Get the least and greatest element in this TreeSet'>

E ceiling(E e)

Returns the least element in this set greater than or equal to the given element, or null if there is no such element.

E floor(E e)

Returns the greatest element in this set less than or equal to the given element, or null if there is no such element.

E higher(E e)

Returns the least element in this set strictly greater than the given element, or null if there is no such element.

E lower(E e)

Returns the greatest element in this set strictly less than the given element, or null if there is no such element.

1. TreeSet class
2. Create TreeSet objects
3. Add elements to a TreeSet
4. Get the least and greatest element in this TreeSet'>
5. The first and last element in this TreeSet
6. Get the head set and tail set
7. Remove element from TreeSet
8. Get the size of this TreeSet
9. Get a subset from this TreeSet