There is an Oracle article I found regarding Java 9 module system
By default, a type in a module is not accessible to other modules unless it’s a public type and you export its package. You expose only the packages you want to expose. With Java 9, this also applies to reflection.
As pointed out in https://stackoverflow.com/a/50251958/134894, the differences between the AccessibleObject#setAccessible
for JDK8 and JDK9 are instructive. Specifically, JDK9 added
This method may be used by a caller in class C to enable access to a member of declaring class D if any of the following hold:
- C and D are in the same module.
- The member is public and D is public in a package that the module containing D exports to at least the module containing C.
- The member is protected static, D is public in a package that the module containing D exports to at least the module containing C, and C is a subclass of D.
- D is in a package that the module containing D opens to at least the module containing C. All packages in unnamed and open modules are open to all modules and so this method always succeeds when D is in an unnamed or open module.
which highlights the significance of modules and their exports (in Java 9)