code: protected ScheduledExecutorService createExecutor(ThreadFactory threadFactory)
      {
          ThreadFactory factory = threadFactory == null
              ? DEFAULT_THREAD_FACTORY
              : threadFactory;
  
          return Executors.newSingleThreadScheduledExecutor(factory);
      }
docs: This method creates the internal {@link java.util.concurrent.ScheduledExecutorService ScheduledExecutorService}.
  It is intended as a hook for custom implementations to create their own executor.
  
  @return A new ScheduledExecutorService