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 map capacity above which alternative hashing is
180 * used for String keys. Alternative hashing reduces the incidence of
181 * collisions due to weak hash code calculation for String keys.
182 * <p/>
183 * This value may be overridden by defining the system property
184 * {@code jdk.map.althashing.threshold}. A property value of {@code 1}
185 * forces alternative hashing to be used at all times whereas
186 * {@code -1} value ensures that alternative hashing is never used.
187 */
188 static final int ALTERNATIVE_HASHING_THRESHOLD_DEFAULT = Integer.MAX_VALUE;
189
190 /**
191 * holds values which can't be initialized until after VM is booted.
192 */
193 private static class Holder {
194
195 /**
196 * Table capacity above which to switch to use alternative hashing.
197 */
198 static final int ALTERNATIVE_HASHING_THRESHOLD;
199
200 static {
201 String altThreshold = java.security.AccessController.doPrivileged(
202 new sun.security.action.GetPropertyAction(
203 "jdk.map.althashing.threshold"));
204
205 int threshold;
206 try {
207 threshold = (null != altThreshold)
208 ? Integer.parseInt(altThreshold)
209 : ALTERNATIVE_HASHING_THRESHOLD_DEFAULT;
210
211 // disable alternative hashing if -1
212 if (threshold == -1) {
213 threshold = Integer.MAX_VALUE;
214 }
215
216 if (threshold < 0) {
217 throw new IllegalArgumentException("value must be positive integer.");
218 }
219 } catch(IllegalArgumentException failed) {
220 throw new Error("Illegal value for 'jdk.map.althashing.threshold'", failed);
221 }
222 ALTERNATIVE_HASHING_THRESHOLD = threshold;
223 }
224 }
225
226 /**
227 * If {@code true} then perform alternative hashing of String keys to reduce
228 * the incidence of collisions due to weak hash code calculation.
229 */
230 transient boolean useAltHashing = false;
231
232 /**
233 * A randomizing value associated with this instance that is applied to
234 * hash code of keys to make hash collisions harder to find. Initialized via
235 * sun.misc.Unsafe when needed.
236 */
237 transient int hashSeed = 0;
238
239 /**
240 * Constructs an empty <tt>HashMap</tt> with the specified initial
241 * capacity and load factor.
242 *
243 * @param initialCapacity the initial capacity
244 * @param loadFactor the load factor
245 * @throws IllegalArgumentException if the initial capacity is negative
246 * or the load factor is nonpositive
247 */
248 public HashMap(int initialCapacity, float loadFactor) {
249 if (initialCapacity < 0)
250 throw new IllegalArgumentException("Illegal initial capacity: " +
251 initialCapacity);
252 if (initialCapacity > MAXIMUM_CAPACITY)
253 initialCapacity = MAXIMUM_CAPACITY;
254 if (loadFactor <= 0 || Float.isNaN(loadFactor))
255 throw new IllegalArgumentException("Illegal load factor: " +
256 loadFactor);
257
258 // Find a power of 2 >= initialCapacity
259 int capacity = (capacity = Integer.highestOneBit(initialCapacity)) != 0
260 ? capacity
261 : 1;
262 capacity <<= (Integer.bitCount(initialCapacity) > 1) ? 1 : 0;
263
264 this.loadFactor = loadFactor;
265 threshold = (int)Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
266 table = new Entry[capacity];
267 initHashSeedAsNeeded(capacity);
268 init();
269 }
270
271 /**
272 * Constructs an empty <tt>HashMap</tt> with the specified initial
273 * capacity and the default load factor (0.75).
274 *
275 * @param initialCapacity the initial capacity.
276 * @throws IllegalArgumentException if the initial capacity is negative.
277 */
278 public HashMap(int initialCapacity) {
279 this(initialCapacity, DEFAULT_LOAD_FACTOR);
280 }
281
282 /**
283 * Constructs an empty <tt>HashMap</tt> with the default initial capacity
284 * (16) and the default load factor (0.75).
