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