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 <tt>Map</tt> interface,
35 * with predictable iteration order. This implementation differs from
36 * <tt>HashMap</tt> 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 <tt>k</tt> is
41 * reinserted into a map <tt>m</tt> if <tt>m.put(k, v)</tt> is invoked when
42 * <tt>m.containsKey(k)</tt> would return <tt>true</tt> 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 <tt>Map</tt> operations, and
82 * permits null elements. Like <tt>HashMap</tt>, it provides constant-time
83 * performance for the basic operations (<tt>add</tt>, <tt>contains</tt> and
84 * <tt>remove</tt>), assuming the hash function disperses elements
85 * properly among the buckets. Performance is likely to be just slightly
86 * below that of <tt>HashMap</tt>, due to the added expense of maintaining the
87 * linked list, with one exception: Iteration over the collection-views
88 * of a <tt>LinkedHashMap</tt> requires time proportional to the <i>size</i>
89 * of the map, regardless of its capacity. Iteration over a <tt>HashMap</tt>
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 <tt>HashMap</tt>. Note, however, that the penalty for choosing an
96 * excessively high value for initial capacity is less severe for this class
97 * than for <tt>HashMap</tt>, 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 <tt>get</tt> is a structural modification.
118 * </strong>)
119 *
120 * <p>The iterators returned by the <tt>iterator</tt> 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 * <tt>remove</tt> 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 <tt>ConcurrentModificationException</tt> 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}/../technotes/guides/collections/index.html">
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
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 private static final long serialVersionUID = 3801124242820219131L;
200
201 /**
202 * The head (eldest) of the doubly linked list.
203 */
204 transient LinkedHashMap.Entry<K,V> head;
205
206 /**
207 * The tail (youngest) of the doubly linked list.
208 */
209 transient LinkedHashMap.Entry<K,V> tail;
210
211 /**
212 * The iteration ordering method for this linked hash map: <tt>true</tt>
213 * for access-order, <tt>false</tt> for insertion-order.
214 *
215 * @serial
216 */
217 final boolean accessOrder;
218
219 // internal utilities
220
221 // link at the end of list
222 private void linkNodeLast(LinkedHashMap.Entry<K,V> p) {
223 LinkedHashMap.Entry<K,V> last = tail;
224 tail = p;
225 if (last == null)
226 head = p;
227 else {
228 p.before = last;
229 last.after = p;
230 }
231 }
232
233 // apply src's links to dst
318 last = b;
319 if (last == null)
320 head = p;
321 else {
322 p.before = last;
323 last.after = p;
324 }
325 tail = p;
326 ++modCount;
327 }
328 }
329
330 void internalWriteEntries(java.io.ObjectOutputStream s) throws IOException {
331 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
332 s.writeObject(e.key);
333 s.writeObject(e.value);
334 }
335 }
336
337 /**
338 * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance
339 * with the specified initial capacity and load factor.
340 *
341 * @param initialCapacity the initial capacity
342 * @param loadFactor the load factor
343 * @throws IllegalArgumentException if the initial capacity is negative
344 * or the load factor is nonpositive
345 */
346 public LinkedHashMap(int initialCapacity, float loadFactor) {
347 super(initialCapacity, loadFactor);
348 accessOrder = false;
349 }
350
351 /**
352 * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance
353 * with the specified initial capacity and a default load factor (0.75).
354 *
355 * @param initialCapacity the initial capacity
356 * @throws IllegalArgumentException if the initial capacity is negative
357 */
358 public LinkedHashMap(int initialCapacity) {
359 super(initialCapacity);
360 accessOrder = false;
361 }
362
363 /**
364 * Constructs an empty insertion-ordered <tt>LinkedHashMap</tt> instance
365 * with the default initial capacity (16) and load factor (0.75).
366 */
367 public LinkedHashMap() {
368 super();
369 accessOrder = false;
370 }
371
372 /**
373 * Constructs an insertion-ordered <tt>LinkedHashMap</tt> instance with
374 * the same mappings as the specified map. The <tt>LinkedHashMap</tt>
375 * instance is created with a default load factor (0.75) and an initial
376 * capacity sufficient to hold the mappings in the specified map.
