What's with "4J" and "J" in database / API names

Question

I have used Twitter4j, linkedin-j and I'm looking at Neo4j and Bio4j. I've also seen "Log4j" and many other database related names with "j" and "4j" in them. I've been looking and I can't find anything that explains the "j" reference.

What's with the "j" / "4j"? What does it mean, if anything?

Answer 1

As far as I know, it is a naming convention meaning "For Java", i.e the library is for Java applications.