code: public static void indexDir(final Indexer indexer, final List<File> knownFiles, final File dir) {
          final List<File> classes = Utils4J.pathsFiles(dir.getPath(), Utils4J::classFile);
          for (final File file : classes) {
              indexClassFile(indexer, knownFiles, file);
          }
      }
docs: Indexes all classes in a directory or it's sub directories.
  
  @param indexer
  Indexer to use.
  @param knownFiles
  List of files already analyzed. New files will be added within this method.
  @param dir
  Directory to analyze.