1 /*
2 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 * questions.
24 */
25
26 package java.util;
27
28 import java.util.function.BiConsumer;
29 import java.util.function.BiFunction;
30 import java.util.function.Function;
31 import java.io.Serializable;
32
33 /**
34 * An object that maps keys to values. A map cannot contain duplicate keys;
35 * each key can map to at most one value.
36 *
37 * <p>This interface takes the place of the <tt>Dictionary</tt> class, which
38 * was a totally abstract class rather than an interface.
39 *
40 * <p>The <tt>Map</tt> interface provides three <i>collection views</i>, which
41 * allow a map's contents to be viewed as a set of keys, collection of values,
42 * or set of key-value mappings. The <i>order</i> of a map is defined as
43 * the order in which the iterators on the map's collection views return their
44 * elements. Some map implementations, like the <tt>TreeMap</tt> class, make
45 * specific guarantees as to their order; others, like the <tt>HashMap</tt>
46 * class, do not.
47 *
48 * <p>Note: great care must be exercised if mutable objects are used as map
49 * keys. The behavior of a map is not specified if the value of an object is
50 * changed in a manner that affects <tt>equals</tt> comparisons while the
51 * object is a key in the map. A special case of this prohibition is that it
52 * is not permissible for a map to contain itself as a key. While it is
53 * permissible for a map to contain itself as a value, extreme caution is
54 * advised: the <tt>equals</tt> and <tt>hashCode</tt> methods are no longer
55 * well defined on such a map.
56 *
57 * <p>All general-purpose map implementation classes should provide two
58 * "standard" constructors: a void (no arguments) constructor which creates an
59 * empty map, and a constructor with a single argument of type <tt>Map</tt>,
60 * which creates a new map with the same key-value mappings as its argument.
61 * In effect, the latter constructor allows the user to copy any map,
62 * producing an equivalent map of the desired class. There is no way to
63 * enforce this recommendation (as interfaces cannot contain constructors) but
64 * all of the general-purpose map implementations in the JDK comply.
65 *
66 * <p>The "destructive" methods contained in this interface, that is, the
67 * methods that modify the map on which they operate, are specified to throw
68 * <tt>UnsupportedOperationException</tt> if this map does not support the
69 * operation. If this is the case, these methods may, but are not required
70 * to, throw an <tt>UnsupportedOperationException</tt> if the invocation would
71 * have no effect on the map. For example, invoking the {@link #putAll(Map)}
72 * method on an unmodifiable map may, but is not required to, throw the
73 * exception if the map whose mappings are to be "superimposed" is empty.
74 *
75 * <p>Some map implementations have restrictions on the keys and values they
76 * may contain. For example, some implementations prohibit null keys and
77 * values, and some have restrictions on the types of their keys. Attempting
78 * to insert an ineligible key or value throws an unchecked exception,
79 * typically <tt>NullPointerException</tt> or <tt>ClassCastException</tt>.
80 * Attempting to query the presence of an ineligible key or value may throw an
81 * exception, or it may simply return false; some implementations will exhibit
82 * the former behavior and some will exhibit the latter. More generally,
83 * attempting an operation on an ineligible key or value whose completion
84 * would not result in the insertion of an ineligible element into the map may
85 * throw an exception or it may succeed, at the option of the implementation.
86 * Such exceptions are marked as "optional" in the specification for this
87 * interface.
88 *
89 * <p>Many methods in Collections Framework interfaces are defined
90 * in terms of the {@link Object#equals(Object) equals} method. For
91 * example, the specification for the {@link #containsKey(Object)
92 * containsKey(Object key)} method says: "returns <tt>true</tt> if and
93 * only if this map contains a mapping for a key <tt>k</tt> such that
94 * <tt>(key==null ? k==null : key.equals(k))</tt>." This specification should
95 * <i>not</i> be construed to imply that invoking <tt>Map.containsKey</tt>
96 * with a non-null argument <tt>key</tt> will cause <tt>key.equals(k)</tt> to
97 * be invoked for any key <tt>k</tt>. Implementations are free to
98 * implement optimizations whereby the <tt>equals</tt> invocation is avoided,
99 * for example, by first comparing the hash codes of the two keys. (The
100 * {@link Object#hashCode()} specification guarantees that two objects with
101 * unequal hash codes cannot be equal.) More generally, implementations of
102 * the various Collections Framework interfaces are free to take advantage of
103 * the specified behavior of underlying {@link Object} methods wherever the
104 * implementor deems it appropriate.
105 *
106 * <p>Some map operations which perform recursive traversal of the map may fail
107 * with an exception for self-referential instances where the map directly or
108 * indirectly contains itself. This includes the {@code clone()},
109 * {@code equals()}, {@code hashCode()} and {@code toString()} methods.
110 * Implementations may optionally handle the self-referential scenario, however
111 * most current implementations do not do so.
112 *
113 * <p>This interface is a member of the
114 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
115 * Java Collections Framework</a>.
116 *
117 * @param <K> the type of keys maintained by this map
118 * @param <V> the type of mapped values
119 *
120 * @author Josh Bloch
121 * @see HashMap
122 * @see TreeMap
123 * @see Hashtable
124 * @see SortedMap
125 * @see Collection
126 * @see Set
127 * @since 1.2
128 */
129 public interface Map<K,V> {
130 // Query Operations
131
132 /**
133 * Returns the number of key-value mappings in this map. If the
134 * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
135 * <tt>Integer.MAX_VALUE</tt>.
136 *
137 * @return the number of key-value mappings in this map
138 */
139 int size();
140
141 /**
142 * Returns <tt>true</tt> if this map contains no key-value mappings.
