1 /*
2 * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.util;
27
28 import java.util.function.Consumer;
29 import java.util.function.BiConsumer;
30 import java.util.function.BiFunction;
31 import java.io.IOException;
32
33 /**
34 * <p>Hash table and linked list implementation of the {@code Map} interface,
35 * with predictable iteration order. This implementation differs from
36 * {@code HashMap} in that it maintains a doubly-linked list running through
37 * all of its entries. This linked list defines the iteration ordering,
38 * which is normally the order in which keys were inserted into the map
39 * (<i>insertion-order</i>). Note that insertion order is not affected
40 * if a key is <i>re-inserted</i> into the map. (A key {@code k} is
41 * reinserted into a map {@code m} if {@code m.put(k, v)} is invoked when
42 * {@code m.containsKey(k)} would return {@code true} immediately prior to
43 * the invocation.)
44 *
45 * <p>This implementation spares its clients from the unspecified, generally
46 * chaotic ordering provided by {@link HashMap} (and {@link Hashtable}),
47 * without incurring the increased cost associated with {@link TreeMap}. It
48 * can be used to produce a copy of a map that has the same order as the
49 * original, regardless of the original map's implementation:
50 * <pre>
51 * void foo(Map m) {
52 * Map copy = new LinkedHashMap(m);
53 * ...
54 * }
55 * </pre>
56 * This technique is particularly useful if a module takes a map on input,
57 * copies it, and later returns results whose order is determined by that of
58 * the copy. (Clients generally appreciate having things returned in the same
59 * order they were presented.)
60 *
61 * <p>A special {@link #LinkedHashMap(int,float,boolean) constructor} is
62 * provided to create a linked hash map whose order of iteration is the order
63 * in which its entries were last accessed, from least-recently accessed to
64 * most-recently (<i>access-order</i>). This kind of map is well-suited to
65 * building LRU caches. Invoking the {@code put}, {@code putIfAbsent},
66 * {@code get}, {@code getOrDefault}, {@code compute}, {@code computeIfAbsent},
67 * {@code computeIfPresent}, or {@code merge} methods results
68 * in an access to the corresponding entry (assuming it exists after the
69 * invocation completes). The {@code replace} methods only result in an access
70 * of the entry if the value is replaced. The {@code putAll} method generates one
71 * entry access for each mapping in the specified map, in the order that
72 * key-value mappings are provided by the specified map's entry set iterator.
73 * <i>No other methods generate entry accesses.</i> In particular, operations
74 * on collection-views do <i>not</i> affect the order of iteration of the
75 * backing map.
76 *
77 * <p>The {@link #removeEldestEntry(Map.Entry)} method may be overridden to
78 * impose a policy for removing stale mappings automatically when new mappings
79 * are added to the map.
80 *
81 * <p>This class provides all of the optional {@code Map} operations, and
82 * permits null elements. Like {@code HashMap}, it provides constant-time
83 * performance for the basic operations ({@code add}, {@code contains} and
84 * {@code remove}), assuming the hash function disperses elements
85 * properly among the buckets. Performance is likely to be just slightly
86 * below that of {@code HashMap}, due to the added expense of maintaining the
87 * linked list, with one exception: Iteration over the collection-views
88 * of a {@code LinkedHashMap} requires time proportional to the <i>size</i>
89 * of the map, regardless of its capacity. Iteration over a {@code HashMap}
90 * is likely to be more expensive, requiring time proportional to its
91 * <i>capacity</i>.
92 *
93 * <p>A linked hash map has two parameters that affect its performance:
94 * <i>initial capacity</i> and <i>load factor</i>. They are defined precisely
95 * as for {@code HashMap}. Note, however, that the penalty for choosing an
96 * excessively high value for initial capacity is less severe for this class
97 * than for {@code HashMap}, as iteration times for this class are unaffected
98 * by capacity.
