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| 1 | /* | ||
| 2 | * Copyright (c) 1997, 2006, 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 | * An object that maps keys to values. A map cannot contain duplicate keys; | ||
| 30 | * each key can map to at most one value. | ||
| 31 | * | ||
| 32 | * <p>This interface takes the place of the <tt>Dictionary</tt> class, which | ||
| 33 | * was a totally abstract class rather than an interface. | ||
| 34 | * | ||
| 35 | * <p>The <tt>Map</tt> interface provides three <i>collection views</i>, which | ||
| 36 | * allow a map's contents to be viewed as a set of keys, collection of values, | ||
| 37 | * or set of key-value mappings. The <i>order</i> of a map is defined as | ||
| 38 | * the order in which the iterators on the map's collection views return their | ||
| 39 | * elements. Some map implementations, like the <tt>TreeMap</tt> class, make | ||
| 40 | * specific guarantees as to their order; others, like the <tt>HashMap</tt> | ||
| 41 | * class, do not. | ||
| 42 | * | ||
| 43 | * <p>Note: great care must be exercised if mutable objects are used as map | ||
| 44 | * keys. The behavior of a map is not specified if the value of an object is | ||
| 45 | * changed in a manner that affects <tt>equals</tt> comparisons while the | ||
| 46 | * object is a key in the map. A special case of this prohibition is that it | ||
| 47 | * is not permissible for a map to contain itself as a key. While it is | ||
| 48 | * permissible for a map to contain itself as a value, extreme caution is | ||
| 49 | * advised: the <tt>equals</tt> and <tt>hashCode</tt> methods are no longer | ||
| 50 | * well defined on such a map. | ||
| 51 | * | ||
| 52 | * <p>All general-purpose map implementation classes should provide two | ||
| 53 | * "standard" constructors: a void (no arguments) constructor which creates an | ||
| 54 | * empty map, and a constructor with a single argument of type <tt>Map</tt>, | ||
| 55 | * which creates a new map with the same key-value mappings as its argument. | ||
| 56 | * In effect, the latter constructor allows the user to copy any map, | ||
| 57 | * producing an equivalent map of the desired class. There is no way to | ||
| 58 | * enforce this recommendation (as interfaces cannot contain constructors) but | ||
| 59 | * all of the general-purpose map implementations in the JDK comply. | ||
| 60 | * | ||
| 61 | * <p>The "destructive" methods contained in this interface, that is, the | ||
| 62 | * methods that modify the map on which they operate, are specified to throw | ||
| 63 | * <tt>UnsupportedOperationException</tt> if this map does not support the | ||
| 64 | * operation. If this is the case, these methods may, but are not required | ||
| 65 | * to, throw an <tt>UnsupportedOperationException</tt> if the invocation would | ||
| 66 | * have no effect on the map. For example, invoking the {@link #putAll(Map)} | ||
| 67 | * method on an unmodifiable map may, but is not required to, throw the | ||
| 68 | * exception if the map whose mappings are to be "superimposed" is empty. | ||
| 69 | * | ||
| 70 | * <p>Some map implementations have restrictions on the keys and values they | ||
| 71 | * may contain. For example, some implementations prohibit null keys and | ||
| 72 | * values, and some have restrictions on the types of their keys. Attempting | ||
| 73 | * to insert an ineligible key or value throws an unchecked exception, | ||
| 74 | * typically <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. | ||
| 75 | * Attempting to query the presence of an ineligible key or value may throw an | ||
| 76 | * exception, or it may simply return false; some implementations will exhibit | ||
| 77 | * the former behavior and some will exhibit the latter. More generally, | ||
| 78 | * attempting an operation on an ineligible key or value whose completion | ||
| 79 | * would not result in the insertion of an ineligible element into the map may | ||
| 80 | * throw an exception or it may succeed, at the option of the implementation. | ||
| 81 | * Such exceptions are marked as "optional" in the specification for this | ||
| 82 | * interface. | ||
