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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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 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>This interface is a member of the
90 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
91 * Java Collections Framework</a>.
92 *
93 * <p>Many methods in Collections Framework interfaces are defined
94 * in terms of the {@link Object#equals(Object) equals} method. For
95 * example, the specification for the {@link #containsKey(Object)
96 * containsKey(Object key)} method says: "returns <tt>true</tt> if and
97 * only if this map contains a mapping for a key <tt>k</tt> such that
98 * <tt>(key==null ? k==null : key.equals(k))</tt>." This specification should
99 * <i>not</i> be construed to imply that invoking <tt>Map.containsKey</tt>
100 * with a non-null argument <tt>key</tt> will cause <tt>key.equals(k)</tt> to
101 * be invoked for any key <tt>k</tt>. Implementations are free to
102 * implement optimizations whereby the <tt>equals</tt> invocation is avoided,
103 * for example, by first comparing the hash codes of the two keys. (The
104 * {@link Object#hashCode()} specification guarantees that two objects with
105 * unequal hash codes cannot be equal.) More generally, implementations of
106 * the various Collections Framework interfaces are free to take advantage of
107 * the specified behavior of underlying {@link Object} methods wherever the
108 * implementor deems it appropriate.
109 *
110 * @param <K> the type of keys maintained by this map
111 * @param <V> the type of mapped values
112 *
113 * @author Josh Bloch
114 * @see HashMap
115 * @see TreeMap
116 * @see Hashtable
117 * @see SortedMap
118 * @see Collection
119 * @see Set
120 * @since 1.2
121 */
122 public interface Map<K,V> {
123 // Query Operations
124
125 /**
126 * Returns the number of key-value mappings in this map. If the
127 * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
128 * <tt>Integer.MAX_VALUE</tt>.
129 *
130 * @return the number of key-value mappings in this map
131 */
132 int size();
133
134 /**
135 * Returns <tt>true</tt> if this map contains no key-value mappings.
136 *
137 * @return <tt>true</tt> if this map contains no key-value mappings
138 */
139 boolean isEmpty();
140
141 /**
142 * Returns <tt>true</tt> if this map contains a mapping for the specified
143 * key. More formally, returns <tt>true</tt> if and only if
144 * this map contains a mapping for a key <tt>k</tt> such that
145 * <tt>(key==null ? k==null : key.equals(k))</tt>. (There can be
146 * at most one such mapping.)
147 *
148 * @param key key whose presence in this map is to be tested
149 * @return <tt>true</tt> if this map contains a mapping for the specified
150 * key
151 * @throws ClassCastException if the key is of an inappropriate type for
152 * this map
153 * (<a href="Collection.html#optional-restrictions">optional</a>)
154 * @throws NullPointerException if the specified key is null and this map
155 * does not permit null keys
156 * (<a href="Collection.html#optional-restrictions">optional</a>)
157 */
158 boolean containsKey(Object key);
159
160 /**
161 * Returns <tt>true</tt> if this map maps one or more keys to the
162 * specified value. More formally, returns <tt>true</tt> if and only if
163 * this map contains at least one mapping to a value <tt>v</tt> such that
164 * <tt>(value==null ? v==null : value.equals(v))</tt>. This operation
165 * will probably require time linear in the map size for most
166 * implementations of the <tt>Map</tt> interface.
167 *
168 * @param value value whose presence in this map is to be tested
169 * @return <tt>true</tt> if this map maps one or more keys to the
170 * specified value
171 * @throws ClassCastException if the value is of an inappropriate type for
172 * this map
173 * (<a href="Collection.html#optional-restrictions">optional</a>)
174 * @throws NullPointerException if the specified value is null and this
175 * map does not permit null values
176 * (<a href="Collection.html#optional-restrictions">optional</a>)
177 */
178 boolean containsValue(Object value);
179
180 /**
181 * Returns the value to which the specified key is mapped,
182 * or {@code null} if this map contains no mapping for the key.
183 *
184 * <p>More formally, if this map contains a mapping from a key
185 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
186 * key.equals(k))}, then this method returns {@code v}; otherwise
187 * it returns {@code null}. (There can be at most one such mapping.)
188 *
189 * <p>If this map permits null values, then a return value of
190 * {@code null} does not <i>necessarily</i> indicate that the map
191 * contains no mapping for the key; it's also possible that the map
192 * explicitly maps the key to {@code null}. The {@link #containsKey
193 * containsKey} operation may be used to distinguish these two cases.
194 *
195 * @param key the key whose associated value is to be returned
196 * @return the value to which the specified key is mapped, or
197 * {@code null} if this map contains no mapping for the key
198 * @throws ClassCastException if the key is of an inappropriate type for
199 * this map
200 * (<a href="Collection.html#optional-restrictions">optional</a>)
201 * @throws NullPointerException if the specified key is null and this map
202 * does not permit null keys
203 * (<a href="Collection.html#optional-restrictions">optional</a>)
204 */
205 V get(Object key);
206
207 // Modification Operations
208
209 /**
210 * Associates the specified value with the specified key in this map
211 * (optional operation). If the map previously contained a mapping for
212 * the key, the old value is replaced by the specified value. (A map
213 * <tt>m</tt> is said to contain a mapping for a key <tt>k</tt> if and only
214 * if {@link #containsKey(Object) m.containsKey(k)} would return
215 * <tt>true</tt>.)