285 */
286 public HashMap() {
287 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
288 }
289
290 /**
291 * Constructs a new <tt>HashMap</tt> with the same mappings as the
292 * specified <tt>Map</tt>. The <tt>HashMap</tt> is created with
293 * default load factor (0.75) and an initial capacity sufficient to
294 * hold the mappings in the specified <tt>Map</tt>.
295 *
296 * @param m the map whose mappings are to be placed in this map
297 * @throws NullPointerException if the specified map is null
298 */
299 public HashMap(Map<? extends K, ? extends V> m) {
300 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
301 DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);
302 putAllForCreate(m);
303 }
304
305 // internal utilities
306
307 /**
308 * Initialization hook for subclasses. This method is called
309 * in all constructors and pseudo-constructors (clone, readObject)
310 * after HashMap has been initialized but before any entries have
311 * been inserted. (In the absence of this method, readObject would
312 * require explicit knowledge of subclasses.)
313 */
314 void init() {
315 }
316
317 /**
318 * Initialize the hashing mask value. We defer initialization until we
319 * really need it.
320 */
321 final boolean initHashSeedAsNeeded(int capacity) {
322 boolean currentAltHashing = useAltHashing;
323 useAltHashing = sun.misc.VM.isBooted() &&
324 (capacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD);
325 boolean switching = currentAltHashing ^ useAltHashing;
326 if (switching) {
327 hashSeed = useAltHashing
328 ? sun.misc.Hashing.randomHashSeed(this)
329 : 0;
330 }
331 return switching;
332 }
333
334 /**
335 * Retrieve object hash code and applies a supplemental hash function to the
336 * result hash, which defends against poor quality hash functions. This is
337 * critical because HashMap uses power-of-two length hash tables, that
338 * otherwise encounter collisions for hashCodes that do not differ
339 * in lower bits. Note: Null keys always map to hash 0, thus index 0.
340 */
341 final int hash(Object k) {
342 int h = 0;
343 if (useAltHashing) {
344 if (k instanceof String) {
345 return sun.misc.Hashing.stringHash32((String) k);
346 }
347 h = hashSeed;
348 }
349
350 h ^= k.hashCode();
351
352 // This function ensures that hashCodes that differ only by
353 // constant multiples at each bit position have a bounded
354 // number of collisions (approximately 8 at default load factor).
355 h ^= (h >>> 20) ^ (h >>> 12);
356 return h ^ (h >>> 7) ^ (h >>> 4);
357 }
358
359 /**
360 * Returns index for hash code h.
361 */
362 static int indexFor(int h, int length) {
363 return h & (length-1);
364 }
365
366 /**
367 * Returns the number of key-value mappings in this map.
368 *
369 * @return the number of key-value mappings in this map
370 */
371 public int size() {
372 return size;
373 }
374
375 /**
376 * Returns <tt>true</tt> if this map contains no key-value mappings.
377 *
378 * @return <tt>true</tt> if this map contains no key-value mappings
379 */
380 public boolean isEmpty() {
381 return size == 0;
382 }
383
384 /**
385 * Returns the value to which the specified key is mapped,
386 * or {@code null} if this map contains no mapping for the key.
387 *
388 * <p>More formally, if this map contains a mapping from a key
389 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
390 * key.equals(k))}, then this method returns {@code v}; otherwise
391 * it returns {@code null}. (There can be at most one such mapping.)
392 *
393 * <p>A return value of {@code null} does not <i>necessarily</i>
394 * indicate that the map contains no mapping for the key; it's also
395 * possible that the map explicitly maps the key to {@code null}.
396 * The {@link #containsKey containsKey} operation may be used to
397 * distinguish these two cases.