| 83 | * | ||
| 84 | * <p>This interface is a member of the | ||
| 85 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> | ||
| 86 | * Java Collections Framework</a>. | ||
| 87 | * | ||
| 88 | * <p>Many methods in Collections Framework interfaces are defined | ||
| 89 | * in terms of the {@link Object#equals(Object) equals} method. For | ||
| 90 | * example, the specification for the {@link #containsKey(Object) | ||
| 91 | * containsKey(Object key)} method says: "returns <tt>true</tt> if and | ||
| 92 | * only if this map contains a mapping for a key <tt>k</tt> such that | ||
| 93 | * <tt>(key==null ? k==null : key.equals(k))</tt>." This specification should | ||
| 94 | * <i>not</i> be construed to imply that invoking <tt>Map.containsKey</tt> | ||
| 95 | * with a non-null argument <tt>key</tt> will cause <tt>key.equals(k)</tt> to | ||
| 96 | * be invoked for any key <tt>k</tt>. Implementations are free to | ||
| 97 | * implement optimizations whereby the <tt>equals</tt> invocation is avoided, | ||
| 98 | * for example, by first comparing the hash codes of the two keys. (The | ||
| 99 | * {@link Object#hashCode()} specification guarantees that two objects with | ||
| 100 | * unequal hash codes cannot be equal.) More generally, implementations of | ||
| 101 | * the various Collections Framework interfaces are free to take advantage of | ||
| 102 | * the specified behavior of underlying {@link Object} methods wherever the | ||
| 103 | * implementor deems it appropriate. | ||
| 104 | * | ||
| 105 | * @param <K> the type of keys maintained by this map | ||
| 106 | * @param <V> the type of mapped values | ||
| 107 | * | ||
| 108 | * @author Josh Bloch | ||
| 109 | * @see HashMap | ||
| 110 | * @see TreeMap | ||
| 111 | * @see Hashtable | ||
| 112 | * @see SortedMap | ||
| 113 | * @see Collection | ||
| 114 | * @see Set | ||
| 115 | * @since 1.2 | ||
| 116 | */ | ||
| 117 | public interface Map<K,V> { | ||
| 118 | // Query Operations | ||
| 119 | |||
| 120 | /** | ||
| 121 | * Returns the number of key-value mappings in this map. If the | ||
| 122 | * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns | ||
| 123 | * <tt>Integer.MAX_VALUE</tt>. | ||
| 124 | * | ||
| 125 | * @return the number of key-value mappings in this map | ||
| 126 | */ | ||
| 127 | int size(); | ||
| 128 | |||
| 129 | /** | ||
| 130 | * Returns <tt>true</tt> if this map contains no key-value mappings. | ||
| 131 | * | ||
| 132 | * @return <tt>true</tt> if this map contains no key-value mappings | ||
| 133 | */ | ||
| 134 | boolean isEmpty(); | ||
| 135 | |||
| 136 | /** | ||
| 137 | * Returns <tt>true</tt> if this map contains a mapping for the specified | ||
| 138 | * key. More formally, returns <tt>true</tt> if and only if | ||
| 139 | * this map contains a mapping for a key <tt>k</tt> such that | ||
| 140 | * <tt>(key==null ? k==null : key.equals(k))</tt>. (There can be | ||
| 141 | * at most one such mapping.) | ||
| 142 | * | ||
| 143 | * @param key key whose presence in this map is to be tested | ||
| 144 | * @return <tt>true</tt> if this map contains a mapping for the specified | ||
| 145 | * key | ||
| 146 | * @throws ClassCastException if the key is of an inappropriate type for | ||
| 147 | * this map | ||
| 148 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 149 | * @throws NullPointerException if the specified key is null and this map | ||
| 150 | * does not permit null keys | ||
| 151 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 152 | */ | ||
| 153 | boolean containsKey(Object key); | ||
| 154 | |||
| 155 | /** | ||
| 156 | * Returns <tt>true</tt> if this map maps one or more keys to the | ||
| 157 | * specified value. More formally, returns <tt>true</tt> if and only if | ||
| 158 | * this map contains at least one mapping to a value <tt>v</tt> such that | ||
| 159 | * <tt>(value==null ? v==null : value.equals(v))</tt>. This operation | ||
| 160 | * will probably require time linear in the map size for most | ||
| 161 | * implementations of the <tt>Map</tt> interface. | ||
| 162 | * | ||
| 163 | * @param value value whose presence in this map is to be tested | ||
| 164 | * @return <tt>true</tt> if this map maps one or more keys to the | ||
