Joanne, there are two different things called RAR.
What you are referring to are J2EE Resource Archives. These are indeed just JAR files with the extension RAR (just like you have WAR and EAR files in J2EE).
But there's also an archive format called RAR, which is an alternative to ZIP files. Such RAR files are something entirely different than J2EE RAR files. I guess that Eideo means this with RAR files. See http://www.rarlab.com
Sorry Eideo, I don't know of any Java API for RAR files. Have a look at http://www.wotsit.org which does have a link to a document that describes the RAR file format. I have no idea if there are official public specifications on the RAR format or if it's a proprietary format.