code: private File newSubdirectory(File parentDirectory, String path) {
          File dir = new File(parentDirectory, path);
  
          if (!dir.exists()) {
              dir.mkdirs();
          }
  
          return dir;
      }
docs: Creates a new subdirectory under the specified parent directory.
  
  @param parentDirectory The directory under which the subdirectory will be created.
  @param path The full path of the subdirectory.
  @return The subdirectory just created.