1 /*
2 * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.util;
27
28 import java.util.function.BiConsumer;
29 import java.util.function.BiFunction;
30 import java.util.function.Function;
31 import java.io.Serializable;
32
33 /**
34 * An object that maps keys to values. A map cannot contain duplicate keys;
35 * each key can map to at most one value.
36 *
37 * <p>This interface takes the place of the {@code Dictionary} class, which
38 * was a totally abstract class rather than an interface.
39 *
40 * <p>The {@code Map} 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 {@code TreeMap} class, make
45 * specific guarantees as to their order; others, like the {@code HashMap}
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 {@code equals} 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 {@code equals} and {@code hashCode} 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 {@code Map},
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 * {@code UnsupportedOperationException} 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 {@code UnsupportedOperationException} 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 {@code NullPointerException} or {@code ClassCastException}.
80 * Attempting to query the presence of an ineligible key or value may throw an
81 * exception, or it may simply return false; some implementations will exhibit
82 * the former behavior and some will exhibit the latter. More generally,
83 * attempting an operation on an ineligible key or value whose completion
84 * would not result in the insertion of an ineligible element into the map may
85 * throw an exception or it may succeed, at the option of the implementation.
86 * Such exceptions are marked as "optional" in the specification for this
87 * interface.
88 *
89 * <p>Many methods in Collections Framework interfaces are defined
90 * in terms of the {@link Object#equals(Object) equals} method. For
91 * example, the specification for the {@link #containsKey(Object)
92 * containsKey(Object key)} method says: "returns {@code true} if and
93 * only if this map contains a mapping for a key {@code k} such that
94 * {@code (key==null ? k==null : key.equals(k))}." This specification should
95 * <i>not</i> be construed to imply that invoking {@code Map.containsKey}
96 * with a non-null argument {@code key} will cause {@code key.equals(k)} to
97 * be invoked for any key {@code k}. Implementations are free to
98 * implement optimizations whereby the {@code equals} invocation is avoided,
99 * for example, by first comparing the hash codes of the two keys. (The
100 * {@link Object#hashCode()} specification guarantees that two objects with
101 * unequal hash codes cannot be equal.) More generally, implementations of
102 * the various Collections Framework interfaces are free to take advantage of
103 * the specified behavior of underlying {@link Object} methods wherever the
104 * implementor deems it appropriate.
105 *
106 * <p>Some map operations which perform recursive traversal of the map may fail
107 * with an exception for self-referential instances where the map directly or
108 * indirectly contains itself. This includes the {@code clone()},
109 * {@code equals()}, {@code hashCode()} and {@code toString()} methods.
110 * Implementations may optionally handle the self-referential scenario, however
111 * most current implementations do not do so.
112 *
113 * <h2><a id="unmodifiable">Unmodifiable Maps</a></h2>
114 * <p>The {@link Map#of() Map.of},
115 * {@link Map#ofEntries(Map.Entry...) Map.ofEntries}, and
116 * {@link Map#copyOf Map.copyOf}
117 * static factory methods provide a convenient way to create unmodifiable maps.
118 * The {@code Map}
119 * instances created by these methods have the following characteristics:
120 *
121 * <ul>
122 * <li>They are <a href="Collection.html#unmodifiable"><i>unmodifiable</i></a>. Keys and values
123 * cannot be added, removed, or updated. Calling any mutator method on the Map
124 * will always cause {@code UnsupportedOperationException} to be thrown.
125 * However, if the contained keys or values are themselves mutable, this may cause the
126 * Map to behave inconsistently or its contents to appear to change.
127 * <li>They disallow {@code null} keys and values. Attempts to create them with
128 * {@code null} keys or values result in {@code NullPointerException}.
129 * <li>They are serializable if all keys and values are serializable.
130 * <li>They reject duplicate keys at creation time. Duplicate keys
131 * passed to a static factory method result in {@code IllegalArgumentException}.
132 * <li>The iteration order of mappings is unspecified and is subject to change.
133 * <li>They are <a href="../lang/doc-files/ValueBased.html">value-based</a>.
134 * Callers should make no assumptions about the identity of the returned instances.
135 * Factories are free to create new instances or reuse existing ones. Therefore,
136 * identity-sensitive operations on these instances (reference equality ({@code ==}),
137 * identity hash code, and synchronization) are unreliable and should be avoided.
138 * <li>They are serialized as specified on the
139 * <a href="{@docRoot}/serialized-form.html#java.util.CollSer">Serialized Form</a>
140 * page.
141 * </ul>
142 *
143 * <p>This interface is a member of the
144 * <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
145 * Java Collections Framework</a>.
146 *
147 * @param <K> the type of keys maintained by this map
148 * @param <V> the type of mapped values
149 *
150 * @author Josh Bloch
151 * @see HashMap
152 * @see TreeMap
153 * @see Hashtable
154 * @see SortedMap
155 * @see Collection
156 * @see Set
157 * @since 1.2
158 */
159 public interface Map<K, V> {
160 // Query Operations
161
162 /**
163 * Returns the number of key-value mappings in this map. If the
164 * map contains more than {@code Integer.MAX_VALUE} elements, returns
165 * {@code Integer.MAX_VALUE}.
166 *
167 * @return the number of key-value mappings in this map
168 */
169 int size();
170
171 /**
172 * Returns {@code true} if this map contains no key-value mappings.
173 *
174 * @return {@code true} if this map contains no key-value mappings
175 */
176 boolean isEmpty();
177
178 /**
179 * Returns {@code true} if this map contains a mapping for the specified
180 * key. More formally, returns {@code true} if and only if
181 * this map contains a mapping for a key {@code k} such that
182 * {@code Objects.equals(key, k)}. (There can be
183 * at most one such mapping.)
184 *
185 * @param key key whose presence in this map is to be tested
186 * @return {@code true} if this map contains a mapping for the specified
187 * key
188 * @throws ClassCastException if the key is of an inappropriate type for
189 * this map
190 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
191 * @throws NullPointerException if the specified key is null and this map
192 * does not permit null keys
193 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
194 */
195 boolean containsKey(Object key);
196
197 /**
198 * Returns {@code true} if this map maps one or more keys to the
199 * specified value. More formally, returns {@code true} if and only if
200 * this map contains at least one mapping to a value {@code v} such that
201 * {@code Objects.equals(value, v)}. This operation
202 * will probably require time linear in the map size for most
203 * implementations of the {@code Map} interface.
204 *
205 * @param value value whose presence in this map is to be tested
206 * @return {@code true} if this map maps one or more keys to the
207 * specified value
208 * @throws ClassCastException if the value is of an inappropriate type for
209 * this map
210 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
211 * @throws NullPointerException if the specified value is null and this
212 * map does not permit null values
213 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
214 */
215 boolean containsValue(Object value);
216
217 /**
218 * Returns the value to which the specified key is mapped,
219 * or {@code null} if this map contains no mapping for the key.
220 *
221 * <p>More formally, if this map contains a mapping from a key
222 * {@code k} to a value {@code v} such that
223 * {@code Objects.equals(key, k)},
224 * then this method returns {@code v}; otherwise
225 * it returns {@code null}. (There can be at most one such mapping.)
226 *
227 * <p>If this map permits null values, then a return value of
228 * {@code null} does not <i>necessarily</i> indicate that the map
229 * contains no mapping for the key; it's also possible that the map
230 * explicitly maps the key to {@code null}. The {@link #containsKey
231 * containsKey} operation may be used to distinguish these two cases.
