code: public void setMode(String mode) {
          checkNotNull(mode, "mode should not be null");
          if (MODE_ASYNC.equals(mode) || MODE_SYNC.equals(mode)) {
              this.mode = mode;
          } else {
              throw new IllegalArgumentException("illegal mode: " + mode);
          }
      }
docs: Sets the mode of this fetching job.
  
  @param mode The mode of this fetching job.