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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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).
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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 name="immutable">Immutable Map Static Factory Methods</a></h2>
114 * <p>The {@link Map#of() Map.of()} and
115 * {@link Map#ofEntries(Map.Entry...) Map.ofEntries()}
116 * static factory methods provide a convenient way to create immutable maps.
117 * The {@code Map}
118 * instances created by these methods have the following characteristics:
119 *
120 * <ul>
121 * <li>They cannot be modified. Attempts to modify them result in
122 * an {@code UnsupportedOperationException}.
123 * <li>They are truly immutable only if the contained keys and values are themselves
124 * immutable. If a key or value is mutated, the behavior of the map is unspecified.
125 * <li>They disallow null keys and values. Attempts to create them with
126 * null keys or values result in {@code NullPointerException}.
127 * <li>They are serializable if all keys and values are serializable.
128 * <li>They reject duplicate keys at creation time. Duplicate keys
129 * passed to a static factory method result in {@code IllegalArgumentException}.
130 * </ul>
131 *
132 * <p>This interface is a member of the
133 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
134 * Java Collections Framework</a>.
135 *
136 * @param <K> the type of keys maintained by this map
137 * @param <V> the type of mapped values
138 *
139 * @author Josh Bloch
140 * @see HashMap
141 * @see TreeMap
142 * @see Hashtable
143 * @see SortedMap
144 * @see Collection
145 * @see Set
146 * @since 1.2
147 */
148 public interface Map<K,V> {
149 // Query Operations
150
151 /**
152 * Returns the number of key-value mappings in this map. If the
153 * map contains more than {@code Integer.MAX_VALUE} elements, returns
154 * {@code Integer.MAX_VALUE}.
155 *
156 * @return the number of key-value mappings in this map
157 */
158 int size();
159
160 /**
161 * Returns {@code true} if this map contains no key-value mappings.
162 *
163 * @return {@code true} if this map contains no key-value mappings
164 */
165 boolean isEmpty();
166
167 /**
168 * Returns {@code true} if this map contains a mapping for the specified
169 * key. More formally, returns {@code true} if and only if
170 * this map contains a mapping for a key {@code k} such that
171 * {@code Objects.equals(key, k)}. (There can be
172 * at most one such mapping.)
173 *
174 * @param key key whose presence in this map is to be tested
175 * @return {@code true} if this map contains a mapping for the specified
176 * key
177 * @throws ClassCastException if the key is of an inappropriate type for
178 * this map
179 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
180 * @throws NullPointerException if the specified key is null and this map
181 * does not permit null keys
182 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
183 */
184 boolean containsKey(Object key);
185
186 /**
187 * Returns {@code true} if this map maps one or more keys to the
188 * specified value. More formally, returns {@code true} if and only if
189 * this map contains at least one mapping to a value {@code v} such that
190 * {@code Objects.equals(value, v)}. This operation
191 * will probably require time linear in the map size for most
192 * implementations of the {@code Map} interface.
193 *
194 * @param value value whose presence in this map is to be tested
195 * @return {@code true} if this map maps one or more keys to the
196 * specified value
197 * @throws ClassCastException if the value is of an inappropriate type for
198 * this map
199 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
200 * @throws NullPointerException if the specified value is null and this
201 * map does not permit null values
202 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
203 */
204 boolean containsValue(Object value);
205
206 /**
207 * Returns the value to which the specified key is mapped,
208 * or {@code null} if this map contains no mapping for the key.
209 *
210 * <p>More formally, if this map contains a mapping from a key
211 * {@code k} to a value {@code v} such that
212 * {@code Objects.equals(key, k)},
213 * then this method returns {@code v}; otherwise
214 * it returns {@code null}. (There can be at most one such mapping.)
215 *
216 * <p>If this map permits null values, then a return value of
217 * {@code null} does not <i>necessarily</i> indicate that the map
218 * contains no mapping for the key; it's also possible that the map
219 * explicitly maps the key to {@code null}. The {@link #containsKey
220 * containsKey} operation may be used to distinguish these two cases.
221 *
222 * @param key the key whose associated value is to be returned
223 * @return the value to which the specified key is mapped, or
224 * {@code null} if this map contains no mapping for the key
225 * @throws ClassCastException if the key is of an inappropriate type for
226 * this map
227 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
228 * @throws NullPointerException if the specified key is null and this map
229 * does not permit null keys
230 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
231 */
232 V get(Object key);
233
234 // Modification Operations
235
236 /**
237 * Associates the specified value with the specified key in this map
238 * (optional operation). If the map previously contained a mapping for
239 * the key, the old value is replaced by the specified value. (A map
240 * {@code m} is said to contain a mapping for a key {@code k} if and only
241 * if {@link #containsKey(Object) m.containsKey(k)} would return
242 * {@code true}.)
243 *
244 * @param key key with which the specified value is to be associated
245 * @param value value to be associated with the specified key
246 * @return the previous value associated with {@code key}, or
247 * {@code null} if there was no mapping for {@code key}.
248 * (A {@code null} return can also indicate that the map
249 * previously associated {@code null} with {@code key},
250 * if the implementation supports {@code null} values.)
251 * @throws UnsupportedOperationException if the {@code put} operation
252 * is not supported by this map
253 * @throws ClassCastException if the class of the specified key or value
254 * prevents it from being stored in this map
255 * @throws NullPointerException if the specified key or value is null
256 * and this map does not permit null keys or values
257 * @throws IllegalArgumentException if some property of the specified key
258 * or value prevents it from being stored in this map
259 */
260 V put(K key, V value);
261
262 /**
263 * Removes the mapping for a key from this map if it is present
264 * (optional operation). More formally, if this map contains a mapping
265 * from key {@code k} to value {@code v} such that
266 * {@code Objects.equals(key, k)}, that mapping
267 * is removed. (The map can contain at most one such mapping.)
268 *
269 * <p>Returns the value to which this map previously associated the key,
270 * or {@code null} if the map contained no mapping for the key.
271 *
272 * <p>If this map permits null values, then a return value of
273 * {@code null} does not <i>necessarily</i> indicate that the map
274 * contained no mapping for the key; it's also possible that the map
275 * explicitly mapped the key to {@code null}.
276 *
277 * <p>The map will not contain a mapping for the specified key once the
278 * call returns.
279 *
280 * @param key key whose mapping is to be removed from the map
281 * @return the previous value associated with {@code key}, or
282 * {@code null} if there was no mapping for {@code key}.
283 * @throws UnsupportedOperationException if the {@code remove} operation
284 * is not supported by this map
285 * @throws ClassCastException if the key is of an inappropriate type for
286 * this map
287 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
288 * @throws NullPointerException if the specified key is null and this
289 * map does not permit null keys
290 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
291 */
292 V remove(Object key);
293
294
295 // Bulk Operations
296
297 /**
298 * Copies all of the mappings from the specified map to this map
299 * (optional operation). The effect of this call is equivalent to that
300 * of calling {@link #put(Object,Object) put(k, v)} on this map once
301 * for each mapping from key {@code k} to value {@code v} in the
302 * specified map. The behavior of this operation is undefined if the
303 * specified map is modified while the operation is in progress.