232 *
233 * @param key the key whose associated value is to be returned
234 * @return the value to which the specified key is mapped, or
235 * {@code null} if this map contains no mapping for the key
236 * @throws ClassCastException if the key is of an inappropriate type for
237 * this map
238 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
239 * @throws NullPointerException if the specified key is null and this map
240 * does not permit null keys
241 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
242 */
243 V get(Object key);
244
245 // Modification Operations
246
247 /**
248 * Associates the specified value with the specified key in this map
249 * (optional operation). If the map previously contained a mapping for
250 * the key, the old value is replaced by the specified value. (A map
251 * {@code m} is said to contain a mapping for a key {@code k} if and only
252 * if {@link #containsKey(Object) m.containsKey(k)} would return
253 * {@code true}.)
254 *
255 * @param key key with which the specified value is to be associated
256 * @param value value to be associated with the specified key
257 * @return the previous value associated with {@code key}, or
258 * {@code null} if there was no mapping for {@code key}.
259 * (A {@code null} return can also indicate that the map
260 * previously associated {@code null} with {@code key},
261 * if the implementation supports {@code null} values.)
262 * @throws UnsupportedOperationException if the {@code put} operation
263 * is not supported by this map
264 * @throws ClassCastException if the class of the specified key or value
265 * prevents it from being stored in this map
266 * @throws NullPointerException if the specified key or value is null
267 * and this map does not permit null keys or values
268 * @throws IllegalArgumentException if some property of the specified key
269 * or value prevents it from being stored in this map
270 */
271 V put(K key, V value);
272
273 /**
274 * Removes the mapping for a key from this map if it is present
275 * (optional operation). More formally, if this map contains a mapping
276 * from key {@code k} to value {@code v} such that
277 * {@code Objects.equals(key, k)}, that mapping
278 * is removed. (The map can contain at most one such mapping.)
279 *
280 * <p>Returns the value to which this map previously associated the key,
281 * or {@code null} if the map contained no mapping for the key.
282 *
283 * <p>If this map permits null values, then a return value of
284 * {@code null} does not <i>necessarily</i> indicate that the map
285 * contained no mapping for the key; it's also possible that the map
286 * explicitly mapped the key to {@code null}.
287 *
288 * <p>The map will not contain a mapping for the specified key once the
289 * call returns.
290 *
291 * @param key key whose mapping is to be removed from the map
292 * @return the previous value associated with {@code key}, or
293 * {@code null} if there was no mapping for {@code key}.
294 * @throws UnsupportedOperationException if the {@code remove} operation
295 * is not supported by this map
296 * @throws ClassCastException if the key is of an inappropriate type for
297 * this map
298 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
299 * @throws NullPointerException if the specified key is null and this
300 * map does not permit null keys
301 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
302 */
303 V remove(Object key);
304
305
306 // Bulk Operations
307
308 /**
309 * Copies all of the mappings from the specified map to this map
310 * (optional operation). The effect of this call is equivalent to that
311 * of calling {@link #put(Object,Object) put(k, v)} on this map once
312 * for each mapping from key {@code k} to value {@code v} in the
313 * specified map. The behavior of this operation is undefined if the
314 * specified map is modified while the operation is in progress.
315 *
316 * @param m mappings to be stored in this map
317 * @throws UnsupportedOperationException if the {@code putAll} operation
318 * is not supported by this map
319 * @throws ClassCastException if the class of a key or value in the
320 * specified map prevents it from being stored in this map
321 * @throws NullPointerException if the specified map is null, or if
322 * this map does not permit null keys or values, and the
323 * specified map contains null keys or values
324 * @throws IllegalArgumentException if some property of a key or value in
325 * the specified map prevents it from being stored in this map
326 */
327 void putAll(Map<? extends K, ? extends V> m);
328
329 /**
330 * Removes all of the mappings from this map (optional operation).
331 * The map will be empty after this call returns.
332 *
333 * @throws UnsupportedOperationException if the {@code clear} operation
334 * is not supported by this map
335 */
336 void clear();
337
338
339 // Views
340
341 /**
342 * Returns a {@link Set} view of the keys contained in this map.
343 * The set is backed by the map, so changes to the map are
344 * reflected in the set, and vice-versa. If the map is modified
345 * while an iteration over the set is in progress (except through
346 * the iterator's own {@code remove} operation), the results of
347 * the iteration are undefined. The set supports element removal,
348 * which removes the corresponding mapping from the map, via the
349 * {@code Iterator.remove}, {@code Set.remove},
350 * {@code removeAll}, {@code retainAll}, and {@code clear}
351 * operations. It does not support the {@code add} or {@code addAll}
352 * operations.
353 *
354 * @return a set view of the keys contained in this map
355 */
356 Set<K> keySet();
357
358 /**
359 * Returns a {@link Collection} view of the values contained in this map.
360 * The collection is backed by the map, so changes to the map are
361 * reflected in the collection, and vice-versa. If the map is
362 * modified while an iteration over the collection is in progress
363 * (except through the iterator's own {@code remove} operation),
364 * the results of the iteration are undefined. The collection
365 * supports element removal, which removes the corresponding
366 * mapping from the map, via the {@code Iterator.remove},
367 * {@code Collection.remove}, {@code removeAll},
368 * {@code retainAll} and {@code clear} operations. It does not
369 * support the {@code add} or {@code addAll} operations.
370 *
371 * @return a collection view of the values contained in this map
372 */
373 Collection<V> values();
374
375 /**
376 * Returns a {@link Set} view of the mappings contained in this map.
377 * The set is backed by the map, so changes to the map are
378 * reflected in the set, and vice-versa. If the map is modified
379 * while an iteration over the set is in progress (except through
380 * the iterator's own {@code remove} operation, or through the
381 * {@code setValue} operation on a map entry returned by the
382 * iterator) the results of the iteration are undefined. The set
383 * supports element removal, which removes the corresponding
384 * mapping from the map, via the {@code Iterator.remove},
385 * {@code Set.remove}, {@code removeAll}, {@code retainAll} and
386 * {@code clear} operations. It does not support the
387 * {@code add} or {@code addAll} operations.
388 *
389 * @return a set view of the mappings contained in this map
390 */
391 Set<Map.Entry<K, V>> entrySet();
392
393 /**
394 * A map entry (key-value pair). The {@code Map.entrySet} method returns
395 * a collection-view of the map, whose elements are of this class. The
396 * <i>only</i> way to obtain a reference to a map entry is from the
397 * iterator of this collection-view. These {@code Map.Entry} objects are
398 * valid <i>only</i> for the duration of the iteration; more formally,
399 * the behavior of a map entry is undefined if the backing map has been
400 * modified after the entry was returned by the iterator, except through
401 * the {@code setValue} operation on the map entry.
402 *
403 * @see Map#entrySet()
404 * @since 1.2
405 */
406 interface Entry<K, V> {
407 /**
408 * Returns the key corresponding to this entry.
409 *
410 * @return the key corresponding to this entry
411 * @throws IllegalStateException implementations may, but are not
412 * required to, throw this exception if the entry has been
413 * removed from the backing map.
414 */
415 K getKey();
416
417 /**
418 * Returns the value corresponding to this entry. If the mapping
419 * has been removed from the backing map (by the iterator's
420 * {@code remove} operation), the results of this call are undefined.
421 *
422 * @return the value corresponding to this entry
423 * @throws IllegalStateException implementations may, but are not
424 * required to, throw this exception if the entry has been
425 * removed from the backing map.
426 */
427 V getValue();
428
429 /**
430 * Replaces the value corresponding to this entry with the specified
431 * value (optional operation). (Writes through to the map.) The
432 * behavior of this call is undefined if the mapping has already been
433 * removed from the map (by the iterator's {@code remove} operation).
