java/util/NavigableMap.java

/*
 * 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
 * {@code lowerEntry}, {@code floorEntry}, {@code ceilingEntry},
 * and {@code 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
 * {@code lowerKey}, {@code floorKey}, {@code ceilingKey}, and
 * {@code 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 {@code 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 {@code subMap}, {@code headMap},
 * and {@code tailMap} 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 {@code firstEntry},
 * {@code pollFirstEntry}, {@code lastEntry}, and
 * {@code 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 {@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 <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.
     *
     * @return the removed first entry of this map,
     *         or {@code null} if this map is empty
     */
    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
     */
    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
     * <tt>{@link Collections#reverseOrder(Comparator) Collections.reverseOrder}(comparator())</tt>.
     * 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 fromExclusive} and {@code toExclusive} 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);
}
Revision:	1.1
Committed:	Sun Dec 16 20:55:09 2012 UTC (11 years, 5 months ago) by dl
Branch:	MAIN
Log Message:	Create src/jdk7 package
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea and Josh Bloch with assistance from members of JCP
3			* JSR-166 Expert Group and released to the public domain, as explained at
4			* http://creativecommons.org/publicdomain/zero/1.0/
5			*/
6
7			package java.util;
8
9			/**
10			* A {@link SortedMap} extended with navigation methods returning the
11			* closest matches for given search targets. Methods
12			* {@code lowerEntry}, {@code floorEntry}, {@code ceilingEntry},
13			* and {@code higherEntry} return {@code Map.Entry} objects
14			* associated with keys respectively less than, less than or equal,
15			* greater than or equal, and greater than a given key, returning
16			* {@code null} if there is no such key. Similarly, methods
17			* {@code lowerKey}, {@code floorKey}, {@code ceilingKey}, and
18			* {@code higherKey} return only the associated keys. All of these
19			* methods are designed for locating, not traversing entries.
20			*
21			* <p>A {@code NavigableMap} may be accessed and traversed in either
22			* ascending or descending key order. The {@code descendingMap}
23			* method returns a view of the map with the senses of all relational
24			* and directional methods inverted. The performance of ascending
25			* operations and views is likely to be faster than that of descending
26			* ones. Methods {@code subMap}, {@code headMap},
27			* and {@code tailMap} differ from the like-named {@code
28			* SortedMap} methods in accepting additional arguments describing
29			* whether lower and upper bounds are inclusive versus exclusive.
30			* Submaps of any {@code NavigableMap} must implement the {@code
31			* NavigableMap} interface.
32			*
33			* <p>This interface additionally defines methods {@code firstEntry},
34			* {@code pollFirstEntry}, {@code lastEntry}, and
35			* {@code pollLastEntry} that return and/or remove the least and
36			* greatest mappings, if any exist, else returning {@code null}.
37			*
38			* <p>Implementations of entry-returning methods are expected to
39			* return {@code Map.Entry} pairs representing snapshots of mappings
40			* at the time they were produced, and thus generally do <em>not</em>
41			* support the optional {@code Entry.setValue} method. Note however
42			* that it is possible to change mappings in the associated map using
43			* method {@code put}.
44			*
45			* <p>Methods
46			* {@link #subMap(Object, Object) subMap(K, K)},
47			* {@link #headMap(Object) headMap(K)}, and
48			* {@link #tailMap(Object) tailMap(K)}
49			* are specified to return {@code SortedMap} to allow existing
50			* implementations of {@code SortedMap} to be compatibly retrofitted to
51			* implement {@code NavigableMap}, but extensions and implementations
52			* of this interface are encouraged to override these methods to return
53			* {@code NavigableMap}. Similarly,
54			* {@link #keySet()} can be overridden to return {@code NavigableSet}.
55			*
56			* <p>This interface is a member of the
57			* <a href="{@docRoot}/../technotes/guides/collections/index.html">
58			* Java Collections Framework</a>.
59			*
60			* @author Doug Lea
61			* @author Josh Bloch
62			* @param <K> the type of keys maintained by this map
63			* @param <V> the type of mapped values
64			* @since 1.6
65			*/
66			public interface NavigableMap<K,V> extends SortedMap<K,V> {
67			/**
68			* Returns a key-value mapping associated with the greatest key
69			* strictly less than the given key, or {@code null} if there is
70			* no such key.
