src/java.base/share/classes/java/util/NavigableMap.java

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 * published by the Free Software Foundation.  Oracle designates this
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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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 {@link SortedMap} extended with navigation methods returning the
 * closest matches for given search targets. Methods
 * {@link #lowerEntry}, {@link #floorEntry}, {@link #ceilingEntry},
 * and {@link #higherEntry} return {@code Map.Entry} objects
 * associated with keys respectively less than, less than or equal,
 * greater than or equal, and greater than a given key, returning
 * {@code null} if there is no such key.  Similarly, methods
 * {@link #lowerKey}, {@link #floorKey}, {@link #ceilingKey}, and
 * {@link #higherKey} return only the associated keys. All of these
 * methods are designed for locating, not traversing entries.
 *
 * <p>A {@code NavigableMap} may be accessed and traversed in either
 * ascending or descending key order.  The {@link #descendingMap}
 * method returns a view of the map 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.  Methods
 * {@link #subMap(Object, boolean, Object, boolean) subMap(K, boolean, K, boolean)},
 * {@link #headMap(Object, boolean) headMap(K, boolean)}, and
 * {@link #tailMap(Object, boolean) tailMap(K, boolean)}
 * differ from the like-named {@code SortedMap} methods in accepting
 * additional arguments describing whether lower and upper bounds are
 * inclusive versus exclusive.  Submaps of any {@code NavigableMap}
 * must implement the {@code NavigableMap} interface.
 *
 * <p>This interface additionally defines methods {@link #firstEntry},
 * {@link #pollFirstEntry}, {@link #lastEntry}, and
 * {@link #pollLastEntry} that return and/or remove the least and
 * greatest mappings, if any exist, else returning {@code null}.
 *
 * <p>The methods
 * {@link #ceilingEntry},
 * {@link #firstEntry},
 * {@link #floorEntry},
 * {@link #higherEntry},
 * {@link #lastEntry},
 * {@link #lowerEntry},
 * {@link #pollFirstEntry}, and
 * {@link #pollLastEntry}
 * return {@link Map.Entry} instances that represent snapshots of mappings as
 * of the time of the call. They do <em>not</em> support mutation of the
 * underlying map via the optional {@link Map.Entry#setValue setValue} method.
 *
 * <p>Methods
 * {@link #subMap(Object, Object) subMap(K, K)},
 * {@link #headMap(Object) headMap(K)}, and
 * {@link #tailMap(Object) tailMap(K)}
 * are specified to return {@code SortedMap} to allow existing
 * implementations of {@code SortedMap} to be compatibly retrofitted to
 * implement {@code NavigableMap}, but extensions and implementations
 * of this interface are encouraged to override these methods to return
 * {@code NavigableMap}.  Similarly,
 * {@link #keySet()} can be overridden to return {@link 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 <K> the type of keys maintained by this map
 * @param <V> the type of mapped values
 * @since 1.6
 */
public interface NavigableMap<K,V> extends SortedMap<K,V> {
    /**
     * Returns a key-value mapping associated with the greatest key
     * strictly less than the given key, or {@code null} if there is
     * no such key.
     *
     * @param key the key
     * @return an entry with the greatest key less than {@code key},
     *         or {@code null} if there is no such key
     * @throws ClassCastException if the specified key cannot be compared
     *         with the keys currently in the map
     * @throws NullPointerException if the specified key is null
     *         and this map does not permit null keys
     */
    Map.Entry<K,V> lowerEntry(K key);

    /**
     * Returns the greatest key strictly less than the given key, or
     * {@code null} if there is no such key.
     *
     * @param key the key
     * @return the greatest key less than {@code key},
     *         or {@code null} if there is no such key
     * @throws ClassCastException if the specified key cannot be compared
     *         with the keys currently in the map
     * @throws NullPointerException if the specified key is null
     *         and this map does not permit null keys
     */
    K lowerKey(K key);

