Top Description Methods
java.util

public Interface NavigableSet<E>

extends SortedSet<E>
Known Direct Implementers
java.util.TreeMap.KeySet, java.util.TreeSet, java.util.concurrent.ConcurrentSkipListMap.KeySet, java.util.concurrent.ConcurrentSkipListSet, java.util.Collections.UnmodifiableNavigableSet, java.util.Collections.SynchronizedNavigableSet, java.util.Collections.CheckedNavigableSet
Type Parameters
<E>
the type of elements maintained by this set
A SortedSet extended with navigation methods reporting closest matches for given search targets. Methods lower, floor, ceiling, and higher 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.

Authors
Doug Lea, Josh Bloch
Since
1.6

Method Summary

Modifier and TypeMethod and Description
public E

Returns:

the least element greater than or equal to e, or null if there is no such element
ceiling(E
the value to match
e)

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

public Iterator<E>

Returns:

an iterator over the elements in this set, in descending order
descendingIterator()

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

public NavigableSet<E>

Returns:

a reverse order view of this set
descendingSet()

Returns a reverse order view of the elements contained in this set.

public E

Returns:

the greatest element less than or equal to e, or null if there is no such element
floor(E
the value to match
e)

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

public NavigableSet<E>

Returns:

a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement
headSet(E
high endpoint of the returned set
toElement, boolean
true if the high endpoint is to be included in the returned view
inclusive)

Returns a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement.

public SortedSet<E>
headSet(E
high endpoint (exclusive) of the returned set
toElement)

Redeclares java.util.SortedSet.headSet.

Returns a view of the portion of this set whose elements are strictly less than toElement.

public E

Returns:

the least element greater than e, or null if there is no such element
higher(E
the value to match
e)

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

public Iterator<E>

Returns:

an iterator over the elements in this set, in ascending order
iterator()

Redeclares java.util.Set.iterator, java.util.Collection.iterator.

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

public E

Returns:

the greatest element less than e, or null if there is no such element
lower(E
the value to match
e)

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

public E

Returns:

the first element, or null if this set is empty
pollFirst()

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

public E

Returns:

the last element, or null if this set is empty
pollLast()

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

public default E
removeFirst()

Overrides default java.util.SortedSet.removeFirst.

Removes and returns the first element of this collection (optional operation).

public default E
removeLast()

Overrides default java.util.SortedSet.removeLast.

Removes and returns the last element of this collection (optional operation).

public default NavigableSet<E>

Returns:

a reverse-ordered view of this collection, as a NavigableSet
reversed()

Overrides default java.util.SortedSet.reversed.

Returns a reverse-ordered view of this collection.

public NavigableSet<E>

Returns:

a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive
subSet(E
low endpoint of the returned set
fromElement, boolean
true if the low endpoint is to be included in the returned view
fromInclusive, E
high endpoint of the returned set
toElement, boolean
true if the high endpoint is to be included in the returned view
toInclusive)

Returns a view of the portion of this set whose elements range from fromElement to toElement.

public SortedSet<E>
subSet(E
low endpoint (inclusive) of the returned set
fromElement, E
high endpoint (exclusive) of the returned set
toElement)

Redeclares java.util.SortedSet.subSet.

Returns a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive.

public NavigableSet<E>

Returns:

a view of the portion of this set whose elements are greater than or equal to fromElement
tailSet(E
low endpoint of the returned set
fromElement, boolean
true if the low endpoint is to be included in the returned view
inclusive)

Returns a view of the portion of this set whose elements are greater than (or equal to, if inclusive is true) fromElement.

public SortedSet<E>
tailSet(E
low endpoint (inclusive) of the returned set
fromElement)

Redeclares java.util.SortedSet.tailSet.

Returns a view of the portion of this set whose elements are greater than or equal to fromElement.