304 *
305 * @param m mappings to be stored in this map
306 * @throws UnsupportedOperationException if the {@code putAll} operation
307 * is not supported by this map
308 * @throws ClassCastException if the class of a key or value in the
309 * specified map prevents it from being stored in this map
310 * @throws NullPointerException if the specified map is null, or if
311 * this map does not permit null keys or values, and the
312 * specified map contains null keys or values
313 * @throws IllegalArgumentException if some property of a key or value in
314 * the specified map prevents it from being stored in this map
315 */
316 void putAll(Map<? extends K, ? extends V> m);
317
318 /**
319 * Removes all of the mappings from this map (optional operation).
320 * The map will be empty after this call returns.
321 *
322 * @throws UnsupportedOperationException if the {@code clear} operation
323 * is not supported by this map
324 */
325 void clear();
326
327
328 // Views
329
330 /**
331 * Returns a {@link Set} view of the keys contained in this map.
332 * The set is backed by the map, so changes to the map are
333 * reflected in the set, and vice-versa. If the map is modified
334 * while an iteration over the set is in progress (except through
335 * the iterator's own {@code remove} operation), the results of
336 * the iteration are undefined. The set supports element removal,
337 * which removes the corresponding mapping from the map, via the
338 * {@code Iterator.remove}, {@code Set.remove},
339 * {@code removeAll}, {@code retainAll}, and {@code clear}
340 * operations. It does not support the {@code add} or {@code addAll}
341 * operations.
342 *
343 * @return a set view of the keys contained in this map
344 */
345 Set<K> keySet();
346
347 /**
348 * Returns a {@link Collection} view of the values contained in this map.
349 * The collection is backed by the map, so changes to the map are
350 * reflected in the collection, and vice-versa. If the map is
351 * modified while an iteration over the collection is in progress
352 * (except through the iterator's own {@code remove} operation),
353 * the results of the iteration are undefined. The collection
354 * supports element removal, which removes the corresponding
355 * mapping from the map, via the {@code Iterator.remove},
356 * {@code Collection.remove}, {@code removeAll},
357 * {@code retainAll} and {@code clear} operations. It does not
358 * support the {@code add} or {@code addAll} operations.
359 *
360 * @return a collection view of the values contained in this map
361 */
362 Collection<V> values();
363
364 /**
365 * Returns a {@link Set} view of the mappings contained in this map.
366 * The set is backed by the map, so changes to the map are
367 * reflected in the set, and vice-versa. If the map is modified
368 * while an iteration over the set is in progress (except through
369 * the iterator's own {@code remove} operation, or through the
370 * {@code setValue} operation on a map entry returned by the
371 * iterator) the results of the iteration are undefined. The set
372 * supports element removal, which removes the corresponding
373 * mapping from the map, via the {@code Iterator.remove},
374 * {@code Set.remove}, {@code removeAll}, {@code retainAll} and
375 * {@code clear} operations. It does not support the
376 * {@code add} or {@code addAll} operations.
377 *
378 * @return a set view of the mappings contained in this map
379 */
380 Set<Map.Entry<K, V>> entrySet();
381
382 /**
383 * A map entry (key-value pair). The {@code Map.entrySet} method returns
384 * a collection-view of the map, whose elements are of this class. The
385 * <i>only</i> way to obtain a reference to a map entry is from the
386 * iterator of this collection-view. These {@code Map.Entry} objects are
387 * valid <i>only</i> for the duration of the iteration; more formally,
388 * the behavior of a map entry is undefined if the backing map has been
389 * modified after the entry was returned by the iterator, except through
390 * the {@code setValue} operation on the map entry.
391 *
392 * @see Map#entrySet()
393 * @since 1.2
394 */
395 interface Entry<K,V> {
396 /**
397 * Returns the key corresponding to this entry.
398 *
399 * @return the key corresponding to this entry
400 * @throws IllegalStateException implementations may, but are not
401 * required to, throw this exception if the entry has been
402 * removed from the backing map.
403 */
404 K getKey();
405
406 /**
407 * Returns the value corresponding to this entry. If the mapping
408 * has been removed from the backing map (by the iterator's
409 * {@code remove} operation), the results of this call are undefined.
410 *
411 * @return the value corresponding to this entry
412 * @throws IllegalStateException implementations may, but are not
413 * required to, throw this exception if the entry has been
414 * removed from the backing map.
415 */
416 V getValue();
417
418 /**
419 * Replaces the value corresponding to this entry with the specified
420 * value (optional operation). (Writes through to the map.) The
421 * behavior of this call is undefined if the mapping has already been
422 * removed from the map (by the iterator's {@code remove} operation).
423 *
424 * @param value new value to be stored in this entry
425 * @return old value corresponding to the entry
426 * @throws UnsupportedOperationException if the {@code put} operation
427 * is not supported by the backing map
428 * @throws ClassCastException if the class of the specified value
429 * prevents it from being stored in the backing map
430 * @throws NullPointerException if the backing map does not permit
431 * null values, and the specified value is null
432 * @throws IllegalArgumentException if some property of this value
433 * prevents it from being stored in the backing map
434 * @throws IllegalStateException implementations may, but are not
435 * required to, throw this exception if the entry has been
436 * removed from the backing map.
437 */
438 V setValue(V value);
439
440 /**
441 * Compares the specified object with this entry for equality.
442 * Returns {@code true} if the given object is also a map entry and
443 * the two entries represent the same mapping. More formally, two
444 * entries {@code e1} and {@code e2} represent the same mapping
445 * if<pre>
446 * (e1.getKey()==null ?
447 * e2.getKey()==null : e1.getKey().equals(e2.getKey())) &&
448 * (e1.getValue()==null ?
449 * e2.getValue()==null : e1.getValue().equals(e2.getValue()))
450 * </pre>
451 * This ensures that the {@code equals} method works properly across
452 * different implementations of the {@code Map.Entry} interface.
453 *
454 * @param o object to be compared for equality with this map entry
455 * @return {@code true} if the specified object is equal to this map
456 * entry
457 */
458 boolean equals(Object o);
459
460 /**
461 * Returns the hash code value for this map entry. The hash code
462 * of a map entry {@code e} is defined to be: <pre>
463 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
464 * (e.getValue()==null ? 0 : e.getValue().hashCode())
465 * </pre>
466 * This ensures that {@code e1.equals(e2)} implies that
467 * {@code e1.hashCode()==e2.hashCode()} for any two Entries
468 * {@code e1} and {@code e2}, as required by the general
469 * contract of {@code Object.hashCode}.
470 *
471 * @return the hash code value for this map entry
472 * @see Object#hashCode()
473 * @see Object#equals(Object)
474 * @see #equals(Object)
475 */
476 int hashCode();
477
478 /**
479 * Returns a comparator that compares {@link Map.Entry} in natural order on key.
480 *
481 * <p>The returned comparator is serializable and throws {@link
482 * NullPointerException} when comparing an entry with a null key.
483 *
484 * @param <K> the {@link Comparable} type of then map keys
485 * @param <V> the type of the map values
486 * @return a comparator that compares {@link Map.Entry} in natural order on key.
487 * @see Comparable
488 * @since 1.8
489 */
490 public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K,V>> comparingByKey() {
491 return (Comparator<Map.Entry<K, V>> & Serializable)
492 (c1, c2) -> c1.getKey().compareTo(c2.getKey());
493 }
494
495 /**
496 * Returns a comparator that compares {@link Map.Entry} in natural order on value.