143 *
144 * @return <tt>true</tt> if this map contains no key-value mappings
145 */
146 boolean isEmpty();
147
148 /**
149 * Returns <tt>true</tt> if this map contains a mapping for the specified
150 * key. More formally, returns <tt>true</tt> if and only if
151 * this map contains a mapping for a key <tt>k</tt> such that
152 * <tt>(key==null ? k==null : key.equals(k))</tt>. (There can be
153 * at most one such mapping.)
154 *
155 * @param key key whose presence in this map is to be tested
156 * @return <tt>true</tt> if this map contains a mapping for the specified
157 * key
158 * @throws ClassCastException if the key is of an inappropriate type for
159 * this map
160 * (<a href="Collection.html#optional-restrictions">optional</a>)
161 * @throws NullPointerException if the specified key is null and this map
162 * does not permit null keys
163 * (<a href="Collection.html#optional-restrictions">optional</a>)
164 */
165 boolean containsKey(Object key);
166
167 /**
168 * Returns <tt>true</tt> if this map maps one or more keys to the
169 * specified value. More formally, returns <tt>true</tt> if and only if
170 * this map contains at least one mapping to a value <tt>v</tt> such that
171 * <tt>(value==null ? v==null : value.equals(v))</tt>. This operation
172 * will probably require time linear in the map size for most
173 * implementations of the <tt>Map</tt> interface.
174 *
175 * @param value value whose presence in this map is to be tested
176 * @return <tt>true</tt> if this map maps one or more keys to the
177 * specified value
178 * @throws ClassCastException if the value is of an inappropriate type for
179 * this map
180 * (<a href="Collection.html#optional-restrictions">optional</a>)
181 * @throws NullPointerException if the specified value is null and this
182 * map does not permit null values
183 * (<a href="Collection.html#optional-restrictions">optional</a>)
184 */
185 boolean containsValue(Object value);
186
187 /**
188 * Returns the value to which the specified key is mapped,
189 * or {@code null} if this map contains no mapping for the key.
190 *
191 * <p>More formally, if this map contains a mapping from a key
192 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
193 * key.equals(k))}, then this method returns {@code v}; otherwise
194 * it returns {@code null}. (There can be at most one such mapping.)
195 *
196 * <p>If this map permits null values, then a return value of
197 * {@code null} does not <i>necessarily</i> indicate that the map
198 * contains no mapping for the key; it's also possible that the map
199 * explicitly maps the key to {@code null}. The {@link #containsKey
200 * containsKey} operation may be used to distinguish these two cases.
201 *
202 * @param key the key whose associated value is to be returned
203 * @return the value to which the specified key is mapped, or
204 * {@code null} if this map contains no mapping for the key
205 * @throws ClassCastException if the key is of an inappropriate type for
206 * this map
207 * (<a href="Collection.html#optional-restrictions">optional</a>)
208 * @throws NullPointerException if the specified key is null and this map
209 * does not permit null keys
210 * (<a href="Collection.html#optional-restrictions">optional</a>)
211 */
212 V get(Object key);
213
214 // Modification Operations
215
216 /**
217 * Associates the specified value with the specified key in this map
218 * (optional operation). If the map previously contained a mapping for
219 * the key, the old value is replaced by the specified value. (A map
220 * <tt>m</tt> is said to contain a mapping for a key <tt>k</tt> if and only
221 * if {@link #containsKey(Object) m.containsKey(k)} would return
222 * <tt>true</tt>.)
223 *
224 * @param key key with which the specified value is to be associated
225 * @param value value to be associated with the specified key
226 * @return the previous value associated with <tt>key</tt>, or
227 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
228 * (A <tt>null</tt> return can also indicate that the map
229 * previously associated <tt>null</tt> with <tt>key</tt>,
230 * if the implementation supports <tt>null</tt> values.)
231 * @throws UnsupportedOperationException if the <tt>put</tt> operation
232 * is not supported by this map
233 * @throws ClassCastException if the class of the specified key or value
234 * prevents it from being stored in this map
235 * @throws NullPointerException if the specified key or value is null
236 * and this map does not permit null keys or values
237 * @throws IllegalArgumentException if some property of the specified key
238 * or value prevents it from being stored in this map
239 */
240 V put(K key, V value);
241
242 /**
243 * Removes the mapping for a key from this map if it is present
244 * (optional operation). More formally, if this map contains a mapping
245 * from key <tt>k</tt> to value <tt>v</tt> such that
246 * <code>(key==null ? k==null : key.equals(k))</code>, that mapping
247 * is removed. (The map can contain at most one such mapping.)
248 *
249 * <p>Returns the value to which this map previously associated the key,
250 * or <tt>null</tt> if the map contained no mapping for the key.
251 *
252 * <p>If this map permits null values, then a return value of
253 * <tt>null</tt> does not <i>necessarily</i> indicate that the map
254 * contained no mapping for the key; it's also possible that the map
255 * explicitly mapped the key to <tt>null</tt>.
256 *
257 * <p>The map will not contain a mapping for the specified key once the
258 * call returns.
259 *
260 * @param key key whose mapping is to be removed from the map
261 * @return the previous value associated with <tt>key</tt>, or
262 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
263 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
264 * is not supported by this map
265 * @throws ClassCastException if the key is of an inappropriate type for
266 * this map
267 * (<a href="Collection.html#optional-restrictions">optional</a>)
268 * @throws NullPointerException if the specified key is null and this
269 * map does not permit null keys
270 * (<a href="Collection.html#optional-restrictions">optional</a>)
271 */
272 V remove(Object key);
273
274
275 // Bulk Operations
276
277 /**
278 * Copies all of the mappings from the specified map to this map
279 * (optional operation). The effect of this call is equivalent to that
280 * of calling {@link #put(Object,Object) put(k, v)} on this map once
281 * for each mapping from key <tt>k</tt> to value <tt>v</tt> in the
282 * specified map. The behavior of this operation is undefined if the
283 * specified map is modified while the operation is in progress.
