A)工厂方法模式

工厂方法是一种创建设计模式，它提供了创建对象的接口，但允许子类改变将要创建的对象的类型。

如果在基类和扩展它的子类中有一个创建方法，您可能会考虑工厂方法。

B)抽象工厂模式

抽象工厂是一种创造性的设计模式，允许在不指定具体类的情况下产生相关或依赖的对象族。

什么是“对象族”?例如，以这组类为例:传输+引擎+控制。这些可能有几种变体:

1-汽车+内燃机+方向盘

2-平面+ JetEngine +轭

如果你的程序不使用产品族，那么你就不需要抽象工厂。

同样，很多人混淆了抽象工厂模式和简单的工厂类声明为抽象。不要那样做!

裁判:https://refactoring.guru/design-patterns/factory-comparison

让我们明确一点，在生产代码中，大多数时候我们使用抽象工厂模式，因为类A是用接口b编程的，而A需要创建b的实例，因此A必须有一个工厂对象来生成b的实例，因此A不依赖于b的任何具体实例，希望它有帮助。

比起工厂方法，我更喜欢抽象工厂。从Tom Dalling上面的例子(顺便说一句，解释得很好)中，我们可以看到抽象工厂是更可组合的，因为我们所需要做的只是将一个不同的工厂传递给构造函数(这里使用构造函数依赖注入)。但是工厂方法要求我们引入一个新类(需要管理更多的东西)并使用子类化。总是选择组合而不是继承。

两者的区别

“工厂方法”和“抽象工厂”的主要区别在于，工厂方法是方法，而抽象工厂是对象。我想很多人都把这两个词搞混了，开始交替使用。我记得当我学习它们的时候，我很难找到它们之间的确切区别。

因为工厂方法只是一个方法，它可以在子类中被重写，因此引用的后半部分:

．.． 工厂方法模式使用的 继承并依赖于一个子类 来处理所需的对象 实例化。

引用假设对象在这里调用自己的工厂方法。因此，唯一可以改变返回值的是子类。

抽象工厂是一个具有多个工厂方法的对象。看看你引言的前半部分:

．.． 使用抽象工厂模式，一个类 委托对象的职责 实例化到另一个对象 作文……

他们说的是，有一个对象A，想要创建一个Foo对象。而不是创建Foo对象本身(例如，使用工厂方法)，它将获得一个不同的对象(抽象工厂)来创建Foo对象。

代码示例

为了向你展示区别，这里有一个正在使用的工厂方法:

class A {
    public void doSomething() {
        Foo f = makeFoo();
        f.whatever();   
    }

    protected Foo makeFoo() {
        return new RegularFoo();
    }
}

class B extends A {
    protected Foo makeFoo() {
        //subclass is overriding the factory method 
        //to return something different
        return new SpecialFoo();
    }
}

这是一个正在使用的抽象工厂:

class A {
    private Factory factory;

    public A(Factory factory) {
        this.factory = factory;
    }

    public void doSomething() {
        //The concrete class of "f" depends on the concrete class
        //of the factory passed into the constructor. If you provide a
        //different factory, you get a different Foo object.
        Foo f = factory.makeFoo();
        f.whatever();
    }
}

interface Factory {
    Foo makeFoo();
    Bar makeBar();
    Aycufcn makeAmbiguousYetCommonlyUsedFakeClassName();
}

//need to make concrete factories that implement the "Factory" interface here

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。

工厂设计模式

generation 1 <- generation 2 <- generation 3
//example
(generation 1) shape <- (generation 2) rectangle, oval <- (generation 3) rectangle impressionism, rectangle surrealism, oval impressionism, oval surrealism

工厂

用例:实例化第2代的一个对象

这是一种创造模式，允许你在一个简单的地方创建第2代。它符合SRP和OCP -所有的更改都在一个类中进行。

enum ShapeType {
    RECTANGLE,
    OVAL
}

class Shape {}

//Concrete Products
//generation 2
class Rectangle extends Shape {}
class Oval extends Shape {}

