java/util/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 java.util;
import java.util.*; // for javadoc (till 6280605 is fixed)

/**
 * A {@link SortedMap} extended with navigation methods returning 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
 * subrange traversals in either direction using <tt>navigableSubMap</tt>.
 * Methods <tt>navigableSubMap</tt>, <tt>navigableHeadMap</tt>, and
 * <tt>navigableTailMap</tt> differ from the similarly named
 * <tt>SortedMap</tt> methods only in their declared return types.
 * Submaps of any <tt>NavigableMap<tt> must implement the
 * <tt>NavigableMap</tt> interface.
 *
 * <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>.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @author Doug Lea
 * @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 <tt>null</tt> if there is
     * no such key.
     *
     * @param key the key
     * @return an entry with the greatest key less than <tt>key</tt>,
     *         or <tt>null</tt> 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
     * <tt>null</tt> if there is no such key.
     *
     * @param key the key
     * @return the greatest key less than <tt>key</tt>,
     *         or <tt>null</tt> 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 <tt>null</tt> if there
     * is no such key.
     *
     * @param key the key
     * @return an entry with the greatest key less than or equal to
     *         <tt>key</tt>, or <tt>null</tt> 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 <tt>null</tt> if there is no such key.
     *
     * @param key the key
     * @return the greatest key less than or equal to <tt>key</tt>,
     *         or <tt>null</tt> 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 <tt>null</tt> if
     * there is no such key.
     *
     * @param key the key
     * @return an entry with the least key greater than or equal to
     *         <tt>key</tt>, or <tt>null</tt> 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 <tt>null</tt> if there is no such key.
     *
     * @param key the key
     * @return the least key greater than or equal to <tt>key</tt>,
     *         or <tt>null</tt> 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 <tt>null</tt> if there
     * is no such key.
     *
     * @param key the key
     * @return an entry with the least key greater than <tt>key</tt>,
     *         or <tt>null</tt> 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
     * <tt>null</tt> if there is no such key.
     *
     * @param key the key
     * @return the least key greater than <tt>key</tt>,
     *         or <tt>null</tt> 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 <tt>null</tt> if the map is empty.
     *
     * @return an entry with the least key,
     *         or <tt>null</tt> if this map is empty
     */
    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 the greatest key,
     *         or <tt>null</tt> 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 <tt>null</tt> if the map is empty.
     *
     * @return the removed first entry of this map,
     *         or <tt>null</tt> 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 <tt>null</tt> if the map is empty.
     *
     * @return the removed last entry of this map,
     *         or <tt>null</tt> if this map is empty
     */
    Map.Entry<K,V> pollLastEntry();

    /**
     * Returns a {@link Set} 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 <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 <tt>add</tt> or <tt>addAll</tt>
     * operations.
     *
     * @return a set view of the keys contained in this map, sorted in
     *         descending order
     */
    Set<K> descendingKeySet();

    /**
     * Returns a {@link Set} view of the mappings contained in this map.
     * The set's iterator returns the entries 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, 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,
     *         sorted in descending key order
     */
    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 map
     * is empty.)  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 <tt>IllegalArgumentException</tt>
     * on an attempt to insert a key outside its range.
     *
     * @param fromKey low endpoint (inclusive) of the keys in the returned map
     * @param toKey high endpoint (exclusive) of the keys in the returned map
     * @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).
     *         Implementations may, but are not required to, throw this
     *         exception if <tt>fromKey</tt> or <tt>toKey</tt>
     *         cannot be compared to keys currently in the map.
     * @throws NullPointerException if <tt>fromKey</tt> or <tt>toKey</tt>
     *         is null and this map does not permit null keys
     * @throws IllegalArgumentException if <tt>fromKey</tt> is greater than
     *         <tt>toKey</tt>; or if this map itself has a restricted
     *         range, and <tt>fromKey</tt> or <tt>toKey</tt> lies
     *         outside the bounds of the range
     */
    NavigableMap<K,V> navigableSubMap(K fromKey, K toKey);

    /**
     * Returns a view of the portion of this map whose keys are
     * strictly less than <tt>toKey</tt>.  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 <tt>IllegalArgumentException</tt>
     * on an attempt to insert a key outside its range.
