By  Scott Lysle July 07, 2008:
This article shall describe an approach that may be used to extract Jar files. Jars are merely files compressed using zip compression; the primary difference between a standard trash zip file and a jar file is that the jar file includes a manifest; also a true jar files can be run as an executable on a machine equipped with the java runtime.

Src: http://www.c-sharpcorner.com/UploadFile/scottlysle/OpenJarsCS07042008191842PM/OpenJarsCS.aspx