For starters, don't tell us to be quick. Everybody who is on here (including the moderators) are all putting in their own time and we don't give a crap about your schedule. Thanks.
Secondly, what exactly do you mean by "java file system"? Do you want to write a filesystem in Java? Do you want to write a file browser in Java? Do you want to write a psuedo-filesystem for browsing the contents of Java archives? The question is awfully vague. I'll assume you want to write a file system driver in Java because it sounds sort of like that. I don't know Java but I'd imagine writing Java code (your driver) to plug into C code (the kernel) and be efficient would be hard and mightn't make a lot of sense. Maybe you could take a look at FUSE
, it has Java bindings and should make it pretty easy to get off the ground.