398 *
399 * @see #put(Object, Object)
400 */
401 public V get(Object key) {
402 if (key == null)
403 return getForNullKey();
404 Entry<K,V> entry = getEntry(key);
405
406 return null == entry ? null : entry.getValue();
407 }
408
409 /**
410 * Offloaded version of get() to look up null keys. Null keys map
411 * to index 0. This null case is split out into separate methods
412 * for the sake of performance in the two most commonly used
413 * operations (get and put), but incorporated with conditionals in
414 * others.
415 */
416 private V getForNullKey() {
417 for (Entry<K,V> e = table[0]; e != null; e = e.next) {
418 if (e.key == null)
419 return e.value;
420 }
421 return null;
422 }
423
424 /**
425 * Returns <tt>true</tt> if this map contains a mapping for the
426 * specified key.
427 *
428 * @param key The key whose presence in this map is to be tested
429 * @return <tt>true</tt> if this map contains a mapping for the specified
430 * key.
431 */
432 public boolean containsKey(Object key) {
433 return getEntry(key) != null;
434 }
435
436 /**
437 * Returns the entry associated with the specified key in the
438 * HashMap. Returns null if the HashMap contains no mapping
439 * for the key.
440 */
441 final Entry<K,V> getEntry(Object key) {
442 int hash = (key == null) ? 0 : hash(key);
443 for (Entry<K,V> e = table[indexFor(hash, table.length)];
444 e != null;
445 e = e.next) {
446 Object k;
447 if (e.hash == hash &&
448 ((k = e.key) == key || (key != null && key.equals(k))))
449 return e;
450 }
451 return null;
452 }
453
454
455 /**
456 * Associates the specified value with the specified key in this map.
457 * If the map previously contained a mapping for the key, the old
458 * value is replaced.
459 *
460 * @param key key with which the specified value is to be associated
461 * @param value value to be associated with the specified key
462 * @return the previous value associated with <tt>key</tt>, or
463 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
464 * (A <tt>null</tt> return can also indicate that the map
465 * previously associated <tt>null</tt> with <tt>key</tt>.)
466 */
467 public V put(K key, V value) {
468 if (key == null)
469 return putForNullKey(value);
470 int hash = hash(key);
471 int i = indexFor(hash, table.length);
472 for (Entry<K,V> e = table[i]; e != null; e = e.next) {
473 Object k;
474 if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
475 V oldValue = e.value;
476 e.value = value;
477 e.recordAccess(this);
478 return oldValue;
479 }
480 }
481
482 modCount++;
483 addEntry(hash, key, value, i);
484 return null;
485 }
486
487 /**
488 * Offloaded version of put for null keys
489 */
490 private V putForNullKey(V value) {
491 for (Entry<K,V> e = table[0]; e != null; e = e.next) {
492 if (e.key == null) {
493 V oldValue = e.value;
494 e.value = value;
495 e.recordAccess(this);
496 return oldValue;
497 }
498 }
499 modCount++;
500 addEntry(0, null, value, 0);
501 return null;
502 }
503
504 /**
505 * This method is used instead of put by constructors and
506 * pseudoconstructors (clone, readObject). It does not resize the table,
507 * check for comodification, etc. It calls createEntry rather than
508 * addEntry.
509 */
510 private void putForCreate(K key, V value) {
511 int hash = null == key ? 0 : hash(key);
512 int i = indexFor(hash, table.length);
513
514 /**
515 * Look for preexisting entry for key. This will never happen for
516 * clone or deserialize. It will only happen for construction if the
517 * input Map is a sorted map whose ordering is inconsistent w/ equals.
518 */
519 for (Entry<K,V> e = table[i]; e != null; e = e.next) {
520 Object k;
521 if (e.hash == hash &&
522 ((k = e.key) == key || (key != null && key.equals(k)))) {
523 e.value = value;
524 return;
525 }
526 }
527
528 createEntry(hash, key, value, i);
529 }
530
531 private void putAllForCreate(Map<? extends K, ? extends V> m) {
532 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
533 putForCreate(e.getKey(), e.getValue());
534 }
535
536 /**
537 * Rehashes the contents of this map into a new array with a
538 * larger capacity. This method is called automatically when the
539 * number of keys in this map reaches its threshold.
