1 /*
2 * Copyright (c) 1997, 2010, 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 import java.io.*;
28
29 /**
30 * Hash table based implementation of the <tt>Map</tt> interface. This
31 * implementation provides all of the optional map operations, and permits
32 * <tt>null</tt> values and the <tt>null</tt> key. (The <tt>HashMap</tt>
33 * class is roughly equivalent to <tt>Hashtable</tt>, except that it is
34 * unsynchronized and permits nulls.) This class makes no guarantees as to
35 * the order of the map; in particular, it does not guarantee that the order
36 * will remain constant over time.
37 *
38 * <p>This implementation provides constant-time performance for the basic
39 * operations (<tt>get</tt> and <tt>put</tt>), assuming the hash function
40 * disperses the elements properly among the buckets. Iteration over
41 * collection views requires time proportional to the "capacity" of the
42 * <tt>HashMap</tt> instance (the number of buckets) plus its size (the number
43 * of key-value mappings). Thus, it's very important not to set the initial
44 * capacity too high (or the load factor too low) if iteration performance is
45 * important.
46 *
47 * <p>An instance of <tt>HashMap</tt> has two parameters that affect its
48 * performance: <i>initial capacity</i> and <i>load factor</i>. The
49 * <i>capacity</i> is the number of buckets in the hash table, and the initial
50 * capacity is simply the capacity at the time the hash table is created. The
51 * <i>load factor</i> is a measure of how full the hash table is allowed to
52 * get before its capacity is automatically increased. When the number of
53 * entries in the hash table exceeds the product of the load factor and the
54 * current capacity, the hash table is <i>rehashed</i> (that is, internal data
55 * structures are rebuilt) so that the hash table has approximately twice the
56 * number of buckets.
57 *
58 * <p>As a general rule, the default load factor (.75) offers a good tradeoff
59 * between time and space costs. Higher values decrease the space overhead
60 * but increase the lookup cost (reflected in most of the operations of the
61 * <tt>HashMap</tt> class, including <tt>get</tt> and <tt>put</tt>). The
62 * expected number of entries in the map and its load factor should be taken
63 * into account when setting its initial capacity, so as to minimize the
64 * number of rehash operations. If the initial capacity is greater
65 * than the maximum number of entries divided by the load factor, no
66 * rehash operations will ever occur.
67 *
68 * <p>If many mappings are to be stored in a <tt>HashMap</tt> instance,
69 * creating it with a sufficiently large capacity will allow the mappings to
70 * be stored more efficiently than letting it perform automatic rehashing as
71 * needed to grow the table.
72 *
73 * <p><strong>Note that this implementation is not synchronized.</strong>
74 * If multiple threads access a hash map concurrently, and at least one of
75 * the threads modifies the map structurally, it <i>must</i> be
76 * synchronized externally. (A structural modification is any operation
77 * that adds or deletes one or more mappings; merely changing the value
78 * associated with a key that an instance already contains is not a
79 * structural modification.) This is typically accomplished by
80 * synchronizing on some object that naturally encapsulates the map.
81 *
82 * If no such object exists, the map should be "wrapped" using the
83 * {@link Collections#synchronizedMap Collections.synchronizedMap}
84 * method. This is best done at creation time, to prevent accidental
85 * unsynchronized access to the map:<pre>
86 * Map m = Collections.synchronizedMap(new HashMap(...));</pre>
87 *
88 * <p>The iterators returned by all of this class's "collection view methods"
89 * are <i>fail-fast</i>: if the map is structurally modified at any time after
90 * the iterator is created, in any way except through the iterator's own
91 * <tt>remove</tt> method, the iterator will throw a
92 * {@link ConcurrentModificationException}. Thus, in the face of concurrent
93 * modification, the iterator fails quickly and cleanly, rather than risking
94 * arbitrary, non-deterministic behavior at an undetermined time in the
95 * future.
96 *
97 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
98 * as it is, generally speaking, impossible to make any hard guarantees in the
99 * presence of unsynchronized concurrent modification. Fail-fast iterators
100 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
101 * Therefore, it would be wrong to write a program that depended on this
102 * exception for its correctness: <i>the fail-fast behavior of iterators
103 * should be used only to detect bugs.</i>
104 *
105 * <p>This class is a member of the
106 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
107 * Java Collections Framework</a>.
108 *
109 * @param <K> the type of keys maintained by this map
110 * @param <V> the type of mapped values
111 *
112 * @author Doug Lea
113 * @author Josh Bloch
114 * @author Arthur van Hoff
115 * @author Neal Gafter
116 * @see Object#hashCode()
117 * @see Collection
118 * @see Map
119 * @see TreeMap
120 * @see Hashtable
121 * @since 1.2
122 */
123
124 public class HashMap<K,V>
125 extends AbstractMap<K,V>
126 implements Map<K,V>, Cloneable, Serializable
127 {
128
129 /**
130 * The default initial capacity - MUST be a power of two.
