递归导入Java [英] Recursive import Java

问题描述

我是Java开发的新手。我有一个关于Java中递归导入的快速问题。

I am a newbie to Java development. I have a quick question regarding recursive imports in Java.

让我们假设包pkg包含以下内容

Lets assume Package "pkg" contains the following

• A类，


• 包B（这又包含B1类）


• 包C（这又包含C1 class）

如果我使用 import pkg。* 为什么我不被允许从包B和C导入类？？

If I use import pkg.* why am I not allowed to import classes from packages "B" and "C" ?.

我想了解Java中不允许我进行递归导入的理由。

I would like to understand the rationale behind in Java's not allowing me to do recursive imports.

推荐答案

你的问题措辞不当，因为如果你导入pkg。* ，你当然可以从包 pkg.B 和 pkg.C 中导入类。也就是说，这样做非常好：

Your question is poorly phrased, because if you import pkg.*, you certainly are allowed to then import classes from packages pkg.B and pkg.C. That is, it is perfectly fine to do this:

import pkg.*;
import pkg.B.*;
import pkg.C.*;

但我认为你真正要问的是为什么，如果你 import pkg。* 它不会自动导入 pkg 子包中声明的类型。要回答这个问题，最好转向 Java语言规范：

But I assume that what you really are asking is why, if you import pkg.* it does not automatically import the types declared in the subpackages of pkg. To answer that, it's best to turn to the Java Language Specification:

包的分层命名结构旨在方便以传统方式组织相关包，但除了禁止具有与该包中声明的顶级类型（第7.6节）相同的简单名称的子包之外，本身没有任何意义。

The hierarchical naming structure for packages is intended to be convenient for organizing related packages in a conventional manner, but has no significance in itself other than the prohibition against a package having a subpackage with the same simple name as a top level type (§7.6) declared in that package.

_{例如，名为 oliver 的包与另一个名为 oliver.twist ，或名为 evelyn.wood 和 evelyn.waugh 的包之间。也就是说，名为 oliver.twist 的包中的代码无法更好地访问包 oliver 中声明的类型。任何其他包中的代码。}

_{For example, there is no special access relationship between a package named oliver and another package named oliver.twist, or between packages named evelyn.wood and evelyn.waugh. That is, the code in a package named oliver.twist has no better access to the types declared within package oliver than code in any other package.}

换句话说，当你 import pkg。* ，您要导入由名为 pkg 的包中包含的编译单元定义的所有顶级类型，但是您是不导入 pkg 的任何子包（例如 pkg.B 或 pkg.C ）。

In other words, when you import pkg.*, you are importing all the top-level types defined by the compilation units contained in the package named pkg, but you are not importing any of the sub-packages of pkg (such as pkg.B or pkg.C).

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