Review

class ReqOptSumScorer {
  /** Returns the score of the current document matching the query.
   * Initially invalid, until {@link #next()} is called the first time.
   * @return The score of the required scorer, eventually increased by the score
   * of the optional scorer when it also matches the current document.
   */
  public float score() throws IOException {
    int curDoc = reqScorer.doc();
    float reqScore = reqScorer.score();
    if (firstTimeOptScorer) {
      firstTimeOptScorer = false;
      if (! optScorer.skipTo(curDoc)) {
        optScorer = null;
        return reqScore;
      }
    } else if (optScorer == null) {
      return reqScore;
    } else if ((optScorer.doc() < curDoc) && (! optScorer.skipTo(curDoc))) {
      optScorer = null;
      return reqScore;
    }
    // assert (optScorer != null) && (optScorer.doc() >= curDoc);
    return (optScorer.doc() == curDoc)
       ? reqScore + optScorer.score()
       : reqScore;
  }

}