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
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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
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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
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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
32 /**
33 * An object that maps keys to values. A map cannot contain duplicate keys;
34 * each key can map to at most one value.
35 *
36 * <p>This interface takes the place of the <tt>Dictionary</tt> class, which
37 * was a totally abstract class rather than an interface.
38 *
39 * <p>The <tt>Map</tt> interface provides three <i>collection views</i>, which
40 * allow a map's contents to be viewed as a set of keys, collection of values,
41 * or set of key-value mappings. The <i>order</i> of a map is defined as
42 * the order in which the iterators on the map's collection views return their
43 * elements. Some map implementations, like the <tt>TreeMap</tt> class, make
44 * specific guarantees as to their order; others, like the <tt>HashMap</tt>
45 * class, do not.
46 *
47 * <p>Note: great care must be exercised if mutable objects are used as map
48 * keys. The behavior of a map is not specified if the value of an object is
49 * changed in a manner that affects <tt>equals</tt> comparisons while the
50 * object is a key in the map. A special case of this prohibition is that it
51 * is not permissible for a map to contain itself as a key. While it is
52 * permissible for a map to contain itself as a value, extreme caution is
53 * advised: the <tt>equals</tt> and <tt>hashCode</tt> methods are no longer
54 * well defined on such a map.
55 *
56 * <p>All general-purpose map implementation classes should provide two
57 * "standard" constructors: a void (no arguments) constructor which creates an
58 * empty map, and a constructor with a single argument of type <tt>Map</tt>,
59 * which creates a new map with the same key-value mappings as its argument.
60 * In effect, the latter constructor allows the user to copy any map,
61 * producing an equivalent map of the desired class. There is no way to
62 * enforce this recommendation (as interfaces cannot contain constructors) but
63 * all of the general-purpose map implementations in the JDK comply.
64 *
65 * <p>The "destructive" methods contained in this interface, that is, the
66 * methods that modify the map on which they operate, are specified to throw
67 * <tt>UnsupportedOperationException</tt> if this map does not support the
68 * operation. If this is the case, these methods may, but are not required
69 * to, throw an <tt>UnsupportedOperationException</tt> if the invocation would
70 * have no effect on the map. For example, invoking the {@link #putAll(Map)}
71 * method on an unmodifiable map may, but is not required to, throw the
72 * exception if the map whose mappings are to be "superimposed" is empty.
73 *
74 * <p>Some map implementations have restrictions on the keys and values they
75 * may contain. For example, some implementations prohibit null keys and
76 * values, and some have restrictions on the types of their keys. Attempting
77 * to insert an ineligible key or value throws an unchecked exception,
78 * typically <tt>NullPointerException</tt> or <tt>ClassCastException</tt>.
79 * Attempting to query the presence of an ineligible key or value may throw an
80 * exception, or it may simply return false; some implementations will exhibit
81 * the former behavior and some will exhibit the latter. More generally,
82 * attempting an operation on an ineligible key or value whose completion
83 * would not result in the insertion of an ineligible element into the map may
84 * throw an exception or it may succeed, at the option of the implementation.
85 * Such exceptions are marked as "optional" in the specification for this
86 * interface.
87 *
88 * <p>This interface is a member of the
89 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
90 * Java Collections Framework</a>.
91 *
92 * <p>Many methods in Collections Framework interfaces are defined
93 * in terms of the {@link Object#equals(Object) equals} method. For
94 * example, the specification for the {@link #containsKey(Object)
95 * containsKey(Object key)} method says: "returns <tt>true</tt> if and
96 * only if this map contains a mapping for a key <tt>k</tt> such that
97 * <tt>(key==null ? k==null : key.equals(k))</tt>." This specification should
98 * <i>not</i> be construed to imply that invoking <tt>Map.containsKey</tt>
99 * with a non-null argument <tt>key</tt> will cause <tt>key.equals(k)</tt> to
100 * be invoked for any key <tt>k</tt>. Implementations are free to
101 * implement optimizations whereby the <tt>equals</tt> invocation is avoided,
102 * for example, by first comparing the hash codes of the two keys. (The
103 * {@link Object#hashCode()} specification guarantees that two objects with
104 * unequal hash codes cannot be equal.) More generally, implementations of
105 * the various Collections Framework interfaces are free to take advantage of
106 * the specified behavior of underlying {@link Object} methods wherever the
107 * implementor deems it appropriate.
108 *
109 * @param <K> the type of keys maintained by this map
110 * @param <V> the type of mapped values
111 *
112 * @author Josh Bloch
113 * @see HashMap
114 * @see TreeMap
115 * @see Hashtable
116 * @see SortedMap
117 * @see Collection
118 * @see Set
119 * @since 1.2
120 */
121 public interface Map<K,V> {
122 // Query Operations
123
124 /**
125 * Returns the number of key-value mappings in this map. If the
126 * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
127 * <tt>Integer.MAX_VALUE</tt>.
128 *
129 * @return the number of key-value mappings in this map
130 */
131 int size();
132
133 /**
134 * Returns <tt>true</tt> if this map contains no key-value mappings.