Inherited from java.util.SortedSet:
addFirstaddLastcomparatorfirstgetFirstgetLastlastspliterator

Method Detail

ceilingback to summary
public 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:E

the value to match

Returns:E

the least element greater than or equal to e, or null if there is no such element

Exceptions
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
descendingIteratorback to summary
public Iterator<E> descendingIterator()

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

Returns:Iterator<E>

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

descendingSetback to summary
public 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:NavigableSet<E>

a reverse order view of this set

floorback to summary
public 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:E

the value to match

Returns:E

the greatest element less than or equal to e, or null if there is no such element

Exceptions
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
headSetback to summary
public 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. 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.

The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.

Parameters
toElement:E

high endpoint of the returned set

inclusive:boolean

true if the high endpoint is to be included in the returned view

Returns:NavigableSet<E>

a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement

Exceptions
ClassCastException:
if toElement is not compatible with this set's comparator (or, if the set has no comparator, if toElement does not implement Comparable). Implementations may, but are not required to, throw this exception if toElement cannot be compared to elements currently in the set.
NullPointerException:
if toElement is null and this set does not permit null elements
IllegalArgumentException:
if this set itself has a restricted range, and toElement lies outside the bounds of the range
headSetback to summary
public SortedSet<E> headSet(E toElement)

Redeclares java.util.SortedSet.headSet.

Doc from java.util.SortedSet.headSet.

Returns a view of the portion of this set whose elements are strictly less than toElement. 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.

The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.

Equivalent to headSet(toElement, false).

Parameters
toElement:E

high endpoint (exclusive) of the returned set

Returns:SortedSet<E>

a view of the portion of this set whose elements are strictly less than toElement

Exceptions
ClassCastException:
if toElement is not compatible with this set's comparator (or, if the set has no comparator, if toElement does not implement Comparable). Implementations may, but are not required to, throw this exception if toElement cannot be compared to elements currently in the set.
NullPointerException:
if toElement is null and this set does not permit null elements
IllegalArgumentException:
if this set itself has a restricted range, and toElement lies outside the bounds of the range
higherback to summary
public 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:E

the value to match

Returns:E

the least element greater than e, or null if there is no such element

Exceptions
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
iteratorback to summary
public Iterator<E> iterator()

Redeclares java.util.Set.iterator, java.util.Collection.iterator.

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

Returns:Iterator<E>

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

lowerback to summary
public 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:E

the value to match

Returns:E

the greatest element less than e, or null if there is no such element

Exceptions
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
pollFirstback to summary
public E pollFirst()

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

Returns:E

the first element, or null if this set is empty

Exceptions
UnsupportedOperationException:
if the pollFirst operation is not supported by this collection
pollLastback to summary
public E pollLast()

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

Returns:E

the last element, or null if this set is empty

Exceptions
UnsupportedOperationException:
if the pollLast operation is not supported by this collection
removeFirstback to summary
public default E removeFirst()

Overrides default java.util.SortedSet.removeFirst.

Doc from java.util.SortedSet.removeFirst.

Removes and returns the first element of this collection (optional operation).

Implementation Specification

If this set is not empty, the implementation in this interface returns the result of calling the pollFirst method. Otherwise, it throws NoSuchElementException.

Returns:E

Doc from java.util.SequencedCollection.removeFirst.

the removed element

Exceptions
NoSuchElementException:
if this collection is empty
UnsupportedOperationException:
if this collection implementation does not support this operation
Since
21
removeLastback to summary
public default E removeLast()

Overrides default java.util.SortedSet.removeLast.

Doc from java.util.SortedSet.removeLast.

Removes and returns the last element of this collection (optional operation).

Implementation Specification

If this set is not empty, the implementation in this interface returns the result of calling the pollLast method. Otherwise, it throws NoSuchElementException.

Returns:E

Doc from java.util.SequencedCollection.removeLast.

the removed element

Exceptions
NoSuchElementException:
if this collection is empty
UnsupportedOperationException:
if this collection implementation does not support this operation
Since
21
reversedback to summary
public default NavigableSet<E> reversed()

Overrides default java.util.SortedSet.reversed.

Doc from java.util.SortedSet.reversed.

