Interface NavigableSet<E>

Type Parameters:: E - the type of elements maintained by this set

All Superinterfaces:: Collection<E>, Iterable<E>, Set<E>, SortedSet<E>

All Known Implementing Classes:: ConcurrentSkipListSet, TreeSet

public interface NavigableSet<E> extends SortedSet<E>

A SortedSet extended with navigation methods reporting closest matches for given search targets. Methods lower(E), floor(E), ceiling(E), and higher(E) return elements respectively less than, less than or equal, greater than or equal, and greater than a given element, returning null if there is no such element.

A NavigableSet may be accessed and traversed in either ascending or descending order. The descendingSet() method returns a view of the set with the senses of all relational and directional methods inverted. The performance of ascending operations and views is likely to be faster than that of descending ones. This interface additionally defines methods pollFirst() and pollLast() that return and remove the lowest and highest element, if one exists, else returning null. Methods subSet(E, boolean, E, boolean), headSet(E, boolean), and tailSet(E, boolean) differ from the like-named SortedSet methods in accepting additional arguments describing whether lower and upper bounds are inclusive versus exclusive. Subsets of any NavigableSet must implement the NavigableSet interface.

The return values of navigation methods may be ambiguous in implementations that permit null elements. However, even in this case the result can be disambiguated by checking contains(null). To avoid such issues, implementations of this interface are encouraged to not permit insertion of null elements. (Note that sorted sets of Comparable elements intrinsically do not permit null.)

Methods subSet(E, E), headSet(E), and tailSet(E) are specified to return SortedSet to allow existing implementations of SortedSet to be compatibly retrofitted to implement NavigableSet, but extensions and implementations of this interface are encouraged to override these methods to return NavigableSet.

This interface is a member of the Java Collections Framework.

Since:: 1.6

Method Summary

Modifier and Type	Method	Description
`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.
`Iterator<E>`	`descendingIterator()`	Returns an iterator over the elements in this set, in descending order.
`NavigableSet<E>`	`descendingSet()`	Returns a reverse order view of the elements contained in this set.
`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.
`SortedSet<E>`	`headSet(E toElement)`	Returns a view of the portion of this set whose elements are strictly less than `toElement`.
`NavigableSet<E>`	`headSet(E toElement, boolean inclusive)`	Returns a view of the portion of this set whose elements are less than (or equal to, if `inclusive` is true) `toElement`.
`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.
`Iterator<E>`	`iterator()`	Returns an iterator over the elements in this set, in ascending order.
`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.
`E`	`pollFirst()`	Retrieves and removes the first (lowest) element, or returns `null` if this set is empty.
`E`	`pollLast()`	Retrieves and removes the last (highest) element, or returns `null` if this set is empty.
`NavigableSet<E>`	`subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)`	Returns a view of the portion of this set whose elements range from `fromElement` to `toElement`.
`SortedSet<E>`	`subSet(E fromElement, E toElement)`	Returns a view of the portion of this set whose elements range from `fromElement`, inclusive, to `toElement`, exclusive.
`SortedSet<E>`	`tailSet(E fromElement)`	Returns a view of the portion of this set whose elements are greater than or equal to `fromElement`.
`NavigableSet<E>`	`tailSet(E fromElement, boolean inclusive)`	Returns a view of the portion of this set whose elements are greater than (or equal to, if `inclusive` is true) `fromElement`.

Methods declared in interface java.util.Collection

parallelStream, removeIf, stream, toArray

Methods declared in interface java.lang.Iterable

forEach

Methods declared in interface java.util.Set

add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, remove, removeAll, retainAll, size, toArray, toArray

Methods declared in interface java.util.SortedSet

comparator, first, last, spliterator

Method Details

lower

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.

Parameters:: e - the value to match
Returns:: the greatest element less than e, or null if there is no such element
Throws:: ClassCastException - if the specified element cannot be compared with the elements currently in the set; NullPointerException - if the specified element is null and this set does not permit null elements

floor

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.

Parameters:: e - the value to match
Returns:: the greatest element less than or equal to e, or null if there is no such element
Throws:: ClassCastException - if the specified element cannot be compared with the elements currently in the set; NullPointerException - if the specified element is null and this set does not permit null elements

ceiling

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.

Parameters:: e - the value to match
Returns:: the least element greater than or equal to e, or null if there is no such element
Throws:: ClassCastException - if the specified element cannot be compared with the elements currently in the set; NullPointerException - if the specified element is null and this set does not permit null elements

higher

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.

Parameters:: e - the value to match
Returns:: the least element greater than e, or null if there is no such element
Throws:: ClassCastException - if the specified element cannot be compared with the elements currently in the set; NullPointerException - if the specified element is null and this set does not permit null elements

pollFirst

E pollFirst()

Retrieves and removes the first (lowest) element, or returns null if this set is empty.

Returns:: the first element, or null if this set is empty

pollLast

E pollLast()

Retrieves and removes the last (highest) element, or returns null if this set is empty.

Returns:: the last element, or null if this set is empty

iterator

Iterator<E> iterator()

Returns an iterator over the elements in this set, in ascending order.

Specified by:: iterator in interface Collection<E>
Specified by:: iterator in interface Iterable<E>
Specified by:: iterator in interface Set<E>
Returns:: an iterator over the elements in this set, in ascending order

descendingSet

NavigableSet<E> descendingSet()

Returns a reverse order view of the elements contained in this set. The descending set is backed by this set, so changes to the set are reflected in the descending set, and vice-versa. If either set is modified while an iteration over either set is in progress (except through the iterator's own remove operation), the results of the iteration are undefined.

The returned set has an ordering equivalent to Collections.reverseOrder(comparator()). The expression s.descendingSet().descendingSet() returns a view of s essentially equivalent to s.

Returns:: a reverse order view of this set

descendingIterator

Iterator<E> descendingIterator()

Returns an iterator over the elements in this set, in descending order. Equivalent in effect to descendingSet().iterator().

Returns:: an iterator over the elements in this set, in descending order

subSet

NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive)

Returns a view of the portion of this set whose elements range from fromElement to toElement. If fromElement and toElement are equal, the returned set is empty unless


 fromInclusive

and toInclusive are both true. The returned set is backed by this set, so changes in the returned set are reflected in this set, and vice-versa. The returned set supports all optional set operations that this set supports.