131 */
132 static final int DEFAULT_INITIAL_CAPACITY = 16;
133
134 /**
135 * The maximum capacity, used if a higher value is implicitly specified
136 * by either of the constructors with arguments.
137 * MUST be a power of two <= 1<<30.
138 */
139 static final int MAXIMUM_CAPACITY = 1 << 30;
140
141 /**
142 * The load factor used when none specified in constructor.
143 */
144 static final float DEFAULT_LOAD_FACTOR = 0.75f;
145
146 /**
147 * The table, resized as necessary. Length MUST Always be a power of two.
148 */
149 transient Entry<K,V>[] table;
150
151 /**
152 * The number of key-value mappings contained in this map.
153 */
154 transient int size;
155
156 /**
157 * The next size value at which to resize (capacity * load factor).
158 * @serial
159 */
160 int threshold;
161
162 /**
163 * The load factor for the hash table.
164 *
165 * @serial
166 */
167 final float loadFactor;
168
169 /**
170 * The number of times this HashMap has been structurally modified
171 * Structural modifications are those that change the number of mappings in
172 * the HashMap or otherwise modify its internal structure (e.g.,
173 * rehash). This field is used to make iterators on Collection-views of
174 * the HashMap fail-fast. (See ConcurrentModificationException).
175 */
176 transient int modCount;
177
178 /**
179 * The default threshold of capacity above which alternate hashing is used.
180 * Alternative hashing reduces the incidence of collisions due to weak hash
181 * code calculation.
182 * <p/>
183 * This value may be overridden by defining the system property
184 * {@code java.util.althashing.threshold}. A property value of {@code 1}
185 * forces alternative hashing to be used at all times whereas
186 * {@code 2147483648 } ({@code Integer.MAX_VALUE}) value ensures that
187 * alternative hashing is never used.
188 */
189 static final int ALTERNATE_HASHING_THRESHOLD_DEFAULT = 0;
190
191 /**
192 * holds values which can't be initialized until after VM is booted.
193 */
194 private static class Holder {
195
196 // Unsafe mechanics
197 /**
198 *
199 */
200 static final sun.misc.Unsafe UNSAFE;
201
202 /**
203 * Offset of "final" hashmask field we must set in
204 * readObject() method.
205 */
206 static final long HASHSEED_OFFSET;
207
208 /**
209 * Table capacity above which to switch to use alternate hashing.
210 */
211 static final int ALTERNATE_HASHING_THRESHOLD;
212
213 static {
214 String altThreshold = java.security.AccessController.doPrivileged(
215 new sun.security.action.GetPropertyAction(
216 "jdk.map.althashing.threshold"));
217
218 int threshold;
219 try {
220 threshold = (null != altThreshold)
221 ? Integer.parseInt(altThreshold)
222 : ALTERNATE_HASHING_THRESHOLD_DEFAULT;
223
224 if(threshold == -1) {
225 threshold = Integer.MAX_VALUE;
226 }
227
228 if(threshold < 0) {
229 throw new IllegalArgumentException("value must be positive integer.");
230 }
231 } catch(IllegalArgumentException failed) {
232 throw new Error("Illegal value for 'jdk.map.althashing.threshold'", failed);
233 }
234 ALTERNATE_HASHING_THRESHOLD = threshold;
235
236 try {
237 UNSAFE = sun.misc.Unsafe.getUnsafe();
238 HASHSEED_OFFSET = UNSAFE.objectFieldOffset(
239 HashMap.class.getDeclaredField("hashSeed"));
240 } catch (NoSuchFieldException | SecurityException e) {
241 throw new Error("Failed to record hashSeed offset", e);
242 }
243 }
244 }
245
246 /**
247 * If {@code true} then perform alternate hashing to reduce the incidence of
248 * collisions due to weak hash code calculation.
249 */
250 transient boolean useAltHashing;
251
252 /**
253 * A randomizing value associated with this instance that is applied to
254 * hash code of keys to make hash collisions harder to find.
255 */
256 transient final int hashSeed = sun.misc.Hashing.randomHashSeed(this);
257
258 /**
259 * Constructs an empty <tt>HashMap</tt> with the specified initial
260 * capacity and load factor.
