src/jsr166x/NavigableMap.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

package jsr166x;

import java.util.*;

/**
 * A {@link SortedMap} extended with navigation methods returning
 * key-value pairs holding the closest matches for given search
 * targets. Methods <tt>lowerEntry</tt>, <tt>floorEntry</tt>,
 * <tt>ceilingEntry</tt>, and <tt>higherEntry</tt> return
 * <tt>Map.Entry</tt> objects associated with keys respectively less
 * than, less than or equal, greater than or equal, and greater than a
 * given key, returning <tt>null</tt> if there is no such key.
 * Similarly, methods <tt>lowerKey</tt>, <tt>floorKey</tt>,
 * <tt>ceilingKey</tt>, and <tt>higherKey</tt> return only the
 * associated keys. All of these methods are designed for locating,
 * not traversing entries.
 *
 * <p>A <tt>NavigableMap</tt> may be viewed and traversed in either
 * ascending or descending key order.  The <tt>Map</tt> methods
 * <tt>keySet</tt> and <tt>entrySet</tt>) return ascending views, and
 * the additional methods <tt>descendingKeySet</tt> and
 * <tt>descendingEntrySet</tt>) return descending views. The
 * performance of ascending traversals is likely to be faster than
 * descending traversals.  Notice that it is possible to perform
 * subrannge traversals in either direction using <tt>SubMap</tt>.
 * 
 * <p>This interface additionally defines methods <tt>firstEntry</tt>,
 * <tt>pollFirstEntry</tt>, <tt>lastEntry</tt>, and
 * <tt>pollLastEntry</tt> that return and/or remove the least and
 * greatest mappings, if any exist, else returning <tt>null</tt>.
 *
 * <p> Implementations of entry-returning methods are expected to
 * return <tt>Map.Entry</tt> pairs representing snapshots of mappings
 * at the time they were produced, and thus generally do <em>not</em>
 * support the optional <tt>Entry.setValue</tt> method. Note however
 * that it is possible to change mappings in the associated map using
 * method <tt>put</tt>.
 *
 * @author Doug Lea
 * @param <K> the type of keys maintained by this map
 * @param <V> the type of mapped values 
 */
public interface NavigableMap<K,V> extends SortedMap<K,V> {
    /**
     * Returns a key-value mapping associated with the least key
     * greater than or equal to the given key, or <tt>null</tt> if there is
     * no such entry. 
     * 
     * @param key the key.
     * @return an Entry associated with ceiling of given key, or <tt>null</tt>
     * if there is no such Entry.
     * @throws ClassCastException if key cannot be compared with the keys
     *            currently in the map.
     * @throws NullPointerException if key is <tt>null</tt> and this map
     * does not support <tt>null</tt> keys.
     */
    public Map.Entry<K,V> ceilingEntry(K key);

    /**
     * Returns least key greater than or equal to the given key, or
     * <tt>null</tt> if there is no such key.
     * 
     * @param key the key.
     * @return the ceiling key, or <tt>null</tt>
     * if there is no such key.
     * @throws ClassCastException if key cannot be compared with the keys
     *            currently in the map.
     * @throws NullPointerException if key is <tt>null</tt> and this map
     * does not support <tt>null</tt> keys.
     */
    public K ceilingKey(K key);

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

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

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

    /**
     * Returns the greatest key
     * less than or equal to the given key, or <tt>null</tt> if there
     * is no such key.
     * 
     * @param key the key.
     * @return the floor of given key, or <tt>null</tt> if there is no
     * such key.
     * @throws ClassCastException if key cannot be compared with the keys
     *            currently in the map.
     * @throws NullPointerException if key is <tt>null</tt> and this map
     * does not support <tt>null</tt> keys.
     */
    public K floorKey(K key);

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

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

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

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

    /**
     * Removes and returns a key-value mapping associated with
     * the least key in this map, or <tt>null</tt> if the map is empty.
     * 
     * @return the removed first entry of this map, or <tt>null</tt>
     * if the map is empty.
     */
    public Map.Entry<K,V> pollFirstEntry();

    /**
     * Removes and returns a key-value mapping associated with
     * the greatest key in this map, or <tt>null</tt> if the map is empty.
     * 
     * @return the removed last entry of this map, or <tt>null</tt>
     * if the map is empty.
     */
    public Map.Entry<K,V> pollLastEntry();

