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。
抽象工厂与工厂方法的主要区别在于，抽象工厂是由组合实现的;但是工厂方法是通过继承实现的。
是的，您没有看错:这两种模式之间的主要区别在于古老的组合与继承之争。
UML图可以在(GoF)书中找到。我想提供代码示例，因为我认为将本文中前两个答案中的示例结合起来会比单独一个答案提供更好的演示。此外，我在类名和方法名中使用了书中的术语。
抽象工厂
The most important point to grasp here is that the abstract factory
is injected into the client. This is why we say that Abstract
Factory is implemented by Composition. Often, a dependency injection
framework would perform that task; but a framework is not required
for DI.
The second critical point is that the concrete factories here are
not Factory Method implementations! Example code for Factory
Method is shown further below.
And finally, the third point to note is the relationship between the
products: in this case the outbound and reply queues. One concrete
factory produces Azure queues, the other MSMQ. The GoF refers to
this product relationship as a "family" and it's important to be
aware that family in this case does not mean class hierarchy.
public class Client {
private final AbstractFactory_MessageQueue factory;
public Client(AbstractFactory_MessageQueue factory) {
// The factory creates message queues either for Azure or MSMQ.
// The client does not know which technology is used.
this.factory = factory;
}
public void sendMessage() {
//The client doesn't know whether the OutboundQueue is Azure or MSMQ.
OutboundQueue out = factory.createProductA();
out.sendMessage("Hello Abstract Factory!");
}
public String receiveMessage() {
//The client doesn't know whether the ReplyQueue is Azure or MSMQ.
ReplyQueue in = factory.createProductB();
return in.receiveMessage();
}
}
public interface AbstractFactory_MessageQueue {
OutboundQueue createProductA();
ReplyQueue createProductB();
}
public class ConcreteFactory_Azure implements AbstractFactory_MessageQueue {
@Override
public OutboundQueue createProductA() {
return new AzureMessageQueue();
}
@Override
public ReplyQueue createProductB() {
return new AzureResponseMessageQueue();
}
}
public class ConcreteFactory_Msmq implements AbstractFactory_MessageQueue {
@Override
public OutboundQueue createProductA() {
return new MsmqMessageQueue();
}
@Override
public ReplyQueue createProductB() {
return new MsmqResponseMessageQueue();
}
}
工厂方法
The most important point to grasp here is that the ConcreteCreator
is the client. In other words, the client is a subclass whose parent defines the factoryMethod(). This is why we say that
Factory Method is implemented by Inheritance.
The second critical point is to remember that the Factory Method
Pattern is nothing more than a specialization of the Template Method
Pattern. The two patterns share an identical structure. They only
differ in purpose. Factory Method is creational (it builds
something) whereas Template Method is behavioral (it computes
something).
And finally, the third point to note is that the Creator (parent)
class invokes its own factoryMethod(). If we remove
anOperation() from the parent class, leaving only a single method
behind, it is no longer the Factory Method pattern. In other words,
Factory Method cannot be implemented with less than two methods in
the parent class; and one must invoke the other.
public abstract class Creator {
public void anOperation() {
Product p = factoryMethod();
p.whatever();
}
protected abstract Product factoryMethod();
}
public class ConcreteCreator extends Creator {
@Override
protected Product factoryMethod() {
return new ConcreteProduct();
}
}
混杂。&杂项工厂图案
请注意，尽管GoF定义了两种不同的工厂模式，但它们并不是唯一存在的工厂模式。它们甚至不一定是最常用的工厂模式。第三个著名的例子是Josh Bloch的《Effective Java》中的静态工厂模式。《头部优先设计模式》一书还包括另一种被称为简单工厂的模式。
不要落入假设每个工厂模式都必须匹配GoF中的一个模式的陷阱。
我的第一个问题是关于抽象工厂。它的角色是否允许您在其中创建一系列具体对象(这取决于您使用的具体工厂)，而不仅仅是单个具体对象?
是的。抽象工厂的目的是:
提供一个接口，用于创建一系列相关或依赖的对象，而无需指定它们的具体类。
根据调用的方法，抽象工厂只返回一个非常大的对象还是多个对象?
理想情况下，它应该为客户端调用的每个方法返回一个对象。
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?
是的。工厂方法使用继承。
抽象工厂模式委托对象实例化的责任通过组合到另一个对象?这是什么意思?
AbstractFactory定义了一个FactoryMethod，而ConcreteFactory负责构建一个ConcreteProduct。只需按照本文中的代码示例进行操作。
你可以在SE的相关文章中找到更多细节:
工厂模式和抽象工厂模式之间的基本区别是什么?
设计模式:工厂vs工厂方法vs抽象工厂
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();
}
}