261 *
262 * @param initialCapacity the initial capacity
263 * @param loadFactor the load factor
264 * @throws IllegalArgumentException if the initial capacity is negative
265 * or the load factor is nonpositive
266 */
267 public HashMap(int initialCapacity, float loadFactor) {
268 if (initialCapacity < 0)
269 throw new IllegalArgumentException("Illegal initial capacity: " +
270 initialCapacity);
271 if (initialCapacity > MAXIMUM_CAPACITY)
272 initialCapacity = MAXIMUM_CAPACITY;
273 if (loadFactor <= 0 || Float.isNaN(loadFactor))
274 throw new IllegalArgumentException("Illegal load factor: " +
275 loadFactor);
276
277 // Find a power of 2 >= initialCapacity
278 int capacity = 1;
279 while (capacity < initialCapacity)
280 capacity <<= 1;
281
282 this.loadFactor = loadFactor;
283 threshold = (int)Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
284 table = new Entry[capacity];
285 useAltHashing = sun.misc.VM.isBooted() &&
286 (capacity >= Holder.ALTERNATE_HASHING_THRESHOLD);
287 init();
288 }
289
290 /**
291 * Constructs an empty <tt>HashMap</tt> with the specified initial
292 * capacity and the default load factor (0.75).
293 *
294 * @param initialCapacity the initial capacity.
295 * @throws IllegalArgumentException if the initial capacity is negative.
296 */
297 public HashMap(int initialCapacity) {
298 this(initialCapacity, DEFAULT_LOAD_FACTOR);
299 }
300
301 /**
302 * Constructs an empty <tt>HashMap</tt> with the default initial capacity
303 * (16) and the default load factor (0.75).
304 */
305 public HashMap() {
306 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
307 }
308
309 /**
310 * Constructs a new <tt>HashMap</tt> with the same mappings as the
311 * specified <tt>Map</tt>. The <tt>HashMap</tt> is created with
312 * default load factor (0.75) and an initial capacity sufficient to
313 * hold the mappings in the specified <tt>Map</tt>.
314 *
315 * @param m the map whose mappings are to be placed in this map
316 * @throws NullPointerException if the specified map is null
317 */
318 public HashMap(Map<? extends K, ? extends V> m) {
319 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
320 DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);
321 putAllForCreate(m);
322 }
323
324 // internal utilities
325
326 /**
327 * Initialization hook for subclasses. This method is called
328 * in all constructors and pseudo-constructors (clone, readObject)
329 * after HashMap has been initialized but before any entries have
330 * been inserted. (In the absence of this method, readObject would
331 * require explicit knowledge of subclasses.)
332 */
333 void init() {
334 }
335
336 /**
337 * Retrieve object hash code and applies a supplemental hash function to the
338 * result hash, which defends against poor quality hash functions. This is
339 * critical because HashMap uses power-of-two length hash tables, that
340 * otherwise encounter collisions for hashCodes that do not differ
341 * in lower bits. Note: Null keys always map to hash 0, thus index 0.
342 */
343 final int hash(Object k) {
344 int h = 0;
345 if (useAltHashing) {
346 if (k instanceof String) {
347 return sun.misc.Hashing.stringHash32((String) k);
348 }
349 h = hashSeed;
350 }
351
352 h ^= k.hashCode();
353
354 // This function ensures that hashCodes that differ only by
355 // constant multiples at each bit position have a bounded
356 // number of collisions (approximately 8 at default load factor).
357 h ^= (h >>> 20) ^ (h >>> 12);
358 return h ^ (h >>> 7) ^ (h >>> 4);
359 }
360
361 /**
362 * Returns index for hash code h.
363 */
364 static int indexFor(int h, int length) {
365 return h & (length-1);
366 }
367
368 /**
369 * Returns the number of key-value mappings in this map.
370 *
371 * @return the number of key-value mappings in this map
372 */
373 public int size() {
374 return size;
375 }
376
377 /**
378 * Returns <tt>true</tt> if this map contains no key-value mappings.
379 *
380 * @return <tt>true</tt> if this map contains no key-value mappings
381 */
382 public boolean isEmpty() {
383 return size == 0;
384 }
385
386 /**
387 * Returns the value to which the specified key is mapped,
388 * or {@code null} if this map contains no mapping for the key.
389 *
390 * <p>More formally, if this map contains a mapping from a key
391 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
392 * key.equals(k))}, then this method returns {@code v}; otherwise
393 * it returns {@code null}. (There can be at most one such mapping.)
394 *
395 * <p>A return value of {@code null} does not <i>necessarily</i>
396 * indicate that the map contains no mapping for the key; it's also
397 * possible that the map explicitly maps the key to {@code null}.
398 * The {@link #containsKey containsKey} operation may be used to
399 * distinguish these two cases.
400 *
401 * @see #put(Object, Object)
402 */
403 public V get(Object key) {
404 if (key == null)
405 return getForNullKey();
406 Entry<K,V> entry = getEntry(key);
407
408 return null == entry ? null : entry.getValue();
409 }
410
411 /**
412 * Offloaded version of get() to look up null keys. Null keys map
413 * to index 0. This null case is split out into separate methods
414 * for the sake of performance in the two most commonly used
415 * operations (get and put), but incorporated with conditionals in
416 * others.
