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="{@docRoot}/java/util/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="{@docRoot}/java/util/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="{@docRoot}/java/util/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="{@docRoot}/java/util/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="{@docRoot}/java/util/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="{@docRoot}/java/util/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="{@docRoot}/java/util/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="{@docRoot}/java/util/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 * @since 1.8
469 */
470 public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K,V>> comparingByKey() {
471 return (Comparator<Map.Entry<K, V>> & Serializable)
472 (c1, c2) -> c1.getKey().compareTo(c2.getKey());
473 }
474
475 /**
476 * Returns a comparator that compares {@link Map.Entry} in natural order on value.
477 *
478 * <p>The returned comparator is serializable and throws {@link
479 * NullPointerException} when comparing an entry with null values.
480 *
481 * @param <K> the type of the map keys
482 * @param <V> the {@link Comparable} type of the map values
483 * @return a comparator that compares {@link Map.Entry} in natural order on value.
484 * @see Comparable
485 * @since 1.8
486 */
487 public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K,V>> comparingByValue() {
488 return (Comparator<Map.Entry<K, V>> & Serializable)
489 (c1, c2) -> c1.getValue().compareTo(c2.getValue());
490 }
491
492 /**
493 * Returns a comparator that compares {@link Map.Entry} by key using the given
494 * {@link Comparator}.
495 *
496 * <p>The returned comparator is serializable if the specified comparator
497 * is also serializable.
498 *
499 * @param <K> the type of the map keys
500 * @param <V> the type of the map values
501 * @param cmp the key {@link Comparator}
502 * @return a comparator that compares {@link Map.Entry} by the key.
503 * @since 1.8
504 */
505 public static <K, V> Comparator<Map.Entry<K, V>> comparingByKey(Comparator<? super K> cmp) {
506 Objects.requireNonNull(cmp);
507 return (Comparator<Map.Entry<K, V>> & Serializable)
508 (c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());
509 }
510
511 /**
512 * Returns a comparator that compares {@link Map.Entry} by value using the given
513 * {@link Comparator}.
514 *
515 * <p>The returned comparator is serializable if the specified comparator
516 * is also serializable.
517 *
518 * @param <K> the type of the map keys
519 * @param <V> the type of the map values
520 * @param cmp the value {@link Comparator}
521 * @return a comparator that compares {@link Map.Entry} by the value.
522 * @since 1.8
523 */
524 public static <K, V> Comparator<Map.Entry<K, V>> comparingByValue(Comparator<? super V> cmp) {
525 Objects.requireNonNull(cmp);
526 return (Comparator<Map.Entry<K, V>> & Serializable)
527 (c1, c2) -> cmp.compare(c1.getValue(), c2.getValue());
528 }
529 }
530
531 // Comparison and hashing
532
533 /**
534 * Compares the specified object with this map for equality. Returns
535 * <tt>true</tt> if the given object is also a map and the two maps
536 * represent the same mappings. More formally, two maps <tt>m1</tt> and
537 * <tt>m2</tt> represent the same mappings if
538 * <tt>m1.entrySet().equals(m2.entrySet())</tt>. This ensures that the
539 * <tt>equals</tt> method works properly across different implementations
540 * of the <tt>Map</tt> interface.
541 *
542 * @param o object to be compared for equality with this map
543 * @return <tt>true</tt> if the specified object is equal to this map
544 */
545 boolean equals(Object o);
546
547 /**
548 * Returns the hash code value for this map. The hash code of a map is
549 * defined to be the sum of the hash codes of each entry in the map's
550 * <tt>entrySet()</tt> view. This ensures that <tt>m1.equals(m2)</tt>
551 * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps
552 * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of
553 * {@link Object#hashCode}.
554 *
555 * @return the hash code value for this map
556 * @see Map.Entry#hashCode()
557 * @see Object#equals(Object)
558 * @see #equals(Object)
559 */
560 int hashCode();
561
562 // Defaultable methods
563
564 /**
565 * Returns the value to which the specified key is mapped, or
566 * {@code defaultValue} if this map contains no mapping for the key.
