| SortedMap.java |
1 /*
2 * %W% %E%
3 *
4 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
5 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6 */
7
8 package java.util;
9
10 /**
11 * A {@link Map} that further provides a <i>total ordering</i> on its keys.
12 * The map is ordered according to the {@linkplain Comparable natural
13 * ordering} of its keys, or by a {@link Comparator} typically
14 * provided at sorted map creation time. This order is reflected when
15 * iterating over the sorted map's collection views (returned by the
16 * <tt>entrySet</tt>, <tt>keySet</tt> and <tt>values</tt> methods).
17 * Several additional operations are provided to take advantage of the
18 * ordering. (This interface is the map analogue of {@link
19 * SortedSet}.)
20 *
21 * <p>All keys inserted into a sorted map must implement the <tt>Comparable</tt>
22 * interface (or be accepted by the specified comparator). Furthermore, all
23 * such keys must be <i>mutually comparable</i>: <tt>k1.compareTo(k2)</tt> (or
24 * <tt>comparator.compare(k1, k2)</tt>) must not throw a
25 * <tt>ClassCastException</tt> for any keys <tt>k1</tt> and <tt>k2</tt> in
26 * the sorted map. Attempts to violate this restriction will cause the
27 * offending method or constructor invocation to throw a
28 * <tt>ClassCastException</tt>.
29 *
30 * <p>Note that the ordering maintained by a sorted map (whether or not an
31 * explicit comparator is provided) must be <i>consistent with equals</i> if
32 * the sorted map is to correctly implement the <tt>Map</tt> interface. (See
33 * the <tt>Comparable</tt> interface or <tt>Comparator</tt> interface for a
34 * precise definition of <i>consistent with equals</i>.) This is so because
35 * the <tt>Map</tt> interface is defined in terms of the <tt>equals</tt>
36 * operation, but a sorted map performs all key comparisons using its
37 * <tt>compareTo</tt> (or <tt>compare</tt>) method, so two keys that are
38 * deemed equal by this method are, from the standpoint of the sorted map,
39 * equal. The behavior of a tree map <i>is</i> well-defined even if its
40 * ordering is inconsistent with equals; it just fails to obey the general
41 * contract of the <tt>Map</tt> interface.
42 *
43 * <p>All general-purpose sorted map implementation classes should
44 * provide four "standard" constructors: 1) A void (no arguments)
45 * constructor, which creates an empty sorted map sorted according to
46 * the natural ordering of its keys. 2) A constructor with a
47 * single argument of type <tt>Comparator</tt>, which creates an empty
48 * sorted map sorted according to the specified comparator. 3) A
49 * constructor with a single argument of type <tt>Map</tt>, which
50 * creates a new map with the same key-value mappings as its argument,
51 * sorted according to the keys' natural ordering. 4) A constructor
52 * with a single argument of type <tt>SortedMap</tt>,
53 * which creates a new sorted map with the same key-value mappings and
54 * the same ordering as the input sorted map. There is no way to
55 * enforce this recommendation, as interfaces cannot contain
56 * constructors.
57 *
58 * <p>Note: several methods return submaps with restricted key ranges.
59 * Such ranges are <i>half-open</i>, that is, they include their low
60 * endpoint but not their high endpoint (where applicable). If you need a
61 * <i>closed range</i> (which includes both endpoints), and the key type
62 * allows for calculation of the successor of a given key, merely request
63 * the subrange from <tt>lowEndpoint</tt> to
64 * <tt>successor(highEndpoint)</tt>. For example, suppose that <tt>m</tt>
65 * is a map whose keys are strings. The following idiom obtains a view
66 * containing all of the key-value mappings in <tt>m</tt> whose keys are
67 * between <tt>low</tt> and <tt>high</tt>, inclusive:<pre>
68 * SortedMap<String, V> sub = m.subMap(low, high+"\0");</pre>
69 *
70 * A similar technique can be used to generate an <i>open range</i>
71 * (which contains neither endpoint). The following idiom obtains a
72 * view containing all of the key-value mappings in <tt>m</tt> whose keys
73 * are between <tt>low</tt> and <tt>high</tt>, exclusive:<pre>
74 * SortedMap<String, V> sub = m.subMap(low+"\0", high);</pre>
75 *
76 * <p>This interface is a member of the
77 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
78 * Java Collections Framework</a>.
