Review

class FilteredQuery {
      public Explanation explain (IndexReader ir, int i) throws IOException {
        Explanation inner = weight.explain (ir, i);
        if (getBoost()!=1) {
          Explanation preBoost = inner;
          inner = new Explanation(inner.getValue()*getBoost(),"product of:");
          inner.addDetail(new Explanation(getBoost(),"boost"));
          inner.addDetail(preBoost);
        }
        Filter f = FilteredQuery.this.filter;
        DocIdSet docIdSet = f.getDocIdSet(ir);
        DocIdSetIterator docIdSetIterator = docIdSet == null ? DocIdSet.EMPTY_DOCIDSET.iterator() : docIdSet.iterator();
        if (docIdSetIterator == null) {
          docIdSetIterator = DocIdSet.EMPTY_DOCIDSET.iterator();
        }
        if (docIdSetIterator.advance(i) == i) {
          return inner;
        } else {
          Explanation result = new Explanation
            (0.0f, "failure to match filter: " + f.toString());
          result.addDetail(inner);
          return result;
        }
      }

}