code: private static void contextWord(String[] words, int index, int distance, String word, Map<String, List<ContextWord>> map){
          String _word = null;
          if(index > -1 && index < words.length){
              _word = words[index];                    
          }
          if(_word != null && Utils.isChineseCharAndLengthAtLeastTwo(_word)){
              addToMap(map, word, _word, distance);
          }
      }
docs: 计算词的相关词
  @param words 词数组
  @param index 相关词索引
  @param distance 词距
  @param word 核心词
  @param map