434 *
435 * @param value new value to be stored in this entry
436 * @return old value corresponding to the entry
437 * @throws UnsupportedOperationException if the {@code put} operation
438 * is not supported by the backing map
439 * @throws ClassCastException if the class of the specified value
440 * prevents it from being stored in the backing map
441 * @throws NullPointerException if the backing map does not permit
442 * null values, and the specified value is null
443 * @throws IllegalArgumentException if some property of this value
444 * prevents it from being stored in the backing map
445 * @throws IllegalStateException implementations may, but are not
446 * required to, throw this exception if the entry has been
447 * removed from the backing map.
448 */
449 V setValue(V value);
450
451 /**
452 * Compares the specified object with this entry for equality.
453 * Returns {@code true} if the given object is also a map entry and
454 * the two entries represent the same mapping. More formally, two
455 * entries {@code e1} and {@code e2} represent the same mapping
456 * if<pre>
457 * (e1.getKey()==null ?
458 * e2.getKey()==null : e1.getKey().equals(e2.getKey())) &&
459 * (e1.getValue()==null ?
460 * e2.getValue()==null : e1.getValue().equals(e2.getValue()))
461 * </pre>
462 * This ensures that the {@code equals} method works properly across
463 * different implementations of the {@code Map.Entry} interface.
464 *
465 * @param o object to be compared for equality with this map entry
466 * @return {@code true} if the specified object is equal to this map
467 * entry
468 */
469 boolean equals(Object o);
470
471 /**
472 * Returns the hash code value for this map entry. The hash code
473 * of a map entry {@code e} is defined to be: <pre>
474 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
475 * (e.getValue()==null ? 0 : e.getValue().hashCode())
476 * </pre>
477 * This ensures that {@code e1.equals(e2)} implies that
478 * {@code e1.hashCode()==e2.hashCode()} for any two Entries
479 * {@code e1} and {@code e2}, as required by the general
480 * contract of {@code Object.hashCode}.
481 *
482 * @return the hash code value for this map entry
483 * @see Object#hashCode()
484 * @see Object#equals(Object)
485 * @see #equals(Object)
486 */
487 int hashCode();
488
489 /**
490 * Returns a comparator that compares {@link Map.Entry} in natural order on key.
491 *
492 * <p>The returned comparator is serializable and throws {@link
493 * NullPointerException} when comparing an entry with a null key.
494 *
495 * @param <K> the {@link Comparable} type of then map keys
496 * @param <V> the type of the map values
497 * @return a comparator that compares {@link Map.Entry} in natural order on key.
498 * @see Comparable
499 * @since 1.8
500 */
501 public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K, V>> comparingByKey() {
502 return (Comparator<Map.Entry<K, V>> & Serializable)
503 (c1, c2) -> c1.getKey().compareTo(c2.getKey());
504 }
505
506 /**
507 * Returns a comparator that compares {@link Map.Entry} in natural order on value.
508 *
509 * <p>The returned comparator is serializable and throws {@link
510 * NullPointerException} when comparing an entry with null values.
511 *
512 * @param <K> the type of the map keys
513 * @param <V> the {@link Comparable} type of the map values
514 * @return a comparator that compares {@link Map.Entry} in natural order on value.
515 * @see Comparable
516 * @since 1.8
517 */
518 public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K, V>> comparingByValue() {
519 return (Comparator<Map.Entry<K, V>> & Serializable)
520 (c1, c2) -> c1.getValue().compareTo(c2.getValue());
521 }
522
523 /**
524 * Returns a comparator that compares {@link Map.Entry} by key using the given
525 * {@link Comparator}.
526 *
527 * <p>The returned comparator is serializable if the specified comparator
528 * is also serializable.
529 *
530 * @param <K> the type of the map keys
531 * @param <V> the type of the map values
532 * @param cmp the key {@link Comparator}
533 * @return a comparator that compares {@link Map.Entry} by the key.
534 * @since 1.8
535 */
536 public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) {
537 Objects.requireNonNull(cmp);
538 return (Comparator<Map.Entry<K, V>> & Serializable)
539 (c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());
540 }
541
542 /**
543 * Returns a comparator that compares {@link Map.Entry} by value using the given
544 * {@link Comparator}.
545 *
546 * <p>The returned comparator is serializable if the specified comparator
547 * is also serializable.
548 *
549 * @param <K> the type of the map keys
550 * @param <V> the type of the map values
551 * @param cmp the value {@link Comparator}
552 * @return a comparator that compares {@link Map.Entry} by the value.
553 * @since 1.8
554 */
555 public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) {
556 Objects.requireNonNull(cmp);
557 return (Comparator<Map.Entry<K, V>> & Serializable)
558 (c1, c2) -> cmp.compare(c1.getValue(), c2.getValue());
559 }
560 }
561
562 // Comparison and hashing
563
564 /**
565 * Compares the specified object with this map for equality. Returns
566 * {@code true} if the given object is also a map and the two maps
567 * represent the same mappings. More formally, two maps {@code m1} and
568 * {@code m2} represent the same mappings if
569 * {@code m1.entrySet().equals(m2.entrySet())}. This ensures that the
570 * {@code equals} method works properly across different implementations
571 * of the {@code Map} interface.
572 *
573 * @param o object to be compared for equality with this map
574 * @return {@code true} if the specified object is equal to this map
575 */
576 boolean equals(Object o);
577
578 /**
579 * Returns the hash code value for this map. The hash code of a map is
580 * defined to be the sum of the hash codes of each entry in the map's
581 * {@code entrySet()} view. This ensures that {@code m1.equals(m2)}
582 * implies that {@code m1.hashCode()==m2.hashCode()} for any two maps
583 * {@code m1} and {@code m2}, as required by the general contract of
584 * {@link Object#hashCode}.
585 *
586 * @return the hash code value for this map
587 * @see Map.Entry#hashCode()
588 * @see Object#equals(Object)
589 * @see #equals(Object)
590 */
591 int hashCode();
592
593 // Defaultable methods
594
595 /**
596 * Returns the value to which the specified key is mapped, or
597 * {@code defaultValue} if this map contains no mapping for the key.
598 *
599 * @implSpec
600 * The default implementation makes no guarantees about synchronization
601 * or atomicity properties of this method. Any implementation providing
602 * atomicity guarantees must override this method and document its
603 * concurrency properties.
604 *
605 * @param key the key whose associated value is to be returned
606 * @param defaultValue the default mapping of the key
607 * @return the value to which the specified key is mapped, or
608 * {@code defaultValue} if this map contains no mapping for the key
609 * @throws ClassCastException if the key is of an inappropriate type for
610 * this map
611 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
612 * @throws NullPointerException if the specified key is null and this map
613 * does not permit null keys
614 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
615 * @since 1.8
616 */
617 default V getOrDefault(Object key, V defaultValue) {
618 V v;
619 return (((v = get(key)) != null) || containsKey(key))
620 ? v
621 : defaultValue;
622 }
623
624 /**
625 * Performs the given action for each entry in this map until all entries
626 * have been processed or the action throws an exception. Unless
627 * otherwise specified by the implementing class, actions are performed in
628 * the order of entry set iteration (if an iteration order is specified.)
629 * Exceptions thrown by the action are relayed to the caller.
630 *
631 * @implSpec
632 * The default implementation is equivalent to, for this {@code map}:
633 * <pre> {@code
634 * for (Map.Entry<K, V> entry : map.entrySet())
635 * action.accept(entry.getKey(), entry.getValue());
636 * }</pre>
637 *
638 * The default implementation makes no guarantees about synchronization
639 * or atomicity properties of this method. Any implementation providing
640 * atomicity guarantees must override this method and document its
641 * concurrency properties.
