code: public JobReference createJobReference(
        String projectId, String jobIdPrefix, @Nullable String location) {
      Preconditions.checkArgument(projectId != null, "projectId must not be null.");
      Preconditions.checkArgument(jobIdPrefix != null, "jobIdPrefix must not be null.");
      Preconditions.checkArgument(jobIdPrefix.matches(BIGQUERY_JOB_ID_PATTERN),
          "jobIdPrefix '%s' must match pattern '%s'", jobIdPrefix, BIGQUERY_JOB_ID_PATTERN);
  
      String fullJobId = String.format("%s-%s", jobIdPrefix, UUID.randomUUID().toString());
      Preconditions.checkArgument(fullJobId.length() <= BIGQUERY_JOB_ID_MAX_LENGTH,
          "fullJobId '%s' has length '%s'; must be less than or equal to %s",
          fullJobId, fullJobId.length(), BIGQUERY_JOB_ID_MAX_LENGTH);
      return new JobReference().setProjectId(projectId).setJobId(fullJobId).setLocation(location);
    }
docs: Creates a new JobReference with a unique jobId generated from {@code jobIdPrefix} plus a
  randomly generated UUID String.