99 *
100 * <p><strong>Note that this implementation is not synchronized.</strong>
101 * If multiple threads access a linked hash map concurrently, and at least
102 * one of the threads modifies the map structurally, it <em>must</em> be
103 * synchronized externally. This is typically accomplished by
104 * synchronizing on some object that naturally encapsulates the map.
105 *
106 * If no such object exists, the map should be "wrapped" using the
107 * {@link Collections#synchronizedMap Collections.synchronizedMap}
108 * method. This is best done at creation time, to prevent accidental
109 * unsynchronized access to the map:<pre>
110 * Map m = Collections.synchronizedMap(new LinkedHashMap(...));</pre>
111 *
112 * A structural modification is any operation that adds or deletes one or more
113 * mappings or, in the case of access-ordered linked hash maps, affects
114 * iteration order. In insertion-ordered linked hash maps, merely changing
115 * the value associated with a key that is already contained in the map is not
116 * a structural modification. <strong>In access-ordered linked hash maps,
117 * merely querying the map with {@code get} is a structural modification.
118 * </strong>)
119 *
120 * <p>The iterators returned by the {@code iterator} method of the collections
121 * returned by all of this class's collection view methods are
122 * <em>fail-fast</em>: if the map is structurally modified at any time after
123 * the iterator is created, in any way except through the iterator's own
124 * {@code remove} method, the iterator will throw a {@link
125 * ConcurrentModificationException}. Thus, in the face of concurrent
126 * modification, the iterator fails quickly and cleanly, rather than risking
127 * arbitrary, non-deterministic behavior at an undetermined time in the future.
128 *
129 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
130 * as it is, generally speaking, impossible to make any hard guarantees in the
131 * presence of unsynchronized concurrent modification. Fail-fast iterators
132 * throw {@code ConcurrentModificationException} on a best-effort basis.
133 * Therefore, it would be wrong to write a program that depended on this
134 * exception for its correctness: <i>the fail-fast behavior of iterators
135 * should be used only to detect bugs.</i>
136 *
137 * <p>The spliterators returned by the spliterator method of the collections
138 * returned by all of this class's collection view methods are
139 * <em><a href="Spliterator.html#binding">late-binding</a></em>,
140 * <em>fail-fast</em>, and additionally report {@link Spliterator#ORDERED}.
141 *
142 * <p>This class is a member of the
143 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
144 * Java Collections Framework</a>.
145 *
146 * @implNote
147 * The spliterators returned by the spliterator method of the collections
148 * returned by all of this class's collection view methods are created from
149 * the iterators of the corresponding collections.
150 *
151 * @param <K> the type of keys maintained by this map
152 * @param <V> the type of mapped values
153 *
154 * @author Josh Bloch
155 * @see Object#hashCode()
156 * @see Collection
157 * @see Map
158 * @see HashMap
159 * @see TreeMap
160 * @see Hashtable
161 * @since 1.4
162 */
163 public class LinkedHashMap<K,V>
164 extends HashMap<K,V>
165 implements Map<K,V>
166 {
167
168 /*
169 * Implementation note. A previous version of this class was
170 * internally structured a little differently. Because superclass
171 * HashMap now uses trees for some of its nodes, class
172 * LinkedHashMap.Entry is now treated as intermediary node class
173 * that can also be converted to tree form. The name of this
174 * class, LinkedHashMap.Entry, is confusing in several ways in its
175 * current context, but cannot be changed. Otherwise, even though
176 * it is not exported outside this package, some existing source
177 * code is known to have relied on a symbol resolution corner case
178 * rule in calls to removeEldestEntry that suppressed compilation
179 * errors due to ambiguous usages. So, we keep the name to
180 * preserve unmodified compilability.
181 *
182 * The changes in node classes also require using two fields
183 * (head, tail) rather than a pointer to a header node to maintain
184 * the doubly-linked before/after list. This class also
185 * previously used a different style of callback methods upon
186 * access, insertion, and removal.
187 */
188
189 /**
190 * HashMap.Node subclass for normal LinkedHashMap entries.
