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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
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 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
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/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * Written by Doug Lea and Josh Bloch with assistance from members of JCP
 * JSR-166 Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util;


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.

Author:Doug Lea, Josh Bloch
Type parameters:
  • <E> – the type of elements maintained by this set
Since:1.6
/**
 * A {@link SortedSet} extended with navigation methods reporting
 * closest matches for given search targets. Methods {@link #lower},
 * {@link #floor}, {@link #ceiling}, and {@link #higher} return elements
 * respectively less than, less than or equal, greater than or equal,
 * and greater than a given element, returning {@code null} if there
 * is no such element.
 *
 * <p>A {@code NavigableSet} may be accessed and traversed in either
 * ascending or descending order.  The {@link #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 {@link
 * #pollFirst} and {@link #pollLast} that return and remove the lowest
 * and highest element, if one exists, else returning {@code null}.
 * Methods
 * {@link #subSet(Object, boolean, Object, boolean) subSet(E, boolean, E, boolean)},
 * {@link #headSet(Object, boolean) headSet(E, boolean)}, and
 * {@link #tailSet(Object, boolean) tailSet(E, boolean)}
 * differ from the like-named {@code SortedSet} methods in accepting
 * additional arguments describing whether lower and upper bounds are
 * inclusive versus exclusive.  Subsets of any {@code NavigableSet}
 * must implement the {@code NavigableSet} interface.
 *
 * <p>The return values of navigation methods may be ambiguous in
 * implementations that permit {@code null} elements. However, even
 * in this case the result can be disambiguated by checking
 * {@code contains(null)}. To avoid such issues, implementations of
 * this interface are encouraged to <em>not</em> permit insertion of
 * {@code null} elements. (Note that sorted sets of {@link
 * Comparable} elements intrinsically do not permit {@code null}.)
 *
 * <p>Methods
 * {@link #subSet(Object, Object) subSet(E, E)},
 * {@link #headSet(Object) headSet(E)}, and
 * {@link #tailSet(Object) tailSet(E)}
 * are specified to return {@code SortedSet} to allow existing
 * implementations of {@code SortedSet} to be compatibly retrofitted to
 * implement {@code NavigableSet}, but extensions and implementations
 * of this interface are encouraged to override these methods to return
 * {@code NavigableSet}.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
 * Java Collections Framework</a>.
 *
 * @author Doug Lea
 * @author Josh Bloch
 * @param <E> the type of elements maintained by this set
 * @since 1.6
 */
public interface NavigableSet<E> extends SortedSet<E> {
    
Returns the greatest element in this set strictly less than the given element, or null if there is no such element. 
Params:
  • e – the value to match
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
Returns:the greatest element less than e, or null if there is no such element
/**
     * Returns the greatest element in this set strictly less than the
     * given element, or {@code null} if there is no such element.
     *
     * @param e the value to match
     * @return the greatest element less than {@code e},
     *         or {@code null} if there is no such element
     * @throws ClassCastException if the specified element cannot be
     *         compared with the elements currently in the set
     * @throws NullPointerException if the specified element is null
     *         and this set does not permit null elements
     */
    E lower(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. 
Params:
  • e – the value to match
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
Returns:the greatest element less than or equal to e, or null if there is no such element
/**
     * Returns the greatest element in this set less than or equal to
     * the given element, or {@code null} if there is no such element.
     *
     * @param e the value to match
     * @return the greatest element less than or equal to {@code e},
     *         or {@code null} if there is no such element
     * @throws ClassCastException if the specified element cannot be
     *         compared with the elements currently in the set
     * @throws NullPointerException if the specified element is null
     *         and this set does not permit null elements
     */
    E floor(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. 
Params:
  • e – the value to match
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
Returns:the least element greater than or equal to e, or null if there is no such element
/**
     * Returns the least element in this set greater than or equal to
     * the given element, or {@code null} if there is no such element.
     *
     * @param e the value to match
     * @return the least element greater than or equal to {@code e},
     *         or {@code null} if there is no such element
     * @throws ClassCastException if the specified element cannot be
     *         compared with the elements currently in the set
     * @throws NullPointerException if the specified element is null
     *         and this set does not permit null elements
     */
    E ceiling(E e);

    
Returns the least element in this set strictly greater than the given element, or null if there is no such element. 
Params:
  • e – the value to match
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
Returns:the least element greater than e, or null if there is no such element
/**
     * Returns the least element in this set strictly greater than the
     * given element, or {@code null} if there is no such element.
     *
     * @param e the value to match
     * @return the least element greater than {@code e},
     *         or {@code null} if there is no such element
     * @throws ClassCastException if the specified element cannot be
     *         compared with the elements currently in the set
     * @throws NullPointerException if the specified element is null
     *         and this set does not permit null elements
     */
    E higher(E e);

    
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
/**
     * Retrieves and removes the first (lowest) element,
     * or returns {@code null} if this set is empty.
     *
     * @return the first element, or {@code null} if this set is empty
     */
    E pollFirst();

    
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
/**
     * Retrieves and removes the last (highest) element,
     * or returns {@code null} if this set is empty.
     *
     * @return the last element, or {@code null} if this set is empty
     */
    E pollLast();

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

Returns:an iterator over the elements in this set, in ascending order
/**
     * Returns an iterator over the elements in this set, in ascending order.
     *
     * @return an iterator over the elements in this set, in ascending order
     */
    Iterator<E> iterator();

    
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
/**
     * 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 {@code remove} operation), the results of
     * the iteration are undefined.
     *
     * <p>The returned set has an ordering equivalent to
     * {@link Collections#reverseOrder(Comparator) Collections.reverseOrder}{@code (comparator())}.
     * The expression {@code s.descendingSet().descendingSet()} returns a
     * view of {@code s} essentially equivalent to {@code s}.
     *
     * @return a reverse order view of this set
     */
    NavigableSet<E> descendingSet();

