How is it planted? Can you get a picture.
If the rhibonzones(don't know if I spelled that right) are planted, the new leaves will not grow in.
If it's just planted in the substrate, try to remove it from it and tie the java fern on a rock or a piece of driftwood and let it root down for around 3-4weeks, then removed what you used to tie it down.
You have use fishing line to tie it down, I normally use cotton though, if though your not suppose to since it will eventually dissolve, it's only in there a month not long term, and it's easier to work with for me personally.
Get some pictures of it up on here if you can. That would help.