仅包含子包的按需导入声明 [英] Import-on-demand declaration with subpackages only

问题描述

相关:我如何编译import pack.*"用ant/javac，什么时候没有这样的类?

假设我们有给定的包结构

Suppose we have the given package structure

parent
|
---a
---b

其中包parent只包含两个子包a和b(包parent下没有类>).

where the package parent only contains the two subpackges a and b (no class is under the package parent).

代码import parent.*，位于除parent 之外的包中，使用Maven(即javac)编译时抛出编译-时间错误.错误是:

The code import parent.*, situated in a package other than parent, compiled with Maven (i.e. javac) throws a compile-time error. The error is:

包父级不存在

我查看了有关这种情况的 Java 语言规范(实际上没有导入类型的按需导入声明).第 7.5.2 段JLS 关于按需导入声明似乎没有指定这种行为.

I looked into the Java Language Specification about such a case (import-on-demand declaration where no types are actually imported). Paragraph 7.5.2 of the JLS about import-on-demand declaration does not seem to specify this behavior.

这是javac的bug吗?我不是在问如何规避编译错误.我想知道为什么 javac 会抛出错误，因为我在 JLS 中找不到它应该的任何引用；让我相信这可能是一个错误.

Is this a bug of javac? I am not asking how to circumvent the compile error. I would like to know why javac throws an error because I cannot find any reference in the JLS that it should; leading me to believe that this might be a bug.

我用 JDK 1.4、1.6、1.7 和 1.8 测试过，错误是一样的.

I tested with JDK 1.4, 1.6, 1.7 and 1.8, the error is the same.

顺便说一下，在 Eclipse 中使用相同的代码没有编译错误(使用 Eclipse Indigo、Juno、Luna 和 Mars 测试).

As a side note, there is no compile error with the same code in Eclipse (tested with Eclipse Indigo, Juno, Luna and Mars).

注意:我在mavenizing"一个仅依赖于 Eclipse 编译器的(旧)现有项目时遇到了这种行为.我花了一段时间才确定这是我遇到的编译错误的根本原因.

NB: I encountered this behaviour when "mavenizing" an (old) existing project that only relied on the Eclipse compiler. It took me a while to identify that this was the root cause of the compile error I was getting.

推荐答案

我认为您正在寻找的是 section7.4.3

I think what you are looking for is section7.4.3

一个包是可观察的，当且仅当:

A package is observable if and only if either:

• 包含包声明的编译单元是可观察的(第 7.3 节).

• A compilation unit containing a declaration of the package is observable (§7.3).

包的子包是可观察的.

包 java、java.lang 和 java.io 始终是可观察的.

The packages java, java.lang, and java.io are always observable.

在 7.5 中.2

如果指定的包或类型不可访问(第 6.6 节)，则会导致编译时错误.

It is a compile-time error if the named package or type is not accessible (§6.6).

因此，如果包中没有任何内容，则它不存在并且错误实际上在 Eclipse 编译器一侧；它在 非常老的错误报告 中有所描述，该报告留在了LATER"中状态，直到最终该状态被弃用，并将其移至 WONT_FIX.如果您认为值得修复，请随时重新打开它(现在 JLS 在这方面已得到澄清)

So if nothing is in a package it does not exists and the bug is actually on the side of the Eclipse compiler; it's described in a very old bug report that was left in "LATER" state until eventually that state was deprecated and it was moved to WONT_FIX instead. Feel free to re-open it if you think it's worth fixing (now that the JLS is clarified in this area)

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