1 /* 2 * Copyright (c) 1997, 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 import java.util.function.BiConsumer; 29 import java.util.function.BiFunction; 30 import java.util.function.Function; 31 import java.io.Serializable; 32 33 // Android-changed: removed link to collections framework docs 34 /** 35 * An object that maps keys to values. A map cannot contain duplicate keys; 36 * each key can map to at most one value. 37 * 38 * <p>This interface takes the place of the {@code Dictionary} class, which 39 * was a totally abstract class rather than an interface. 40 * 41 * <p>The {@code Map} interface provides three <i>collection views</i>, which 42 * allow a map's contents to be viewed as a set of keys, collection of values, 43 * or set of key-value mappings. The <i>order</i> of a map is defined as 44 * the order in which the iterators on the map's collection views return their 45 * elements. Some map implementations, like the {@code TreeMap} class, make 46 * specific guarantees as to their order; others, like the {@code HashMap} 47 * class, do not. 48 * 49 * <p>Note: great care must be exercised if mutable objects are used as map 50 * keys. The behavior of a map is not specified if the value of an object is 51 * changed in a manner that affects {@code equals} comparisons while the 52 * object is a key in the map. A special case of this prohibition is that it 53 * is not permissible for a map to contain itself as a key. While it is 54 * permissible for a map to contain itself as a value, extreme caution is 55 * advised: the {@code equals} and {@code hashCode} methods are no longer 56 * well defined on such a map. 57 * 58 * <p>All general-purpose map implementation classes should provide two 59 * "standard" constructors: a void (no arguments) constructor which creates an 60 * empty map, and a constructor with a single argument of type {@code Map}, 61 * which creates a new map with the same key-value mappings as its argument. 62 * In effect, the latter constructor allows the user to copy any map, 63 * producing an equivalent map of the desired class. There is no way to 64 * enforce this recommendation (as interfaces cannot contain constructors) but 65 * all of the general-purpose map implementations in the JDK comply. 66 * 67 * <p>The "destructive" methods contained in this interface, that is, the 68 * methods that modify the map on which they operate, are specified to throw 69 * {@code UnsupportedOperationException} if this map does not support the 70 * operation. If this is the case, these methods may, but are not required 71 * to, throw an {@code UnsupportedOperationException} if the invocation would 72 * have no effect on the map. For example, invoking the {@link #putAll(Map)} 73 * method on an unmodifiable map may, but is not required to, throw the 74 * exception if the map whose mappings are to be "superimposed" is empty. 75 * 76 * <p>Some map implementations have restrictions on the keys and values they 77 * may contain. For example, some implementations prohibit null keys and 78 * values, and some have restrictions on the types of their keys. Attempting 79 * to insert an ineligible key or value throws an unchecked exception, 80 * typically {@code NullPointerException} or {@code ClassCastException}. 81 * Attempting to query the presence of an ineligible key or value may throw an 82 * exception, or it may simply return false; some implementations will exhibit 83 * the former behavior and some will exhibit the latter. More generally, 84 * attempting an operation on an ineligible key or value whose completion 85 * would not result in the insertion of an ineligible element into the map may 86 * throw an exception or it may succeed, at the option of the implementation. 87 * Such exceptions are marked as "optional" in the specification for this 88 * interface. 89 * 90 * <p>Many methods in Collections Framework interfaces are defined 91 * in terms of the {@link Object#equals(Object) equals} method. For 92 * example, the specification for the {@link #containsKey(Object) 93 * containsKey(Object key)} method says: "returns {@code true} if and 94 * only if this map contains a mapping for a key {@code k} such that 95 * {@code (key==null ? k==null : key.equals(k))}." This specification should 96 * <i>not</i> be construed to imply that invoking {@code Map.containsKey} 97 * with a non-null argument {@code key} will cause {@code key.equals(k)} to 98 * be invoked for any key {@code k}. Implementations are free to 99 * implement optimizations whereby the {@code equals} invocation is avoided, 100 * for example, by first comparing the hash codes of the two keys. (The 101 * {@link Object#hashCode()} specification guarantees that two objects with 102 * unequal hash codes cannot be equal.) More generally, implementations of 103 * the various Collections Framework interfaces are free to take advantage of 104 * the specified behavior of underlying {@link Object} methods wherever the 105 * implementor deems it appropriate. 106 * 107 * <p>Some map operations which perform recursive traversal of the map may fail 108 * with an exception for self-referential instances where the map directly or 109 * indirectly contains itself. This includes the {@code clone()}, 110 * {@code equals()}, {@code hashCode()} and {@code toString()} methods. 111 * Implementations may optionally handle the self-referential scenario, however 112 * most current implementations do not do so. 113 * 114 * <h2><a id="unmodifiable">Unmodifiable Maps</a></h2> 115 * <p>The {@link Map#of() Map.of}, 116 * {@link Map#ofEntries(Map.Entry...) Map.ofEntries}, and 117 * {@link Map#copyOf Map.copyOf} 118 * static factory methods provide a convenient way to create unmodifiable maps. 119 * The {@code Map} 120 * instances created by these methods have the following characteristics: 121 * 122 * <ul> 123 * <li>They are <em>structurally immutable</em>. Keys and values cannot be added, 124 * removed, or updated. Calling any mutator method will always cause 125 * {@code UnsupportedOperationException} to be thrown. 126 * However, if the contained keys or values are themselves mutable, this may cause the 127 * Map to behave inconsistently or its contents to appear to change. 128 * <li>They disallow {@code null} keys and values. Attempts to create them with 129 * {@code null} keys or values result in {@code NullPointerException}. 130 * <li>They are serializable if all keys and values are serializable. 131 * <li>They reject duplicate keys at creation time. Duplicate keys 132 * passed to a static factory method result in {@code IllegalArgumentException}. 133 * <li>The iteration order of mappings is unspecified and is subject to change. 134 * <li>They are <a href="../lang/doc-files/ValueBased.html">value-based</a>. 135 * Callers should make no assumptions about the identity of the returned instances. 136 * Factories are free to create new instances or reuse existing ones. Therefore, 137 * identity-sensitive operations on these instances (reference equality ({@code ==}), 138 * identity hash code, and synchronization) are unreliable and should be avoided. 139 * <li>They are serialized as specified on the 140 * <a href="{@docRoot}/serialized-form.html#java.util.CollSer">Serialized Form</a> 141 * page. 142 * </ul> 143 * 144 * @param <K> the type of keys maintained by this map 145 * @param <V> the type of mapped values 146 * 147 * @author Josh Bloch 148 * @see HashMap 149 * @see TreeMap 150 * @see Hashtable 151 * @see SortedMap 152 * @see Collection 153 * @see Set 154 * @since 1.2 155 */ 156 // Android-changed: fix doc links to Collection#optional-restrictions 157 public interface Map<K, V> { 158 // Query Operations 159 160 /** 161 * Returns the number of key-value mappings in this map. If the 162 * map contains more than {@code Integer.MAX_VALUE} elements, returns 163 * {@code Integer.MAX_VALUE}. 164 * 165 * @return the number of key-value mappings in this map 166 */ size()167 int size(); 168 169 /** 170 * Returns {@code true} if this map contains no key-value mappings. 171 * 172 * @return {@code true} if this map contains no key-value mappings 173 */ isEmpty()174 boolean isEmpty(); 175 176 /** 177 * Returns {@code true} if this map contains a mapping for the specified 178 * key. More formally, returns {@code true} if and only if 179 * this map contains a mapping for a key {@code k} such that 180 * {@code Objects.equals(key, k)}. (There can be 181 * at most one such mapping.) 182 * 183 * @param key key whose presence in this map is to be tested 184 * @return {@code true} if this map contains a mapping for the specified 185 * key 186 * @throws ClassCastException if the key is of an inappropriate type for 187 * this map 188 * (<a href="Collection.html#optional-restrictions">optional</a>) 189 * @throws NullPointerException if the specified key is null and this map 190 * does not permit null keys 191 * (<a href="Collection.html#optional-restrictions">optional</a>) 192 */ containsKey(Object key)193 boolean containsKey(Object key); 194 195 /** 196 * Returns {@code true} if this map maps one or more keys to the 197 * specified value. More formally, returns {@code true} if and only if 198 * this map contains at least one mapping to a value {@code v} such that 199 * {@code Objects.equals(value, v)}. This operation 200 * will probably require time linear in the map size for most 201 * implementations of the {@code Map} interface. 