79 *
80 * @param <K> the type of keys maintained by this map
81 * @param <V> the type of mapped values
82 *
83 * @author Josh Bloch
84 * @version %I%, %G%
85 * @see Map
86 * @see TreeMap
87 * @see SortedSet
88 * @see Comparator
89 * @see Comparable
90 * @see Collection
91 * @see ClassCastException
92 * @since 1.2
93 */
94
95 public interface SortedMap<K,V> extends Map<K,V> {
96 /**
97 * Returns the comparator used to order the keys in this map, or
98 * <tt>null</tt> if this map uses the {@linkplain Comparable
99 * natural ordering} of its keys.
100 *
101 * @return the comparator used to order the keys in this map,
102 * or <tt>null</tt> if this map uses the natural ordering
103 * of its keys
104 */
105 Comparator<? super K> comparator();
106
107 /**
108 * Returns a view of the portion of this map whose keys range from
109 * <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive. (If
110 * <tt>fromKey</tt> and <tt>toKey</tt> are equal, the returned map
111 * is empty.) The returned map is backed by this map, so changes
112 * in the returned map are reflected in this map, and vice-versa.
113 * The returned map supports all optional map operations that this
114 * map supports.
115 *
116 * <p>The returned map will throw an <tt>IllegalArgumentException</tt>
117 * on an attempt to insert a key outside its range.
118 *
119 * @param fromKey low endpoint (inclusive) of the keys in the returned map
120 * @param toKey high endpoint (exclusive) of the keys in the returned map
121 * @return a view of the portion of this map whose keys range from
122 * <tt>fromKey</tt>, inclusive, to <tt>toKey</tt>, exclusive
123 * @throws ClassCastException if <tt>fromKey</tt> and <tt>toKey</tt>
124 * cannot be compared to one another using this map's comparator
125 * (or, if the map has no comparator, using natural ordering).
126 * Implementations may, but are not required to, throw this
127 * exception if <tt>fromKey</tt> or <tt>toKey</tt>
128 * cannot be compared to keys currently in the map.
129 * @throws NullPointerException if <tt>fromKey</tt> or <tt>toKey</tt>
130 * is null and this map does not permit null keys
131 * @throws IllegalArgumentException if <tt>fromKey</tt> is greater than
132 * <tt>toKey</tt>; or if this map itself has a restricted
133 * range, and <tt>fromKey</tt> or <tt>toKey</tt> lies
134 * outside the bounds of the range
135 */
136 SortedMap<K,V> subMap(K fromKey, K toKey);
137
138 /**
139 * Returns a view of the portion of this map whose keys are
140 * strictly less than <tt>toKey</tt>. The returned map is backed
141 * by this map, so changes in the returned map are reflected in
142 * this map, and vice-versa. The returned map supports all
143 * optional map operations that this map supports.
144 *
145 * <p>The returned map will throw an <tt>IllegalArgumentException</tt>
146 * on an attempt to insert a key outside its range.
147 *
148 * @param toKey high endpoint (exclusive) of the keys in the returned map
149 * @return a view of the portion of this map whose keys are strictly
150 * less than <tt>toKey</tt>
151 * @throws ClassCastException if <tt>toKey</tt> is not compatible
152 * with this map's comparator (or, if the map has no comparator,
153 * if <tt>toKey</tt> does not implement {@link Comparable}).
154 * Implementations may, but are not required to, throw this
155 * exception if <tt>toKey</tt> cannot be compared to keys
156 * currently in the map.
157 * @throws NullPointerException if <tt>toKey</tt> is null and
158 * this map does not permit null keys
159 * @throws IllegalArgumentException if this map itself has a
160 * restricted range, and <tt>toKey</tt> lies outside the
161 * bounds of the range
162 */
163 SortedMap<K,V> headMap(K toKey);
164
165 /**
166 * Returns a view of the portion of this map whose keys are
167 * greater than or equal to <tt>fromKey</tt>. The returned map is
168 * backed by this map, so changes in the returned map are
169 * reflected in this map, and vice-versa. The returned map
170 * supports all optional map operations that this map supports.