540 *
541 * If current capacity is MAXIMUM_CAPACITY, this method does not
542 * resize the map, but sets threshold to Integer.MAX_VALUE.
543 * This has the effect of preventing future calls.
544 *
545 * @param newCapacity the new capacity, MUST be a power of two;
546 * must be greater than current capacity unless current
547 * capacity is MAXIMUM_CAPACITY (in which case value
548 * is irrelevant).
549 */
550 void resize(int newCapacity) {
551 Entry[] oldTable = table;
552 int oldCapacity = oldTable.length;
553 if (oldCapacity == MAXIMUM_CAPACITY) {
554 threshold = Integer.MAX_VALUE;
555 return;
556 }
557
558 Entry[] newTable = new Entry[newCapacity];
559 transfer(newTable, initHashSeedAsNeeded(newCapacity));
560 table = newTable;
561 threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
562 }
563
564 /**
565 * Transfers all entries from current table to newTable.
566 */
567 void transfer(Entry[] newTable, boolean rehash) {
568 int newCapacity = newTable.length;
569 for (Entry<K,V> e : table) {
570 while(null != e) {
571 Entry<K,V> next = e.next;
572 if (rehash) {
573 e.hash = null == e.key ? 0 : hash(e.key);
574 }
575 int i = indexFor(e.hash, newCapacity);
576 e.next = newTable[i];
577 newTable[i] = e;
578 e = next;
579 }
580 }
581 }
582
583 /**
584 * Copies all of the mappings from the specified map to this map.
585 * These mappings will replace any mappings that this map had for
586 * any of the keys currently in the specified map.
587 *
588 * @param m mappings to be stored in this map
589 * @throws NullPointerException if the specified map is null
590 */
591 public void putAll(Map<? extends K, ? extends V> m) {
592 int numKeysToBeAdded = m.size();
593 if (numKeysToBeAdded == 0)
594 return;
595
596 /*
597 * Expand the map if the map if the number of mappings to be added
598 * is greater than or equal to threshold. This is conservative; the
599 * obvious condition is (m.size() + size) >= threshold, but this
600 * condition could result in a map with twice the appropriate capacity,
601 * if the keys to be added overlap with the keys already in this map.
602 * By using the conservative calculation, we subject ourself
603 * to at most one extra resize.
604 */
605 if (numKeysToBeAdded > threshold) {
606 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
607 if (targetCapacity > MAXIMUM_CAPACITY)
608 targetCapacity = MAXIMUM_CAPACITY;
609 int newCapacity = table.length;
610 while (newCapacity < targetCapacity)
611 newCapacity <<= 1;
612 if (newCapacity > table.length)
613 resize(newCapacity);
614 }
615
616 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
617 put(e.getKey(), e.getValue());
618 }
619
620 /**
621 * Removes the mapping for the specified key from this map if present.
622 *
623 * @param key key whose mapping is to be removed from the map
624 * @return the previous value associated with <tt>key</tt>, or
625 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
626 * (A <tt>null</tt> return can also indicate that the map
627 * previously associated <tt>null</tt> with <tt>key</tt>.)
628 */
629 public V remove(Object key) {
630 Entry<K,V> e = removeEntryForKey(key);
631 return (e == null ? null : e.value);
632 }
633
634 /**
635 * Removes and returns the entry associated with the specified key
636 * in the HashMap. Returns null if the HashMap contains no mapping
637 * for this key.
