Java NavigableSet 问题

将NavigableSet 从大到小读取，和从小到大读取，为什么floor和ceiling结果就不一样了

根据ｊｄｋ文档，descendingSet方法返回一个ｖｉｅｗ，会把所以的结果反转。

https://docs.oracle.com/javase/8/docs/api/java/util/NavigableSet.html
The descendingSet method returns a view of the set with the senses of all relational and directional methods inverted.