接口中的变量 [英] Variables in Interface

问题描述

为什么接口中使用的变量是PUBLIC STATIC FINAL？为什么特别是静态？

Why is that a variable used in an Interface is PUBLIC STATIC FINAL? Why "static" in particular?

推荐答案

在接口中声明的字段无论如何都只能是一个常量，所以它为什么要依赖您使用哪个实例来访问它？

A field declared in an interface can only be a constant anyway, so why would it depend on which instance you use to access it?

现在将字段放在接口中的风格往往很差。该接口旨在反映实现它的类的功能 - 这与常量的概念完全正交。使用接口只是来声明一堆常量当然是一个令人讨厌的想法。我偶尔会发现使接口类型暴露出简单实现的常量很有用 - 例如，过滤接口可能有ALLOW_ALL和ALLOW_NONE字段。

Putting fields in interfaces is often poor style anyway these days. The interface is meant to reflect the capabilities of classes that implement it - which is completely orthogonal to the idea of a constant. It's certainly a nasty idea to use an interface just to declare a bunch of constants. I do occasionally find it useful to make the interface type expose constants which are simple implementations - so a filtering interface might have "ALLOW_ALL" and "ALLOW_NONE" fields, for example.

我想你可以设想实现一个接口 实际上为你的类添加一个实例字段的场景 - 但这会破坏封装，不仅仅是隐含的public，但也可以通过指定部分实现而不是API。

I suppose you could conceive of a scenario where implementing an interface did actually add an instance field to your class - but that would break encapsulation not only in terms of it being implicitly public, but also by specifying part of the implementation instead of the API.

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