JDK 9 build b148
includes an important Refresh of the module system  , summary of
changes are listed here
This refresh includes a disruptive change that is important to
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