I got a java fern from Petsmart in one of those tubes on the shelf.
It had black thread tying the rhizome together.
Another plant I had with the thread rotted and died off mostly, I think because of how tightly they packed the rhizomes together and smothered them with the thread.
This time I very carefully removed the thread and got around 10 or so separate plants from the one I bought. Even two pieces of bare root sprouted leaves. The pieces I tied to drift wood are doing well enough to form babies on the tops of the leaves, and sprouted additional leaves from the root. I'm not sure if all the tubes of java fern are like this, but I am very happy with what I got out of buying one plant.
I know you guys/gals don't want to spend $6 - $7 for a plant though. Just wanted to share my good experience in case you ran into java fern in tubes.