1 /* 2 * Copyright (c) 1998, 2018, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.util; 27 28 /** 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}.) 37 * 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}. 46 * 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. 59 * 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: 64 * <ol> 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> 75 * </ol> 76 * 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> 88 * 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> 94 * 95 * <p>This interface is a member of the 96 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> 97 * Java Collections Framework</a>. 98 * 99 * @param <K> the type of keys maintained by this map 100 * @param <V> the type of mapped values 101 * 102 * @author Josh Bloch 103 * @see Map 104 * @see TreeMap 105 * @see SortedSet 106 * @see Comparator 107 * @see Comparable 108 * @see Collection 109 * @see ClassCastException 110 * @since 1.2 111 */ 112 113 public interface SortedMap<K,V> extends Map<K,V> { 114 /** 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. 118 * 119 * @return the comparator used to order the keys in this map, 120 * or {@code null} if this map uses the natural ordering 121 * of its keys 122 */ comparator()123 Comparator<? super K> comparator(); 124 125 /** 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 132 * map supports. 133 * 134 * <p>The returned map will throw an {@code IllegalArgumentException} 135 * on an attempt to insert a key outside its range. 136 * 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 153 */ subMap(K fromKey, K toKey)154 SortedMap<K,V> subMap(K fromKey, K toKey); 155 156 /** 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. 162 * 163 * <p>The returned map will throw an {@code IllegalArgumentException} 164 * on an attempt to insert a key outside its range. 165 * 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 180 */ headMap(K toKey)181 SortedMap<K,V> headMap(K toKey); 182 183 /** 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. 189 * 190 * <p>The returned map will throw an {@code IllegalArgumentException} 191 * on an attempt to insert a key outside its range. 192 * 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 207 */ tailMap(K fromKey)208 SortedMap<K,V> tailMap(K fromKey); 209 210 /** 211 * Returns the first (lowest) key currently in this map. 212 * 213 * @return the first (lowest) key currently in this map 214 * @throws NoSuchElementException if this map is empty 215 */ firstKey()216 K firstKey(); 217 218 /** 219 * Returns the last (highest) key currently in this map. 220 * 221 * @return the last (highest) key currently in this map 222 * @throws NoSuchElementException if this map is empty 223 */ lastKey()224 K lastKey(); 225 226 /** 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} 238 * operations. 239 * 240 * @return a set view of the keys contained in this map, sorted in 241 * ascending order 242 */ keySet()243 Set<K> keySet(); 244 245 /** 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. 259 * 260 * @return a collection view of the values contained in this map, 261 * sorted in ascending key order 262 */ values()263 Collection<V> values(); 264 265 /** 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. 279 * 280 * @return a set view of the mappings contained in this map, 281 * sorted in ascending key order 282 */ entrySet()283 Set<Map.Entry<K, V>> entrySet(); 284 } 285