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>, Set<E>, SortedSet<E>
    All Known Implementing Classes:
    ConcurrentSkipListSet


    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
    Author:
    Doug Lea, Josh Bloch
    • Method Detail

      • 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