135 *
136 * @return <tt>true</tt> if this map contains no key-value mappings
137 */
138 boolean isEmpty();
139
140 /**
141 * Returns <tt>true</tt> if this map contains a mapping for the specified
142 * key. More formally, returns <tt>true</tt> if and only if
143 * this map contains a mapping for a key <tt>k</tt> such that
144 * <tt>(key==null ? k==null : key.equals(k))</tt>. (There can be
145 * at most one such mapping.)
146 *
147 * @param key key whose presence in this map is to be tested
148 * @return <tt>true</tt> if this map contains a mapping for the specified
149 * key
150 * @throws ClassCastException if the key is of an inappropriate type for
151 * this map
152 * (<a href="Collection.html#optional-restrictions">optional</a>)
153 * @throws NullPointerException if the specified key is null and this map
154 * does not permit null keys
155 * (<a href="Collection.html#optional-restrictions">optional</a>)
156 */
157 boolean containsKey(Object key);
158
159 /**
160 * Returns <tt>true</tt> if this map maps one or more keys to the
161 * specified value. More formally, returns <tt>true</tt> if and only if
162 * this map contains at least one mapping to a value <tt>v</tt> such that
163 * <tt>(value==null ? v==null : value.equals(v))</tt>. This operation
164 * will probably require time linear in the map size for most
165 * implementations of the <tt>Map</tt> interface.
166 *
167 * @param value value whose presence in this map is to be tested
168 * @return <tt>true</tt> if this map maps one or more keys to the
169 * specified value
170 * @throws ClassCastException if the value is of an inappropriate type for
171 * this map
172 * (<a href="Collection.html#optional-restrictions">optional</a>)
173 * @throws NullPointerException if the specified value is null and this
174 * map does not permit null values
175 * (<a href="Collection.html#optional-restrictions">optional</a>)
176 */
177 boolean containsValue(Object value);
178
179 /**
180 * Returns the value to which the specified key is mapped,
181 * or {@code null} if this map contains no mapping for the key.
182 *
183 * <p>More formally, if this map contains a mapping from a key
184 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
185 * key.equals(k))}, then this method returns {@code v}; otherwise
186 * it returns {@code null}. (There can be at most one such mapping.)
187 *
188 * <p>If this map permits null values, then a return value of
189 * {@code null} does not <i>necessarily</i> indicate that the map
190 * contains no mapping for the key; it's also possible that the map
191 * explicitly maps the key to {@code null}. The {@link #containsKey
192 * containsKey} operation may be used to distinguish these two cases.
193 *
194 * @param key the key whose associated value is to be returned
195 * @return the value to which the specified key is mapped, or
196 * {@code null} if this map contains no mapping for the key
197 * @throws ClassCastException if the key is of an inappropriate type for
198 * this map
199 * (<a href="Collection.html#optional-restrictions">optional</a>)
200 * @throws NullPointerException if the specified key is null and this map
201 * does not permit null keys
202 * (<a href="Collection.html#optional-restrictions">optional</a>)
203 */
204 V get(Object key);
205
206 // Modification Operations
207
208 /**
209 * Associates the specified value with the specified key in this map
210 * (optional operation). If the map previously contained a mapping for
211 * the key, the old value is replaced by the specified value. (A map
212 * <tt>m</tt> is said to contain a mapping for a key <tt>k</tt> if and only
213 * if {@link #containsKey(Object) m.containsKey(k)} would return
214 * <tt>true</tt>.)
215 *
216 * @param key key with which the specified value is to be associated
217 * @param value value to be associated with the specified key
218 * @return the previous value associated with <tt>key</tt>, or
219 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
220 * (A <tt>null</tt> return can also indicate that the map
221 * previously associated <tt>null</tt> with <tt>key</tt>,
222 * if the implementation supports <tt>null</tt> values.)
223 * @throws UnsupportedOperationException if the <tt>put</tt> operation
224 * is not supported by this map
225 * @throws ClassCastException if the class of the specified key or value
226 * prevents it from being stored in this map
227 * @throws NullPointerException if the specified key or value is null
228 * and this map does not permit null keys or values
229 * @throws IllegalArgumentException if some property of the specified key
230 * or value prevents it from being stored in this map
231 */
232 V put(K key, V value);
233
234 /**
235 * Removes the mapping for a key from this map if it is present
236 * (optional operation). More formally, if this map contains a mapping
237 * from key <tt>k</tt> to value <tt>v</tt> such that
238 * <code>(key==null ? k==null : key.equals(k))</code>, that mapping
239 * is removed. (The map can contain at most one such mapping.)
240 *
241 * <p>Returns the value to which this map previously associated the key,
242 * or <tt>null</tt> if the map contained no mapping for the key.
243 *
244 * <p>If this map permits null values, then a return value of
245 * <tt>null</tt> does not <i>necessarily</i> indicate that the map
246 * contained no mapping for the key; it's also possible that the map
247 * explicitly mapped the key to <tt>null</tt>.
248 *
249 * <p>The map will not contain a mapping for the specified key once the
250 * call returns.