Returns a reverse-ordered view of this collection. The encounter order of elements in the returned view is the inverse of the encounter order of elements in this collection. The reverse ordering affects all order-sensitive operations, including those on the view collections of the returned view. If the collection implementation permits modifications to this view, the modifications "write through" to the underlying collection. Changes to the underlying collection might or might not be visible in this reversed view, depending upon the implementation.

This method is equivalent to descendingSet.

Implementation Specification

The implementation in this interface returns the result of calling the descendingSet method.

Returns:NavigableSet<E>

a reverse-ordered view of this collection, as a NavigableSet

Since
21
subSetback to summary
public 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.

The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.

Parameters
fromElement:E

low endpoint of the returned set

fromInclusive:boolean

true if the low endpoint is to be included in the returned view

toElement:E

high endpoint of the returned set

toInclusive:boolean

true if the high endpoint is to be included in the returned view

Returns:NavigableSet<E>

a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive

Exceptions
ClassCastException:
if fromElement and toElement cannot be compared to one another using this set's comparator (or, if the set has no comparator, using natural ordering). Implementations may, but are not required to, throw this exception if fromElement or toElement cannot be compared to elements currently in the set.
NullPointerException:
if fromElement or toElement is null and this set does not permit null elements
IllegalArgumentException:
if fromElement is greater than toElement; or if this set itself has a restricted range, and fromElement or toElement lies outside the bounds of the range.
subSetback to summary
public SortedSet<E> subSet(E fromElement, E toElement)

Redeclares java.util.SortedSet.subSet.

Doc from java.util.SortedSet.subSet.

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

The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.

Equivalent to subSet(fromElement, true, toElement, false).

Parameters
fromElement:E

low endpoint (inclusive) of the returned set

toElement:E

high endpoint (exclusive) of the returned set

Returns:SortedSet<E>

a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive

Exceptions
ClassCastException:
if fromElement and toElement cannot be compared to one another using this set's comparator (or, if the set has no comparator, using natural ordering). Implementations may, but are not required to, throw this exception if fromElement or toElement cannot be compared to elements currently in the set.
NullPointerException:
if fromElement or toElement is null and this set does not permit null elements
IllegalArgumentException:
if fromElement is greater than toElement; or if this set itself has a restricted range, and fromElement or toElement lies outside the bounds of the range
tailSetback to summary
public 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. 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.

The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.

Parameters
fromElement:E

low endpoint of the returned set

inclusive:boolean

true if the low endpoint is to be included in the returned view

Returns:NavigableSet<E>

a view of the portion of this set whose elements are greater than or equal to fromElement

Exceptions
ClassCastException:
if fromElement is not compatible with this set's comparator (or, if the set has no comparator, if fromElement does not implement Comparable). Implementations may, but are not required to, throw this exception if fromElement cannot be compared to elements currently in the set.
NullPointerException:
if fromElement is null and this set does not permit null elements
IllegalArgumentException:
if this set itself has a restricted range, and fromElement lies outside the bounds of the range
tailSetback to summary
public SortedSet<E> tailSet(E fromElement)

Redeclares java.util.SortedSet.tailSet.

Doc from java.util.SortedSet.tailSet.

Returns a view of the portion of this set whose elements are greater than or equal to fromElement. 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.

The returned set will throw an IllegalArgumentException on an attempt to insert an element outside its range.

Equivalent to tailSet(fromElement, true).

Parameters
fromElement:E

low endpoint (inclusive) of the returned set

Returns:SortedSet<E>

a view of the portion of this set whose elements are greater than or equal to fromElement

Exceptions
ClassCastException:
if fromElement is not compatible with this set's comparator (or, if the set has no comparator, if fromElement does not implement Comparable). Implementations may, but are not required to, throw this exception if fromElement cannot be compared to elements currently in the set.
NullPointerException:
if fromElement is null and this set does not permit null elements
IllegalArgumentException:
if this set itself has a restricted range, and fromElement lies outside the bounds of the range