After doing a little research, it seems the the .jar file extension is actually alot like a .zip file extension, where the .jar file itself hold multiple other files that are compressed into the one file. Unfortunately, in order to unzip a .jar file, you will need the JDK tools on your PC. This means that you will have to extract the files from the .jar file on your PC before moving the files over to your phone.
I have a Samsung Gravity-T phone, aka, T669 and a message appears when I am trying to oen a jar. file I have on a memory card in the phone saying t is an unsupported file type. I'm desperte to find out how to make it wrk. It es an executable jar file that is supported by java se if I understand correctly.