216 *
217 * @param key key with which the specified value is to be associated
218 * @param value value to be associated with the specified key
219 * @return the previous value associated with <tt>key</tt>, or
220 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
221 * (A <tt>null</tt> return can also indicate that the map
222 * previously associated <tt>null</tt> with <tt>key</tt>,
223 * if the implementation supports <tt>null</tt> values.)
224 * @throws UnsupportedOperationException if the <tt>put</tt> operation
225 * is not supported by this map
226 * @throws ClassCastException if the class of the specified key or value
227 * prevents it from being stored in this map
228 * @throws NullPointerException if the specified key or value is null
229 * and this map does not permit null keys or values
230 * @throws IllegalArgumentException if some property of the specified key
231 * or value prevents it from being stored in this map
232 */
233 V put(K key, V value);
234
235 /**
236 * Removes the mapping for a key from this map if it is present
237 * (optional operation). More formally, if this map contains a mapping
238 * from key <tt>k</tt> to value <tt>v</tt> such that
239 * <code>(key==null ? k==null : key.equals(k))</code>, that mapping
240 * is removed. (The map can contain at most one such mapping.)
241 *
242 * <p>Returns the value to which this map previously associated the key,
243 * or <tt>null</tt> if the map contained no mapping for the key.
244 *
245 * <p>If this map permits null values, then a return value of
246 * <tt>null</tt> does not <i>necessarily</i> indicate that the map
247 * contained no mapping for the key; it's also possible that the map
248 * explicitly mapped the key to <tt>null</tt>.
249 *
250 * <p>The map will not contain a mapping for the specified key once the
251 * call returns.
252 *
253 * @param key key whose mapping is to be removed from the map
254 * @return the previous value associated with <tt>key</tt>, or
255 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
256 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
257 * is not supported by this map
258 * @throws ClassCastException if the key is of an inappropriate type for
259 * this map
260 * (<a href="Collection.html#optional-restrictions">optional</a>)
261 * @throws NullPointerException if the specified key is null and this
262 * map does not permit null keys
263 * (<a href="Collection.html#optional-restrictions">optional</a>)
264 */
265 V remove(Object key);
266
267
268 // Bulk Operations
269
270 /**
271 * Copies all of the mappings from the specified map to this map
272 * (optional operation). The effect of this call is equivalent to that
273 * of calling {@link #put(Object,Object) put(k, v)} on this map once
274 * for each mapping from key <tt>k</tt> to value <tt>v</tt> in the
275 * specified map. The behavior of this operation is undefined if the
276 * specified map is modified while the operation is in progress.
277 *
278 * @param m mappings to be stored in this map
279 * @throws UnsupportedOperationException if the <tt>putAll</tt> operation
280 * is not supported by this map
281 * @throws ClassCastException if the class of a key or value in the
282 * specified map prevents it from being stored in this map
283 * @throws NullPointerException if the specified map is null, or if
284 * this map does not permit null keys or values, and the
285 * specified map contains null keys or values
286 * @throws IllegalArgumentException if some property of a key or value in
287 * the specified map prevents it from being stored in this map
288 */
289 void putAll(Map<? extends K, ? extends V> m);
290
291 /**
292 * Removes all of the mappings from this map (optional operation).
293 * The map will be empty after this call returns.
294 *
295 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
296 * is not supported by this map
297 */
298 void clear();
299
300
301 // Views
302
303 /**
304 * Returns a {@link Set} view of the keys contained in this map.
305 * The set is backed by the map, so changes to the map are
306 * reflected in the set, and vice-versa. If the map is modified
307 * while an iteration over the set is in progress (except through
308 * the iterator's own <tt>remove</tt> operation), the results of
309 * the iteration are undefined. The set supports element removal,
310 * which removes the corresponding mapping from the map, via the
311 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
312 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
313 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
314 * operations.
315 *
316 * @return a set view of the keys contained in this map
317 */
318 Set<K> keySet();
319
320 /**
321 * Returns a {@link Collection} view of the values contained in this map.
322 * The collection is backed by the map, so changes to the map are
323 * reflected in the collection, and vice-versa. If the map is
324 * modified while an iteration over the collection is in progress
325 * (except through the iterator's own <tt>remove</tt> operation),
326 * the results of the iteration are undefined. The collection
327 * supports element removal, which removes the corresponding
328 * mapping from the map, via the <tt>Iterator.remove</tt>,
329 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
330 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
331 * support the <tt>add</tt> or <tt>addAll</tt> operations.
332 *
333 * @return a collection view of the values contained in this map
334 */
335 Collection<V> values();
336
337 /**
338 * Returns a {@link Set} view of the mappings contained in this map.
