On 12/3/2015 10:04 AM, Peter Levart wrote:
Loosely related to this debate, I would like to ask what's the story
with modular jars that can run on JDK8 classpath and as modules on JDK9.
How is one supposed to create such jar file as it must have:
- classes compiled with JDK8 javac (or JDK9 javac with -source 8 -target
8 or -release 8)
- module-info.class which can only be produced with JDK9 javac, but not
with -source 8 -target 8 or -release 8
Is one expected to invoke javac twice, 1st for sources (excluding
module-info.java), 2nd just for module-info.java ?
Yes (or get your build tool to do it).
More generally, anyone creating a multi-release JAR file (you didn't ask
about them, and they are not necessary to achieve what you want above,
but I mention them for completeness) will invoke javac multiple times.
It's the cost of doing business.
Wouldn't it be nice
for jar tool to be able to fabricate the module-info.class from scratch
using just command-line options?
No. How does a Java compiler know what's exported from a module, in
order to enforce accessibility, if the module declaration isn't
fabricated until packaging time?
I expect you will say, "Encode exports somewhere other than the module
declaration, such as with @Exported annotations on types or packages."
To which I repeat: "if we're going to introduce the concept of a
module to millions of Java developers, we see value in consolidating
both kinds of configuration [dependencies and exports] in one place".
Alex