251 *
252 * @param key key whose mapping is to be removed from the map
253 * @return the previous value associated with <tt>key</tt>, or
254 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
255 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
256 * is not supported by this map
257 * @throws ClassCastException if the key is of an inappropriate type for
258 * this map
259 * (<a href="Collection.html#optional-restrictions">optional</a>)
260 * @throws NullPointerException if the specified key is null and this
261 * map does not permit null keys
262 * (<a href="Collection.html#optional-restrictions">optional</a>)
263 */
264 V remove(Object key);
265
266
267 // Bulk Operations
268
269 /**
270 * Copies all of the mappings from the specified map to this map
271 * (optional operation). The effect of this call is equivalent to that
272 * of calling {@link #put(Object,Object) put(k, v)} on this map once
273 * for each mapping from key <tt>k</tt> to value <tt>v</tt> in the
274 * specified map. The behavior of this operation is undefined if the
275 * specified map is modified while the operation is in progress.
276 *
277 * @param m mappings to be stored in this map
278 * @throws UnsupportedOperationException if the <tt>putAll</tt> operation
279 * is not supported by this map
280 * @throws ClassCastException if the class of a key or value in the
281 * specified map prevents it from being stored in this map
282 * @throws NullPointerException if the specified map is null, or if
283 * this map does not permit null keys or values, and the
284 * specified map contains null keys or values
285 * @throws IllegalArgumentException if some property of a key or value in
286 * the specified map prevents it from being stored in this map
287 */
288 void putAll(Map<? extends K, ? extends V> m);
289
290 /**
291 * Removes all of the mappings from this map (optional operation).
292 * The map will be empty after this call returns.
293 *
294 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
295 * is not supported by this map
296 */
297 void clear();
298
299
300 // Views
301
302 /**
303 * Returns a {@link Set} view of the keys contained in this map.
304 * The set is backed by the map, so changes to the map are
305 * reflected in the set, and vice-versa. If the map is modified
306 * while an iteration over the set is in progress (except through
307 * the iterator's own <tt>remove</tt> operation), the results of
308 * the iteration are undefined. The set supports element removal,
309 * which removes the corresponding mapping from the map, via the
310 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
311 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
312 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
313 * operations.
314 *
315 * @return a set view of the keys contained in this map
316 */
317 Set<K> keySet();
318
319 /**
320 * Returns a {@link Collection} view of the values contained in this map.
321 * The collection is backed by the map, so changes to the map are
322 * reflected in the collection, and vice-versa. If the map is
323 * modified while an iteration over the collection is in progress
324 * (except through the iterator's own <tt>remove</tt> operation),
325 * the results of the iteration are undefined. The collection
326 * supports element removal, which removes the corresponding
327 * mapping from the map, via the <tt>Iterator.remove</tt>,
328 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
329 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
330 * support the <tt>add</tt> or <tt>addAll</tt> operations.
331 *
332 * @return a collection view of the values contained in this map
333 */
334 Collection<V> values();
335
336 /**
337 * Returns a {@link Set} view of the mappings contained in this map.
338 * The set is backed by the map, so changes to the map are
339 * reflected in the set, and vice-versa. If the map is modified
340 * while an iteration over the set is in progress (except through
341 * the iterator's own <tt>remove</tt> operation, or through the
342 * <tt>setValue</tt> operation on a map entry returned by the
343 * iterator) the results of the iteration are undefined. The set
344 * supports element removal, which removes the corresponding
345 * mapping from the map, via the <tt>Iterator.remove</tt>,
346 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
347 * <tt>clear</tt> operations. It does not support the
348 * <tt>add</tt> or <tt>addAll</tt> operations.
349 *
350 * @return a set view of the mappings contained in this map
351 */
352 Set<Map.Entry<K, V>> entrySet();
353
354 /**
355 * A map entry (key-value pair). The <tt>Map.entrySet</tt> method returns
356 * a collection-view of the map, whose elements are of this class. The
357 * <i>only</i> way to obtain a reference to a map entry is from the
358 * iterator of this collection-view. These <tt>Map.Entry</tt> objects are
359 * valid <i>only</i> for the duration of the iteration; more formally,
360 * the behavior of a map entry is undefined if the backing map has been
361 * modified after the entry was returned by the iterator, except through
362 * the <tt>setValue</tt> operation on the map entry.
363 *
364 * @see Map#entrySet()
365 * @since 1.2
366 */
367 interface Entry<K,V> {
368 /**
369 * Returns the key corresponding to this entry.
370 *
371 * @return the key corresponding to this entry
372 * @throws IllegalStateException implementations may, but are not
373 * required to, throw this exception if the entry has been
374 * removed from the backing map.
375 */
376 K getKey();
377
378 /**
379 * Returns the value corresponding to this entry. If the mapping
380 * has been removed from the backing map (by the iterator's
381 * <tt>remove</tt> operation), the results of this call are undefined.
382 *
383 * @return the value corresponding to this entry
384 * @throws IllegalStateException implementations may, but are not
385 * required to, throw this exception if the entry has been
386 * removed from the backing map.
387 */
388 V getValue();
389
390 /**
391 * Replaces the value corresponding to this entry with the specified
392 * value (optional operation). (Writes through to the map.) The
393 * behavior of this call is undefined if the mapping has already been
394 * removed from the map (by the iterator's <tt>remove</tt> operation).