377 *
378 * @param m the map whose mappings are to be placed in this map
379 * @throws NullPointerException if the specified map is null
380 */
381 public LinkedHashMap(Map<? extends K, ? extends V> m) {
382 super();
383 accessOrder = false;
384 putMapEntries(m, false);
385 }
386
387 /**
388 * Constructs an empty <tt>LinkedHashMap</tt> instance with the
389 * specified initial capacity, load factor and ordering mode.
390 *
391 * @param initialCapacity the initial capacity
392 * @param loadFactor the load factor
393 * @param accessOrder the ordering mode - <tt>true</tt> for
394 * access-order, <tt>false</tt> for insertion-order
395 * @throws IllegalArgumentException if the initial capacity is negative
396 * or the load factor is nonpositive
397 */
398 public LinkedHashMap(int initialCapacity,
399 float loadFactor,
400 boolean accessOrder) {
401 super(initialCapacity, loadFactor);
402 this.accessOrder = accessOrder;
403 }
404
405
406 /**
407 * Returns <tt>true</tt> if this map maps one or more keys to the
408 * specified value.
409 *
410 * @param value value whose presence in this map is to be tested
411 * @return <tt>true</tt> if this map maps one or more keys to the
412 * specified value
413 */
414 public boolean containsValue(Object value) {
415 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
416 V v = e.value;
417 if (v == value || (value != null && value.equals(v)))
418 return true;
419 }
420 return false;
421 }
422
423 /**
424 * Returns the value to which the specified key is mapped,
425 * or {@code null} if this map contains no mapping for the key.
426 *
427 * <p>More formally, if this map contains a mapping from a key
428 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
429 * key.equals(k))}, then this method returns {@code v}; otherwise
430 * it returns {@code null}. (There can be at most one such mapping.)
431 *
448 * {@inheritDoc}
449 */
450 public V getOrDefault(Object key, V defaultValue) {
451 Node<K,V> e;
452 if ((e = getNode(hash(key), key)) == null)
453 return defaultValue;
454 if (accessOrder)
455 afterNodeAccess(e);
456 return e.value;
457 }
458
459 /**
460 * {@inheritDoc}
461 */
462 public void clear() {
463 super.clear();
464 head = tail = null;
465 }
466
467 /**
468 * Returns <tt>true</tt> if this map should remove its eldest entry.
469 * This method is invoked by <tt>put</tt> and <tt>putAll</tt> after
470 * inserting a new entry into the map. It provides the implementor
471 * with the opportunity to remove the eldest entry each time a new one
472 * is added. This is useful if the map represents a cache: it allows
473 * the map to reduce memory consumption by deleting stale entries.
474 *
475 * <p>Sample use: this override will allow the map to grow up to 100
476 * entries and then delete the eldest entry each time a new entry is
477 * added, maintaining a steady state of 100 entries.
478 * <pre>
479 * private static final int MAX_ENTRIES = 100;
480 *
481 * protected boolean removeEldestEntry(Map.Entry eldest) {
482 * return size() > MAX_ENTRIES;
483 * }
484 * </pre>
485 *
486 * <p>This method typically does not modify the map in any way,
487 * instead allowing the map to modify itself as directed by its
488 * return value. It <i>is</i> permitted for this method to modify
489 * the map directly, but if it does so, it <i>must</i> return
490 * <tt>false</tt> (indicating that the map should not attempt any
491 * further modification). The effects of returning <tt>true</tt>
492 * after modifying the map from within this method are unspecified.
493 *
494 * <p>This implementation merely returns <tt>false</tt> (so that this
495 * map acts like a normal map - the eldest element is never removed).
496 *
497 * @param eldest The least recently inserted entry in the map, or if
498 * this is an access-ordered map, the least recently accessed
499 * entry. This is the entry that will be removed it this
500 * method returns <tt>true</tt>. If the map was empty prior
501 * to the <tt>put</tt> or <tt>putAll</tt> invocation resulting
502 * in this invocation, this will be the entry that was just
503 * inserted; in other words, if the map contains a single
504 * entry, the eldest entry is also the newest.
505 * @return <tt>true</tt> if the eldest entry should be removed
506 * from the map; <tt>false</tt> if it should be retained.
