code: public ListIterator<IWord> findFirstWordIteratorByLabel(String label)
      {
          ListIterator<IWord> listIterator = this.wordList.listIterator();
          while (listIterator.hasNext())
          {
              IWord word = listIterator.next();
              if (label.equals(word.getLabel()))
              {
                  return listIterator;
              }
          }
          return null;
      }
docs: 找出第一个词性为label的单词的指针（不检查复合词内部的简单词）<br>
  若要查看该单词，请调用 previous<br>
  若要删除该单词，请调用 remove<br>
  
  @param label
  @return