Please help i want to read 3d files in DWG format and to convert them into java files or more preciesly into xith scenegraphs.please tell me how to go about it…thanks in advance 
To be honest, I would suggest to forget about it…
DWG is a proprietary format. As far as I know the only available (sucessfull) attempt to read from it is http://www.opendesign.com/. I think this will be very difficult to port to java.
You could think of importing DXF files since DWG files can be easily exported/converted to DXF files.
Vincent