191 */
192 static class Entry<K,V> extends HashMap.Node<K,V> {
193 Entry<K,V> before, after;
194 Entry(int hash, K key, V value, Node<K,V> next) {
195 super(hash, key, value, next);
196 }
197 }
198
199 @java.io.Serial
200 private static final long serialVersionUID = 3801124242820219131L;
201
202 /**
203 * The head (eldest) of the doubly linked list.
204 */
205 transient LinkedHashMap.Entry<K,V> head;
206
207 /**
208 * The tail (youngest) of the doubly linked list.
209 */
210 transient LinkedHashMap.Entry<K,V> tail;
211
212 /**
213 * The iteration ordering method for this linked hash map: {@code true}
214 * for access-order, {@code false} for insertion-order.
215 *
216 * @serial
217 */
218 final boolean accessOrder;
219
220 // internal utilities
221
222 // link at the end of list
223 private void linkNodeLast(LinkedHashMap.Entry<K,V> p) {
224 LinkedHashMap.Entry<K,V> last = tail;
225 tail = p;
226 if (last == null)
227 head = p;
228 else {
229 p.before = last;
230 last.after = p;
231 }
232 }
233
234 // apply src's links to dst
235 private void transferLinks(LinkedHashMap.Entry<K,V> src,
236 LinkedHashMap.Entry<K,V> dst) {
237 LinkedHashMap.Entry<K,V> b = dst.before = src.before;
238 LinkedHashMap.Entry<K,V> a = dst.after = src.after;
239 if (b == null)
240 head = dst;
241 else
242 b.after = dst;
243 if (a == null)
244 tail = dst;
245 else
246 a.before = dst;
247 }
248
249 // overrides of HashMap hook methods
250
251 void reinitialize() {
252 super.reinitialize();
253 head = tail = null;
254 }
255
256 Node<K,V> newNode(int hash, K key, V value, Node<K,V> e) {
257 LinkedHashMap.Entry<K,V> p =
258 new LinkedHashMap.Entry<>(hash, key, value, e);
259 linkNodeLast(p);
260 return p;
261 }
262
263 Node<K,V> replacementNode(Node<K,V> p, Node<K,V> next) {
264 LinkedHashMap.Entry<K,V> q = (LinkedHashMap.Entry<K,V>)p;
265 LinkedHashMap.Entry<K,V> t =
266 new LinkedHashMap.Entry<>(q.hash, q.key, q.value, next);
267 transferLinks(q, t);
268 return t;
269 }
270
271 TreeNode<K,V> newTreeNode(int hash, K key, V value, Node<K,V> next) {
272 TreeNode<K,V> p = new TreeNode<>(hash, key, value, next);
273 linkNodeLast(p);
274 return p;
275 }
276
277 TreeNode<K,V> replacementTreeNode(Node<K,V> p, Node<K,V> next) {
278 LinkedHashMap.Entry<K,V> q = (LinkedHashMap.Entry<K,V>)p;
279 TreeNode<K,V> t = new TreeNode<>(q.hash, q.key, q.value, next);
280 transferLinks(q, t);
281 return t;
282 }
283
284 void afterNodeRemoval(Node<K,V> e) { // unlink
285 LinkedHashMap.Entry<K,V> p =
286 (LinkedHashMap.Entry<K,V>)e, b = p.before, a = p.after;
287 p.before = p.after = null;
288 if (b == null)
289 head = a;
290 else
291 b.after = a;
292 if (a == null)
293 tail = b;
294 else
295 a.before = b;
296 }
297
298 void afterNodeInsertion(boolean evict) { // possibly remove eldest
299 LinkedHashMap.Entry<K,V> first;
300 if (evict && (first = head) != null && removeEldestEntry(first)) {
301 K key = first.key;
302 removeNode(hash(key), key, null, false, true);
303 }
304 }
305
306 void afterNodeAccess(Node<K,V> e) { // move node to last
307 LinkedHashMap.Entry<K,V> last;
308 if (accessOrder && (last = tail) != e) {
309 LinkedHashMap.Entry<K,V> p =
310 (LinkedHashMap.Entry<K,V>)e, b = p.before, a = p.after;
311 p.after = null;
312 if (b == null)
313 head = a;
314 else
315 b.after = a;
316 if (a != null)
317 a.before = b;
318 else
319 last = b;
320 if (last == null)
321 head = p;
322 else {
323 p.before = last;
324 last.after = p;
325 }
326 tail = p;
327 ++modCount;
328 }
329 }
330
331 void internalWriteEntries(java.io.ObjectOutputStream s) throws IOException {
332 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
333 s.writeObject(e.key);
334 s.writeObject(e.value);
335 }
336 }
337
338 /**
339 * Constructs an empty insertion-ordered {@code LinkedHashMap} instance
340 * with the specified initial capacity and load factor.