284 *
285 * @param m mappings to be stored in this map
286 * @throws UnsupportedOperationException if the <tt>putAll</tt> operation
287 * is not supported by this map
288 * @throws ClassCastException if the class of a key or value in the
289 * specified map prevents it from being stored in this map
290 * @throws NullPointerException if the specified map is null, or if
291 * this map does not permit null keys or values, and the
292 * specified map contains null keys or values
293 * @throws IllegalArgumentException if some property of a key or value in
294 * the specified map prevents it from being stored in this map
295 */
296 void putAll(Map<? extends K, ? extends V> m);
297
298 /**
299 * Removes all of the mappings from this map (optional operation).
300 * The map will be empty after this call returns.
301 *
302 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
303 * is not supported by this map
304 */
305 void clear();
306
307
308 // Views
309
310 /**
311 * Returns a {@link Set} view of the keys contained in this map.
312 * The set is backed by the map, so changes to the map are
313 * reflected in the set, and vice-versa. If the map is modified
314 * while an iteration over the set is in progress (except through
315 * the iterator's own <tt>remove</tt> operation), the results of
316 * the iteration are undefined. The set supports element removal,
317 * which removes the corresponding mapping from the map, via the
318 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
319 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
320 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
321 * operations.
322 *
323 * @return a set view of the keys contained in this map
324 */
325 Set<K> keySet();
326
327 /**
328 * Returns a {@link Collection} view of the values contained in this map.
329 * The collection is backed by the map, so changes to the map are
330 * reflected in the collection, and vice-versa. If the map is
331 * modified while an iteration over the collection is in progress
332 * (except through the iterator's own <tt>remove</tt> operation),
333 * the results of the iteration are undefined. The collection
334 * supports element removal, which removes the corresponding
335 * mapping from the map, via the <tt>Iterator.remove</tt>,
336 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
337 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
338 * support the <tt>add</tt> or <tt>addAll</tt> operations.
339 *
340 * @return a collection view of the values contained in this map
341 */
342 Collection<V> values();
343
344 /**
345 * Returns a {@link Set} view of the mappings contained in this map.
346 * The set is backed by the map, so changes to the map are
347 * reflected in the set, and vice-versa. If the map is modified
348 * while an iteration over the set is in progress (except through
349 * the iterator's own <tt>remove</tt> operation, or through the
350 * <tt>setValue</tt> operation on a map entry returned by the
351 * iterator) the results of the iteration are undefined. The set
352 * supports element removal, which removes the corresponding
353 * mapping from the map, via the <tt>Iterator.remove</tt>,
354 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
355 * <tt>clear</tt> operations. It does not support the
356 * <tt>add</tt> or <tt>addAll</tt> operations.
357 *
358 * @return a set view of the mappings contained in this map
359 */
360 Set<Map.Entry<K, V>> entrySet();
361
362 /**
363 * A map entry (key-value pair). The <tt>Map.entrySet</tt> method returns
364 * a collection-view of the map, whose elements are of this class. The
365 * <i>only</i> way to obtain a reference to a map entry is from the
366 * iterator of this collection-view. These <tt>Map.Entry</tt> objects are
367 * valid <i>only</i> for the duration of the iteration; more formally,
368 * the behavior of a map entry is undefined if the backing map has been
369 * modified after the entry was returned by the iterator, except through
370 * the <tt>setValue</tt> operation on the map entry.
371 *
372 * @see Map#entrySet()
373 * @since 1.2
374 */
375 interface Entry<K,V> {
376 /**
377 * Returns the key corresponding to this entry.
378 *
379 * @return the key corresponding to this entry
380 * @throws IllegalStateException implementations may, but are not
381 * required to, throw this exception if the entry has been
382 * removed from the backing map.
383 */
384 K getKey();
385
386 /**
387 * Returns the value corresponding to this entry. If the mapping
388 * has been removed from the backing map (by the iterator's
389 * <tt>remove</tt> operation), the results of this call are undefined.
390 *
391 * @return the value corresponding to this entry
392 * @throws IllegalStateException implementations may, but are not
393 * required to, throw this exception if the entry has been
394 * removed from the backing map.
395 */
396 V getValue();
397
398 /**
399 * Replaces the value corresponding to this entry with the specified
400 * value (optional operation). (Writes through to the map.) The
401 * behavior of this call is undefined if the mapping has already been
402 * removed from the map (by the iterator's <tt>remove</tt> operation).
403 *
404 * @param value new value to be stored in this entry
405 * @return old value corresponding to the entry
406 * @throws UnsupportedOperationException if the <tt>put</tt> operation
407 * is not supported by the backing map
408 * @throws ClassCastException if the class of the specified value
409 * prevents it from being stored in the backing map
410 * @throws NullPointerException if the backing map does not permit
411 * null values, and the specified value is null
412 * @throws IllegalArgumentException if some property of this value
413 * prevents it from being stored in the backing map
414 * @throws IllegalStateException implementations may, but are not
415 * required to, throw this exception if the entry has been
416 * removed from the backing map.
417 */
418 V setValue(V value);
419
420 /**
421 * Compares the specified object with this entry for equality.
422 * Returns <tt>true</tt> if the given object is also a map entry and
423 * the two entries represent the same mapping. More formally, two
424 * entries <tt>e1</tt> and <tt>e2</tt> represent the same mapping
425 * if<pre>
426 * (e1.getKey()==null ?
427 * e2.getKey()==null : e1.getKey().equals(e2.getKey())) &&
428 * (e1.getValue()==null ?