395 *
396 * @param value new value to be stored in this entry
397 * @return old value corresponding to the entry
398 * @throws UnsupportedOperationException if the <tt>put</tt> operation
399 * is not supported by the backing map
400 * @throws ClassCastException if the class of the specified value
401 * prevents it from being stored in the backing map
402 * @throws NullPointerException if the backing map does not permit
403 * null values, and the specified value is null
404 * @throws IllegalArgumentException if some property of this value
405 * prevents it from being stored in the backing map
406 * @throws IllegalStateException implementations may, but are not
407 * required to, throw this exception if the entry has been
408 * removed from the backing map.
409 */
410 V setValue(V value);
411
412 /**
413 * Compares the specified object with this entry for equality.
414 * Returns <tt>true</tt> if the given object is also a map entry and
415 * the two entries represent the same mapping. More formally, two
416 * entries <tt>e1</tt> and <tt>e2</tt> represent the same mapping
417 * if<pre>
418 * (e1.getKey()==null ?
419 * e2.getKey()==null : e1.getKey().equals(e2.getKey())) &&
420 * (e1.getValue()==null ?
421 * e2.getValue()==null : e1.getValue().equals(e2.getValue()))
422 * </pre>
423 * This ensures that the <tt>equals</tt> method works properly across
424 * different implementations of the <tt>Map.Entry</tt> interface.
425 *
426 * @param o object to be compared for equality with this map entry
427 * @return <tt>true</tt> if the specified object is equal to this map
428 * entry
429 */
430 boolean equals(Object o);
431
432 /**
433 * Returns the hash code value for this map entry. The hash code
434 * of a map entry <tt>e</tt> is defined to be: <pre>
435 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
436 * (e.getValue()==null ? 0 : e.getValue().hashCode())
437 * </pre>
438 * This ensures that <tt>e1.equals(e2)</tt> implies that
439 * <tt>e1.hashCode()==e2.hashCode()</tt> for any two Entries
440 * <tt>e1</tt> and <tt>e2</tt>, as required by the general
441 * contract of <tt>Object.hashCode</tt>.
442 *
443 * @return the hash code value for this map entry
444 * @see Object#hashCode()
445 * @see Object#equals(Object)
446 * @see #equals(Object)
447 */
448 int hashCode();
449 }
450
451 // Comparison and hashing
452
453 /**
454 * Compares the specified object with this map for equality. Returns
455 * <tt>true</tt> if the given object is also a map and the two maps
456 * represent the same mappings. More formally, two maps <tt>m1</tt> and
457 * <tt>m2</tt> represent the same mappings if
458 * <tt>m1.entrySet().equals(m2.entrySet())</tt>. This ensures that the
459 * <tt>equals</tt> method works properly across different implementations
460 * of the <tt>Map</tt> interface.
461 *
462 * @param o object to be compared for equality with this map
463 * @return <tt>true</tt> if the specified object is equal to this map
464 */
465 boolean equals(Object o);
466
467 /**
468 * Returns the hash code value for this map. The hash code of a map is
469 * defined to be the sum of the hash codes of each entry in the map's
470 * <tt>entrySet()</tt> view. This ensures that <tt>m1.equals(m2)</tt>
471 * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps
472 * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of
473 * {@link Object#hashCode}.
474 *
475 * @return the hash code value for this map
476 * @see Map.Entry#hashCode()
477 * @see Object#equals(Object)
478 * @see #equals(Object)
479 */
480 int hashCode();
481
482 // Defaultable methods
483
484 /**
485 * Returns the value to which the specified key is mapped,
486 * or {@code defaultValue} if this map contains no mapping
487 * for the key.
488 *
489 * <p>The default implementation makes no guarantees about synchronization
490 * or atomicity properties of this method. Any implementation providing
491 * atomicity guarantees must override this method and document its
492 * concurrency properties.
493 *
494 * @param key the key whose associated value is to be returned
495 * @return the value to which the specified key is mapped, or
496 * {@code defaultValue} if this map contains no mapping for the key
497 * @throws ClassCastException if the key is of an inappropriate type for
498 * this map
499 * (<a href="Collection.html#optional-restrictions">optional</a>)
500 * @throws NullPointerException if the specified key is null and this map
501 * does not permit null keys
502 * (<a href="Collection.html#optional-restrictions">optional</a>)
503 */
504 default V getOrDefault(Object key, V defaultValue) {
505 V v;
506 return (((v = get(key)) != null) || containsKey(key))
507 ? v
508 : defaultValue;
509 }
510
511 /**
512 * Performs the given action on each entry in this map, in the order entries
513 * are returned by an entry set iterator (which may be unspecified), until
514 * all entries have been processed or the action throws an {@code Exception}.
515 * Exceptions thrown by the action are relayed to the caller.
516 *
517 * <p>The default implementation should be overridden by implementations if
518 * they can provide a more performant implementation than an iterator-based
519 * one.
520 *
521 * <p>The default implementation makes no guarantees about synchronization
522 * or atomicity properties of this method. Any implementation providing
523 * atomicity guarantees must override this method and document its
524 * concurrency properties.