202 * 203 * @param value value whose presence in this map is to be tested 204 * @return {@code true} if this map maps one or more keys to the 205 * specified value 206 * @throws ClassCastException if the value is of an inappropriate type for 207 * this map 208 * (<a href="Collection.html#optional-restrictions">optional</a>) 209 * @throws NullPointerException if the specified value is null and this 210 * map does not permit null values 211 * (<a href="Collection.html#optional-restrictions">optional</a>) 212 */ containsValue(Object value)213 boolean containsValue(Object value); 214 215 /** 216 * Returns the value to which the specified key is mapped, 217 * or {@code null} if this map contains no mapping for the key. 218 * 219 * <p>More formally, if this map contains a mapping from a key 220 * {@code k} to a value {@code v} such that 221 * {@code Objects.equals(key, k)}, 222 * then this method returns {@code v}; otherwise 223 * it returns {@code null}. (There can be at most one such mapping.) 224 * 225 * <p>If this map permits null values, then a return value of 226 * {@code null} does not <i>necessarily</i> indicate that the map 227 * contains no mapping for the key; it's also possible that the map 228 * explicitly maps the key to {@code null}. The {@link #containsKey 229 * containsKey} operation may be used to distinguish these two cases. 230 * 231 * @param key the key whose associated value is to be returned 232 * @return the value to which the specified key is mapped, or 233 * {@code null} if this map contains no mapping for the key 234 * @throws ClassCastException if the key is of an inappropriate type for 235 * this map 236 * (<a href="Collection.html#optional-restrictions">optional</a>) 237 * @throws NullPointerException if the specified key is null and this map 238 * does not permit null keys 239 * (<a href="Collection.html#optional-restrictions">optional</a>) 240 */ get(Object key)241 V get(Object key); 242 243 // Modification Operations 244 245 /** 246 * Associates the specified value with the specified key in this map 247 * (optional operation). If the map previously contained a mapping for 248 * the key, the old value is replaced by the specified value. (A map 249 * {@code m} is said to contain a mapping for a key {@code k} if and only 250 * if {@link #containsKey(Object) m.containsKey(k)} would return 251 * {@code true}.) 252 * 253 * @param key key with which the specified value is to be associated 254 * @param value value to be associated with the specified key 255 * @return the previous value associated with {@code key}, or 256 * {@code null} if there was no mapping for {@code key}. 257 * (A {@code null} return can also indicate that the map 258 * previously associated {@code null} with {@code key}, 259 * if the implementation supports {@code null} values.) 260 * @throws UnsupportedOperationException if the {@code put} operation 261 * is not supported by this map 262 * @throws ClassCastException if the class of the specified key or value 263 * prevents it from being stored in this map 264 * @throws NullPointerException if the specified key or value is null 265 * and this map does not permit null keys or values 266 * @throws IllegalArgumentException if some property of the specified key 267 * or value prevents it from being stored in this map 268 */ put(K key, V value)269 V put(K key, V value); 270 271 /** 272 * Removes the mapping for a key from this map if it is present 273 * (optional operation). More formally, if this map contains a mapping 274 * from key {@code k} to value {@code v} such that 275 * {@code Objects.equals(key, k)}, that mapping 276 * is removed. (The map can contain at most one such mapping.) 277 * 278 * <p>Returns the value to which this map previously associated the key, 279 * or {@code null} if the map contained no mapping for the key. 280 * 281 * <p>If this map permits null values, then a return value of 282 * {@code null} does not <i>necessarily</i> indicate that the map 283 * contained no mapping for the key; it's also possible that the map 284 * explicitly mapped the key to {@code null}. 285 * 286 * <p>The map will not contain a mapping for the specified key once the 287 * call returns. 288 * 289 * @param key key whose mapping is to be removed from the map 290 * @return the previous value associated with {@code key}, or 291 * {@code null} if there was no mapping for {@code key}. 292 * @throws UnsupportedOperationException if the {@code remove} operation 293 * is not supported by this map 294 * @throws ClassCastException if the key is of an inappropriate type for 295 * this map 296 * (<a href="Collection.html#optional-restrictions">optional</a>) 297 * @throws NullPointerException if the specified key is null and this 298 * map does not permit null keys 299 * (<a href="Collection.html#optional-restrictions">optional</a>) 300 */ remove(Object key)301 V remove(Object key); 302 303 304 // Bulk Operations 305 306 /** 307 * Copies all of the mappings from the specified map to this map 308 * (optional operation). The effect of this call is equivalent to that 309 * of calling {@link #put(Object,Object) put(k, v)} on this map once 310 * for each mapping from key {@code k} to value {@code v} in the 311 * specified map. The behavior of this operation is undefined if the 312 * specified map is modified while the operation is in progress. 313 * 314 * @param m mappings to be stored in this map 315 * @throws UnsupportedOperationException if the {@code putAll} operation 316 * is not supported by this map 317 * @throws ClassCastException if the class of a key or value in the 318 * specified map prevents it from being stored in this map 319 * @throws NullPointerException if the specified map is null, or if 320 * this map does not permit null keys or values, and the 321 * specified map contains null keys or values 322 * @throws IllegalArgumentException if some property of a key or value in 323 * the specified map prevents it from being stored in this map 324 */ putAll(Map<? extends K, ? extends V> m)325 void putAll(Map<? extends K, ? extends V> m); 326 327 /** 328 * Removes all of the mappings from this map (optional operation). 329 * The map will be empty after this call returns. 330 * 331 * @throws UnsupportedOperationException if the {@code clear} operation 332 * is not supported by this map 333 */ clear()334 void clear(); 335 336 337 // Views 338 339 /** 340 * Returns a {@link Set} view of the keys contained in this map. 341 * The set is backed by the map, so changes to the map are 342 * reflected in the set, and vice-versa. If the map is modified 343 * while an iteration over the set is in progress (except through 344 * the iterator's own {@code remove} operation), the results of 345 * the iteration are undefined. The set supports element removal, 346 * which removes the corresponding mapping from the map, via the 347 * {@code Iterator.remove}, {@code Set.remove}, 348 * {@code removeAll}, {@code retainAll}, and {@code clear} 349 * operations. It does not support the {@code add} or {@code addAll} 350 * operations. 351 * 352 * @return a set view of the keys contained in this map 353 */ keySet()354 Set<K> keySet(); 355 356 /** 357 * Returns a {@link Collection} view of the values contained in this map. 358 * The collection is backed by the map, so changes to the map are 359 * reflected in the collection, and vice-versa. If the map is 360 * modified while an iteration over the collection is in progress 361 * (except through the iterator's own {@code remove} operation), 362 * the results of the iteration are undefined. The collection 363 * supports element removal, which removes the corresponding 364 * mapping from the map, via the {@code Iterator.remove}, 365 * {@code Collection.remove}, {@code removeAll}, 366 * {@code retainAll} and {@code clear} operations. It does not 367 * support the {@code add} or {@code addAll} operations. 368 * 369 * @return a collection view of the values contained in this map 370 */ values()371 Collection<V> values(); 372 373 /** 374 * Returns a {@link Set} view of the mappings contained in this map. 375 * The set is backed by the map, so changes to the map are 376 * reflected in the set, and vice-versa. If the map is modified 377 * while an iteration over the set is in progress (except through 378 * the iterator's own {@code remove} operation, or through the 379 * {@code setValue} operation on a map entry returned by the 380 * iterator) the results of the iteration are undefined. The set 381 * supports element removal, which removes the corresponding 382 * mapping from the map, via the {@code Iterator.remove}, 383 * {@code Set.remove}, {@code removeAll}, {@code retainAll} and 384 * {@code clear} operations. It does not support the 385 * {@code add} or {@code addAll} operations. 