    /**
     * Returns a key-value mapping associated with the greatest key
     * less than or equal to the given key, or {@code null} if there
     * is no such key.
     *
     * @param key the key
     * @return an entry with the greatest key less than or equal to
     *         {@code key}, or {@code null} if there is no such key
     * @throws ClassCastException if the specified key cannot be compared
     *         with the keys currently in the map
     * @throws NullPointerException if the specified key is null
     *         and this map does not permit null keys
     */
    Map.Entry<K,V> floorEntry(K key);

    /**
     * Returns the greatest key less than or equal to the given key,
     * or {@code null} if there is no such key.
     *
     * @param key the key
     * @return the greatest key less than or equal to {@code key},
     *         or {@code null} if there is no such key
     * @throws ClassCastException if the specified key cannot be compared
     *         with the keys currently in the map
     * @throws NullPointerException if the specified key is null
     *         and this map does not permit null keys
     */
    K floorKey(K key);

    /**
     * Returns a key-value mapping associated with the least key
     * greater than or equal to the given key, or {@code null} if
     * there is no such key.
     *
     * @param key the key
     * @return an entry with the least key greater than or equal to
     *         {@code key}, or {@code null} if there is no such key
     * @throws ClassCastException if the specified key cannot be compared
     *         with the keys currently in the map
     * @throws NullPointerException if the specified key is null
     *         and this map does not permit null keys
     */
    Map.Entry<K,V> ceilingEntry(K key);

    /**
     * Returns the least key greater than or equal to the given key,
     * or {@code null} if there is no such key.
     *
     * @param key the key
     * @return the least key greater than or equal to {@code key},
     *         or {@code null} if there is no such key
     * @throws ClassCastException if the specified key cannot be compared
     *         with the keys currently in the map
     * @throws NullPointerException if the specified key is null
     *         and this map does not permit null keys
     */
    K ceilingKey(K key);

    /**
     * Returns a key-value mapping associated with the least key
     * strictly greater than the given key, or {@code null} if there
     * is no such key.
     *
     * @param key the key
     * @return an entry with the least key greater than {@code key},
     *         or {@code null} if there is no such key
     * @throws ClassCastException if the specified key cannot be compared
     *         with the keys currently in the map
     * @throws NullPointerException if the specified key is null
     *         and this map does not permit null keys
     */
    Map.Entry<K,V> higherEntry(K key);

    /**
     * Returns the least key strictly greater than the given key, or
     * {@code null} if there is no such key.
     *
     * @param key the key
     * @return the least key greater than {@code key},
     *         or {@code null} if there is no such key
     * @throws ClassCastException if the specified key cannot be compared
     *         with the keys currently in the map
     * @throws NullPointerException if the specified key is null
     *         and this map does not permit null keys
     */
    K higherKey(K key);

    /**
     * Returns a key-value mapping associated with the least
     * key in this map, or {@code null} if the map is empty.
     *
     * @return an entry with the least key,
     *         or {@code null} if this map is empty
     */
    Map.Entry<K,V> firstEntry();

    /**
     * Returns a key-value mapping associated with the greatest
     * key in this map, or {@code null} if the map is empty.
     *
     * @return an entry with the greatest key,
     *         or {@code null} if this map is empty
     */
    Map.Entry<K,V> lastEntry();

    /**
     * Removes and returns a key-value mapping associated with
     * the least key in this map, or {@code null} if the map is empty
     * (optional operation).
     *
     * @return the removed first entry of this map,
     *         or {@code null} if this map is empty
     *
     * @throws UnsupportedOperationException if the {@code pollFirstEntry}
     *         operation is not supported by this map
     */
    Map.Entry<K,V> pollFirstEntry();

    /**
     * Removes and returns a key-value mapping associated with
     * the greatest key in this map, or {@code null} if the map is empty
     * (optional operation).
     *
     * @return the removed last entry of this map,
     *         or {@code null} if this map is empty
     *
     * @throws UnsupportedOperationException if the {@code pollLastEntry}
     *         operation is not supported by this map
     */
    Map.Entry<K,V> pollLastEntry();

