code: public BaseWindowedBolt<T> eventTimeWindow(Time size) {
          long s = size.toMilliseconds();
          ensurePositiveTime(s);
  
          setSizeAndSlide(s, DEFAULT_SLIDE);
          this.windowAssigner = TumblingEventTimeWindows.of(s);
          return this;
      }
docs: define a tumbling event time window
  
  @param size window size