638 */
639 final Entry<K,V> removeEntryForKey(Object key) {
640 int hash = (key == null) ? 0 : hash(key);
641 int i = indexFor(hash, table.length);
642 Entry<K,V> prev = table[i];
643 Entry<K,V> e = prev;
644
645 while (e != null) {
646 Entry<K,V> next = e.next;
647 Object k;
648 if (e.hash == hash &&
649 ((k = e.key) == key || (key != null && key.equals(k)))) {
650 modCount++;
651 size--;
652 if (prev == e)
653 table[i] = next;
654 else
655 prev.next = next;
656 e.recordRemoval(this);
657 return e;
658 }
659 prev = e;
660 e = next;
661 }
662
663 return e;
664 }
665
666 /**
667 * Special version of remove for EntrySet using {@code Map.Entry.equals()}
668 * for matching.
669 */
670 final Entry<K,V> removeMapping(Object o) {
671 if (!(o instanceof Map.Entry))
672 return null;
673
674 Map.Entry<K,V> entry = (Map.Entry<K,V>) o;
675 Object key = entry.getKey();
676 int hash = (key == null) ? 0 : hash(key);
677 int i = indexFor(hash, table.length);
678 Entry<K,V> prev = table[i];
679 Entry<K,V> e = prev;
680
681 while (e != null) {
682 Entry<K,V> next = e.next;
683 if (e.hash == hash && e.equals(entry)) {
684 modCount++;
685 size--;
686 if (prev == e)
687 table[i] = next;
688 else
689 prev.next = next;
690 e.recordRemoval(this);
691 return e;
692 }
693 prev = e;
694 e = next;
695 }
696
697 return e;
698 }
699
700 /**
701 * Removes all of the mappings from this map.
702 * The map will be empty after this call returns.
703 */
704 public void clear() {
705 modCount++;
706 Entry[] tab = table;
707 for (int i = 0; i < tab.length; i++)
708 tab[i] = null;
709 size = 0;
710 }
711
712 /**
713 * Returns <tt>true</tt> if this map maps one or more keys to the
714 * specified value.
715 *
716 * @param value value whose presence in this map is to be tested
717 * @return <tt>true</tt> if this map maps one or more keys to the
718 * specified value
719 */
720 public boolean containsValue(Object value) {
721 if (value == null)
722 return containsNullValue();
723
724 Entry[] tab = table;
725 for (int i = 0; i < tab.length ; i++)
726 for (Entry e = tab[i] ; e != null ; e = e.next)
727 if (value.equals(e.value))
728 return true;
729 return false;
730 }
731
732 /**
733 * Special-case code for containsValue with null argument
734 */
735 private boolean containsNullValue() {
736 Entry[] tab = table;
737 for (int i = 0; i < tab.length ; i++)
738 for (Entry e = tab[i] ; e != null ; e = e.next)
739 if (e.value == null)
740 return true;
741 return false;
742 }
743
744 /**
745 * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and
746 * values themselves are not cloned.
747 *
748 * @return a shallow copy of this map
749 */
750 public Object clone() {
751 HashMap<K,V> result = null;
752 try {
753 result = (HashMap<K,V>)super.clone();
754 } catch (CloneNotSupportedException e) {
755 // assert false;
756 }
757 result.table = new Entry[table.length];
758 result.entrySet = null;
759 result.modCount = 0;
760 result.size = 0;
761 result.init();
762 result.putAllForCreate(this);
763
764 return result;
765 }
766
767 static class Entry<K,V> implements Map.Entry<K,V> {
768 final K key;
769 V value;
770 Entry<K,V> next;
771 int hash;
772
773 /**
774 * Creates new entry.
