Java 9 overlapping non-exported packages

Question

Various resources (infoq, jigsaw-dev, osdir) indicate that having the same package in different java modules will lead to a LayerInstantiationException, even when t

Answer 1

This definition is open to interpretation. It remains correct as Jigsaw ensures that two modules never define shared packages by crashing the class loading in case of such a conflict.

If you look into Java 9's class loader implementation, you can see that a package name is mapped by to a single module. Its therefore impossible two have two modules to declare ownership. It is however possible that two class loaders in child-parent relationship define the same package.