386 * 387 * @return a set view of the mappings contained in this map 388 */ entrySet()389 Set<Map.Entry<K, V>> entrySet(); 390 391 /** 392 * A map entry (key-value pair). The {@code Map.entrySet} method returns 393 * a collection-view of the map, whose elements are of this class. The 394 * <i>only</i> way to obtain a reference to a map entry is from the 395 * iterator of this collection-view. These {@code Map.Entry} objects are 396 * valid <i>only</i> for the duration of the iteration; more formally, 397 * the behavior of a map entry is undefined if the backing map has been 398 * modified after the entry was returned by the iterator, except through 399 * the {@code setValue} operation on the map entry. 400 * 401 * @see Map#entrySet() 402 * @since 1.2 403 */ 404 interface Entry<K, V> { 405 /** 406 * Returns the key corresponding to this entry. 407 * 408 * @return the key corresponding to this entry 409 * @throws IllegalStateException implementations may, but are not 410 * required to, throw this exception if the entry has been 411 * removed from the backing map. 412 */ getKey()413 K getKey(); 414 415 /** 416 * Returns the value corresponding to this entry. If the mapping 417 * has been removed from the backing map (by the iterator's 418 * {@code remove} operation), the results of this call are undefined. 419 * 420 * @return the value corresponding to this entry 421 * @throws IllegalStateException implementations may, but are not 422 * required to, throw this exception if the entry has been 423 * removed from the backing map. 424 */ getValue()425 V getValue(); 426 427 /** 428 * Replaces the value corresponding to this entry with the specified 429 * value (optional operation). (Writes through to the map.) The 430 * behavior of this call is undefined if the mapping has already been 431 * removed from the map (by the iterator's {@code remove} operation). 432 * 433 * @param value new value to be stored in this entry 434 * @return old value corresponding to the entry 435 * @throws UnsupportedOperationException if the {@code put} operation 436 * is not supported by the backing map 437 * @throws ClassCastException if the class of the specified value 438 * prevents it from being stored in the backing map 439 * @throws NullPointerException if the backing map does not permit 440 * null values, and the specified value is null 441 * @throws IllegalArgumentException if some property of this value 442 * prevents it from being stored in the backing map 443 * @throws IllegalStateException implementations may, but are not 444 * required to, throw this exception if the entry has been 445 * removed from the backing map. 446 */ setValue(V value)447 V setValue(V value); 448 449 /** 450 * Compares the specified object with this entry for equality. 451 * Returns {@code true} if the given object is also a map entry and 452 * the two entries represent the same mapping. More formally, two 453 * entries {@code e1} and {@code e2} represent the same mapping 454 * if<pre> 455 * (e1.getKey()==null ? 456 * e2.getKey()==null : e1.getKey().equals(e2.getKey())) && 457 * (e1.getValue()==null ? 458 * e2.getValue()==null : e1.getValue().equals(e2.getValue())) 459 * </pre> 460 * This ensures that the {@code equals} method works properly across 461 * different implementations of the {@code Map.Entry} interface. 462 * 463 * @param o object to be compared for equality with this map entry 464 * @return {@code true} if the specified object is equal to this map 465 * entry 466 */ equals(Object o)467 boolean equals(Object o); 468 469 /** 470 * Returns the hash code value for this map entry. The hash code 471 * of a map entry {@code e} is defined to be: <pre> 472 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^ 473 * (e.getValue()==null ? 0 : e.getValue().hashCode()) 474 * </pre> 475 * This ensures that {@code e1.equals(e2)} implies that 476 * {@code e1.hashCode()==e2.hashCode()} for any two Entries 477 * {@code e1} and {@code e2}, as required by the general 478 * contract of {@code Object.hashCode}. 479 * 480 * @return the hash code value for this map entry 481 * @see Object#hashCode() 482 * @see Object#equals(Object) 483 * @see #equals(Object) 484 */ hashCode()485 int hashCode(); 486 487 /** 488 * Returns a comparator that compares {@link Map.Entry} in natural order on key. 489 * 490 * <p>The returned comparator is serializable and throws {@link 491 * NullPointerException} when comparing an entry with a null key. 492 * 493 * @param <K> the {@link Comparable} type of then map keys 494 * @param <V> the type of the map values 495 * @return a comparator that compares {@link Map.Entry} in natural order on key. 496 * @see Comparable 497 * @since 1.8 498 */ comparingByKey()499 public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K, V>> comparingByKey() { 500 return (Comparator<Map.Entry<K, V>> & Serializable) 501 (c1, c2) -> c1.getKey().compareTo(c2.getKey()); 502 } 503 504 /** 505 * Returns a comparator that compares {@link Map.Entry} in natural order on value. 506 * 507 * <p>The returned comparator is serializable and throws {@link 508 * NullPointerException} when comparing an entry with null values. 509 * 510 * @param <K> the type of the map keys 511 * @param <V> the {@link Comparable} type of the map values 512 * @return a comparator that compares {@link Map.Entry} in natural order on value. 513 * @see Comparable 514 * @since 1.8 515 */ comparingByValue()516 public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K, V>> comparingByValue() { 517 return (Comparator<Map.Entry<K, V>> & Serializable) 518 (c1, c2) -> c1.getValue().compareTo(c2.getValue()); 519 } 520 521 /** 522 * Returns a comparator that compares {@link Map.Entry} by key using the given 523 * {@link Comparator}. 524 * 525 * <p>The returned comparator is serializable if the specified comparator 526 * is also serializable. 527 * 528 * @param <K> the type of the map keys 529 * @param <V> the type of the map values 530 * @param cmp the key {@link Comparator} 531 * @return a comparator that compares {@link Map.Entry} by the key. 532 * @since 1.8 533 */ comparingByKey(Comparator<? super K> cmp)534 public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) { 535 Objects.requireNonNull(cmp); 536 return (Comparator<Map.Entry<K, V>> & Serializable) 537 (c1, c2) -> cmp.compare(c1.getKey(), c2.getKey()); 538 } 539 540 /** 541 * Returns a comparator that compares {@link Map.Entry} by value using the given 542 * {@link Comparator}. 543 * 544 * <p>The returned comparator is serializable if the specified comparator 545 * is also serializable. 546 * 547 * @param <K> the type of the map keys 548 * @param <V> the type of the map values 549 * @param cmp the value {@link Comparator} 550 * @return a comparator that compares {@link Map.Entry} by the value. 551 * @since 1.8 552 */ comparingByValue(Comparator<? super V> cmp)553 public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) { 554 Objects.requireNonNull(cmp); 555 return (Comparator<Map.Entry<K, V>> & Serializable) 556 (c1, c2) -> cmp.compare(c1.getValue(), c2.getValue()); 557 } 558 } 559 560 // Comparison and hashing 561 562 /** 563 * Compares the specified object with this map for equality. Returns 564 * {@code true} if the given object is also a map and the two maps 565 * represent the same mappings. More formally, two maps {@code m1} and 566 * {@code m2} represent the same mappings if 567 * {@code m1.entrySet().equals(m2.entrySet())}. This ensures that the 568 * {@code equals} method works properly across different implementations 569 * of the {@code Map} interface. 570 * 571 * @param o object to be compared for equality with this map 572 * @return {@code true} if the specified object is equal to this map 573 */ equals(Object o)574 boolean equals(Object o); 575 576 /** 577 * Returns the hash code value for this map. The hash code of a map is 578 * defined to be the sum of the hash codes of each entry in the map's 579 * {@code entrySet()} view. This ensures that {@code m1.equals(m2)} 580 * implies that {@code m1.hashCode()==m2.hashCode()} for any two maps 581 * {@code m1} and {@code m2}, as required by the general contract of 582 * {@link Object#hashCode}. 583 * 584 * @return the hash code value for this map 585 * @see Map.Entry#hashCode() 586 * @see Object#equals(Object) 587 * @see #equals(Object) 588 */ hashCode()589 int hashCode(); 590 591 // Defaultable methods 592 593 /** 594 * Returns the value to which the specified key is mapped, or 595 * {@code defaultValue} if this map contains no mapping for the key. 596 * 597 * @implSpec 598 * The default implementation makes no guarantees about synchronization 599 * or atomicity properties of this method. Any implementation providing 600 * atomicity guarantees must override this method and document its 601 * concurrency properties. 