Suppose I try to extract a file from a jar file, and the file I ask
for isn't in the archive, but what I ask for is a substring of
something that is in the jar file:

athyra$ ls
foo.jar
athyra$ jar tf foo.jar
META-INF/
META-INF/MANIFEST.MF
foo.pl

jar will extract the file that's in the archive, even though it's not
what I asked for.

athyra$ jar xf foo.jar foo
athyra$ ls
foo.jar foo.pl

Furthermore, if this other file already exists, jar will clobber it.

athyra$ echo blah >| foo.pl
athyra$ sum foo.pl
57449 1
athyra$ jar xf foo.jar foo
athyra$ sum foo.pl
54618 1