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Root module resolution in jdk9

Rde1-OracleSep 4 2017 — edited Sep 8 2017

I'm beginning to look at the JDK 9 impact on our source base.  I'm trying to understand if we need to use any --add-modules switches for our code.

One example class is  This is not in the default root module, but is found at compile and runtime.  I assume that this is because of the rule defining that "Every non-java.* module on the upgrade module path or among the system modules that exports at least one package, without qualification, is also a root." (from JEP 261).

Now if I try using the class with --limit-modules, I get results I do not understand:

$ java

Error: Could not find or load main class

Caused by: java.lang.ClassNotFoundException:


$ java

Error: Main method not found in class, please define the main method as:

   public static void main(String[] args)

or a JavaFX application class must extend javafx.application.Application

If I run the latter with --show-module-resolution, I see:

bash-4.1$ /usr/java/jdk9/bin/java --show-module-resolution

root jdk.httpserver jrt:/jdk.httpserver

root jrt:/

root jdk.unsupported jrt:/jdk.unsupported requires java.datatransfer jrt:/java.datatransfer requires java.xml jrt:/java.xml


So my question is - what is different about the module that causes the extra root modules to be available?  I cannot see anything in the module-info which would cause this.



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Added on Sep 4 2017
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