Understanding errors with JPMS modules

Question

I am having a rough time deciphering what these errors mean, let alone even begin to resolve them. I am trying to use java platform modules (using jdk 14) with a simple "gr

Answer 1

TL;DR — I've solved your split packages errors in this clone of your project using the mrJar Gradle plugin¹.

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The long-winded answer

„…I am having a rough time deciphering what these errors mean…“

Welcome to the world of split packages…

„…'Split packages' is an old Java term where two packages having the same name exist in different libraries/applications. Java 9 does not allow split packages in different modules for the reason of the reliable configuration…“

That quote's from this blog.

„…If you have come across these (or similar) issues…“

As several other Stack Overflow questions attest, split packages are an inevitability for anybody structuring their projects as JPMS modules.

„…could you please shed some light on how you were able to resolve them?…“

Referring back to the TL;DR, I've resolved your project's split packages issue by applying the plugin I proposed. Download and build the demo to examine the results.

As I mention in that demo's documentation, Java 14⁺ support will be added to that plugin within the next day or two. As soon as it is, I will update the demo and edit this answer. But I figured rather than wait until then, you (and other interested lurkers) could benefit today from version 0.0.16's JDK 13 support.

Another solution I recently proposed is an implementation of Mark Reinhold's suggested „Bridges to the class path“ approach. Numbers 2 and 3 that I mentioned in the comments take that approach. But personally I prefer the plugin approach. It's a lot easier and is way less effort.

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^{1 I have it on good authority that the mrJar plugin is in the process of being upgraded with JDK14+ support. Release of v0.0.17 is expected to be announced within the next 1-2 days.}