341 *
342 * @param initialCapacity the initial capacity
343 * @param loadFactor the load factor
344 * @throws IllegalArgumentException if the initial capacity is negative
345 * or the load factor is nonpositive
346 */
347 public LinkedHashMap(int initialCapacity, float loadFactor) {
348 super(initialCapacity, loadFactor);
349 accessOrder = false;
350 }
351
352 /**
353 * Constructs an empty insertion-ordered {@code LinkedHashMap} instance
354 * with the specified initial capacity and a default load factor (0.75).
355 *
356 * @param initialCapacity the initial capacity
357 * @throws IllegalArgumentException if the initial capacity is negative
358 */
359 public LinkedHashMap(int initialCapacity) {
360 super(initialCapacity);
361 accessOrder = false;
362 }
363
364 /**
365 * Constructs an empty insertion-ordered {@code LinkedHashMap} instance
366 * with the default initial capacity (16) and load factor (0.75).
367 */
368 public LinkedHashMap() {
369 super();
370 accessOrder = false;
371 }
372
373 /**
374 * Constructs an insertion-ordered {@code LinkedHashMap} instance with
375 * the same mappings as the specified map. The {@code LinkedHashMap}
376 * instance is created with a default load factor (0.75) and an initial
377 * capacity sufficient to hold the mappings in the specified map.
378 *
379 * @param m the map whose mappings are to be placed in this map
380 * @throws NullPointerException if the specified map is null
381 */
382 public LinkedHashMap(Map<? extends K, ? extends V> m) {
383 super();
384 accessOrder = false;
385 putMapEntries(m, false);
386 }
387
388 /**
389 * Constructs an empty {@code LinkedHashMap} instance with the
390 * specified initial capacity, load factor and ordering mode.
391 *
392 * @param initialCapacity the initial capacity
393 * @param loadFactor the load factor
394 * @param accessOrder the ordering mode - {@code true} for
395 * access-order, {@code false} for insertion-order
396 * @throws IllegalArgumentException if the initial capacity is negative
397 * or the load factor is nonpositive
398 */
399 public LinkedHashMap(int initialCapacity,
400 float loadFactor,
401 boolean accessOrder) {
402 super(initialCapacity, loadFactor);
403 this.accessOrder = accessOrder;
404 }
405
406
407 /**
408 * Returns {@code true} if this map maps one or more keys to the
409 * specified value.
410 *
411 * @param value value whose presence in this map is to be tested
412 * @return {@code true} if this map maps one or more keys to the
413 * specified value
414 */
415 public boolean containsValue(Object value) {
416 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
417 V v = e.value;
418 if (v == value || (value != null && value.equals(v)))
419 return true;
420 }
421 return false;
422 }
423
424 /**
425 * Returns the value to which the specified key is mapped,
426 * or {@code null} if this map contains no mapping for the key.
427 *
428 * <p>More formally, if this map contains a mapping from a key
429 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
430 * key.equals(k))}, then this method returns {@code v}; otherwise
431 * it returns {@code null}. (There can be at most one such mapping.)
432 *
433 * <p>A return value of {@code null} does not <i>necessarily</i>
434 * indicate that the map contains no mapping for the key; it's also
435 * possible that the map explicitly maps the key to {@code null}.