339 * The set is backed by the map, so changes to the map are
340 * reflected in the set, and vice-versa. If the map is modified
341 * while an iteration over the set is in progress (except through
342 * the iterator's own <tt>remove</tt> operation, or through the
343 * <tt>setValue</tt> operation on a map entry returned by the
344 * iterator) the results of the iteration are undefined. The set
345 * supports element removal, which removes the corresponding
346 * mapping from the map, via the <tt>Iterator.remove</tt>,
347 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
348 * <tt>clear</tt> operations. It does not support the
349 * <tt>add</tt> or <tt>addAll</tt> operations.
350 *
351 * @return a set view of the mappings contained in this map
352 */
353 Set<Map.Entry<K, V>> entrySet();
354
355 /**
356 * A map entry (key-value pair). The <tt>Map.entrySet</tt> method returns
357 * a collection-view of the map, whose elements are of this class. The
358 * <i>only</i> way to obtain a reference to a map entry is from the
359 * iterator of this collection-view. These <tt>Map.Entry</tt> objects are
360 * valid <i>only</i> for the duration of the iteration; more formally,
361 * the behavior of a map entry is undefined if the backing map has been
362 * modified after the entry was returned by the iterator, except through
363 * the <tt>setValue</tt> operation on the map entry.
364 *
365 * @see Map#entrySet()
366 * @since 1.2
367 */
368 interface Entry<K,V> {
369 /**
370 * Returns the key corresponding to this entry.
371 *
372 * @return the key corresponding to this entry
373 * @throws IllegalStateException implementations may, but are not
374 * required to, throw this exception if the entry has been
375 * removed from the backing map.
376 */
377 K getKey();
378
379 /**
380 * Returns the value corresponding to this entry. If the mapping
381 * has been removed from the backing map (by the iterator's
382 * <tt>remove</tt> operation), the results of this call are undefined.
383 *
384 * @return the value corresponding to this entry
385 * @throws IllegalStateException implementations may, but are not
386 * required to, throw this exception if the entry has been
387 * removed from the backing map.
388 */
389 V getValue();
390
391 /**
392 * Replaces the value corresponding to this entry with the specified
393 * value (optional operation). (Writes through to the map.) The
394 * behavior of this call is undefined if the mapping has already been
395 * removed from the map (by the iterator's <tt>remove</tt> operation).
396 *
397 * @param value new value to be stored in this entry
398 * @return old value corresponding to the entry
399 * @throws UnsupportedOperationException if the <tt>put</tt> operation
400 * is not supported by the backing map
401 * @throws ClassCastException if the class of the specified value
402 * prevents it from being stored in the backing map
403 * @throws NullPointerException if the backing map does not permit
404 * null values, and the specified value is null
405 * @throws IllegalArgumentException if some property of this value
406 * prevents it from being stored in the backing map
407 * @throws IllegalStateException implementations may, but are not
408 * required to, throw this exception if the entry has been
409 * removed from the backing map.
410 */
411 V setValue(V value);
412
413 /**
414 * Compares the specified object with this entry for equality.
415 * Returns <tt>true</tt> if the given object is also a map entry and
416 * the two entries represent the same mapping. More formally, two
417 * entries <tt>e1</tt> and <tt>e2</tt> represent the same mapping
418 * if<pre>
419 * (e1.getKey()==null ?
420 * e2.getKey()==null : e1.getKey().equals(e2.getKey())) &&
421 * (e1.getValue()==null ?
422 * e2.getValue()==null : e1.getValue().equals(e2.getValue()))
423 * </pre>
424 * This ensures that the <tt>equals</tt> method works properly across
425 * different implementations of the <tt>Map.Entry</tt> interface.
426 *
427 * @param o object to be compared for equality with this map entry
428 * @return <tt>true</tt> if the specified object is equal to this map
429 * entry
430 */
431 boolean equals(Object o);
432
433 /**
434 * Returns the hash code value for this map entry. The hash code
435 * of a map entry <tt>e</tt> is defined to be: <pre>
436 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
437 * (e.getValue()==null ? 0 : e.getValue().hashCode())
438 * </pre>
439 * This ensures that <tt>e1.equals(e2)</tt> implies that
440 * <tt>e1.hashCode()==e2.hashCode()</tt> for any two Entries
441 * <tt>e1</tt> and <tt>e2</tt>, as required by the general
442 * contract of <tt>Object.hashCode</tt>.
443 *
444 * @return the hash code value for this map entry
445 * @see Object#hashCode()
446 * @see Object#equals(Object)
447 * @see #equals(Object)
448 */
449 int hashCode();
450
451 /**
452 * Returns a comparator that compares {@link Map.Entry} in natural order on key.
453 *
454 * <p>The returned comparator is serializable and throws {@link
455 * NullPointerException} when comparing an entry with a null key.
456 *
457 * @param <K> the {@link Comparable} type of then map keys
458 * @param <V> the type of the map values
459 * @return a comparator that compares {@link Map.Entry} in natural order on key.
460 * @see Comparable
461 */
462 public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K,V>> comparingByKey() {
463 return (Comparator<Map.Entry<K, V>> & Serializable)
464 (c1, c2) -> c1.getKey().compareTo(c2.getKey());
465 }
466
467 /**
468 * Returns a comparator that compares {@link Map.Entry} in natural order on value.
