I found this, from the previous posts on this forum. [1] and so far it seems I got it working.
The trick was: "to use a common super type or interface and cast as needed." I used Composite Design Pattern. [1] https://groups.google.com/group/google-web-toolkit/browse_thread/thread/c5411fe74fabd8ba/61e53348a581e111?lnk=gst -- You received this message because you are subscribed to the Google Groups "Google Web Toolkit" group. To post to this group, send email to google-web-tool...@googlegroups.com. To unsubscribe from this group, send email to google-web-toolkit+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-web-toolkit?hl=en.