436 * The {@link #containsKey containsKey} operation may be used to
437 * distinguish these two cases.
438 */
439 public V get(Object key) {
440 Node<K,V> e;
441 if ((e = getNode(hash(key), key)) == null)
442 return null;
443 if (accessOrder)
444 afterNodeAccess(e);
445 return e.value;
446 }
447
448 /**
449 * {@inheritDoc}
450 */
451 public V getOrDefault(Object key, V defaultValue) {
452 Node<K,V> e;
453 if ((e = getNode(hash(key), key)) == null)
454 return defaultValue;
455 if (accessOrder)
456 afterNodeAccess(e);
457 return e.value;
458 }
459
460 /**
461 * {@inheritDoc}
462 */
463 public void clear() {
464 super.clear();
465 head = tail = null;
466 }
467
468 /**
469 * Returns {@code true} if this map should remove its eldest entry.
470 * This method is invoked by {@code put} and {@code putAll} after
471 * inserting a new entry into the map. It provides the implementor
472 * with the opportunity to remove the eldest entry each time a new one
473 * is added. This is useful if the map represents a cache: it allows
474 * the map to reduce memory consumption by deleting stale entries.
475 *
476 * <p>Sample use: this override will allow the map to grow up to 100
477 * entries and then delete the eldest entry each time a new entry is
478 * added, maintaining a steady state of 100 entries.
479 * <pre>
480 * private static final int MAX_ENTRIES = 100;
481 *
482 * protected boolean removeEldestEntry(Map.Entry eldest) {
483 * return size() > MAX_ENTRIES;
484 * }
485 * </pre>
486 *
487 * <p>This method typically does not modify the map in any way,
488 * instead allowing the map to modify itself as directed by its
489 * return value. It <i>is</i> permitted for this method to modify
490 * the map directly, but if it does so, it <i>must</i> return
491 * {@code false} (indicating that the map should not attempt any
492 * further modification). The effects of returning {@code true}
493 * after modifying the map from within this method are unspecified.
494 *
495 * <p>This implementation merely returns {@code false} (so that this
496 * map acts like a normal map - the eldest element is never removed).
497 *
498 * @param eldest The least recently inserted entry in the map, or if
499 * this is an access-ordered map, the least recently accessed
500 * entry. This is the entry that will be removed it this
501 * method returns {@code true}. If the map was empty prior
502 * to the {@code put} or {@code putAll} invocation resulting
503 * in this invocation, this will be the entry that was just
504 * inserted; in other words, if the map contains a single
505 * entry, the eldest entry is also the newest.
506 * @return {@code true} if the eldest entry should be removed
507 * from the map; {@code false} if it should be retained.
508 */
509 protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {
510 return false;
511 }
512
513 /**
514 * Returns a {@link Set} view of the keys contained in this map.
515 * The set is backed by the map, so changes to the map are
516 * reflected in the set, and vice-versa. If the map is modified
517 * while an iteration over the set is in progress (except through
518 * the iterator's own {@code remove} operation), the results of
519 * the iteration are undefined. The set supports element removal,
520 * which removes the corresponding mapping from the map, via the
521 * {@code Iterator.remove}, {@code Set.remove},
522 * {@code removeAll}, {@code retainAll}, and {@code clear}
523 * operations. It does not support the {@code add} or {@code addAll}
524 * operations.
525 * Its {@link Spliterator} typically provides faster sequential
526 * performance but much poorer parallel performance than that of
527 * {@code HashMap}.
