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29 * A {@link Map} that further provides a <em>total ordering</em> on its keys.
30 * The map is ordered according to the {@linkplain Comparable natural
31 * ordering} of its keys, or by a {@link Comparator} typically
32 * provided at sorted map creation time. This order is reflected when
33 * iterating over the sorted map's collection views (returned by the
34 * {@code entrySet}, {@code keySet} and {@code values} methods).
35 * Several additional operations are provided to take advantage of the
36 * ordering. (This interface is the map analogue of {@link SortedSet}.)
38 * <p>All keys inserted into a sorted map must implement the {@code Comparable}
39 * interface (or be accepted by the specified comparator). Furthermore, all
40 * such keys must be <em>mutually comparable</em>: {@code k1.compareTo(k2)} (or
41 * {@code comparator.compare(k1, k2)}) must not throw a
42 * {@code ClassCastException} for any keys {@code k1} and {@code k2} in
43 * the sorted map. Attempts to violate this restriction will cause the
44 * offending method or constructor invocation to throw a
45 * {@code ClassCastException}.
47 * <p>Note that the ordering maintained by a sorted map (whether or not an
48 * explicit comparator is provided) must be <em>consistent with equals</em> if
49 * the sorted map is to correctly implement the {@code Map} interface. (See
50 * the {@code Comparable} interface or {@code Comparator} interface for a
51 * precise definition of <em>consistent with equals</em>.) This is so because
52 * the {@code Map} interface is defined in terms of the {@code equals}
53 * operation, but a sorted map performs all key comparisons using its
54 * {@code compareTo} (or {@code compare}) method, so two keys that are
55 * deemed equal by this method are, from the standpoint of the sorted map,
56 * equal. The behavior of a tree map <em>is</em> well-defined even if its
57 * ordering is inconsistent with equals; it just fails to obey the general
58 * contract of the {@code Map} interface.
60 * <p>All general-purpose sorted map implementation classes should provide four
61 * "standard" constructors. It is not possible to enforce this recommendation
62 * though as required constructors cannot be specified by interfaces. The
63 * expected "standard" constructors for all sorted map implementations are:
65 * <li>A void (no arguments) constructor, which creates an empty sorted map
66 * sorted according to the natural ordering of its keys.</li>
67 * <li>A constructor with a single argument of type {@code Comparator}, which
68 * creates an empty sorted map sorted according to the specified comparator.</li>
69 * <li>A constructor with a single argument of type {@code Map}, which creates
70 * a new map with the same key-value mappings as its argument, sorted
71 * according to the keys' natural ordering.</li>
72 * <li>A constructor with a single argument of type {@code SortedMap}, which
73 * creates a new sorted map with the same key-value mappings and the same
74 * ordering as the input sorted map.</li>
77 * <p><strong>Note</strong>: several methods return submaps with restricted key
78 * ranges. Such ranges are <em>half-open</em>, that is, they include their low
79 * endpoint but not their high endpoint (where applicable). If you need a
80 * <em>closed range</em> (which includes both endpoints), and the key type
81 * allows for calculation of the successor of a given key, merely request
82 * the subrange from {@code lowEndpoint} to
83 * {@code successor(highEndpoint)}. For example, suppose that {@code m}
84 * is a map whose keys are strings. The following idiom obtains a view
85 * containing all of the key-value mappings in {@code m} whose keys are
86 * between {@code low} and {@code high}, inclusive:<pre>
87 * SortedMap<String, V> sub = m.subMap(low, high+"\0");</pre>
89 * A similar technique can be used to generate an <em>open range</em>
90 * (which contains neither endpoint). The following idiom obtains a
91 * view containing all of the key-value mappings in {@code m} whose keys
92 * are between {@code low} and {@code high}, exclusive:<pre>
93 * SortedMap<String, V> sub = m.subMap(low+"\0", high);</pre>
95 * <p>This interface is a member of the
96 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
97 * Java Collections Framework</a>.
99 * @param <K> the type of keys maintained by this map
100 * @param <V> the type of mapped values
109 * @see ClassCastException
113 public interface SortedMap<K,V> extends Map<K,V> {
115 * Returns the comparator used to order the keys in this map, or
116 * {@code null} if this map uses the {@linkplain Comparable
117 * natural ordering} of its keys.
119 * @return the comparator used to order the keys in this map,
120 * or {@code null} if this map uses the natural ordering
123 Comparator<? super K> comparator();
126 * Returns a view of the portion of this map whose keys range from
127 * {@code fromKey}, inclusive, to {@code toKey}, exclusive. (If
128 * {@code fromKey} and {@code toKey} are equal, the returned map
129 * is empty.) The returned map is backed by this map, so changes
130 * in the returned map are reflected in this map, and vice-versa.
131 * The returned map supports all optional map operations that this
134 * <p>The returned map will throw an {@code IllegalArgumentException}
135 * on an attempt to insert a key outside its range.
137 * @param fromKey low endpoint (inclusive) of the keys in the returned map
138 * @param toKey high endpoint (exclusive) of the keys in the returned map
139 * @return a view of the portion of this map whose keys range from
140 * {@code fromKey}, inclusive, to {@code toKey}, exclusive
141 * @throws ClassCastException if {@code fromKey} and {@code toKey}
142 * cannot be compared to one another using this map's comparator
143 * (or, if the map has no comparator, using natural ordering).
144 * Implementations may, but are not required to, throw this
145 * exception if {@code fromKey} or {@code toKey}
146 * cannot be compared to keys currently in the map.