//Factory
class Factory {
    Shape createShape(ShapeType type) {

        switch (type) {
            case RECTANGLE:
                return new Rectangle();
            case OVAL:
                return new Oval();
        }
    }
}

//Creator
class Painter {

    private Factory factory;

    Painter(Factory factory) {
        this.factory = factory;
    }

    Shape prepareShape(ShapeType type) {
        return factory.createShape(type);
    }
}

//using
class Main {
    void main() {
        Painter painter = new Painter(new Factory());

        Shape shape1 = painter.prepareShape(ShapeType.RECTANGLE);
        Shape shape2 = painter.prepareShape(ShapeType.OVAL);
    }
}

工厂方法

用例:实例化第3代的一个对象

有助于与下一代家庭成员合作。每个画家都有自己的风格，印象派、超现实主义……工厂方法使用抽象创造者作为工厂(抽象方法)，具体创造者是这种方法的实现

enum ShapeType {
    RECTANGLE,
    OVAL
}

class Shape {}

//Concrete Products
//generation 2
class Rectangle extends Shape {}
class Oval extends Shape {}

//generation 3
class RectangleImpressionism extends Rectangle {}
class OvalImpressionism extends Oval {}
class RectangleSurrealism extends Rectangle {}
class OvalSurrealism extends Oval {}

//Creator
abstract class Painter {

    Shape prepareShape(ShapeType type) {
        return createShape(type);
    }

    //Factory method
    abstract Shape createShape(ShapeType type);
}

//Concrete Creators
class PainterImpressionism {

    @override
    Shape createShape(ShapeType type) {
        switch (type) {
            case RECTANGLE:
                return new RectangleImpressionism();
            case OVAL:
                return new OvalImpressionism();
        }
    }
}

class PainterSurrealism {

    @override
    Shape createShape(ShapeType type) {
        switch (type) {
            case RECTANGLE:
                return new RectangleSurrealism();
            case OVAL:
                return new OvalSurrealism();
        }
    }
}

//using
class Main {
    void main() {
        Painter painterImpressionism = new PainterImpressionism();
        Shape shape1 = painterImpressionism.prepareShape(ShapeType.RECTANGLE);

        Painter painterSurrealism = new PainterSurrealism();
        Shape shape2 = painterSurrealism.prepareShape(ShapeType.RECTANGLE);
    }
}

抽象工厂

用例:实例化第3代的所有对象

工厂是抽象工厂和具象工厂的一部分

//Concrete Products
//generation 2
class Rectangle extends Shape {}
class Oval extends Shape {}

//generation 3
class RectangleImpressionism extends Rectangle {}
class OvalImpressionism extends Oval {}
class RectangleSurrealism extends Rectangle {}
class OvalSurrealism extends Oval {}

//Abstract Factory
interface Factory {
    Rectangle createRectangle();
    Oval createOval();
}

//Concrete Factories
class ImpressionismFactory implements Factory {
    @Override
    public Rectangle createRectangle() {
        return new RectangleImpressionism();
    }

    @Override
    public Oval createOval() {
        return new OvalImpressionism();
    }
}

class SurrealismFactory implements Factory {
    @Override
    public Rectangle createRectangle() {
        return new RectangleSurrealism();
    }

    @Override
    public Oval createOval() {
        return new OvalSurrealism();
    }
}

//Creator
class Painter {

    Rectangle rectangle;
    Oval oval;

    Painter(Factory factory) {
        rectangle = factory.createRectangle();
        rectangle.resize();

        oval = factory.createOval();
        oval.resize();
    }
}

//using
class Main {
    void main() {
        Painter painter1 = new Painter(new ImpressionismFactory());
        Shape shape1 = painter1.rectangle;
        Shape shape2 = painter1.oval;

        Painter painter2 = new Painter(new ImpressionismFactory());
        Shape shape3 = painter2.rectangle;
        Shape shape4 = painter1.oval;
    }
}