602 * 603 * @param key the key whose associated value is to be returned 604 * @param defaultValue the default mapping of the key 605 * @return the value to which the specified key is mapped, or 606 * {@code defaultValue} if this map contains no mapping for the key 607 * @throws ClassCastException if the key is of an inappropriate type for 608 * this map 609 * (<a href="Collection.html#optional-restrictions">optional</a>) 610 * @throws NullPointerException if the specified key is null and this map 611 * does not permit null keys 612 * (<a href="Collection.html#optional-restrictions">optional</a>) 613 * @since 1.8 614 */ getOrDefault(Object key, V defaultValue)615 default V getOrDefault(Object key, V defaultValue) { 616 V v; 617 return (((v = get(key)) != null) || containsKey(key)) 618 ? v 619 : defaultValue; 620 } 621 622 /** 623 * Performs the given action for each entry in this map until all entries 624 * have been processed or the action throws an exception. Unless 625 * otherwise specified by the implementing class, actions are performed in 626 * the order of entry set iteration (if an iteration order is specified.) 627 * Exceptions thrown by the action are relayed to the caller. 628 * 629 * @implSpec 630 * The default implementation is equivalent to, for this {@code map}: 631 * <pre> {@code 632 * for (Map.Entry<K, V> entry : map.entrySet()) 633 * action.accept(entry.getKey(), entry.getValue()); 634 * }</pre> 635 * 636 * The default implementation makes no guarantees about synchronization 637 * or atomicity properties of this method. Any implementation providing 638 * atomicity guarantees must override this method and document its 639 * concurrency properties. 640 * 641 * @param action The action to be performed for each entry 642 * @throws NullPointerException if the specified action is null 643 * @throws ConcurrentModificationException if an entry is found to be 644 * removed during iteration 645 * @since 1.8 646 */ forEach(BiConsumer<? super K, ? super V> action)647 default void forEach(BiConsumer<? super K, ? super V> action) { 648 Objects.requireNonNull(action); 649 for (Map.Entry<K, V> entry : entrySet()) { 650 K k; 651 V v; 652 try { 653 k = entry.getKey(); 654 v = entry.getValue(); 655 } catch (IllegalStateException ise) { 656 // this usually means the entry is no longer in the map. 657 throw new ConcurrentModificationException(ise); 658 } 659 action.accept(k, v); 660 } 661 } 662 663 /** 664 * Replaces each entry's value with the result of invoking the given 665 * function on that entry until all entries have been processed or the 666 * function throws an exception. Exceptions thrown by the function are 667 * relayed to the caller. 668 * 669 * @implSpec 670 * <p>The default implementation is equivalent to, for this {@code map}: 671 * <pre> {@code 672 * for (Map.Entry<K, V> entry : map.entrySet()) 673 * entry.setValue(function.apply(entry.getKey(), entry.getValue())); 674 * }</pre> 675 * 676 * <p>The default implementation makes no guarantees about synchronization 677 * or atomicity properties of this method. Any implementation providing 678 * atomicity guarantees must override this method and document its 679 * concurrency properties. 680 * 681 * @param function the function to apply to each entry 682 * @throws UnsupportedOperationException if the {@code set} operation 683 * is not supported by this map's entry set iterator. 684 * @throws ClassCastException if the class of a replacement value 685 * prevents it from being stored in this map 686 * @throws NullPointerException if the specified function is null, or the 687 * specified replacement value is null, and this map does not permit null 688 * values 689 * @throws ClassCastException if a replacement value is of an inappropriate 690 * type for this map 691 * (<a href="Collection.html#optional-restrictions">optional</a>) 692 * @throws NullPointerException if function or a replacement value is null, 693 * and this map does not permit null keys or values 694 * (<a href="Collection.html#optional-restrictions">optional</a>) 695 * @throws IllegalArgumentException if some property of a replacement value 696 * prevents it from being stored in this map 697 * (<a href="Collection.html#optional-restrictions">optional</a>) 698 * @throws ConcurrentModificationException if an entry is found to be 699 * removed during iteration 700 * @since 1.8 701 */ replaceAll(BiFunction<? super K, ? super V, ? extends V> function)702 default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 703 Objects.requireNonNull(function); 704 for (Map.Entry<K, V> entry : entrySet()) { 705 K k; 706 V v; 707 try { 708 k = entry.getKey(); 709 v = entry.getValue(); 710 } catch (IllegalStateException ise) { 711 // this usually means the entry is no longer in the map. 712 throw new ConcurrentModificationException(ise); 713 } 714 715 // ise thrown from function is not a cme. 716 v = function.apply(k, v); 717 718 try { 719 entry.setValue(v); 720 } catch (IllegalStateException ise) { 721 // this usually means the entry is no longer in the map. 722 throw new ConcurrentModificationException(ise); 723 } 724 } 725 } 726 727 /** 728 * If the specified key is not already associated with a value (or is mapped 729 * to {@code null}) associates it with the given value and returns 730 * {@code null}, else returns the current value. 731 * 732 * @implSpec 733 * The default implementation is equivalent to, for this {@code 734 * map}: 735 * 736 * <pre> {@code 737 * V v = map.get(key); 738 * if (v == null) 739 * v = map.put(key, value); 740 * 741 * return v; 742 * }</pre> 743 * 744 * <p>The default implementation makes no guarantees about synchronization 745 * or atomicity properties of this method. Any implementation providing 746 * atomicity guarantees must override this method and document its 747 * concurrency properties. 748 * 749 * @param key key with which the specified value is to be associated 750 * @param value value to be associated with the specified key 751 * @return the previous value associated with the specified key, or 752 * {@code null} if there was no mapping for the key. 753 * (A {@code null} return can also indicate that the map 754 * previously associated {@code null} with the key, 755 * if the implementation supports null values.) 756 * @throws UnsupportedOperationException if the {@code put} operation 757 * is not supported by this map 758 * (<a href="Collection.html#optional-restrictions">optional</a>) 759 * @throws ClassCastException if the key or value is of an inappropriate 760 * type for this map 761 * (<a href="Collection.html#optional-restrictions">optional</a>) 762 * @throws NullPointerException if the specified key or value is null, 763 * and this map does not permit null keys or values 764 * (<a href="Collection.html#optional-restrictions">optional</a>) 765 * @throws IllegalArgumentException if some property of the specified key 766 * or value prevents it from being stored in this map 767 * (<a href="Collection.html#optional-restrictions">optional</a>) 768 * @since 1.8 769 */ putIfAbsent(K key, V value)770 default V putIfAbsent(K key, V value) { 771 V v = get(key); 772 if (v == null) { 773 v = put(key, value); 774 } 775 776 return v; 777 } 778 779 /** 780 * Removes the entry for the specified key only if it is currently 781 * mapped to the specified value. 782 * 783 * @implSpec 784 * The default implementation is equivalent to, for this {@code map}: 785 * 786 * <pre> {@code 787 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) { 788 * map.remove(key); 789 * return true; 790 * } else 791 * return false; 792 * }</pre> 793 * 794 * <p>The default implementation makes no guarantees about synchronization 795 * or atomicity properties of this method. Any implementation providing 796 * atomicity guarantees must override this method and document its 797 * concurrency properties. 798 * 799 * @param key key with which the specified value is associated 800 * @param value value expected to be associated with the specified key 801 * @return {@code true} if the value was removed 802 * @throws UnsupportedOperationException if the {@code remove} operation 803 * is not supported by this map 804 * (<a href="Collection.html#optional-restrictions">optional</a>) 805 * @throws ClassCastException if the key or value is of an inappropriate 806 * type for this map 807 * (<a href="Collection.html#optional-restrictions">optional</a>) 808 * @throws NullPointerException if the specified key or value is null, 809 * and this map does not permit null keys or values 810 * (<a href="Collection.html#optional-restrictions">optional</a>) 811 * @since 1.8 812 */ remove(Object key, Object value)813 default boolean remove(Object key, Object value) { 814 Object curValue = get(key); 815 if (!Objects.equals(curValue, value) || 816 (curValue == null && !containsKey(key))) { 817 return false; 818 } 819 remove(key); 820 return true; 821 } 822 823 /** 824 * Replaces the entry for the specified key only if currently 825 * mapped to the specified value. 826 * 827 * @implSpec 828 * The default implementation is equivalent to, for this {@code map}: 829 * 830 * <pre> {@code 831 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) { 832 * map.put(key, newValue); 833 * return true; 834 * } else 835 * return false; 836 * }</pre> 837 * 838 * The default implementation does not throw NullPointerException 839 * for maps that do not support null values if oldValue is null unless 840 * newValue is also null. 841 * 842 * <p>The default implementation makes no guarantees about synchronization 843 * or atomicity properties of this method. Any implementation providing 844 * atomicity guarantees must override this method and document its 845 * concurrency properties. 