147 * @throws NullPointerException if {@code fromKey} or {@code toKey}
148 * is null and this map does not permit null keys
149 * @throws IllegalArgumentException if {@code fromKey} is greater than
150 * {@code toKey}; or if this map itself has a restricted
151 * range, and {@code fromKey} or {@code toKey} lies
152 * outside the bounds of the range
154 SortedMap<K,V> subMap(K fromKey, K toKey);
157 * Returns a view of the portion of this map whose keys are
158 * strictly less than {@code toKey}. The returned map is backed
159 * by this map, so changes in the returned map are reflected in
160 * this map, and vice-versa. The returned map supports all
161 * optional map operations that this map supports.
163 * <p>The returned map will throw an {@code IllegalArgumentException}
164 * on an attempt to insert a key outside its range.
166 * @param toKey high endpoint (exclusive) of the keys in the returned map
167 * @return a view of the portion of this map whose keys are strictly
168 * less than {@code toKey}
169 * @throws ClassCastException if {@code toKey} is not compatible
170 * with this map's comparator (or, if the map has no comparator,
171 * if {@code toKey} does not implement {@link Comparable}).
172 * Implementations may, but are not required to, throw this
173 * exception if {@code toKey} cannot be compared to keys
174 * currently in the map.
175 * @throws NullPointerException if {@code toKey} is null and
176 * this map does not permit null keys
177 * @throws IllegalArgumentException if this map itself has a
178 * restricted range, and {@code toKey} lies outside the
179 * bounds of the range
181 SortedMap<K,V> headMap(K toKey);
184 * Returns a view of the portion of this map whose keys are
185 * greater than or equal to {@code fromKey}. The returned map is
186 * backed by this map, so changes in the returned map are
187 * reflected in this map, and vice-versa. The returned map
188 * supports all optional map operations that this map supports.
190 * <p>The returned map will throw an {@code IllegalArgumentException}
191 * on an attempt to insert a key outside its range.
193 * @param fromKey low endpoint (inclusive) of the keys in the returned map
194 * @return a view of the portion of this map whose keys are greater
195 * than or equal to {@code fromKey}
196 * @throws ClassCastException if {@code fromKey} is not compatible
197 * with this map's comparator (or, if the map has no comparator,
198 * if {@code fromKey} does not implement {@link Comparable}).
199 * Implementations may, but are not required to, throw this
200 * exception if {@code fromKey} cannot be compared to keys
201 * currently in the map.
202 * @throws NullPointerException if {@code fromKey} is null and
203 * this map does not permit null keys
204 * @throws IllegalArgumentException if this map itself has a
205 * restricted range, and {@code fromKey} lies outside the
206 * bounds of the range
208 SortedMap<K,V> tailMap(K fromKey);
211 * Returns the first (lowest) key currently in this map.
213 * @return the first (lowest) key currently in this map
214 * @throws NoSuchElementException if this map is empty
219 * Returns the last (highest) key currently in this map.
221 * @return the last (highest) key currently in this map
222 * @throws NoSuchElementException if this map is empty
227 * Returns a {@link Set} view of the keys contained in this map.
228 * The set's iterator returns the keys in ascending order.
229 * The set is backed by the map, so changes to the map are
230 * reflected in the set, and vice-versa. If the map is modified
231 * while an iteration over the set is in progress (except through
232 * the iterator's own {@code remove} operation), the results of
233 * the iteration are undefined. The set supports element removal,
234 * which removes the corresponding mapping from the map, via the
235 * {@code Iterator.remove}, {@code Set.remove},
236 * {@code removeAll}, {@code retainAll}, and {@code clear}
237 * operations. It does not support the {@code add} or {@code addAll}
240 * @return a set view of the keys contained in this map, sorted in
246 * Returns a {@link Collection} view of the values contained in this map.
247 * The collection's iterator returns the values in ascending order
248 * of the corresponding keys.
249 * The collection is backed by the map, so changes to the map are
250 * reflected in the collection, and vice-versa. If the map is
251 * modified while an iteration over the collection is in progress
252 * (except through the iterator's own {@code remove} operation),
253 * the results of the iteration are undefined. The collection
254 * supports element removal, which removes the corresponding
255 * mapping from the map, via the {@code Iterator.remove},
256 * {@code Collection.remove}, {@code removeAll},
257 * {@code retainAll} and {@code clear} operations. It does not
258 * support the {@code add} or {@code addAll} operations.
260 * @return a collection view of the values contained in this map,
261 * sorted in ascending key order
263 Collection<V> values();
266 * Returns a {@link Set} view of the mappings contained in this map.
267 * The set's iterator returns the entries in ascending key order.
268 * The set is backed by the map, so changes to the map are
269 * reflected in the set, and vice-versa. If the map is modified
270 * while an iteration over the set is in progress (except through
271 * the iterator's own {@code remove} operation, or through the
272 * {@code setValue} operation on a map entry returned by the
273 * iterator) the results of the iteration are undefined. The set
274 * supports element removal, which removes the corresponding
275 * mapping from the map, via the {@code Iterator.remove},
276 * {@code Set.remove}, {@code removeAll}, {@code retainAll} and
277 * {@code clear} operations. It does not support the
278 * {@code add} or {@code addAll} operations.
280 * @return a set view of the mappings contained in this map,
281 * sorted in ascending key order
283 Set<Map.Entry<K, V>> entrySet();