Hi Reimelt,
Java program should keep working after OS upgrade, backwards incompatible changes are usually carefully kept out of Java Virtual Machine. However, if one has slipped in, it might be that your problems could just solved by updating/downgrading Java Runtime Environment in use -- no need for recompiling the program then.
If you already tried JRE update/downgrade and it did not work for you, then please report the exact error the program gives when you run it from command prompt. Or if it runs, but does something incorrectly, please describe the exact problem with it.
My suggested budget is just placeholder right now, because I do not know the problem details yet -- as I said, recompilation might not even be necessary.
best,
Taimo