1 /* 2 * Copyright (c) 1997, 2013, 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 /** 34 * An object that maps keys to values. A map cannot contain duplicate keys; 35 * each key can map to at most one value. 36 * 37 * <p>This interface takes the place of the <tt>Dictionary</tt> class, which 38 * was a totally abstract class rather than an interface. 39 * 40 * <p>The <tt>Map</tt> interface provides three <i>collection views</i>, which 41 * allow a map's contents to be viewed as a set of keys, collection of values, 42 * or set of key-value mappings. The <i>order</i> of a map is defined as 43 * the order in which the iterators on the map's collection views return their 44 * elements. Some map implementations, like the <tt>TreeMap</tt> class, make 45 * specific guarantees as to their order; others, like the <tt>HashMap</tt> 46 * class, do not. 47 * 48 * <p>Note: great care must be exercised if mutable objects are used as map 49 * keys. The behavior of a map is not specified if the value of an object is 50 * changed in a manner that affects <tt>equals</tt> comparisons while the 51 * object is a key in the map. A special case of this prohibition is that it 52 * is not permissible for a map to contain itself as a key. While it is 53 * permissible for a map to contain itself as a value, extreme caution is 54 * advised: the <tt>equals</tt> and <tt>hashCode</tt> methods are no longer 55 * well defined on such a map. 56 * 57 * <p>All general-purpose map implementation classes should provide two 58 * "standard" constructors: a void (no arguments) constructor which creates an 59 * empty map, and a constructor with a single argument of type <tt>Map</tt>, 60 * which creates a new map with the same key-value mappings as its argument. 61 * In effect, the latter constructor allows the user to copy any map, 62 * producing an equivalent map of the desired class. There is no way to 63 * enforce this recommendation (as interfaces cannot contain constructors) but 64 * all of the general-purpose map implementations in the JDK comply. 65 * 66 * <p>The "destructive" methods contained in this interface, that is, the 67 * methods that modify the map on which they operate, are specified to throw 68 * <tt>UnsupportedOperationException</tt> if this map does not support the 69 * operation. If this is the case, these methods may, but are not required 70 * to, throw an <tt>UnsupportedOperationException</tt> if the invocation would 71 * have no effect on the map. For example, invoking the {@link #putAll(Map)} 72 * method on an unmodifiable map may, but is not required to, throw the 73 * exception if the map whose mappings are to be "superimposed" is empty. 74 * 75 * <p>Some map implementations have restrictions on the keys and values they 76 * may contain. For example, some implementations prohibit null keys and 77 * values, and some have restrictions on the types of their keys. Attempting 78 * to insert an ineligible key or value throws an unchecked exception, 79 * typically <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. 80 * Attempting to query the presence of an ineligible key or value may throw an 81 * exception, or it may simply return false; some implementations will exhibit 82 * the former behavior and some will exhibit the latter. More generally, 83 * attempting an operation on an ineligible key or value whose completion 84 * would not result in the insertion of an ineligible element into the map may 85 * throw an exception or it may succeed, at the option of the implementation. 86 * Such exceptions are marked as "optional" in the specification for this 87 * interface. 88 * 89 * <p>Many methods in Collections Framework interfaces are defined 90 * in terms of the {@link Object#equals(Object) equals} method. For 91 * example, the specification for the {@link #containsKey(Object) 92 * containsKey(Object key)} method says: "returns <tt>true</tt> if and 93 * only if this map contains a mapping for a key <tt>k</tt> such that 94 * <tt>(key==null ? k==null : key.equals(k))</tt>." This specification should 95 * <i>not</i> be construed to imply that invoking <tt>Map.containsKey</tt> 96 * with a non-null argument <tt>key</tt> will cause <tt>key.equals(k)</tt> to 97 * be invoked for any key <tt>k</tt>. Implementations are free to 98 * implement optimizations whereby the <tt>equals</tt> invocation is avoided, 99 * for example, by first comparing the hash codes of the two keys. (The 100 * {@link Object#hashCode()} specification guarantees that two objects with 101 * unequal hash codes cannot be equal.) More generally, implementations of 102 * the various Collections Framework interfaces are free to take advantage of 103 * the specified behavior of underlying {@link Object} methods wherever the 104 * implementor deems it appropriate. 105 * 106 * <p>Some map operations which perform recursive traversal of the map may fail 107 * with an exception for self-referential instances where the map directly or 108 * indirectly contains itself. This includes the {@code clone()}, 109 * {@code equals()}, {@code hashCode()} and {@code toString()} methods. 110 * Implementations may optionally handle the self-referential scenario, however 111 * most current implementations do not do so. 112 * 113 * <p>This interface is a member of the 114 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 115 * Java Collections Framework</a>. 116 * 117 * @param <K> the type of keys maintained by this map 118 * @param <V> the type of mapped values 119 * 120 * @author Josh Bloch 121 * @see HashMap 122 * @see TreeMap 123 * @see Hashtable 124 * @see SortedMap 125 * @see Collection 126 * @see Set 127 * @since 1.2 128 */ 129 public interface Map<K,V> { 130 // Query Operations 131 132 /** 133 * Returns the number of key-value mappings in this map. If the 134 * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns 135 * <tt>Integer.MAX_VALUE</tt>. 136 * 137 * @return the number of key-value mappings in this map 138 */ 139 int size(); 140 141 /** 142 * Returns <tt>true</tt> if this map contains no key-value mappings. 