code: private void addTokens(Queue<String> words,
                             int focusIndex,
                             int distance,
                             Map<Pair<Integer>, Double> matrixEntryToCount) {
          for (String word : words) {
              // skip adding co-occurence values for words that are not
              // accepted by the filter
              if (!word.equals(IteratorFactory.EMPTY_TOKEN)) {
                  int index = termToIndex.getDimension(word);
                  if (index >= 0) {
                      // Get the current number of times that the focus word has
                      // co-occurred with this word before after it.  Weight the
                      // word appropriately baed on distance
                      Pair<Integer> p = new Pair<Integer>(index, focusIndex);
                      double value = weighting.weight(distance, windowSize);
                      Double curCount = matrixEntryToCount.get(p);
                      matrixEntryToCount.put(p, (curCount == null)
                                             ? value : value + curCount);
                  }
              }
              distance++;
          }
      }
docs: Adds co-occurrence counts between the list of previous words in {@code
  words} and the focus word represented by {@code focusIndex} which start
  at {@code distance} tokens away from the focus word.  All Counts will be
  added into {@code matrixEntryToCount}.