497 *
498 * <p>The returned comparator is serializable and throws {@link
499 * NullPointerException} when comparing an entry with null values.
500 *
501 * @param <K> the type of the map keys
502 * @param <V> the {@link Comparable} type of the map values
503 * @return a comparator that compares {@link Map.Entry} in natural order on value.
504 * @see Comparable
505 * @since 1.8
506 */
507 public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K,V>> comparingByValue() {
508 return (Comparator<Map.Entry<K, V>> & Serializable)
509 (c1, c2) -> c1.getValue().compareTo(c2.getValue());
510 }
511
512 /**
513 * Returns a comparator that compares {@link Map.Entry} by key using the given
514 * {@link Comparator}.
515 *
516 * <p>The returned comparator is serializable if the specified comparator
517 * is also serializable.
518 *
519 * @param <K> the type of the map keys
520 * @param <V> the type of the map values
521 * @param cmp the key {@link Comparator}
522 * @return a comparator that compares {@link Map.Entry} by the key.
523 * @since 1.8
524 */
525 public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) {
526 Objects.requireNonNull(cmp);
527 return (Comparator<Map.Entry<K, V>> & Serializable)
528 (c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());
529 }
530
531 /**
532 * Returns a comparator that compares {@link Map.Entry} by value using the given
533 * {@link Comparator}.
534 *
535 * <p>The returned comparator is serializable if the specified comparator
536 * is also serializable.
537 *
538 * @param <K> the type of the map keys
539 * @param <V> the type of the map values
540 * @param cmp the value {@link Comparator}
541 * @return a comparator that compares {@link Map.Entry} by the value.
542 * @since 1.8
543 */
544 public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) {
545 Objects.requireNonNull(cmp);
546 return (Comparator<Map.Entry<K, V>> & Serializable)
547 (c1, c2) -> cmp.compare(c1.getValue(), c2.getValue());
548 }
549 }
550
551 // Comparison and hashing
552
553 /**
554 * Compares the specified object with this map for equality. Returns
555 * {@code true} if the given object is also a map and the two maps
556 * represent the same mappings. More formally, two maps {@code m1} and
557 * {@code m2} represent the same mappings if
558 * {@code m1.entrySet().equals(m2.entrySet())}. This ensures that the
559 * {@code equals} method works properly across different implementations
560 * of the {@code Map} interface.
561 *
562 * @param o object to be compared for equality with this map
563 * @return {@code true} if the specified object is equal to this map
564 */
565 boolean equals(Object o);
566
567 /**
568 * Returns the hash code value for this map. The hash code of a map is
569 * defined to be the sum of the hash codes of each entry in the map's
570 * {@code entrySet()} view. This ensures that {@code m1.equals(m2)}
571 * implies that {@code m1.hashCode()==m2.hashCode()} for any two maps
572 * {@code m1} and {@code m2}, as required by the general contract of
573 * {@link Object#hashCode}.
574 *
575 * @return the hash code value for this map
576 * @see Map.Entry#hashCode()
577 * @see Object#equals(Object)
578 * @see #equals(Object)
579 */
580 int hashCode();
581
582 // Defaultable methods
583
584 /**
585 * Returns the value to which the specified key is mapped, or
586 * {@code defaultValue} if this map contains no mapping for the key.
587 *
588 * @implSpec
589 * The default implementation makes no guarantees about synchronization
590 * or atomicity properties of this method. Any implementation providing
591 * atomicity guarantees must override this method and document its
592 * concurrency properties.
593 *
594 * @param key the key whose associated value is to be returned
595 * @param defaultValue the default mapping of the key
596 * @return the value to which the specified key is mapped, or
597 * {@code defaultValue} if this map contains no mapping for the key
598 * @throws ClassCastException if the key is of an inappropriate type for
599 * this map
600 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
601 * @throws NullPointerException if the specified key is null and this map
602 * does not permit null keys
603 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
604 * @since 1.8
605 */
606 default V getOrDefault(Object key, V defaultValue) {
607 V v;
608 return (((v = get(key)) != null) || containsKey(key))
609 ? v
610 : defaultValue;
611 }
612
613 /**
614 * Performs the given action for each entry in this map until all entries
615 * have been processed or the action throws an exception. Unless
616 * otherwise specified by the implementing class, actions are performed in
617 * the order of entry set iteration (if an iteration order is specified.)
618 * Exceptions thrown by the action are relayed to the caller.
619 *
620 * @implSpec
621 * The default implementation is equivalent to, for this {@code map}:
622 * <pre> {@code
623 * for (Map.Entry<K, V> entry : map.entrySet())
624 * action.accept(entry.getKey(), entry.getValue());
625 * }</pre>
626 *
627 * The default implementation makes no guarantees about synchronization
628 * or atomicity properties of this method. Any implementation providing
629 * atomicity guarantees must override this method and document its
630 * concurrency properties.
631 *
632 * @param action The action to be performed for each entry
633 * @throws NullPointerException if the specified action is null
634 * @throws ConcurrentModificationException if an entry is found to be
635 * removed during iteration
636 * @since 1.8
637 */
638 default void forEach(BiConsumer<? super K, ? super V> action) {
639 Objects.requireNonNull(action);
640 for (Map.Entry<K, V> entry : entrySet()) {
641 K k;
642 V v;
643 try {
644 k = entry.getKey();
645 v = entry.getValue();
646 } catch(IllegalStateException ise) {
647 // this usually means the entry is no longer in the map.
648 throw new ConcurrentModificationException(ise);
649 }
650 action.accept(k, v);
651 }
652 }
653
654 /**
655 * Replaces each entry's value with the result of invoking the given
656 * function on that entry until all entries have been processed or the
657 * function throws an exception. Exceptions thrown by the function are
658 * relayed to the caller.
659 *
660 * @implSpec
661 * <p>The default implementation is equivalent to, for this {@code map}:
662 * <pre> {@code
663 * for (Map.Entry<K, V> entry : map.entrySet())
664 * entry.setValue(function.apply(entry.getKey(), entry.getValue()));
665 * }</pre>
666 *
667 * <p>The default implementation makes no guarantees about synchronization
668 * or atomicity properties of this method. Any implementation providing
669 * atomicity guarantees must override this method and document its
670 * concurrency properties.
671 *
672 * @param function the function to apply to each entry
673 * @throws UnsupportedOperationException if the {@code set} operation
674 * is not supported by this map's entry set iterator.
675 * @throws ClassCastException if the class of a replacement value
676 * prevents it from being stored in this map
677 * @throws NullPointerException if the specified function is null, or the
678 * specified replacement value is null, and this map does not permit null
679 * values
680 * @throws ClassCastException if a replacement value is of an inappropriate
681 * type for this map
682 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
683 * @throws NullPointerException if function or a replacement value is null,
684 * and this map does not permit null keys or values
685 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
686 * @throws IllegalArgumentException if some property of a replacement value
687 * prevents it from being stored in this map
688 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
689 * @throws ConcurrentModificationException if an entry is found to be
690 * removed during iteration
691 * @since 1.8
692 */
693 default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
694 Objects.requireNonNull(function);
695 for (Map.Entry<K, V> entry : entrySet()) {
696 K k;
697 V v;
698 try {
699 k = entry.getKey();
700 v = entry.getValue();
701 } catch(IllegalStateException ise) {
702 // this usually means the entry is no longer in the map.