429 * e2.getValue()==null : e1.getValue().equals(e2.getValue()))
430 * </pre>
431 * This ensures that the <tt>equals</tt> method works properly across
432 * different implementations of the <tt>Map.Entry</tt> interface.
433 *
434 * @param o object to be compared for equality with this map entry
435 * @return <tt>true</tt> if the specified object is equal to this map
436 * entry
437 */
438 boolean equals(Object o);
439
440 /**
441 * Returns the hash code value for this map entry. The hash code
442 * of a map entry <tt>e</tt> is defined to be: <pre>
443 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
444 * (e.getValue()==null ? 0 : e.getValue().hashCode())
445 * </pre>
446 * This ensures that <tt>e1.equals(e2)</tt> implies that
447 * <tt>e1.hashCode()==e2.hashCode()</tt> for any two Entries
448 * <tt>e1</tt> and <tt>e2</tt>, as required by the general
449 * contract of <tt>Object.hashCode</tt>.
450 *
451 * @return the hash code value for this map entry
452 * @see Object#hashCode()
453 * @see Object#equals(Object)
454 * @see #equals(Object)
455 */
456 int hashCode();
457
458 /**
459 * Returns a comparator that compares {@link Map.Entry} in natural order on key.
460 *
461 * <p>The returned comparator is serializable and throws {@link
462 * NullPointerException} when comparing an entry with a null key.
463 *
464 * @param <K> the {@link Comparable} type of then map keys
465 * @param <V> the type of the map values
466 * @return a comparator that compares {@link Map.Entry} in natural order on key.
467 * @see Comparable
468 */
469 public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K,V>> comparingByKey() {
470 return (Comparator<Map.Entry<K, V>> & Serializable)
471 (c1, c2) -> c1.getKey().compareTo(c2.getKey());
472 }
473
474 /**
475 * Returns a comparator that compares {@link Map.Entry} in natural order on value.
476 *
477 * <p>The returned comparator is serializable and throws {@link
478 * NullPointerException} when comparing an entry with null values.
479 *
480 * @param <K> the type of the map keys
481 * @param <V> the {@link Comparable} type of the map values
482 * @return a comparator that compares {@link Map.Entry} in natural order on value.
483 * @see Comparable
484 */
485 public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K,V>> comparingByValue() {
486 return (Comparator<Map.Entry<K, V>> & Serializable)
487 (c1, c2) -> c1.getValue().compareTo(c2.getValue());
488 }
489
490 /**
491 * Returns a comparator that compares {@link Map.Entry} by key using the given
492 * {@link Comparator}.
493 *
494 * <p>The returned comparator is serializable if the specified comparator
495 * is also serializable.
496 *
497 * @param <K> the type of the map keys
498 * @param <V> the type of the map values
499 * @param cmp the key {@link Comparator}
500 * @return a comparator that compares {@link Map.Entry} by the key.
501 */
502 public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) {
503 Objects.requireNonNull(cmp);
504 return (Comparator<Map.Entry<K, V>> & Serializable)
505 (c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());
506 }
507
508 /**
509 * Returns a comparator that compares {@link Map.Entry} by value using the given
510 * {@link Comparator}.
511 *
512 * <p>The returned comparator is serializable if the specified comparator
513 * is also serializable.
514 *
515 * @param <K> the type of the map keys
516 * @param <V> the type of the map values
517 * @param cmp the value {@link Comparator}
518 * @return a comparator that compares {@link Map.Entry} by the value.
519 */
520 public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) {
521 Objects.requireNonNull(cmp);
522 return (Comparator<Map.Entry<K, V>> & Serializable)
523 (c1, c2) -> cmp.compare(c1.getValue(), c2.getValue());
524 }
525 }
526
527 // Comparison and hashing
528
529 /**
530 * Compares the specified object with this map for equality. Returns
531 * <tt>true</tt> if the given object is also a map and the two maps
532 * represent the same mappings. More formally, two maps <tt>m1</tt> and
533 * <tt>m2</tt> represent the same mappings if
534 * <tt>m1.entrySet().equals(m2.entrySet())</tt>. This ensures that the
535 * <tt>equals</tt> method works properly across different implementations
536 * of the <tt>Map</tt> interface.
537 *
538 * @param o object to be compared for equality with this map
539 * @return <tt>true</tt> if the specified object is equal to this map
540 */
541 boolean equals(Object o);
542
543 /**
544 * Returns the hash code value for this map. The hash code of a map is
545 * defined to be the sum of the hash codes of each entry in the map's
546 * <tt>entrySet()</tt> view. This ensures that <tt>m1.equals(m2)</tt>
547 * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps
548 * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of
549 * {@link Object#hashCode}.
550 *
551 * @return the hash code value for this map
552 * @see Map.Entry#hashCode()
553 * @see Object#equals(Object)
554 * @see #equals(Object)
555 */
556 int hashCode();
557
558 // Defaultable methods
559
560 /**
561 * Returns the value to which the specified key is mapped,
562 * or {@code defaultValue} if this map contains no mapping
563 * for the key.
564 *
565 * <p>The default implementation makes no guarantees about synchronization
566 * or atomicity properties of this method. Any implementation providing
567 * atomicity guarantees must override this method and document its
568 * concurrency properties.