846 * 847 * @param key key with which the specified value is associated 848 * @param oldValue value expected to be associated with the specified key 849 * @param newValue value to be associated with the specified key 850 * @return {@code true} if the value was replaced 851 * @throws UnsupportedOperationException if the {@code put} operation 852 * is not supported by this map 853 * (<a href="Collection.html#optional-restrictions">optional</a>) 854 * @throws ClassCastException if the class of a specified key or value 855 * prevents it from being stored in this map 856 * @throws NullPointerException if a specified key or newValue is null, 857 * and this map does not permit null keys or values 858 * @throws NullPointerException if oldValue is null and this map does not 859 * permit null values 860 * (<a href="Collection.html#optional-restrictions">optional</a>) 861 * @throws IllegalArgumentException if some property of a specified key 862 * or value prevents it from being stored in this map 863 * @since 1.8 864 */ replace(K key, V oldValue, V newValue)865 default boolean replace(K key, V oldValue, V newValue) { 866 Object curValue = get(key); 867 if (!Objects.equals(curValue, oldValue) || 868 (curValue == null && !containsKey(key))) { 869 return false; 870 } 871 put(key, newValue); 872 return true; 873 } 874 875 /** 876 * Replaces the entry for the specified key only if it is 877 * currently mapped to some value. 878 * 879 * @implSpec 880 * The default implementation is equivalent to, for this {@code map}: 881 * 882 * <pre> {@code 883 * if (map.containsKey(key)) { 884 * return map.put(key, value); 885 * } else 886 * return null; 887 * }</pre> 888 * 889 * <p>The default implementation makes no guarantees about synchronization 890 * or atomicity properties of this method. Any implementation providing 891 * atomicity guarantees must override this method and document its 892 * concurrency properties. 893 * 894 * @param key key with which the specified value is associated 895 * @param value value to be associated with the specified key 896 * @return the previous value associated with the specified key, or 897 * {@code null} if there was no mapping for the key. 898 * (A {@code null} return can also indicate that the map 899 * previously associated {@code null} with the key, 900 * if the implementation supports null values.) 901 * @throws UnsupportedOperationException if the {@code put} operation 902 * is not supported by this map 903 * (<a href="Collection.html#optional-restrictions">optional</a>) 904 * @throws ClassCastException if the class of the specified key or value 905 * prevents it from being stored in this map 906 * (<a href="Collection.html#optional-restrictions">optional</a>) 907 * @throws NullPointerException if the specified key or value is null, 908 * and this map does not permit null keys or values 909 * @throws IllegalArgumentException if some property of the specified key 910 * or value prevents it from being stored in this map 911 * @since 1.8 912 */ replace(K key, V value)913 default V replace(K key, V value) { 914 V curValue; 915 if (((curValue = get(key)) != null) || containsKey(key)) { 916 curValue = put(key, value); 917 } 918 return curValue; 919 } 920 921 /** 922 * If the specified key is not already associated with a value (or is mapped 923 * to {@code null}), attempts to compute its value using the given mapping 924 * function and enters it into this map unless {@code null}. 925 * 926 * <p>If the mapping function returns {@code null}, no mapping is recorded. 927 * If the mapping function itself throws an (unchecked) exception, the 928 * exception is rethrown, and no mapping is recorded. The most 929 * common usage is to construct a new object serving as an initial 930 * mapped value or memoized result, as in: 931 * 932 * <pre> {@code 933 * map.computeIfAbsent(key, k -> new Value(f(k))); 934 * }</pre> 935 * 936 * <p>Or to implement a multi-value map, {@code Map<K,Collection<V>>}, 937 * supporting multiple values per key: 938 * 939 * <pre> {@code 940 * map.computeIfAbsent(key, k -> new HashSet<V>()).add(v); 941 * }</pre> 942 * 943 * <p>The mapping function should not modify this map during computation. 944 * 945 * @implSpec 946 * The default implementation is equivalent to the following steps for this 947 * {@code map}, then returning the current value or {@code null} if now 948 * absent: 949 * 950 * <pre> {@code 951 * if (map.get(key) == null) { 952 * V newValue = mappingFunction.apply(key); 953 * if (newValue != null) 954 * map.put(key, newValue); 955 * } 956 * }</pre> 957 * 958 * <p>The default implementation makes no guarantees about detecting if the 959 * mapping function modifies this map during computation and, if 960 * appropriate, reporting an error. Non-concurrent implementations should 961 * override this method and, on a best-effort basis, throw a 962 * {@code ConcurrentModificationException} if it is detected that the 963 * mapping function modifies this map during computation. Concurrent 964 * implementations should override this method and, on a best-effort basis, 965 * throw an {@code IllegalStateException} if it is detected that the 966 * mapping function modifies this map during computation and as a result 967 * computation would never complete. 968 * 969 * <p>The default implementation makes no guarantees about synchronization 970 * or atomicity properties of this method. Any implementation providing 971 * atomicity guarantees must override this method and document its 972 * concurrency properties. In particular, all implementations of 973 * subinterface {@link java.util.concurrent.ConcurrentMap} must document 974 * whether the mapping function is applied once atomically only if the value 975 * is not present. 976 * 977 * @param key key with which the specified value is to be associated 978 * @param mappingFunction the mapping function to compute a value 979 * @return the current (existing or computed) value associated with 980 * the specified key, or null if the computed value is null 981 * @throws NullPointerException if the specified key is null and 982 * this map does not support null keys, or the mappingFunction 983 * is null 984 * @throws UnsupportedOperationException if the {@code put} operation 985 * is not supported by this map 986 * (<a href="Collection.html#optional-restrictions">optional</a>) 987 * @throws ClassCastException if the class of the specified key or value 988 * prevents it from being stored in this map 989 * (<a href="Collection.html#optional-restrictions">optional</a>) 990 * @throws IllegalArgumentException if some property of the specified key 991 * or value prevents it from being stored in this map 992 * (<a href="Collection.html#optional-restrictions">optional</a>) 993 * @since 1.8 994 */ computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction)995 default V computeIfAbsent(K key, 996 Function<? super K, ? extends V> mappingFunction) { 997 Objects.requireNonNull(mappingFunction); 998 V v; 999 if ((v = get(key)) == null) { 1000 V newValue; 1001 if ((newValue = mappingFunction.apply(key)) != null) { 1002 put(key, newValue); 1003 return newValue; 1004 } 1005 } 1006 1007 return v; 1008 } 1009 1010 /** 1011 * If the value for the specified key is present and non-null, attempts to 1012 * compute a new mapping given the key and its current mapped value. 1013 * 1014 * <p>If the remapping function returns {@code null}, the mapping is removed. 1015 * If the remapping function itself throws an (unchecked) exception, the 1016 * exception is rethrown, and the current mapping is left unchanged. 1017 * 1018 * <p>The remapping function should not modify this map during computation. 1019 * 1020 * @implSpec 1021 * The default implementation is equivalent to performing the following 1022 * steps for this {@code map}, then returning the current value or 1023 * {@code null} if now absent: 1024 * 1025 * <pre> {@code 1026 * if (map.get(key) != null) { 1027 * V oldValue = map.get(key); 1028 * V newValue = remappingFunction.apply(key, oldValue); 1029 * if (newValue != null) 1030 * map.put(key, newValue); 1031 * else 1032 * map.remove(key); 1033 * } 1034 * }</pre> 1035 * 1036 * <p>The default implementation makes no guarantees about detecting if the 1037 * remapping function modifies this map during computation and, if 1038 * appropriate, reporting an error. Non-concurrent implementations should 1039 * override this method and, on a best-effort basis, throw a 1040 * {@code ConcurrentModificationException} if it is detected that the 1041 * remapping function modifies this map during computation. Concurrent 1042 * implementations should override this method and, on a best-effort basis, 1043 * throw an {@code IllegalStateException} if it is detected that the 1044 * remapping function modifies this map during computation and as a result 1045 * computation would never complete. 