567 *
568 * @implSpec
569 * The default implementation makes no guarantees about synchronization
570 * or atomicity properties of this method. Any implementation providing
571 * atomicity guarantees must override this method and document its
572 * concurrency properties.
573 *
574 * @param key the key whose associated value is to be returned
575 * @param defaultValue the default mapping of the key
576 * @return the value to which the specified key is mapped, or
577 * {@code defaultValue} if this map contains no mapping for the key
578 * @throws ClassCastException if the key is of an inappropriate type for
579 * this map
580 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
581 * @throws NullPointerException if the specified key is null and this map
582 * does not permit null keys
583 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
584 * @since 1.8
585 */
586 default V getOrDefault(Object key, V defaultValue) {
587 V v;
588 return (((v = get(key)) != null) || containsKey(key))
589 ? v
590 : defaultValue;
591 }
592
593 /**
594 * Performs the given action for each entry in this map until all entries
595 * have been processed or the action throws an exception. Unless
596 * otherwise specified by the implementing class, actions are performed in
597 * the order of entry set iteration (if an iteration order is specified.)
598 * Exceptions thrown by the action are relayed to the caller.
599 *
600 * @implSpec
601 * The default implementation is equivalent to, for this {@code map}:
602 * <pre> {@code
603 * for (Map.Entry<K, V> entry : map.entrySet())
604 * action.accept(entry.getKey(), entry.getValue());
605 * }</pre>
606 *
607 * The default implementation makes no guarantees about synchronization
608 * or atomicity properties of this method. Any implementation providing
609 * atomicity guarantees must override this method and document its
610 * concurrency properties.
611 *
612 * @param action The action to be performed for each entry
613 * @throws NullPointerException if the specified action is null
614 * @throws ConcurrentModificationException if an entry is found to be
615 * removed during iteration
616 * @since 1.8
617 */
618 default void forEach(BiConsumer<? super K, ? super V> action) {
619 Objects.requireNonNull(action);
620 for (Map.Entry<K, V> entry : entrySet()) {
621 K k;
622 V v;
623 try {
624 k = entry.getKey();
625 v = entry.getValue();
626 } catch(IllegalStateException ise) {
627 // this usually means the entry is no longer in the map.
628 throw new ConcurrentModificationException(ise);
629 }
630 action.accept(k, v);
631 }
632 }
633
634 /**
635 * Replaces each entry's value with the result of invoking the given
636 * function on that entry until all entries have been processed or the
637 * function throws an exception. Exceptions thrown by the function are
638 * relayed to the caller.
639 *
640 * @implSpec
641 * <p>The default implementation is equivalent to, for this {@code map}:
642 * <pre> {@code
643 * for (Map.Entry<K, V> entry : map.entrySet())
644 * entry.setValue(function.apply(entry.getKey(), entry.getValue()));
645 * }</pre>
646 *
647 * <p>The default implementation makes no guarantees about synchronization
648 * or atomicity properties of this method. Any implementation providing
649 * atomicity guarantees must override this method and document its
650 * concurrency properties.
651 *
652 * @param function the function to apply to each entry
653 * @throws UnsupportedOperationException if the {@code set} operation
654 * is not supported by this map's entry set iterator.
655 * @throws ClassCastException if the class of a replacement value
656 * prevents it from being stored in this map
657 * @throws NullPointerException if the specified function is null, or the
658 * specified replacement value is null, and this map does not permit null
659 * values
660 * @throws ClassCastException if a replacement value is of an inappropriate
661 * type for this map
662 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
663 * @throws NullPointerException if function or a replacement value is null,
664 * and this map does not permit null keys or values
665 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
666 * @throws IllegalArgumentException if some property of a replacement value
667 * prevents it from being stored in this map
668 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
669 * @throws ConcurrentModificationException if an entry is found to be
670 * removed during iteration
671 * @since 1.8
672 */
673 default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
674 Objects.requireNonNull(function);
675 for (Map.Entry<K, V> entry : entrySet()) {
676 K k;
677 V v;
678 try {
679 k = entry.getKey();
680 v = entry.getValue();
681 } catch(IllegalStateException ise) {
682 // this usually means the entry is no longer in the map.