703 throw new ConcurrentModificationException(ise);
704 }
705
706 // ise thrown from function is not a cme.
707 v = function.apply(k, v);
708
709 try {
710 entry.setValue(v);
711 } catch(IllegalStateException ise) {
712 // this usually means the entry is no longer in the map.
713 throw new ConcurrentModificationException(ise);
714 }
715 }
716 }
717
718 /**
719 * If the specified key is not already associated with a value (or is mapped
720 * to {@code null}) associates it with the given value and returns
721 * {@code null}, else returns the current value.
722 *
723 * @implSpec
724 * The default implementation is equivalent to, for this {@code
725 * map}:
726 *
727 * <pre> {@code
728 * V v = map.get(key);
729 * if (v == null)
730 * v = map.put(key, value);
731 *
732 * return v;
733 * }</pre>
734 *
735 * <p>The default implementation makes no guarantees about synchronization
736 * or atomicity properties of this method. Any implementation providing
737 * atomicity guarantees must override this method and document its
738 * concurrency properties.
739 *
740 * @param key key with which the specified value is to be associated
741 * @param value value to be associated with the specified key
742 * @return the previous value associated with the specified key, or
743 * {@code null} if there was no mapping for the key.
744 * (A {@code null} return can also indicate that the map
745 * previously associated {@code null} with the key,
746 * if the implementation supports null values.)
747 * @throws UnsupportedOperationException if the {@code put} operation
748 * is not supported by this map
749 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
750 * @throws ClassCastException if the key or value is of an inappropriate
751 * type for this map
752 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
753 * @throws NullPointerException if the specified key or value is null,
754 * and this map does not permit null keys or values
755 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
756 * @throws IllegalArgumentException if some property of the specified key
757 * or value prevents it from being stored in this map
758 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
759 * @since 1.8
760 */
761 default V putIfAbsent(K key, V value) {
762 V v = get(key);
763 if (v == null) {
764 v = put(key, value);
765 }
766
767 return v;
768 }
769
770 /**
771 * Removes the entry for the specified key only if it is currently
772 * mapped to the specified value.
773 *
774 * @implSpec
775 * The default implementation is equivalent to, for this {@code map}:
776 *
777 * <pre> {@code
778 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
779 * map.remove(key);
780 * return true;
781 * } else
782 * return false;
783 * }</pre>
784 *
785 * <p>The default implementation makes no guarantees about synchronization
786 * or atomicity properties of this method. Any implementation providing
787 * atomicity guarantees must override this method and document its
788 * concurrency properties.
789 *
790 * @param key key with which the specified value is associated
791 * @param value value expected to be associated with the specified key
792 * @return {@code true} if the value was removed
793 * @throws UnsupportedOperationException if the {@code remove} operation
794 * is not supported by this map
795 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
796 * @throws ClassCastException if the key or value is of an inappropriate
797 * type for this map
798 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
799 * @throws NullPointerException if the specified key or value is null,
800 * and this map does not permit null keys or values
801 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
802 * @since 1.8
803 */
804 default boolean remove(Object key, Object value) {
805 Object curValue = get(key);
806 if (!Objects.equals(curValue, value) ||
807 (curValue == null && !containsKey(key))) {
808 return false;
809 }
810 remove(key);
811 return true;
812 }
813
814 /**
815 * Replaces the entry for the specified key only if currently
816 * mapped to the specified value.
817 *
818 * @implSpec
819 * The default implementation is equivalent to, for this {@code map}:
820 *
821 * <pre> {@code
822 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
823 * map.put(key, newValue);
824 * return true;
825 * } else
826 * return false;
827 * }</pre>
828 *
829 * The default implementation does not throw NullPointerException
830 * for maps that do not support null values if oldValue is null unless
831 * newValue is also null.
832 *
833 * <p>The default implementation makes no guarantees about synchronization
834 * or atomicity properties of this method. Any implementation providing
835 * atomicity guarantees must override this method and document its
836 * concurrency properties.
837 *
838 * @param key key with which the specified value is associated
839 * @param oldValue value expected to be associated with the specified key
840 * @param newValue value to be associated with the specified key
841 * @return {@code true} if the value was replaced
842 * @throws UnsupportedOperationException if the {@code put} operation
843 * is not supported by this map
844 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
845 * @throws ClassCastException if the class of a specified key or value
846 * prevents it from being stored in this map
847 * @throws NullPointerException if a specified key or newValue is null,
848 * and this map does not permit null keys or values
849 * @throws NullPointerException if oldValue is null and this map does not
850 * permit null values
851 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
852 * @throws IllegalArgumentException if some property of a specified key
853 * or value prevents it from being stored in this map
854 * @since 1.8
855 */
856 default boolean replace(K key, V oldValue, V newValue) {
857 Object curValue = get(key);
858 if (!Objects.equals(curValue, oldValue) ||
859 (curValue == null && !containsKey(key))) {
860 return false;
861 }
862 put(key, newValue);
863 return true;
864 }
865
866 /**
867 * Replaces the entry for the specified key only if it is
868 * currently mapped to some value.
869 *
870 * @implSpec
871 * The default implementation is equivalent to, for this {@code map}:
872 *
873 * <pre> {@code
874 * if (map.containsKey(key)) {
875 * return map.put(key, value);
876 * } else
877 * return null;
878 * }</pre>
879 *
880 * <p>The default implementation makes no guarantees about synchronization
881 * or atomicity properties of this method. Any implementation providing
882 * atomicity guarantees must override this method and document its
883 * concurrency properties.
884 *
885 * @param key key with which the specified value is associated
886 * @param value value to be associated with the specified key
887 * @return the previous value associated with the specified key, or
888 * {@code null} if there was no mapping for the key.
889 * (A {@code null} return can also indicate that the map
890 * previously associated {@code null} with the key,
891 * if the implementation supports null values.)
892 * @throws UnsupportedOperationException if the {@code put} operation
893 * is not supported by this map
894 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
895 * @throws ClassCastException if the class of the specified key or value
896 * prevents it from being stored in this map
897 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
898 * @throws NullPointerException if the specified key or value is null,
899 * and this map does not permit null keys or values
900 * @throws IllegalArgumentException if some property of the specified key
901 * or value prevents it from being stored in this map
902 * @since 1.8
903 */
904 default V replace(K key, V value) {
905 V curValue;
906 if (((curValue = get(key)) != null) || containsKey(key)) {
907 curValue = put(key, value);
908 }
909 return curValue;
910 }
911
912 /**
913 * If the specified key is not already associated with a value (or is mapped
914 * to {@code null}), attempts to compute its value using the given mapping
915 * function and enters it into this map unless {@code null}.
916 *
917 * <p>If the mapping function returns {@code null}, no mapping is recorded.
918 * If the mapping function itself throws an (unchecked) exception, the
919 * exception is rethrown, and no mapping is recorded. The most
920 * common usage is to construct a new object serving as an initial
921 * mapped value or memoized result, as in:
922 *
923 * <pre> {@code
924 * map.computeIfAbsent(key, k -> new Value(f(k)));
925 * }</pre>
926 *
927 * <p>Or to implement a multi-value map, {@code Map<K,Collection<V>>},
928 * supporting multiple values per key:
929 *
930 * <pre> {@code
931 * map.computeIfAbsent(key, k -> new HashSet<V>()).add(v);
932 * }</pre>
933 *
934 * <p>The mapping function should not modify this map during computation.