775 */
776 Entry(int h, K k, V v, Entry<K,V> n) {
777 value = v;
778 next = n;
779 key = k;
780 hash = h;
781 }
782
783 public final K getKey() {
784 return key;
785 }
786
787 public final V getValue() {
788 return value;
789 }
790
791 public final V setValue(V newValue) {
792 V oldValue = value;
793 value = newValue;
794 return oldValue;
795 }
796
797 public final boolean equals(Object o) {
798 if (!(o instanceof Map.Entry))
799 return false;
800 Map.Entry e = (Map.Entry)o;
801 Object k1 = getKey();
802 Object k2 = e.getKey();
803 if (k1 == k2 || (k1 != null && k1.equals(k2))) {
804 Object v1 = getValue();
805 Object v2 = e.getValue();
806 if (v1 == v2 || (v1 != null && v1.equals(v2)))
807 return true;
808 }
809 return false;
810 }
811
812 public final int hashCode() {
813 return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
814 }
815
816 public final String toString() {
817 return getKey() + "=" + getValue();
818 }
819
820 /**
821 * This method is invoked whenever the value in an entry is
822 * overwritten by an invocation of put(k,v) for a key k that's already
823 * in the HashMap.
824 */
825 void recordAccess(HashMap<K,V> m) {
826 }
827
828 /**
829 * This method is invoked whenever the entry is
830 * removed from the table.
831 */
832 void recordRemoval(HashMap<K,V> m) {
833 }
834 }
835
836 /**
837 * Adds a new entry with the specified key, value and hash code to
838 * the specified bucket. It is the responsibility of this
839 * method to resize the table if appropriate.
840 *
841 * Subclass overrides this to alter the behavior of put method.
842 */
843 void addEntry(int hash, K key, V value, int bucketIndex) {
844 if ((size >= threshold) && (null != table[bucketIndex])) {
845 resize(2 * table.length);
846 hash = (null != key) ? hash(key) : 0;
847 bucketIndex = indexFor(hash, table.length);
848 }
849
850 createEntry(hash, key, value, bucketIndex);
851 }
852
853 /**
854 * Like addEntry except that this version is used when creating entries
855 * as part of Map construction or "pseudo-construction" (cloning,
856 * deserialization). This version needn't worry about resizing the table.
857 *
858 * Subclass overrides this to alter the behavior of HashMap(Map),
859 * clone, and readObject.
860 */
861 void createEntry(int hash, K key, V value, int bucketIndex) {
862 Entry<K,V> e = table[bucketIndex];
863 table[bucketIndex] = new Entry<>(hash, key, value, e);
864 size++;
865 }
866
867 private abstract class HashIterator<E> implements Iterator<E> {
868 Entry<K,V> next; // next entry to return
869 int expectedModCount; // For fast-fail
870 int index; // current slot
871 Entry<K,V> current; // current entry
872
873 HashIterator() {
874 expectedModCount = modCount;
875 if (size > 0) { // advance to first entry
876 Entry[] t = table;
877 while (index < t.length && (next = t[index++]) == null)
878 ;
879 }
880 }
881
882 public final boolean hasNext() {
883 return next != null;
884 }
885
886 final Entry<K,V> nextEntry() {
887 if (modCount != expectedModCount)
888 throw new ConcurrentModificationException();
889 Entry<K,V> e = next;
890 if (e == null)
891 throw new NoSuchElementException();
892
893 if ((next = e.next) == null) {
894 Entry[] t = table;
895 while (index < t.length && (next = t[index++]) == null)
896 ;
897 }
898 current = e;
899 return e;
900 }
901
902 public void remove() {
903 if (current == null)
904 throw new IllegalStateException();
905 if (modCount != expectedModCount)
906 throw new ConcurrentModificationException();
907 Object k = current.key;
908 current = null;
909 HashMap.this.removeEntryForKey(k);
910 expectedModCount = modCount;
911 }
912 }
913
914 private final class ValueIterator extends HashIterator<V> {
915 public V next() {
916 return nextEntry().value;
917 }
918 }
919
920 private final class KeyIterator extends HashIterator<K> {
921 public K next() {
922 return nextEntry().getKey();
923 }
924 }
925
926 private final class EntryIterator extends HashIterator<Map.Entry<K,V>> {
927 public Map.Entry<K,V> next() {
928 return nextEntry();
929 }
930 }
931
932 // Subclass overrides these to alter behavior of views' iterator() method
933 Iterator<K> newKeyIterator() {
934 return new KeyIterator();
935 }
936 Iterator<V> newValueIterator() {
937 return new ValueIterator();
938 }
939 Iterator<Map.Entry<K,V>> newEntryIterator() {
940 return new EntryIterator();
941 }
942
943
944 // Views
945
946 private transient Set<Map.Entry<K,V>> entrySet = null;
947
948 /**
949 * Returns a {@link Set} view of the keys contained in this map.
