JDK 9 build b148 <https://jdk9.java.net/download/>
includes an important
Refresh of the module system  , summary of changes are listed here
*This refresh includes a disruptive change that is important to understand.
*For those that have been trying out modules with regular JDK 9 builds
then be aware that `requires public` changes to `requires transitive`.
In addition, the binary representation of the module declaration
(module-info.class) has changed so that you need to recompile any
modules that were compiled with previous JDK 9 builds.
As things stand today in JDK 9 then you use setAccessible to break into
non-public elements of any type in exported packages. However, it cannot
be used to break into any type in non-exported package. The current
specified behavior was a compromise for the initial integration of the
module system. It is of course not very satisfactory, hence the
#AwkwardStrongEncapsulation issue  on the JSR 376 issues list. With
the updated proposal in the JSR, this refresh changes setAccessible
further so that it cannot be used to break into non-public types, or
non-public elements of public types, in exported packages. Code that
uses setAccessible to hack into the private constructor of
java.lang.invoke.MethodHandles.Lookup will be disappointed for example.
This change will expose hacks in many existing libraries and tools. As a
workaround then a new command line option `--add-opens` can be used to
open specific packages for "deep reflection". For example, a really
popular build tool fails with this refresh because it uses setAccessible
+ core reflection to hack into a private field of an unmodifiable
collection so that it can mutate it, facepalm! This code will continue
to work as before when run with `--add-opens
java.base/java.util=ALL-UNNAMED` to open the package java.util in module
java.base to "all unnamed modules" (think class path).
*Any help reporting issues to popular tools and libraries would be
A debugging aid that is useful to identify issues is to run with
-Dsun.reflect.debugModuleAccessChecks=true to get a stack trace when
setAccessible fails, this is particularly useful when code swallows
exceptions without any logging.
Quality Engineering Manager
Oracle EMEA , Dublin, Ireland