NavigableSet in Java

NavigableSet interface provides some interesting methods. Their method signatures are as follows:
Method | Description
------ | ------
E lower(E e) | Returns greatest element that is < e, or null if no such element
E floor(E e) | Returns greatest element that is <= e, or null if no such element
E ceiling(E e) | Returns smallest element that is >= e, or null if no such element
E higher(E e) | Returns smallest element that is > e, or null if no such element