143 * 144 * @return <tt>true</tt> if this map contains no key-value mappings 145 */ 146 boolean isEmpty(); 147 148 /** 149 * Returns <tt>true</tt> if this map contains a mapping for the specified 150 * key. More formally, returns <tt>true</tt> if and only if 151 * this map contains a mapping for a key <tt>k</tt> such that 152 * <tt>(key==null ? k==null : key.equals(k))</tt>. (There can be 153 * at most one such mapping.) 154 * 155 * @param key key whose presence in this map is to be tested 156 * @return <tt>true</tt> if this map contains a mapping for the specified 157 * key 158 * @throws ClassCastException if the key is of an inappropriate type for 159 * this map 160 * (<a href="Collection.html#optional-restrictions">optional</a>) 161 * @throws NullPointerException if the specified key is null and this map 162 * does not permit null keys 163 * (<a href="Collection.html#optional-restrictions">optional</a>) 164 */ 165 boolean containsKey(Object key); 166 167 /** 168 * Returns <tt>true</tt> if this map maps one or more keys to the 169 * specified value. More formally, returns <tt>true</tt> if and only if 170 * this map contains at least one mapping to a value <tt>v</tt> such that 171 * <tt>(value==null ? v==null : value.equals(v))</tt>. This operation 172 * will probably require time linear in the map size for most 173 * implementations of the <tt>Map</tt> interface. 174 * 175 * @param value value whose presence in this map is to be tested 176 * @return <tt>true</tt> if this map maps one or more keys to the 177 * specified value 178 * @throws ClassCastException if the value is of an inappropriate type for 179 * this map 180 * (<a href="Collection.html#optional-restrictions">optional</a>) 181 * @throws NullPointerException if the specified value is null and this 182 * map does not permit null values 183 * (<a href="Collection.html#optional-restrictions">optional</a>) 184 */ 185 boolean containsValue(Object value); 186 187 /** 188 * Returns the value to which the specified key is mapped, 189 * or {@code null} if this map contains no mapping for the key. 190 * 191 * <p>More formally, if this map contains a mapping from a key 192 * {@code k} to a value {@code v} such that {@code (key==null ? k==null : 193 * key.equals(k))}, then this method returns {@code v}; otherwise 194 * it returns {@code null}. (There can be at most one such mapping.) 195 * 196 * <p>If this map permits null values, then a return value of 197 * {@code null} does not <i>necessarily</i> indicate that the map 198 * contains no mapping for the key; it's also possible that the map 199 * explicitly maps the key to {@code null}. The {@link #containsKey 200 * containsKey} operation may be used to distinguish these two cases. 201 * 202 * @param key the key whose associated value is to be returned 203 * @return the value to which the specified key is mapped, or 204 * {@code null} if this map contains no mapping for the key 205 * @throws ClassCastException if the key is of an inappropriate type for 206 * this map 207 * (<a href="Collection.html#optional-restrictions">optional</a>) 208 * @throws NullPointerException if the specified key is null and this map 209 * does not permit null keys 210 * (<a href="Collection.html#optional-restrictions">optional</a>) 211 */ 212 V get(Object key); 213 214 // Modification Operations 215 216 /** 217 * Associates the specified value with the specified key in this map 218 * (optional operation). If the map previously contained a mapping for 219 * the key, the old value is replaced by the specified value. (A map 220 * <tt>m</tt> is said to contain a mapping for a key <tt>k</tt> if and only 221 * if {@link #containsKey(Object) m.containsKey(k)} would return 222 * <tt>true</tt>.) 223 * 224 * @param key key with which the specified value is to be associated 225 * @param value value to be associated with the specified key 226 * @return the previous value associated with <tt>key</tt>, or 227 * <tt>null</tt> if there was no mapping for <tt>key</tt>. 228 * (A <tt>null</tt> return can also indicate that the map 229 * previously associated <tt>null</tt> with <tt>key</tt>, 230 * if the implementation supports <tt>null</tt> values.) 231 * @throws UnsupportedOperationException if the <tt>put</tt> operation 232 * is not supported by this map 233 * @throws ClassCastException if the class of the specified key or value 234 * prevents it from being stored in this map 235 * @throws NullPointerException if the specified key or value is null 236 * and this map does not permit null keys or values 237 * @throws IllegalArgumentException if some property of the specified key 238 * or value prevents it from being stored in this map 239 */ 240 V put(K key, V value); 241 242 /** 243 * Removes the mapping for a key from this map if it is present 244 * (optional operation). More formally, if this map contains a mapping 245 * from key <tt>k</tt> to value <tt>v</tt> such that 246 * <code>(key==null ? k==null : key.equals(k))</code>, that mapping 247 * is removed. (The map can contain at most one such mapping.) 248 * 249 * <p>Returns the value to which this map previously associated the key, 250 * or <tt>null</tt> if the map contained no mapping for the key. 251 * 252 * <p>If this map permits null values, then a return value of 253 * <tt>null</tt> does not <i>necessarily</i> indicate that the map 254 * contained no mapping for the key; it's also possible that the map 255 * explicitly mapped the key to <tt>null</tt>. 256 * 257 * <p>The map will not contain a mapping for the specified key once the 258 * call returns. 259 * 260 * @param key key whose mapping is to be removed from the map 261 * @return the previous value associated with <tt>key</tt>, or 262 * <tt>null</tt> if there was no mapping for <tt>key</tt>. 