Review

class Query {
  /** Expert: called when re-writing queries under MultiSearcher.
   *
   * Create a single query suitable for use by all subsearchers (in 1-1
   * correspondence with queries). This is an optimization of the OR of
   * all queries. We handle the common optimization cases of equal
   * queries and overlapping clauses of boolean OR queries (as generated
   * by MultiTermQuery.rewrite() and RangeQuery.rewrite()).
   * Be careful overriding this method as queries[0] determines which
   * method will be called and is not necessarily of the same type as
   * the other queries.
  */
  public Query combine(Query[] queries) {
    HashSet uniques = new HashSet();
    for (int i = 0; i < queries.length; i++) {
      Query query = queries[i];
      BooleanClause[] clauses = null;
      // check if we can split the query into clauses
      boolean splittable = (query instanceof BooleanQuery);
      if(splittable){
        BooleanQuery bq = (BooleanQuery) query;
        splittable = bq.isCoordDisabled();
        clauses = bq.getClauses();
        for (int j = 0; splittable && j < clauses.length; j++) {
          splittable = (clauses[j].getOccur() == BooleanClause.Occur.SHOULD);
        }
      }
      if(splittable){
        for (int j = 0; j < clauses.length; j++) {
          uniques.add(clauses[j].getQuery());
        }
      } else {
        uniques.add(query);
      }
    }
    // optimization: if we have just one query, just return it
    if(uniques.size() == 1){
        return (Query)uniques.iterator().next();
    }
    Iterator it = uniques.iterator();
    BooleanQuery result = new BooleanQuery(true);
    while (it.hasNext())
      result.add((Query) it.next(), BooleanClause.Occur.SHOULD);
    return result;
  }

}