642 *
643 * @param action The action to be performed for each entry
644 * @throws NullPointerException if the specified action is null
645 * @throws ConcurrentModificationException if an entry is found to be
646 * removed during iteration
647 * @since 1.8
648 */
649 default void forEach(BiConsumer<? super K, ? super V> action) {
650 Objects.requireNonNull(action);
651 for (Map.Entry<K, V> entry : entrySet()) {
652 K k;
653 V v;
654 try {
655 k = entry.getKey();
656 v = entry.getValue();
657 } catch (IllegalStateException ise) {
658 // this usually means the entry is no longer in the map.
659 throw new ConcurrentModificationException(ise);
660 }
661 action.accept(k, v);
662 }
663 }
664
665 /**
666 * Replaces each entry's value with the result of invoking the given
667 * function on that entry until all entries have been processed or the
668 * function throws an exception. Exceptions thrown by the function are
669 * relayed to the caller.
670 *
671 * @implSpec
672 * <p>The default implementation is equivalent to, for this {@code map}:
673 * <pre> {@code
674 * for (Map.Entry<K, V> entry : map.entrySet())
675 * entry.setValue(function.apply(entry.getKey(), entry.getValue()));
676 * }</pre>
677 *
678 * <p>The default implementation makes no guarantees about synchronization
679 * or atomicity properties of this method. Any implementation providing
680 * atomicity guarantees must override this method and document its
681 * concurrency properties.
682 *
683 * @param function the function to apply to each entry
684 * @throws UnsupportedOperationException if the {@code set} operation
685 * is not supported by this map's entry set iterator.
686 * @throws ClassCastException if the class of a replacement value
687 * prevents it from being stored in this map
688 * @throws NullPointerException if the specified function is null, or the
689 * specified replacement value is null, and this map does not permit null
690 * values
691 * @throws ClassCastException if a replacement value is of an inappropriate
692 * type for this map
693 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
694 * @throws NullPointerException if function or a replacement value is null,
695 * and this map does not permit null keys or values
696 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
697 * @throws IllegalArgumentException if some property of a replacement value
698 * prevents it from being stored in this map
699 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
700 * @throws ConcurrentModificationException if an entry is found to be
701 * removed during iteration
702 * @since 1.8
703 */
704 default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
705 Objects.requireNonNull(function);
706 for (Map.Entry<K, V> entry : entrySet()) {
707 K k;
708 V v;
709 try {
710 k = entry.getKey();
711 v = entry.getValue();
712 } catch (IllegalStateException ise) {
713 // this usually means the entry is no longer in the map.
714 throw new ConcurrentModificationException(ise);
715 }
716
717 // ise thrown from function is not a cme.
718 v = function.apply(k, v);
719
720 try {
721 entry.setValue(v);
722 } catch (IllegalStateException ise) {
723 // this usually means the entry is no longer in the map.
724 throw new ConcurrentModificationException(ise);
725 }
726 }
727 }
728
729 /**
730 * If the specified key is not already associated with a value (or is mapped
731 * to {@code null}) associates it with the given value and returns
732 * {@code null}, else returns the current value.
733 *
734 * @implSpec
735 * The default implementation is equivalent to, for this {@code
736 * map}:
737 *
738 * <pre> {@code
739 * V v = map.get(key);
740 * if (v == null)
741 * v = map.put(key, value);
742 *
743 * return v;
744 * }</pre>
745 *
746 * <p>The default implementation makes no guarantees about synchronization
747 * or atomicity properties of this method. Any implementation providing
748 * atomicity guarantees must override this method and document its
749 * concurrency properties.
750 *
751 * @param key key with which the specified value is to be associated
752 * @param value value to be associated with the specified key
753 * @return the previous value associated with the specified key, or
754 * {@code null} if there was no mapping for the key.
755 * (A {@code null} return can also indicate that the map
756 * previously associated {@code null} with the key,
757 * if the implementation supports null values.)
758 * @throws UnsupportedOperationException if the {@code put} operation
759 * is not supported by this map
760 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
761 * @throws ClassCastException if the key or value is of an inappropriate
762 * type for this map
763 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
764 * @throws NullPointerException if the specified key or value is null,
765 * and this map does not permit null keys or values
766 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
767 * @throws IllegalArgumentException if some property of the specified key
768 * or value prevents it from being stored in this map
769 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
770 * @since 1.8
771 */
772 default V putIfAbsent(K key, V value) {
773 V v = get(key);
774 if (v == null) {
775 v = put(key, value);
776 }
777
778 return v;
779 }
780
781 /**
782 * Removes the entry for the specified key only if it is currently
783 * mapped to the specified value.
784 *
785 * @implSpec
786 * The default implementation is equivalent to, for this {@code map}:
787 *
788 * <pre> {@code
789 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
790 * map.remove(key);
791 * return true;
792 * } else
793 * return false;
794 * }</pre>
795 *
796 * <p>The default implementation makes no guarantees about synchronization
797 * or atomicity properties of this method. Any implementation providing
798 * atomicity guarantees must override this method and document its
799 * concurrency properties.
800 *
801 * @param key key with which the specified value is associated
802 * @param value value expected to be associated with the specified key
803 * @return {@code true} if the value was removed
804 * @throws UnsupportedOperationException if the {@code remove} operation
805 * is not supported by this map
806 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
807 * @throws ClassCastException if the key or value is of an inappropriate
808 * type for this map
809 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
810 * @throws NullPointerException if the specified key or value is null,
811 * and this map does not permit null keys or values
812 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
813 * @since 1.8
814 */
815 default boolean remove(Object key, Object value) {
816 Object curValue = get(key);
817 if (!Objects.equals(curValue, value) ||
818 (curValue == null && !containsKey(key))) {
819 return false;
820 }
821 remove(key);
822 return true;
823 }
824
825 /**
826 * Replaces the entry for the specified key only if currently
827 * mapped to the specified value.
828 *
829 * @implSpec
830 * The default implementation is equivalent to, for this {@code map}:
831 *
832 * <pre> {@code
833 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
834 * map.put(key, newValue);
835 * return true;
836 * } else
837 * return false;
838 * }</pre>
839 *
840 * The default implementation does not throw NullPointerException
841 * for maps that do not support null values if oldValue is null unless
842 * newValue is also null.
843 *
844 * <p>The default implementation makes no guarantees about synchronization
845 * or atomicity properties of this method. Any implementation providing
846 * atomicity guarantees must override this method and document its
847 * concurrency properties.
848 *
849 * @param key key with which the specified value is associated
850 * @param oldValue value expected to be associated with the specified key
851 * @param newValue value to be associated with the specified key
852 * @return {@code true} if the value was replaced
853 * @throws UnsupportedOperationException if the {@code put} operation
854 * is not supported by this map
855 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
856 * @throws ClassCastException if the class of a specified key or value
857 * prevents it from being stored in this map
858 * @throws NullPointerException if a specified key or newValue is null,
859 * and this map does not permit null keys or values
860 * @throws NullPointerException if oldValue is null and this map does not
861 * permit null values
862 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
863 * @throws IllegalArgumentException if some property of a specified key
864 * or value prevents it from being stored in this map
865 * @since 1.8
866 */
867 default boolean replace(K key, V oldValue, V newValue) {
868 Object curValue = get(key);
869 if (!Objects.equals(curValue, oldValue) ||
870 (curValue == null && !containsKey(key))) {
871 return false;
872 }
873 put(key, newValue);
874 return true;
875 }
876
877 /**
878 * Replaces the entry for the specified key only if it is
879 * currently mapped to some value.