171 *
172 * <p>The returned map will throw an <tt>IllegalArgumentException</tt>
173 * on an attempt to insert a key outside its range.
174 *
175 * @param fromKey low endpoint (inclusive) of the keys in the returned map
176 * @return a view of the portion of this map whose keys are greater
177 * than or equal to <tt>fromKey</tt>
178 * @throws ClassCastException if <tt>fromKey</tt> is not compatible
179 * with this map's comparator (or, if the map has no comparator,
180 * if <tt>fromKey</tt> does not implement {@link Comparable}).
181 * Implementations may, but are not required to, throw this
182 * exception if <tt>fromKey</tt> cannot be compared to keys
183 * currently in the map.
184 * @throws NullPointerException if <tt>fromKey</tt> is null and
185 * this map does not permit null keys
186 * @throws IllegalArgumentException if this map itself has a
187 * restricted range, and <tt>fromKey</tt> lies outside the
188 * bounds of the range
189 */
190 SortedMap<K,V> tailMap(K fromKey);
191
192 /**
193 * Returns the first (lowest) key currently in this map.
194 *
195 * @return the first (lowest) key currently in this map
196 * @throws NoSuchElementException if this map is empty
197 */
198 K firstKey();
199
200 /**
201 * Returns the last (highest) key currently in this map.
202 *
203 * @return the last (highest) key currently in this map
204 * @throws NoSuchElementException if this map is empty
205 */
206 K lastKey();
207
208 /**
209 * Returns a {@link Set} view of the keys contained in this map.
210 * The set's iterator returns the keys in ascending order.
211 * The set is backed by the map, so changes to the map are
212 * reflected in the set, and vice-versa. If the map is modified
213 * while an iteration over the set is in progress (except through
214 * the iterator's own <tt>remove</tt> operation), the results of
215 * the iteration are undefined. The set supports element removal,
216 * which removes the corresponding mapping from the map, via the
217 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
218 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
219 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
220 * operations.
221 *
222 * @return a set view of the keys contained in this map, sorted in
223 * ascending order
224 */
225 Set<K> keySet();
226
227 /**
228 * Returns a {@link Collection} view of the values contained in this map.
229 * The collection's iterator returns the values in ascending order
230 * of the corresponding keys.
231 * The collection is backed by the map, so changes to the map are
232 * reflected in the collection, and vice-versa. If the map is
233 * modified while an iteration over the collection is in progress
234 * (except through the iterator's own <tt>remove</tt> operation),
235 * the results of the iteration are undefined. The collection
236 * supports element removal, which removes the corresponding
237 * mapping from the map, via the <tt>Iterator.remove</tt>,
238 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
239 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
240 * support the <tt>add</tt> or <tt>addAll</tt> operations.
241 *
242 * @return a collection view of the values contained in this map,
243 * sorted in ascending key order
244 */
245 Collection<V> values();
246
247 /**
248 * Returns a {@link Set} view of the mappings contained in this map.
249 * The set's iterator returns the entries in ascending key order.
250 * The set is backed by the map, so changes to the map are
251 * reflected in the set, and vice-versa. If the map is modified
252 * while an iteration over the set is in progress (except through
253 * the iterator's own <tt>remove</tt> operation, or through the
254 * <tt>setValue</tt> operation on a map entry returned by the
255 * iterator) the results of the iteration are undefined. The set
256 * supports element removal, which removes the corresponding
257 * mapping from the map, via the <tt>Iterator.remove</tt>,
258 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
259 * <tt>clear</tt> operations. It does not support the
260 * <tt>add</tt> or <tt>addAll</tt> operations.
261 *
262 * @return a set view of the mappings contained in this map,
263 * sorted in ascending key order
264 */
265 Set<Map.Entry<K, V>> entrySet();
266 }
267