使用工厂设计模式如何阻止类必须预期必须创建的对象类 [英] How does using the factory design pattern stop a class having to anticipate the class of objects it must create

问题描述

据我了解，工厂设计模式允许通过使用单独的对象来创建对象，其唯一目的是创建第一个对象.可以使用不同类型的工厂来创建不同类型的对象.

As I understand it the factory design pattern allows objects to be created through the use of a separate object that's sole aim is to create the first one. Different types of factory can be used to create different types of object.

我知道这隐藏了主对象的实例化，但是可以肯定的是，它只是被工厂实例化所取代了?

I understand that this hides the instantiation of the primary object however surely this is just replaced by the instantiation of the factory?

此设计模式的一个共同优点是，它停止了一个类，必须预见必须创建的对象的类.但是可以肯定的是，如果工厂应该创建一个特定的类，那么主要类仍然需要预测要使用哪种类型的工厂?

A common advantage for this design pattern is that it stops a class having to anticipate the class of objects it must create. However surely if the factory is supposed to create a specific class the main class still needs to anticipate what kind of factory to use?

我认为我误解了工厂的主要目的?

I assume I'm misunderstanding the main purpose of a factory?

推荐答案

这个问题比看起来要复杂得多，因为工厂的种类很多，因此客户端以不同的方式获取和调用它们.

The question is more complex than it seems, because there are many kinds of factories, so clients obtain and invoke them in different ways.

• 对于静态工厂而言，您是正确的:客户端保留了对工厂课.这样可以将产品类抽象化.因此，通过预期工厂，客户不必预测工厂的确切产量.

• In the case of a Static Factory you are correct: the client retains a concrete dependency on a factory class. This allows the product class to be abstracted. So by anticipating the factory, the client doesn't have to anticipate the exact output of the factory.

对于抽象工厂，客户端将其作为依赖项注入，表示应在组合根目录中创建.因此客户既不知道具体的工厂类别，也不知道具体的产品类别.

In the case of an Abstract Factory, the client has it injected as a dependency, which means it should be created in the composition root. So the client knows neither the concrete factory class nor the concrete product classes.

对于工厂方法，客户端是工厂，并为其父母提供具体产品.

In the case of a Factory Method, the client is the factory and provides a concrete product for its parent to consume.

工厂比这三个工厂多，可以用不同的方式调用.但是这三点说明了工厂使用方式之间的巨大差异.

There are more factories than these three, which may be invoked in different ways; but these three show how extreme the differences can be in the way factories are used.

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