683 throw new ConcurrentModificationException(ise);
684 }
685
686 // ise thrown from function is not a cme.
687 v = function.apply(k, v);
688
689 try {
690 entry.setValue(v);
691 } catch(IllegalStateException ise) {
692 // this usually means the entry is no longer in the map.
693 throw new ConcurrentModificationException(ise);
694 }
695 }
696 }
697
698 /**
699 * If the specified key is not already associated with a value (or is mapped
700 * to {@code null}) associates it with the given value and returns
701 * {@code null}, else returns the current value.
702 *
703 * @implSpec
704 * The default implementation is equivalent to, for this {@code
705 * map}:
706 *
707 * <pre> {@code
708 * V v = map.get(key);
709 * if (v == null)
710 * v = map.put(key, value);
711 *
712 * return v;
713 * }</pre>
714 *
715 * <p>The default implementation makes no guarantees about synchronization
716 * or atomicity properties of this method. Any implementation providing
717 * atomicity guarantees must override this method and document its
718 * concurrency properties.
719 *
720 * @param key key with which the specified value is to be associated
721 * @param value value to be associated with the specified key
722 * @return the previous value associated with the specified key, or
723 * {@code null} if there was no mapping for the key.
724 * (A {@code null} return can also indicate that the map
725 * previously associated {@code null} with the key,
726 * if the implementation supports null values.)
727 * @throws UnsupportedOperationException if the {@code put} operation
728 * is not supported by this map
729 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
730 * @throws ClassCastException if the key or value is of an inappropriate
731 * type for this map
732 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
733 * @throws NullPointerException if the specified key or value is null,
734 * and this map does not permit null keys or values
735 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
736 * @throws IllegalArgumentException if some property of the specified key
737 * or value prevents it from being stored in this map
738 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
739 * @since 1.8
740 */
741 default V putIfAbsent(K key, V value) {
742 V v = get(key);
743 if (v == null) {
744 v = put(key, value);
745 }
746
747 return v;
748 }
749
750 /**
751 * Removes the entry for the specified key only if it is currently
752 * mapped to the specified value.
753 *
754 * @implSpec
755 * The default implementation is equivalent to, for this {@code map}:
756 *
757 * <pre> {@code
758 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
759 * map.remove(key);
760 * return true;
761 * } else
762 * return false;
763 * }</pre>
764 *
765 * <p>The default implementation makes no guarantees about synchronization
766 * or atomicity properties of this method. Any implementation providing
767 * atomicity guarantees must override this method and document its
768 * concurrency properties.
769 *
770 * @param key key with which the specified value is associated
771 * @param value value expected to be associated with the specified key
772 * @return {@code true} if the value was removed
773 * @throws UnsupportedOperationException if the {@code remove} operation
774 * is not supported by this map
775 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
776 * @throws ClassCastException if the key or value is of an inappropriate
777 * type for this map
778 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
779 * @throws NullPointerException if the specified key or value is null,
780 * and this map does not permit null keys or values
781 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
782 * @since 1.8
783 */
784 default boolean remove(Object key, Object value) {
785 Object curValue = get(key);
786 if (!Objects.equals(curValue, value) ||
787 (curValue == null && !containsKey(key))) {
788 return false;
789 }
790 remove(key);
791 return true;
792 }
793
794 /**
795 * Replaces the entry for the specified key only if currently
796 * mapped to the specified value.
797 *
798 * @implSpec
799 * The default implementation is equivalent to, for this {@code map}:
800 *
801 * <pre> {@code
802 * if (map.containsKey(key) && Objects.equals(map.get(key), value)) {
803 * map.put(key, newValue);
804 * return true;
805 * } else
806 * return false;
807 * }</pre>
808 *
809 * The default implementation does not throw NullPointerException
810 * for maps that do not support null values if oldValue is null unless
811 * newValue is also null.