528 *
529 * @return a set view of the keys contained in this map
530 */
531 public Set<K> keySet() {
532 Set<K> ks = keySet;
533 if (ks == null) {
534 ks = new LinkedKeySet();
535 keySet = ks;
536 }
537 return ks;
538 }
539
540 @Override
541 final <T> T[] keysToArray(T[] a) {
542 Object[] r = a;
543 int idx = 0;
544 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
545 r[idx++] = e.key;
546 }
547 return a;
548 }
549
550 @Override
551 final <T> T[] valuesToArray(T[] a) {
552 Object[] r = a;
553 int idx = 0;
554 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
555 r[idx++] = e.value;
556 }
557 return a;
558 }
559
560 final class LinkedKeySet extends AbstractSet<K> {
561 public final int size() { return size; }
562 public final void clear() { LinkedHashMap.this.clear(); }
563 public final Iterator<K> iterator() {
564 return new LinkedKeyIterator();
565 }
566 public final boolean contains(Object o) { return containsKey(o); }
567 public final boolean remove(Object key) {
568 return removeNode(hash(key), key, null, false, true) != null;
569 }
570 public final Spliterator<K> spliterator() {
571 return Spliterators.spliterator(this, Spliterator.SIZED |
572 Spliterator.ORDERED |
573 Spliterator.DISTINCT);
574 }
575
576 public Object[] toArray() {
577 return keysToArray(new Object[size]);
578 }
579
580 public <T> T[] toArray(T[] a) {
581 return keysToArray(prepareArray(a));
582 }
583
584 public final void forEach(Consumer<? super K> action) {
585 if (action == null)
586 throw new NullPointerException();
587 int mc = modCount;
588 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
589 action.accept(e.key);
590 if (modCount != mc)
591 throw new ConcurrentModificationException();
592 }
593 }
594
595 /**
596 * Returns a {@link Collection} view of the values contained in this map.
597 * The collection is backed by the map, so changes to the map are
598 * reflected in the collection, and vice-versa. If the map is
599 * modified while an iteration over the collection is in progress
600 * (except through the iterator's own {@code remove} operation),
601 * the results of the iteration are undefined. The collection
602 * supports element removal, which removes the corresponding
603 * mapping from the map, via the {@code Iterator.remove},
604 * {@code Collection.remove}, {@code removeAll},
605 * {@code retainAll} and {@code clear} operations. It does not
606 * support the {@code add} or {@code addAll} operations.
607 * Its {@link Spliterator} typically provides faster sequential
608 * performance but much poorer parallel performance than that of
609 * {@code HashMap}.
610 *
611 * @return a view of the values contained in this map
612 */
613 public Collection<V> values() {
614 Collection<V> vs = values;
615 if (vs == null) {
616 vs = new LinkedValues();
617 values = vs;
618 }
619 return vs;
620 }
621
622 final class LinkedValues extends AbstractCollection<V> {
623 public final int size() { return size; }
624 public final void clear() { LinkedHashMap.this.clear(); }
625 public final Iterator<V> iterator() {
626 return new LinkedValueIterator();
627 }
628 public final boolean contains(Object o) { return containsValue(o); }
629 public final Spliterator<V> spliterator() {
630 return Spliterators.spliterator(this, Spliterator.SIZED |
631 Spliterator.ORDERED);
632 }
633
634 public Object[] toArray() {
635 return valuesToArray(new Object[size]);
636 }
637
638 public <T> T[] toArray(T[] a) {
639 return valuesToArray(prepareArray(a));
640 }
641
642 public final void forEach(Consumer<? super V> action) {
643 if (action == null)
644 throw new NullPointerException();
645 int mc = modCount;
646 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
647 action.accept(e.value);
648 if (modCount != mc)
649 throw new ConcurrentModificationException();
650 }
651 }
652
653 /**
654 * Returns a {@link Set} view of the mappings contained in this map.
655 * The set is backed by the map, so changes to the map are
656 * reflected in the set, and vice-versa. If the map is modified
657 * while an iteration over the set is in progress (except through
658 * the iterator's own {@code remove} operation, or through the
659 * {@code setValue} operation on a map entry returned by the
660 * iterator) the results of the iteration are undefined. The set
661 * supports element removal, which removes the corresponding
662 * mapping from the map, via the {@code Iterator.remove},
663 * {@code Set.remove}, {@code removeAll}, {@code retainAll} and
664 * {@code clear} operations. It does not support the
665 * {@code add} or {@code addAll} operations.