1046 * 1047 * <p>The default implementation makes no guarantees about synchronization 1048 * or atomicity properties of this method. Any implementation providing 1049 * atomicity guarantees must override this method and document its 1050 * concurrency properties. In particular, all implementations of 1051 * subinterface {@link java.util.concurrent.ConcurrentMap} must document 1052 * whether the remapping function is applied once atomically only if the 1053 * value is not present. 1054 * 1055 * @param key key with which the specified value is to be associated 1056 * @param remappingFunction the remapping function to compute a value 1057 * @return the new value associated with the specified key, or null if none 1058 * @throws NullPointerException if the specified key is null and 1059 * this map does not support null keys, or the 1060 * remappingFunction is null 1061 * @throws UnsupportedOperationException if the {@code put} operation 1062 * is not supported by this map 1063 * (<a href="Collection.html#optional-restrictions">optional</a>) 1064 * @throws ClassCastException if the class of the specified key or value 1065 * prevents it from being stored in this map 1066 * (<a href="Collection.html#optional-restrictions">optional</a>) 1067 * @throws IllegalArgumentException if some property of the specified key 1068 * or value prevents it from being stored in this map 1069 * (<a href="Collection.html#optional-restrictions">optional</a>) 1070 * @since 1.8 1071 */ computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)1072 default V computeIfPresent(K key, 1073 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 1074 Objects.requireNonNull(remappingFunction); 1075 V oldValue; 1076 if ((oldValue = get(key)) != null) { 1077 V newValue = remappingFunction.apply(key, oldValue); 1078 if (newValue != null) { 1079 put(key, newValue); 1080 return newValue; 1081 } else { 1082 remove(key); 1083 return null; 1084 } 1085 } else { 1086 return null; 1087 } 1088 } 1089 1090 /** 1091 * Attempts to compute a mapping for the specified key and its current 1092 * mapped value (or {@code null} if there is no current mapping). For 1093 * example, to either create or append a {@code String} msg to a value 1094 * mapping: 1095 * 1096 * <pre> {@code 1097 * map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))}</pre> 1098 * (Method {@link #merge merge()} is often simpler to use for such purposes.) 1099 * 1100 * <p>If the remapping function returns {@code null}, the mapping is removed 1101 * (or remains absent if initially absent). If the remapping function 1102 * itself throws an (unchecked) exception, the exception is rethrown, and 1103 * the current mapping is left unchanged. 1104 * 1105 * <p>The remapping function should not modify this map during computation. 1106 * 1107 * @implSpec 1108 * The default implementation is equivalent to performing the following 1109 * steps for this {@code map}, then returning the current value or 1110 * {@code null} if absent: 1111 * 1112 * <pre> {@code 1113 * V oldValue = map.get(key); 1114 * V newValue = remappingFunction.apply(key, oldValue); 1115 * if (oldValue != null) { 1116 * if (newValue != null) 1117 * map.put(key, newValue); 1118 * else 1119 * map.remove(key); 1120 * } else { 1121 * if (newValue != null) 1122 * map.put(key, newValue); 1123 * else 1124 * return null; 1125 * } 1126 * }</pre> 1127 * 1128 * <p>The default implementation makes no guarantees about detecting if the 1129 * remapping function modifies this map during computation and, if 1130 * appropriate, reporting an error. Non-concurrent implementations should 1131 * override this method and, on a best-effort basis, throw a 1132 * {@code ConcurrentModificationException} if it is detected that the 1133 * remapping function modifies this map during computation. Concurrent 1134 * implementations should override this method and, on a best-effort basis, 1135 * throw an {@code IllegalStateException} if it is detected that the 1136 * remapping function modifies this map during computation and as a result 1137 * computation would never complete. 1138 * 1139 * <p>The default implementation makes no guarantees about synchronization 1140 * or atomicity properties of this method. Any implementation providing 1141 * atomicity guarantees must override this method and document its 1142 * concurrency properties. In particular, all implementations of 1143 * subinterface {@link java.util.concurrent.ConcurrentMap} must document 1144 * whether the remapping function is applied once atomically only if the 1145 * value is not present. 1146 * 1147 * @param key key with which the specified value is to be associated 1148 * @param remappingFunction the remapping function to compute a value 1149 * @return the new value associated with the specified key, or null if none 1150 * @throws NullPointerException if the specified key is null and 1151 * this map does not support null keys, or the 1152 * remappingFunction is null 1153 * @throws UnsupportedOperationException if the {@code put} operation 1154 * is not supported by this map 1155 * (<a href="Collection.html#optional-restrictions">optional</a>) 1156 * @throws ClassCastException if the class of the specified key or value 1157 * prevents it from being stored in this map 1158 * (<a href="Collection.html#optional-restrictions">optional</a>) 1159 * @throws IllegalArgumentException if some property of the specified key 1160 * or value prevents it from being stored in this map 1161 * (<a href="Collection.html#optional-restrictions">optional</a>) 1162 * @since 1.8 1163 */ compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)1164 default V compute(K key, 1165 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 1166 Objects.requireNonNull(remappingFunction); 1167 V oldValue = get(key); 1168 1169 V newValue = remappingFunction.apply(key, oldValue); 1170 if (newValue == null) { 1171 // delete mapping 1172 if (oldValue != null || containsKey(key)) { 1173 // something to remove 1174 remove(key); 1175 return null; 1176 } else { 1177 // nothing to do. Leave things as they were. 1178 return null; 1179 } 1180 } else { 1181 // add or replace old mapping 1182 put(key, newValue); 1183 return newValue; 1184 } 1185 } 1186 1187 /** 1188 * If the specified key is not already associated with a value or is 1189 * associated with null, associates it with the given non-null value. 1190 * Otherwise, replaces the associated value with the results of the given 1191 * remapping function, or removes if the result is {@code null}. This 1192 * method may be of use when combining multiple mapped values for a key. 1193 * For example, to either create or append a {@code String msg} to a 1194 * value mapping: 1195 * 1196 * <pre> {@code 1197 * map.merge(key, msg, String::concat) 1198 * }</pre> 1199 * 1200 * <p>If the remapping function returns {@code null}, the mapping is removed. 1201 * If the remapping function itself throws an (unchecked) exception, the 1202 * exception is rethrown, and the current mapping is left unchanged. 1203 * 1204 * <p>The remapping function should not modify this map during computation. 1205 * 1206 * @implSpec 1207 * The default implementation is equivalent to performing the following 1208 * steps for this {@code map}, then returning the current value or 1209 * {@code null} if absent: 1210 * 1211 * <pre> {@code 1212 * V oldValue = map.get(key); 1213 * V newValue = (oldValue == null) ? value : 1214 * remappingFunction.apply(oldValue, value); 1215 * if (newValue == null) 1216 * map.remove(key); 1217 * else 1218 * map.put(key, newValue); 1219 * }</pre> 1220 * 1221 * <p>The default implementation makes no guarantees about detecting if the 1222 * remapping function modifies this map during computation and, if 1223 * appropriate, reporting an error. Non-concurrent implementations should 1224 * override this method and, on a best-effort basis, throw a 1225 * {@code ConcurrentModificationException} if it is detected that the 1226 * remapping function modifies this map during computation. Concurrent 1227 * implementations should override this method and, on a best-effort basis, 1228 * throw an {@code IllegalStateException} if it is detected that the 1229 * remapping function modifies this map during computation and as a result 1230 * computation would never complete. 1231 * 1232 * <p>The default implementation makes no guarantees about synchronization 1233 * or atomicity properties of this method. Any implementation providing 1234 * atomicity guarantees must override this method and document its 1235 * concurrency properties. In particular, all implementations of 1236 * subinterface {@link java.util.concurrent.ConcurrentMap} must document 1237 * whether the remapping function is applied once atomically only if the 1238 * value is not present. 