    /**
     * Returns a set view of the keys contained in this map, in
     * descending key 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 <tt>remove</tt> operation),
     * the results of the iteration are undefined.  The set supports
     * element removal, which removes the corresponding mapping from
     * the map, via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
     * <tt>removeAll</tt> <tt>retainAll</tt>, and <tt>clear</tt>
     * operations.  It does not support the add or <tt>addAll</tt>
     * operations.
     *
     * @return a set view of the keys contained in this map.
     */
    Set<K> descendingKeySet();

    /**
     * Returns a set view of the mappings contained in this map, in
     * descending key order.  Each element in the returned set is a
     * {@link Map.Entry}.  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 <tt>remove</tt> operation,
     * or through the <tt>setValue</tt> operation on a map entry
     * returned by the iterator) the results of the iteration are
     * undefined.  The set supports element removal, which removes the
     * corresponding mapping from the map, via the
     * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
     * <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt>
     * operations.  It does not support the <tt>add</tt> or
     * <tt>addAll</tt> operations.
     *
     * @return a set view of the mappings contained in this map.
     */
    Set<Map.Entry<K, V>> descendingEntrySet();

    /**
     * Returns a view of the portion of this map whose keys range from
     * <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive.  (If
     * <tt>fromKey</tt> and <tt>toKey</tt> are equal, the returned sorted map
     * is empty.)  The returned sorted map is backed by this map, so changes
     * in the returned sorted map are reflected in this map, and vice-versa.

     * @param fromKey low endpoint (inclusive) of the subMap.
     * @param toKey high endpoint (exclusive) of the subMap.
     *
     * @return a view of the portion of this map whose keys range from
     * <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive.
     *
     * @throws ClassCastException if <tt>fromKey</tt> and
     * <tt>toKey</tt> cannot be compared to one another using this
     * map's comparator (or, if the map has no comparator, using
     * natural ordering).
     * @throws IllegalArgumentException if <tt>fromKey</tt> is greater
     * than <tt>toKey</tt>.
     * @throws NullPointerException if <tt>fromKey</tt> or
     * <tt>toKey</tt> is <tt>null</tt> and this map does not support
     * <tt>null</tt> keys.
     */
    public NavigableMap<K,V> subMap(K fromKey, K toKey);

    /**
     * Returns a view of the portion of this map whose keys are strictly less
     * than <tt>toKey</tt>.  The returned sorted map is backed by this map, so
     * changes in the returned sorted map are reflected in this map, and
     * vice-versa.  
     * @param toKey high endpoint (exclusive) of the headMap.
     * @return a view of the portion of this map whose keys are strictly
     *                less than <tt>toKey</tt>.
     *
     * @throws ClassCastException if <tt>toKey</tt> is not compatible
     *         with this map's comparator (or, if the map has no comparator,
     *         if <tt>toKey</tt> does not implement <tt>Comparable</tt>).
     * @throws NullPointerException if <tt>toKey</tt> is <tt>null</tt>
     * and this map does not support <tt>null</tt> keys.
     */
    public NavigableMap<K,V> headMap(K toKey);