     *
     * @param toKey high endpoint (exclusive) of the keys in the returned map
     * @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 {@link Comparable}).
     *         Implementations may, but are not required to, throw this
     *         exception if <tt>toKey</tt> cannot be compared to keys
     *         currently in the map.
     * @throws NullPointerException if <tt>toKey</tt> is null
     *         and this map does not permit null keys
     * @throws IllegalArgumentException if this map itself has a
     *         restricted range, and <tt>toKey</tt> lies outside the
     *         bounds of the range
     */
    NavigableMap<K,V> navigableHeadMap(K toKey);

    /**
     * Returns a view of the portion of this map whose keys are
     * greater than or equal to <tt>fromKey</tt>.  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 <tt>IllegalArgumentException</tt>
     * on an attempt to insert a key outside its range.
     *
     * @param fromKey low endpoint (inclusive) of the keys in the returned map
     * @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 {@link Comparable}).
     *         Implementations may, but are not required to, throw this
     *         exception if <tt>fromKey</tt> cannot be compared to keys
     *         currently in the map.
     * @throws NullPointerException if <tt>fromKey</tt> is null
     *         and this map does not permit null keys
     * @throws IllegalArgumentException if this map itself has a
     *         restricted range, and <tt>fromKey</tt> lies outside the
     *         bounds of the range
     */
    NavigableMap<K,V> navigableTailMap(K fromKey);
}
Revision:	1.11
Committed:	Wed Jul 20 02:18:52 2005 UTC (18 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.10:	+3 -2 lines
Log Message:	doc fixes
#	Content
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 java.util;
8	import java.util.*; // for javadoc (till 6280605 is fixed)
9
10	/**
11	* A {@link SortedMap} extended with navigation methods returning the
12	* closest matches for given search targets. Methods
13	* <tt>lowerEntry</tt>, <tt>floorEntry</tt>, <tt>ceilingEntry</tt>,
14	* and <tt>higherEntry</tt> return <tt>Map.Entry</tt> objects
15	* associated with keys respectively less than, less than or equal,
16	* greater than or equal, and greater than a given key, returning
17	* <tt>null</tt> if there is no such key. Similarly, methods
18	* <tt>lowerKey</tt>, <tt>floorKey</tt>, <tt>ceilingKey</tt>, and
19	* <tt>higherKey</tt> return only the associated keys. All of these
20	* methods are designed for locating, not traversing entries.
21	*
22	* <p>A <tt>NavigableMap</tt> may be viewed and traversed in either
23	* ascending or descending key order. The <tt>Map</tt> methods
24	* <tt>keySet</tt> and <tt>entrySet</tt> return ascending views, and
25	* the additional methods <tt>descendingKeySet</tt> and
26	* <tt>descendingEntrySet</tt> return descending views. The
27	* performance of ascending traversals is likely to be faster than
28	* descending traversals. Notice that it is possible to perform
29	* subrange traversals in either direction using <tt>navigableSubMap</tt>.
30	* Methods <tt>navigableSubMap</tt>, <tt>navigableHeadMap</tt>, and
31	* <tt>navigableTailMap</tt> differ from the similarly named
32	* <tt>SortedMap</tt> methods only in their declared return types.
33	* Submaps of any <tt>NavigableMap<tt> must implement the
34	* <tt>NavigableMap</tt> interface.
35	*
36	* <p>This interface additionally defines methods <tt>firstEntry</tt>,
37	* <tt>pollFirstEntry</tt>, <tt>lastEntry</tt>, and
38	* <tt>pollLastEntry</tt> that return and/or remove the least and
39	* greatest mappings, if any exist, else returning <tt>null</tt>.
