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<?,?>[] 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 private static class Holder {
179 /**
180 *
181 */
182 static final sun.misc.Unsafe UNSAFE;
183
184 /**
185 * Offset of "final" hashSeed field we must set in
186 * readObject() method.
187 */
188 static final long HASHSEED_OFFSET;
189
190 static {
191 try {
192 UNSAFE = sun.misc.Unsafe.getUnsafe();
193 HASHSEED_OFFSET = UNSAFE.objectFieldOffset(
194 HashMap.class.getDeclaredField("hashSeed"));
195 } catch (NoSuchFieldException | SecurityException e) {
196 throw new InternalError("Failed to record hashSeed offset", e);
197 }
198 }
199 }
200
201 /**
202 * A randomizing value associated with this instance that is applied to
203 * hash code of keys to make hash collisions harder to find.
204 */
205 transient final int hashSeed = sun.misc.Hashing.randomHashSeed(this);
206
207 /**
208 * Constructs an empty <tt>HashMap</tt> with the specified initial
209 * capacity and load factor.
210 *
211 * @param initialCapacity the initial capacity
212 * @param loadFactor the load factor
213 * @throws IllegalArgumentException if the initial capacity is negative
214 * or the load factor is nonpositive
215 */
216 public HashMap(int initialCapacity, float loadFactor) {
217 if (initialCapacity < 0)
218 throw new IllegalArgumentException("Illegal initial capacity: " +
219 initialCapacity);
220 if (initialCapacity > MAXIMUM_CAPACITY)
221 initialCapacity = MAXIMUM_CAPACITY;
222 if (loadFactor <= 0 || Float.isNaN(loadFactor))
223 throw new IllegalArgumentException("Illegal load factor: " +
224 loadFactor);
225
226 // Find a power of 2 >= initialCapacity
227 int capacity = 1;
228 while (capacity < initialCapacity)
229 capacity <<= 1;
230
231 this.loadFactor = loadFactor;
232 threshold = (int)Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
233 table = new Entry[capacity];
234 init();
235 }
236
237 /**
238 * Constructs an empty <tt>HashMap</tt> with the specified initial
239 * capacity and the default load factor (0.75).
240 *
241 * @param initialCapacity the initial capacity.
242 * @throws IllegalArgumentException if the initial capacity is negative.
243 */
244 public HashMap(int initialCapacity) {
245 this(initialCapacity, DEFAULT_LOAD_FACTOR);
246 }
247
248 /**
249 * Constructs an empty <tt>HashMap</tt> with the default initial capacity
250 * (16) and the default load factor (0.75).
251 */
252 public HashMap() {
253 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
254 }
255
256 /**
257 * Constructs a new <tt>HashMap</tt> with the same mappings as the
258 * specified <tt>Map</tt>. The <tt>HashMap</tt> is created with
259 * default load factor (0.75) and an initial capacity sufficient to
260 * hold the mappings in the specified <tt>Map</tt>.
261 *
262 * @param m the map whose mappings are to be placed in this map
263 * @throws NullPointerException if the specified map is null
264 */
265 public HashMap(Map<? extends K, ? extends V> m) {
266 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
267 DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);
268 putAllForCreate(m);
269 }
270
271 // internal utilities
272
273 /**
274 * Initialization hook for subclasses. This method is called
275 * in all constructors and pseudo-constructors (clone, readObject)
276 * after HashMap has been initialized but before any entries have
277 * been inserted. (In the absence of this method, readObject would
278 * require explicit knowledge of subclasses.)
279 */
280 void init() {
281 }
282
283 /**
284 * Retrieve object hash code and applies a supplemental hash function to the
285 * result hash, which defends against poor quality hash functions. This is
286 * critical because HashMap uses power-of-two length hash tables, that
287 * otherwise encounter collisions for hashCodes that do not differ
288 * in lower bits.
289 */
290 final int hash(Object k) {
291 if (k instanceof String) {
292 return ((String) k).hash32();
293 }
294 int h = hashSeed ^ k.hashCode();
295
296 // This function ensures that hashCodes that differ only by
297 // constant multiples at each bit position have a bounded
298 // number of collisions (approximately 8 at default load factor).
299 h ^= (h >>> 20) ^ (h >>> 12);
300 return h ^ (h >>> 7) ^ (h >>> 4);
301 }
302
303 /**
304 * Returns index for hash code h.
305 */
306 static int indexFor(int h, int length) {
307 return h & (length-1);
308 }
309
310 /**
311 * Returns the number of key-value mappings in this map.
312 *
313 * @return the number of key-value mappings in this map
314 */
315 public int size() {
316 return size;
317 }
318
319 /**
320 * Returns <tt>true</tt> if this map contains no key-value mappings.
