I've never heard of a -i flag for jar.
For the most jar is just like tar, if you've used that before. As for extracting the files from the jar file use:
jar -xvf filename.jar
I usually always list the files in the archive prior to extracting, just to make sure it's creating directories for me.
jar -tvf filename.jar
Jar options: -x (extract) -v (verbose) -f (file) -t (table of contents )