812 *
813 * <p>The default implementation makes no guarantees about synchronization
814 * or atomicity properties of this method. Any implementation providing
815 * atomicity guarantees must override this method and document its
816 * concurrency properties.
817 *
818 * @param key key with which the specified value is associated
819 * @param oldValue value expected to be associated with the specified key
820 * @param newValue value to be associated with the specified key
821 * @return {@code true} if the value was replaced
822 * @throws UnsupportedOperationException if the {@code put} operation
823 * is not supported by this map
824 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
825 * @throws ClassCastException if the class of a specified key or value
826 * prevents it from being stored in this map
827 * @throws NullPointerException if a specified key or newValue is null,
828 * and this map does not permit null keys or values
829 * @throws NullPointerException if oldValue is null and this map does not
830 * permit null values
831 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
832 * @throws IllegalArgumentException if some property of a specified key
833 * or value prevents it from being stored in this map
834 * @since 1.8
835 */
836 default boolean replace(K key, V oldValue, V newValue) {
837 Object curValue = get(key);
838 if (!Objects.equals(curValue, oldValue) ||
839 (curValue == null && !containsKey(key))) {
840 return false;
841 }
842 put(key, newValue);
843 return true;
844 }
845
846 /**
847 * Replaces the entry for the specified key only if it is
848 * currently mapped to some value.
849 *
850 * @implSpec
851 * The default implementation is equivalent to, for this {@code map}:
852 *
853 * <pre> {@code
854 * if (map.containsKey(key)) {
855 * return map.put(key, value);
856 * } else
857 * return null;
858 * }</pre>
859 *
860 * <p>The default implementation makes no guarantees about synchronization
861 * or atomicity properties of this method. Any implementation providing
862 * atomicity guarantees must override this method and document its
863 * concurrency properties.
864 *
865 * @param key key with which the specified value is associated
866 * @param value value to be associated with the specified key
867 * @return the previous value associated with the specified key, or
868 * {@code null} if there was no mapping for the key.
869 * (A {@code null} return can also indicate that the map
870 * previously associated {@code null} with the key,
871 * if the implementation supports null values.)
872 * @throws UnsupportedOperationException if the {@code put} operation
873 * is not supported by this map
874 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
875 * @throws ClassCastException if the class of the specified key or value
876 * prevents it from being stored in this map
877 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
878 * @throws NullPointerException if the specified key or value is null,
879 * and this map does not permit null keys or values
880 * @throws IllegalArgumentException if some property of the specified key
881 * or value prevents it from being stored in this map
882 * @since 1.8
883 */
884 default V replace(K key, V value) {
885 V curValue;
886 if (((curValue = get(key)) != null) || containsKey(key)) {
887 curValue = put(key, value);
888 }
889 return curValue;
890 }
891
892 /**
893 * If the specified key is not already associated with a value (or is mapped
894 * to {@code null}), attempts to compute its value using the given mapping
895 * function and enters it into this map unless {@code null}.
896 *
897 * <p>If the mapping function returns {@code null}, no mapping is recorded.
898 * If the mapping function itself throws an (unchecked) exception, the
899 * exception is rethrown, and no mapping is recorded. The most
900 * common usage is to construct a new object serving as an initial
901 * mapped value or memoized result, as in:
902 *
903 * <pre> {@code
904 * map.computeIfAbsent(key, k -> new Value(f(k)));
905 * }</pre>
906 *
907 * <p>Or to implement a multi-value map, {@code Map<K,Collection<V>>},
908 * supporting multiple values per key:
909 *
910 * <pre> {@code
911 * map.computeIfAbsent(key, k -> new HashSet<V>()).add(v);
912 * }</pre>
913 *
914 * <p>The mapping function should not modify this map during computation.