469 *
470 * <p>The returned comparator is serializable and throws {@link
471 * NullPointerException} when comparing an entry with null values.
472 *
473 * @param <K> the type of the map keys
474 * @param <V> the {@link Comparable} type of the map values
475 * @return a comparator that compares {@link Map.Entry} in natural order on value.
476 * @see Comparable
477 */
478 public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K,V>> comparingByValue() {
479 return (Comparator<Map.Entry<K, V>> & Serializable)
480 (c1, c2) -> c1.getValue().compareTo(c2.getValue());
481 }
482
483 /**
484 * Returns a comparator that compares {@link Map.Entry} by key using the given
485 * {@link Comparator}.
486 *
487 * <p>The returned comparator is serializable if the specified comparator
488 * is also serializable.
489 *
490 * @param <K> the type of the map keys
491 * @param <V> the type of the map values
492 * @param cmp the key {@link Comparator}
493 * @return a comparator that compares {@link Map.Entry} by the key.
494 */
495 public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) {
496 Objects.requireNonNull(cmp);
497 return (Comparator<Map.Entry<K, V>> & Serializable)
498 (c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());
499 }
500
501 /**
502 * Returns a comparator that compares {@link Map.Entry} by value using the given
503 * {@link Comparator}.
504 *
505 * <p>The returned comparator is serializable if the specified comparator
506 * is also serializable.
507 *
508 * @param <K> the type of the map keys
509 * @param <V> the type of the map values
510 * @param cmp the value {@link Comparator}
511 * @return a comparator that compares {@link Map.Entry} by the value.
512 */
513 public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) {
514 Objects.requireNonNull(cmp);
515 return (Comparator<Map.Entry<K, V>> & Serializable)
516 (c1, c2) -> cmp.compare(c1.getValue(), c2.getValue());
517 }
518 }
519
520 // Comparison and hashing
521
522 /**
523 * Compares the specified object with this map for equality. Returns
524 * <tt>true</tt> if the given object is also a map and the two maps
525 * represent the same mappings. More formally, two maps <tt>m1</tt> and
526 * <tt>m2</tt> represent the same mappings if
527 * <tt>m1.entrySet().equals(m2.entrySet())</tt>. This ensures that the
528 * <tt>equals</tt> method works properly across different implementations
529 * of the <tt>Map</tt> interface.
530 *
531 * @param o object to be compared for equality with this map
532 * @return <tt>true</tt> if the specified object is equal to this map
533 */
534 boolean equals(Object o);
535
536 /**
537 * Returns the hash code value for this map. The hash code of a map is
538 * defined to be the sum of the hash codes of each entry in the map's
539 * <tt>entrySet()</tt> view. This ensures that <tt>m1.equals(m2)</tt>
540 * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps
541 * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of
542 * {@link Object#hashCode}.
543 *
544 * @return the hash code value for this map
545 * @see Map.Entry#hashCode()
546 * @see Object#equals(Object)
547 * @see #equals(Object)
548 */
549 int hashCode();
550
551 // Defaultable methods
552
553 /**
554 * Returns the value to which the specified key is mapped,
555 * or {@code defaultValue} if this map contains no mapping
556 * for the key.
557 *
558 * <p>The default implementation makes no guarantees about synchronization
559 * or atomicity properties of this method. Any implementation providing
560 * atomicity guarantees must override this method and document its
561 * concurrency properties.
562 *
563 * @param key the key whose associated value is to be returned
564 * @return the value to which the specified key is mapped, or
565 * {@code defaultValue} if this map contains no mapping for the key
566 * @throws ClassCastException if the key is of an inappropriate type for
567 * this map
568 * (<a href="Collection.html#optional-restrictions">optional</a>)
569 * @throws NullPointerException if the specified key is null and this map
570 * does not permit null keys
571 * (<a href="Collection.html#optional-restrictions">optional</a>)
572 */
573 default V getOrDefault(Object key, V defaultValue) {
574 V v;
575 return (((v = get(key)) != null) || containsKey(key))
576 ? v
577 : defaultValue;
578 }
579
580 /**
581 * Performs the given action on each entry in this map, in the order entries
582 * are returned by an entry set iterator (which may be unspecified), until
583 * all entries have been processed or the action throws an {@code Exception}.
584 * Exceptions thrown by the action are relayed to the caller.
585 *
586 * <p>The default implementation should be overridden by implementations if
587 * they can provide a more performant implementation than an iterator-based
588 * one.
589 *
590 * <p>The default implementation makes no guarantees about synchronization
591 * or atomicity properties of this method. Any implementation providing
592 * atomicity guarantees must override this method and document its
593 * concurrency properties.
594 *
595 * @implSpec The default implementation is equivalent to, for this
596 * {@code map}:
597 * <pre> {@code
598 * for ((Map.Entry<K, V> entry : map.entrySet())
599 * action.accept(entry.getKey(), entry.getValue());
600 * }</pre>
601 *
602 * @param action The action to be performed for each entry
603 * @throws NullPointerException if the specified action is null
604 * @throws ConcurrentModificationException if an entry is found to be
605 * removed during iteration
606 * @since 1.8
607 */
608 default void forEach(BiConsumer<? super K, ? super V> action) {
609 Objects.requireNonNull(action);
610 for (Map.Entry<K, V> entry : entrySet()) {
611 K k;
612 V v;
613 try {
614 k = entry.getKey();
615 v = entry.getValue();
616 } catch(IllegalStateException ise) {
617 // this usually means the entry is no longer in the map.
