When I was recently working on a large restructuring and refactoring where I also replaced Ant by Maven, it was really necessary to compare the complete content of two different JAR files. It was required to know that the result of the restructuring and refactoring hadn't changed the artifacts, thus the JAR files. In the JAR files were different Class files present. When I compared the content of the two JAR files (with a binary compare) all the content was radically changed. This was partly because the compiler compiled the Class files at a different timestamp.