我知道有很多关于这两种模式之间差异的帖子，但有一些东西我找不到。
From what I have been reading, I see that the factory method pattern allows you to define how to create a single concrete product but hiding the implementation from the client as they will see a generic product. My first question is about the abstract factory. Is its role to allow you to create families of concrete objects in (that can depend on what specific factory you use) rather than just a single concrete object? Does the abstract factory only return one very large object or many objects depending on what methods you call?
我最后两个问题是关于一句我在很多地方都见过的引语，我不能完全理解:
两者之间的一个区别是
使用抽象工厂模式，a
类委托的责任
对象实例化到另一个对象
通过合成，而工厂
方法模式使用继承和
类依赖于子类来处理
所需的对象实例化。
我的理解是，工厂方法模式有一个Creator接口，它将使ConcreteCreator负责知道要实例化哪个ConcreteProduct。这就是使用继承来处理对象实例化的意思吗?
现在，关于引用，抽象工厂模式是如何通过组合将对象实例化的责任委托给另一个对象的?这是什么意思?在我看来，抽象工厂模式似乎也使用继承来完成构造过程，但我仍然在学习这些模式。
任何帮助，特别是最后一个问题，将非常感激。
之前的很多回答都没有提供抽象工厂和工厂方法模式之间的代码比较。下面是我试图用Java来解释它。我希望它能帮助那些需要简单解释的人。
正如GoF所言:抽象工厂提供了一个接口，无需指定就可以创建相关或依赖的对象族
具体的阶级。
public class Client {
public static void main(String[] args) {
ZooFactory zooFactory = new HerbivoreZooFactory();
Animal animal1 = zooFactory.animal1();
Animal animal2 = zooFactory.animal2();
animal1.sound();
animal2.sound();
System.out.println();
AnimalFactory animalFactory = new CowAnimalFactory();
Animal animal = animalFactory.createAnimal();
animal.sound();
}
}
public interface Animal {
public void sound();
}
public class Cow implements Animal {
@Override
public void sound() {
System.out.println("Cow moos");
}
}
public class Deer implements Animal {
@Override
public void sound() {
System.out.println("Deer grunts");
}
}
public class Hyena implements Animal {
@Override
public void sound() {
System.out.println("Hyena.java");
}
}
public class Lion implements Animal {
@Override
public void sound() {
System.out.println("Lion roars");
}
}
public interface ZooFactory {
Animal animal1();
Animal animal2();
}
public class CarnivoreZooFactory implements ZooFactory {
@Override
public Animal animal1() {
return new Lion();
}
@Override
public Animal animal2() {
return new Hyena();
}
}
public class HerbivoreZooFactory implements ZooFactory {
@Override
public Animal animal1() {
return new Cow();
}
@Override
public Animal animal2() {
return new Deer();
}
}
public interface AnimalFactory {
public Animal createAnimal();
}
public class CowAnimalFactory implements AnimalFactory {
@Override
public Animal createAnimal() {
return new Cow();
}
}
public class DeerAnimalFactory implements AnimalFactory {
@Override
public Animal createAnimal() {
return new Deer();
}
}
public class HyenaAnimalFactory implements AnimalFactory {
@Override
public Animal createAnimal() {
return new Hyena();
}
}
public class LionAnimalFactory implements AnimalFactory {
@Override
public Animal createAnimal() {
return new Lion();
}
}
抽象工厂创建了一个基类，其抽象方法定义了应该创建的对象的方法。派生基类的每个工厂类都可以创建每种对象类型的自己的实现。
工厂方法只是一个用于在类中创建对象的简单方法。它通常添加在聚合根中(Order类有一个名为CreateOrderLine的方法)
抽象工厂
在下面的示例中，我们设计了一个接口，这样我们就可以将队列创建与消息传递系统分离，因此可以为不同的队列系统创建实现，而不必更改代码库。
interface IMessageQueueFactory
{
IMessageQueue CreateOutboundQueue(string name);
IMessageQueue CreateReplyQueue(string name);
}
public class AzureServiceBusQueueFactory : IMessageQueueFactory
{
IMessageQueue CreateOutboundQueue(string name)
{
//init queue
return new AzureMessageQueue(/*....*/);
}
IMessageQueue CreateReplyQueue(string name)
{
//init response queue
return new AzureResponseMessageQueue(/*....*/);
}
}
public class MsmqFactory : IMessageQueueFactory
{
IMessageQueue CreateOutboundQueue(string name)
{
//init queue
return new MsmqMessageQueue(/*....*/);
}
IMessageQueue CreateReplyQueue(string name)
{
//init response queue
return new MsmqResponseMessageQueue(/*....*/);
}
}
工厂方法
HTTP服务器的问题在于，我们总是需要为每个请求提供响应。
public interface IHttpRequest
{
// .. all other methods ..