417 */
418 private V getForNullKey() {
419 for (Entry<K,V> e = table[0]; e != null; e = e.next) {
420 if (e.key == null)
421 return e.value;
422 }
423 return null;
424 }
425
426 /**
427 * Returns <tt>true</tt> if this map contains a mapping for the
428 * specified key.
429 *
430 * @param key The key whose presence in this map is to be tested
431 * @return <tt>true</tt> if this map contains a mapping for the specified
432 * key.
433 */
434 public boolean containsKey(Object key) {
435 return getEntry(key) != null;
436 }
437
438 /**
439 * Returns the entry associated with the specified key in the
440 * HashMap. Returns null if the HashMap contains no mapping
441 * for the key.
442 */
443 final Entry<K,V> getEntry(Object key) {
444 int hash = (key == null) ? 0 : hash(key);
445 for (Entry<K,V> e = table[indexFor(hash, table.length)];
446 e != null;
447 e = e.next) {
448 Object k;
449 if (e.hash == hash &&
450 ((k = e.key) == key || (key != null && key.equals(k))))
451 return e;
452 }
453 return null;
454 }
455
456
457 /**
458 * Associates the specified value with the specified key in this map.
459 * If the map previously contained a mapping for the key, the old
460 * value is replaced.
461 *
462 * @param key key with which the specified value is to be associated
463 * @param value value to be associated with the specified key
464 * @return the previous value associated with <tt>key</tt>, or
465 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
466 * (A <tt>null</tt> return can also indicate that the map
467 * previously associated <tt>null</tt> with <tt>key</tt>.)
468 */
469 public V put(K key, V value) {
470 if (key == null)
471 return putForNullKey(value);
472 int hash = hash(key);
473 int i = indexFor(hash, table.length);
474 for (Entry<K,V> e = table[i]; e != null; e = e.next) {
475 Object k;
476 if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
477 V oldValue = e.value;
478 e.value = value;
479 e.recordAccess(this);
480 return oldValue;
481 }
482 }
483
484 modCount++;
485 addEntry(hash, key, value, i);
486 return null;
487 }
488
489 /**
490 * Offloaded version of put for null keys
491 */
492 private V putForNullKey(V value) {
493 for (Entry<K,V> e = table[0]; e != null; e = e.next) {
494 if (e.key == null) {
495 V oldValue = e.value;
496 e.value = value;
497 e.recordAccess(this);
498 return oldValue;
499 }
500 }
501 modCount++;
502 addEntry(0, null, value, 0);
503 return null;
504 }
505
506 /**
507 * This method is used instead of put by constructors and
508 * pseudoconstructors (clone, readObject). It does not resize the table,
509 * check for comodification, etc. It calls createEntry rather than
510 * addEntry.
511 */
512 private void putForCreate(K key, V value) {
513 int hash = null == key ? 0 : hash(key);
514 int i = indexFor(hash, table.length);
515
516 /**
517 * Look for preexisting entry for key. This will never happen for
518 * clone or deserialize. It will only happen for construction if the
519 * input Map is a sorted map whose ordering is inconsistent w/ equals.
520 */
521 for (Entry<K,V> e = table[i]; e != null; e = e.next) {
522 Object k;
523 if (e.hash == hash &&
524 ((k = e.key) == key || (key != null && key.equals(k)))) {
525 e.value = value;
526 return;
527 }
528 }
529
530 createEntry(hash, key, value, i);
531 }
532
533 private void putAllForCreate(Map<? extends K, ? extends V> m) {
534 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
535 putForCreate(e.getKey(), e.getValue());
536 }
537
538 /**
539 * Rehashes the contents of this map into a new array with a
540 * larger capacity. This method is called automatically when the
541 * number of keys in this map reaches its threshold.
542 *
543 * If current capacity is MAXIMUM_CAPACITY, this method does not
544 * resize the map, but sets threshold to Integer.MAX_VALUE.
545 * This has the effect of preventing future calls.
546 *
547 * @param newCapacity the new capacity, MUST be a power of two;
548 * must be greater than current capacity unless current
549 * capacity is MAXIMUM_CAPACITY (in which case value
550 * is irrelevant).
551 */
552 void resize(int newCapacity) {
553 Entry[] oldTable = table;
554 int oldCapacity = oldTable.length;
555 if (oldCapacity == MAXIMUM_CAPACITY) {
556 threshold = Integer.MAX_VALUE;
557 return;
558 }
559
560 Entry[] newTable = new Entry[newCapacity];
561 boolean oldAltHashing = useAltHashing;
562 useAltHashing |= sun.misc.VM.isBooted() &&
563 (newCapacity >= Holder.ALTERNATE_HASHING_THRESHOLD);
564 boolean rehash = oldAltHashing ^ useAltHashing;
565 transfer(newTable, rehash);
566 table = newTable;
567 threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
568 }
569
570 /**
571 * Transfers all entries from current table to newTable.
