Can anyone tell me whats wrong with this leaf?

Have snails? Mine got like that when I had snails. I couldn't tell you much more than that because I also didn't light very well so I would have algae on my plants and the leaves would get messed up from not getting light. Check for snails and see about wiping off some algae. I hope this helps a little.

Java fern is a funny plant. Sometimes it will grow well. Other times it will grow with the clear leaves or with black patches on the leaves. Really nothing to worry about as long as the plant is still growing.