对一篇文档中的单词进行统计，并将单词出现的频率由高到低进行排列，并打印，便于对一篇文章高频词汇进行统计，非常实用，并通过测试-Statistics on the word in a document, and the frequency of the word appears to be arranged by the high to low, and print, easy to a high frequency vocabulary for statistics, very practical, and through the test