572 */
573 void transfer(Entry[] newTable, boolean rehash) {
574 int newCapacity = newTable.length;
575 for (Entry<K,V> e : table) {
576 while(null != e) {
577 Entry<K,V> next = e.next;
578 if(rehash) {
579 e.hash = null == e.key ? 0 : hash(e.key);
580 }
581 int i = indexFor(e.hash, newCapacity);
582 e.next = newTable[i];
583 newTable[i] = e;
584 e = next;
585 }
586 }
587 }
588
589 /**
590 * Copies all of the mappings from the specified map to this map.
591 * These mappings will replace any mappings that this map had for
592 * any of the keys currently in the specified map.
593 *
594 * @param m mappings to be stored in this map
595 * @throws NullPointerException if the specified map is null
596 */
597 public void putAll(Map<? extends K, ? extends V> m) {
598 int numKeysToBeAdded = m.size();
599 if (numKeysToBeAdded == 0)
600 return;
601
602 /*
603 * Expand the map if the map if the number of mappings to be added
604 * is greater than or equal to threshold. This is conservative; the
605 * obvious condition is (m.size() + size) >= threshold, but this
606 * condition could result in a map with twice the appropriate capacity,
607 * if the keys to be added overlap with the keys already in this map.
608 * By using the conservative calculation, we subject ourself
609 * to at most one extra resize.
610 */
611 if (numKeysToBeAdded > threshold) {
612 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
613 if (targetCapacity > MAXIMUM_CAPACITY)
614 targetCapacity = MAXIMUM_CAPACITY;
615 int newCapacity = table.length;
616 while (newCapacity < targetCapacity)
617 newCapacity <<= 1;
618 if (newCapacity > table.length)
619 resize(newCapacity);
620 }
621
622 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
623 put(e.getKey(), e.getValue());
624 }
625
626 /**
627 * Removes the mapping for the specified key from this map if present.
628 *
629 * @param key key whose mapping is to be removed from the map
630 * @return the previous value associated with <tt>key</tt>, or
631 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
632 * (A <tt>null</tt> return can also indicate that the map
633 * previously associated <tt>null</tt> with <tt>key</tt>.)
634 */
635 public V remove(Object key) {
636 Entry<K,V> e = removeEntryForKey(key);
637 return (e == null ? null : e.value);
638 }
639
640 /**
641 * Removes and returns the entry associated with the specified key
642 * in the HashMap. Returns null if the HashMap contains no mapping
643 * for this key.
644 */
645 final Entry<K,V> removeEntryForKey(Object key) {
646 int hash = (key == null) ? 0 : hash(key);
647 int i = indexFor(hash, table.length);
648 Entry<K,V> prev = table[i];
649 Entry<K,V> e = prev;
650
651 while (e != null) {
652 Entry<K,V> next = e.next;
653 Object k;
654 if (e.hash == hash &&
655 ((k = e.key) == key || (key != null && key.equals(k)))) {
656 modCount++;
657 size--;
658 if (prev == e)
659 table[i] = next;
660 else
661 prev.next = next;
662 e.recordRemoval(this);
663 return e;
664 }
665 prev = e;
666 e = next;
667 }
668
669 return e;
670 }
671
672 /**
673 * Special version of remove for EntrySet using {@code Map.Entry.equals()}
674 * for matching.
675 */
676 final Entry<K,V> removeMapping(Object o) {
677 if (!(o instanceof Map.Entry))
678 return null;
679
680 Map.Entry<K,V> entry = (Map.Entry<K,V>) o;
681 Object key = entry.getKey();
682 int hash = (key == null) ? 0 : hash(key.hashCode());
683 int i = indexFor(hash, table.length);
684 Entry<K,V> prev = table[i];
685 Entry<K,V> e = prev;
686
687 while (e != null) {
688 Entry<K,V> next = e.next;
689 if (e.hash == hash && e.equals(entry)) {
690 modCount++;
691 size--;
692 if (prev == e)
693 table[i] = next;
694 else
695 prev.next = next;
696 e.recordRemoval(this);
697 return e;
698 }
699 prev = e;
700 e = next;
701 }
702
703 return e;
704 }
705
706 /**
707 * Removes all of the mappings from this map.
708 * The map will be empty after this call returns.