618 throw new ConcurrentModificationException(ise);
619 }
620 action.accept(k, v);
621 }
622 }
623
624 /**
625 * Replaces each entry's value with the result of invoking the given
626 * function on that entry, in the order entries are returned by an entry
627 * set iterator, until all entries have been processed or the function
628 * throws an exception.
629 *
630 * <p>The default implementation makes no guarantees about synchronization
631 * or atomicity properties of this method. Any implementation providing
632 * atomicity guarantees must override this method and document its
633 * concurrency properties.
634 *
635 * @implSpec
636 * <p>The default implementation is equivalent to, for this {@code map}:
637 * <pre> {@code
638 * for ((Map.Entry<K, V> entry : map.entrySet())
639 * entry.setValue(function.apply(entry.getKey(), entry.getValue()));
640 * }</pre>
641 *
642 * @param function the function to apply to each entry
643 * @throws UnsupportedOperationException if the {@code set} operation
644 * is not supported by this map's entry set iterator.
645 * @throws ClassCastException if the class of a replacement value
646 * prevents it from being stored in this map
647 * @throws NullPointerException if the specified function is null, or the
648 * specified replacement value is null, and this map does not permit null
649 * values
650 * @throws ClassCastException if a replacement value is of an inappropriate
651 * type for this map
652 * (<a href="Collection.html#optional-restrictions">optional</a>)
653 * @throws NullPointerException if function or a replacement value is null,
654 * and this map does not permit null keys or values
655 * (<a href="Collection.html#optional-restrictions">optional</a>)
656 * @throws IllegalArgumentException if some property of a replacement value
657 * prevents it from being stored in this map
658 * (<a href="Collection.html#optional-restrictions">optional</a>)
659 * @throws ConcurrentModificationException if an entry is found to be
660 * removed during iteration
661 * @since 1.8
662 */
663 default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
664 Objects.requireNonNull(function);
665 for (Map.Entry<K, V> entry : entrySet()) {
666 K k;
667 V v;
668 try {
669 k = entry.getKey();
670 v = entry.getValue();
671 } catch(IllegalStateException ise) {
672 // this usually means the entry is no longer in the map.
673 throw new ConcurrentModificationException(ise);
674 }
675
676 // ise thrown from function is not a cme.
677 v = function.apply(k, v);
678
679 try {
680 entry.setValue(v);
681 } catch(IllegalStateException ise) {
682 // this usually means the entry is no longer in the map.
683 throw new ConcurrentModificationException(ise);
684 }
685 }
686 }
687
688 /**
689 * If the specified key is not already associated with a value (or is mapped
690 * to {@code null}) associates it with the given value and returns
691 * {@code null}, else returns the current value.
692 *
693 * <p>The default implementation makes no guarantees about synchronization
694 * or atomicity properties of this method. Any implementation providing
695 * atomicity guarantees must override this method and document its
696 * concurrency properties.
697 *
698 * @implSpec
699 * The default implementation is equivalent to, for this {@code
700 * map}:
701 *
702 * <pre> {@code
703 * if (map.get(key) == null)
704 * return map.put(key, value);
705 * else
706 * return map.get(key);
707 * }</pre>
708 *
709 * @param key key with which the specified value is to be associated
710 * @param value value to be associated with the specified key
711 * @return the previous value associated with the specified key, or
712 * {@code null} if there was no mapping for the key.
713 * (A {@code null} return can also indicate that the map
714 * previously associated {@code null} with the key,
715 * if the implementation supports null values.)
716 * @throws UnsupportedOperationException if the {@code put} operation
717 * is not supported by this map
718 * (<a href="Collection.html#optional-restrictions">optional</a>)
719 * @throws ClassCastException if the key or value is of an inappropriate
720 * type for this map
721 * (<a href="Collection.html#optional-restrictions">optional</a>)
722 * @throws NullPointerException if the specified key or value is null,
723 * and this map does not permit null keys or values
724 * (<a href="Collection.html#optional-restrictions">optional</a>)
725 * @throws IllegalArgumentException if some property of the specified key
726 * or value prevents it from being stored in this map
727 * (<a href="Collection.html#optional-restrictions">optional</a>)
728 * @throws ConcurrentModificationException if a modification of the map is
729 * detected during insertion of the value.
730 * @since 1.8
731 */
732 default V putIfAbsent(K key, V value) {
733 V v = get(key);
734 if (v == null) {
735 if (put(key, value) != null) {
736 throw new ConcurrentModificationException();
737 }
738 }
739
740 return v;
741 }
742
743 /**
744 * Removes the entry for the specified key only if it is currently
745 * mapped to the specified value.
746 *
747 * <p>The default implementation makes no guarantees about synchronization
748 * or atomicity properties of this method. Any implementation providing
749 * atomicity guarantees must override this method and document its
750 * concurrency properties.
