you can change the attributes and make java jar applications fullscreen in nokia 5800 or any other phone.
1. first open the jar file with 7zip or the archive software of your choice.
2. then open the manifest folder and then the manifest.mf file.
3. now edit the manifest file and add these lines in it.
4. you will be asked to save the changes made in the archive when closing it. save it and now the fullscreen app is ready.
Simple isnt it.