709 */
710 public void clear() {
711 modCount++;
712 Entry[] tab = table;
713 for (int i = 0; i < tab.length; i++)
714 tab[i] = null;
715 size = 0;
716 }
717
718 /**
719 * Returns <tt>true</tt> if this map maps one or more keys to the
720 * specified value.
721 *
722 * @param value value whose presence in this map is to be tested
723 * @return <tt>true</tt> if this map maps one or more keys to the
724 * specified value
725 */
726 public boolean containsValue(Object value) {
727 if (value == null)
728 return containsNullValue();
729
730 Entry[] tab = table;
731 for (int i = 0; i < tab.length ; i++)
732 for (Entry e = tab[i] ; e != null ; e = e.next)
733 if (value.equals(e.value))
734 return true;
735 return false;
736 }
737
738 /**
739 * Special-case code for containsValue with null argument
740 */
741 private boolean containsNullValue() {
742 Entry[] tab = table;
743 for (int i = 0; i < tab.length ; i++)
744 for (Entry e = tab[i] ; e != null ; e = e.next)
745 if (e.value == null)
746 return true;
747 return false;
748 }
749
750 /**
751 * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and
752 * values themselves are not cloned.
753 *
754 * @return a shallow copy of this map
755 */
756 public Object clone() {
757 HashMap<K,V> result = null;
758 try {
759 result = (HashMap<K,V>)super.clone();
760 } catch (CloneNotSupportedException e) {
761 // assert false;
762 }
763 result.table = new Entry[table.length];
764 result.entrySet = null;
765 result.modCount = 0;
766 result.size = 0;
767 result.init();
768 result.putAllForCreate(this);
769
770 return result;
771 }
772
773 static class Entry<K,V> implements Map.Entry<K,V> {
774 final K key;
775 V value;
776 Entry<K,V> next;
777 int hash;
778
779 /**
780 * Creates new entry.
781 */
782 Entry(int h, K k, V v, Entry<K,V> n) {
783 value = v;
784 next = n;
785 key = k;
786 hash = h;
787 }
788
789 public final K getKey() {
790 return key;
791 }
792
793 public final V getValue() {
794 return value;
795 }
796
797 public final V setValue(V newValue) {
798 V oldValue = value;
799 value = newValue;
800 return oldValue;
801 }
802
803 public final boolean equals(Object o) {
804 if (!(o instanceof Map.Entry))
805 return false;
806 Map.Entry e = (Map.Entry)o;
807 Object k1 = getKey();
808 Object k2 = e.getKey();
809 if (k1 == k2 || (k1 != null && k1.equals(k2))) {
810 Object v1 = getValue();
811 Object v2 = e.getValue();
812 if (v1 == v2 || (v1 != null && v1.equals(v2)))
813 return true;
814 }
815 return false;
816 }
817
818 public final int hashCode() {
819 return (key==null ? 0 : key.hashCode()) ^
820 (value==null ? 0 : value.hashCode());
821 }
822
823 public final String toString() {
824 return getKey() + "=" + getValue();
825 }
826
827 /**
828 * This method is invoked whenever the value in an entry is
829 * overwritten by an invocation of put(k,v) for a key k that's already
830 * in the HashMap.
831 */
832 void recordAccess(HashMap<K,V> m) {
833 }
834
835 /**
836 * This method is invoked whenever the entry is
837 * removed from the table.
838 */
839 void recordRemoval(HashMap<K,V> m) {
840 }
841 }
842
843 /**
844 * Adds a new entry with the specified key, value and hash code to
845 * the specified bucket. It is the responsibility of this
846 * method to resize the table if appropriate.
847 *
848 * Subclass overrides this to alter the behavior of put method.
849 */
850 void addEntry(int hash, K key, V value, int bucketIndex) {
851 if ((size >= threshold) && (null != table[bucketIndex])) {
852 resize(2 * table.length);
853 hash = hash(key);
854 bucketIndex = indexFor(hash, table.length);
855 }
856
857 createEntry(hash, key, value, bucketIndex);
858 }
859
860 /**
861 * Like addEntry except that this version is used when creating entries
862 * as part of Map construction or "pseudo-construction" (cloning,
863 * deserialization). This version needn't worry about resizing the table.
864 *
865 * Subclass overrides this to alter the behavior of HashMap(Map),
866 * clone, and readObject.