880 *
881 * @implSpec
882 * The default implementation is equivalent to, for this {@code map}:
883 *
884 * <pre> {@code
885 * if (map.containsKey(key)) {
886 * return map.put(key, value);
887 * } else
888 * return null;
889 * }</pre>
890 *
891 * <p>The default implementation makes no guarantees about synchronization
892 * or atomicity properties of this method. Any implementation providing
893 * atomicity guarantees must override this method and document its
894 * concurrency properties.
895 *
896 * @param key key with which the specified value is associated
897 * @param value value to be associated with the specified key
898 * @return the previous value associated with the specified key, or
899 * {@code null} if there was no mapping for the key.
900 * (A {@code null} return can also indicate that the map
901 * previously associated {@code null} with the key,
902 * if the implementation supports null values.)
903 * @throws UnsupportedOperationException if the {@code put} operation
904 * is not supported by this map
905 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
906 * @throws ClassCastException if the class of the specified key or value
907 * prevents it from being stored in this map
908 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
909 * @throws NullPointerException if the specified key or value is null,
910 * and this map does not permit null keys or values
911 * @throws IllegalArgumentException if some property of the specified key
912 * or value prevents it from being stored in this map
913 * @since 1.8
914 */
915 default V replace(K key, V value) {
916 V curValue;
917 if (((curValue = get(key)) != null) || containsKey(key)) {
918 curValue = put(key, value);
919 }
920 return curValue;
921 }
922
923 /**
924 * If the specified key is not already associated with a value (or is mapped
925 * to {@code null}), attempts to compute its value using the given mapping
926 * function and enters it into this map unless {@code null}.
927 *
928 * <p>If the mapping function returns {@code null}, no mapping is recorded.
929 * If the mapping function itself throws an (unchecked) exception, the
930 * exception is rethrown, and no mapping is recorded. The most
931 * common usage is to construct a new object serving as an initial
932 * mapped value or memoized result, as in:
933 *
934 * <pre> {@code
935 * map.computeIfAbsent(key, k -> new Value(f(k)));
936 * }</pre>
937 *
938 * <p>Or to implement a multi-value map, {@code Map<K,Collection<V>>},
939 * supporting multiple values per key:
940 *
941 * <pre> {@code
942 * map.computeIfAbsent(key, k -> new HashSet<V>()).add(v);
943 * }</pre>
944 *
945 * <p>The mapping function should not modify this map during computation.
946 *
947 * @implSpec
948 * The default implementation is equivalent to the following steps for this
949 * {@code map}, then returning the current value or {@code null} if now
950 * absent:
951 *
952 * <pre> {@code
953 * if (map.get(key) == null) {
954 * V newValue = mappingFunction.apply(key);
955 * if (newValue != null)
956 * map.put(key, newValue);
957 * }
958 * }</pre>
959 *
960 * <p>The default implementation makes no guarantees about detecting if the
961 * mapping function modifies this map during computation and, if
962 * appropriate, reporting an error. Non-concurrent implementations should
963 * override this method and, on a best-effort basis, throw a
964 * {@code ConcurrentModificationException} if it is detected that the
965 * mapping function modifies this map during computation. Concurrent
966 * implementations should override this method and, on a best-effort basis,
967 * throw an {@code IllegalStateException} if it is detected that the
968 * mapping function modifies this map during computation and as a result
969 * computation would never complete.
970 *
971 * <p>The default implementation makes no guarantees about synchronization
972 * or atomicity properties of this method. Any implementation providing
973 * atomicity guarantees must override this method and document its
974 * concurrency properties. In particular, all implementations of
975 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
976 * whether the mapping function is applied once atomically only if the value
977 * is not present.
978 *
979 * @param key key with which the specified value is to be associated
980 * @param mappingFunction the mapping function to compute a value
981 * @return the current (existing or computed) value associated with
982 * the specified key, or null if the computed value is null
983 * @throws NullPointerException if the specified key is null and
984 * this map does not support null keys, or the mappingFunction
985 * is null
986 * @throws UnsupportedOperationException if the {@code put} operation
987 * is not supported by this map
988 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
989 * @throws ClassCastException if the class of the specified key or value
990 * prevents it from being stored in this map
991 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
992 * @throws IllegalArgumentException if some property of the specified key
993 * or value prevents it from being stored in this map
994 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
995 * @since 1.8
996 */
997 default V computeIfAbsent(K key,
998 Function<? super K, ? extends V> mappingFunction) {
999 Objects.requireNonNull(mappingFunction);
1000 V v;
1001 if ((v = get(key)) == null) {
1002 V newValue;
1003 if ((newValue = mappingFunction.apply(key)) != null) {
1004 put(key, newValue);
1005 return newValue;
1006 }
1007 }
1008
1009 return v;
1010 }
1011
1012 /**
1013 * If the value for the specified key is present and non-null, attempts to
1014 * compute a new mapping given the key and its current mapped value.
1015 *
1016 * <p>If the remapping function returns {@code null}, the mapping is removed.
1017 * If the remapping function itself throws an (unchecked) exception, the
1018 * exception is rethrown, and the current mapping is left unchanged.
1019 *
1020 * <p>The remapping function should not modify this map during computation.
1021 *
1022 * @implSpec
1023 * The default implementation is equivalent to performing the following
1024 * steps for this {@code map}, then returning the current value or
1025 * {@code null} if now absent:
1026 *
1027 * <pre> {@code
1028 * if (map.get(key) != null) {
1029 * V oldValue = map.get(key);
1030 * V newValue = remappingFunction.apply(key, oldValue);
1031 * if (newValue != null)
1032 * map.put(key, newValue);
1033 * else
1034 * map.remove(key);
1035 * }
1036 * }</pre>
1037 *
1038 * <p>The default implementation makes no guarantees about detecting if the
1039 * remapping function modifies this map during computation and, if
1040 * appropriate, reporting an error. Non-concurrent implementations should
1041 * override this method and, on a best-effort basis, throw a
1042 * {@code ConcurrentModificationException} if it is detected that the
1043 * remapping function modifies this map during computation. Concurrent
1044 * implementations should override this method and, on a best-effort basis,
1045 * throw an {@code IllegalStateException} if it is detected that the
1046 * remapping function modifies this map during computation and as a result
1047 * computation would never complete.
1048 *
1049 * <p>The default implementation makes no guarantees about synchronization
1050 * or atomicity properties of this method. Any implementation providing
1051 * atomicity guarantees must override this method and document its
1052 * concurrency properties. In particular, all implementations of
1053 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1054 * whether the remapping function is applied once atomically only if the
1055 * value is not present.
1056 *
1057 * @param key key with which the specified value is to be associated
1058 * @param remappingFunction the remapping function to compute a value
1059 * @return the new value associated with the specified key, or null if none
1060 * @throws NullPointerException if the specified key is null and
1061 * this map does not support null keys, or the
1062 * remappingFunction is null
1063 * @throws UnsupportedOperationException if the {@code put} operation
1064 * is not supported by this map
1065 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1066 * @throws ClassCastException if the class of the specified key or value
1067 * prevents it from being stored in this map
1068 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1069 * @throws IllegalArgumentException if some property of the specified key
1070 * or value prevents it from being stored in this map
1071 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1072 * @since 1.8
1073 */
1074 default V computeIfPresent(K key,
1075 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1076 Objects.requireNonNull(remappingFunction);
1077 V oldValue;
1078 if ((oldValue = get(key)) != null) {
1079 V newValue = remappingFunction.apply(key, oldValue);
1080 if (newValue != null) {
1081 put(key, newValue);
1082 return newValue;
1083 } else {
1084 remove(key);
1085 return null;
1086 }
1087 } else {
1088 return null;
1089 }
1090 }
1091
1092 /**
1093 * Attempts to compute a mapping for the specified key and its current
1094 * mapped value (or {@code null} if there is no current mapping). For
1095 * example, to either create or append a {@code String} msg to a value
1096 * mapping:
1097 *
1098 * <pre> {@code
1099 * map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))}</pre>
1100 * (Method {@link #merge merge()} is often simpler to use for such purposes.)