263 * @throws UnsupportedOperationException if the <tt>remove</tt> operation 264 * is not supported by this map 265 * @throws ClassCastException if the key is of an inappropriate type for 266 * this map 267 * (<a href="Collection.html#optional-restrictions">optional</a>) 268 * @throws NullPointerException if the specified key is null and this 269 * map does not permit null keys 270 * (<a href="Collection.html#optional-restrictions">optional</a>) 271 */ 272 V remove(Object key); 273 274 275 // Bulk Operations 276 277 /** 278 * Copies all of the mappings from the specified map to this map 279 * (optional operation). The effect of this call is equivalent to that 280 * of calling {@link #put(Object,Object) put(k, v)} on this map once 281 * for each mapping from key <tt>k</tt> to value <tt>v</tt> in the 282 * specified map. The behavior of this operation is undefined if the 283 * specified map is modified while the operation is in progress. 284 * 285 * @param m mappings to be stored in this map 286 * @throws UnsupportedOperationException if the <tt>putAll</tt> operation 287 * is not supported by this map 288 * @throws ClassCastException if the class of a key or value in the 289 * specified map prevents it from being stored in this map 290 * @throws NullPointerException if the specified map is null, or if 291 * this map does not permit null keys or values, and the 292 * specified map contains null keys or values 293 * @throws IllegalArgumentException if some property of a key or value in 294 * the specified map prevents it from being stored in this map 295 */ 296 void putAll(Map<? extends K, ? extends V> m); 297 298 /** 299 * Removes all of the mappings from this map (optional operation). 300 * The map will be empty after this call returns. 301 * 302 * @throws UnsupportedOperationException if the <tt>clear</tt> operation 303 * is not supported by this map 304 */ 305 void clear(); 306 307 308 // Views 309 310 /** 311 * Returns a {@link Set} view of the keys contained in this map. 312 * The set is backed by the map, so changes to the map are 313 * reflected in the set, and vice-versa. If the map is modified 314 * while an iteration over the set is in progress (except through 315 * the iterator's own <tt>remove</tt> operation), the results of 316 * the iteration are undefined. The set supports element removal, 317 * which removes the corresponding mapping from the map, via the 318 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, 319 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> 320 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> 321 * operations. 322 * 323 * @return a set view of the keys contained in this map 324 */ 325 Set<K> keySet(); 326 327 /** 328 * Returns a {@link Collection} view of the values contained in this map. 329 * The collection is backed by the map, so changes to the map are 330 * reflected in the collection, and vice-versa. If the map is 331 * modified while an iteration over the collection is in progress 332 * (except through the iterator's own <tt>remove</tt> operation), 333 * the results of the iteration are undefined. The collection 334 * supports element removal, which removes the corresponding 335 * mapping from the map, via the <tt>Iterator.remove</tt>, 336 * <tt>Collection.remove</tt>, <tt>removeAll</tt>, 337 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not 338 * support the <tt>add</tt> or <tt>addAll</tt> operations. 339 * 340 * @return a collection view of the values contained in this map 341 */ 342 Collection<V> values(); 343 344 /** 345 * Returns a {@link Set} view of the mappings contained in this map. 346 * The set is backed by the map, so changes to the map are 347 * reflected in the set, and vice-versa. If the map is modified 348 * while an iteration over the set is in progress (except through 349 * the iterator's own <tt>remove</tt> operation, or through the 350 * <tt>setValue</tt> operation on a map entry returned by the 351 * iterator) the results of the iteration are undefined. The set 352 * supports element removal, which removes the corresponding 353 * mapping from the map, via the <tt>Iterator.remove</tt>, 354 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and 355 * <tt>clear</tt> operations. It does not support the 356 * <tt>add</tt> or <tt>addAll</tt> operations. 357 * 358 * @return a set view of the mappings contained in this map 359 */ 360 Set<Map.Entry<K, V>> entrySet(); 361 362 /** 363 * A map entry (key-value pair). The <tt>Map.entrySet</tt> method returns 364 * a collection-view of the map, whose elements are of this class. The 365 * <i>only</i> way to obtain a reference to a map entry is from the 366 * iterator of this collection-view. These <tt>Map.Entry</tt> objects are 367 * valid <i>only</i> for the duration of the iteration; more formally, 368 * the behavior of a map entry is undefined if the backing map has been 369 * modified after the entry was returned by the iterator, except through 370 * the <tt>setValue</tt> operation on the map entry. 371 * 372 * @see Map#entrySet() 373 * @since 1.2 374 */ 375 interface Entry<K,V> { 376 /** 377 * Returns the key corresponding to this entry. 378 * 379 * @return the key 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 K getKey(); 385 386 /** 387 * Returns the value corresponding to this entry. If the mapping 388 * has been removed from the backing map (by the iterator's 389 * <tt>remove</tt> operation), the results of this call are undefined. 390 * 391 * @return the value corresponding to this entry 392 * @throws IllegalStateException implementations may, but are not 393 * required to, throw this exception if the entry has been 394 * removed from the backing map. 395 */ 396 V getValue(); 397 398 /** 399 * Replaces the value corresponding to this entry with the specified 400 * value (optional operation). (Writes through to the map.) The 401 * behavior of this call is undefined if the mapping has already been 402 * removed from the map (by the iterator's <tt>remove</tt> operation). 403 * 404 * @param value new value to be stored in this entry 405 * @return old value corresponding to the entry 406 * @throws UnsupportedOperationException if the <tt>put</tt> operation 407 * is not supported by the backing map 408 * @throws ClassCastException if the class of the specified value 409 * prevents it from being stored in the backing map 410 * @throws NullPointerException if the backing map does not permit 411 * null values, and the specified value is null 412 * @throws IllegalArgumentException if some property of this value 413 * prevents it from being stored in the backing map 414 * @throws IllegalStateException implementations may, but are not 415 * required to, throw this exception if the entry has been 416 * removed from the backing map. 417 */ 418 V setValue(V value); 419 420 /** 421 * Compares the specified object with this entry for equality. 