    /**
     * Returns a view of the portion of this map whose keys are
     * greater than or equal to <tt>fromKey</tt>.  The returned sorted
     * map is backed by this map, so changes in the returned sorted
     * map are reflected in this map, and vice-versa.
     * @param fromKey low endpoint (inclusive) of the tailMap.
     * @return a view of the portion of this map whose keys are greater
     *                than or equal to <tt>fromKey</tt>.
     * @throws ClassCastException if <tt>fromKey</tt> is not compatible
     *         with this map's comparator (or, if the map has no comparator,
     *         if <tt>fromKey</tt> does not implement <tt>Comparable</tt>).
     * @throws NullPointerException if <tt>fromKey</tt> is <tt>null</tt>
     * and this map does not support <tt>null</tt> keys.
     */
    public NavigableMap<K,V>  tailMap(K fromKey);
}
Revision:	1.3
Committed:	Tue Dec 21 17:27:44 2004 UTC (19 years, 4 months ago) by dl
Branch:	MAIN
Changes since 1.2:	+122 -16 lines
Log Message:	Improved Navigable interface, and associated ConcurrentSkipList* implementations
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain, as explained at
4			* http://creativecommons.org/licenses/publicdomain
5			*/
6
7			package jsr166x;
8
9			import java.util.*;
10
11			/**
12	dl	1.2	* A {@link SortedMap} extended with navigation methods returning
13			* key-value pairs holding the closest matches for given search
14			* targets. Methods <tt>lowerEntry</tt>, <tt>floorEntry</tt>,
15			* <tt>ceilingEntry</tt>, and <tt>higherEntry</tt> return
16			* <tt>Map.Entry</tt> objects associated with keys respectively less
17			* than, less than or equal, greater than or equal, and greater than a
18	dl	1.3	* given key, returning <tt>null</tt> if there is no such key.
19			* Similarly, methods <tt>lowerKey</tt>, <tt>floorKey</tt>,
20			* <tt>ceilingKey</tt>, and <tt>higherKey</tt> return only the
21			* associated keys. All of these methods are designed for locating,
22			* not traversing entries.
23			*
24			* <p>A <tt>NavigableMap</tt> may be viewed and traversed in either
25			* ascending or descending key order. The <tt>Map</tt> methods
26			* <tt>keySet</tt> and <tt>entrySet</tt>) return ascending views, and
27			* the additional methods <tt>descendingKeySet</tt> and
28			* <tt>descendingEntrySet</tt>) return descending views. The
29			* performance of ascending traversals is likely to be faster than
30			* descending traversals. Notice that it is possible to perform
31			* subrannge traversals in either direction using <tt>SubMap</tt>.
32			*
33			* <p>This interface additionally defines methods <tt>firstEntry</tt>,
34	dl	1.2	* <tt>pollFirstEntry</tt>, <tt>lastEntry</tt>, and
35			* <tt>pollLastEntry</tt> that return and/or remove the least and
36			* greatest mappings, if any exist, else returning <tt>null</tt>.
37	dl	1.1	*
38	dl	1.3	* <p> Implementations of entry-returning methods are expected to
39			* return <tt>Map.Entry</tt> pairs representing snapshots of mappings
40			* at the time they were produced, and thus generally do <em>not</em>
41			* support the optional <tt>Entry.setValue</tt> method. Note however
42			* that it is possible to change mappings in the associated map using
43			* method <tt>put</tt>.
44	dl	1.1	*
45			* @author Doug Lea
46			* @param <K> the type of keys maintained by this map
47			* @param <V> the type of mapped values
48			*/
49			public interface NavigableMap<K,V> extends SortedMap<K,V> {
50			/**
51			* Returns a key-value mapping associated with the least key
52	dl	1.2	* greater than or equal to the given key, or <tt>null</tt> if there is
53	dl	1.1	* no such entry.
54			*
55			* @param key the key.
56	dl	1.2	* @return an Entry associated with ceiling of given key, or <tt>null</tt>
57	dl	1.1	* if there is no such Entry.
58			* @throws ClassCastException if key cannot be compared with the keys
59			* currently in the map.
60			* @throws NullPointerException if key is <tt>null</tt> and this map
61			* does not support <tt>null</tt> keys.
62			*/
63			public Map.Entry<K,V> ceilingEntry(K key);
64
65			/**
66	dl	1.3	* Returns least key greater than or equal to the given key, or
67			* <tt>null</tt> if there is no such key.
68			*
69			* @param key the key.
70			* @return the ceiling key, or <tt>null</tt>
71			* if there is no such key.
72			* @throws ClassCastException if key cannot be compared with the keys
73			* currently in the map.
74			* @throws NullPointerException if key is <tt>null</tt> and this map
75			* does not support <tt>null</tt> keys.
76			*/
77			public K ceilingKey(K key);
78
79			/**
80	dl	1.1	* Returns a key-value mapping associated with the greatest
81	dl	1.2	* key strictly less than the given key, or <tt>null</tt> if there is no