71			*
72			* @param key the key
73			* @return an entry with the greatest key less than {@code key},
74			* or {@code null} if there is no such key
75			* @throws ClassCastException if the specified key cannot be compared
76			* with the keys currently in the map
77			* @throws NullPointerException if the specified key is null
78			* and this map does not permit null keys
79			*/
80			Map.Entry<K,V> lowerEntry(K key);
81
82			/**
83			* Returns the greatest key strictly less than the given key, or
84			* {@code null} if there is no such key.
85			*
86			* @param key the key
87			* @return the greatest key less than {@code key},
88			* or {@code null} if there is no such key
89			* @throws ClassCastException if the specified key cannot be compared
90			* with the keys currently in the map
91			* @throws NullPointerException if the specified key is null
92			* and this map does not permit null keys
93			*/
94			K lowerKey(K key);
95
96			/**
97			* Returns a key-value mapping associated with the greatest key
98			* less than or equal to the given key, or {@code null} if there
99			* is no such key.
100			*
101			* @param key the key
102			* @return an entry with the greatest key less than or equal to
103			* {@code key}, or {@code null} if there is no such key
104			* @throws ClassCastException if the specified key cannot be compared
105			* with the keys currently in the map
106			* @throws NullPointerException if the specified key is null
107			* and this map does not permit null keys
108			*/
109			Map.Entry<K,V> floorEntry(K key);
110
111			/**
112			* Returns the greatest key less than or equal to the given key,
113			* or {@code null} if there is no such key.
114			*
115			* @param key the key
116			* @return the greatest key less than or equal to {@code key},
117			* or {@code null} if there is no such key
118			* @throws ClassCastException if the specified key cannot be compared
119			* with the keys currently in the map
120			* @throws NullPointerException if the specified key is null
121			* and this map does not permit null keys
122			*/
123			K floorKey(K key);
124
125			/**
126			* Returns a key-value mapping associated with the least key
127			* greater than or equal to the given key, or {@code null} if
128			* there is no such key.
129			*
130			* @param key the key
131			* @return an entry with the least key greater than or equal to
132			* {@code key}, or {@code null} if there is no such key
133			* @throws ClassCastException if the specified key cannot be compared
134			* with the keys currently in the map
135			* @throws NullPointerException if the specified key is null
136			* and this map does not permit null keys
137			*/
138			Map.Entry<K,V> ceilingEntry(K key);
139
140			/**
141			* Returns the least key greater than or equal to the given key,
142			* or {@code null} if there is no such key.
143			*
144			* @param key the key
145			* @return the least key greater than or equal to {@code key},
146			* or {@code null} if there is no such key
147			* @throws ClassCastException if the specified key cannot be compared
148			* with the keys currently in the map
149			* @throws NullPointerException if the specified key is null
150			* and this map does not permit null keys
151			*/
152			K ceilingKey(K key);
153
154			/**
155			* Returns a key-value mapping associated with the least key
156			* strictly greater than the given key, or {@code null} if there
157			* is no such key.
158			*
159			* @param key the key
160			* @return an entry with the least key greater than {@code key},
161			* or {@code null} if there is no such key
162			* @throws ClassCastException if the specified key cannot be compared
163			* with the keys currently in the map
164			* @throws NullPointerException if the specified key is null
165			* and this map does not permit null keys
166			*/
167			Map.Entry<K,V> higherEntry(K key);
168
169			/**
170			* Returns the least key strictly greater than the given key, or
171			* {@code null} if there is no such key.
172			*
173			* @param key the key
174			* @return the least key greater than {@code key},
175			* or {@code null} if there is no such key
176			* @throws ClassCastException if the specified key cannot be compared
177			* with the keys currently in the map
178			* @throws NullPointerException if the specified key is null
179			* and this map does not permit null keys
180			*/
181			K higherKey(K key);
182
183			/**
184			* Returns a key-value mapping associated with the least
185			* key in this map, or {@code null} if the map is empty.
186			*
187			* @return an entry with the least key,
188			* or {@code null} if this map is empty
189			*/
190			Map.Entry<K,V> firstEntry();
191
192			/**
193			* Returns a key-value mapping associated with the greatest
194			* key in this map, or {@code null} if the map is empty.
195			*
196			* @return an entry with the greatest key,
197			* or {@code null} if this map is empty
198			*/
199			Map.Entry<K,V> lastEntry();
200
201			/**
202			* Removes and returns a key-value mapping associated with
203			* the least key in this map, or {@code null} if the map is empty.