    /**
     * Returns a reverse order view of the mappings contained in this map.
     * The descending map is backed by this map, so changes to the map are
     * reflected in the descending map, and vice-versa.  If either map is
     * modified while an iteration over a collection view of either map
     * is in progress (except through the iterator's own {@code remove}
     * operation), the results of the iteration are undefined.
     *
     * <p>The returned map has an ordering equivalent to
     * {@link Collections#reverseOrder(Comparator) Collections.reverseOrder}{@code (comparator())}.
     * The expression {@code m.descendingMap().descendingMap()} returns a
     * view of {@code m} essentially equivalent to {@code m}.
     *
     * @return a reverse order view of this map
     */
    NavigableMap<K,V> descendingMap();

    /**
     * Returns a {@link NavigableSet} view of the keys contained in this map.
     * The set's iterator returns the keys in ascending order.
     * The set is backed by the map, so changes to the map are reflected in
     * the set, and vice-versa.  If the map is modified while an iteration
     * over the set is in progress (except through the iterator's own {@code
     * remove} operation), the results of the iteration are undefined.  The
     * set supports element removal, which removes the corresponding mapping
     * from the map, via the {@code Iterator.remove}, {@code Set.remove},
     * {@code removeAll}, {@code retainAll}, and {@code clear} operations.
     * It does not support the {@code add} or {@code addAll} operations.
     *
     * @return a navigable set view of the keys in this map
     */
    NavigableSet<K> navigableKeySet();

    /**
     * Returns a reverse order {@link NavigableSet} view of the keys contained in this map.
     * The set's iterator returns the keys in descending order.
     * The set is backed by the map, so changes to the map are reflected in
     * the set, and vice-versa.  If the map is modified while an iteration
     * over the set is in progress (except through the iterator's own {@code
     * remove} operation), the results of the iteration are undefined.  The
     * set supports element removal, which removes the corresponding mapping
     * from the map, via the {@code Iterator.remove}, {@code Set.remove},
     * {@code removeAll}, {@code retainAll}, and {@code clear} operations.
     * It does not support the {@code add} or {@code addAll} operations.
     *
     * @return a reverse order navigable set view of the keys in this map
     */
    NavigableSet<K> descendingKeySet();

    /**
     * Returns a view of the portion of this map whose keys range from
     * {@code fromKey} to {@code toKey}.  If {@code fromKey} and
     * {@code toKey} are equal, the returned map is empty unless
     * {@code fromInclusive} and {@code toInclusive} are both true.  The
     * returned map is backed by this map, so changes in the returned map are
     * reflected in this map, and vice-versa.  The returned map supports all
     * optional map operations that this map supports.
     *
     * <p>The returned map will throw an {@code IllegalArgumentException}
     * on an attempt to insert a key outside of its range, or to construct a
     * submap either of whose endpoints lie outside its range.
     *
     * @param fromKey low endpoint of the keys in the returned map
     * @param fromInclusive {@code true} if the low endpoint
     *        is to be included in the returned view
     * @param toKey high endpoint of the keys in the returned map
     * @param toInclusive {@code true} if the high endpoint
     *        is to be included in the returned view
     * @return a view of the portion of this map whose keys range from
     *         {@code fromKey} to {@code toKey}
     * @throws ClassCastException if {@code fromKey} and {@code toKey}
     *         cannot be compared to one another using this map's comparator
     *         (or, if the map has no comparator, using natural ordering).
     *         Implementations may, but are not required to, throw this
     *         exception if {@code fromKey} or {@code toKey}
     *         cannot be compared to keys currently in the map.
     * @throws NullPointerException if {@code fromKey} or {@code toKey}
     *         is null and this map does not permit null keys
     * @throws IllegalArgumentException if {@code fromKey} is greater than
     *         {@code toKey}; or if this map itself has a restricted
     *         range, and {@code fromKey} or {@code toKey} lies
     *         outside the bounds of the range
     */
    NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive,
                             K toKey,   boolean toInclusive);