1239 * 1240 * @param key key with which the resulting value is to be associated 1241 * @param value the non-null value to be merged with the existing value 1242 * associated with the key or, if no existing value or a null value 1243 * is associated with the key, to be associated with the key 1244 * @param remappingFunction the remapping function to recompute a value if 1245 * present 1246 * @return the new value associated with the specified key, or null if no 1247 * value is associated with the key 1248 * @throws UnsupportedOperationException if the {@code put} operation 1249 * is not supported by this map 1250 * (<a href="Collection.html#optional-restrictions">optional</a>) 1251 * @throws ClassCastException if the class of the specified key or value 1252 * prevents it from being stored in this map 1253 * (<a href="Collection.html#optional-restrictions">optional</a>) 1254 * @throws IllegalArgumentException if some property of the specified key 1255 * or value prevents it from being stored in this map 1256 * (<a href="Collection.html#optional-restrictions">optional</a>) 1257 * @throws NullPointerException if the specified key is null and this map 1258 * does not support null keys or the value or remappingFunction is 1259 * null 1260 * @since 1.8 1261 */ merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction)1262 default V merge(K key, V value, 1263 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 1264 Objects.requireNonNull(remappingFunction); 1265 Objects.requireNonNull(value); 1266 V oldValue = get(key); 1267 V newValue = (oldValue == null) ? value : 1268 remappingFunction.apply(oldValue, value); 1269 if (newValue == null) { 1270 remove(key); 1271 } else { 1272 put(key, newValue); 1273 } 1274 return newValue; 1275 } 1276 1277 /** 1278 * Returns an unmodifiable map containing zero mappings. 1279 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details. 1280 * 1281 * @param <K> the {@code Map}'s key type 1282 * @param <V> the {@code Map}'s value type 1283 * @return an empty {@code Map} 1284 * 1285 * @since 9 1286 */ of()1287 static <K, V> Map<K, V> of() { 1288 return ImmutableCollections.Map0.instance(); 1289 } 1290 1291 /** 1292 * Returns an unmodifiable map containing a single mapping. 1293 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details. 1294 * 1295 * @param <K> the {@code Map}'s key type 1296 * @param <V> the {@code Map}'s value type 1297 * @param k1 the mapping's key 1298 * @param v1 the mapping's value 1299 * @return a {@code Map} containing the specified mapping 1300 * @throws NullPointerException if the key or the value is {@code null} 1301 * 1302 * @since 9 1303 */ of(K k1, V v1)1304 static <K, V> Map<K, V> of(K k1, V v1) { 1305 return new ImmutableCollections.Map1<>(k1, v1); 1306 } 1307 1308 /** 1309 * Returns an unmodifiable map containing two mappings. 1310 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details. 1311 * 1312 * @param <K> the {@code Map}'s key type 1313 * @param <V> the {@code Map}'s value type 1314 * @param k1 the first mapping's key 1315 * @param v1 the first mapping's value 1316 * @param k2 the second mapping's key 1317 * @param v2 the second mapping's value 1318 * @return a {@code Map} containing the specified mappings 1319 * @throws IllegalArgumentException if the keys are duplicates 1320 * @throws NullPointerException if any key or value is {@code null} 1321 * 1322 * @since 9 1323 */ of(K k1, V v1, K k2, V v2)1324 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2) { 1325 return new ImmutableCollections.MapN<>(k1, v1, k2, v2); 1326 } 1327 1328 /** 1329 * Returns an unmodifiable map containing three mappings. 1330 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details. 1331 * 1332 * @param <K> the {@code Map}'s key type 1333 * @param <V> the {@code Map}'s value type 1334 * @param k1 the first mapping's key 1335 * @param v1 the first mapping's value 1336 * @param k2 the second mapping's key 1337 * @param v2 the second mapping's value 1338 * @param k3 the third mapping's key 1339 * @param v3 the third mapping's value 1340 * @return a {@code Map} containing the specified mappings 1341 * @throws IllegalArgumentException if there are any duplicate keys 1342 * @throws NullPointerException if any key or value is {@code null} 1343 * 1344 * @since 9 1345 */ of(K k1, V v1, K k2, V v2, K k3, V v3)1346 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3) { 1347 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3); 1348 } 1349 1350 /** 1351 * Returns an unmodifiable map containing four mappings. 1352 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details. 1353 * 1354 * @param <K> the {@code Map}'s key type 1355 * @param <V> the {@code Map}'s value type 1356 * @param k1 the first mapping's key 1357 * @param v1 the first mapping's value 1358 * @param k2 the second mapping's key 1359 * @param v2 the second mapping's value 1360 * @param k3 the third mapping's key 1361 * @param v3 the third mapping's value 1362 * @param k4 the fourth mapping's key 1363 * @param v4 the fourth mapping's value 1364 * @return a {@code Map} containing the specified mappings 1365 * @throws IllegalArgumentException if there are any duplicate keys 1366 * @throws NullPointerException if any key or value is {@code null} 1367 * 1368 * @since 9 1369 */ of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4)1370 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) { 1371 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4); 1372 } 1373 1374 /** 1375 * Returns an unmodifiable map containing five mappings. 1376 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details. 1377 * 1378 * @param <K> the {@code Map}'s key type 1379 * @param <V> the {@code Map}'s value type 1380 * @param k1 the first mapping's key 1381 * @param v1 the first mapping's value 1382 * @param k2 the second mapping's key 1383 * @param v2 the second mapping's value 1384 * @param k3 the third mapping's key 1385 * @param v3 the third mapping's value 1386 * @param k4 the fourth mapping's key 1387 * @param v4 the fourth mapping's value 1388 * @param k5 the fifth mapping's key 1389 * @param v5 the fifth mapping's value 1390 * @return a {@code Map} containing the specified mappings 1391 * @throws IllegalArgumentException if there are any duplicate keys 1392 * @throws NullPointerException if any key or value is {@code null} 1393 * 1394 * @since 9 1395 */ of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5)1396 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) { 1397 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5); 1398 } 1399 1400 /** 1401 * Returns an unmodifiable map containing six mappings. 1402 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details. 1403 * 1404 * @param <K> the {@code Map}'s key type 1405 * @param <V> the {@code Map}'s value type 1406 * @param k1 the first mapping's key 1407 * @param v1 the first mapping's value 1408 * @param k2 the second mapping's key 1409 * @param v2 the second mapping's value 1410 * @param k3 the third mapping's key 1411 * @param v3 the third mapping's value 1412 * @param k4 the fourth mapping's key 1413 * @param v4 the fourth mapping's value 1414 * @param k5 the fifth mapping's key 1415 * @param v5 the fifth mapping's value 1416 * @param k6 the sixth mapping's key 1417 * @param v6 the sixth mapping's value 1418 * @return a {@code Map} containing the specified mappings 1419 * @throws IllegalArgumentException if there are any duplicate keys 1420 * @throws NullPointerException if any key or value is {@code null} 1421 * 1422 * @since 9 1423 */ of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6)1424 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, 1425 K k6, V v6) { 1426 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5, 1427 k6, v6); 1428 } 1429 1430 /** 1431 * Returns an unmodifiable map containing seven mappings. 1432 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details. 1433 * 1434 * @param <K> the {@code Map}'s key type 1435 * @param <V> the {@code Map}'s value type 1436 * @param k1 the first mapping's key 1437 * @param v1 the first mapping's value 1438 * @param k2 the second mapping's key 1439 * @param v2 the second mapping's value 1440 * @param k3 the third mapping's key 1441 * @param v3 the third mapping's value 1442 * @param k4 the fourth mapping's key 1443 * @param v4 the fourth mapping's value 1444 * @param k5 the fifth mapping's key 1445 * @param v5 the fifth mapping's value 1446 * @param k6 the sixth mapping's key 1447 * @param v6 the sixth mapping's value 1448 * @param k7 the seventh mapping's key 1449 * @param v7 the seventh mapping's value 1450 * @return a {@code Map} containing the specified mappings 1451 * @throws IllegalArgumentException if there are any duplicate keys 1452 * @throws NullPointerException if any key or value is {@code null} 1453 * 1454 * @since 9 1455 */ of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7)1456 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, 1457 K k6, V v6, K k7, V v7) { 1458 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5, 1459 k6, v6, k7, v7); 1460 } 1461 1462 /** 1463 * Returns an unmodifiable map containing eight mappings. 1464 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details. 