422 * Returns <tt>true</tt> if the given object is also a map entry and 423 * the two entries represent the same mapping. More formally, two 424 * entries <tt>e1</tt> and <tt>e2</tt> represent the same mapping 425 * if<pre> 426 * (e1.getKey()==null ? 427 * e2.getKey()==null : e1.getKey().equals(e2.getKey())) && 428 * (e1.getValue()==null ? 429 * e2.getValue()==null : e1.getValue().equals(e2.getValue())) 430 * </pre> 431 * This ensures that the <tt>equals</tt> method works properly across 432 * different implementations of the <tt>Map.Entry</tt> interface. 433 * 434 * @param o object to be compared for equality with this map entry 435 * @return <tt>true</tt> if the specified object is equal to this map 436 * entry 437 */ 438 boolean equals(Object o); 439 440 /** 441 * Returns the hash code value for this map entry. The hash code 442 * of a map entry <tt>e</tt> is defined to be: <pre> 443 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^ 444 * (e.getValue()==null ? 0 : e.getValue().hashCode()) 445 * </pre> 446 * This ensures that <tt>e1.equals(e2)</tt> implies that 447 * <tt>e1.hashCode()==e2.hashCode()</tt> for any two Entries 448 * <tt>e1</tt> and <tt>e2</tt>, as required by the general 449 * contract of <tt>Object.hashCode</tt>. 450 * 451 * @return the hash code value for this map entry 452 * @see Object#hashCode() 453 * @see Object#equals(Object) 454 * @see #equals(Object) 455 */ 456 int hashCode(); 457 458 /** 459 * Returns a comparator that compares {@link Map.Entry} in natural order on key. 460 * 461 * <p>The returned comparator is serializable and throws {@link 462 * NullPointerException} when comparing an entry with a null key. 463 * 464 * @param <K> the {@link Comparable} type of then map keys 465 * @param <V> the type of the map values 466 * @return a comparator that compares {@link Map.Entry} in natural order on key. 467 * @see Comparable 468 * @since 1.8 469 */ 470 public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K,V>> comparingByKey() { 471 return (Comparator<Map.Entry<K, V>> & Serializable) 472 (c1, c2) -> c1.getKey().compareTo(c2.getKey()); 473 } 474 475 /** 476 * Returns a comparator that compares {@link Map.Entry} in natural order on value. 477 * 478 * <p>The returned comparator is serializable and throws {@link 479 * NullPointerException} when comparing an entry with null values. 480 * 481 * @param <K> the type of the map keys 482 * @param <V> the {@link Comparable} type of the map values 483 * @return a comparator that compares {@link Map.Entry} in natural order on value. 484 * @see Comparable 485 * @since 1.8 486 */ 487 public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K,V>> comparingByValue() { 488 return (Comparator<Map.Entry<K, V>> & Serializable) 489 (c1, c2) -> c1.getValue().compareTo(c2.getValue()); 490 } 491 492 /** 493 * Returns a comparator that compares {@link Map.Entry} by key using the given 494 * {@link Comparator}. 495 * 496 * <p>The returned comparator is serializable if the specified comparator 497 * is also serializable. 498 * 499 * @param <K> the type of the map keys 500 * @param <V> the type of the map values 501 * @param cmp the key {@link Comparator} 502 * @return a comparator that compares {@link Map.Entry} by the key. 503 * @since 1.8 504 */ 505 public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) { 506 Objects.requireNonNull(cmp); 507 return (Comparator<Map.Entry<K, V>> & Serializable) 508 (c1, c2) -> cmp.compare(c1.getKey(), c2.getKey()); 509 } 510 511 /** 512 * Returns a comparator that compares {@link Map.Entry} by value using the given 513 * {@link Comparator}. 514 * 515 * <p>The returned comparator is serializable if the specified comparator 516 * is also serializable. 517 * 518 * @param <K> the type of the map keys 519 * @param <V> the type of the map values 520 * @param cmp the value {@link Comparator} 521 * @return a comparator that compares {@link Map.Entry} by the value. 522 * @since 1.8 523 */ 524 public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) { 525 Objects.requireNonNull(cmp); 526 return (Comparator<Map.Entry<K, V>> & Serializable) 527 (c1, c2) -> cmp.compare(c1.getValue(), c2.getValue()); 528 } 529 } 530 531 // Comparison and hashing 532 533 /** 534 * Compares the specified object with this map for equality. Returns 535 * <tt>true</tt> if the given object is also a map and the two maps 536 * represent the same mappings. More formally, two maps <tt>m1</tt> and 537 * <tt>m2</tt> represent the same mappings if 538 * <tt>m1.entrySet().equals(m2.entrySet())</tt>. This ensures that the 539 * <tt>equals</tt> method works properly across different implementations 540 * of the <tt>Map</tt> interface. 541 * 542 * @param o object to be compared for equality with this map 543 * @return <tt>true</tt> if the specified object is equal to this map 544 */ 545 boolean equals(Object o); 546 547 /** 548 * Returns the hash code value for this map. The hash code of a map is 549 * defined to be the sum of the hash codes of each entry in the map's 550 * <tt>entrySet()</tt> view. This ensures that <tt>m1.equals(m2)</tt> 551 * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps 552 * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of 553 * {@link Object#hashCode}. 554 * 555 * @return the hash code value for this map 556 * @see Map.Entry#hashCode() 557 * @see Object#equals(Object) 558 * @see #equals(Object) 559 */ 560 int hashCode(); 561 562 // Defaultable methods 563 564 /** 565 * Returns the value to which the specified key is mapped, or 566 * {@code defaultValue} if this map contains no mapping for the key. 567 * 568 * @implSpec 569 * The default implementation makes no guarantees about synchronization 570 * or atomicity properties of this method. Any implementation providing 571 * atomicity guarantees must override this method and document its 572 * concurrency properties. 