40	*
41	* <p> Implementations of entry-returning methods are expected to
42	* return <tt>Map.Entry</tt> pairs representing snapshots of mappings
43	* at the time they were produced, and thus generally do <em>not</em>
44	* support the optional <tt>Entry.setValue</tt> method. Note however
45	* that it is possible to change mappings in the associated map using
46	* method <tt>put</tt>.
47	*
48	* <p>This interface is a member of the
49	* <a href="{@docRoot}/../guide/collections/index.html">
50	* Java Collections Framework</a>.
51	*
52	* @author Doug Lea
53	* @param <K> the type of keys maintained by this map
54	* @param <V> the type of mapped values
55	* @since 1.6
56	*/
57	public interface NavigableMap<K,V> extends SortedMap<K,V> {
58	/**
59	* Returns a key-value mapping associated with the greatest key
60	* strictly less than the given key, or <tt>null</tt> if there is
61	* no such key.
62	*
63	* @param key the key
64	* @return an entry with the greatest key less than <tt>key</tt>,
65	* or <tt>null</tt> if there is no such key
66	* @throws ClassCastException if the specified key cannot be compared
67	* with the keys currently in the map
68	* @throws NullPointerException if the specified key is null
69	* and this map does not permit null keys
70	*/
71	Map.Entry<K,V> lowerEntry(K key);
72
73	/**
74	* Returns the greatest key strictly less than the given key, or
75	* <tt>null</tt> if there is no such key.
76	*
77	* @param key the key
78	* @return the greatest key less than <tt>key</tt>,
79	* or <tt>null</tt> if there is no such key
80	* @throws ClassCastException if the specified key cannot be compared
81	* with the keys currently in the map
82	* @throws NullPointerException if the specified key is null
83	* and this map does not permit null keys
84	*/
85	K lowerKey(K key);
86
87	/**
88	* Returns a key-value mapping associated with the greatest key
89	* less than or equal to the given key, or <tt>null</tt> if there
90	* is no such key.
91	*
92	* @param key the key
93	* @return an entry with the greatest key less than or equal to
94	* <tt>key</tt>, or <tt>null</tt> if there is no such key
95	* @throws ClassCastException if the specified key cannot be compared
96	* with the keys currently in the map
97	* @throws NullPointerException if the specified key is null
98	* and this map does not permit null keys
99	*/
100	Map.Entry<K,V> floorEntry(K key);
101
102	/**
103	* Returns the greatest key less than or equal to the given key,
104	* or <tt>null</tt> if there is no such key.
105	*
106	* @param key the key
107	* @return the greatest key less than or equal to <tt>key</tt>,
108	* or <tt>null</tt> if there is no such key
109	* @throws ClassCastException if the specified key cannot be compared
110	* with the keys currently in the map
111	* @throws NullPointerException if the specified key is null
112	* and this map does not permit null keys
113	*/
114	K floorKey(K key);
115
116	/**
117	* Returns a key-value mapping associated with the least key
118	* greater than or equal to the given key, or <tt>null</tt> if
119	* there is no such key.
120	*
121	* @param key the key
122	* @return an entry with the least key greater than or equal to
123	* <tt>key</tt>, or <tt>null</tt> if there is no such key
124	* @throws ClassCastException if the specified key cannot be compared
125	* with the keys currently in the map
126	* @throws NullPointerException if the specified key is null
127	* and this map does not permit null keys
128	*/
129	Map.Entry<K,V> ceilingEntry(K key);
130
131	/**
132	* Returns the least key greater than or equal to the given key,
133	* or <tt>null</tt> if there is no such key.
134	*
135	* @param key the key
136	* @return the least key greater than or equal to <tt>key</tt>,
137	* or <tt>null</tt> if there is no such key
138	* @throws ClassCastException if the specified key cannot be compared
139	* with the keys currently in the map
140	* @throws NullPointerException if the specified key is null
141	* and this map does not permit null keys
142	*/
143	K ceilingKey(K key);
144
145	/**
146	* Returns a key-value mapping associated with the least key
147	* strictly greater than the given key, or <tt>null</tt> if there
148	* is no such key.