950 * The set is backed by the map, so changes to the map are
951 * reflected in the set, and vice-versa. If the map is modified
952 * while an iteration over the set is in progress (except through
953 * the iterator's own <tt>remove</tt> operation), the results of
954 * the iteration are undefined. The set supports element removal,
955 * which removes the corresponding mapping from the map, via the
956 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
957 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
958 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
959 * operations.
960 */
961 public Set<K> keySet() {
962 Set<K> ks = keySet;
963 return (ks != null ? ks : (keySet = new KeySet()));
964 }
965
966 private final class KeySet extends AbstractSet<K> {
967 public Iterator<K> iterator() {
968 return newKeyIterator();
969 }
970 public int size() {
971 return size;
972 }
973 public boolean contains(Object o) {
974 return containsKey(o);
975 }
976 public boolean remove(Object o) {
977 return HashMap.this.removeEntryForKey(o) != null;
978 }
979 public void clear() {
980 HashMap.this.clear();
981 }
982 }
983
984 /**
985 * Returns a {@link Collection} view of the values contained in this map.
986 * The collection is backed by the map, so changes to the map are
987 * reflected in the collection, and vice-versa. If the map is
988 * modified while an iteration over the collection is in progress
989 * (except through the iterator's own <tt>remove</tt> operation),
990 * the results of the iteration are undefined. The collection
991 * supports element removal, which removes the corresponding
992 * mapping from the map, via the <tt>Iterator.remove</tt>,
993 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
994 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
995 * support the <tt>add</tt> or <tt>addAll</tt> operations.
996 */
997 public Collection<V> values() {
998 Collection<V> vs = values;
999 return (vs != null ? vs : (values = new Values()));
1000 }
1001
1002 private final class Values extends AbstractCollection<V> {
1003 public Iterator<V> iterator() {
1004 return newValueIterator();
1005 }
1006 public int size() {
1007 return size;
1008 }
1009 public boolean contains(Object o) {
1010 return containsValue(o);
1011 }
1012 public void clear() {
1013 HashMap.this.clear();
1014 }
1015 }
1016
1017 /**
1018 * Returns a {@link Set} view of the mappings contained in this map.
1019 * The set is backed by the map, so changes to the map are
1020 * reflected in the set, and vice-versa. If the map is modified
1021 * while an iteration over the set is in progress (except through
1022 * the iterator's own <tt>remove</tt> operation, or through the
1023 * <tt>setValue</tt> operation on a map entry returned by the
1024 * iterator) the results of the iteration are undefined. The set
1025 * supports element removal, which removes the corresponding
1026 * mapping from the map, via the <tt>Iterator.remove</tt>,
1027 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
1028 * <tt>clear</tt> operations. It does not support the
1029 * <tt>add</tt> or <tt>addAll</tt> operations.