    
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
/**
     * Returns an iterator over the elements in this set, in descending order.
     * Equivalent in effect to {@code descendingSet().iterator()}.
     *
     * @return an iterator over the elements in this set, in descending order
     */
    Iterator<E> descendingIterator();

    
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. 
Params:
  • 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
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.
Returns:a view of the portion of this set whose elements range from fromElement, inclusive, to toElement, exclusive
/**
     * Returns a view of the portion of this set whose elements range from
     * {@code fromElement} to {@code toElement}.  If {@code fromElement} and
     * {@code toElement} are equal, the returned set is empty unless {@code
     * fromInclusive} and {@code 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.
     *
     * <p>The returned set will throw an {@code IllegalArgumentException}
     * on an attempt to insert an element outside its range.
     *
     * @param fromElement low endpoint of the returned set
     * @param fromInclusive {@code true} if the low endpoint
     *        is to be included in the returned view
     * @param toElement high endpoint of the returned set
     * @param toInclusive {@code true} if the high endpoint
     *        is to be included in the returned view
     * @return a view of the portion of this set whose elements range from
     *         {@code fromElement}, inclusive, to {@code toElement}, exclusive
     * @throws ClassCastException if {@code fromElement} and
     *         {@code 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 {@code fromElement} or
     *         {@code toElement} cannot be compared to elements currently in
     *         the set.
     * @throws NullPointerException if {@code fromElement} or
     *         {@code toElement} is null and this set does
     *         not permit null elements
     * @throws IllegalArgumentException if {@code fromElement} is
     *         greater than {@code toElement}; or if this set itself
     *         has a restricted range, and {@code fromElement} or
     *         {@code toElement} lies outside the bounds of the range.
     */
    NavigableSet<E> subSet(E fromElement, boolean fromInclusive,
                           E toElement,   boolean toInclusive);

    
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. 
Params:
  • toElement – high endpoint of the returned set
  • inclusive – true if the high endpoint is to be included in the returned view
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
Returns:a view of the portion of this set whose elements are less than (or equal to, if inclusive is true) toElement
/**
     * Returns a view of the portion of this set whose elements are less than
     * (or equal to, if {@code inclusive} is true) {@code 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.
     *
     * <p>The returned set will throw an {@code IllegalArgumentException}
     * on an attempt to insert an element outside its range.
     *
     * @param toElement high endpoint of the returned set
     * @param inclusive {@code true} if the high endpoint
     *        is to be included in the returned view
     * @return a view of the portion of this set whose elements are less than
     *         (or equal to, if {@code inclusive} is true) {@code toElement}
     * @throws ClassCastException if {@code toElement} is not compatible
     *         with this set's comparator (or, if the set has no comparator,
     *         if {@code toElement} does not implement {@link Comparable}).
     *         Implementations may, but are not required to, throw this
     *         exception if {@code toElement} cannot be compared to elements
     *         currently in the set.
     * @throws NullPointerException if {@code toElement} is null and
     *         this set does not permit null elements
     * @throws IllegalArgumentException if this set itself has a
     *         restricted range, and {@code toElement} lies outside the
     *         bounds of the range
     */
    NavigableSet<E> headSet(E toElement, 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. 
Params:
  • fromElement – low endpoint of the returned set
  • inclusive – true if the low endpoint is to be included in the returned view
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
Returns:a view of the portion of this set whose elements are greater than or equal to fromElement
/**
     * Returns a view of the portion of this set whose elements are greater
     * than (or equal to, if {@code inclusive} is true) {@code 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.
     *
     * <p>The returned set will throw an {@code IllegalArgumentException}
     * on an attempt to insert an element outside its range.
     *
     * @param fromElement low endpoint of the returned set
     * @param inclusive {@code true} if the low endpoint
     *        is to be included in the returned view
     * @return a view of the portion of this set whose elements are greater
     *         than or equal to {@code fromElement}
     * @throws ClassCastException if {@code fromElement} is not compatible
     *         with this set's comparator (or, if the set has no comparator,
     *         if {@code fromElement} does not implement {@link Comparable}).
     *         Implementations may, but are not required to, throw this
     *         exception if {@code fromElement} cannot be compared to elements
     *         currently in the set.
     * @throws NullPointerException if {@code fromElement} is null
     *         and this set does not permit null elements
     * @throws IllegalArgumentException if this set itself has a
     *         restricted range, and {@code fromElement} lies outside the
     *         bounds of the range
     */
    NavigableSet<E> tailSet(E fromElement, boolean inclusive);

    
{@inheritDoc}

Equivalent to subSet(fromElement, true, toElement, false). 
Throws:
/**
     * {@inheritDoc}
     *
     * <p>Equivalent to {@code subSet(fromElement, true, toElement, false)}.
     *
     * @throws ClassCastException       {@inheritDoc}
     * @throws NullPointerException     {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     */
    SortedSet<E> subSet(E fromElement, E toElement);

    
{@inheritDoc}

Equivalent to headSet(toElement, false). 
Throws:
/**
     * {@inheritDoc}
     *
     * <p>Equivalent to {@code headSet(toElement, false)}.
     *
     * @throws ClassCastException       {@inheritDoc}
     * @throws NullPointerException     {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     */
    SortedSet<E> headSet(E toElement);

    
{@inheritDoc}

Equivalent to tailSet(fromElement, true). 
Throws:
/**
     * {@inheritDoc}
     *
     * <p>Equivalent to {@code tailSet(fromElement, true)}.
     *
     * @throws ClassCastException       {@inheritDoc}
     * @throws NullPointerException     {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     */
    SortedSet<E> tailSet(E fromElement);
}