工厂方法(Factory Method)模式，又称虚构造子(Virtual Constructor)模式或多态工厂模式。工厂模式定义创建对象的借口，并由派生类决定哪一个类来创建对象。也就是说，工厂方法将创建对象的责任委托给派生类。这是因为基类并不知道要创建的对象是哪一个类的实例，所以将创建对象的责任委托给派生类，或者将实际创建工作延迟到派生类中完成。
TCPU = class(TObject)
end;
end;
end;
public
//将对象的创建转移到派生类
function CreateCPU: TCPU; virtual; abstract;
end;
public
function CreateCPU; TCPU; override;
end;
public
function CreateCPU: TCPU; override
end;
end;
TAMDCPU
= class(TCPU)end;
TIntelCPU
= class(TCPU)end;
TCPUFactory
= class(TObject)public
//将对象的创建转移到派生类
function CreateCPU: TCPU; virtual; abstract;
end;
TAMDCPUFactory
= class(TCPUFactory)public
function CreateCPU; TCPU; override;
end;
TIntelCPUFactory
= class(TCPUFactory)public
function CreateCPU: TCPU; override
end;
看一下具体的实现
function TAMDCPUFactory.CreateCPU: TCPU;
begin
Result := TAMDCPU.Create;
end;
begin
Result := TAMDCPU.Create;
end;
再来看客户端，在未使用工厂方法前
TComputer = class(TObject)
private
FAMDCPU: TAMDCPU;
public
end;
private
FAMDCPU: TAMDCPU;
public
end;
FAMDCPU :
= TAMDCPU.Create;
使用工厂方法以后
TComputer = class(TObject)
private
FAMDCPU: TCPU;
AMDCPUFactory; TFactory;
public
end;
private
FAMDCPU: TCPU;
AMDCPUFactory; TFactory;
public
end;
FAMDCPU :
= AMDCPUFactory.CreateCPU;
这个时候，TComputer类中的FAMDCPU声明为了一个TCPU而不是具体的CPU.
再来看参数化工厂
TCPUFactory = class(TObject)
public
function CreateCPU(CPUType: TCPUType): TCPU;
end; function TCPUFactory.CreateCPU(CPUType: TCPUType): TCPU;
begin
case CPUType of
tpAMD: Result := TAMDCPU.Create;
tpIntel: Result := TIntelCPU.Create;
end;
end;
public
function CreateCPU(CPUType: TCPUType): TCPU;
end; function TCPUFactory.CreateCPU(CPUType: TCPUType): TCPU;
begin
case CPUType of
tpAMD: Result := TAMDCPU.Create;
tpIntel: Result := TIntelCPU.Create;
end;
end;
参数化工厂把不同对象的创建以一个统一的接口实现。