915 *
916 * @implSpec
917 * The default implementation is equivalent to the following steps for this
918 * {@code map}, then returning the current value or {@code null} if now
919 * absent:
920 *
921 * <pre> {@code
922 * if (map.get(key) == null) {
923 * V newValue = mappingFunction.apply(key);
924 * if (newValue != null)
925 * map.put(key, newValue);
926 * }
927 * }</pre>
928 *
929 * <p>The default implementation makes no guarantees about detecting if the
930 * mapping function modifies this map during computation and, if
931 * appropriate, reporting an error. Non-concurrent implementations should
932 * override this method and, on a best-effort basis, throw a
933 * {@code ConcurrentModificationException} if it is detected that the
934 * mapping function modifies this map during computation. Concurrent
935 * implementations should override this method and, on a best-effort basis,
936 * throw an {@code IllegalStateException} if it is detected that the
937 * mapping function modifies this map during computation and as a result
938 * computation would never complete.
939 *
940 * <p>The default implementation makes no guarantees about synchronization
941 * or atomicity properties of this method. Any implementation providing
942 * atomicity guarantees must override this method and document its
943 * concurrency properties. In particular, all implementations of
944 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
945 * whether the mapping function is applied once atomically only if the value
946 * is not present.
947 *
948 * @param key key with which the specified value is to be associated
949 * @param mappingFunction the mapping function to compute a value
950 * @return the current (existing or computed) value associated with
951 * the specified key, or null if the computed value is null
952 * @throws NullPointerException if the specified key is null and
953 * this map does not support null keys, or the mappingFunction
954 * is null
955 * @throws UnsupportedOperationException if the {@code put} operation
956 * is not supported by this map
957 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
958 * @throws ClassCastException if the class of the specified key or value
959 * prevents it from being stored in this map
960 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
961 * @since 1.8
962 */
963 default V computeIfAbsent(K key,
964 Function<? super K, ? extends V> mappingFunction) {
965 Objects.requireNonNull(mappingFunction);
966 V v;
967 if ((v = get(key)) == null) {
968 V newValue;
969 if ((newValue = mappingFunction.apply(key)) != null) {
970 put(key, newValue);
971 return newValue;
972 }
973 }
974
975 return v;
976 }
977
978 /**
979 * If the value for the specified key is present and non-null, attempts to
980 * compute a new mapping given the key and its current mapped value.
981 *
982 * <p>If the remapping function returns {@code null}, the mapping is removed.
983 * If the remapping function itself throws an (unchecked) exception, the
984 * exception is rethrown, and the current mapping is left unchanged.
985 *
986 * <p>The remapping function should not modify this map during computation.
987 *
988 * @implSpec
989 * The default implementation is equivalent to performing the following
990 * steps for this {@code map}, then returning the current value or
991 * {@code null} if now absent:
992 *
993 * <pre> {@code
994 * if (map.get(key) != null) {
995 * V oldValue = map.get(key);
996 * V newValue = remappingFunction.apply(key, oldValue);
997 * if (newValue != null)
998 * map.put(key, newValue);
999 * else
1000 * map.remove(key);
1001 * }
1002 * }</pre>
1003 *
1004 * <p>The default implementation makes no guarantees about detecting if the
1005 * remapping function modifies this map during computation and, if
1006 * appropriate, reporting an error. Non-concurrent implementations should
1007 * override this method and, on a best-effort basis, throw a
1008 * {@code ConcurrentModificationException} if it is detected that the
1009 * remapping function modifies this map during computation. Concurrent
1010 * implementations should override this method and, on a best-effort basis,
1011 * throw an {@code IllegalStateException} if it is detected that the
1012 * remapping function modifies this map during computation and as a result
1013 * computation would never complete.
1014 *
1015 * <p>The default implementation makes no guarantees about synchronization
1016 * or atomicity properties of this method. Any implementation providing
1017 * atomicity guarantees must override this method and document its
1018 * concurrency properties. In particular, all implementations of
1019 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1020 * whether the remapping function is applied once atomically only if the
1021 * value is not present.