525 *
526 * @implSpec The default implementation is equivalent to, for this
527 * {@code map}:
528 * <pre> {@code
529 * for ((Map.Entry<K, V> entry : map.entrySet())
530 * action.accept(entry.getKey(), entry.getValue());
531 * }</pre>
532 *
533 * @param action The action to be performed for each entry
534 * @throws NullPointerException if the specified action is null
535 * @throws ConcurrentModificationException if an entry is found to be
536 * removed during iteration
537 * @since 1.8
538 */
539 default void forEach(BiConsumer<? super K, ? super V> action) {
540 Objects.requireNonNull(action);
541 for (Map.Entry<K, V> entry : entrySet()) {
542 K k;
543 V v;
544 try {
545 k = entry.getKey();
546 v = entry.getValue();
547 } catch(IllegalStateException ise) {
548 throw new ConcurrentModificationException(ise);
549 }
550 action.accept(k, v);
551 }
552 }
553
554 /**
555 * Replaces each entry's value with the result of invoking the given
556 * function on that entry, in the order entries are returned by an entry
557 * set iterator, until all entries have been processed or the function
558 * throws an exception.
559 *
560 * <p>The default implementation makes no guarantees about synchronization
561 * or atomicity properties of this method. Any implementation providing
562 * atomicity guarantees must override this method and document its
563 * concurrency properties.
564 *
565 * @implSpec
566 * <p>The default implementation is equivalent to, for this {@code map}:
567 * <pre> {@code
568 * for ((Map.Entry<K, V> entry : map.entrySet())
569 * entry.setValue(function.apply(entry.getKey(), entry.getValue()));
570 * }</pre>
571 *
572 * @param function the function to apply to each entry
573 * @throws UnsupportedOperationException if the {@code set} operation
574 * is not supported by this map's entry set iterator.
575 * @throws ClassCastException if the class of a replacement value
576 * prevents it from being stored in this map
577 * @throws NullPointerException if the specified function is null, or the
578 * specified replacement value is null, and this map does not permit null
579 * values
580 * @throws ClassCastException if a replacement value is of an inappropriate
581 * type for this map
582 * (<a href="Collection.html#optional-restrictions">optional</a>)
583 * @throws NullPointerException if function or a replacement value is null,
584 * and this map does not permit null keys or values
585 * (<a href="Collection.html#optional-restrictions">optional</a>)
586 * @throws IllegalArgumentException if some property of a replacement value
587 * prevents it from being stored in this map
588 * (<a href="Collection.html#optional-restrictions">optional</a>)
589 * @throws ConcurrentModificationException if an entry is found to be
590 * removed during iteration
591 * @since 1.8
592 */
593 default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
594 Objects.requireNonNull(function);
595 for (Map.Entry<K, V> entry : entrySet()) {
596 K k;
597 V v;
598 try {
599 k = entry.getKey();
600 v = entry.getValue();
601 } catch(IllegalStateException ise) {
602 throw new ConcurrentModificationException(ise);
603 }
604 entry.setValue(function.apply(k, v));
605 }
606 }
607
608 /**
609 * If the specified key is not already associated with a value (or is mapped
610 * to {@code null}) associates it with the given value and returns
611 * {@code null}, else returns the current value.
612 *
613 * <p>The default implementation makes no guarantees about synchronization
614 * or atomicity properties of this method. Any implementation providing
615 * atomicity guarantees must override this method and document its
616 * concurrency properties.
617 *
618 * @implSpec
619 * The default implementation is equivalent to, for this {@code
620 * map}:
621 *
622 * <pre> {@code
623 * if (map.get(key) == null)
624 * return map.put(key, value);
625 * else
626 * return map.get(key);
627 * }</pre>
628 *
629 * @param key key with which the specified value is to be associated
630 * @param value value to be associated with the specified key
631 * @return the previous value associated with the specified key, or
632 * {@code 1} if there was no mapping for the key.
633 * (A {@code null} return can also indicate that the map
634 * previously associated {@code null} with the key,
635 * if the implementation supports null values.)
636 * @throws UnsupportedOperationException if the {@code put} operation
637 * is not supported by this map
638 * (<a href="Collection.html#optional-restrictions">optional</a>)
639 * @throws ClassCastException if the key or value is of an inappropriate
640 * type for this map
641 * (<a href="Collection.html#optional-restrictions">optional</a>)
642 * @throws NullPointerException if the specified key or value is null,
643 * and this map does not permit null keys or values
644 * (<a href="Collection.html#optional-restrictions">optional</a>)
645 * @throws IllegalArgumentException if some property of the specified key
646 * or value prevents it from being stored in this map
647 * (<a href="Collection.html#optional-restrictions">optional</a>)
648 * @throws ConcurrentModificationException if a modification of the map is
649 * detected during insertion of the value.
650 * @since 1.8
651 */
652 default V putIfAbsent(K key, V value) {
653 V v = get(key);
654 if (v == null) {
655 if (put(key, value) != null) {
656 throw new ConcurrentModificationException();
657 }
658 }
659
660 return v;
661 }
662
663 /**
664 * Removes the entry for the specified key only if it is currently
665 * mapped to the specified value.
