yes, .jar are Java ARchives. They are an [misspell]agrupation[/misspell] grouping of all your .class archives (binary code) with some other configuration files (like manifests [plain text]). (If my mind doesn't fail me, I think it's almost equivalent to a .zip file).
Yo can execute a .jar archive if you have a virtual machine that understands the java language. So, you can install the official jre (http://java.sun.com
) or kaffe (http://www.kaffe.org/
) (I'm sure there are more virtual machines, but I only know this two)
With the official jre installed, you can run your app with:
java -jar file.jar