1030 *
1031 * @return a set view of the mappings contained in this map
1032 */
1033 public Set<Map.Entry<K,V>> entrySet() {
1034 return entrySet0();
1035 }
1036
1037 private Set<Map.Entry<K,V>> entrySet0() {
1038 Set<Map.Entry<K,V>> es = entrySet;
1039 return es != null ? es : (entrySet = new EntrySet());
1040 }
1041
1042 private final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
1043 public Iterator<Map.Entry<K,V>> iterator() {
1044 return newEntryIterator();
1045 }
1046 public boolean contains(Object o) {
1047 if (!(o instanceof Map.Entry))
1048 return false;
1049 Map.Entry<K,V> e = (Map.Entry<K,V>) o;
1050 Entry<K,V> candidate = getEntry(e.getKey());
1051 return candidate != null && candidate.equals(e);
1052 }
1053 public boolean remove(Object o) {
1054 return removeMapping(o) != null;
1055 }
1056 public int size() {
1057 return size;
1058 }
1059 public void clear() {
1060 HashMap.this.clear();
1061 }
1062 }
1063
1064 /**
1065 * Save the state of the <tt>HashMap</tt> instance to a stream (i.e.,
1066 * serialize it).
1067 *
1068 * @serialData The <i>capacity</i> of the HashMap (the length of the
1069 * bucket array) is emitted (int), followed by the
1070 * <i>size</i> (an int, the number of key-value
1071 * mappings), followed by the key (Object) and value (Object)
1072 * for each key-value mapping. The key-value mappings are
1073 * emitted in no particular order.
1074 */
1075 private void writeObject(java.io.ObjectOutputStream s)
1076 throws IOException
1077 {
1078 Iterator<Map.Entry<K,V>> i =
1079 (size > 0) ? entrySet0().iterator() : null;
1080
1081 // Write out the threshold, loadfactor, and any hidden stuff
1082 s.defaultWriteObject();
1083
1084 // Write out number of buckets
1085 s.writeInt(table.length);
1086
1087 // Write out size (number of Mappings)
1088 s.writeInt(size);
1089
1090 // Write out keys and values (alternating)
1091 if (size > 0) {
1092 for(Map.Entry<K,V> e : entrySet0()) {
1093 s.writeObject(e.getKey());
1094 s.writeObject(e.getValue());
1095 }
1096 }
1097 }
1098
1099 private static final long serialVersionUID = 362498820763181265L;
1100
1101 /**
1102 * Reconstitute the {@code HashMap} instance from a stream (i.e.,
1103 * deserialize it).
1104 */
1105 private void readObject(java.io.ObjectInputStream s)
1106 throws IOException, ClassNotFoundException
1107 {
1108 // Read in the threshold (ignored), loadfactor, and any hidden stuff
1109 s.defaultReadObject();
1110 if (loadFactor <= 0 || Float.isNaN(loadFactor))
1111 throw new InvalidObjectException("Illegal load factor: " +
1112 loadFactor);
1113
1114 // Read in number of buckets and allocate the bucket array;
1115 s.readInt(); // ignored
1116
1117 // Read number of mappings
1118 int mappings = s.readInt();
1119 if (mappings < 0)
1120 throw new InvalidObjectException("Illegal mappings count: " +
1121 mappings);
1122
1123 int initialCapacity = (int) Math.min(
1124 // capacity chosen by number of mappings
1125 // and desired load (if >= 0.25)
1126 mappings * Math.min(1 / loadFactor, 4.0f),
1127 // we have limits...
1128 HashMap.MAXIMUM_CAPACITY);
1129 // find smallest power of two which holds all mappings
1130 int capacity = (capacity = Integer.highestOneBit(initialCapacity)) != 0
1131 ? capacity
1132 : 1;
1133 capacity <<= (Integer.bitCount(initialCapacity) > 1) ? 1 : 0;
1134
1135 table = new Entry[capacity];
1136 threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
1137 initHashSeedAsNeeded(capacity);
1138
1139 init(); // Give subclass a chance to do its thing.
1140
1141 // Read the keys and values, and put the mappings in the HashMap
1142 for (int i=0; i<mappings; i++) {
1143 K key = (K) s.readObject();
1144 V value = (V) s.readObject();
1145 putForCreate(key, value);
1146 }
1147 }
1148
1149 // These methods are used when serializing HashSets
1150 int capacity() { return table.length; }
1151 float loadFactor() { return loadFactor; }
1152 }