569 *
570 * @param key the key whose associated value is to be returned
571 * @param defaultValue the default mapping of the key
572 * @return the value to which the specified key is mapped, or
573 * {@code defaultValue} if this map contains no mapping for the key
574 * @throws ClassCastException if the key is of an inappropriate type for
575 * this map
576 * (<a href="Collection.html#optional-restrictions">optional</a>)
577 * @throws NullPointerException if the specified key is null and this map
578 * does not permit null keys
579 * (<a href="Collection.html#optional-restrictions">optional</a>)
580 * @since 1.8
581 */
582 default V getOrDefault(Object key, V defaultValue) {
583 V v;
584 return (((v = get(key)) != null) || containsKey(key))
585 ? v
586 : defaultValue;
587 }
588
589 /**
590 * Performs the given action on each entry in this map, in the order entries
591 * are returned by an entry set iterator (which may be unspecified), until
592 * all entries have been processed or the action throws an {@code Exception}.
593 * Exceptions thrown by the action are relayed to the caller.
594 *
595 * <p>The default implementation should be overridden by implementations if
596 * they can provide a more performant implementation than an iterator-based
597 * one.
598 *
599 * <p>The default implementation makes no guarantees about synchronization
600 * or atomicity properties of this method. Any implementation providing
601 * atomicity guarantees must override this method and document its
602 * concurrency properties.
603 *
604 * @implSpec The default implementation is equivalent to, for this
605 * {@code map}:
606 * <pre> {@code
607 * for ((Map.Entry<K, V> entry : map.entrySet())
608 * action.accept(entry.getKey(), entry.getValue());
609 * }</pre>
610 *
611 * @param action The action to be performed for each entry
612 * @throws NullPointerException if the specified action is null
613 * @throws ConcurrentModificationException if an entry is found to be
614 * removed during iteration
615 * @since 1.8
616 */
617 default void forEach(BiConsumer<? super K, ? super V> action) {
618 Objects.requireNonNull(action);
619 for (Map.Entry<K, V> entry : entrySet()) {
620 K k;
621 V v;
622 try {
623 k = entry.getKey();
624 v = entry.getValue();
625 } catch(IllegalStateException ise) {
626 // this usually means the entry is no longer in the map.
627 throw new ConcurrentModificationException(ise);
628 }
629 action.accept(k, v);
630 }
631 }
632
633 /**
634 * Replaces each entry's value with the result of invoking the given
635 * function on that entry, in the order entries are returned by an entry
636 * set iterator, until all entries have been processed or the function
637 * throws an exception.
638 *
639 * <p>The default implementation makes no guarantees about synchronization
640 * or atomicity properties of this method. Any implementation providing
641 * atomicity guarantees must override this method and document its
642 * concurrency properties.
643 *
644 * @implSpec
645 * <p>The default implementation is equivalent to, for this {@code map}:
646 * <pre> {@code
647 * for ((Map.Entry<K, V> entry : map.entrySet())
648 * entry.setValue(function.apply(entry.getKey(), entry.getValue()));
649 * }</pre>
650 *
651 * @param function the function to apply to each entry
652 * @throws UnsupportedOperationException if the {@code set} operation
653 * is not supported by this map's entry set iterator.
654 * @throws ClassCastException if the class of a replacement value
655 * prevents it from being stored in this map
656 * @throws NullPointerException if the specified function is null, or the
657 * specified replacement value is null, and this map does not permit null
658 * values
659 * @throws ClassCastException if a replacement value is of an inappropriate
660 * type for this map
661 * (<a href="Collection.html#optional-restrictions">optional</a>)
662 * @throws NullPointerException if function or a replacement value is null,
663 * and this map does not permit null keys or values
664 * (<a href="Collection.html#optional-restrictions">optional</a>)
665 * @throws IllegalArgumentException if some property of a replacement value
666 * prevents it from being stored in this map
667 * (<a href="Collection.html#optional-restrictions">optional</a>)
668 * @throws ConcurrentModificationException if an entry is found to be
669 * removed during iteration
670 * @since 1.8
671 */
672 default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
673 Objects.requireNonNull(function);
674 for (Map.Entry<K, V> entry : entrySet()) {
675 K k;
676 V v;
677 try {
678 k = entry.getKey();
679 v = entry.getValue();
680 } catch(IllegalStateException ise) {
681 // this usually means the entry is no longer in the map.
682 throw new ConcurrentModificationException(ise);
683 }
684
685 // ise thrown from function is not a cme.
686 v = function.apply(k, v);
687
688 try {
689 entry.setValue(v);
690 } catch(IllegalStateException ise) {
691 // this usually means the entry is no longer in the map.
692 throw new ConcurrentModificationException(ise);
693 }
694 }
695 }
696
697 /**
698 * If the specified key is not already associated with a value (or is mapped
699 * to {@code null}) associates it with the given value and returns
700 * {@code null}, else returns the current value.
701 *
702 * <p>The default implementation makes no guarantees about synchronization
703 * or atomicity properties of this method. Any implementation providing
704 * atomicity guarantees must override this method and document its
705 * concurrency properties.
706 *
707 * @implSpec
708 * The default implementation is equivalent to, for this {@code
709 * map}:
710 *
711 * <pre> {@code
712 * if (map.get(key) == null)
713 * return map.put(key, value);
714 * else
715 * return map.get(key);
716 * }</pre>
717 *
718 * @param key key with which the specified value is to be associated
719 * @param value value to be associated with the specified key
720 * @return the previous value associated with the specified key, or
721 * {@code null} if there was no mapping for the key.
722 * (A {@code null} return can also indicate that the map
723 * previously associated {@code null} with the key,
724 * if the implementation supports null values.)
725 * @throws UnsupportedOperationException if the {@code put} operation
726 * is not supported by this map
727 * (<a href="Collection.html#optional-restrictions">optional</a>)
728 * @throws ClassCastException if the key or value is of an inappropriate
729 * type for this map
730 * (<a href="Collection.html#optional-restrictions">optional</a>)
731 * @throws NullPointerException if the specified key or value is null,
732 * and this map does not permit null keys or values
733 * (<a href="Collection.html#optional-restrictions">optional</a>)
734 * @throws IllegalArgumentException if some property of the specified key
735 * or value prevents it from being stored in this map
736 * (<a href="Collection.html#optional-restrictions">optional</a>)
737 * @throws ConcurrentModificationException if a modification of the map is
738 * detected during insertion of the value.