1101 *
1102 * <p>If the remapping function returns {@code null}, the mapping is removed
1103 * (or remains absent if initially absent). If the remapping function
1104 * itself throws an (unchecked) exception, the exception is rethrown, and
1105 * the current mapping is left unchanged.
1106 *
1107 * <p>The remapping function should not modify this map during computation.
1108 *
1109 * @implSpec
1110 * The default implementation is equivalent to performing the following
1111 * steps for this {@code map}, then returning the current value or
1112 * {@code null} if absent:
1113 *
1114 * <pre> {@code
1115 * V oldValue = map.get(key);
1116 * V newValue = remappingFunction.apply(key, oldValue);
1117 * if (oldValue != null) {
1118 * if (newValue != null)
1119 * map.put(key, newValue);
1120 * else
1121 * map.remove(key);
1122 * } else {
1123 * if (newValue != null)
1124 * map.put(key, newValue);
1125 * else
1126 * return null;
1127 * }
1128 * }</pre>
1129 *
1130 * <p>The default implementation makes no guarantees about detecting if the
1131 * remapping function modifies this map during computation and, if
1132 * appropriate, reporting an error. Non-concurrent implementations should
1133 * override this method and, on a best-effort basis, throw a
1134 * {@code ConcurrentModificationException} if it is detected that the
1135 * remapping function modifies this map during computation. Concurrent
1136 * implementations should override this method and, on a best-effort basis,
1137 * throw an {@code IllegalStateException} if it is detected that the
1138 * remapping function modifies this map during computation and as a result
1139 * computation would never complete.
1140 *
1141 * <p>The default implementation makes no guarantees about synchronization
1142 * or atomicity properties of this method. Any implementation providing
1143 * atomicity guarantees must override this method and document its
1144 * concurrency properties. In particular, all implementations of
1145 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1146 * whether the remapping function is applied once atomically only if the
1147 * value is not present.
1148 *
1149 * @param key key with which the specified value is to be associated
1150 * @param remappingFunction the remapping function to compute a value
1151 * @return the new value associated with the specified key, or null if none
1152 * @throws NullPointerException if the specified key is null and
1153 * this map does not support null keys, or the
1154 * remappingFunction is null
1155 * @throws UnsupportedOperationException if the {@code put} operation
1156 * is not supported by this map
1157 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1158 * @throws ClassCastException if the class of the specified key or value
1159 * prevents it from being stored in this map
1160 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1161 * @throws IllegalArgumentException if some property of the specified key
1162 * or value prevents it from being stored in this map
1163 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1164 * @since 1.8
1165 */
1166 default V compute(K key,
1167 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1168 Objects.requireNonNull(remappingFunction);
1169 V oldValue = get(key);
1170
1171 V newValue = remappingFunction.apply(key, oldValue);
1172 if (newValue == null) {
1173 // delete mapping
1174 if (oldValue != null || containsKey(key)) {
1175 // something to remove
1176 remove(key);
1177 return null;
1178 } else {
1179 // nothing to do. Leave things as they were.
1180 return null;
1181 }
1182 } else {
1183 // add or replace old mapping
1184 put(key, newValue);
1185 return newValue;
1186 }
1187 }
1188
1189 /**
1190 * If the specified key is not already associated with a value or is
1191 * associated with null, associates it with the given non-null value.
1192 * Otherwise, replaces the associated value with the results of the given
1193 * remapping function, or removes if the result is {@code null}. This
1194 * method may be of use when combining multiple mapped values for a key.
1195 * For example, to either create or append a {@code String msg} to a
1196 * value mapping:
1197 *
1198 * <pre> {@code
1199 * map.merge(key, msg, String::concat)
1200 * }</pre>
1201 *
1202 * <p>If the remapping function returns {@code null}, the mapping is removed.
1203 * If the remapping function itself throws an (unchecked) exception, the
1204 * exception is rethrown, and the current mapping is left unchanged.
1205 *
1206 * <p>The remapping function should not modify this map during computation.
1207 *
1208 * @implSpec
1209 * The default implementation is equivalent to performing the following
1210 * steps for this {@code map}, then returning the current value or
1211 * {@code null} if absent:
1212 *
1213 * <pre> {@code
1214 * V oldValue = map.get(key);
1215 * V newValue = (oldValue == null) ? value :
1216 * remappingFunction.apply(oldValue, value);
1217 * if (newValue == null)
1218 * map.remove(key);
1219 * else
1220 * map.put(key, newValue);
1221 * }</pre>
1222 *
1223 * <p>The default implementation makes no guarantees about detecting if the
1224 * remapping function modifies this map during computation and, if
1225 * appropriate, reporting an error. Non-concurrent implementations should
1226 * override this method and, on a best-effort basis, throw a
1227 * {@code ConcurrentModificationException} if it is detected that the
1228 * remapping function modifies this map during computation. Concurrent
1229 * implementations should override this method and, on a best-effort basis,
1230 * throw an {@code IllegalStateException} if it is detected that the
1231 * remapping function modifies this map during computation and as a result
1232 * computation would never complete.
1233 *
1234 * <p>The default implementation makes no guarantees about synchronization
1235 * or atomicity properties of this method. Any implementation providing
1236 * atomicity guarantees must override this method and document its
1237 * concurrency properties. In particular, all implementations of
1238 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1239 * whether the remapping function is applied once atomically only if the
1240 * value is not present.
1241 *
1242 * @param key key with which the resulting value is to be associated
1243 * @param value the non-null value to be merged with the existing value
1244 * associated with the key or, if no existing value or a null value
1245 * is associated with the key, to be associated with the key
1246 * @param remappingFunction the remapping function to recompute a value if
1247 * present
1248 * @return the new value associated with the specified key, or null if no
1249 * value is associated with the key
1250 * @throws UnsupportedOperationException if the {@code put} operation
1251 * is not supported by this map
1252 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1253 * @throws ClassCastException if the class of the specified key or value
1254 * prevents it from being stored in this map
1255 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1256 * @throws IllegalArgumentException if some property of the specified key
1257 * or value prevents it from being stored in this map
1258 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1259 * @throws NullPointerException if the specified key is null and this map
1260 * does not support null keys or the value or remappingFunction is
1261 * null
1262 * @since 1.8
1263 */
1264 default V merge(K key, V value,
1265 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
1266 Objects.requireNonNull(remappingFunction);
1267 Objects.requireNonNull(value);
1268 V oldValue = get(key);
1269 V newValue = (oldValue == null) ? value :
1270 remappingFunction.apply(oldValue, value);
1271 if (newValue == null) {
1272 remove(key);
1273 } else {
1274 put(key, newValue);
1275 }
1276 return newValue;
1277 }
1278
1279 /**
1280 * Returns an unmodifiable map containing zero mappings.
1281 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
1282 *
1283 * @param <K> the {@code Map}'s key type
1284 * @param <V> the {@code Map}'s value type
1285 * @return an empty {@code Map}
1286 *
1287 * @since 9
1288 */
1289 static <K, V> Map<K, V> of() {
1290 return ImmutableCollections.emptyMap();
1291 }
1292
1293 /**
1294 * Returns an unmodifiable map containing a single mapping.
1295 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
1296 *
1297 * @param <K> the {@code Map}'s key type
1298 * @param <V> the {@code Map}'s value type
1299 * @param k1 the mapping's key
1300 * @param v1 the mapping's value
1301 * @return a {@code Map} containing the specified mapping
1302 * @throws NullPointerException if the key or the value is {@code null}
1303 *
1304 * @since 9
1305 */
1306 static <K, V> Map<K, V> of(K k1, V v1) {
1307 return new ImmutableCollections.Map1<>(k1, v1);
1308 }
1309
1310 /**
1311 * Returns an unmodifiable map containing two mappings.
