NavigableMap.java

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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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 *
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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>Implementations of entry-returning methods are expected to
 * return {@code Map.Entry} pairs representing snapshots of mappings
 * at the time they were produced, and thus generally do <em>not</em>
 * support the optional {@code Entry.setValue} method. Note however
 * that it is possible to change mappings in the associated map using
 * method {@code put}.
 *
 * <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>.
 *
 * @param <K> the type of keys maintained by this map
 * @param <V> the type of mapped values
 *
 * @author Doug Lea
 * @author Josh Bloch
 * @since 1.6
 */
// 可导航Map的接口，要求Map必须有序，支持定位元素的起点/终点和前驱/后继，以及截取子视图
public interface NavigableMap<K, V> extends SortedMap<K, V> {
    
    /**
     * 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
     */
    /*
     * 〖前驱〗
     * 获取【backing区间】中尽量靠右侧的，且其targetKey<key的【可视】元素，并返回其key
     * （这里的关系运算符标记的是元素遍历的先后关系）
     */
    K lowerKey(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
     */
    /*
     * 〖后继〗
     * 获取【backing区间】中尽量靠左侧的，且其targetKey>key的【可视】元素
     * （这里的关系运算符标记的是元素遍历的先后关系）
     */
    K higherKey(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
     */
    /*
     * 【前驱】
     * 获取【backing区间】中尽量靠右侧的，且其targetKey<=key的【可视】元素
     * （这里的关系运算符标记的是元素遍历的先后关系）
     */
    K floorKey(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
     */
    /*
     * 【后继】
     * 获取【backing区间】中尽量靠左侧的，且其targetKey>=key的【可视】元素
     * （这里的关系运算符标记的是元素遍历的先后关系）
     */
    K ceilingKey(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
     */
    // 获取【backing区间】中尽量靠左侧的【可视】元素，然后将其包装为只读entry返回
    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
     */
    // 获取【backing区间】中尽量靠右侧的【可视】元素，然后将其包装为只读entry返回
    Map.Entry<K, V> lastEntry();
    
    /**
     * 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
     */
    /*
     * 〖前驱〗
     * 获取【backing区间】中尽量靠右侧的，且其targetKey<key的【可视】元素，然后将其包装为只读entry返回
     * （这里的关系运算符标记的是元素遍历的先后关系）
     */
    Map.Entry<K, V> lowerEntry(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
     */
    /*
     * 〖后继〗
     * 获取【backing区间】中尽量靠左侧的，且其targetKey>key的【可视】元素，然后将其包装为只读entry返回
     * （这里的关系运算符标记的是元素遍历的先后关系）
     */
    Map.Entry<K, V> higherEntry(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
     */
    /*
     * 【前驱】
     * 获取【backing区间】中尽量靠右侧的，且其targetKey<=key的【可视】元素，然后将其包装为只读entry返回
     * （这里的关系运算符标记的是元素遍历的先后关系）
     */
    Map.Entry<K, V> floorEntry(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
     */
    /*
     * 【后继】
     * 获取【backing区间】中尽量靠左侧的，且其targetKey>=key的【可视】元素，然后将其包装为只读entry返回
     * （这里的关系运算符标记的是元素遍历的先后关系）
     */
    Map.Entry<K, V> ceilingEntry(K key);
    
    
    /**
     * Removes and returns a key-value mapping associated with
     * the least key in this map, or {@code null} if the map is empty.
     *
     * @return the removed first entry of this map,
     * or {@code null} if this map is empty
     */
    // 移除【backing区间】中尽量靠左侧的【可视】元素，并将其包装为只读版本的Entry后返回
    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.
     *
     * @return the removed last entry of this map,
     * or {@code null} if this map is empty
     */
    // 移除【backing区间】中尽量靠右侧的【可视】元素，并将其包装为只读版本的Entry后返回
    Map.Entry<K, V> pollLastEntry();
    
    
    /**
     * 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
     */
    // 获取当前Map中的key的集合
    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
     */
    // 获取【逆序】Map中的key的集合
    NavigableSet<K> descendingKeySet();
    
    
    /**
     * {@inheritDoc}
     *
     * <p>Equivalent to {@code subMap(fromKey, true, toKey, false)}.
     *
     * @throws ClassCastException       {@inheritDoc}
     * @throws NullPointerException     {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     */
    // 获取【理论区间】为[fromKey, toKey)的SubMap
    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}
     */
    // 获取【理论区间】上限为toKey(不包含)的SubMap
    SortedMap<K, V> headMap(K toKey);
    
    /**
     * {@inheritDoc}
     *
     * <p>Equivalent to {@code tailMap(fromKey, true)}.
     *
     * @throws ClassCastException       {@inheritDoc}
     * @throws NullPointerException     {@inheritDoc}
     * @throws IllegalArgumentException {@inheritDoc}
     */
    // 获取【理论区间】下限为fromKey(包含)的SubMap
    SortedMap<K, V> tailMap(K fromKey);
    
    
    /**
     * 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
     */
    // 获取【理论区间】为〖fromKey, toKey〗的SubMap，区间下限/上限是否为闭区间由fromInclusive和toInclusive参数决定
    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
     */
    // 获取【理论区间】上限为toKey的SubMap，区间上限是否为闭区间由inclusive参数决定
    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
     */
    // 获取【理论区间】下限为fromKey的SubMap，区间下限是否为闭区间由inclusive参数决定
    NavigableMap<K, V> tailMap(K fromKey, boolean inclusive);
    
    
    /**
     * 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
     */
    // 获取【逆序】Map
    NavigableMap<K, V> descendingMap();
    
}