573 * 574 * @param key the key whose associated value is to be returned 575 * @param defaultValue the default mapping of the key 576 * @return the value to which the specified key is mapped, or 577 * {@code defaultValue} if this map contains no mapping for the key 578 * @throws ClassCastException if the key is of an inappropriate type for 579 * this map 580 * (<a href="Collection.html#optional-restrictions">optional</a>) 581 * @throws NullPointerException if the specified key is null and this map 582 * does not permit null keys 583 * (<a href="Collection.html#optional-restrictions">optional</a>) 584 * @since 1.8 585 */ 586 default V getOrDefault(Object key, V defaultValue) { 587 V v; 588 return (((v = get(key)) != null) || containsKey(key)) 589 ? v 590 : defaultValue; 591 } 592 593 /** 594 * Performs the given action for each entry in this map until all entries 595 * have been processed or the action throws an exception. Unless 596 * otherwise specified by the implementing class, actions are performed in 597 * the order of entry set iteration (if an iteration order is specified.) 598 * Exceptions thrown by the action are relayed to the caller. 599 * 600 * @implSpec 601 * The default implementation is equivalent to, for this {@code map}: 602 * <pre> {@code 603 * for ((Map.Entry<K, V> entry : map.entrySet()) 604 * action.accept(entry.getKey(), entry.getValue()); 605 * }</pre> 606 * 607 * The default implementation makes no guarantees about synchronization 608 * or atomicity properties of this method. Any implementation providing 609 * atomicity guarantees must override this method and document its 610 * concurrency properties. 611 * 612 * @param action The action to be performed for each entry 613 * @throws NullPointerException if the specified action is null 614 * @throws ConcurrentModificationException if an entry is found to be 615 * removed during iteration 616 * @since 1.8 617 */ 618 default void forEach(BiConsumer<? super K, ? super V> action) { 619 Objects.requireNonNull(action); 620 for (Map.Entry<K, V> entry : entrySet()) { 621 K k; 622 V v; 623 try { 624 k = entry.getKey(); 625 v = entry.getValue(); 626 } catch(IllegalStateException ise) { 627 // this usually means the entry is no longer in the map. 628 throw new ConcurrentModificationException(ise); 629 } 630 action.accept(k, v); 631 } 632 } 633 634 /** 635 * Replaces each entry's value with the result of invoking the given 636 * function on that entry until all entries have been processed or the 637 * function throws an exception. Exceptions thrown by the function are 638 * relayed to the caller. 639 * 640 * @implSpec 641 * <p>The default implementation is equivalent to, for this {@code map}: 642 * <pre> {@code 643 * for ((Map.Entry<K, V> entry : map.entrySet()) 644 * entry.setValue(function.apply(entry.getKey(), entry.getValue())); 645 * }</pre> 646 * 647 * <p>The default implementation makes no guarantees about synchronization 648 * or atomicity properties of this method. Any implementation providing 649 * atomicity guarantees must override this method and document its 650 * concurrency properties. 651 * 652 * @param function the function to apply to each entry 653 * @throws UnsupportedOperationException if the {@code set} operation 654 * is not supported by this map's entry set iterator. 655 * @throws ClassCastException if the class of a replacement value 656 * prevents it from being stored in this map 657 * @throws NullPointerException if the specified function is null, or the 658 * specified replacement value is null, and this map does not permit null 659 * values 660 * @throws ClassCastException if a replacement value is of an inappropriate 661 * type for this map 662 * (<a href="Collection.html#optional-restrictions">optional</a>) 663 * @throws NullPointerException if function or a replacement value is null, 664 * and this map does not permit null keys or values 665 * (<a href="Collection.html#optional-restrictions">optional</a>) 666 * @throws IllegalArgumentException if some property of a replacement value 667 * prevents it from being stored in this map 668 * (<a href="Collection.html#optional-restrictions">optional</a>) 669 * @throws ConcurrentModificationException if an entry is found to be 670 * removed during iteration 671 * @since 1.8 672 */ 673 default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 674 Objects.requireNonNull(function); 675 for (Map.Entry<K, V> entry : entrySet()) { 676 K k; 677 V v; 678 try { 679 k = entry.getKey(); 680 v = entry.getValue(); 681 } catch(IllegalStateException ise) { 682 // this usually means the entry is no longer in the map. 683 throw new ConcurrentModificationException(ise); 684 } 685 686 // ise thrown from function is not a cme. 687 v = function.apply(k, v); 688 689 try { 690 entry.setValue(v); 691 } catch(IllegalStateException ise) { 692 // this usually means the entry is no longer in the map. 693 throw new ConcurrentModificationException(ise); 694 } 695 } 696 } 697 698 /** 699 * If the specified key is not already associated with a value (or is mapped 700 * to {@code null}) associates it with the given value and returns 701 * {@code null}, else returns the current value. 702 * 703 * @implSpec 704 * The default implementation is equivalent to, for this {@code 705 * map}: 706 * 707 * <pre> {@code 708 * V v = map.get(key); 709 * if (v == null) 710 * v = map.put(key, value); 711 * 712 * return v; 713 * }</pre> 714 * 715 * <p>The default implementation makes no guarantees about synchronization 716 * or atomicity properties of this method. Any implementation providing 717 * atomicity guarantees must override this method and document its 718 * concurrency properties. 719 * 720 * @param key key with which the specified value is to be associated 721 * @param value value to be associated with the specified key 722 * @return the previous value associated with the specified key, or 723 * {@code null} if there was no mapping for the key. 724 * (A {@code null} return can also indicate that the map 725 * previously associated {@code null} with the key, 726 * if the implementation supports null values.) 