code: private void statistics(String word, int times, Map<String, AtomicInteger> container){
          container.putIfAbsent(word, new AtomicInteger());
          container.get(word).addAndGet(times);
      }
docs: 统计词频
  @param word 词
  @param times 词频
  @param container 内存中保存词频的数据结构