751 *
752 * @implSpec
753 * The default implementation is equivalent to, for this {@code map}:
754 *
755 * <pre> {@code
756 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
757 * map.remove(key);
758 * return true;
759 * } else
760 * return false;
761 * }</pre>
762 *
763 * @param key key with which the specified value is associated
764 * @param value value expected to be associated with the specified key
765 * @return {@code true} if the value was removed
766 * @throws UnsupportedOperationException if the {@code remove} operation
767 * is not supported by this map
768 * (<a href="Collection.html#optional-restrictions">optional</a>)
769 * @throws ClassCastException if the key or value is of an inappropriate
770 * type for this map
771 * (<a href="Collection.html#optional-restrictions">optional</a>)
772 * @throws NullPointerException if the specified key or value is null,
773 * and this map does not permit null keys or values
774 * (<a href="Collection.html#optional-restrictions">optional</a>)
775 * @since 1.8
776 */
777 default boolean remove(Object key, Object value) {
778 Object curValue = get(key);
779 if (!Objects.equals(curValue, value) ||
780 (curValue == null && !containsKey(key))) {
781 return false;
782 }
783 remove(key);
784 return true;
785 }
786
787 /**
788 * Replaces the entry for the specified key only if currently
789 * mapped to the specified value.
790 *
791 * <p>The default implementation makes no guarantees about synchronization
792 * or atomicity properties of this method. Any implementation providing
793 * atomicity guarantees must override this method and document its
794 * concurrency properties.
795 *
796 * @implSpec
797 * The default implementation is equivalent to, for this {@code map}:
798 *
799 * <pre> {@code
800 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
801 * map.put(key, newValue);
802 * return true;
803 * } else
804 * return false;
805 * }</pre>
806 *
807 * @param key key with which the specified value is associated
808 * @param oldValue value expected to be associated with the specified key
809 * @param newValue value to be associated with the specified key
810 * @return {@code true} if the value was replaced
811 * @throws UnsupportedOperationException if the {@code put} operation
812 * is not supported by this map
813 * (<a href="Collection.html#optional-restrictions">optional</a>)
814 * @throws ClassCastException if the class of a specified key or value
815 * prevents it from being stored in this map
816 * @throws NullPointerException if a specified key or value is null,
817 * and this map does not permit null keys or values
818 * @throws IllegalArgumentException if some property of a specified key
819 * or value prevents it from being stored in this map
820 * @since 1.8
821 */
822 default boolean replace(K key, V oldValue, V newValue) {
823 Object curValue = get(key);
824 if (!Objects.equals(curValue, oldValue) ||
825 (curValue == null && !containsKey(key))) {
826 return false;
827 }
828 put(key, newValue);
829 return true;
830 }
831
832 /**
833 * Replaces the entry for the specified key only if it is
834 * currently mapped to some value.
835 *
836 * <p>The default implementation makes no guarantees about synchronization
837 * or atomicity properties of this method. Any implementation providing
838 * atomicity guarantees must override this method and document its
839 * concurrency properties.
840 *
841 * @implSpec
842 * The default implementation is equivalent to, for this {@code map}:
843 *
844 * <pre> {@code
845 * if (map.containsKey(key)) {
846 * return map.put(key, value);
847 * } else
848 * return null;
849 * }</pre>
850 *
851 * @param key key with which the specified value is associated
852 * @param value value to be associated with the specified key
853 * @return the previous value associated with the specified key, or
854 * {@code null} if there was no mapping for the key.
855 * (A {@code null} return can also indicate that the map
856 * previously associated {@code null} with the key,
857 * if the implementation supports null values.)
858 * @throws UnsupportedOperationException if the {@code put} operation
859 * is not supported by this map
860 * (<a href="Collection.html#optional-restrictions">optional</a>)
861 * @throws ClassCastException if the class of the specified key or value
862 * prevents it from being stored in this map
863 * (<a href="Collection.html#optional-restrictions">optional</a>)
864 * @throws NullPointerException if the specified key or value is null,
865 * and this map does not permit null keys or values
866 * @throws IllegalArgumentException if some property of the specified key
867 * or value prevents it from being stored in this map
868 * @since 1.8
869 */
870 default V replace(K key, V value) {
871 return containsKey(key) ? put(key, value) : null;
872 }
873
874 /**
875 * If the specified key is not already associated with a value (or
876 * is mapped to {@code null}), attempts to compute its value using
877 * the given mapping function and enters it into this map unless
878 * {@code null}.
879 *
880 * <p>If the function returns {@code null} no mapping is recorded. If
881 * the function itself throws an (unchecked) exception, the
882 * exception is rethrown, and no mapping is recorded. The most
883 * common usage is to construct a new object serving as an initial
884 * mapped value or memoized result, as in:
885 *
886 * <pre> {@code
887 * map.computeIfAbsent(key, k -> new Value(f(k)));
888 * }</pre>
889 *
890 * <p>The default implementation makes no guarantees about synchronization
891 * or atomicity properties of this method. Any implementation providing
892 * atomicity guarantees must override this method and document its
893 * concurrency properties. In particular, all implementations of
894 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
895 * whether the function is applied once atomically only if the value is not
896 * present. Any class that permits null values must document
897 * whether and how this method distinguishes absence from null mappings.