82	dl	1.1	* such entry.
83			*
84			* @param key the key.
85			* @return an Entry with greatest key less than the given
86	dl	1.2	* key, or <tt>null</tt> if there is no such Entry.
87	dl	1.1	* @throws ClassCastException if key cannot be compared with the keys
88			* currently in the map.
89			* @throws NullPointerException if key is <tt>null</tt> and this map
90			* does not support <tt>null</tt> keys.
91			*/
92			public Map.Entry<K,V> lowerEntry(K key);
93
94			/**
95	dl	1.3	* Returns the greatest key strictly less than the given key, or
96			* <tt>null</tt> if there is no such key.
97			*
98			* @param key the key.
99			* @return the greatest key less than the given
100			* key, or <tt>null</tt> if there is no such key.
101			* @throws ClassCastException if key cannot be compared with the keys
102			* currently in the map.
103			* @throws NullPointerException if key is <tt>null</tt> and this map
104			* does not support <tt>null</tt> keys.
105			*/
106			public K lowerKey(K key);
107
108			/**
109			* Returns a key-value mapping associated with the greatest key
110			* less than or equal to the given key, or <tt>null</tt> if there
111			* is no such entry.
112	dl	1.1	*
113			* @param key the key.
114	dl	1.2	* @return an Entry associated with floor of given key, or <tt>null</tt>
115	dl	1.1	* if there is no such Entry.
116			* @throws ClassCastException if key cannot be compared with the keys
117			* currently in the map.
118			* @throws NullPointerException if key is <tt>null</tt> and this map
119			* does not support <tt>null</tt> keys.
120			*/
121			public Map.Entry<K,V> floorEntry(K key);
122
123			/**
124	dl	1.3	* Returns the greatest key
125			* less than or equal to the given key, or <tt>null</tt> if there
126			* is no such key.
127			*
128			* @param key the key.
129			* @return the floor of given key, or <tt>null</tt> if there is no
130			* such key.
131			* @throws ClassCastException if key cannot be compared with the keys
132			* currently in the map.
133			* @throws NullPointerException if key is <tt>null</tt> and this map
134			* does not support <tt>null</tt> keys.
135			*/
136			public K floorKey(K key);
137
138			/**
139			* Returns a key-value mapping associated with the least key
140			* strictly greater than the given key, or <tt>null</tt> if there
141			* is no such entry.
142	dl	1.1	*
143			* @param key the key.
144			* @return an Entry with least key greater than the given key, or
145	dl	1.2	* <tt>null</tt> if there is no such Entry.
146	dl	1.1	* @throws ClassCastException if key cannot be compared with the keys
147			* currently in the map.
148			* @throws NullPointerException if key is <tt>null</tt> and this map
149			* does not support <tt>null</tt> keys.
150			*/
151			public Map.Entry<K,V> higherEntry(K key);
152
153			/**
154	dl	1.3	* Returns the least key strictly greater than the given key, or
155			* <tt>null</tt> if there is no such key.
156			*
157			* @param key the key.
158			* @return the least key greater than the given key, or
159			* <tt>null</tt> if there is no such key.
160			* @throws ClassCastException if key cannot be compared with the keys
161			* currently in the map.
162			* @throws NullPointerException if key is <tt>null</tt> and this map
163			* does not support <tt>null</tt> keys.
164			*/
165			public K higherKey(K key);
166
167			/**
168	dl	1.1	* Returns a key-value mapping associated with the least
169	dl	1.2	* key in this map, or <tt>null</tt> if the map is empty.
170	dl	1.1	*
171	dl	1.2	* @return an Entry with least key, or <tt>null</tt>
172	dl	1.1	* if the map is empty.
173			*/
174			public Map.Entry<K,V> firstEntry();
175
176			/**
177			* Returns a key-value mapping associated with the greatest
178	dl	1.2	* key in this map, or <tt>null</tt> if the map is empty.
179	dl	1.1	*
180	dl	1.2	* @return an Entry with greatest key, or <tt>null</tt>
181	dl	1.1	* if the map is empty.
182			*/
183			public Map.Entry<K,V> lastEntry();
184
185			/**
186			* Removes and returns a key-value mapping associated with
187	dl	1.2	* the least key in this map, or <tt>null</tt> if the map is empty.
188	dl	1.1	*
189	dl	1.2	* @return the removed first entry of this map, or <tt>null</tt>
190	dl	1.1	* if the map is empty.
191			*/
192			public Map.Entry<K,V> pollFirstEntry();
193
194			/**
195			* Removes and returns a key-value mapping associated with
196	dl	1.2	* the greatest key in this map, or <tt>null</tt> if the map is empty.
197	dl	1.1	*
198	dl	1.2	* @return the removed last entry of this map, or <tt>null</tt>
199	dl	1.1	* if the map is empty.
200			*/
201			public Map.Entry<K,V> pollLastEntry();
202
203			/**
204	dl	1.3	* Returns a set view of the keys contained in this map, in
