Java Platform Module System

Stephan Herrmann stephan.herrmann at
Mon May 1 19:40:45 UTC 2017

On 01.05.2017 20:47, Alex Buckley wrote:
> Yes, the API spec for java.lang.module will be updated to define the readability relation.


> But instead of waiting for that, I
> recommend you watch because readability has been stable for a long time.

I thought we agreed that challenging JLS is the best service we can give to the community? :)
I prefer not to undermine my scrutiny with too much of an assumed intuitive understanding.

>>      BTW: while pondering if the given package specification is sufficient,
>>      I wonder if "requires transitive" should work through multiple levels:
>>        M1
>>        M2 requires transitive M1
>>        M3 requires transitive M2
>>        M4 requires M3
>>      Does M4 read M1?
> It does work through multiple levels, in order to support arbitrary amounts of refactoring: once you've released a module that
> someone else reuses (via 'requires'), then you've committed to your module's name and API but are free to refactor its content into
> deeper modules which your original module "reuses" (via 'requires transitive') for the benefit of consumers. There is no
> "re-exporting", just modules being made to read one another.
> So, going top down (because resolution starts from a set of root modules) :- M4 requires and thus reads M3, and M3 requires
> transitive M2, so M4 reads M2. Since M4 reads M2, and M2 requires transitive M1, we have M4 reads M1.
>>      Looking at 7.7.1:
>>        [...]
> I understand the point; when we clarify the API spec for readability, I'll make sure the JLS usage of "depends" is explicitly aligned.

Thanks, this part resolved.

>> Revisiting other references to "Java Platform Module System" inside JLS,
>> what about the two occurrences in the body of 7.7:
>> - One reference is used to discriminate "dependence" from "dependency":
>>    From a quick scan, I believe this sentence:
>>      "Generally, the  rules  of  the  Java  programming  language  are
>>       more  interested  in  dependences  than dependencies."
>>    can probably be made stronger:
>>      "The rules of the Java programming language are not interested in
>>       dependencies, only in dependences.".
>>    Or perhaps the paragraph about dependencies could be removed entirely.
>>    If this interpretation is wrong, another reference to detailed
>> specification
>>    would be needed. Perhaps it is only JLS, that is agnostic to
>> dependencies,
>>    whereas the API specification part indeed uses this concept?
> This text is an informative note distinguishing the "dependence" expressed rather statically in the Language, from the "dependency"
> module determined rather dynamically by the JPMS. I see no reason to change it.

Asked differently: when it says
      "Generally, the rules of the Java programming language are
       more  interested  in  dependences  than dependencies."
which are the aspects where the rules of the Java programming language *are*
interested in dependencies?

>> - Another reference links "automatic modules" into JLS and will probably
>>    link to ModuleFinder.of(Path...), right?
> This text is also an informative note. Automatic modules are discovered through ModuleFinder.of, sure, and they appear in other
> places in the java.lang.module API too -- but none of that is the point of the note. The point of the note is that the developer
> doesn't specify 'requires' any differently for an automatic module than for an explicit module.

You make it sound as if automatic modules are relevant only at runtime.
But how then could requiring an automatic module be resolved at compile time?
Asked differently: how to you plan to ensure that different compilers can resolve
automatic modules in the same way?


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