Review

class BooleanQuery.BooleanWeight {
    public Explanation explain(IndexReader reader, int doc)
      throws IOException {
      final int minShouldMatch =
        BooleanQuery.this.getMinimumNumberShouldMatch();
      ComplexExplanation sumExpl = new ComplexExplanation();
      sumExpl.setDescription("sum of:");
      int coord = 0;
      int maxCoord = 0;
      float sum = 0.0f;
      boolean fail = false;
      int shouldMatchCount = 0;
      for (Iterator wIter = weights.iterator(), cIter = clauses.iterator(); wIter.hasNext();) {
        Weight w = (Weight) wIter.next();
        BooleanClause c = (BooleanClause) cIter.next();
        if (w.scorer(reader, true, true) == null) {
          continue;
        }
        Explanation e = w.explain(reader, doc);
        if (!c.isProhibited()) maxCoord++;
        if (e.isMatch()) {
          if (!c.isProhibited()) {
            sumExpl.addDetail(e);
            sum += e.getValue();
            coord++;
          } else {
            Explanation r =
              new Explanation(0.0f, "match on prohibited clause (" + c.getQuery().toString() + ")");
            r.addDetail(e);
            sumExpl.addDetail(r);
            fail = true;
          }
          if (c.getOccur() == Occur.SHOULD)
            shouldMatchCount++;
        } else if (c.isRequired()) {
          Explanation r = new Explanation(0.0f, "no match on required clause (" + c.getQuery().toString() + ")");
          r.addDetail(e);
          sumExpl.addDetail(r);
          fail = true;
        }
      }
      if (fail) {
        sumExpl.setMatch(Boolean.FALSE);
        sumExpl.setValue(0.0f);
        sumExpl.setDescription
          ("Failure to meet condition(s) of required/prohibited clause(s)");
        return sumExpl;
      } else if (shouldMatchCount < minShouldMatch) {
        sumExpl.setMatch(Boolean.FALSE);
        sumExpl.setValue(0.0f);
        sumExpl.setDescription("Failure to match minimum number "+
                               "of optional clauses: " + minShouldMatch);
        return sumExpl;
      }
      
      sumExpl.setMatch(0 < coord ? Boolean.TRUE : Boolean.FALSE);
      sumExpl.setValue(sum);
      
      float coordFactor = similarity.coord(coord, maxCoord);
      if (coordFactor == 1.0f)                      // coord is no-op
        return sumExpl;                             // eliminate wrapper
      else {
        ComplexExplanation result = new ComplexExplanation(sumExpl.isMatch(),
                                                           sum*coordFactor,
                                                           "product of:");
        result.addDetail(sumExpl);
        result.addDetail(new Explanation(coordFactor,
                                         "coord("+coord+"/"+maxCoord+")"));
        return result;
      }
    }

}