666 *
667 * <p>The default implementation makes no guarantees about synchronization
668 * or atomicity properties of this method. Any implementation providing
669 * atomicity guarantees must override this method and document its
670 * concurrency properties.
671 *
672 * @implSpec
673 * The default implementation is equivalent to, for this {@code map}:
674 *
675 * <pre> {@code
676 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
677 * map.remove(key);
678 * return true;
679 * } else
680 * return false;
681 * }</pre>
682 *
683 * @param key key with which the specified value is associated
684 * @param value value expected to be associated with the specified key
685 * @return {@code true} if the value was removed
686 * @throws UnsupportedOperationException if the {@code remove} operation
687 * is not supported by this map
688 * (<a href="Collection.html#optional-restrictions">optional</a>)
689 * @throws ClassCastException if the key or value is of an inappropriate
690 * type for this map
691 * (<a href="Collection.html#optional-restrictions">optional</a>)
692 * @throws NullPointerException if the specified key or value is null,
693 * and this map does not permit null keys or values
694 * (<a href="Collection.html#optional-restrictions">optional</a>)
695 * @since 1.8
696 */
697 default boolean remove(Object key, Object value) {
698 Object curValue = get(key);
699 if (!Objects.equals(curValue, value) ||
700 (curValue == null && !containsKey(key))) {
701 return false;
702 }
703 remove(key);
704 return true;
705 }
706
707 /**
708 * Replaces the entry for the specified key only if currently
709 * mapped to the specified value.
710 *
711 * <p>The default implementation makes no guarantees about synchronization
712 * or atomicity properties of this method. Any implementation providing
713 * atomicity guarantees must override this method and document its
714 * concurrency properties.
715 *
716 * @implSpec
717 * The default implementation is equivalent to, for this {@code map}:
718 *
719 * <pre> {@code
720 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
721 * map.put(key, newValue);
722 * return true;
723 * } else
724 * return false;
725 * }</pre>
726 *
727 * @param key key with which the specified value is associated
728 * @param oldValue value expected to be associated with the specified key
729 * @param newValue value to be associated with the specified key
730 * @return {@code true} if the value was replaced
731 * @throws UnsupportedOperationException if the {@code put} operation
732 * is not supported by this map
733 * (<a href="Collection.html#optional-restrictions">optional</a>)
734 * @throws ClassCastException if the class of a specified key or value
735 * prevents it from being stored in this map
736 * @throws NullPointerException if a specified key or value is null,
737 * and this map does not permit null keys or values
738 * @throws IllegalArgumentException if some property of a specified key
739 * or value prevents it from being stored in this map
740 * @since 1.8
741 */
742 default boolean replace(K key, V oldValue, V newValue) {
743 Object curValue = get(key);
744 if (!Objects.equals(curValue, oldValue) ||
745 (curValue == null && !containsKey(key))) {
746 return false;
747 }
748 put(key, newValue);
749 return true;
750 }
751
752 /**
753 * Replaces the entry for the specified key only if it is
754 * currently mapped to some value.
755 *
756 * <p>The default implementation makes no guarantees about synchronization
757 * or atomicity properties of this method. Any implementation providing
758 * atomicity guarantees must override this method and document its
759 * concurrency properties.
760 *
761 * @implSpec
762 * The default implementation is equivalent to, for this {@code map}:
763 *
764 * <pre> {@code
765 * if (map.containsKey(key)) {
766 * return map.put(key, value);
767 * } else
768 * return null;
769 * }</pre>
770 *
771 * @param key key with which the specified value is associated
772 * @param value value to be associated with the specified key
773 * @return the previous value associated with the specified key, or
774 * {@code null} if there was no mapping for the key.
775 * (A {@code null} return can also indicate that the map
776 * previously associated {@code null} with the key,
777 * if the implementation supports null values.)
778 * @throws UnsupportedOperationException if the {@code put} operation
779 * is not supported by this map
780 * (<a href="Collection.html#optional-restrictions">optional</a>)
781 * @throws ClassCastException if the class of the specified key or value
782 * prevents it from being stored in this map
783 * (<a href="Collection.html#optional-restrictions">optional</a>)
784 * @throws NullPointerException if the specified key or value is null,
785 * and this map does not permit null keys or values
786 * @throws IllegalArgumentException if some property of the specified key
787 * or value prevents it from being stored in this map
788 * @since 1.8
789 */
790 default V replace(K key, V value) {
791 return containsKey(key) ? put(key, value) : null;
792 }
793
794 /**
795 * If the specified key is not already associated with a value (or
796 * is mapped to {@code null}), attempts to compute its value using
797 * the given mapping function and enters it into this map unless
798 * {@code null}.
799 *
800 * <p>If the function returns {@code null} no mapping is recorded. If
801 * the function itself throws an (unchecked) exception, the
802 * exception is rethrown, and no mapping is recorded. The most
803 * common usage is to construct a new object serving as an initial
804 * mapped value or memoized result, as in:
805 *
806 * <pre> {@code
807 * map.computeIfAbsent(key, k -> new Value(f(k)));
808 * }</pre>
809 *
810 * <p>The default implementation makes no guarantees about synchronization
811 * or atomicity properties of this method. Any implementation providing
812 * atomicity guarantees must override this method and document its
813 * concurrency properties. In particular, all implementations of
814 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
815 * whether the function is applied once atomically only if the value is not
816 * present. Any class that permits null values must document
817 * whether and how this method distinguishes absence from null mappings.