IHttpResponse CreateResponse(int httpStatusCode);
}
如果没有工厂方法，HTTP服务器用户(即程序员)将被迫使用特定于实现的类，这就违背了IHttpRequest接口的目的。
因此，我们引入工厂方法，以便响应类的创建也被抽象出来。
总结
区别在于，包含工厂方法的类的预期目的不是创建对象，而抽象工厂应该只用于创建对象。
使用工厂方法时应该小心，因为在创建对象时很容易破坏LSP(里斯科夫替换原则)。
为了使它非常简单，界面最小，请关注“//1”:
class FactoryProgram
{
static void Main()
{
object myType = Program.MyFactory("byte");
Console.WriteLine(myType.GetType().Name);
myType = Program.MyFactory("float"); //3
Console.WriteLine(myType.GetType().Name);
Console.ReadKey();
}
static object MyFactory(string typeName)
{
object desiredType = null; //1
switch (typeName)
{
case "byte": desiredType = new System.Byte(); break; //2
case "long": desiredType = new System.Int64(); break;
case "float": desiredType = new System.Single(); break;
default: throw new System.NotImplementedException();
}
return desiredType;
}
}
这里的要点:1。Factory和AbstractFactory机制必须使用继承(System。对象->字节，浮点…所以如果你在程序中有继承，那么根据设计2，工厂(抽象工厂很可能不在那里)已经在那里了。Creator (MyFactory)知道具体类型，因此返回具体类型对象给调用者(Main);在抽象工厂中，返回类型是一个接口。
interface IVehicle { string VehicleName { get; set; } }
interface IVehicleFactory
{
IVehicle CreateSingleVehicle(string vehicleType);
}
class HondaFactory : IVehicleFactory
{
public IVehicle CreateSingleVehicle(string vehicleType)
{
switch (vehicleType)
{
case "Sports": return new SportsBike();
case "Regular":return new RegularBike();
default: throw new ApplicationException(string.Format("Vehicle '{0}' cannot be created", vehicleType));
}
}
}
class HeroFactory : IVehicleFactory
{
public IVehicle CreateSingleVehicle(string vehicleType)
{
switch (vehicleType)
{
case "Sports": return new SportsBike();
case "Scooty": return new Scooty();
case "DarkHorse":return new DarkHorseBike();
default: throw new ApplicationException(string.Format("Vehicle '{0}' cannot be created", vehicleType));
}
}
}
class RegularBike : IVehicle { public string VehicleName { get { return "Regular Bike- Name"; } set { VehicleName = value; } } }
class SportsBike : IVehicle { public string VehicleName { get { return "Sports Bike- Name"; } set { VehicleName = value; } } }
class RegularScooter : IVehicle { public string VehicleName { get { return "Regular Scooter- Name"; } set { VehicleName = value; } } }
class Scooty : IVehicle { public string VehicleName { get { return "Scooty- Name"; } set { VehicleName = value; } } }
class DarkHorseBike : IVehicle { public string VehicleName { get { return "DarkHorse Bike- Name"; } set { VehicleName = value; } } }
class Program
{
static void Main(string[] args)
{
IVehicleFactory honda = new HondaFactory(); //1
RegularBike hondaRegularBike = (RegularBike)honda.CreateSingleVehicle("Regular"); //2
SportsBike hondaSportsBike = (SportsBike)honda.CreateSingleVehicle("Sports");
Console.WriteLine("******* Honda **********"+hondaRegularBike.VehicleName+ hondaSportsBike.VehicleName);
IVehicleFactory hero = new HeroFactory();
DarkHorseBike heroDarkHorseBike = (DarkHorseBike)hero.CreateSingleVehicle("DarkHorse");
SportsBike heroSportsBike = (SportsBike)hero.CreateSingleVehicle("Sports");
Scooty heroScooty = (Scooty)hero.CreateSingleVehicle("Scooty");
Console.WriteLine("******* Hero **********"+heroDarkHorseBike.VehicleName + heroScooty.VehicleName+ heroSportsBike.VehicleName);
Console.ReadKey();
}
}
Important points: 1. Requirement: Honda would create "Regular", "Sports" but Hero would create "DarkHorse", "Sports" and "Scooty". 2. why two interfaces? One for manufacturer type(IVehicleFactory) and another for product factory(IVehicle); other way to understand 2 interfaces is abstract factory is all about creating related objects 2. The catch is the IVehicleFactory's children returning and IVehicle(instead of concrete in factory); so I get parent variable(IVehicle); then I create actual concrete type by calling CreateSingleVehicle and then casting parent object to actual child object. What would happen if I do RegularBike heroRegularBike = (RegularBike)hero.CreateSingleVehicle("Regular");; you will get ApplicationException and that's why we need generic abstract factory which I would explain if required. Hope it helps from beginner to intermediate audience.
