This class in java-gj.jar has:

ModifiedRegistry() {
    DataObject.getRegistry().addChangeListener(this);
}
public void stateChanged(ChangeEvent evt) {
    Collection objs = (Collection)evt.getSource();
    // ...

Very bad. Javadoc for DO.R.aCL says only:

/** Add new listener to changes in the set of
modified objects.
 * @param chl listener to add
 */

Says nothing about the source of the change event
or what type it will be. If anything, you would
expect it to be the DO.R instance itself.

I tried to fix DO.ModifiedRegistry to use the DO.R
as the event source (see nbdev for more). But then
I get a CCE from the java module.

Attaching CCE and attempted patch. Please apply
the openide patch while fixing broken java module
code.