1022 *
1023 * @param key key with which the specified value is to be associated
1024 * @param remappingFunction the remapping function to compute a value
1025 * @return the new value associated with the specified key, or null if none
1026 * @throws NullPointerException if the specified key is null and
1027 * this map does not support null keys, or the
1028 * remappingFunction is null
1029 * @throws UnsupportedOperationException if the {@code put} operation
1030 * is not supported by this map
1031 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1032 * @throws ClassCastException if the class of the specified key or value
1033 * prevents it from being stored in this map
1034 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1035 * @since 1.8
1036 */
1037 default V computeIfPresent(K key,
1038 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1039 Objects.requireNonNull(remappingFunction);
1040 V oldValue;
1041 if ((oldValue = get(key)) != null) {
1042 V newValue = remappingFunction.apply(key, oldValue);
1043 if (newValue != null) {
1044 put(key, newValue);
1045 return newValue;
1046 } else {
1047 remove(key);
1048 return null;
1049 }
1050 } else {
1051 return null;
1052 }
1053 }
1054
1055 /**
1056 * Attempts to compute a mapping for the specified key and its current
1057 * mapped value (or {@code null} if there is no current mapping). For
1058 * example, to either create or append a {@code String} msg to a value
1059 * mapping:
1060 *
1061 * <pre> {@code
1062 * map.compute(key, (k, v) -> (v == null) ? msg : v.concat(msg))}</pre>
1063 * (Method {@link #merge merge()} is often simpler to use for such purposes.)
1064 *
1065 * <p>If the remapping function returns {@code null}, the mapping is removed
1066 * (or remains absent if initially absent). If the remapping function
1067 * itself throws an (unchecked) exception, the exception is rethrown, and
1068 * the current mapping is left unchanged.
1069 *
1070 * <p>The remapping function should not modify this map during computation.
1071 *
1072 * @implSpec
1073 * The default implementation is equivalent to performing the following
1074 * steps for this {@code map}, then returning the current value or
1075 * {@code null} if absent:
1076 *
1077 * <pre> {@code
1078 * V oldValue = map.get(key);
1079 * V newValue = remappingFunction.apply(key, oldValue);
1080 * if (oldValue != null ) {
1081 * if (newValue != null)
1082 * map.put(key, newValue);
1083 * else
1084 * map.remove(key);
1085 * } else {
1086 * if (newValue != null)
1087 * map.put(key, newValue);
1088 * else
1089 * return null;
1090 * }
1091 * }</pre>
1092 *
1093 * <p>The default implementation makes no guarantees about detecting if the
1094 * remapping function modifies this map during computation and, if
1095 * appropriate, reporting an error. Non-concurrent implementations should
1096 * override this method and, on a best-effort basis, throw a
1097 * {@code ConcurrentModificationException} if it is detected that the
1098 * remapping function modifies this map during computation. Concurrent
1099 * implementations should override this method and, on a best-effort basis,
1100 * throw an {@code IllegalStateException} if it is detected that the
1101 * remapping function modifies this map during computation and as a result
1102 * computation would never complete.
1103 *
1104 * <p>The default implementation makes no guarantees about synchronization
1105 * or atomicity properties of this method. Any implementation providing
1106 * atomicity guarantees must override this method and document its
1107 * concurrency properties. In particular, all implementations of
1108 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1109 * whether the remapping function is applied once atomically only if the
1110 * value is not present.
1111 *
1112 * @param key key with which the specified value is to be associated
1113 * @param remappingFunction the remapping function to compute a value
1114 * @return the new value associated with the specified key, or null if none
1115 * @throws NullPointerException if the specified key is null and
1116 * this map does not support null keys, or the
1117 * remappingFunction is null
1118 * @throws UnsupportedOperationException if the {@code put} operation
1119 * is not supported by this map
1120 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1121 * @throws ClassCastException if the class of the specified key or value
1122 * prevents it from being stored in this map
1123 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1124 * @since 1.8
1125 */
1126 default V compute(K key,
1127 BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1128 Objects.requireNonNull(remappingFunction);
1129 V oldValue = get(key);
1130
1131 V newValue = remappingFunction.apply(key, oldValue);
1132 if (newValue == null) {
1133 // delete mapping
1134 if (oldValue != null || containsKey(key)) {
1135 // something to remove
1136 remove(key);
1137 return null;
1138 } else {
1139 // nothing to do. Leave things as they were.
