仅按子包进口按需报告 [英] Import-on-demand declaration with subpackages only
问题描述
相关：如何编译import pack。*与ant / javac，当没有这样的类？
假设我们有给定的包结构
parent
|
--- a
--- b
其中包 parent 只包含两个子包 a 和 b （没有类是在父项的包下
代码 import parent。* 位于一个包含不同于 parent 的包，并使用Maven编译（即 javac ）抛出一个编译时错误。错误是：
包父不存在
我研究了有关这种情况的Java语言规范（实际导入没有类型的按需导入的声明）。 第7.5.2段关于import-on-demand声明的JLS 似乎没有指定这种行为。
这是一个 javac的错误？我不是问如何规避编译错误。我想知道为什么 javac 抛出一个错误，因为我在JLS中找不到任何引用;导致我相信这可能是一个错误。
我使用JDK 1.4,1.6,1.7和1.8进行测试，错误是一样的。
作为附注，Eclipse中没有使用相同的代码编译错误（使用Eclipse Indigo，Juno，Luna和Mars进行测试）。
注意：当mavenizing只依赖于Eclipse编译器的（旧的）现有项目时，我遇到这种情况。我花了一段时间来确定这是编译错误的根本原因。
我想你是什么正在寻找的是 section7.4.3
一个包是可观察的，当且仅当以下两者之一：
包含该包的声明的编译单元是
observable（§7.3）。
A包的子包是可以观察到的。
包java，java.lang和java.io总是可以观察到的。
而在 7.5.2
这是一个如果命名的包或类型不可访问，则编译时错误（§6.6）。
所以如果没有g在一个包中它不存在，并且该bug实际上在Eclipse编译器的一边;它在LATER中留下的非常旧的错误报告中进行了描述状态，直到最终该状态被弃用，并将其移动到WONT_FIX。如果您认为这是值得修复的话，请随时重新打开（现在JLS已经在此领域得到澄清）
Related : How can I compile "import pack.*" with ant/javac, when there are no such classes?
Suppose we have the given package structure
parent
|
---a
---b
where the package parent only contains the two subpackges a and b (no class is under the package parent).
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:
package parent does not exist
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.
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.
I tested with JDK 1.4, 1.6, 1.7 and 1.8, the error is the same.
As a side note, there is no compile error with the same code in Eclipse (tested with Eclipse Indigo, Juno, Luna and Mars).
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.
I think what you are looking for is section7.4.3
A package is observable if and only if either:
A compilation unit containing a declaration of the package is observable (§7.3).
A subpackage of the package is observable.
The packages java, java.lang, and java.io are always observable.
And in 7.5.2
It is a compile-time error if the named package or type is not accessible (§6.6).
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)
这篇关于仅按子包进口按需报告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！