507 */
508 protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {
509 return false;
510 }
511
512 /**
513 * Returns a {@link Set} view of the keys contained in this map.
514 * The set is backed by the map, so changes to the map are
515 * reflected in the set, and vice-versa. If the map is modified
516 * while an iteration over the set is in progress (except through
517 * the iterator's own <tt>remove</tt> operation), the results of
518 * the iteration are undefined. The set supports element removal,
519 * which removes the corresponding mapping from the map, via the
520 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
521 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
522 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
523 * operations.
524 * Its {@link Spliterator} typically provides faster sequential
525 * performance but much poorer parallel performance than that of
526 * {@code HashMap}.
527 *
528 * @return a set view of the keys contained in this map
529 */
530 public Set<K> keySet() {
531 Set<K> ks;
532 return (ks = keySet) == null ? (keySet = new LinkedKeySet()) : ks;
533 }
534
535 final class LinkedKeySet extends AbstractSet<K> {
536 public final int size() { return size; }
537 public final void clear() { LinkedHashMap.this.clear(); }
538 public final Iterator<K> iterator() {
539 return new LinkedKeyIterator();
540 }
541 public final boolean contains(Object o) { return containsKey(o); }
542 public final boolean remove(Object key) {
546 return Spliterators.spliterator(this, Spliterator.SIZED |
547 Spliterator.ORDERED |
548 Spliterator.DISTINCT);
549 }
550 public final void forEach(Consumer<? super K> action) {
551 if (action == null)
552 throw new NullPointerException();
553 int mc = modCount;
554 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
555 action.accept(e.key);
556 if (modCount != mc)
557 throw new ConcurrentModificationException();
558 }
559 }
560
561 /**
562 * Returns a {@link Collection} view of the values contained in this map.
563 * The collection is backed by the map, so changes to the map are
564 * reflected in the collection, and vice-versa. If the map is
565 * modified while an iteration over the collection is in progress
566 * (except through the iterator's own <tt>remove</tt> operation),
567 * the results of the iteration are undefined. The collection
568 * supports element removal, which removes the corresponding
569 * mapping from the map, via the <tt>Iterator.remove</tt>,
570 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
571 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
572 * support the <tt>add</tt> or <tt>addAll</tt> operations.
573 * Its {@link Spliterator} typically provides faster sequential
574 * performance but much poorer parallel performance than that of
575 * {@code HashMap}.
576 *
577 * @return a view of the values contained in this map
578 */
579 public Collection<V> values() {
580 Collection<V> vs;
581 return (vs = values) == null ? (values = new LinkedValues()) : vs;
582 }
583
584 final class LinkedValues extends AbstractCollection<V> {
585 public final int size() { return size; }
586 public final void clear() { LinkedHashMap.this.clear(); }
587 public final Iterator<V> iterator() {
588 return new LinkedValueIterator();
589 }
590 public final boolean contains(Object o) { return containsValue(o); }
591 public final Spliterator<V> spliterator() {
592 return Spliterators.spliterator(this, Spliterator.SIZED |
593 Spliterator.ORDERED);
594 }
595 public final void forEach(Consumer<? super V> action) {
596 if (action == null)
597 throw new NullPointerException();
598 int mc = modCount;
599 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
600 action.accept(e.value);
601 if (modCount != mc)
602 throw new ConcurrentModificationException();
603 }
604 }
605
606 /**
607 * Returns a {@link Set} view of the mappings contained in this map.
608 * The set is backed by the map, so changes to the map are
609 * reflected in the set, and vice-versa. If the map is modified
610 * while an iteration over the set is in progress (except through
611 * the iterator's own <tt>remove</tt> operation, or through the
612 * <tt>setValue</tt> operation on a map entry returned by the
613 * iterator) the results of the iteration are undefined. The set
614 * supports element removal, which removes the corresponding
615 * mapping from the map, via the <tt>Iterator.remove</tt>,
616 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
617 * <tt>clear</tt> operations. It does not support the
618 * <tt>add</tt> or <tt>addAll</tt> operations.
619 * Its {@link Spliterator} typically provides faster sequential
620 * performance but much poorer parallel performance than that of
621 * {@code HashMap}.
