I find it difficult to believe that a rank would be created with the sole purpose of being a Java expert instead of an expert in programming/comp sci/etc. Realistically, once you know a few languages, you "know" most of them and it's a matter of applying knowledge than simply writing code.
I suppose if you knew a lot about the internals of the JVM and such, then perhaps I could accept a "Java Expert" rank. But it seems rather superficial on a lot of sites.
@Parameter
I would think that you would need a working knowledge of the JVM, and by extension, bytecode and class file formats, etc. to be an "expert".