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;
        DocIdSetIterator docIdSetIterator = f.getDocIdSet(ir).iterator();
        if (docIdSetIterator.skipTo(i) && (docIdSetIterator.doc() == i)) {
          return inner;
        } else {
          Explanation result = new Explanation
            (0.0f, "failure to match filter: " + f.toString());
          result.addDetail(inner);
          return result;
        }
      }

}