727 * @throws UnsupportedOperationException if the {@code put} operation 728 * is not supported by this map 729 * (<a href="Collection.html#optional-restrictions">optional</a>) 730 * @throws ClassCastException if the key or value is of an inappropriate 731 * type for this map 732 * (<a href="Collection.html#optional-restrictions">optional</a>) 733 * @throws NullPointerException if the specified key or value is null, 734 * and this map does not permit null keys or values 735 * (<a href="Collection.html#optional-restrictions">optional</a>) 736 * @throws IllegalArgumentException if some property of the specified key 737 * or value prevents it from being stored in this map 738 * (<a href="Collection.html#optional-restrictions">optional</a>) 739 * @since 1.8 740 */ 741 default V putIfAbsent(K key, V value) { 742 V v = get(key); 743 if (v == null) { 744 v = put(key, value); 745 } 746 747 return v; 748 } 749 750 /** 751 * Removes the entry for the specified key only if it is currently 752 * mapped to the specified value. 753 * 754 * @implSpec 755 * The default implementation is equivalent to, for this {@code map}: 756 * 757 * <pre> {@code 758 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) { 759 * map.remove(key); 760 * return true; 761 * } else 762 * return false; 763 * }</pre> 764 * 765 * <p>The default implementation makes no guarantees about synchronization 766 * or atomicity properties of this method. Any implementation providing 767 * atomicity guarantees must override this method and document its 768 * concurrency properties. 769 * 770 * @param key key with which the specified value is associated 771 * @param value value expected to be associated with the specified key 772 * @return {@code true} if the value was removed 773 * @throws UnsupportedOperationException if the {@code remove} operation 774 * is not supported by this map 775 * (<a href="Collection.html#optional-restrictions">optional</a>) 776 * @throws ClassCastException if the key or value is of an inappropriate 777 * type for this map 778 * (<a href="Collection.html#optional-restrictions">optional</a>) 779 * @throws NullPointerException if the specified key or value is null, 780 * and this map does not permit null keys or values 781 * (<a href="Collection.html#optional-restrictions">optional</a>) 782 * @since 1.8 783 */ 784 default boolean remove(Object key, Object value) { 785 Object curValue = get(key); 786 if (!Objects.equals(curValue, value) || 787 (curValue == null && !containsKey(key))) { 788 return false; 789 } 790 remove(key); 791 return true; 792 } 793 794 /** 795 * Replaces the entry for the specified key only if currently 796 * mapped to the specified value. 797 * 798 * @implSpec 799 * The default implementation is equivalent to, for this {@code map}: 800 * 801 * <pre> {@code 802 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) { 803 * map.put(key, newValue); 804 * return true; 805 * } else 806 * return false; 807 * }</pre> 808 * 809 * The default implementation does not throw NullPointerException 810 * for maps that do not support null values if oldValue is null unless 811 * newValue is also null. 812 * 813 * <p>The default implementation makes no guarantees about synchronization 814 * or atomicity properties of this method. Any implementation providing 815 * atomicity guarantees must override this method and document its 816 * concurrency properties. 817 * 818 * @param key key with which the specified value is associated 819 * @param oldValue value expected to be associated with the specified key 820 * @param newValue value to be associated with the specified key 821 * @return {@code true} if the value was replaced 822 * @throws UnsupportedOperationException if the {@code put} operation 823 * is not supported by this map 824 * (<a href="Collection.html#optional-restrictions">optional</a>) 825 * @throws ClassCastException if the class of a specified key or value 826 * prevents it from being stored in this map 827 * @throws NullPointerException if a specified key or newValue is null, 828 * and this map does not permit null keys or values 829 * @throws NullPointerException if oldValue is null and this map does not 830 * permit null values 831 * (<a href="Collection.html#optional-restrictions">optional</a>) 832 * @throws IllegalArgumentException if some property of a specified key 833 * or value prevents it from being stored in this map 834 * @since 1.8 835 */ 836 default boolean replace(K key, V oldValue, V newValue) { 837 Object curValue = get(key); 838 if (!Objects.equals(curValue, oldValue) || 839 (curValue == null && !containsKey(key))) { 840 return false; 841 } 842 put(key, newValue); 843 return true; 844 } 845 846 /** 847 * Replaces the entry for the specified key only if it is 848 * currently mapped to some value. 849 * 850 * @implSpec 851 * The default implementation is equivalent to, for this {@code map}: 852 * 853 * <pre> {@code 854 * if (map.containsKey(key)) { 855 * return map.put(key, value); 856 * } else 857 * return null; 858 * }</pre> 859 * 860 * <p>The default implementation makes no guarantees about synchronization 861 * or atomicity properties of this method. Any implementation providing 862 * atomicity guarantees must override this method and document its 863 * concurrency properties. 864 * 865 * @param key key with which the specified value is associated 866 * @param value value to be associated with the specified key 867 * @return the previous value associated with the specified key, or 868 * {@code null} if there was no mapping for the key. 869 * (A {@code null} return can also indicate that the map 870 * previously associated {@code null} with the key, 871 * if the implementation supports null values.) 