1312 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
1313 *
1314 * @param <K> the {@code Map}'s key type
1315 * @param <V> the {@code Map}'s value type
1316 * @param k1 the first mapping's key
1317 * @param v1 the first mapping's value
1318 * @param k2 the second mapping's key
1319 * @param v2 the second mapping's value
1320 * @return a {@code Map} containing the specified mappings
1321 * @throws IllegalArgumentException if the keys are duplicates
1322 * @throws NullPointerException if any key or value is {@code null}
1323 *
1324 * @since 9
1325 */
1326 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2) {
1327 return new ImmutableCollections.MapN<>(k1, v1, k2, v2);
1328 }
1329
1330 /**
1331 * Returns an unmodifiable map containing three mappings.
1332 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
1333 *
1334 * @param <K> the {@code Map}'s key type
1335 * @param <V> the {@code Map}'s value type
1336 * @param k1 the first mapping's key
1337 * @param v1 the first mapping's value
1338 * @param k2 the second mapping's key
1339 * @param v2 the second mapping's value
1340 * @param k3 the third mapping's key
1341 * @param v3 the third mapping's value
1342 * @return a {@code Map} containing the specified mappings
1343 * @throws IllegalArgumentException if there are any duplicate keys
1344 * @throws NullPointerException if any key or value is {@code null}
1345 *
1346 * @since 9
1347 */
1348 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3) {
1349 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3);
1350 }
1351
1352 /**
1353 * Returns an unmodifiable map containing four mappings.
1354 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
1355 *
1356 * @param <K> the {@code Map}'s key type
1357 * @param <V> the {@code Map}'s value type
1358 * @param k1 the first mapping's key
1359 * @param v1 the first mapping's value
1360 * @param k2 the second mapping's key
1361 * @param v2 the second mapping's value
1362 * @param k3 the third mapping's key
1363 * @param v3 the third mapping's value
1364 * @param k4 the fourth mapping's key
1365 * @param v4 the fourth mapping's value
1366 * @return a {@code Map} containing the specified mappings
1367 * @throws IllegalArgumentException if there are any duplicate keys
1368 * @throws NullPointerException if any key or value is {@code null}
1369 *
1370 * @since 9
1371 */
1372 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
1373 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4);
1374 }
1375
1376 /**
1377 * Returns an unmodifiable map containing five mappings.
1378 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
1379 *
1380 * @param <K> the {@code Map}'s key type
1381 * @param <V> the {@code Map}'s value type
1382 * @param k1 the first mapping's key
1383 * @param v1 the first mapping's value
1384 * @param k2 the second mapping's key
1385 * @param v2 the second mapping's value
1386 * @param k3 the third mapping's key
1387 * @param v3 the third mapping's value
1388 * @param k4 the fourth mapping's key
1389 * @param v4 the fourth mapping's value
1390 * @param k5 the fifth mapping's key
1391 * @param v5 the fifth mapping's value
1392 * @return a {@code Map} containing the specified mappings
1393 * @throws IllegalArgumentException if there are any duplicate keys
1394 * @throws NullPointerException if any key or value is {@code null}
1395 *
1396 * @since 9
1397 */
1398 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
1399 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5);
1400 }
1401
1402 /**
1403 * Returns an unmodifiable map containing six mappings.
1404 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
1405 *
1406 * @param <K> the {@code Map}'s key type
1407 * @param <V> the {@code Map}'s value type
1408 * @param k1 the first mapping's key
1409 * @param v1 the first mapping's value
1410 * @param k2 the second mapping's key
1411 * @param v2 the second mapping's value
1412 * @param k3 the third mapping's key
1413 * @param v3 the third mapping's value
1414 * @param k4 the fourth mapping's key
1415 * @param v4 the fourth mapping's value
1416 * @param k5 the fifth mapping's key
1417 * @param v5 the fifth mapping's value
1418 * @param k6 the sixth mapping's key
1419 * @param v6 the sixth mapping's value
1420 * @return a {@code Map} containing the specified mappings
1421 * @throws IllegalArgumentException if there are any duplicate keys
1422 * @throws NullPointerException if any key or value is {@code null}
1423 *
1424 * @since 9
1425 */
1426 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
1427 K k6, V v6) {
1428 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
1429 k6, v6);
1430 }
1431
1432 /**
1433 * Returns an unmodifiable map containing seven mappings.
1434 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
1435 *
1436 * @param <K> the {@code Map}'s key type
1437 * @param <V> the {@code Map}'s value type
1438 * @param k1 the first mapping's key
1439 * @param v1 the first mapping's value
1440 * @param k2 the second mapping's key
1441 * @param v2 the second mapping's value
1442 * @param k3 the third mapping's key
1443 * @param v3 the third mapping's value
1444 * @param k4 the fourth mapping's key
1445 * @param v4 the fourth mapping's value
1446 * @param k5 the fifth mapping's key
1447 * @param v5 the fifth mapping's value
1448 * @param k6 the sixth mapping's key
1449 * @param v6 the sixth mapping's value
1450 * @param k7 the seventh mapping's key
1451 * @param v7 the seventh mapping's value
1452 * @return a {@code Map} containing the specified mappings
1453 * @throws IllegalArgumentException if there are any duplicate keys
1454 * @throws NullPointerException if any key or value is {@code null}
1455 *
1456 * @since 9
1457 */
1458 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
1459 K k6, V v6, K k7, V v7) {
1460 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
1461 k6, v6, k7, v7);
1462 }
1463
1464 /**
1465 * Returns an unmodifiable map containing eight mappings.
1466 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
1467 *
1468 * @param <K> the {@code Map}'s key type
1469 * @param <V> the {@code Map}'s value type
1470 * @param k1 the first mapping's key
1471 * @param v1 the first mapping's value
1472 * @param k2 the second mapping's key
1473 * @param v2 the second mapping's value
1474 * @param k3 the third mapping's key
1475 * @param v3 the third mapping's value
1476 * @param k4 the fourth mapping's key
1477 * @param v4 the fourth mapping's value
1478 * @param k5 the fifth mapping's key
1479 * @param v5 the fifth mapping's value
1480 * @param k6 the sixth mapping's key
1481 * @param v6 the sixth mapping's value
1482 * @param k7 the seventh mapping's key
1483 * @param v7 the seventh mapping's value
1484 * @param k8 the eighth mapping's key
1485 * @param v8 the eighth mapping's value
1486 * @return a {@code Map} containing the specified mappings
1487 * @throws IllegalArgumentException if there are any duplicate keys
1488 * @throws NullPointerException if any key or value is {@code null}
1489 *
1490 * @since 9
1491 */
1492 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
1493 K k6, V v6, K k7, V v7, K k8, V v8) {
1494 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
1495 k6, v6, k7, v7, k8, v8);
1496 }
1497
1498 /**
1499 * Returns an unmodifiable map containing nine mappings.
