You could look at the "code complete" plugin:
Sorry I misunderstood your question, I think you are looking for ctags (and maybe cscope),
I use ctags all the time but it works best for c, but I found it quite usable even for java.
I don't have a good tutorial right now but if you google for words like vim ctags tutorial you will find some usable links... (I hope anyway)
I also found this, that will create a index of all the java files under the src dir,
for both ctags and cscope
ctags -R src/ & find src/ -name '*.java' > cscope.files && cscope -b
It work really nice under Linux, but if you are sitting on windows this also works under cygwin.
That was one really confusing answer... but maybe it could be usable anyway :)