1140 return null;
1141 }
1142 } else {
1143 // add or replace old mapping
1144 put(key, newValue);
1145 return newValue;
1146 }
1147 }
1148
1149 /**
1150 * If the specified key is not already associated with a value or is
1151 * associated with null, associates it with the given non-null value.
1152 * Otherwise, replaces the associated value with the results of the given
1153 * remapping function, or removes if the result is {@code null}. This
1154 * method may be of use when combining multiple mapped values for a key.
1155 * For example, to either create or append a {@code String msg} to a
1156 * value mapping:
1157 *
1158 * <pre> {@code
1159 * map.merge(key, msg, String::concat)
1160 * }</pre>
1161 *
1162 * <p>If the remapping function returns {@code null}, the mapping is removed.
1163 * If the remapping function itself throws an (unchecked) exception, the
1164 * exception is rethrown, and the current mapping is left unchanged.
1165 *
1166 * <p>The remapping function should not modify this map during computation.
1167 *
1168 * @implSpec
1169 * The default implementation is equivalent to performing the following
1170 * steps for this {@code map}, then returning the current value or
1171 * {@code null} if absent:
1172 *
1173 * <pre> {@code
1174 * V oldValue = map.get(key);
1175 * V newValue = (oldValue == null) ? value :
1176 * remappingFunction.apply(oldValue, value);
1177 * if (newValue == null)
1178 * map.remove(key);
1179 * else
1180 * map.put(key, newValue);
1181 * }</pre>
1182 *
1183 * <p>The default implementation makes no guarantees about detecting if the
1184 * remapping function modifies this map during computation and, if
1185 * appropriate, reporting an error. Non-concurrent implementations should
1186 * override this method and, on a best-effort basis, throw a
1187 * {@code ConcurrentModificationException} if it is detected that the
1188 * remapping function modifies this map during computation. Concurrent
1189 * implementations should override this method and, on a best-effort basis,
1190 * throw an {@code IllegalStateException} if it is detected that the
1191 * remapping function modifies this map during computation and as a result
1192 * computation would never complete.
1193 *
1194 * <p>The default implementation makes no guarantees about synchronization
1195 * or atomicity properties of this method. Any implementation providing
1196 * atomicity guarantees must override this method and document its
1197 * concurrency properties. In particular, all implementations of
1198 * subinterface {@link java.util.concurrent.ConcurrentMap} must document
1199 * whether the remapping function is applied once atomically only if the
1200 * value is not present.
1201 *
1202 * @param key key with which the resulting value is to be associated
1203 * @param value the non-null value to be merged with the existing value
1204 * associated with the key or, if no existing value or a null value
1205 * is associated with the key, to be associated with the key
1206 * @param remappingFunction the remapping function to recompute a value if
1207 * present
1208 * @return the new value associated with the specified key, or null if no
1209 * value is associated with the key
1210 * @throws UnsupportedOperationException if the {@code put} operation
1211 * is not supported by this map
1212 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1213 * @throws ClassCastException if the class of the specified key or value
1214 * prevents it from being stored in this map
1215 * (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
1216 * @throws NullPointerException if the specified key is null and this map
1217 * does not support null keys or the value or remappingFunction is
1218 * null
1219 * @since 1.8
1220 */
1221 default V merge(K key, V value,
1222 BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
1223 Objects.requireNonNull(remappingFunction);
1224 Objects.requireNonNull(value);
1225 V oldValue = get(key);
1226 V newValue = (oldValue == null) ? value :
1227 remappingFunction.apply(oldValue, value);
1228 if(newValue == null) {
1229 remove(key);
1230 } else {
1231 put(key, newValue);
1232 }
1233 return newValue;
1234 }
1235 }