public static void iterateFileGroupFiles(final UpdatedFiles updatedFiles, final Callback callback) {
    final List<FileGroup> groups = updatedFiles.getTopLevelGroups();
    for (FileGroup group : groups) {
      iterateGroup(group, callback);

      // for changed on server
      for (FileGroup childGroup : group.getChildren()) {
        iterateGroup(childGroup, callback);
      }
    }
  }
public static void iterateFileGroupFiles(final UpdatedFiles updatedFiles, final Callback callback)