622 *
623 * @return a set view of the mappings contained in this map
624 */
625 public Set<Map.Entry<K,V>> entrySet() {
626 Set<Map.Entry<K,V>> es;
627 return (es = entrySet) == null ? (entrySet = new LinkedEntrySet()) : es;
628 }
629
630 final class LinkedEntrySet extends AbstractSet<Map.Entry<K,V>> {
631 public final int size() { return size; }
632 public final void clear() { LinkedHashMap.this.clear(); }
633 public final Iterator<Map.Entry<K,V>> iterator() {
634 return new LinkedEntryIterator();
635 }
636 public final boolean contains(Object o) {
637 if (!(o instanceof Map.Entry))
638 return false;
|
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}/../technotes/guides/collections/index.html">
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
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 private static final long serialVersionUID = 3801124242820219131L;
200
201 /**
202 * The head (eldest) of the doubly linked list.
203 */
204 transient LinkedHashMap.Entry<K,V> head;
205
206 /**
207 * The tail (youngest) of the doubly linked list.
208 */
209 transient LinkedHashMap.Entry<K,V> tail;
210
211 /**
212 * The iteration ordering method for this linked hash map: {@code true}
213 * for access-order, {@code false} for insertion-order.
214 *
215 * @serial
216 */
217 final boolean accessOrder;
218
219 // internal utilities
220
221 // link at the end of list
222 private void linkNodeLast(LinkedHashMap.Entry<K,V> p) {
223 LinkedHashMap.Entry<K,V> last = tail;
224 tail = p;
225 if (last == null)
226 head = p;
227 else {
228 p.before = last;
229 last.after = p;
230 }
231 }
232
233 // apply src's links to dst
318 last = b;
319 if (last == null)
320 head = p;
321 else {
322 p.before = last;
323 last.after = p;
324 }
325 tail = p;
326 ++modCount;
327 }
328 }
329
330 void internalWriteEntries(java.io.ObjectOutputStream s) throws IOException {
331 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
332 s.writeObject(e.key);
333 s.writeObject(e.value);
334 }
335 }
336
337 /**
338 * Constructs an empty insertion-ordered {@code LinkedHashMap} instance
339 * with the specified initial capacity and load factor.
340 *
341 * @param initialCapacity the initial capacity
342 * @param loadFactor the load factor
343 * @throws IllegalArgumentException if the initial capacity is negative
344 * or the load factor is nonpositive
345 */
346 public LinkedHashMap(int initialCapacity, float loadFactor) {
347 super(initialCapacity, loadFactor);
348 accessOrder = false;
349 }
350
351 /**
352 * Constructs an empty insertion-ordered {@code LinkedHashMap} instance
353 * with the specified initial capacity and a default load factor (0.75).
354 *
355 * @param initialCapacity the initial capacity
356 * @throws IllegalArgumentException if the initial capacity is negative
357 */
358 public LinkedHashMap(int initialCapacity) {
359 super(initialCapacity);
360 accessOrder = false;
361 }
362
363 /**
364 * Constructs an empty insertion-ordered {@code LinkedHashMap} instance
365 * with the default initial capacity (16) and load factor (0.75).
366 */
367 public LinkedHashMap() {
368 super();
369 accessOrder = false;
370 }
371
372 /**
373 * Constructs an insertion-ordered {@code LinkedHashMap} instance with
374 * the same mappings as the specified map. The {@code LinkedHashMap}
375 * instance is created with a default load factor (0.75) and an initial
376 * capacity sufficient to hold the mappings in the specified map.
377 *
378 * @param m the map whose mappings are to be placed in this map
379 * @throws NullPointerException if the specified map is null
380 */
381 public LinkedHashMap(Map<? extends K, ? extends V> m) {
382 super();
383 accessOrder = false;
384 putMapEntries(m, false);
385 }
386
387 /**
388 * Constructs an empty {@code LinkedHashMap} instance with the
389 * specified initial capacity, load factor and ordering mode.
390 *
391 * @param initialCapacity the initial capacity
392 * @param loadFactor the load factor
393 * @param accessOrder the ordering mode - {@code true} for
394 * access-order, {@code false} for insertion-order
395 * @throws IllegalArgumentException if the initial capacity is negative
396 * or the load factor is nonpositive
397 */
398 public LinkedHashMap(int initialCapacity,
399 float loadFactor,
400 boolean accessOrder) {
401 super(initialCapacity, loadFactor);
402 this.accessOrder = accessOrder;
403 }
404
405
406 /**
407 * Returns {@code true} if this map maps one or more keys to the
408 * specified value.