935 *
936 * @implSpec
937 * The default implementation is equivalent to the following steps for this
938 * {@code map}, then returning the current value or {@code null} if now
939 * absent:
940 *
941 * <pre> {@code
942 * if (map.get(key) == null) {
943 * V newValue = mappingFunction.apply(key);
944 * if (newValue != null)
945 * map.put(key, newValue);
946 * }
947 * }</pre>
948 *
949 * <p>The default implementation makes no guarantees about detecting if the
950 * mapping function modifies this map during computation and, if
951 * appropriate, reporting an error. Non-concurrent implementations should
952 * override this method and, on a best-effort basis, throw a
953 * {@code ConcurrentModificationException} if it is detected that the
954 * mapping function modifies this map during computation. Concurrent
955 * implementations should override this method and, on a best-effort basis,
956 * throw an {@code IllegalStateException} if it is detected that the
957 * mapping function modifies this map during computation and as a result
958 * computation would never complete.
959 *
960 * <p>The default implementation makes no guarantees about synchronization
961 * or atomicity properties of this method. Any implementation providing
962 * atomicity guarantees must override this method and document its
963 * concurrency properties. In particular, all implementations of
964 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
965 * whether the mapping function is applied once atomically only if the value
966 * is not present.
967 *
968 * @param key key with which the specified value is to be associated
969 * @param mappingFunction the mapping function to compute a value
970 * @return the current (existing or computed) value associated with
971 * the specified key, or null if the computed value is null
972 * @throws NullPointerException if the specified key is null and
973 * this map does not support null keys, or the mappingFunction
974 * is null
975 * @throws UnsupportedOperationException if the {@code put} operation
976 * is not supported by this map
977 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
978 * @throws ClassCastException if the class of the specified key or value
979 * prevents it from being stored in this map
980 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
981 * @since 1.8
982 */
983 default V computeIfAbsent(K key,
984 Function<? super K, ? extends V> mappingFunction) {
985 Objects.requireNonNull(mappingFunction);
986 V v;
987 if ((v = get(key)) == null) {
988 V newValue;
989 if ((newValue = mappingFunction.apply(key)) != null) {
990 put(key, newValue);
991 return newValue;
992 }
993 }
994
995 return v;
996 }
997
998 /**
999 * If the value for the specified key is present and non-null, attempts to
1000 * compute a new mapping given the key and its current mapped value.
1001 *
1002 * <p>If the remapping function returns {@code null}, the mapping is removed.
1003 * If the remapping function itself throws an (unchecked) exception, the
1004 * exception is rethrown, and the current mapping is left unchanged.
1005 *
1006 * <p>The remapping function should not modify this map during computation.
1007 *
1008 * @implSpec
1009 * The default implementation is equivalent to performing the following
1010 * steps for this {@code map}, then returning the current value or
1011 * {@code null} if now absent:
1012 *
1013 * <pre> {@code
1014 * if (map.get(key) != null) {
1015 * V oldValue = map.get(key);
1016 * V newValue = remappingFunction.apply(key, oldValue);
1017 * if (newValue != null)
1018 * map.put(key, newValue);
1019 * else
1020 * map.remove(key);
1021 * }
1022 * }</pre>
1023 *
1024 * <p>The default implementation makes no guarantees about detecting if the
1025 * remapping function modifies this map during computation and, if
1026 * appropriate, reporting an error. Non-concurrent implementations should
1027 * override this method and, on a best-effort basis, throw a
1028 * {@code ConcurrentModificationException} if it is detected that the
1029 * remapping function modifies this map during computation. Concurrent
1030 * implementations should override this method and, on a best-effort basis,
1031 * throw an {@code IllegalStateException} if it is detected that the
1032 * remapping function modifies this map during computation and as a result
1033 * computation would never complete.
1034 *
1035 * <p>The default implementation makes no guarantees about synchronization
1036 * or atomicity properties of this method. Any implementation providing
1037 * atomicity guarantees must override this method and document its
1038 * concurrency properties. In particular, all implementations of
1039 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1040 * whether the remapping function is applied once atomically only if the
1041 * value is not present.
1042 *
1043 * @param key key with which the specified value is to be associated
1044 * @param remappingFunction the remapping function to compute a value
1045 * @return the new value associated with the specified key, or null if none
1046 * @throws NullPointerException if the specified key is null and
1047 * this map does not support null keys, or the
1048 * remappingFunction is null
1049 * @throws UnsupportedOperationException if the {@code put} operation
1050 * is not supported by this map
1051 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1052 * @throws ClassCastException if the class of the specified key or value
1053 * prevents it from being stored in this map
1054 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1055 * @since 1.8
1056 */
1057 default V computeIfPresent(K key,
1058 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1059 Objects.requireNonNull(remappingFunction);
1060 V oldValue;
1061 if ((oldValue = get(key)) != null) {
1062 V newValue = remappingFunction.apply(key, oldValue);
1063 if (newValue != null) {
1064 put(key, newValue);
1065 return newValue;
1066 } else {
1067 remove(key);
1068 return null;
1069 }
1070 } else {
1071 return null;
1072 }
1073 }
1074
1075 /**
1076 * Attempts to compute a mapping for the specified key and its current
1077 * mapped value (or {@code null} if there is no current mapping). For
1078 * example, to either create or append a {@code String} msg to a value
1079 * mapping:
1080 *
1081 * <pre> {@code
1082 * map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))}</pre>
1083 * (Method {@link #merge merge()} is often simpler to use for such purposes.)
1084 *
1085 * <p>If the remapping function returns {@code null}, the mapping is removed
1086 * (or remains absent if initially absent). If the remapping function
1087 * itself throws an (unchecked) exception, the exception is rethrown, and
1088 * the current mapping is left unchanged.
1089 *
1090 * <p>The remapping function should not modify this map during computation.
1091 *
1092 * @implSpec
1093 * The default implementation is equivalent to performing the following
1094 * steps for this {@code map}, then returning the current value or
1095 * {@code null} if absent:
1096 *
1097 * <pre> {@code
1098 * V oldValue = map.get(key);
1099 * V newValue = remappingFunction.apply(key, oldValue);
1100 * if (oldValue != null ) {
1101 * if (newValue != null)
1102 * map.put(key, newValue);
1103 * else
1104 * map.remove(key);
1105 * } else {
1106 * if (newValue != null)
1107 * map.put(key, newValue);
1108 * else
1109 * return null;
1110 * }
1111 * }</pre>
1112 *
1113 * <p>The default implementation makes no guarantees about detecting if the
1114 * remapping function modifies this map during computation and, if
1115 * appropriate, reporting an error. Non-concurrent implementations should
1116 * override this method and, on a best-effort basis, throw a
1117 * {@code ConcurrentModificationException} if it is detected that the
1118 * remapping function modifies this map during computation. Concurrent
1119 * implementations should override this method and, on a best-effort basis,
1120 * throw an {@code IllegalStateException} if it is detected that the
1121 * remapping function modifies this map during computation and as a result
1122 * computation would never complete.
1123 *
1124 * <p>The default implementation makes no guarantees about synchronization
1125 * or atomicity properties of this method. Any implementation providing
1126 * atomicity guarantees must override this method and document its
1127 * concurrency properties. In particular, all implementations of
1128 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1129 * whether the remapping function is applied once atomically only if the
1130 * value is not present.