| 165 | * specified value | ||
| 166 | * @throws ClassCastException if the value is of an inappropriate type for | ||
| 167 | * this map | ||
| 168 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 169 | * @throws NullPointerException if the specified value is null and this | ||
| 170 | * map does not permit null values | ||
| 171 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 172 | */ | ||
| 173 | boolean containsValue(Object value); | ||
| 174 | |||
| 175 | /** | ||
| 176 | * Returns the value to which the specified key is mapped, | ||
| 177 | * or {@code null} if this map contains no mapping for the key. | ||
| 178 | * | ||
| 179 | * <p>More formally, if this map contains a mapping from a key | ||
| 180 | * {@code k} to a value {@code v} such that {@code (key==null ? k==null : | ||
| 181 | * key.equals(k))}, then this method returns {@code v}; otherwise | ||
| 182 | * it returns {@code null}. (There can be at most one such mapping.) | ||
| 183 | * | ||
| 184 | * <p>If this map permits null values, then a return value of | ||
| 185 | * {@code null} does not <i>necessarily</i> indicate that the map | ||
| 186 | * contains no mapping for the key; it's also possible that the map | ||
| 187 | * explicitly maps the key to {@code null}. The {@link #containsKey | ||
| 188 | * containsKey} operation may be used to distinguish these two cases. | ||
| 189 | * | ||
| 190 | * @param key the key whose associated value is to be returned | ||
| 191 | * @return the value to which the specified key is mapped, or | ||
| 192 | * {@code null} if this map contains no mapping for the key | ||
| 193 | * @throws ClassCastException if the key is of an inappropriate type for | ||
| 194 | * this map | ||
| 195 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 196 | * @throws NullPointerException if the specified key is null and this map | ||
| 197 | * does not permit null keys | ||
| 198 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 199 | */ | ||
| 200 | V get(Object key); | ||
| 201 | |||
| 202 | // Modification Operations | ||
| 203 | |||
| 204 | /** | ||
| 205 | * Associates the specified value with the specified key in this map | ||
| 206 | * (optional operation). If the map previously contained a mapping for | ||
| 207 | * the key, the old value is replaced by the specified value. (A map | ||
| 208 | * <tt>m</tt> is said to contain a mapping for a key <tt>k</tt> if and only | ||
| 209 | * if {@link #containsKey(Object) m.containsKey(k)} would return | ||
| 210 | * <tt>true</tt>.) | ||
| 211 | * | ||
| 212 | * @param key key with which the specified value is to be associated | ||
| 213 | * @param value value to be associated with the specified key | ||
| 214 | * @return the previous value associated with <tt>key</tt>, or | ||
| 215 | * <tt>null</tt> if there was no mapping for <tt>key</tt>. | ||
| 216 | * (A <tt>null</tt> return can also indicate that the map | ||
| 217 | * previously associated <tt>null</tt> with <tt>key</tt>, | ||
| 218 | * if the implementation supports <tt>null</tt> values.) | ||
| 219 | * @throws UnsupportedOperationException if the <tt>put</tt> operation | ||
| 220 | * is not supported by this map | ||
| 221 | * @throws ClassCastException if the class of the specified key or value | ||
| 222 | * prevents it from being stored in this map | ||
| 223 | * @throws NullPointerException if the specified key or value is null | ||
| 224 | * and this map does not permit null keys or values | ||
| 225 | * @throws IllegalArgumentException if some property of the specified key | ||
| 226 | * or value prevents it from being stored in this map | ||
| 227 | */ | ||
| 228 | V put(K key, V value); | ||
| 229 | |||
| 230 | /** | ||
| 231 | * Removes the mapping for a key from this map if it is present | ||
| 232 | * (optional operation). More formally, if this map contains a mapping | ||
| 233 | * from key <tt>k</tt> to value <tt>v</tt> such that | ||
| 234 | * <code>(key==null ? k==null : key.equals(k))</code>, that mapping | ||
| 235 | * is removed. (The map can contain at most one such mapping.) | ||
| 236 | * | ||