409 *
410 * @param value value whose presence in this map is to be tested
411 * @return {@code true} if this map maps one or more keys to the
412 * specified value
413 */
414 public boolean containsValue(Object value) {
415 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
416 V v = e.value;
417 if (v == value || (value != null && value.equals(v)))
418 return true;
419 }
420 return false;
421 }
422
423 /**
424 * Returns the value to which the specified key is mapped,
425 * or {@code null} if this map contains no mapping for the key.
426 *
427 * <p>More formally, if this map contains a mapping from a key
428 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
429 * key.equals(k))}, then this method returns {@code v}; otherwise
430 * it returns {@code null}. (There can be at most one such mapping.)
431 *
448 * {@inheritDoc}
449 */
450 public V getOrDefault(Object key, V defaultValue) {
451 Node<K,V> e;
452 if ((e = getNode(hash(key), key)) == null)
453 return defaultValue;
454 if (accessOrder)
455 afterNodeAccess(e);
456 return e.value;
457 }
458
459 /**
460 * {@inheritDoc}
461 */
462 public void clear() {
463 super.clear();
464 head = tail = null;
465 }
466
467 /**
468 * Returns {@code true} if this map should remove its eldest entry.
469 * This method is invoked by {@code put} and {@code putAll} after
470 * inserting a new entry into the map. It provides the implementor
471 * with the opportunity to remove the eldest entry each time a new one
472 * is added. This is useful if the map represents a cache: it allows
473 * the map to reduce memory consumption by deleting stale entries.
474 *
475 * <p>Sample use: this override will allow the map to grow up to 100
476 * entries and then delete the eldest entry each time a new entry is
477 * added, maintaining a steady state of 100 entries.
478 * <pre>
479 * private static final int MAX_ENTRIES = 100;
480 *
481 * protected boolean removeEldestEntry(Map.Entry eldest) {
482 * return size() > MAX_ENTRIES;
483 * }
484 * </pre>
485 *
486 * <p>This method typically does not modify the map in any way,
487 * instead allowing the map to modify itself as directed by its
488 * return value. It <i>is</i> permitted for this method to modify
489 * the map directly, but if it does so, it <i>must</i> return
490 * {@code false} (indicating that the map should not attempt any
491 * further modification). The effects of returning {@code true}
492 * after modifying the map from within this method are unspecified.
493 *
494 * <p>This implementation merely returns {@code false} (so that this
495 * map acts like a normal map - the eldest element is never removed).
496 *
497 * @param eldest The least recently inserted entry in the map, or if
498 * this is an access-ordered map, the least recently accessed
499 * entry. This is the entry that will be removed it this
500 * method returns {@code true}. If the map was empty prior
501 * to the {@code put} or {@code putAll} invocation resulting
502 * in this invocation, this will be the entry that was just
503 * inserted; in other words, if the map contains a single
504 * entry, the eldest entry is also the newest.
505 * @return {@code true} if the eldest entry should be removed
506 * from the map; {@code false} if it should be retained.
507 */
508 protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {
509 return false;
510 }
511
512 /**
513 * Returns a {@link Set} view of the keys contained in this map.
514 * The set is backed by the map, so changes to the map are
515 * reflected in the set, and vice-versa. If the map is modified
516 * while an iteration over the set is in progress (except through
517 * the iterator's own {@code remove} operation), the results of
518 * the iteration are undefined. The set supports element removal,
519 * which removes the corresponding mapping from the map, via the
520 * {@code Iterator.remove}, {@code Set.remove},
521 * {@code removeAll}, {@code retainAll}, and {@code clear}
522 * operations. It does not support the {@code add} or {@code addAll}
523 * operations.
524 * Its {@link Spliterator} typically provides faster sequential
525 * performance but much poorer parallel performance than that of
526 * {@code HashMap}.