818 *
819 * @implSpec
820 * The default implementation is equivalent to the following
821 * steps for this {@code map}, then returning the current value or
822 * {@code null} if now absent:
823 *
824 * <pre> {@code
825 * if (map.get(key) == null) {
826 * V newValue = mappingFunction.apply(key);
827 * if (newValue != null)
828 * map.putIfAbsent(key, newValue);
829 * }
830 * }</pre>
831 *
832 * @param key key with which the specified value is to be associated
833 * @param mappingFunction the function to compute a value
834 * @return the current (existing or computed) value associated with
835 * the specified key, or null if the computed value is null
836 * @throws NullPointerException if the specified key is null and
837 * this map does not support null keys, or the
838 * mappingFunction is null
839 * @throws UnsupportedOperationException if the {@code put} operation
840 * is not supported by this map
841 * (<a href="Collection.html#optional-restrictions">optional</a>)
842 * @throws ClassCastException if the class of the specified key or value
843 * prevents it from being stored in this map
844 * (<a href="Collection.html#optional-restrictions">optional</a>)
845 * @since 1.8
846 */
847 default V computeIfAbsent(K key,
848 Function<? super K, ? extends V> mappingFunction) {
849 V v, newValue;
850 return ((v = get(key)) == null &&
851 (newValue = mappingFunction.apply(key)) != null &&
852 (v = putIfAbsent(key, newValue)) == null) ? newValue : v;
853 }
854
855 /**
856 * If the value for the specified key is present and non-null, attempts to
857 * compute a new mapping given the key and its current mapped value.
858 *
859 * <p>If the function returns {@code null}, the mapping is removed. If the
860 * function itself throws an (unchecked) exception, the exception is
861 * rethrown, and the current mapping is left unchanged.
862 *
863 * <p>The default implementation makes no guarantees about synchronization
864 * or atomicity properties of this method. Any implementation providing
865 * atomicity guarantees must override this method and document its
866 * concurrency properties. In particular, all implementations of
867 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
868 * whether the function is applied once atomically only if the value is not
869 * present. Any class that permits null values must document
870 * whether and how this method distinguishes absence from null mappings.
871 *
872 * @implSpec
873 * The default implementation is equivalent to performing the
874 * following steps for this {@code map}, then returning the
875 * current value or {@code null} if now absent:
876 *
877 * <pre> {@code
878 * if (map.get(key) != null) {
879 * V oldValue = map.get(key);
880 * V newValue = remappingFunction.apply(key, oldValue);
881 * if (newValue != null)
882 * map.replace(key, oldValue, newValue);
883 * else
884 * map.remove(key, oldValue);
885 * }
886 * }</pre>
887 *
888 * In concurrent contexts, the default implementation may retry
889 * these steps when multiple threads attempt updates.
890 *
891 * @param key key with which the specified value is to be associated
892 * @param remappingFunction the function to compute a value
893 * @return the new value associated with the specified key, or null if none
894 * @throws NullPointerException if the specified key is null and
895 * this map does not support null keys, or the
896 * remappingFunction is null
897 * @throws UnsupportedOperationException if the {@code put} operation
898 * is not supported by this map
899 * (<a href="Collection.html#optional-restrictions">optional</a>)
900 * @throws ClassCastException if the class of the specified key or value
901 * prevents it from being stored in this map
902 * (<a href="Collection.html#optional-restrictions">optional</a>)
903 * @since 1.8
904 */
905 default V computeIfPresent(K key,
906 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
907 V oldValue;
908 while ((oldValue = get(key)) != null) {
909 V newValue = remappingFunction.apply(key, oldValue);
910 if (newValue != null) {
911 if (replace(key, oldValue, newValue))
912 return newValue;
913 } else if (remove(key, oldValue))
914 return null;
915 }
916 return oldValue;
917 }
918
919 /**
920 * Attempts to compute a mapping for the specified key and its
921 * current mapped value (or {@code null} if there is no current
922 * mapping). For example, to either create or append a {@code
923 * String msg} to a value mapping:
924 *
925 * <pre> {@code
926 * map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))}</pre>
927 * (Method {@link #merge merge()} is often simpler to use for such purposes.)
928 *
929 * <p>If the function returns {@code null}, the mapping is removed (or
930 * remains absent if initially absent). If the function itself throws an
931 * (unchecked) exception, the exception is rethrown, and the current mapping
932 * is left unchanged.
933 *
934 * <p>The default implementation makes no guarantees about synchronization
935 * or atomicity properties of this method. Any implementation providing
936 * atomicity guarantees must override this method and document its
937 * concurrency properties. In particular, all implementations of
938 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
939 * whether the function is applied once atomically only if the value is not
940 * present. Any class that permits null values must document
941 * whether and how this method distinguishes absence from null mappings.