| 237 | * <p>Returns the value to which this map previously associated the key, | ||
| 238 | * or <tt>null</tt> if the map contained no mapping for the key. | ||
| 239 | * | ||
| 240 | * <p>If this map permits null values, then a return value of | ||
| 241 | * <tt>null</tt> does not <i>necessarily</i> indicate that the map | ||
| 242 | * contained no mapping for the key; it's also possible that the map | ||
| 243 | * explicitly mapped the key to <tt>null</tt>. | ||
| 244 | * | ||
| 245 | * <p>The map will not contain a mapping for the specified key once the | ||
| 246 | * call returns. | ||
| 247 | * | ||
| 248 | * @param key key whose mapping is to be removed from the map | ||
| 249 | * @return the previous value associated with <tt>key</tt>, or | ||
| 250 | * <tt>null</tt> if there was no mapping for <tt>key</tt>. | ||
| 251 | * @throws UnsupportedOperationException if the <tt>remove</tt> operation | ||
| 252 | * is not supported by this map | ||
| 253 | * @throws ClassCastException if the key is of an inappropriate type for | ||
| 254 | * this map | ||
| 255 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 256 | * @throws NullPointerException if the specified key is null and this | ||
| 257 | * map does not permit null keys | ||
| 258 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 259 | */ | ||
| 260 | V remove(Object key); | ||
| 261 | |||
| 262 | |||
| 263 | // Bulk Operations | ||
| 264 | |||
| 265 | /** | ||
| 266 | * Copies all of the mappings from the specified map to this map | ||
| 267 | * (optional operation). The effect of this call is equivalent to that | ||
| 268 | * of calling {@link #put(Object,Object) put(k, v)} on this map once | ||
| 269 | * for each mapping from key <tt>k</tt> to value <tt>v</tt> in the | ||
| 270 | * specified map. The behavior of this operation is undefined if the | ||
| 271 | * specified map is modified while the operation is in progress. | ||
| 272 | * | ||
| 273 | * @param m mappings to be stored in this map | ||
| 274 | * @throws UnsupportedOperationException if the <tt>putAll</tt> operation | ||
| 275 | * is not supported by this map | ||
| 276 | * @throws ClassCastException if the class of a key or value in the | ||
| 277 | * specified map prevents it from being stored in this map | ||
| 278 | * @throws NullPointerException if the specified map is null, or if | ||
| 279 | * this map does not permit null keys or values, and the | ||
| 280 | * specified map contains null keys or values | ||
| 281 | * @throws IllegalArgumentException if some property of a key or value in | ||
| 282 | * the specified map prevents it from being stored in this map | ||
| 283 | */ | ||
| 284 | void putAll(Map<? extends K, ? extends V> m); | ||
| 285 | |||
| 286 | /** | ||
| 287 | * Removes all of the mappings from this map (optional operation). | ||
| 288 | * The map will be empty after this call returns. | ||
| 289 | * | ||
| 290 | * @throws UnsupportedOperationException if the <tt>clear</tt> operation | ||
| 291 | * is not supported by this map | ||
| 292 | */ | ||
| 293 | void clear(); | ||
| 294 | |||
| 295 | |||
| 296 | // Views | ||
| 297 | |||
| 298 | /** | ||
| 299 | * Returns a {@link Set} view of the keys contained in this map. | ||
| 300 | * The set is backed by the map, so changes to the map are | ||
| 301 | * reflected in the set, and vice-versa. If the map is modified | ||
| 302 | * while an iteration over the set is in progress (except through | ||
| 303 | * the iterator's own <tt>remove</tt> operation), the results of | ||
| 304 | * the iteration are undefined. The set supports element removal, | ||
| 305 | * which removes the corresponding mapping from the map, via the | ||
| 306 | * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, | ||
| 307 | * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> | ||
| 308 | * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> | ||
| 309 | * operations. | ||
| 310 | * | ||
| 311 | * @return a set view of the keys contained in this map | ||
| 312 | */ | ||
| 313 | Set<K> keySet(); | ||
| 314 | |||
| 315 | /** | ||
| 316 | * Returns a {@link Collection} view of the values contained in this map. | ||
| 317 | * The collection is backed by the map, so changes to the map are | ||