1131 *
1132 * @param key key with which the specified value is to be associated
1133 * @param remappingFunction the remapping function to compute a value
1134 * @return the new value associated with the specified key, or null if none
1135 * @throws NullPointerException if the specified key is null and
1136 * this map does not support null keys, or the
1137 * remappingFunction is null
1138 * @throws UnsupportedOperationException if the {@code put} operation
1139 * is not supported by this map
1140 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1141 * @throws ClassCastException if the class of the specified key or value
1142 * prevents it from being stored in this map
1143 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1144 * @since 1.8
1145 */
1146 default V compute(K key,
1147 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1148 Objects.requireNonNull(remappingFunction);
1149 V oldValue = get(key);
1150
1151 V newValue = remappingFunction.apply(key, oldValue);
1152 if (newValue == null) {
1153 // delete mapping
1154 if (oldValue != null || containsKey(key)) {
1155 // something to remove
1156 remove(key);
1157 return null;
1158 } else {
1159 // nothing to do. Leave things as they were.
1160 return null;
1161 }
1162 } else {
1163 // add or replace old mapping
1164 put(key, newValue);
1165 return newValue;
1166 }
1167 }
1168
1169 /**
1170 * If the specified key is not already associated with a value or is
1171 * associated with null, associates it with the given non-null value.
1172 * Otherwise, replaces the associated value with the results of the given
1173 * remapping function, or removes if the result is {@code null}. This
1174 * method may be of use when combining multiple mapped values for a key.
1175 * For example, to either create or append a {@code String msg} to a
1176 * value mapping:
1177 *
1178 * <pre> {@code
1179 * map.merge(key, msg, String::concat)
1180 * }</pre>
1181 *
1182 * <p>If the remapping function returns {@code null}, the mapping is removed.
1183 * If the remapping function itself throws an (unchecked) exception, the
1184 * exception is rethrown, and the current mapping is left unchanged.
1185 *
1186 * <p>The remapping function should not modify this map during computation.
1187 *
1188 * @implSpec
1189 * The default implementation is equivalent to performing the following
1190 * steps for this {@code map}, then returning the current value or
1191 * {@code null} if absent:
1192 *
1193 * <pre> {@code
1194 * V oldValue = map.get(key);
1195 * V newValue = (oldValue == null) ? value :
1196 * remappingFunction.apply(oldValue, value);
1197 * if (newValue == null)
1198 * map.remove(key);
1199 * else
1200 * map.put(key, newValue);
1201 * }</pre>
1202 *
1203 * <p>The default implementation makes no guarantees about detecting if the
1204 * remapping function modifies this map during computation and, if
1205 * appropriate, reporting an error. Non-concurrent implementations should
1206 * override this method and, on a best-effort basis, throw a
1207 * {@code ConcurrentModificationException} if it is detected that the
1208 * remapping function modifies this map during computation. Concurrent
1209 * implementations should override this method and, on a best-effort basis,
1210 * throw an {@code IllegalStateException} if it is detected that the
1211 * remapping function modifies this map during computation and as a result
1212 * computation would never complete.
1213 *
1214 * <p>The default implementation makes no guarantees about synchronization
1215 * or atomicity properties of this method. Any implementation providing
1216 * atomicity guarantees must override this method and document its
1217 * concurrency properties. In particular, all implementations of
1218 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1219 * whether the remapping function is applied once atomically only if the
1220 * value is not present.
1221 *
1222 * @param key key with which the resulting value is to be associated
1223 * @param value the non-null value to be merged with the existing value
1224 * associated with the key or, if no existing value or a null value
1225 * is associated with the key, to be associated with the key
1226 * @param remappingFunction the remapping function to recompute a value if
1227 * present
1228 * @return the new value associated with the specified key, or null if no
1229 * value is associated with the key
1230 * @throws UnsupportedOperationException if the {@code put} operation
1231 * is not supported by this map
1232 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1233 * @throws ClassCastException if the class of the specified key or value
1234 * prevents it from being stored in this map
1235 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1236 * @throws NullPointerException if the specified key is null and this map
1237 * does not support null keys or the value or remappingFunction is
1238 * null
1239 * @since 1.8
1240 */
1241 default V merge(K key, V value,
1242 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
1243 Objects.requireNonNull(remappingFunction);
1244 Objects.requireNonNull(value);
1245 V oldValue = get(key);
1246 V newValue = (oldValue == null) ? value :
1247 remappingFunction.apply(oldValue, value);
1248 if(newValue == null) {
1249 remove(key);
1250 } else {
1251 put(key, newValue);
1252 }
1253 return newValue;
1254 }
1255
1256 /**
1257 * Creates an immutable map containing zero mappings.
1258 * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
1259 *
1260 * @param <K> the map's key type
1261 * @param <V> the map's value type
1262 * @return the newly created map
1263 *
1264 * @since 9
1265 */
1266 static <K,V> Map<K,V> of() {
1267 return Collections.emptyMap();
1268 }
1269
1270 /**
1271 * Creates an immutable map containing a single mapping.
1272 * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
1273 *
1274 * @param <K> the map's key type
1275 * @param <V> the map's value type
1276 * @param k1 the mapping's key
1277 * @param v1 the mapping's value
1278 * @return the newly created map
1279 * @throws NullPointerException if the key or the value is null
1280 *
1281 * @since 9
1282 */
1283 static <K,V> Map<K,V> of(K k1, V v1) {
1284 return Collections.singletonMap(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
1285 }
1286
1287 /**
1288 * Creates an immutable map containing two mappings.
1289 * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
1290 *
1291 * @param <K> the map's key type
1292 * @param <V> the map's value type
1293 * @param k1 the first mapping's key
1294 * @param v1 the first mapping's value
1295 * @param k2 the second mapping's key
1296 * @param v2 the second mapping's value
1297 * @return the newly created map
1298 * @throws IllegalArgumentException if the keys are duplicates
1299 * @throws NullPointerException if any key or value is null
1300 *
1301 * @since 9
1302 */
1303 static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2) {
1304 Map<K,V> map = new HashMap<>(3);
1305 map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
1306 map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
1307 if (map.size() != 2) {
1308 throw new IllegalArgumentException("duplicate keys");
1309 }
1310 return Collections.unmodifiableMap(map);
1311 }
1312
1313 /**
1314 * Creates an immutable map containing three mappings.
1315 * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
1316 *
1317 * @param <K> the map's key type
1318 * @param <V> the map's value type
1319 * @param k1 the first mapping's key
1320 * @param v1 the first mapping's value
1321 * @param k2 the second mapping's key
1322 * @param v2 the second mapping's value
1323 * @param k3 the third mapping's key
1324 * @param v3 the third mapping's value
1325 * @return the newly created map
1326 * @throws IllegalArgumentException if any keys are duplicates
1327 * @throws NullPointerException if any key or value is null
1328 *
1329 * @since 9
1330 */
1331 static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2, K k3, V v3) {
1332 Map<K,V> map = new HashMap<>(5);
1333 map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
1334 map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
1335 map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
1336 if (map.size() != 3) {
1337 throw new IllegalArgumentException("duplicate keys");
1338 }
1339 return Collections.unmodifiableMap(map);
1340 }
1341
1342 /**
1343 * Creates an immutable map containing four mappings.