739 * @since 1.8
740 */
741 default V putIfAbsent(K key, V value) {
742 V v = get(key);
743 if (v == null) {
744 if (put(key, value) != null) {
745 throw new ConcurrentModificationException();
746 }
747 }
748
749 return v;
750 }
751
752 /**
753 * Removes the entry for the specified key only if it is currently
754 * mapped to the specified value.
755 *
756 * <p>The default implementation makes no guarantees about synchronization
757 * or atomicity properties of this method. Any implementation providing
758 * atomicity guarantees must override this method and document its
759 * concurrency properties.
760 *
761 * @implSpec
762 * The default implementation is equivalent to, for this {@code map}:
763 *
764 * <pre> {@code
765 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
766 * map.remove(key);
767 * return true;
768 * } else
769 * return false;
770 * }</pre>
771 *
772 * @param key key with which the specified value is associated
773 * @param value value expected to be associated with the specified key
774 * @return {@code true} if the value was removed
775 * @throws UnsupportedOperationException if the {@code remove} operation
776 * is not supported by this map
777 * (<a href="Collection.html#optional-restrictions">optional</a>)
778 * @throws ClassCastException if the key or value is of an inappropriate
779 * type for this map
780 * (<a href="Collection.html#optional-restrictions">optional</a>)
781 * @throws NullPointerException if the specified key or value is null,
782 * and this map does not permit null keys or values
783 * (<a href="Collection.html#optional-restrictions">optional</a>)
784 * @since 1.8
785 */
786 default boolean remove(Object key, Object value) {
787 Object curValue = get(key);
788 if (!Objects.equals(curValue, value) ||
789 (curValue == null && !containsKey(key))) {
790 return false;
791 }
792 if(curValue != remove(key)) {
793 throw new ConcurrentModificationException("value unexpectedly changed");
794 }
795 return true;
796 }
797
798 /**
799 * Replaces the entry for the specified key only if currently
800 * mapped to the specified value.
801 *
802 * <p>The default implementation makes no guarantees about synchronization
803 * or atomicity properties of this method. Any implementation providing
804 * atomicity guarantees must override this method and document its
805 * concurrency properties.
806 *
807 * @implSpec
808 * The default implementation is equivalent to, for this {@code map}:
809 *
810 * <pre> {@code
811 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
812 * map.put(key, newValue);
813 * return true;
814 * } else
815 * return false;
816 * }</pre>
817 *
818 * The default implementation does not throw NullPointerException
819 * for maps that do not support null values if oldValue is null unless
820 * newValue is also null.
821 *
822 * @param key key with which the specified value is associated
823 * @param oldValue value expected to be associated with the specified key
824 * @param newValue value to be associated with the specified key
825 * @return {@code true} if the value was replaced
826 * @throws UnsupportedOperationException if the {@code put} operation
827 * is not supported by this map
828 * (<a href="Collection.html#optional-restrictions">optional</a>)
829 * @throws ClassCastException if the class of a specified key or value
830 * prevents it from being stored in this map
831 * @throws NullPointerException if a specified key or newValue is null,
832 * and this map does not permit null keys or values
833 * @throws NullPointerException if oldValue is null and this map does not
834 * permit null values
835 * (<a href="Collection.html#optional-restrictions">optional</a>)
836 * @throws IllegalArgumentException if some property of a specified key
837 * or value prevents it from being stored in this map
838 * @since 1.8
839 */
840 default boolean replace(K key, V oldValue, V newValue) {
841 Object curValue = get(key);
842 if (!Objects.equals(curValue, oldValue) ||
843 (curValue == null && !containsKey(key))) {
844 return false;
845 }
846 if(curValue == put(key, newValue)) {
847 return true;
848 }
849 throw new ConcurrentModificationException("value unexpectedly changed");
850 }
851
852 /**
853 * Replaces the entry for the specified key only if it is
854 * currently mapped to some value.
855 *
856 * <p>The default implementation makes no guarantees about synchronization
857 * or atomicity properties of this method. Any implementation providing
858 * atomicity guarantees must override this method and document its
859 * concurrency properties.
860 *
861 * @implSpec
862 * The default implementation is equivalent to, for this {@code map}:
863 *
864 * <pre> {@code
865 * if (map.containsKey(key)) {
866 * return map.put(key, value);
867 * } else
868 * return null;
869 * }</pre>
870 *
871 * @param key key with which the specified value is associated
872 * @param value value to be associated with the specified key
873 * @return the previous value associated with the specified key, or
874 * {@code null} if there was no mapping for the key.
875 * (A {@code null} return can also indicate that the map
876 * previously associated {@code null} with the key,
877 * if the implementation supports null values.)
878 * @throws UnsupportedOperationException if the {@code put} operation
879 * is not supported by this map
880 * (<a href="Collection.html#optional-restrictions">optional</a>)
881 * @throws ClassCastException if the class of the specified key or value
882 * prevents it from being stored in this map
883 * (<a href="Collection.html#optional-restrictions">optional</a>)
884 * @throws NullPointerException if the specified key or value is null,
885 * and this map does not permit null keys or values
886 * @throws IllegalArgumentException if some property of the specified key
887 * or value prevents it from being stored in this map
888 * @since 1.8
889 */
890 default V replace(K key, V value) {
891 V curValue;
892 if(((curValue = get(key)) != null) || containsKey(key)) {
893 if(curValue == put(key, value)) {
894 return curValue;
895 }
896 } else {
897 return curValue;
898 }
899 throw new ConcurrentModificationException("value unexpectedly changed");
900 }
901
902 /**
903 * If the specified key is not already associated with a value (or
904 * is mapped to {@code null}), attempts to compute its value using
905 * the given mapping function and enters it into this map unless
906 * {@code null}.
