静态工厂方法vs实例（正常）构造函数？ [英] Static factory methods vs Instance (normal) constructors?

问题描述

在两种语言都可用的语言中，您是否希望看到返回实例的实例构造函数或静态方法？

例如，如果从创建 String char [] ：

<

String.FromCharacters（chars）;

new String（chars）;

解决方案>

在有效Java，第2版中，Joshua Bloch一定会推荐前者。有几个原因我可以记住，毫无疑问，我不能：

• 你可以给这个方法一个有意义的名字。如果你有两种方法来构造一个实例，它们都接受一个int，但对int有不同的含义，使用一个正常的方法使调用代码更容易阅读。


• A


• 您可以为潜在预期失败情况返回null，而构造函数总是 可返回值或抛出异常


• 您可以返回一个非声明的类型（例如返回派生类）


• 作为工厂，可能多次返回对同一对象的引用

缺点：

• 目前不是惯用的开发者更习惯于看到新


• 如果你看到知道您收到了一个新实例（按


• 在C＃3中，构造函数调用能够使用对象初始化表达式以紧凑的方式设置字段/属性;该功能不适用于静态方法调用

In a language where both are available, would you prefer to see an instance constructor or a static method that returns an instance?

For example, if you're creating a String from a char[]:

1. String.FromCharacters(chars);

2. new String(chars);

解决方案

In Effective Java, 2nd edition, Joshua Bloch certainly recommends the former. There are a few reasons I can remember, and doubtless some I can't:

• You can give the method a meaningful name. If you've got two ways of constructing an instance both of which take an int, but have different meanings for that int, using a normal method makes the calling code much more readable.
• A corollary of the first - you can have different factory methods with the same parameter list
• You can return null for "potentially expected failure" cases whereas a constructor will always either return a value or throw an exception
• You can return a type other than the declared (e.g. return a derived class)
• You can use it as a factory, to potentially return a reference to the same object several times

The downsides:

• It's not as idiomatic, currently - developers are more used to seeing "new"
• If you see "new" you know you're getting a new instance (modulo the oddity I mentioned recently)
• You need to make appropriate constructors available for subclasses
• In C# 3, constructor calls are able to set fields/properties in a compact manner with object initializer expressions; the feature doesn't apply to static method calls

这篇关于静态工厂方法vs实例（正常）构造函数？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！