1344 * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
1345 *
1346 * @param <K> the map's key type
1347 * @param <V> the map's value type
1348 * @param k1 the first mapping's key
1349 * @param v1 the first mapping's value
1350 * @param k2 the second mapping's key
1351 * @param v2 the second mapping's value
1352 * @param k3 the third mapping's key
1353 * @param v3 the third mapping's value
1354 * @param k4 the fourth mapping's key
1355 * @param v4 the fourth mapping's value
1356 * @return the newly created map
1357 * @throws IllegalArgumentException if any keys are duplicates
1358 * @throws NullPointerException if any key or value is null
1359 *
1360 * @since 9
1361 */
1362 static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
1363 Map<K,V> map = new HashMap<>(6);
1364 map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
1365 map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
1366 map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
1367 map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
1368 if (map.size() != 4) {
1369 throw new IllegalArgumentException("duplicate keys");
1370 }
1371 return Collections.unmodifiableMap(map);
1372 }
1373
1374 /**
1375 * Creates an immutable map containing five mappings.
1376 * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
1377 *
1378 * @param <K> the map's key type
1379 * @param <V> the map's value type
1380 * @param k1 the first mapping's key
1381 * @param v1 the first mapping's value
1382 * @param k2 the second mapping's key
1383 * @param v2 the second mapping's value
1384 * @param k3 the third mapping's key
1385 * @param v3 the third mapping's value
1386 * @param k4 the fourth mapping's key
1387 * @param v4 the fourth mapping's value
1388 * @param k5 the fifth mapping's key
1389 * @param v5 the fifth mapping's value
1390 * @return the newly created map
1391 * @throws IllegalArgumentException if any keys are duplicates
1392 * @throws NullPointerException if any key or value is null
1393 *
1394 * @since 9
1395 */
1396 static <K,V> Map<K,V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
1397 Map<K,V> map = new HashMap<>(7);
1398 map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
1399 map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
1400 map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
1401 map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
1402 map.put(Objects.requireNonNull(k5), Objects.requireNonNull(v5));
1403 if (map.size() != 5) {
1404 throw new IllegalArgumentException("duplicate keys");
1405 }
1406 return Collections.unmodifiableMap(map);
1407 }
1408
1409 /**
1410 * Creates an immutable map containing six mappings.
1411 * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
1412 *
1413 * @param <K> the map's key type
1414 * @param <V> the map's value type
1415 * @param k1 the first mapping's key
1416 * @param v1 the first mapping's value
1417 * @param k2 the second mapping's key
1418 * @param v2 the second mapping's value
1419 * @param k3 the third mapping's key
1420 * @param v3 the third mapping's value
1421 * @param k4 the fourth mapping's key
1422 * @param v4 the fourth mapping's value
1423 * @param k5 the fifth mapping's key
1424 * @param v5 the fifth mapping's value
1425 * @param k6 the sixth mapping's key
1426 * @param v6 the sixth mapping's value
1427 * @return the newly created map
1428 * @throws IllegalArgumentException if any keys are duplicates
1429 * @throws NullPointerException if any key or value is null
1430 *
1431 * @since 9
1432 */
1433 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,
1434 K k6, V v6) {
1435 Map<K,V> map = new HashMap<>(9);
1436 map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
1437 map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
1438 map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
1439 map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
1440 map.put(Objects.requireNonNull(k5), Objects.requireNonNull(v5));
1441 map.put(Objects.requireNonNull(k6), Objects.requireNonNull(v6));
1442 if (map.size() != 6) {
1443 throw new IllegalArgumentException("duplicate keys");
1444 }
1445 return Collections.unmodifiableMap(map);
1446 }
1447
1448 /**
1449 * Creates an immutable map containing seven mappings.
1450 * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
1451 *
1452 * @param <K> the map's key type
1453 * @param <V> the map's value type
1454 * @param k1 the first mapping's key
1455 * @param v1 the first mapping's value
1456 * @param k2 the second mapping's key
1457 * @param v2 the second mapping's value
1458 * @param k3 the third mapping's key
1459 * @param v3 the third mapping's value
1460 * @param k4 the fourth mapping's key
1461 * @param v4 the fourth mapping's value
1462 * @param k5 the fifth mapping's key
1463 * @param v5 the fifth mapping's value
1464 * @param k6 the sixth mapping's key
1465 * @param v6 the sixth mapping's value
1466 * @param k7 the seventh mapping's key
1467 * @param v7 the seventh mapping's value
1468 * @return the newly created map
1469 * @throws IllegalArgumentException if any keys are duplicates
1470 * @throws NullPointerException if any key or value is null
1471 *
1472 * @since 9
1473 */
1474 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,
1475 K k6, V v6, K k7, V v7) {
1476 Map<K,V> map = new HashMap<>(10);
1477 map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
1478 map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
1479 map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
1480 map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
1481 map.put(Objects.requireNonNull(k5), Objects.requireNonNull(v5));
1482 map.put(Objects.requireNonNull(k6), Objects.requireNonNull(v6));
1483 map.put(Objects.requireNonNull(k7), Objects.requireNonNull(v7));
1484 if (map.size() != 7) {
1485 throw new IllegalArgumentException("duplicate keys");
1486 }
1487 return Collections.unmodifiableMap(map);
1488 }
1489
1490 /**
1491 * Creates an immutable map containing eight mappings.
1492 * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
1493 *
1494 * @param <K> the map's key type
1495 * @param <V> the map's value type
1496 * @param k1 the first mapping's key
1497 * @param v1 the first mapping's value
1498 * @param k2 the second mapping's key
1499 * @param v2 the second mapping's value
1500 * @param k3 the third mapping's key
1501 * @param v3 the third mapping's value
1502 * @param k4 the fourth mapping's key
1503 * @param v4 the fourth mapping's value
1504 * @param k5 the fifth mapping's key
1505 * @param v5 the fifth mapping's value
1506 * @param k6 the sixth mapping's key
1507 * @param v6 the sixth mapping's value
1508 * @param k7 the seventh mapping's key
1509 * @param v7 the seventh mapping's value
1510 * @param k8 the eighth mapping's key
1511 * @param v8 the eighth mapping's value
1512 * @return the newly created map
1513 * @throws IllegalArgumentException if any keys are duplicates
1514 * @throws NullPointerException if any key or value is null
1515 *
1516 * @since 9
1517 */
1518 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,
1519 K k6, V v6, K k7, V v7, K k8, V v8) {
1520 Map<K,V> map = new HashMap<>(11);
1521 map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
1522 map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
1523 map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
1524 map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
1525 map.put(Objects.requireNonNull(k5), Objects.requireNonNull(v5));
1526 map.put(Objects.requireNonNull(k6), Objects.requireNonNull(v6));
1527 map.put(Objects.requireNonNull(k7), Objects.requireNonNull(v7));
1528 map.put(Objects.requireNonNull(k8), Objects.requireNonNull(v8));
1529 if (map.size() != 8) {
1530 throw new IllegalArgumentException("duplicate keys");
1531 }
1532 return Collections.unmodifiableMap(map);
1533 }
1534
1535 /**
1536 * Creates an immutable map containing nine mappings.