898 *
899 * @implSpec
900 * The default implementation is equivalent to the following
901 * steps for this {@code map}, then returning the current value or
902 * {@code null} if now absent:
903 *
904 * <pre> {@code
905 * if (map.get(key) == null) {
906 * V newValue = mappingFunction.apply(key);
907 * if (newValue != null)
908 * map.putIfAbsent(key, newValue);
909 * }
910 * }</pre>
911 *
912 * @param key key with which the specified value is to be associated
913 * @param mappingFunction the function to compute a value
914 * @return the current (existing or computed) value associated with
915 * the specified key, or null if the computed value is null
916 * @throws NullPointerException if the specified key is null and
917 * this map does not support null keys, or the
918 * mappingFunction is null
919 * @throws UnsupportedOperationException if the {@code put} operation
920 * is not supported by this map
921 * (<a href="Collection.html#optional-restrictions">optional</a>)
922 * @throws ClassCastException if the class of the specified key or value
923 * prevents it from being stored in this map
924 * (<a href="Collection.html#optional-restrictions">optional</a>)
925 * @since 1.8
926 */
927 default V computeIfAbsent(K key,
928 Function<? super K, ? extends V> mappingFunction) {
929 V v, newValue;
930 return ((v = get(key)) == null &&
931 (newValue = mappingFunction.apply(key)) != null &&
932 (v = putIfAbsent(key, newValue)) == null) ? newValue : v;
933 }
934
935 /**
936 * If the value for the specified key is present and non-null, attempts to
937 * compute a new mapping given the key and its current mapped value.
938 *
939 * <p>If the function returns {@code null}, the mapping is removed. If the
940 * function itself throws an (unchecked) exception, the exception is
941 * rethrown, and the current mapping is left unchanged.
942 *
943 * <p>The default implementation makes no guarantees about synchronization
944 * or atomicity properties of this method. Any implementation providing
945 * atomicity guarantees must override this method and document its
946 * concurrency properties. In particular, all implementations of
947 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
948 * whether the function is applied once atomically only if the value is not
949 * present. Any class that permits null values must document
950 * whether and how this method distinguishes absence from null mappings.
951 *
952 * @implSpec
953 * The default implementation is equivalent to performing the
954 * following steps for this {@code map}, then returning the
955 * current value or {@code null} if now absent:
956 *
957 * <pre> {@code
958 * if (map.get(key) != null) {
959 * V oldValue = map.get(key);
960 * V newValue = remappingFunction.apply(key, oldValue);
961 * if (newValue != null)
962 * map.replace(key, oldValue, newValue);
963 * else
964 * map.remove(key, oldValue);
965 * }
966 * }</pre>
967 *
968 * In concurrent contexts, the default implementation may retry
969 * these steps when multiple threads attempt updates.
970 *
971 * @param key key with which the specified value is to be associated
972 * @param remappingFunction the function to compute a value
973 * @return the new value associated with the specified key, or null if none
974 * @throws NullPointerException if the specified key is null and
975 * this map does not support null keys, or the
976 * remappingFunction is null
977 * @throws UnsupportedOperationException if the {@code put} operation
978 * is not supported by this map
979 * (<a href="Collection.html#optional-restrictions">optional</a>)
980 * @throws ClassCastException if the class of the specified key or value
981 * prevents it from being stored in this map
982 * (<a href="Collection.html#optional-restrictions">optional</a>)
983 * @since 1.8
984 */
985 default V computeIfPresent(K key,
986 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
987 V oldValue;
988 while ((oldValue = get(key)) != null) {
989 V newValue = remappingFunction.apply(key, oldValue);
990 if (newValue != null) {
991 if (replace(key, oldValue, newValue))
992 return newValue;
993 } else if (remove(key, oldValue))
994 return null;
995 }
996 return oldValue;
997 }
998
999 /**
1000 * Attempts to compute a mapping for the specified key and its
1001 * current mapped value (or {@code null} if there is no current
1002 * mapping). For example, to either create or append a {@code
1003 * String msg} to a value mapping:
1004 *
1005 * <pre> {@code
1006 * map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))}</pre>
1007 * (Method {@link #merge merge()} is often simpler to use for such purposes.)
1008 *
1009 * <p>If the function returns {@code null}, the mapping is removed (or
1010 * remains absent if initially absent). If the function itself throws an
1011 * (unchecked) exception, the exception is rethrown, and the current mapping
1012 * is left unchanged.
1013 *
1014 * <p>The default implementation makes no guarantees about synchronization
1015 * or atomicity properties of this method. Any implementation providing
1016 * atomicity guarantees must override this method and document its
1017 * concurrency properties. In particular, all implementations of
1018 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1019 * whether the function is applied once atomically only if the value is not
1020 * present. Any class that permits null values must document
1021 * whether and how this method distinguishes absence from null mappings.