149	*
150	* @param key the key
151	* @return an entry with the least key greater than <tt>key</tt>,
152	* or <tt>null</tt> if there is no such key
153	* @throws ClassCastException if the specified key cannot be compared
154	* with the keys currently in the map
155	* @throws NullPointerException if the specified key is null
156	* and this map does not permit null keys
157	*/
158	Map.Entry<K,V> higherEntry(K key);
159
160	/**
161	* Returns the least key strictly greater than the given key, or
162	* <tt>null</tt> if there is no such key.
163	*
164	* @param key the key
165	* @return the least key greater than <tt>key</tt>,
166	* or <tt>null</tt> if there is no such key
167	* @throws ClassCastException if the specified key cannot be compared
168	* with the keys currently in the map
169	* @throws NullPointerException if the specified key is null
170	* and this map does not permit null keys
171	*/
172	K higherKey(K key);
173
174	/**
175	* Returns a key-value mapping associated with the least
176	* key in this map, or <tt>null</tt> if the map is empty.
177	*
178	* @return an entry with the least key,
179	* or <tt>null</tt> if this map is empty
180	*/
181	Map.Entry<K,V> firstEntry();
182
183	/**
184	* Returns a key-value mapping associated with the greatest
185	* key in this map, or <tt>null</tt> if the map is empty.
186	*
187	* @return an entry with the greatest key,
188	* or <tt>null</tt> if this map is empty
189	*/
190	Map.Entry<K,V> lastEntry();
191
192	/**
193	* Removes and returns a key-value mapping associated with
194	* the least key in this map, or <tt>null</tt> if the map is empty.
195	*
196	* @return the removed first entry of this map,
197	* or <tt>null</tt> if this map is empty
198	*/
199	Map.Entry<K,V> pollFirstEntry();
200
201	/**
202	* Removes and returns a key-value mapping associated with
203	* the greatest key in this map, or <tt>null</tt> if the map is empty.
204	*
205	* @return the removed last entry of this map,
206	* or <tt>null</tt> if this map is empty
207	*/
208	Map.Entry<K,V> pollLastEntry();
209
210	/**
211	* Returns a {@link Set} view of the keys contained in this map.
212	* The set's iterator returns the keys in descending order.
213	* The set is backed by the map, so changes to the map are
214	* reflected in the set, and vice-versa. If the map is modified
215	* while an iteration over the set is in progress (except through
216	* the iterator's own <tt>remove</tt> operation), the results of
217	* the iteration are undefined. The set supports element removal,
218	* which removes the corresponding mapping from the map, via the
219	* <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
220	* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
221	* operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
222	* operations.
223	*
224	* @return a set view of the keys contained in this map, sorted in
225	* descending order
226	*/
227	Set<K> descendingKeySet();
228
229	/**
230	* Returns a {@link Set} view of the mappings contained in this map.
231	* The set's iterator returns the entries in descending key order.
232	* The set is backed by the map, so changes to the map are
233	* reflected in the set, and vice-versa. If the map is modified
234	* while an iteration over the set is in progress (except through
235	* the iterator's own <tt>remove</tt> operation, or through the
236	* <tt>setValue</tt> operation on a map entry returned by the
237	* iterator) the results of the iteration are undefined. The set
238	* supports element removal, which removes the corresponding
239	* mapping from the map, via the <tt>Iterator.remove</tt>,
240	* <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
241	* <tt>clear</tt> operations. It does not support the
242	* <tt>add</tt> or <tt>addAll</tt> operations.
243	*
244	* @return a set view of the mappings contained in this map,
245	* sorted in descending key order
246	*/
247	Set<Map.Entry<K, V>> descendingEntrySet();
248
249	/**
250	* Returns a view of the portion of this map whose keys range from
251	* <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive. (If
252	* <tt>fromKey</tt> and <tt>toKey</tt> are equal, the returned map
253	* is empty.) The returned map is backed by this map, so changes
254	* in the returned map are reflected in this map, and vice-versa.