1465 * 1466 * @param <K> the {@code Map}'s key type 1467 * @param <V> the {@code Map}'s value type 1468 * @param k1 the first mapping's key 1469 * @param v1 the first mapping's value 1470 * @param k2 the second mapping's key 1471 * @param v2 the second mapping's value 1472 * @param k3 the third mapping's key 1473 * @param v3 the third mapping's value 1474 * @param k4 the fourth mapping's key 1475 * @param v4 the fourth mapping's value 1476 * @param k5 the fifth mapping's key 1477 * @param v5 the fifth mapping's value 1478 * @param k6 the sixth mapping's key 1479 * @param v6 the sixth mapping's value 1480 * @param k7 the seventh mapping's key 1481 * @param v7 the seventh mapping's value 1482 * @param k8 the eighth mapping's key 1483 * @param v8 the eighth mapping's value 1484 * @return a {@code Map} containing the specified mappings 1485 * @throws IllegalArgumentException if there are any duplicate keys 1486 * @throws NullPointerException if any key or value is {@code null} 1487 * 1488 * @since 9 1489 */ of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7, K k8, V v8)1490 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, 1491 K k6, V v6, K k7, V v7, K k8, V v8) { 1492 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5, 1493 k6, v6, k7, v7, k8, v8); 1494 } 1495 1496 /** 1497 * Returns an unmodifiable map containing nine mappings. 1498 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details. 1499 * 1500 * @param <K> the {@code Map}'s key type 1501 * @param <V> the {@code Map}'s value type 1502 * @param k1 the first mapping's key 1503 * @param v1 the first mapping's value 1504 * @param k2 the second mapping's key 1505 * @param v2 the second mapping's value 1506 * @param k3 the third mapping's key 1507 * @param v3 the third mapping's value 1508 * @param k4 the fourth mapping's key 1509 * @param v4 the fourth mapping's value 1510 * @param k5 the fifth mapping's key 1511 * @param v5 the fifth mapping's value 1512 * @param k6 the sixth mapping's key 1513 * @param v6 the sixth mapping's value 1514 * @param k7 the seventh mapping's key 1515 * @param v7 the seventh mapping's value 1516 * @param k8 the eighth mapping's key 1517 * @param v8 the eighth mapping's value 1518 * @param k9 the ninth mapping's key 1519 * @param v9 the ninth mapping's value 1520 * @return a {@code Map} containing the specified mappings 1521 * @throws IllegalArgumentException if there are any duplicate keys 1522 * @throws NullPointerException if any key or value is {@code null} 1523 * 1524 * @since 9 1525 */ of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9)1526 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, 1527 K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9) { 1528 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5, 1529 k6, v6, k7, v7, k8, v8, k9, v9); 1530 } 1531 1532 /** 1533 * Returns an unmodifiable map containing ten mappings. 1534 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details. 1535 * 1536 * @param <K> the {@code Map}'s key type 1537 * @param <V> the {@code Map}'s value type 1538 * @param k1 the first mapping's key 1539 * @param v1 the first mapping's value 1540 * @param k2 the second mapping's key 1541 * @param v2 the second mapping's value 1542 * @param k3 the third mapping's key 1543 * @param v3 the third mapping's value 1544 * @param k4 the fourth mapping's key 1545 * @param v4 the fourth mapping's value 1546 * @param k5 the fifth mapping's key 1547 * @param v5 the fifth mapping's value 1548 * @param k6 the sixth mapping's key 1549 * @param v6 the sixth mapping's value 1550 * @param k7 the seventh mapping's key 1551 * @param v7 the seventh mapping's value 1552 * @param k8 the eighth mapping's key 1553 * @param v8 the eighth mapping's value 1554 * @param k9 the ninth mapping's key 1555 * @param v9 the ninth mapping's value 1556 * @param k10 the tenth mapping's key 1557 * @param v10 the tenth mapping's value 1558 * @return a {@code Map} containing the specified mappings 1559 * @throws IllegalArgumentException if there are any duplicate keys 1560 * @throws NullPointerException if any key or value is {@code null} 1561 * 1562 * @since 9 1563 */ of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9, K k10, V v10)1564 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5, 1565 K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9, K k10, V v10) { 1566 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5, 1567 k6, v6, k7, v7, k8, v8, k9, v9, k10, v10); 1568 } 1569 1570 /** 1571 * Returns an unmodifiable map containing keys and values extracted from the given entries. 1572 * The entries themselves are not stored in the map. 1573 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details. 1574 * 1575 * @apiNote 1576 * It is convenient to create the map entries using the {@link Map#entry Map.entry()} method. 1577 * For example, 1578 * 1579 * <pre>{@code 1580 * import static java.util.Map.entry; 1581 * 1582 * Map<Integer,String> map = Map.ofEntries( 1583 * entry(1, "a"), 1584 * entry(2, "b"), 1585 * entry(3, "c"), 1586 * ... 1587 * entry(26, "z")); 1588 * }</pre> 1589 * 1590 * @param <K> the {@code Map}'s key type 1591 * @param <V> the {@code Map}'s value type 1592 * @param entries {@code Map.Entry}s containing the keys and values from which the map is populated 1593 * @return a {@code Map} containing the specified mappings 1594 * @throws IllegalArgumentException if there are any duplicate keys 1595 * @throws NullPointerException if any entry, key, or value is {@code null}, or if 1596 * the {@code entries} array is {@code null} 1597 * 1598 * @see Map#entry Map.entry() 1599 * @since 9 1600 */ 1601 @SafeVarargs 1602 @SuppressWarnings("varargs") ofEntries(Entry<? extends K, ? extends V>.... entries)1603 static <K, V> Map<K, V> ofEntries(Entry<? extends K, ? extends V>... entries) { 1604 if (entries.length == 0) { // implicit null check of entries 1605 return ImmutableCollections.Map0.instance(); 1606 } else if (entries.length == 1) { 1607 return new ImmutableCollections.Map1<>(entries[0].getKey(), 1608 entries[0].getValue()); 1609 } else { 1610 Object[] kva = new Object[entries.length << 1]; 1611 int a = 0; 1612 for (Entry<? extends K, ? extends V> entry : entries) { 1613 kva[a++] = entry.getKey(); 1614 kva[a++] = entry.getValue(); 1615 } 1616 return new ImmutableCollections.MapN<>(kva); 1617 } 1618 } 1619 1620 /** 1621 * Returns an unmodifiable {@link Entry} containing the given key and value. 1622 * These entries are suitable for populating {@code Map} instances using the 1623 * {@link Map#ofEntries Map.ofEntries()} method. 1624 * The {@code Entry} instances created by this method have the following characteristics: 1625 * 1626 * <ul> 1627 * <li>They disallow {@code null} keys and values. Attempts to create them using a {@code null} 1628 * key or value result in {@code NullPointerException}. 1629 * <li>They are unmodifiable. Calls to {@link Entry#setValue Entry.setValue()} 1630 * on a returned {@code Entry} result in {@code UnsupportedOperationException}. 1631 * <li>They are not serializable. 1632 * <li>They are <a href="../lang/doc-files/ValueBased.html">value-based</a>. 1633 * Callers should make no assumptions about the identity of the returned instances. 1634 * This method is free to create new instances or reuse existing ones. Therefore, 1635 * identity-sensitive operations on these instances (reference equality ({@code ==}), 1636 * identity hash code, and synchronization) are unreliable and should be avoided. 1637 * </ul> 1638 * 1639 * @apiNote 1640 * For a serializable {@code Entry}, see {@link AbstractMap.SimpleEntry} or 1641 * {@link AbstractMap.SimpleImmutableEntry}. 1642 * 1643 * @param <K> the key's type 1644 * @param <V> the value's type 1645 * @param k the key 1646 * @param v the value 1647 * @return an {@code Entry} containing the specified key and value 1648 * @throws NullPointerException if the key or value is {@code null} 1649 * 1650 * @see Map#ofEntries Map.ofEntries() 1651 * @since 9 1652 */ entry(K k, V v)1653 static <K, V> Entry<K, V> entry(K k, V v) { 1654 // KeyValueHolder checks for nulls 1655 return new KeyValueHolder<>(k, v); 1656 } 1657 1658 /** 1659 * Returns an <a href="#unmodifiable">unmodifiable Map</a> containing the entries 1660 * of the given Map. The given Map must not be null, and it must not contain any 1661 * null keys or values. If the given Map is subsequently modified, the returned 1662 * Map will not reflect such modifications. 1663 * 1664 * @implNote 1665 * If the given Map is an <a href="#unmodifiable">unmodifiable Map</a>, 1666 * calling copyOf will generally not create a copy. 1667 * 1668 * @param <K> the {@code Map}'s key type 1669 * @param <V> the {@code Map}'s value type 1670 * @param map a {@code Map} from which entries are drawn, must be non-null 1671 * @return a {@code Map} containing the entries of the given {@code Map} 1672 * @throws NullPointerException if map is null, or if it contains any null keys or values 1673 * @since 10 1674 */ 1675 @SuppressWarnings({"rawtypes","unchecked"}) copyOf(Map<? extends K, ? extends V> map)1676 static <K, V> Map<K, V> copyOf(Map<? extends K, ? extends V> map) { 1677 if (map instanceof ImmutableCollections.AbstractImmutableMap) { 1678 return (Map<K,V>)map; 1679 } else { 1680 return (Map<K,V>)Map.ofEntries(map.entrySet().toArray(new Entry[0])); 1681 } 1682 } 1683 } 1684