As mentioned here: https://www.redhat.com/archives/fedora-devel-java-list/2005-March/msg00178.html
gcj will fail if asked to compile a .jar that contains a given .class twice. At the very least it should emit a better error message. -- Summary: gcj failure if .jar contains same .class twice Product: gcc Version: 4.0.0 Status: UNCONFIRMED Severity: normal Priority: P2 Component: java AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: tromey at gcc dot gnu dot org CC: gcc-bugs at gcc dot gnu dot org,java-prs at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20502