For both working with class files and working with jar files there are multiple tools you could use. Which one is appropriate depends on what you're trying to do - care to tell us about that?
on your way in you may have missed that we have a policy on screen names here at JavaRanch. Basically, it must consist of a first name, a space, and a last name, and not be obviously fictitious. Since yours does not conform with it, please take a moment to change it, which you can do right here.