867 */
868 void createEntry(int hash, K key, V value, int bucketIndex) {
869 Entry<K,V> e = table[bucketIndex];
870 table[bucketIndex] = new Entry<>(hash, key, value, e);
871 size++;
872 }
873
874 private abstract class HashIterator<E> implements Iterator<E> {
875 Entry<K,V> next; // next entry to return
876 int expectedModCount; // For fast-fail
877 int index; // current slot
878 Entry<K,V> current; // current entry
879
880 HashIterator() {
881 expectedModCount = modCount;
882 if (size > 0) { // advance to first entry
883 Entry[] t = table;
884 while (index < t.length && (next = t[index++]) == null)
885 ;
886 }
887 }
888
889 public final boolean hasNext() {
890 return next != null;
891 }
892
893 final Entry<K,V> nextEntry() {
894 if (modCount != expectedModCount)
895 throw new ConcurrentModificationException();
896 Entry<K,V> e = next;
897 if (e == null)
898 throw new NoSuchElementException();
899
900 if ((next = e.next) == null) {
901 Entry[] t = table;
902 while (index < t.length && (next = t[index++]) == null)
903 ;
904 }
905 current = e;
906 return e;
907 }
908
909 public void remove() {
910 if (current == null)
911 throw new IllegalStateException();
912 if (modCount != expectedModCount)
913 throw new ConcurrentModificationException();
914 Object k = current.key;
915 current = null;
916 HashMap.this.removeEntryForKey(k);
917 expectedModCount = modCount;
918 }
919 }
920
921 private final class ValueIterator extends HashIterator<V> {
922 public V next() {
923 return nextEntry().value;
924 }
925 }
926
927 private final class KeyIterator extends HashIterator<K> {
928 public K next() {
929 return nextEntry().getKey();
930 }
931 }
932
933 private final class EntryIterator extends HashIterator<Map.Entry<K,V>> {
934 public Map.Entry<K,V> next() {
935 return nextEntry();
936 }
937 }
938
939 // Subclass overrides these to alter behavior of views' iterator() method
940 Iterator<K> newKeyIterator() {
941 return new KeyIterator();
942 }
943 Iterator<V> newValueIterator() {
944 return new ValueIterator();
945 }
946 Iterator<Map.Entry<K,V>> newEntryIterator() {
947 return new EntryIterator();
948 }
949
950
951 // Views
952
953 private transient Set<Map.Entry<K,V>> entrySet = null;
954
955 /**
956 * Returns a {@link Set} view of the keys contained in this map.
957 * The set is backed by the map, so changes to the map are
958 * reflected in the set, and vice-versa. If the map is modified
959 * while an iteration over the set is in progress (except through
960 * the iterator's own <tt>remove</tt> operation), the results of
961 * the iteration are undefined. The set supports element removal,
962 * which removes the corresponding mapping from the map, via the
963 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
964 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
965 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
966 * operations.
967 */
968 public Set<K> keySet() {
969 Set<K> ks = keySet;
970 return (ks != null ? ks : (keySet = new KeySet()));
971 }
972
973 private final class KeySet extends AbstractSet<K> {
974 public Iterator<K> iterator() {
975 return newKeyIterator();
976 }
977 public int size() {
978 return size;
979 }
980 public boolean contains(Object o) {
981 return containsKey(o);
982 }
983 public boolean remove(Object o) {
984 return HashMap.this.removeEntryForKey(o) != null;
985 }
986 public void clear() {
987 HashMap.this.clear();
988 }
989 }
990
991 /**
992 * Returns a {@link Collection} view of the values contained in this map.
993 * The collection is backed by the map, so changes to the map are
994 * reflected in the collection, and vice-versa. If the map is
995 * modified while an iteration over the collection is in progress
996 * (except through the iterator's own <tt>remove</tt> operation),
997 * the results of the iteration are undefined. The collection
998 * supports element removal, which removes the corresponding
999 * mapping from the map, via the <tt>Iterator.remove</tt>,
1000 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
1001 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
1002 * support the <tt>add</tt> or <tt>addAll</tt> operations.
1003 */
1004 public Collection<V> values() {
1005 Collection<V> vs = values;
1006 return (vs != null ? vs : (values = new Values()));
1007 }
1008
1009 private final class Values extends AbstractCollection<V> {
1010 public Iterator<V> iterator() {
1011 return newValueIterator();
1012 }
1013 public int size() {
1014 return size;
1015 }
1016 public boolean contains(Object o) {
1017 return containsValue(o);
1018 }
1019 public void clear() {
1020 HashMap.this.clear();
1021 }
1022 }
1023
1024 /**
1025 * Returns a {@link Set} view of the mappings contained in this map.
1026 * The set is backed by the map, so changes to the map are
1027 * reflected in the set, and vice-versa. If the map is modified
1028 * while an iteration over the set is in progress (except through
1029 * the iterator's own <tt>remove</tt> operation, or through the
1030 * <tt>setValue</tt> operation on a map entry returned by the
1031 * iterator) the results of the iteration are undefined. The set
1032 * supports element removal, which removes the corresponding
1033 * mapping from the map, via the <tt>Iterator.remove</tt>,
1034 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
1035 * <tt>clear</tt> operations. It does not support the
1036 * <tt>add</tt> or <tt>addAll</tt> operations.
