code: private void addDirectoryClasses(final Path location, final Path subPath) {
          for (final File file : location.toFile().listFiles()) {
              if (file.isDirectory())
                  addDirectoryClasses(location.resolve(file.getName()), subPath.resolve(file.getName()));
              else if (file.isFile() && file.getName().endsWith(".class")) {
                  final String classFileName = subPath.resolve(file.getName()).toString();
                  classes.add(toQualifiedClassName(classFileName));
              }
          }
      }
docs: Adds all classes in the given directory location to the set of known classes.
  
  @param location The location of the current directory
  @param subPath  The sub-path which is relevant for the package names or {@code null} if currently in the root directory