907 *
908 * <p>If the function returns {@code null} no mapping is recorded. If
909 * the function itself throws an (unchecked) exception, the
910 * exception is rethrown, and no mapping is recorded. The most
911 * common usage is to construct a new object serving as an initial
912 * mapped value or memoized result, as in:
913 *
914 * <pre> {@code
915 * map.computeIfAbsent(key, k -> new Value(f(k)));
916 * }</pre>
917 *
918 * <p>The default implementation makes no guarantees about synchronization
919 * or atomicity properties of this method. Any implementation providing
920 * atomicity guarantees must override this method and document its
921 * concurrency properties. In particular, all implementations of
922 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
923 * whether the function is applied once atomically only if the value is not
924 * present.
925 *
926 * @implSpec
927 * The default implementation is equivalent to the following
928 * steps for this {@code map}, then returning the current value or
929 * {@code null} if now absent:
930 *
931 * <pre> {@code
932 * if (map.get(key) == null) {
933 * V newValue = mappingFunction.apply(key);
934 * if (newValue != null)
935 * map.putIfAbsent(key, newValue);
936 * }
937 * }</pre>
938 *
939 * @param key key with which the specified value is to be associated
940 * @param mappingFunction the function to compute a value
941 * @return the current (existing or computed) value associated with
942 * the specified key, or null if the computed value is null
943 * @throws NullPointerException if the specified key is null and
944 * this map does not support null keys, or the
945 * mappingFunction is null
946 * @throws UnsupportedOperationException if the {@code put} operation
947 * is not supported by this map
948 * (<a href="Collection.html#optional-restrictions">optional</a>)
949 * @throws ClassCastException if the class of the specified key or value
950 * prevents it from being stored in this map
951 * (<a href="Collection.html#optional-restrictions">optional</a>)
952 * @since 1.8
953 */
954 default V computeIfAbsent(K key,
955 Function<? super K, ? extends V> mappingFunction) {
956 Objects.requireNonNull(mappingFunction);
957 V v;
958 if ((v = get(key)) == null) {
959 V newValue;
960 if ((newValue = mappingFunction.apply(key)) != null) {
961 if (null == putIfAbsent(key, newValue))
962 return newValue;
963 throw new ConcurrentModificationException("expected value changed");
964 }
965 }
966
967 return v;
968 }
969
970 /**
971 * If the value for the specified key is present and non-null, attempts to
972 * compute a new mapping given the key and its current mapped value.
973 *
974 * <p>If the function returns {@code null}, the mapping is removed. If the
975 * function itself throws an (unchecked) exception, the exception is
976 * rethrown, and the current mapping is left unchanged.
977 *
978 * <p>The default implementation makes no guarantees about synchronization
979 * or atomicity properties of this method. Any implementation providing
980 * atomicity guarantees must override this method and document its
981 * concurrency properties. In particular, all implementations of
982 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
983 * whether the function is applied once atomically only if the value is not
984 * present. Any class that permits null values must document
985 * whether and how this method distinguishes absence from null mappings.
986 *
987 * @implSpec
988 * The default implementation is equivalent to performing the
989 * following steps for this {@code map}, then returning the
990 * current value or {@code null} if now absent:
991 *
992 * <pre> {@code
993 * if (map.get(key) != null) {
994 * V oldValue = map.get(key);
995 * V newValue = remappingFunction.apply(key, oldValue);
996 * if (newValue != null)
997 * map.replace(key, oldValue, newValue);
998 * else
999 * map.remove(key, oldValue);
1000 * }
1001 * }</pre>
1002 *
1003 * @param key key with which the specified value is to be associated
1004 * @param remappingFunction the function to compute a value
1005 * @return the new value associated with the specified key, or null if none
1006 * @throws NullPointerException if the specified key is null and
1007 * this map does not support null keys, or the
1008 * remappingFunction is null
1009 * @throws UnsupportedOperationException if the {@code put} operation
1010 * is not supported by this map
1011 * (<a href="Collection.html#optional-restrictions">optional</a>)
1012 * @throws ClassCastException if the class of the specified key or value
1013 * prevents it from being stored in this map
1014 * (<a href="Collection.html#optional-restrictions">optional</a>)
1015 * @since 1.8
1016 */
1017 default V computeIfPresent(K key,
1018 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1019 Objects.requireNonNull(remappingFunction);
1020 V oldValue;
1021 if((oldValue = get(key)) != null) {
1022 V newValue = remappingFunction.apply(key, oldValue);
1023 if (newValue != null) {
1024 if (replace(key, oldValue, newValue))
1025 return newValue;
1026 } else if (remove(key, oldValue))
1027 return null;
1028 } else {
1029 return null;
1030 }
1031 throw new ConcurrentModificationException("unexpected value change");
1032 }
1033
1034 /**
1035 * Attempts to compute a mapping for the specified key and its
1036 * current mapped value (or {@code null} if there is no current
1037 * mapping). For example, to either create or append a {@code
1038 * String msg} to a value mapping:
1039 *
1040 * <pre> {@code
1041 * map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))}</pre>
1042 * (Method {@link #merge merge()} is often simpler to use for such purposes.)
1043 *
1044 * <p>If the function returns {@code null}, the mapping is removed (or
1045 * remains absent if initially absent). If the function itself throws an
1046 * (unchecked) exception, the exception is rethrown, and the current mapping
1047 * is left unchanged.
