code: public JobID getNewJobId() throws IOException {
      JobID id = new JobID(getTrackerIdentifier(), nextJobId.getAndIncrement());
  
      // get the user group info
      UserGroupInformation ugi = UserGroupInformation.getCurrentUGI();
  
      // mark the user for this id
      jobToUserMap.put(id, ugi.getUserName());
  
      LOG.info("Job id " + id + " assigned to user " + ugi.getUserName());
  
      return id;
    }
docs: Allocates a new JobId string.