1500 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
1501 *
1502 * @param <K> the {@code Map}'s key type
1503 * @param <V> the {@code Map}'s value type
1504 * @param k1 the first mapping's key
1505 * @param v1 the first mapping's value
1506 * @param k2 the second mapping's key
1507 * @param v2 the second mapping's value
1508 * @param k3 the third mapping's key
1509 * @param v3 the third mapping's value
1510 * @param k4 the fourth mapping's key
1511 * @param v4 the fourth mapping's value
1512 * @param k5 the fifth mapping's key
1513 * @param v5 the fifth mapping's value
1514 * @param k6 the sixth mapping's key
1515 * @param v6 the sixth mapping's value
1516 * @param k7 the seventh mapping's key
1517 * @param v7 the seventh mapping's value
1518 * @param k8 the eighth mapping's key
1519 * @param v8 the eighth mapping's value
1520 * @param k9 the ninth mapping's key
1521 * @param v9 the ninth mapping's value
1522 * @return a {@code Map} containing the specified mappings
1523 * @throws IllegalArgumentException if there are any duplicate keys
1524 * @throws NullPointerException if any key or value is {@code null}
1525 *
1526 * @since 9
1527 */
1528 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
1529 K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9) {
1530 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
1531 k6, v6, k7, v7, k8, v8, k9, v9);
1532 }
1533
1534 /**
1535 * Returns an unmodifiable map containing ten mappings.
1536 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
1537 *
1538 * @param <K> the {@code Map}'s key type
1539 * @param <V> the {@code Map}'s value type
1540 * @param k1 the first mapping's key
1541 * @param v1 the first mapping's value
1542 * @param k2 the second mapping's key
1543 * @param v2 the second mapping's value
1544 * @param k3 the third mapping's key
1545 * @param v3 the third mapping's value
1546 * @param k4 the fourth mapping's key
1547 * @param v4 the fourth mapping's value
1548 * @param k5 the fifth mapping's key
1549 * @param v5 the fifth mapping's value
1550 * @param k6 the sixth mapping's key
1551 * @param v6 the sixth mapping's value
1552 * @param k7 the seventh mapping's key
1553 * @param v7 the seventh mapping's value
1554 * @param k8 the eighth mapping's key
1555 * @param v8 the eighth mapping's value
1556 * @param k9 the ninth mapping's key
1557 * @param v9 the ninth mapping's value
1558 * @param k10 the tenth mapping's key
1559 * @param v10 the tenth mapping's value
1560 * @return a {@code Map} containing the specified mappings
1561 * @throws IllegalArgumentException if there are any duplicate keys
1562 * @throws NullPointerException if any key or value is {@code null}
1563 *
1564 * @since 9
1565 */
1566 static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
1567 K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9, K k10, V v10) {
1568 return new ImmutableCollections.MapN<>(k1, v1, k2, v2, k3, v3, k4, v4, k5, v5,
1569 k6, v6, k7, v7, k8, v8, k9, v9, k10, v10);
1570 }
1571
1572 /**
1573 * Returns an unmodifiable map containing keys and values extracted from the given entries.
1574 * The entries themselves are not stored in the map.
1575 * See <a href="#unmodifiable">Unmodifiable Maps</a> for details.
1576 *
1577 * @apiNote
1578 * It is convenient to create the map entries using the {@link Map#entry Map.entry()} method.
1579 * For example,
1580 *
1581 * <pre>{@code
1582 * import static java.util.Map.entry;
1583 *
1584 * Map<Integer,String> map = Map.ofEntries(
1585 * entry(1, "a"),
1586 * entry(2, "b"),
1587 * entry(3, "c"),
1588 * ...
1589 * entry(26, "z"));
1590 * }</pre>
1591 *
1592 * @param <K> the {@code Map}'s key type
1593 * @param <V> the {@code Map}'s value type
1594 * @param entries {@code Map.Entry}s containing the keys and values from which the map is populated
1595 * @return a {@code Map} containing the specified mappings
1596 * @throws IllegalArgumentException if there are any duplicate keys
1597 * @throws NullPointerException if any entry, key, or value is {@code null}, or if
1598 * the {@code entries} array is {@code null}
1599 *
1600 * @see Map#entry Map.entry()
1601 * @since 9
1602 */
1603 @SafeVarargs
1604 @SuppressWarnings("varargs")
1605 static <K, V> Map<K, V> ofEntries(Entry<? extends K, ? extends V>... entries) {
1606 if (entries.length == 0) { // implicit null check of entries array
1607 return ImmutableCollections.emptyMap();
1608 } else if (entries.length == 1) {
1609 // implicit null check of the array slot
1610 return new ImmutableCollections.Map1<>(entries[0].getKey(),
1611 entries[0].getValue());
1612 } else {
1613 Object[] kva = new Object[entries.length << 1];
1614 int a = 0;
1615 for (Entry<? extends K, ? extends V> entry : entries) {
1616 // implicit null checks of each array slot
1617 kva[a++] = entry.getKey();
1618 kva[a++] = entry.getValue();
1619 }
1620 return new ImmutableCollections.MapN<>(kva);
1621 }
1622 }
1623
1624 /**
1625 * Returns an unmodifiable {@link Entry} containing the given key and value.
1626 * These entries are suitable for populating {@code Map} instances using the
1627 * {@link Map#ofEntries Map.ofEntries()} method.
1628 * The {@code Entry} instances created by this method have the following characteristics:
1629 *
1630 * <ul>
1631 * <li>They disallow {@code null} keys and values. Attempts to create them using a {@code null}
1632 * key or value result in {@code NullPointerException}.
1633 * <li>They are unmodifiable. Calls to {@link Entry#setValue Entry.setValue()}
1634 * on a returned {@code Entry} result in {@code UnsupportedOperationException}.
1635 * <li>They are not serializable.
1636 * <li>They are <a href="../lang/doc-files/ValueBased.html">value-based</a>.
1637 * Callers should make no assumptions about the identity of the returned instances.
1638 * This method is free to create new instances or reuse existing ones. Therefore,
1639 * identity-sensitive operations on these instances (reference equality ({@code ==}),
1640 * identity hash code, and synchronization) are unreliable and should be avoided.
1641 * </ul>
1642 *
1643 * @apiNote
1644 * For a serializable {@code Entry}, see {@link AbstractMap.SimpleEntry} or
1645 * {@link AbstractMap.SimpleImmutableEntry}.
1646 *
1647 * @param <K> the key's type
1648 * @param <V> the value's type
1649 * @param k the key
1650 * @param v the value
1651 * @return an {@code Entry} containing the specified key and value
1652 * @throws NullPointerException if the key or value is {@code null}
1653 *
1654 * @see Map#ofEntries Map.ofEntries()
1655 * @since 9
1656 */
1657 static <K, V> Entry<K, V> entry(K k, V v) {
1658 // KeyValueHolder checks for nulls
1659 return new KeyValueHolder<>(k, v);
1660 }
1661
1662 /**
1663 * Returns an <a href="#unmodifiable">unmodifiable Map</a> containing the entries
1664 * of the given Map. The given Map must not be null, and it must not contain any
1665 * null keys or values. If the given Map is subsequently modified, the returned
1666 * Map will not reflect such modifications.
1667 *
1668 * @implNote
1669 * If the given Map is an <a href="#unmodifiable">unmodifiable Map</a>,
1670 * calling copyOf will generally not create a copy.
1671 *
1672 * @param <K> the {@code Map}'s key type
1673 * @param <V> the {@code Map}'s value type
1674 * @param map a {@code Map} from which entries are drawn, must be non-null
1675 * @return a {@code Map} containing the entries of the given {@code Map}
1676 * @throws NullPointerException if map is null, or if it contains any null keys or values
1677 * @since 10
1678 */
1679 @SuppressWarnings({"rawtypes","unchecked"})
1680 static <K, V> Map<K, V> copyOf(Map<? extends K, ? extends V> map) {
1681 if (map instanceof ImmutableCollections.AbstractImmutableMap) {
1682 return (Map<K,V>)map;
1683 } else {
1684 return (Map<K,V>)Map.ofEntries(map.entrySet().toArray(new Entry[0]));
1685 }
1686 }
1687 }