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 function is applied once atomically only if the value is not
1055 * present. Any class that permits null values must document
1056 * whether and how this method distinguishes absence from null mappings.
1057 *
1058 * @implSpec
1059 * The default implementation is equivalent to performing the following
1060 * steps for this {@code map}, then returning the current value or
1061 * {@code null} if absent:
1062 *
1063 * <pre> {@code
1064 * V oldValue = map.get(key);
1065 * V newValue = remappingFunction.apply(key, oldValue);
1066 * if (oldValue != null ) {
1067 * if (newValue != null)
1068 * map.replace(key, oldValue, newValue);
1069 * else
1070 * map.remove(key, oldValue);
1071 * } else {
1072 * if (newValue != null)
1073 * map.putIfAbsent(key, newValue);
1074 * else
1075 * return null;
1076 * }
1077 * }</pre>
1078 *
1079 * @param key key with which the specified value is to be associated
1080 * @param remappingFunction the function to compute a value
1081 * @return the new value associated with the specified key, or null if none
1082 * @throws NullPointerException if the specified key is null and
1083 * this map does not support null keys, or the
1084 * remappingFunction is null
1085 * @throws UnsupportedOperationException if the {@code put} operation
1086 * is not supported by this map
1087 * (<a href="Collection.html#optional-restrictions">optional</a>)
1088 * @throws ClassCastException if the class of the specified key or value
1089 * prevents it from being stored in this map
1090 * (<a href="Collection.html#optional-restrictions">optional</a>)
1091 * @since 1.8
1092 */
1093 default V compute(K key,
1094 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1095 Objects.requireNonNull(remappingFunction);
1096 V oldValue = get(key);
1097
1098 V newValue = remappingFunction.apply(key, oldValue);
1099 if (newValue == null) {
1100 // delete mapping
1101 if(oldValue != null || containsKey(key)) {
1102 // something to remove
1103 if (remove(key, oldValue)) {
1104 // removed the old value as expected
1105 return null;
1106 }
1107 } else {
1108 // nothing to do. Leave things as they were.
1109 return null;
1110 }
1111 } else {
1112 // add or replace old mapping
1113 if (oldValue != null) {
1114 // replace
1115 if (replace(key, oldValue, newValue)) {
1116 // replaced as expected.
1117 return newValue;
1118 }
1119 } else {
1120 // add (replace if oldValue was null)
1121 if (putIfAbsent(key, newValue) == null) {
1122 // replaced
1123 return newValue;
1124 }
1125 }
1126 }
1127 throw new ConcurrentModificationException("expected value change");
1128 }
1129
1130 /**
1131 * If the specified key is not already associated with a value or is
1132 * associated with null, associates it with the given value.
1133 * Otherwise, replaces the value with the results of the given
1134 * remapping function, or removes if the result is {@code null}. This
1135 * method may be of use when combining multiple mapped values for a key.
1136 * For example, to either create or append a {@code String msg} to a
1137 * value mapping:
1138 *
1139 * <pre> {@code
1140 * map.merge(key, msg, String::concat)
1141 * }</pre>
1142 *
1143 * <p>If the function returns {@code null}, the mapping is removed (or
1144 * remains absent if initially absent). If the function itself throws an
1145 * (unchecked) exception, the exception is rethrown, and the current mapping
1146 * is left unchanged.
1147 *
1148 * <p>The default implementation makes no guarantees about synchronization
1149 * or atomicity properties of this method. Any implementation providing
1150 * atomicity guarantees must override this method and document its
1151 * concurrency properties. In particular, all implementations of
1152 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1153 * whether the function is applied once atomically only if the value is not
1154 * present.
1155 *
1156 * @implSpec
1157 * The default implementation is equivalent to performing the
1158 * following steps for this {@code map}, then returning the
1159 * current value or {@code null} if absent:
1160 *
1161 * <pre> {@code
1162 * V oldValue = map.get(key);
1163 * V newValue = (oldValue == null) ? value :
1164 * remappingFunction.apply(oldValue, value);
1165 * if (newValue == null)
1166 * map.remove(key, oldValue);
1167 * else if (oldValue == null)
1168 * map.putIfAbsent(key, newValue);
1169 * else
1170 * map.replace(key, oldValue, newValue);
1171 * }</pre>
1172 *
1173 * @param key key with which the specified value is to be associated
1174 * @param value the value to use if absent
1175 * @param remappingFunction the function to recompute a value if present
1176 * @return the new value associated with the specified key, or null if none
1177 * @throws UnsupportedOperationException if the {@code put} operation
1178 * is not supported by this map
1179 * (<a href="Collection.html#optional-restrictions">optional</a>)
1180 * @throws ClassCastException if the class of the specified key or value
1181 * prevents it from being stored in this map
1182 * (<a href="Collection.html#optional-restrictions">optional</a>)
1183 * @throws NullPointerException if the specified key is null and
1184 * this map does not support null keys, or the
1185 * remappingFunction is null
1186 * @since 1.8
1187 */
1188 default V merge(K key, V value,
1189 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
1190 Objects.requireNonNull(remappingFunction);
1191 V oldValue = get(key);
1192 if (oldValue != null) {
1193 V newValue = remappingFunction.apply(oldValue, value);
1194 if (newValue != null) {
1195 if (replace(key, oldValue, newValue))
1196 return newValue;
1197 } else if (remove(key, oldValue)) {
1198 return null;
1199 }
1200 } else {
1201 if (value == null) {
1202 if(remove(key) == null) {
1203 return null;
1204 }
1205 } else {
1206 if (putIfAbsent(key, value) == null) {
1207 return value;
1208 }
1209 }
1210 }
1211 throw new ConcurrentModificationException("unexpected value change");
1212 }
1213 }