string): Person;
begin
      if RaceType='Yellow' then
               result:=YellowPerson.YellowPerson
            else
            if RaceType='Black' then
                result:=BlackPerson.BlackPerson
            else
            if RaceType='Write' then
                 result:=WritePerson.WritePerson
            else
                 result:=YellowPerson.YellowPerson;
end;

Function Person()function Person.GetRace: string;
begin
 result:=race;
end;

Function Person()function Person.GetSex: string;
begin
  result:=sex;
end;

{ YellowPerson }

constructor YellowPerson.YellowPerson;
begin
            sex:='Man';
            race:='Yellow';
end;
procedure YellowPerson.GetInfo;
   begin
    inherited;
      WriteLn('the '+race+' Person Info:'+sex);
   end;
{ WritePerson }

procedure WritePerson.GetInfo;
begin
  inherited;
     WriteLn('the '+race+' Person Info:'+sex);
end;

constructor WritePerson.WritePerson;
begin
            sex:='Man';
            race:='Write';
end;

{ BlackPerson }

constructor BlackPerson.BlackPerson;
begin
            sex:='Man';
            race:='Black';
end;

procedure BlackPerson.GetInfo;
begin
  inherited;
      WriteLn('the '+race+' Person Info:'+sex);
end;

var
PP:Person;
begin

   PP:=Person.GetPerson('Yellow');
   PP.GetInfo;
   WriteLn('..');
   PP:=Person.GetPerson('Black');
   PP.GetInfo;
   WriteLn('..');
   PP:=Person.GetPerson('Write');
   PP.GetInfo;
   WriteLn('..error.');
   PP:=Person.GetPerson('Write11');
   PP.GetInfo;
end.

我们甚至可以将3种角色全部合并！

程序代码(C#)：

using  System;

namespace  SimFactoryPlus2
{
    /**//// <summary>
    ///============== Program Description==============
    ///Name:SimFactory.cs
    ///Objective:SimFactory 
    ///Date:2006-02-09 
    ///Written By coffee.liu
    ///================================================
    /// </summary>
    class Class1
    {
        /**//// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main(string[] args)
        {
            Person PP=Person.GetPerson("Yellow");
            PP.GetInfo();
            Console.WriteLine(".");
            PP=Person.GetPerson("Black");
            PP.GetInfo();
            Console.WriteLine(".");
            PP=Person.GetPerson("Write");
            PP.GetInfo();
        }
    }
    public  class Person
    {
        private class YellowPerson:Person
        {
            public YellowPerson()
            {
                sex="Man";
                race="Yellow";
            }
            public YellowPerson(string Ysex)
            {
                sex=Ysex;
                race="Yellow";
            }
            public override void GetInfo()
            {
                Console.WriteLine("the "+race+" Person Info:"+sex); 
            }
        }
        private class BlackPerson:Person
        {
            public BlackPerson()
            {
                sex="Man";
                race="Black";
            }
            public BlackPerson(string Bsex)
            {
                sex=Bsex;
                race="Black";
            }
            public override void GetInfo()
            {
                Console.WriteLine("the "+race+" Person Info:"+sex); 
            }
        }
        private class WritePerson:Person
        {
            public WritePerson()
            {
                sex="Man";
                race="Write";
            }
            public WritePerson(string Wsex)
            {
                sex=Wsex;
                race="Write";
            }
            public override void GetInfo()
            {
                Console.WriteLine("the "+race+" Person Info:"+sex); 
            }
        }

        protected string sex,race;
        public string GetSex()
        {
            return sex;
        }
        public string GetRace()
        {
            return race;
        }
        public virtual void GetInfo()
        {
        }
        public static Person GetPerson(string RaceType)
        {
            if (RaceType=="Yellow")
                return new YellowPerson();
            else
                if (RaceType=="Black")
                return new BlackPerson();
            else
                if (RaceType=="Write")
                return new WritePerson();
            else
                return new YellowPerson();
            
        }

    }
}

程序代码（Pascal）

program SimFactoryPlus2;
      //==============  Program Description ==============
     // Name:SimFactory.dpr
     // Objective:SimFactory
     // Date : 2006 - 04 - 23
     // Written By coffee.liu
     //================================================
{$APPTYPE CONSOLE}

uses
  SysUtils;
  type Person = Class protected class
       protected
        sex:string;
        race:string;
        constructor Create(Se:string;Ra:String);
        public Function GetSex()function GetSex():string;
        public Function GetRace()function GetRace():string;
        public procedure GetInfo;
        Class functionclass Function GetPerson()function  GetPerson(RaceType:string):Person;
   end;
{ Person }

constructor Person.Create(Se:string;Ra:String);
begin
  inherited create;
   sex:=Se;
   race:=Ra;
end;

procedure Person.GetInfo;
begin
WriteLn('the '+race+' Person Info:'+sex);
end;

Class functionclass Function Person()function Person.GetPerson(RaceType: string): Person;
begin
      if RaceType='Yellow' then
               result:=person.Create('Man','Yellow')
            else
            if RaceType='Black' then
                result:=person.Create('Man','Black')
            else
            if RaceType='Write' then
                 result:=person.Create('Man','Write')
            else
                 result:=person.Create('Man','Yellow');
end;

Function Person()function Person.GetRace: string;
begin
 result:=race;
end;

Function Person()function Person.GetSex: string;
begin
  result:=sex;
end;
var
PP:Person;
begin

   PP:=Person.GetPerson('Yellow');
   PP.GetInfo;
   WriteLn('..');
   PP:=Person.GetPerson('Black');
   PP.GetInfo;
   WriteLn('..');
   PP:=Person.GetPerson('Write');
   PP.GetInfo;
   WriteLn('..error.');
   PP:=Person.GetPerson('Write11');
   PP.GetInfo;
end.

注意上面Pascal代码由于功能上的限制其实已经退化。
小结：
简单工厂能返回具有相同方法的类的实例，他们可以是不同的派生子类的实例，也可以是实际上毫无关系仅仅是共享了相同借口的类。不管哪种形式，这些实例中的方法必须是相同的，并且能够交替使用。