204			*
205			* @return the removed first entry of this map,
206			* or {@code null} if this map is empty
207			*/
208			Map.Entry<K,V> pollFirstEntry();
209
210			/**
211			* Removes and returns a key-value mapping associated with
212			* the greatest key in this map, or {@code null} if the map is empty.
213			*
214			* @return the removed last entry of this map,
215			* or {@code null} if this map is empty
216			*/
217			Map.Entry<K,V> pollLastEntry();
218
219			/**
220			* Returns a reverse order view of the mappings contained in this map.
221			* The descending map is backed by this map, so changes to the map are
222			* reflected in the descending map, and vice-versa. If either map is
223			* modified while an iteration over a collection view of either map
224			* is in progress (except through the iterator's own {@code remove}
225			* operation), the results of the iteration are undefined.
226			*
227			* <p>The returned map has an ordering equivalent to
228			* <tt>{@link Collections#reverseOrder(Comparator) Collections.reverseOrder}(comparator())</tt>.
229			* The expression {@code m.descendingMap().descendingMap()} returns a
230			* view of {@code m} essentially equivalent to {@code m}.
231			*
232			* @return a reverse order view of this map
233			*/
234			NavigableMap<K,V> descendingMap();
235
236			/**
237			* Returns a {@link NavigableSet} view of the keys contained in this map.
238			* The set's iterator returns the keys in ascending order.
239			* The set is backed by the map, so changes to the map are reflected in
240			* the set, and vice-versa. If the map is modified while an iteration
241			* over the set is in progress (except through the iterator's own {@code
242			* remove} operation), the results of the iteration are undefined. The
243			* set supports element removal, which removes the corresponding mapping
244			* from the map, via the {@code Iterator.remove}, {@code Set.remove},
245			* {@code removeAll}, {@code retainAll}, and {@code clear} operations.
246			* It does not support the {@code add} or {@code addAll} operations.
247			*
248			* @return a navigable set view of the keys in this map
249			*/
250			NavigableSet<K> navigableKeySet();
251
252			/**
253			* Returns a reverse order {@link NavigableSet} view of the keys contained in this map.
254			* The set's iterator returns the keys in descending order.
255			* The set is backed by the map, so changes to the map are reflected in
256			* the set, and vice-versa. If the map is modified while an iteration
257			* over the set is in progress (except through the iterator's own {@code
258			* remove} operation), the results of the iteration are undefined. The
259			* set supports element removal, which removes the corresponding mapping
260			* from the map, via the {@code Iterator.remove}, {@code Set.remove},
261			* {@code removeAll}, {@code retainAll}, and {@code clear} operations.
262			* It does not support the {@code add} or {@code addAll} operations.
263			*
264			* @return a reverse order navigable set view of the keys in this map
265			*/
266			NavigableSet<K> descendingKeySet();
267
268			/**
269			* Returns a view of the portion of this map whose keys range from
270			* {@code fromKey} to {@code toKey}. If {@code fromKey} and
271			* {@code toKey} are equal, the returned map is empty unless
272			* {@code fromExclusive} and {@code toExclusive} are both true. The
273			* returned map is backed by this map, so changes in the returned map are
274			* reflected in this map, and vice-versa. The returned map supports all
275			* optional map operations that this map supports.
276			*
277			* <p>The returned map will throw an {@code IllegalArgumentException}
278			* on an attempt to insert a key outside of its range, or to construct a
279			* submap either of whose endpoints lie outside its range.
280			*
281			* @param fromKey low endpoint of the keys in the returned map
282			* @param fromInclusive {@code true} if the low endpoint
283			* is to be included in the returned view
284			* @param toKey high endpoint of the keys in the returned map
285			* @param toInclusive {@code true} if the high endpoint
286			* is to be included in the returned view
287			* @return a view of the portion of this map whose keys range from
288			* {@code fromKey} to {@code toKey}
289			* @throws ClassCastException if {@code fromKey} and {@code toKey}
290			* cannot be compared to one another using this map's comparator
291			* (or, if the map has no comparator, using natural ordering).
292			* Implementations may, but are not required to, throw this
293			* exception if {@code fromKey} or {@code toKey}
294			* cannot be compared to keys currently in the map.
