OGo provides broad Java support and the future will bring even more. Besides examples of Swing applications, SWT applications and Portlets, the JOGI API wraps the OGo XML-RPC server into convinient Java objects.
In the future JIGS will be used to provide Java access to all OGo objects (on MacOSX you can use the Apple provided Java/ObjC bridge).
Finally you can easily integrate JSP's and Servlets into the OGo WebUI to integrate existing applications or to enhance OGo using Java.