872 * @throws UnsupportedOperationException if the {@code put} operation 873 * is not supported by this map 874 * (<a href="Collection.html#optional-restrictions">optional</a>) 875 * @throws ClassCastException if the class of the specified key or value 876 * prevents it from being stored in this map 877 * (<a href="Collection.html#optional-restrictions">optional</a>) 878 * @throws NullPointerException if the specified key or value is null, 879 * and this map does not permit null keys or values 880 * @throws IllegalArgumentException if some property of the specified key 881 * or value prevents it from being stored in this map 882 * @since 1.8 883 */ 884 default V replace(K key, V value) { 885 V curValue; 886 if (((curValue = get(key)) != null) || containsKey(key)) { 887 curValue = put(key, value); 888 } 889 return curValue; 890 } 891 892 /** 893 * If the specified key is not already associated with a value (or is mapped 894 * to {@code null}), attempts to compute its value using the given mapping 895 * function and enters it into this map unless {@code null}. 896 * 897 * <p>If the function returns {@code null} no mapping is recorded. If 898 * the function itself throws an (unchecked) exception, the 899 * exception is rethrown, and no mapping is recorded. The most 900 * common usage is to construct a new object serving as an initial 901 * mapped value or memoized result, as in: 902 * 903 * <pre> {@code 904 * map.computeIfAbsent(key, k -> new Value(f(k))); 905 * }</pre> 906 * 907 * <p>Or to implement a multi-value map, {@code Map<K,Collection<V>>}, 908 * supporting multiple values per key: 909 * 910 * <pre> {@code 911 * map.computeIfAbsent(key, k -> new HashSet<V>()).add(v); 912 * }</pre> 913 * 914 * 915 * @implSpec 916 * The default implementation is equivalent to the following steps for this 917 * {@code map}, then returning the current value or {@code null} if now 918 * absent: 919 * 920 * <pre> {@code 921 * if (map.get(key) == null) { 922 * V newValue = mappingFunction.apply(key); 923 * if (newValue != null) 924 * map.put(key, newValue); 925 * } 926 * }</pre> 927 * 928 * <p>The default implementation makes no guarantees about synchronization 929 * or atomicity properties of this method. Any implementation providing 930 * atomicity guarantees must override this method and document its 931 * concurrency properties. In particular, all implementations of 932 * subinterface {@link java.util.concurrent.ConcurrentMap} must document 933 * whether the function is applied once atomically only if the value is not 934 * present. 935 * 936 * @param key key with which the specified value is to be associated 937 * @param mappingFunction the function to compute a value 938 * @return the current (existing or computed) value associated with 939 * the specified key, or null if the computed value is null 940 * @throws NullPointerException if the specified key is null and 941 * this map does not support null keys, or the mappingFunction 942 * is null 943 * @throws UnsupportedOperationException if the {@code put} operation 944 * is not supported by this map 945 * (<a href="Collection.html#optional-restrictions">optional</a>) 946 * @throws ClassCastException if the class of the specified key or value 947 * prevents it from being stored in this map 948 * (<a href="Collection.html#optional-restrictions">optional</a>) 949 * @since 1.8 950 */ 951 default V computeIfAbsent(K key, 952 Function<? super K, ? extends V> mappingFunction) { 953 Objects.requireNonNull(mappingFunction); 954 V v; 955 if ((v = get(key)) == null) { 956 V newValue; 957 if ((newValue = mappingFunction.apply(key)) != null) { 958 put(key, newValue); 959 return newValue; 960 } 961 } 962 963 return v; 964 } 965 966 /** 967 * If the value for the specified key is present and non-null, attempts to 968 * compute a new mapping given the key and its current mapped value. 969 * 970 * <p>If the function returns {@code null}, the mapping is removed. If the 971 * function itself throws an (unchecked) exception, the exception is 972 * rethrown, and the current mapping is left unchanged. 973 * 974 * @implSpec 975 * The default implementation is equivalent to performing the following 976 * steps for this {@code map}, then returning the current value or 977 * {@code null} if now absent: 978 * 979 * <pre> {@code 980 * if (map.get(key) != null) { 981 * V oldValue = map.get(key); 982 * V newValue = remappingFunction.apply(key, oldValue); 983 * if (newValue != null) 984 * map.put(key, newValue); 985 * else 986 * map.remove(key); 987 * } 988 * }</pre> 989 * 990 * <p>The default implementation makes no guarantees about synchronization 991 * or atomicity properties of this method. Any implementation providing 992 * atomicity guarantees must override this method and document its 993 * concurrency properties. In particular, all implementations of 994 * subinterface {@link java.util.concurrent.ConcurrentMap} must document 995 * whether the function is applied once atomically only if the value is not 996 * present. 997 * 998 * @param key key with which the specified value is to be associated 999 * @param remappingFunction the function to compute a value 1000 * @return the new value associated with the specified key, or null if none 1001 * @throws NullPointerException if the specified key is null and 1002 * this map does not support null keys, or the 1003 * remappingFunction is null 1004 * @throws UnsupportedOperationException if the {@code put} operation 1005 * is not supported by this map 1006 * (<a href="Collection.html#optional-restrictions">optional</a>) 1007 * @throws ClassCastException if the class of the specified key or value 1008 * prevents it from being stored in this map 1009 * (<a href="Collection.html#optional-restrictions">optional</a>) 1010 * @since 1.8 1011 */ 1012 default V computeIfPresent(K key, 1013 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 1014 Objects.requireNonNull(remappingFunction); 1015 V oldValue; 1016 if ((oldValue = get(key)) != null) { 1017 V newValue = remappingFunction.apply(key, oldValue); 1018 if (newValue != null) { 1019 put(key, newValue); 1020 return newValue; 1021 } else { 1022 remove(key); 1023 return null; 1024 } 1025 } else { 1026 return null; 1027 } 1028 } 1029 1030 /** 1031 * Attempts to compute a mapping for the specified key and its current 1032 * mapped value (or {@code null} if there is no current mapping). For 1033 * example, to either create or append a {@code String} msg to a value 1034 * mapping: 1035 * 1036 * <pre> {@code 1037 * map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))}</pre> 1038 * (Method {@link #merge merge()} is often simpler to use for such purposes.) 