    /**
     * Returns a view of the portion of this map whose keys are less than (or
     * equal to, if {@code inclusive} is true) {@code toKey}.  The returned
     * map is backed by this map, so changes in the returned map are reflected
     * in this map, and vice-versa.  The returned map supports all optional
     * map operations that this map supports.
     *
     * <p>The returned map will throw an {@code IllegalArgumentException}
     * on an attempt to insert a key outside its range.
     *
     * @param toKey high endpoint of the keys in the returned map
     * @param inclusive {@code true} if the high endpoint
     *        is to be included in the returned view
     * @return a view of the portion of this map whose keys are less than
     *         (or equal to, if {@code inclusive} is true) {@code toKey}
     * @throws ClassCastException if {@code toKey} is not compatible
     *         with this map's comparator (or, if the map has no comparator,
     *         if {@code toKey} does not implement {@link Comparable}).
     *         Implementations may, but are not required to, throw this
     *         exception if {@code toKey} cannot be compared to keys
     *         currently in the map.
     * @throws NullPointerException if {@code toKey} is null
     *         and this map does not permit null keys
     * @throws IllegalArgumentException if this map itself has a
     *         restricted range, and {@code toKey} lies outside the
     *         bounds of the range
     */
    NavigableMap<K,V> headMap(K toKey, boolean inclusive);

    /**
     * Returns a view of the portion of this map whose keys are greater than (or
     * equal to, if {@code inclusive} is true) {@code fromKey}.  The returned
     * map is backed by this map, so changes in the returned map are reflected
     * in this map, and vice-versa.  The returned map supports all optional
     * map operations that this map supports.
     *
     * <p>The returned map will throw an {@code IllegalArgumentException}
     * on an attempt to insert a key outside its range.
     *
     * @param fromKey low endpoint of the keys in the returned map
     * @param inclusive {@code true} if the low endpoint
     *        is to be included in the returned view
     * @return a view of the portion of this map whose keys are greater than
     *         (or equal to, if {@code inclusive} is true) {@code fromKey}
     * @throws ClassCastException if {@code fromKey} is not compatible
     *         with this map's comparator (or, if the map has no comparator,
     *         if {@code fromKey} does not implement {@link Comparable}).
     *         Implementations may, but are not required to, throw this
     *         exception if {@code fromKey} cannot be compared to keys
     *         currently in the map.
     * @throws NullPointerException if {@code fromKey} is null
     *         and this map does not permit null keys
     * @throws IllegalArgumentException if this map itself has a
     *         restricted range, and {@code fromKey} lies outside the
     *         bounds of the range
     */
    NavigableMap<K,V> tailMap(K fromKey, boolean inclusive);

    /**
     * {@inheritDoc}
     *
     * <p>Equivalent to {@code subMap(fromKey, true, toKey, false)}.
     *
     * @throws ClassCastException       {@inheritDoc}
     * @throws NullPointerException     {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     */
    SortedMap<K,V> subMap(K fromKey, K toKey);

    /**
     * {@inheritDoc}
     *
     * <p>Equivalent to {@code headMap(toKey, false)}.
     *
     * @throws ClassCastException       {@inheritDoc}
     * @throws NullPointerException     {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     */
    SortedMap<K,V> headMap(K toKey);

    /**
     * {@inheritDoc}
     *
     * <p>Equivalent to {@code tailMap(fromKey, true)}.
     *
     * @throws ClassCastException       {@inheritDoc}
     * @throws NullPointerException     {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     */
    SortedMap<K,V> tailMap(K fromKey);

    /**
     * {@inheritDoc}
     * <p>
     * This method is equivalent to {@link #descendingMap descendingMap}.
     *
     * @implSpec
     * The implementation in this interface returns the result of calling the
     * {@code descendingMap} method.
     *
     * @return a reverse-ordered view of this map, as a {@code NavigableMap}
     * @since 21
     */
    default NavigableMap<K, V> reversed() {
        return this.descendingMap();
    }
}