205			* descending key order. The set is backed by the map, so changes
206			* to the map are reflected in the set, and vice-versa. If the
207			* map is modified while an iteration over the set is in progress
208			* (except through the iterator's own <tt>remove</tt> operation),
209			* the results of the iteration are undefined. The set supports
210			* element removal, which removes the corresponding mapping from
211			* the map, via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
212			* <tt>removeAll</tt> <tt>retainAll</tt>, and <tt>clear</tt>
213			* operations. It does not support the add or <tt>addAll</tt>
214			* operations.
215			*
216			* @return a set view of the keys contained in this map.
217			*/
218			Set<K> descendingKeySet();
219
220			/**
221			* Returns a set view of the mappings contained in this map, in
222			* descending key order. Each element in the returned set is a
223			* {@link Map.Entry}. The set is backed by the map, so changes to
224			* the map are reflected in the set, and vice-versa. If the map
225			* is modified while an iteration over the set is in progress
226			* (except through the iterator's own <tt>remove</tt> operation,
227			* or through the <tt>setValue</tt> operation on a map entry
228			* returned by the iterator) the results of the iteration are
229			* undefined. The set supports element removal, which removes the
230			* corresponding mapping from the map, via the
231			* <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
232			* <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt>
233			* operations. It does not support the <tt>add</tt> or
234			* <tt>addAll</tt> operations.
235			*
236			* @return a set view of the mappings contained in this map.
237			*/
238			Set<Map.Entry<K, V>> descendingEntrySet();
239
240			/**
241	dl	1.1	* Returns a view of the portion of this map whose keys range from
242			* <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive. (If
243			* <tt>fromKey</tt> and <tt>toKey</tt> are equal, the returned sorted map
244			* is empty.) The returned sorted map is backed by this map, so changes
245			* in the returned sorted map are reflected in this map, and vice-versa.
246
247			* @param fromKey low endpoint (inclusive) of the subMap.
248			* @param toKey high endpoint (exclusive) of the subMap.
249			*
250			* @return a view of the portion of this map whose keys range from
251			* <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive.
252			*
253			* @throws ClassCastException if <tt>fromKey</tt> and
254			* <tt>toKey</tt> cannot be compared to one another using this
255			* map's comparator (or, if the map has no comparator, using
256			* natural ordering).
257			* @throws IllegalArgumentException if <tt>fromKey</tt> is greater
258			* than <tt>toKey</tt>.
259			* @throws NullPointerException if <tt>fromKey</tt> or
260			* <tt>toKey</tt> is <tt>null</tt> and this map does not support
261			* <tt>null</tt> keys.
262			*/
263			public NavigableMap<K,V> subMap(K fromKey, K toKey);
264
265			/**
266			* Returns a view of the portion of this map whose keys are strictly less
267			* than <tt>toKey</tt>. The returned sorted map is backed by this map, so
268			* changes in the returned sorted map are reflected in this map, and
269			* vice-versa.
270			* @param toKey high endpoint (exclusive) of the headMap.
271			* @return a view of the portion of this map whose keys are strictly
272			* less than <tt>toKey</tt>.
273			*
274			* @throws ClassCastException if <tt>toKey</tt> is not compatible
275			* with this map's comparator (or, if the map has no comparator,
276			* if <tt>toKey</tt> does not implement <tt>Comparable</tt>).
277			* @throws NullPointerException if <tt>toKey</tt> is <tt>null</tt>
278			* and this map does not support <tt>null</tt> keys.
279			*/
280			public NavigableMap<K,V> headMap(K toKey);
281
282			/**
283			* Returns a view of the portion of this map whose keys are
284			* greater than or equal to <tt>fromKey</tt>. The returned sorted
285			* map is backed by this map, so changes in the returned sorted
286			* map are reflected in this map, and vice-versa.
287			* @param fromKey low endpoint (inclusive) of the tailMap.
288			* @return a view of the portion of this map whose keys are greater
289			* than or equal to <tt>fromKey</tt>.
290			* @throws ClassCastException if <tt>fromKey</tt> is not compatible
291			* with this map's comparator (or, if the map has no comparator,
292			* if <tt>fromKey</tt> does not implement <tt>Comparable</tt>).
293			* @throws NullPointerException if <tt>fromKey</tt> is <tt>null</tt>
294			* and this map does not support <tt>null</tt> keys.
295			*/
296			public NavigableMap<K,V> tailMap(K fromKey);
297			}