527 *
528 * @return a set view of the keys contained in this map
529 */
530 public Set<K> keySet() {
531 Set<K> ks;
532 return (ks = keySet) == null ? (keySet = new LinkedKeySet()) : ks;
533 }
534
535 final class LinkedKeySet extends AbstractSet<K> {
536 public final int size() { return size; }
537 public final void clear() { LinkedHashMap.this.clear(); }
538 public final Iterator<K> iterator() {
539 return new LinkedKeyIterator();
540 }
541 public final boolean contains(Object o) { return containsKey(o); }
542 public final boolean remove(Object key) {
546 return Spliterators.spliterator(this, Spliterator.SIZED |
547 Spliterator.ORDERED |
548 Spliterator.DISTINCT);
549 }
550 public final void forEach(Consumer<? super K> action) {
551 if (action == null)
552 throw new NullPointerException();
553 int mc = modCount;
554 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
555 action.accept(e.key);
556 if (modCount != mc)
557 throw new ConcurrentModificationException();
558 }
559 }
560
561 /**
562 * Returns a {@link Collection} view of the values contained in this map.
563 * The collection is backed by the map, so changes to the map are
564 * reflected in the collection, and vice-versa. If the map is
565 * modified while an iteration over the collection is in progress
566 * (except through the iterator's own {@code remove} operation),
567 * the results of the iteration are undefined. The collection
568 * supports element removal, which removes the corresponding
569 * mapping from the map, via the {@code Iterator.remove},
570 * {@code Collection.remove}, {@code removeAll},
571 * {@code retainAll} and {@code clear} operations. It does not
572 * support the {@code add} or {@code addAll} operations.
573 * Its {@link Spliterator} typically provides faster sequential
574 * performance but much poorer parallel performance than that of
575 * {@code HashMap}.
576 *
577 * @return a view of the values contained in this map
578 */
579 public Collection<V> values() {
580 Collection<V> vs;
581 return (vs = values) == null ? (values = new LinkedValues()) : vs;
582 }
583
584 final class LinkedValues extends AbstractCollection<V> {
585 public final int size() { return size; }
586 public final void clear() { LinkedHashMap.this.clear(); }
587 public final Iterator<V> iterator() {
588 return new LinkedValueIterator();
589 }
590 public final boolean contains(Object o) { return containsValue(o); }
591 public final Spliterator<V> spliterator() {
592 return Spliterators.spliterator(this, Spliterator.SIZED |
593 Spliterator.ORDERED);
594 }
595 public final void forEach(Consumer<? super V> action) {
596 if (action == null)
597 throw new NullPointerException();
598 int mc = modCount;
599 for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after)
600 action.accept(e.value);
601 if (modCount != mc)
602 throw new ConcurrentModificationException();
603 }
604 }
605
606 /**
607 * Returns a {@link Set} view of the mappings contained in this map.
608 * The set is backed by the map, so changes to the map are
609 * reflected in the set, and vice-versa. If the map is modified
610 * while an iteration over the set is in progress (except through
611 * the iterator's own {@code remove} operation, or through the
612 * {@code setValue} operation on a map entry returned by the
613 * iterator) the results of the iteration are undefined. The set
614 * supports element removal, which removes the corresponding
615 * mapping from the map, via the {@code Iterator.remove},
616 * {@code Set.remove}, {@code removeAll}, {@code retainAll} and
617 * {@code clear} operations. It does not support the
618 * {@code add} or {@code addAll} operations.
619 * Its {@link Spliterator} typically provides faster sequential
620 * performance but much poorer parallel performance than that of
621 * {@code HashMap}.
622 *
623 * @return a set view of the mappings contained in this map
624 */
625 public Set<Map.Entry<K,V>> entrySet() {
626 Set<Map.Entry<K,V>> es;
627 return (es = entrySet) == null ? (entrySet = new LinkedEntrySet()) : es;
628 }
629
630 final class LinkedEntrySet extends AbstractSet<Map.Entry<K,V>> {
631 public final int size() { return size; }
632 public final void clear() { LinkedHashMap.this.clear(); }
633 public final Iterator<Map.Entry<K,V>> iterator() {
634 return new LinkedEntryIterator();
635 }
636 public final boolean contains(Object o) {
637 if (!(o instanceof Map.Entry))
638 return false;
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