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SortedSet is a subinterface of Set, which guarantees that the elements in the set are sorted.

Additionally, it provides the methods first() and last() for returning the first and last elements in the set, and headSet(toElement) and tailSet(fromElement) for returning 21.2 Sets 803 a portion of the set whose elements are less than toElement and greater than or equal to fromElement, respectively.

NavigableSet extends SortedSet to provide navigation methods lower(e),
floor(e),ceiling(e), and higher(e) that return elements respectively less than, less than or equal, greater than or equal, and greater than a given element and return null if there is no such element. The pollFirst() and pollLast() methods remove and return the first and last element in the tree set, respectively.