942 *
943 * @implSpec
944 * The default implementation is equivalent to performing the following
945 * steps for this {@code map}, then returning the current value or
946 * {@code null} if absent:
947 *
948 * <pre> {@code
949 * V oldValue = map.get(key);
950 * V newValue = remappingFunction.apply(key, oldValue);
951 * if (oldValue != null ) {
952 * if (newValue != null)
953 * map.replace(key, oldValue, newValue);
954 * else
955 * map.remove(key, oldValue);
956 * } else {
957 * if (newValue != null)
958 * map.putIfAbsent(key, newValue);
959 * else
960 * return null;
961 * }
962 * }</pre>
963 *
964 * In concurrent contexts, the default implementation may retry
965 * these steps when multiple threads attempt updates.
966 *
967 * @param key key with which the specified value is to be associated
968 * @param remappingFunction the function to compute a value
969 * @return the new value associated with the specified key, or null if none
970 * @throws NullPointerException if the specified key is null and
971 * this map does not support null keys, or the
972 * remappingFunction is null
973 * @throws UnsupportedOperationException if the {@code put} operation
974 * is not supported by this map
975 * (<a href="Collection.html#optional-restrictions">optional</a>)
976 * @throws ClassCastException if the class of the specified key or value
977 * prevents it from being stored in this map
978 * (<a href="Collection.html#optional-restrictions">optional</a>)
979 * @since 1.8
980 */
981 default V compute(K key,
982 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
983 V oldValue = get(key);
984 for (;;) {
985 V newValue = remappingFunction.apply(key, oldValue);
986 if (oldValue != null) {
987 if (newValue != null) {
988 if (replace(key, oldValue, newValue))
989 return newValue;
990 } else if (remove(key, oldValue)) {
991 return null;
992 }
993 oldValue = get(key);
994 } else {
995 if (newValue != null) {
996 if ((oldValue = putIfAbsent(key, newValue)) == null)
997 return newValue;
998 } else {
999 return null;
1000 }
1001 }
1002 }
1003 }
1004
1005 /**
1006 * If the specified key is not already associated with a value or is
1007 * associated with null, associates it with the given value.
1008 * Otherwise, replaces the value with the results of the given
1009 * remapping function, or removes if the result is {@code null}. This
1010 * method may be of use when combining multiple mapped values for a key.
1011 * For example, to either create or append a {@code String msg} to a
1012 * value mapping:
1013 *
1014 * <pre> {@code
1015 * map.merge(key, msg, String::concat)
1016 * }</pre>
1017 *
1018 * <p>If the function returns {@code null}, the mapping is removed (or
1019 * remains absent if initially absent). If the function itself throws an
1020 * (unchecked) exception, the exception is rethrown, and the current mapping
1021 * is left unchanged.
1022 *
1023 * <p>The default implementation makes no guarantees about synchronization
1024 * or atomicity properties of this method. Any implementation providing
1025 * atomicity guarantees must override this method and document its
1026 * concurrency properties. In particular, all implementations of
1027 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1028 * whether the function is applied once atomically only if the value is not
1029 * present. Any class that permits null values must document
1030 * whether and how this method distinguishes absence from null mappings.
1031 *
1032 * @implSpec
1033 * The default implementation is equivalent to performing the
1034 * following steps for this {@code map}, then returning the
1035 * current value or {@code null} if absent:
1036 *
1037 * <pre> {@code
1038 * V oldValue = map.get(key);
1039 * V newValue = (oldValue == null) ? value :
1040 * remappingFunction.apply(oldValue, value);
1041 * if (newValue == null)
1042 * map.remove(key, oldValue);
1043 * else if (oldValue == null)
1044 * map.putIfAbsent(key, newValue);
1045 * else
1046 * map.replace(key, oldValue, newValue);
1047 * }</pre>
1048 *
1049 * In concurrent contexts, the default implementation may retry
1050 * these steps when multiple threads attempt updates.
1051 *
1052 * @param key key with which the specified value is to be associated
1053 * @param value the value to use if absent
1054 * @param remappingFunction the function to recompute a value if present
1055 * @return the new value associated with the specified key, or null if none
1056 * @throws UnsupportedOperationException if the {@code put} operation
1057 * is not supported by this map
1058 * (<a href="Collection.html#optional-restrictions">optional</a>)
1059 * @throws ClassCastException if the class of the specified key or value
1060 * prevents it from being stored in this map
1061 * (<a href="Collection.html#optional-restrictions">optional</a>)
1062 * @throws NullPointerException if the specified key is null and
1063 * this map does not support null keys, or the
1064 * remappingFunction is null
1065 * @since 1.8
1066 */
1067 default V merge(K key, V value,
1068 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
1069 V oldValue = get(key);
1070 for (;;) {
1071 if (oldValue != null) {
1072 V newValue = remappingFunction.apply(oldValue, value);
1073 if (newValue != null) {
1074 if (replace(key, oldValue, newValue))
1075 return newValue;
1076 } else if (remove(key, oldValue)) {
1077 return null;
1078 }
1079 oldValue = get(key);
1080 } else {
1081 if (value == null) {
1082 return null;
1083 }
1084
1085 if ((oldValue = putIfAbsent(key, value)) == null) {
1086 return value;
1087 }
1088 }
1089 }
1090 }
1091 }