code: boolean doJarFile(String jarname) throws IOException {
          try (JarFile jf = new JarFile(jarname)) {
              Stream<String> files =
                  jf.stream()
                    .map(JarEntry::getName);
              return doFileNames(files);
          }
      }
docs: Processes all class files in the given jar file.
  
  @param jarname the name of the jar file to process
  @return true for success, false for failure
  @throws IOException if an I/O error occurs