255	* The returned map supports all optional map operations that this
256	* map supports.
257	*
258	* <p>The returned map will throw an <tt>IllegalArgumentException</tt>
259	* on an attempt to insert a key outside its range.
260	*
261	* @param fromKey low endpoint (inclusive) of the keys in the returned map
262	* @param toKey high endpoint (exclusive) of the keys in the returned map
263	* @return a view of the portion of this map whose keys range from
264	* <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive
265	* @throws ClassCastException if <tt>fromKey</tt> and <tt>toKey</tt>
266	* cannot be compared to one another using this map's comparator
267	* (or, if the map has no comparator, using natural ordering).
268	* Implementations may, but are not required to, throw this
269	* exception if <tt>fromKey</tt> or <tt>toKey</tt>
270	* cannot be compared to keys currently in the map.
271	* @throws NullPointerException if <tt>fromKey</tt> or <tt>toKey</tt>
272	* is null and this map does not permit null keys
273	* @throws IllegalArgumentException if <tt>fromKey</tt> is greater than
274	* <tt>toKey</tt>; or if this map itself has a restricted
275	* range, and <tt>fromKey</tt> or <tt>toKey</tt> lies
276	* outside the bounds of the range
277	*/
278	NavigableMap<K,V> navigableSubMap(K fromKey, K toKey);
279
280	/**
281	* Returns a view of the portion of this map whose keys are
282	* strictly less than <tt>toKey</tt>. The returned map is backed
283	* by this map, so changes in the returned map are reflected in
284	* this map, and vice-versa. The returned map supports all
285	* optional map operations that this map supports.
286	*
287	* <p>The returned map will throw an <tt>IllegalArgumentException</tt>
288	* on an attempt to insert a key outside its range.
289	*
290	* @param toKey high endpoint (exclusive) of the keys in the returned map
291	* @return a view of the portion of this map whose keys are strictly
292	* less than <tt>toKey</tt>
293	* @throws ClassCastException if <tt>toKey</tt> is not compatible
294	* with this map's comparator (or, if the map has no comparator,
295	* if <tt>toKey</tt> does not implement {@link Comparable}).
296	* Implementations may, but are not required to, throw this
297	* exception if <tt>toKey</tt> cannot be compared to keys
298	* currently in the map.
299	* @throws NullPointerException if <tt>toKey</tt> is null
300	* and this map does not permit null keys
301	* @throws IllegalArgumentException if this map itself has a
302	* restricted range, and <tt>toKey</tt> lies outside the
303	* bounds of the range
304	*/
305	NavigableMap<K,V> navigableHeadMap(K toKey);
306
307	/**
308	* Returns a view of the portion of this map whose keys are
309	* greater than or equal to <tt>fromKey</tt>. The returned map is
310	* backed by this map, so changes in the returned map are
311	* reflected in this map, and vice-versa. The returned map
312	* supports all optional map operations that this map supports.
313	*
314	* <p>The returned map will throw an <tt>IllegalArgumentException</tt>
315	* on an attempt to insert a key outside its range.
316	*
317	* @param fromKey low endpoint (inclusive) of the keys in the returned map
318	* @return a view of the portion of this map whose keys are greater
319	* than or equal to <tt>fromKey</tt>
320	* @throws ClassCastException if <tt>fromKey</tt> is not compatible
321	* with this map's comparator (or, if the map has no comparator,
322	* if <tt>fromKey</tt> does not implement {@link Comparable}).
323	* Implementations may, but are not required to, throw this
324	* exception if <tt>fromKey</tt> cannot be compared to keys
325	* currently in the map.
326	* @throws NullPointerException if <tt>fromKey</tt> is null
327	* and this map does not permit null keys
328	* @throws IllegalArgumentException if this map itself has a
329	* restricted range, and <tt>fromKey</tt> lies outside the
330	* bounds of the range
331	*/
332	NavigableMap<K,V> navigableTailMap(K fromKey);
333	}