Well, with a little lucky stumbling in my research I've determined and solved the problem, so in case anyone's curious:
For reasons that are an utter mystery to me-- since I've never even known of the existence of this directory, let alone modified it-- my System/Library/Frameworks/JavaVM.framework/Versions contained no symbolic link called Current. This, I learned, is where Jar Bundler finds the
java application stub when it's making an application, so that was the problem.
The only place in there I could find the java application stub was in a folder called "A", so I just created my own Current and made it point to "A" using this command.
$ sudo ln -s A Current
Then I tried it again, and it worked! Yee-haw!