666 * Its {@link Spliterator} typically provides faster sequential
667 * performance but much poorer parallel performance than that of
668 * {@code HashMap}.
669 *
670 * @return a set view of the mappings contained in this map
671 */
672 public Set<Map.Entry<K,V>> entrySet() {
673 Set<Map.Entry<K,V>> es;
674 return (es = entrySet) == null ? (entrySet = new LinkedEntrySet()) : es;
675 }
676
677 final class LinkedEntrySet extends AbstractSet<Map.Entry<K,V>> {
678 public final int size() { return size; }
679 public final void clear() { LinkedHashMap.this.clear(); }
680 public final Iterator<Map.Entry<K,V>> iterator() {
681 return new LinkedEntryIterator();
682 }
683 public final boolean contains(Object o) {
684 if (!(o instanceof Map.Entry))
685 return false;
686 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
687 Object key = e.getKey();
688 Node<K,V> candidate = getNode(hash(key), key);
689 return candidate != null && candidate.equals(e);
690 }
691 public final boolean remove(Object o) {
692 if (o instanceof Map.Entry) {
693 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
694 Object key = e.getKey();
695 Object value = e.getValue();
696 return removeNode(hash(key), key, value, true, true) != null;
697 }
698 return false;
699 }
700 public final Spliterator<Map.Entry<K,V>> spliterator() {
701 return Spliterators.spliterator(this, Spliterator.SIZED |
702 Spliterator.ORDERED |
703 Spliterator.DISTINCT);
704 }
705 public final void forEach(Consumer<? super Map.Entry<K,V>> action) {
706 if (action == null)
707 throw new NullPointerException();
708 int mc = modCount;
709 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
710 action.accept(e);
711 if (modCount != mc)
712 throw new ConcurrentModificationException();
713 }
714 }
715
716 // Map overrides
717
718 public void forEach(BiConsumer<? super K, ? super V> action) {
719 if (action == null)
720 throw new NullPointerException();
721 int mc = modCount;
722 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
723 action.accept(e.key, e.value);
724 if (modCount != mc)
725 throw new ConcurrentModificationException();
726 }
727
728 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
729 if (function == null)
730 throw new NullPointerException();
731 int mc = modCount;
732 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
733 e.value = function.apply(e.key, e.value);
734 if (modCount != mc)
735 throw new ConcurrentModificationException();
736 }
737
738 // Iterators
739
740 abstract class LinkedHashIterator {
741 LinkedHashMap.Entry<K,V> next;
742 LinkedHashMap.Entry<K,V> current;
743 int expectedModCount;
744
745 LinkedHashIterator() {
746 next = head;
747 expectedModCount = modCount;
748 current = null;
749 }
750
751 public final boolean hasNext() {
752 return next != null;
753 }
754
755 final LinkedHashMap.Entry<K,V> nextNode() {
756 LinkedHashMap.Entry<K,V> e = next;
757 if (modCount != expectedModCount)
758 throw new ConcurrentModificationException();
759 if (e == null)
760 throw new NoSuchElementException();
761 current = e;
762 next = e.after;
763 return e;
764 }
765
766 public final void remove() {
767 Node<K,V> p = current;
768 if (p == null)
769 throw new IllegalStateException();
770 if (modCount != expectedModCount)
771 throw new ConcurrentModificationException();
772 current = null;
773 removeNode(p.hash, p.key, null, false, false);
774 expectedModCount = modCount;
775 }
776 }
777
778 final class LinkedKeyIterator extends LinkedHashIterator
779 implements Iterator<K> {
780 public final K next() { return nextNode().getKey(); }
781 }
782
783 final class LinkedValueIterator extends LinkedHashIterator
784 implements Iterator<V> {
785 public final V next() { return nextNode().value; }
786 }
787
788 final class LinkedEntryIterator extends LinkedHashIterator
789 implements Iterator<Map.Entry<K,V>> {
790 public final Map.Entry<K,V> next() { return nextNode(); }
791 }
792
793
794 }