1037 *
1038 * @return a set view of the mappings contained in this map
1039 */
1040 public Set<Map.Entry<K,V>> entrySet() {
1041 return entrySet0();
1042 }
1043
1044 private Set<Map.Entry<K,V>> entrySet0() {
1045 Set<Map.Entry<K,V>> es = entrySet;
1046 return es != null ? es : (entrySet = new EntrySet());
1047 }
1048
1049 private final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
1050 public Iterator<Map.Entry<K,V>> iterator() {
1051 return newEntryIterator();
1052 }
1053 public boolean contains(Object o) {
1054 if (!(o instanceof Map.Entry))
1055 return false;
1056 Map.Entry<K,V> e = (Map.Entry<K,V>) o;
1057 Entry<K,V> candidate = getEntry(e.getKey());
1058 return candidate != null && candidate.equals(e);
1059 }
1060 public boolean remove(Object o) {
1061 return removeMapping(o) != null;
1062 }
1063 public int size() {
1064 return size;
1065 }
1066 public void clear() {
1067 HashMap.this.clear();
1068 }
1069 }
1070
1071 /**
1072 * Save the state of the <tt>HashMap</tt> instance to a stream (i.e.,
1073 * serialize it).
1074 *
1075 * @serialData The <i>capacity</i> of the HashMap (the length of the
1076 * bucket array) is emitted (int), followed by the
1077 * <i>size</i> (an int, the number of key-value
1078 * mappings), followed by the key (Object) and value (Object)
1079 * for each key-value mapping. The key-value mappings are
1080 * emitted in no particular order.
1081 */
1082 private void writeObject(java.io.ObjectOutputStream s)
1083 throws IOException
1084 {
1085 Iterator<Map.Entry<K,V>> i =
1086 (size > 0) ? entrySet0().iterator() : null;
1087
1088 // Write out the threshold, loadfactor, and any hidden stuff
1089 s.defaultWriteObject();
1090
1091 // Write out number of buckets
1092 s.writeInt(table.length);
1093
1094 // Write out size (number of Mappings)
1095 s.writeInt(size);
1096
1097 // Write out keys and values (alternating)
1098 if (size > 0) {
1099 for(Map.Entry<K,V> e : entrySet0()) {
1100 s.writeObject(e.getKey());
1101 s.writeObject(e.getValue());
1102 }
1103 }
1104 }
1105
1106 private static final long serialVersionUID = 362498820763181265L;
1107
1108 /**
1109 * Reconstitute the {@code HashMap} instance from a stream (i.e.,
1110 * deserialize it).
1111 */
1112 private void readObject(java.io.ObjectInputStream s)
1113 throws IOException, ClassNotFoundException
1114 {
1115 // Read in the threshold (ignored), loadfactor, and any hidden stuff
1116 s.defaultReadObject();
1117 if (loadFactor <= 0 || Float.isNaN(loadFactor))
1118 throw new InvalidObjectException("Illegal load factor: " +
1119 loadFactor);
1120
1121 // set hashSeed (can only happen after VM boot)
1122 Holder.UNSAFE.putIntVolatile(this, Holder.HASHSEED_OFFSET,
1123 sun.misc.Hashing.randomHashSeed(this));
1124
1125 // Read in number of buckets and allocate the bucket array;
1126 s.readInt(); // ignored
1127
1128 // Read number of mappings
1129 int mappings = s.readInt();
1130 if (mappings < 0)
1131 throw new InvalidObjectException("Illegal mappings count: " +
1132 mappings);
1133
1134 int initialCapacity = (int) Math.min(
1135 // capacity chosen by number of mappings
1136 // and desired load (if >= 0.25)
1137 mappings * Math.min(1 / loadFactor, 4.0f),
1138 // we have limits...
1139 HashMap.MAXIMUM_CAPACITY);
1140 int capacity = 1;
1141 // find smallest power of two which holds all mappings
1142 while (capacity < initialCapacity) {
1143 capacity <<= 1;
1144 }
1145
1146 table = new Entry[capacity];
1147 threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
1148 useAltHashing = sun.misc.VM.isBooted() &&
1149 (capacity >= Holder.ALTERNATE_HASHING_THRESHOLD);
1150
1151 init(); // Give subclass a chance to do its thing.
1152
1153 // Read the keys and values, and put the mappings in the HashMap
1154 for (int i=0; i<mappings; i++) {
1155 K key = (K) s.readObject();
1156 V value = (V) s.readObject();
1157 putForCreate(key, value);
1158 }
1159 }
1160
1161 // These methods are used when serializing HashSets
1162 int capacity() { return table.length; }
1163 float loadFactor() { return loadFactor; }
1164 }