| 318 | * reflected in the collection, and vice-versa. If the map is | ||
| 319 | * modified while an iteration over the collection is in progress | ||
| 320 | * (except through the iterator's own <tt>remove</tt> operation), | ||
| 321 | * the results of the iteration are undefined. The collection | ||
| 322 | * supports element removal, which removes the corresponding | ||
| 323 | * mapping from the map, via the <tt>Iterator.remove</tt>, | ||
| 324 | * <tt>Collection.remove</tt>, <tt>removeAll</tt>, | ||
| 325 | * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not | ||
| 326 | * support the <tt>add</tt> or <tt>addAll</tt> operations. | ||
| 327 | * | ||
| 328 | * @return a collection view of the values contained in this map | ||
| 329 | */ | ||
| 330 | Collection<V> values(); | ||
| 331 | |||
| 332 | /** | ||
| 333 | * Returns a {@link Set} view of the mappings contained in this map. | ||
| 334 | * The set is backed by the map, so changes to the map are | ||
| 335 | * reflected in the set, and vice-versa. If the map is modified | ||
| 336 | * while an iteration over the set is in progress (except through | ||
| 337 | * the iterator's own <tt>remove</tt> operation, or through the | ||
| 338 | * <tt>setValue</tt> operation on a map entry returned by the | ||
| 339 | * iterator) the results of the iteration are undefined. The set | ||
| 340 | * supports element removal, which removes the corresponding | ||
| 341 | * mapping from the map, via the <tt>Iterator.remove</tt>, | ||
| 342 | * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and | ||
| 343 | * <tt>clear</tt> operations. It does not support the | ||
| 344 | * <tt>add</tt> or <tt>addAll</tt> operations. | ||
| 345 | * | ||
| 346 | * @return a set view of the mappings contained in this map | ||
| 347 | */ | ||
| 348 | Set<Map.Entry<K, V>> entrySet(); | ||
| 349 | |||
| 350 | /** | ||
| 351 | * A map entry (key-value pair). The <tt>Map.entrySet</tt> method returns | ||
| 352 | * a collection-view of the map, whose elements are of this class. The | ||
| 353 | * <i>only</i> way to obtain a reference to a map entry is from the | ||
| 354 | * iterator of this collection-view. These <tt>Map.Entry</tt> objects are | ||
| 355 | * valid <i>only</i> for the duration of the iteration; more formally, | ||
| 356 | * the behavior of a map entry is undefined if the backing map has been | ||
| 357 | * modified after the entry was returned by the iterator, except through | ||
| 358 | * the <tt>setValue</tt> operation on the map entry. | ||
| 359 | * | ||
| 360 | * @see Map#entrySet() | ||
| 361 | * @since 1.2 | ||
| 362 | */ | ||
| 363 | interface Entry<K,V> { | ||
| 364 | /** | ||
| 365 | * Returns the key corresponding to this entry. | ||
| 366 | * | ||
| 367 | * @return the key corresponding to this entry | ||
| 368 | * @throws IllegalStateException implementations may, but are not | ||
| 369 | * required to, throw this exception if the entry has been | ||
| 370 | * removed from the backing map. | ||
| 371 | */ | ||
| 372 | K getKey(); | ||
| 373 | |||
| 374 | /** | ||
| 375 | * Returns the value corresponding to this entry. If the mapping | ||
| 376 | * has been removed from the backing map (by the iterator's | ||
| 377 | * <tt>remove</tt> operation), the results of this call are undefined. | ||
| 378 | * | ||
| 379 | * @return the value corresponding to this entry | ||
| 380 | * @throws IllegalStateException implementations may, but are not | ||
| 381 | * required to, throw this exception if the entry has been | ||
| 382 | * removed from the backing map. | ||
| 383 | */ | ||
| 384 | V getValue(); | ||
| 385 | |||
| 386 | /** | ||
| 387 | * Replaces the value corresponding to this entry with the specified | ||
| 388 | * value (optional operation). (Writes through to the map.) The | ||
| 389 | * behavior of this call is undefined if the mapping has already been | ||
| 390 | * removed from the map (by the iterator's <tt>remove</tt> operation). | ||
| 391 | * | ||
| 392 | * @param value new value to be stored in this entry | ||
| 393 | * @return old value corresponding to the entry | ||
