code: public TimeCounter start() {
          switch (state) {
              case UNSTARTED:
                  watch.start();
                  break;
              case RUNNING:
                  throw new IllegalStateException("Already started. ");
              case STOPPED:
                  watch.resume();
          }
          state = State.RUNNING;
          return this;
      }
docs: Starts or resumes the time count.
  
  @return This {@link TimeCounter}.