1039 * 1040 * <p>If the function returns {@code null}, the mapping is removed (or 1041 * remains absent if initially absent). If the function itself throws an 1042 * (unchecked) exception, the exception is rethrown, and the current mapping 1043 * is left unchanged. 1044 * 1045 * @implSpec 1046 * The default implementation is equivalent to performing the following 1047 * steps for this {@code map}, then returning the current value or 1048 * {@code null} if absent: 1049 * 1050 * <pre> {@code 1051 * V oldValue = map.get(key); 1052 * V newValue = remappingFunction.apply(key, oldValue); 1053 * if (oldValue != null ) { 1054 * if (newValue != null) 1055 * map.put(key, newValue); 1056 * else 1057 * map.remove(key); 1058 * } else { 1059 * if (newValue != null) 1060 * map.put(key, newValue); 1061 * else 1062 * return null; 1063 * } 1064 * }</pre> 1065 * 1066 * <p>The default implementation makes no guarantees about synchronization 1067 * or atomicity properties of this method. Any implementation providing 1068 * atomicity guarantees must override this method and document its 1069 * concurrency properties. In particular, all implementations of 1070 * subinterface {@link java.util.concurrent.ConcurrentMap} must document 1071 * whether the function is applied once atomically only if the value is not 1072 * present. 1073 * 1074 * @param key key with which the specified value is to be associated 1075 * @param remappingFunction the function to compute a value 1076 * @return the new value associated with the specified key, or null if none 1077 * @throws NullPointerException if the specified key is null and 1078 * this map does not support null keys, or the 1079 * remappingFunction is null 1080 * @throws UnsupportedOperationException if the {@code put} operation 1081 * is not supported by this map 1082 * (<a href="Collection.html#optional-restrictions">optional</a>) 1083 * @throws ClassCastException if the class of the specified key or value 1084 * prevents it from being stored in this map 1085 * (<a href="Collection.html#optional-restrictions">optional</a>) 1086 * @since 1.8 1087 */ 1088 default V compute(K key, 1089 BiFunction<? super K, ? super V, ? extends V> remappingFunction) { 1090 Objects.requireNonNull(remappingFunction); 1091 V oldValue = get(key); 1092 1093 V newValue = remappingFunction.apply(key, oldValue); 1094 if (newValue == null) { 1095 // delete mapping 1096 if (oldValue != null || containsKey(key)) { 1097 // something to remove 1098 remove(key); 1099 return null; 1100 } else { 1101 // nothing to do. Leave things as they were. 1102 return null; 1103 } 1104 } else { 1105 // add or replace old mapping 1106 put(key, newValue); 1107 return newValue; 1108 } 1109 } 1110 1111 /** 1112 * If the specified key is not already associated with a value or is 1113 * associated with null, associates it with the given value. 1114 * Otherwise, replaces the value with the results of the given 1115 * remapping function, or removes if the result is {@code null}. This 1116 * method may be of use when combining multiple mapped values for a key. 1117 * For example, to either create or append a {@code String msg} to a 1118 * value mapping: 1119 * 1120 * <pre> {@code 1121 * map.merge(key, msg, String::concat) 1122 * }</pre> 1123 * 1124 * <p>If the function returns {@code null}, the mapping is removed (or 1125 * remains absent if initially absent). If the function itself throws an 1126 * (unchecked) exception, the exception is rethrown, and the current mapping 1127 * is left unchanged. 1128 * 1129 * @implSpec 1130 * The default implementation is equivalent to performing the 1131 * following steps for this {@code map}, then returning the 1132 * current value or {@code null} if absent: 1133 * 1134 * <pre> {@code 1135 * V oldValue = map.get(key); 1136 * V newValue = (oldValue == null) ? value : 1137 * remappingFunction.apply(oldValue, value); 1138 * if (newValue == null) 1139 * map.remove(key); 1140 * else 1141 * map.put(key, newValue); 1142 * }</pre> 1143 * 1144 * <p>The default implementation makes no guarantees about synchronization 1145 * or atomicity properties of this method. Any implementation providing 1146 * atomicity guarantees must override this method and document its 1147 * concurrency properties. In particular, all implementations of 1148 * subinterface {@link java.util.concurrent.ConcurrentMap} must document 1149 * whether the function is applied once atomically only if the value is not 1150 * present. 1151 * 1152 * @param key key with which the specified value is to be associated 1153 * @param value the value to use if absent 1154 * @param remappingFunction the function to recompute a value if present 1155 * @return the new value associated with the specified key, or null if none 1156 * @throws UnsupportedOperationException if the {@code put} operation 1157 * is not supported by this map 1158 * (<a href="Collection.html#optional-restrictions">optional</a>) 1159 * @throws ClassCastException if the class of the specified key or value 1160 * prevents it from being stored in this map 1161 * (<a href="Collection.html#optional-restrictions">optional</a>) 1162 * @throws NullPointerException if the specified key is null and 1163 * this map does not support null keys, or the remappingFunction 1164 * is null 1165 * @since 1.8 1166 */ 1167 default V merge(K key, V value, 1168 BiFunction<? super V, ? super V, ? extends V> remappingFunction) { 1169 Objects.requireNonNull(remappingFunction); 1170 V oldValue = get(key); 1171 V newValue = (oldValue == null) ? value : 1172 remappingFunction.apply(oldValue, value); 1173 if(newValue == null) { 1174 remove(key); 1175 } else { 1176 put(key, newValue); 1177 } 1178 return newValue; 1179 } 1180 }