1537 * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
1538 *
1539 * @param <K> the map's key type
1540 * @param <V> the map's value type
1541 * @param k1 the first mapping's key
1542 * @param v1 the first mapping's value
1543 * @param k2 the second mapping's key
1544 * @param v2 the second mapping's value
1545 * @param k3 the third mapping's key
1546 * @param v3 the third mapping's value
1547 * @param k4 the fourth mapping's key
1548 * @param v4 the fourth mapping's value
1549 * @param k5 the fifth mapping's key
1550 * @param v5 the fifth mapping's value
1551 * @param k6 the sixth mapping's key
1552 * @param v6 the sixth mapping's value
1553 * @param k7 the seventh mapping's key
1554 * @param v7 the seventh mapping's value
1555 * @param k8 the eighth mapping's key
1556 * @param v8 the eighth mapping's value
1557 * @param k9 the ninth mapping's key
1558 * @param v9 the ninth mapping's value
1559 * @return the newly created map
1560 * @throws IllegalArgumentException if any keys are duplicates
1561 * @throws NullPointerException if any key or value is null
1562 *
1563 * @since 9
1564 */
1565 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,
1566 K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9) {
1567 Map<K,V> map = new HashMap<>(13);
1568 map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
1569 map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
1570 map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
1571 map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
1572 map.put(Objects.requireNonNull(k5), Objects.requireNonNull(v5));
1573 map.put(Objects.requireNonNull(k6), Objects.requireNonNull(v6));
1574 map.put(Objects.requireNonNull(k7), Objects.requireNonNull(v7));
1575 map.put(Objects.requireNonNull(k8), Objects.requireNonNull(v8));
1576 map.put(Objects.requireNonNull(k9), Objects.requireNonNull(v9));
1577 if (map.size() != 9) {
1578 throw new IllegalArgumentException("duplicate keys");
1579 }
1580 return Collections.unmodifiableMap(map);
1581 }
1582
1583 /**
1584 * Creates an immutable map containing ten mappings.
1585 * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
1586 *
1587 * @param <K> the map's key type
1588 * @param <V> the map's value type
1589 * @param k1 the first mapping's key
1590 * @param v1 the first mapping's value
1591 * @param k2 the second mapping's key
1592 * @param v2 the second mapping's value
1593 * @param k3 the third mapping's key
1594 * @param v3 the third mapping's value
1595 * @param k4 the fourth mapping's key
1596 * @param v4 the fourth mapping's value
1597 * @param k5 the fifth mapping's key
1598 * @param v5 the fifth mapping's value
1599 * @param k6 the sixth mapping's key
1600 * @param v6 the sixth mapping's value
1601 * @param k7 the seventh mapping's key
1602 * @param v7 the seventh mapping's value
1603 * @param k8 the eighth mapping's key
1604 * @param v8 the eighth mapping's value
1605 * @param k9 the ninth mapping's key
1606 * @param v9 the ninth mapping's value
1607 * @param k10 the tenth mapping's key
1608 * @param v10 the tenth mapping's value
1609 * @return the newly created map
1610 * @throws IllegalArgumentException if any keys are duplicates
1611 * @throws NullPointerException if any key or value is null
1612 *
1613 * @since 9
1614 */
1615 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,
1616 K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9, K k10, V v10) {
1617 Map<K,V> map = new HashMap<>(14);
1618 map.put(Objects.requireNonNull(k1), Objects.requireNonNull(v1));
1619 map.put(Objects.requireNonNull(k2), Objects.requireNonNull(v2));
1620 map.put(Objects.requireNonNull(k3), Objects.requireNonNull(v3));
1621 map.put(Objects.requireNonNull(k4), Objects.requireNonNull(v4));
1622 map.put(Objects.requireNonNull(k5), Objects.requireNonNull(v5));
1623 map.put(Objects.requireNonNull(k6), Objects.requireNonNull(v6));
1624 map.put(Objects.requireNonNull(k7), Objects.requireNonNull(v7));
1625 map.put(Objects.requireNonNull(k8), Objects.requireNonNull(v8));
1626 map.put(Objects.requireNonNull(k9), Objects.requireNonNull(v9));
1627 map.put(Objects.requireNonNull(k10), Objects.requireNonNull(v10));
1628 if (map.size() != 10) {
1629 throw new IllegalArgumentException("duplicate keys");
1630 }
1631 return Collections.unmodifiableMap(map);
1632 }
1633
1634 /**
1635 * Creates an immutable map containing keys and values from the given entries.
1636 * See <a href="#immutable">Immutable Map Static Factory Methods</a> for details.
1637 *
1638 * @apiNote
1639 * It is convenient to create the map entries using the {@link Map#entry Map.entry()} method.
1640 * For example,
1641 *
1642 * <pre>{@code
1643 * import static java.util.Map.entry;
1644 *
1645 * Map<Integer,String> map = Map.ofEntries(
1646 * entry(1, "a"),
1647 * entry(2, "b"),
1648 * entry(3, "c"),
1649 * ...
1650 * entry(26, "z"));
1651 * }</pre>
1652 *
1653 * @param <K> the map's key type
1654 * @param <V> the map's value type
1655 * @param entries the keys and values with which the map is populated
1656 * @return the newly created {@code Map}
1657 * @throws IllegalArgumentException if any keys are duplicates
1658 * @throws NullPointerException if any entry, key, or value is null, or if
1659 * the {@code entries} array is null
1660 *
1661 * @see Map#entry Map.entry()
1662 * @since 9
1663 */
1664 @SafeVarargs
1665 @SuppressWarnings("varargs")
1666 static <K,V> Map<K,V> ofEntries(Entry<K,V>... entries) {
1667 Map<K,V> map = new HashMap<>(entries.length * 4 / 3 + 1); // throws NPE if entries is null
1668 for (Entry<K,V> e : entries) {
1669 Objects.requireNonNull(e);
1670 map.put(Objects.requireNonNull(e.getKey()), Objects.requireNonNull(e.getValue()));
1671 }
1672 if (map.size() != entries.length) {
1673 throw new IllegalArgumentException("duplicate elements");
1674 }
1675 return Collections.unmodifiableMap(map);
1676 }
1677
1678 /**
1679 * Creates an immutable {@link Entry} containing the given key and value.
1680 * These entries are suitable for populating {@code Map} instances using the
1681 * {@link Map#ofEntries Map.ofEntries()} method.
1682 * The key and the value must not be null. Calling {@link Entry#setValue Entry.setValue()}
1683 * on the returned {@code Entry} results in an {@code UnsupportedOperationException}
1684 * being thrown. The returned {@code Entry} is not guaranteed to be serializable.
1685 *
1686 * <p>The returned {@code Entry} is a <a href="../lang/doc-files/ValueBased.html">value-based</a>
1687 * class; use of identity-sensitive operations (including reference equality
1688 * ({@code ==}), identity hash code, or synchronization) on any returned values
1689 * may have unpredictable results and should be avoided.
1690 *
1691 * @param <K> the key's type
1692 * @param <V> the value's type
1693 * @param k the key
1694 * @param v the value
1695 * @return the new {@code Entry}
1696 * @throws NullPointerException if the key or value is null
1697 *
1698 * @see Map#ofEntries Map.ofEntries()
1699 * @since 9
1700 */
1701 static <K,V> Entry<K,V> entry(K k, V v) {
1702 // KeyValueHolder checks for nulls
1703 return new KeyValueHolder<>(k, v);
1704 }
1705 }