I have not looked into Java support in a long time. Microsoft used to have a version of Java that supported COM/ActiveX directly and worked well with HyperSizer. But after a lawsuit with Sun, they are no longer allowed to distribute that version of Java, so I lost track of how to interface Java with HyperSizer.
J# is a java-like environment, however, I don't think it is true java. It actually runs on the .NET common language run-time, which is not platform independent like the java virtual machine. Since it is a .NET tool, I would assume that you can get native support for ActiveX to call HyperSizer from within the J# environment, but I've never tried it. We have successfully interfaced with HyperSizer using C#, but I'm not sure how difficult it would be to go to J#.
For this J/Invoke product, is it calling ActiveX dlls? Or the older style standard DLLs? HyperSizer exposes its methods using COM/ActiveX, therefore if this product can call ActiveX DLLs, it can also call HyperSizer. However, if it is just linking directly to a DLL, like calling a function from the Windows API, that is not really the same thing and I don't think it would work with HyperSizer.
Let me know if this helps.