code: boolean isDeadEnd()
      {
          if (isAccepting())
          {
              return false;
          }
          for (Transition<DFAState<T>> next : transitions.values())
          {
              if (next.getTo() != this)
              {
                  return false;
              }
          }
          return true;
      }
docs: Returns true if state doesn't contain any outbound transition
  and is not accepting state
  @return