Module java.base
Package java.util

Interface NavigableSet<E>

Type Parameters:
E - the type of elements maintained by this set
All Superinterfaces:
Collection<E>, Iterable<E>, SequencedCollection<E>, SequencedSet<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.
    default E
    removeFirst()
    Removes and returns the first element of this collection (optional operation).
    default E
    removeLast()
    Removes and returns the last element of this collection (optional operation).
    default NavigableSet<E>
    reversed()
    Returns a reverse-ordered view of this collection.
    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

    addFirst, addLast, comparator, first, getFirst, getLast, 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.

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

      Parameters:
      fromElement - low endpoint of the returned set
      fromInclusive - true if the low endpoint is to be included in the returned view
      toElement - high endpoint of the returned set
      toInclusive - true if the high endpoint is to be included in the returned view
      Returns:
      a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive
      Throws:
      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.

    • headSet

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

    • tailSet

      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 - low endpoint of the returned set
      inclusive - true if the low endpoint is to be included in the returned view
      Returns:
      a view of the portion of this set whose elements are greater than or equal to fromElement
      Throws:
      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

    • subSet

      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. (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).

      Specified by:
      subSet in interface SortedSet<E>
      Parameters:
      fromElement - low endpoint (inclusive) of the returned set
      toElement - high endpoint (exclusive) of the returned set
      Returns:
      a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive
      Throws:
      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

    • headSet

      SortedSet<E> headSet(E toElement)
      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).

      Specified by:
      headSet in interface SortedSet<E>
      Parameters:
      toElement - high endpoint (exclusive) of the returned set
      Returns:
      a view of the portion of this set whose elements are strictly less than toElement
      Throws:
      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

    • tailSet

      SortedSet<E> tailSet(E fromElement)
      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).

      Specified by:
      tailSet in interface SortedSet<E>
      Parameters:
      fromElement - low endpoint (inclusive) of the returned set
      Returns:
      a view of the portion of this set whose elements are greater than or equal to fromElement
      Throws:
      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

    • removeFirst

      default E removeFirst()
      Removes and returns the first element of this collection (optional operation).
      Specified by:
      removeFirst in interface SequencedCollection<E>
      Specified by:
      removeFirst in interface SortedSet<E>
      Implementation Requirements:
      If this set is not empty, the implementation in this interface returns the result of calling the pollFirst method. Otherwise, it throws NoSuchElementException.
      Returns:
      the removed element
      Throws:
      NoSuchElementException - if this collection is empty
      UnsupportedOperationException - if this collection implementation does not support this operation
      Since:
      21

    • removeLast

      default E removeLast()
      Removes and returns the last element of this collection (optional operation).
      Specified by:
      removeLast in interface SequencedCollection<E>
      Specified by:
      removeLast in interface SortedSet<E>
      Implementation Requirements:
      If this set is not empty, the implementation in this interface returns the result of calling the pollLast method. Otherwise, it throws NoSuchElementException.
      Returns:
      the removed element
      Throws:
      NoSuchElementException - if this collection is empty
      UnsupportedOperationException - if this collection implementation does not support this operation
      Since:
      21

    • reversed

      default NavigableSet<E> 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.

      Specified by:
      reversed in interface SequencedCollection<E>
      Specified by:
      reversed in interface SequencedSet<E>
      Specified by:
      reversed in interface SortedSet<E>
      Implementation Requirements:
      The implementation in this interface returns the result of calling the descendingSet method.
      Returns:
      a reverse-ordered view of this collection, as a NavigableSet
      Since:
      21