| 394 | * @throws UnsupportedOperationException if the <tt>put</tt> operation | ||
| 395 | * is not supported by the backing map | ||
| 396 | * @throws ClassCastException if the class of the specified value | ||
| 397 | * prevents it from being stored in the backing map | ||
| 398 | * @throws NullPointerException if the backing map does not permit | ||
| 399 | * null values, and the specified value is null | ||
| 400 | * @throws IllegalArgumentException if some property of this value | ||
| 401 | * prevents it from being stored in the backing map | ||
| 402 | * @throws IllegalStateException implementations may, but are not | ||
| 403 | * required to, throw this exception if the entry has been | ||
| 404 | * removed from the backing map. | ||
| 405 | */ | ||
| 406 | V setValue(V value); | ||
| 407 | |||
| 408 | /** | ||
| 409 | * Compares the specified object with this entry for equality. | ||
| 410 | * Returns <tt>true</tt> if the given object is also a map entry and | ||
| 411 | * the two entries represent the same mapping. More formally, two | ||
| 412 | * entries <tt>e1</tt> and <tt>e2</tt> represent the same mapping | ||
| 413 | * if<pre> | ||
| 414 | * (e1.getKey()==null ? | ||
| 415 | * e2.getKey()==null : e1.getKey().equals(e2.getKey())) && | ||
| 416 | * (e1.getValue()==null ? | ||
| 417 | * e2.getValue()==null : e1.getValue().equals(e2.getValue())) | ||
| 418 | * </pre> | ||
| 419 | * This ensures that the <tt>equals</tt> method works properly across | ||
| 420 | * different implementations of the <tt>Map.Entry</tt> interface. | ||
| 421 | * | ||
| 422 | * @param o object to be compared for equality with this map entry | ||
| 423 | * @return <tt>true</tt> if the specified object is equal to this map | ||
| 424 | * entry | ||
| 425 | */ | ||
| 426 | boolean equals(Object o); | ||
| 427 | |||
| 428 | /** | ||
| 429 | * Returns the hash code value for this map entry. The hash code | ||
| 430 | * of a map entry <tt>e</tt> is defined to be: <pre> | ||
| 431 | * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^ | ||
| 432 | * (e.getValue()==null ? 0 : e.getValue().hashCode()) | ||
| 433 | * </pre> | ||
| 434 | * This ensures that <tt>e1.equals(e2)</tt> implies that | ||
| 435 | * <tt>e1.hashCode()==e2.hashCode()</tt> for any two Entries | ||
| 436 | * <tt>e1</tt> and <tt>e2</tt>, as required by the general | ||
| 437 | * contract of <tt>Object.hashCode</tt>. | ||
| 438 | * | ||
| 439 | * @return the hash code value for this map entry | ||
| 440 | * @see Object#hashCode() | ||
| 441 | * @see Object#equals(Object) | ||
| 442 | * @see #equals(Object) | ||
| 443 | */ | ||
| 444 | int hashCode(); | ||
| 445 | } | ||
| 446 | |||
| 447 | // Comparison and hashing | ||
| 448 | |||
| 449 | /** | ||
| 450 | * Compares the specified object with this map for equality. Returns | ||
| 451 | * <tt>true</tt> if the given object is also a map and the two maps | ||
| 452 | * represent the same mappings. More formally, two maps <tt>m1</tt> and | ||
| 453 | * <tt>m2</tt> represent the same mappings if | ||
| 454 | * <tt>m1.entrySet().equals(m2.entrySet())</tt>. This ensures that the | ||
| 455 | * <tt>equals</tt> method works properly across different implementations | ||
| 456 | * of the <tt>Map</tt> interface. | ||
| 457 | * | ||
| 458 | * @param o object to be compared for equality with this map | ||
| 459 | * @return <tt>true</tt> if the specified object is equal to this map | ||
| 460 | */ | ||
| 461 | boolean equals(Object o); | ||
| 462 | |||
| 463 | /** | ||
| 464 | * Returns the hash code value for this map. The hash code of a map is | ||
| 465 | * defined to be the sum of the hash codes of each entry in the map's | ||
| 466 | * <tt>entrySet()</tt> view. This ensures that <tt>m1.equals(m2)</tt> | ||
| 467 | * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps | ||
| 468 | * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of | ||
| 469 | * {@link Object#hashCode}. | ||
| 470 | * | ||
| 471 | * @return the hash code value for this map | ||
| 472 | * @see Map.Entry#hashCode() | ||
| 473 | * @see Object#equals(Object) | ||
| 474 | * @see #equals(Object) | ||
| 475 | */ | ||
| 476 | int hashCode(); | ||
| 477 | |||
| 478 | } | ||