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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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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

 * particular file as subject to the "Classpath" exception as provided

 * 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

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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

 */

package java.util;

/**

 * A {@link SortedSet} extended with navigation methods reporting

 * closest matches for given search targets. Methods {@code lower},

 * {@code floor}, {@code ceiling}, and {@code 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.  A {@code NavigableSet} may be accessed and

 * traversed in either ascending or descending order.  The {@code

 * 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

 * {@code pollFirst} and {@code pollLast} that return and remove the

 * lowest and highest element, if one exists, else returning {@code

 * null}.  Methods {@code subSet}, {@code headSet},

 * and {@code tailSet} 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}/../technotes/guides/collections/index.html">

 * 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 {@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 {@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 {@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 {@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 {@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 {@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.

     *

     * @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 {@code remove} operation), the results of

     * the iteration are undefined.

     *

     * <p>The returned set has an ordering equivalent to

     * <tt>{@link Collections#reverseOrder(Comparator) Collections.reverseOrder}(comparator())</tt>.

     * 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 {@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

     * {@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 {@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 {@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}

     *

     * <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}

     *

     * <p>Equivalent to {@code headSet(toElement, false)}.

     *

     * @throws ClassCastException       {@inheritDoc}

     * @throws NullPointerException     {@inheritDoc}

     * @throws IllegalArgumentException {@inheritDoc}

na     */

    SortedSet<E> headSet(E toElement);

    /**

     * {@inheritDoc}

     *

     * <p>Equivalent to {@code tailSet(fromElement, true)}.

     *

     * @throws ClassCastException       {@inheritDoc}

     * @throws NullPointerException     {@inheritDoc}

     * @throws IllegalArgumentException {@inheritDoc}

     */

    SortedSet<E> tailSet(E fromElement);

}