295			* @throws NullPointerException if {@code fromKey} or {@code toKey}
296			* is null and this map does not permit null keys
297			* @throws IllegalArgumentException if {@code fromKey} is greater than
298			* {@code toKey}; or if this map itself has a restricted
299			* range, and {@code fromKey} or {@code toKey} lies
300			* outside the bounds of the range
301			*/
302			NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive,
303			K toKey, boolean toInclusive);
304
305			/**
306			* Returns a view of the portion of this map whose keys are less than (or
307			* equal to, if {@code inclusive} is true) {@code toKey}. The returned
308			* map is backed by this map, so changes in the returned map are reflected
309			* in this map, and vice-versa. The returned map supports all optional
310			* map operations that this map supports.
311			*
312			* <p>The returned map will throw an {@code IllegalArgumentException}
313			* on an attempt to insert a key outside its range.
314			*
315			* @param toKey high endpoint of the keys in the returned map
316			* @param inclusive {@code true} if the high endpoint
317			* is to be included in the returned view
318			* @return a view of the portion of this map whose keys are less than
319			* (or equal to, if {@code inclusive} is true) {@code toKey}
320			* @throws ClassCastException if {@code toKey} is not compatible
321			* with this map's comparator (or, if the map has no comparator,
322			* if {@code toKey} does not implement {@link Comparable}).
323			* Implementations may, but are not required to, throw this
324			* exception if {@code toKey} cannot be compared to keys
325			* currently in the map.
326			* @throws NullPointerException if {@code toKey} is null
327			* and this map does not permit null keys
328			* @throws IllegalArgumentException if this map itself has a
329			* restricted range, and {@code toKey} lies outside the
330			* bounds of the range
331			*/
332			NavigableMap<K,V> headMap(K toKey, boolean inclusive);
333
334			/**
335			* Returns a view of the portion of this map whose keys are greater than (or
336			* equal to, if {@code inclusive} is true) {@code fromKey}. The returned
337			* map is backed by this map, so changes in the returned map are reflected
338			* in this map, and vice-versa. The returned map supports all optional
339			* map operations that this map supports.
340			*
341			* <p>The returned map will throw an {@code IllegalArgumentException}
342			* on an attempt to insert a key outside its range.
343			*
344			* @param fromKey low endpoint of the keys in the returned map
345			* @param inclusive {@code true} if the low endpoint
346			* is to be included in the returned view
347			* @return a view of the portion of this map whose keys are greater than
348			* (or equal to, if {@code inclusive} is true) {@code fromKey}
349			* @throws ClassCastException if {@code fromKey} is not compatible
350			* with this map's comparator (or, if the map has no comparator,
351			* if {@code fromKey} does not implement {@link Comparable}).
352			* Implementations may, but are not required to, throw this
353			* exception if {@code fromKey} cannot be compared to keys
354			* currently in the map.
355			* @throws NullPointerException if {@code fromKey} is null
356			* and this map does not permit null keys
357			* @throws IllegalArgumentException if this map itself has a
358			* restricted range, and {@code fromKey} lies outside the
359			* bounds of the range
360			*/
361			NavigableMap<K,V> tailMap(K fromKey, boolean inclusive);
362
363			/**
364			* {@inheritDoc}
365			*
366			* <p>Equivalent to {@code subMap(fromKey, true, toKey, false)}.
367			*
368			* @throws ClassCastException {@inheritDoc}
369			* @throws NullPointerException {@inheritDoc}
370			* @throws IllegalArgumentException {@inheritDoc}
371			*/
372			SortedMap<K,V> subMap(K fromKey, K toKey);
373
374			/**
375			* {@inheritDoc}
376			*
377			* <p>Equivalent to {@code headMap(toKey, false)}.
378			*
379			* @throws ClassCastException {@inheritDoc}
380			* @throws NullPointerException {@inheritDoc}
381			* @throws IllegalArgumentException {@inheritDoc}
382			*/
383			SortedMap<K,V> headMap(K toKey);
384
385			/**
386			* {@inheritDoc}
387			*
388			* <p>Equivalent to {@code tailMap(fromKey, true)}.
389			*
390			* @throws ClassCastException {@inheritDoc}
391			* @throws NullPointerException {@inheritDoc}
392			* @throws IllegalArgumentException {@inheritDoc}
393			*/
394			SortedMap<K,V> tailMap(K fromKey);
395			}