1022 *
1023 * @implSpec
1024 * The default implementation is equivalent to performing the following
1025 * steps for this {@code map}, then returning the current value or
1026 * {@code null} if absent:
1027 *
1028 * <pre> {@code
1029 * V oldValue = map.get(key);
1030 * V newValue = remappingFunction.apply(key, oldValue);
1031 * if (oldValue != null ) {
1032 * if (newValue != null)
1033 * map.replace(key, oldValue, newValue);
1034 * else
1035 * map.remove(key, oldValue);
1036 * } else {
1037 * if (newValue != null)
1038 * map.putIfAbsent(key, newValue);
1039 * else
1040 * return null;
1041 * }
1042 * }</pre>
1043 *
1044 * In concurrent contexts, the default implementation may retry
1045 * these steps when multiple threads attempt updates.
1046 *
1047 * @param key key with which the specified value is to be associated
1048 * @param remappingFunction the function to compute a value
1049 * @return the new value associated with the specified key, or null if none
1050 * @throws NullPointerException if the specified key is null and
1051 * this map does not support null keys, or the
1052 * remappingFunction is null
1053 * @throws UnsupportedOperationException if the {@code put} operation
1054 * is not supported by this map
1055 * (<a href="Collection.html#optional-restrictions">optional</a>)
1056 * @throws ClassCastException if the class of the specified key or value
1057 * prevents it from being stored in this map
1058 * (<a href="Collection.html#optional-restrictions">optional</a>)
1059 * @since 1.8
1060 */
1061 default V compute(K key,
1062 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1063 V oldValue = get(key);
1064 for (;;) {
1065 V newValue = remappingFunction.apply(key, oldValue);
1066 if (newValue == null) {
1067 // delete mapping
1068 if(oldValue != null || containsKey(key)) {
1069 // something to remove
1070 if (remove(key, oldValue)) {
1071 // removed the old value as expected
1072 return null;
1073 }
1074
1075 // some other value replaced old value. try again.
1076 oldValue = get(key);
1077 } else {
1078 // nothing to do. Leave things as they were.
1079 return null;
1080 }
1081 } else {
1082 // add or replace old mapping
1083 if (oldValue != null) {
1084 // replace
1085 if (replace(key, oldValue, newValue)) {
1086 // replaced as expected.
1087 return newValue;
1088 }
1089
1090 // some other value replaced old value. try again.
1091 oldValue = get(key);
1092 } else {
1093 // add (replace if oldValue was null)
1094 if ((oldValue = putIfAbsent(key, newValue)) == null) {
1095 // replaced
1096 return newValue;
1097 }
1098
1099 // some other value replaced old value. try again.
1100 }
1101 }
1102 }
1103 }
1104
1105 /**
1106 * If the specified key is not already associated with a value or is
1107 * associated with null, associates it with the given value.
1108 * Otherwise, replaces the value with the results of the given
1109 * remapping function, or removes if the result is {@code null}. This
1110 * method may be of use when combining multiple mapped values for a key.
1111 * For example, to either create or append a {@code String msg} to a
1112 * value mapping:
1113 *
1114 * <pre> {@code
1115 * map.merge(key, msg, String::concat)
1116 * }</pre>
1117 *
1118 * <p>If the function returns {@code null}, the mapping is removed (or
1119 * remains absent if initially absent). If the function itself throws an
1120 * (unchecked) exception, the exception is rethrown, and the current mapping
1121 * is left unchanged.
1122 *
1123 * <p>The default implementation makes no guarantees about synchronization
1124 * or atomicity properties of this method. Any implementation providing
1125 * atomicity guarantees must override this method and document its
1126 * concurrency properties. In particular, all implementations of
1127 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1128 * whether the function is applied once atomically only if the value is not
1129 * present. Any class that permits null values must document
1130 * whether and how this method distinguishes absence from null mappings.
1131 *
1132 * @implSpec
1133 * The default implementation is equivalent to performing the
1134 * following steps for this {@code map}, then returning the
1135 * current value or {@code null} if absent:
1136 *
1137 * <pre> {@code
1138 * V oldValue = map.get(key);
1139 * V newValue = (oldValue == null) ? value :
1140 * remappingFunction.apply(oldValue, value);
1141 * if (newValue == null)
1142 * map.remove(key, oldValue);
1143 * else if (oldValue == null)
1144 * map.putIfAbsent(key, newValue);
1145 * else
1146 * map.replace(key, oldValue, newValue);
1147 * }</pre>
1148 *
1149 * In concurrent contexts, the default implementation may retry
1150 * these steps when multiple threads attempt updates.
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
1164 * remappingFunction 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 V oldValue = get(key);
1170 for (;;) {
1171 if (oldValue != null) {
1172 V newValue = remappingFunction.apply(oldValue, value);
1173 if (newValue != null) {
1174 if (replace(key, oldValue, newValue))
1175 return newValue;
1176 } else if (remove(key, oldValue)) {
1177 return null;
1178 }
1179 oldValue = get(key);
1180 } else {
1181 if (value == null) {
1182 return null;
1183 }
1184
1185 if ((oldValue = putIfAbsent(key, value)) == null) {
1186 return value;
1187 }
1188 }
1189 }
1190 }
1191 }