You can't convert a .jar to .apk and expect it to run on an android. Jars are for older j2me phones and don't convert without significant changes to the source code. It'd be like saying I have an linux program and I want it to run on windows. You would have to recompile the source code for windows (except with android you would have to make CHANGES to the source code first). You best bet would be to look for an alternative app for android, or contact the developers of the .jar and ask them to remake the app for android.