321 *
322 * @return <tt>true</tt> if this map contains no key-value mappings
323 */
324 public boolean isEmpty() {
325 return size == 0;
326 }
327
328 /**
329 * Returns the value to which the specified key is mapped,
330 * or {@code null} if this map contains no mapping for the key.
331 *
332 * <p>More formally, if this map contains a mapping from a key
333 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
334 * key.equals(k))}, then this method returns {@code v}; otherwise
335 * it returns {@code null}. (There can be at most one such mapping.)
336 *
337 * <p>A return value of {@code null} does not <i>necessarily</i>
338 * indicate that the map contains no mapping for the key; it's also
339 * possible that the map explicitly maps the key to {@code null}.
340 * The {@link #containsKey containsKey} operation may be used to
341 * distinguish these two cases.
342 *
343 * @see #put(Object, Object)
344 */
345 @SuppressWarnings("unchecked")
346 public V get(Object key) {
347 Entry<K,V> entry = getEntry(key);
348
349 return null == entry ? null : entry.getValue();
350 }
351
352 /**
353 * Returns <tt>true</tt> if this map contains a mapping for the
354 * specified key.
355 *
356 * @param key The key whose presence in this map is to be tested
357 * @return <tt>true</tt> if this map contains a mapping for the specified
358 * key.
359 */
360 public boolean containsKey(Object key) {
361 return getEntry(key) != null;
362 }
363
364 /**
365 * Returns the entry associated with the specified key in the
366 * HashMap. Returns null if the HashMap contains no mapping
367 * for the key.
368 */
369 @SuppressWarnings("unchecked")
370 final Entry<K,V> getEntry(Object key) {
371 int hash = (key == null) ? 0 : hash(key);
372 for (Entry<?,?> e = table[indexFor(hash, table.length)];
373 e != null;
374 e = e.next) {
375 Object k;
376 if (e.hash == hash &&
377 ((k = e.key) == key || (key != null && key.equals(k))))
378 return (Entry<K,V>)e;
379 }
380 return null;
381 }
382
383
384 /**
385 * Associates the specified value with the specified key in this map.
386 * If the map previously contained a mapping for the key, the old
387 * value is replaced.
388 *
389 * @param key key with which the specified value is to be associated
390 * @param value value to be associated with the specified key
391 * @return the previous value associated with <tt>key</tt>, or
392 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
393 * (A <tt>null</tt> return can also indicate that the map
394 * previously associated <tt>null</tt> with <tt>key</tt>.)
395 */
396 public V put(K key, V value) {
397 if (key == null)
398 return putForNullKey(value);
399 int hash = hash(key);
400 int i = indexFor(hash, table.length);
401 @SuppressWarnings("unchecked")
402 Entry<K,V> e = (Entry<K,V>)table[i];
403 for(; e != null; e = e.next) {
404 Object k;
405 if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
406 V oldValue = e.value;
407 e.value = value;
408 e.recordAccess(this);
409 return oldValue;
410 }
411 }
412
413 modCount++;
414 addEntry(hash, key, value, i);
415 return null;
416 }
417
418 /**
419 * Offloaded version of put for null keys
420 */
421 private V putForNullKey(V value) {
422 @SuppressWarnings("unchecked")
423 Entry<K,V> e = (Entry<K,V>)table[0];
424 for(; e != null; e = e.next) {
425 if (e.key == null) {
426 V oldValue = e.value;
427 e.value = value;
428 e.recordAccess(this);
429 return oldValue;
430 }
431 }
432 modCount++;
433 addEntry(0, null, value, 0);
434 return null;
435 }
436
437 /**
438 * This method is used instead of put by constructors and
439 * pseudoconstructors (clone, readObject). It does not resize the table,
440 * check for comodification, etc. It calls createEntry rather than
441 * addEntry.
442 */
443 private void putForCreate(K key, V value) {
444 int hash = null == key ? 0 : hash(key);
445 int i = indexFor(hash, table.length);
446
447 /**
448 * Look for preexisting entry for key. This will never happen for
449 * clone or deserialize. It will only happen for construction if the
450 * input Map is a sorted map whose ordering is inconsistent w/ equals.
451 */
452 for (@SuppressWarnings("unchecked")
453 Entry<?,V> e = (Entry<?,V>)table[i]; e != null; e = e.next) {
454 Object k;
455 if (e.hash == hash &&
456 ((k = e.key) == key || (key != null && key.equals(k)))) {
457 e.value = value;
458 return;
459 }
460 }
461
462 createEntry(hash, key, value, i);
463 }
464
465 private void putAllForCreate(Map<? extends K, ? extends V> m) {
466 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
467 putForCreate(e.getKey(), e.getValue());
468 }
469
470 /**
471 * Rehashes the contents of this map into a new array with a
472 * larger capacity. This method is called automatically when the
473 * number of keys in this map reaches its threshold.
474 *
475 * If current capacity is MAXIMUM_CAPACITY, this method does not
476 * resize the map, but sets threshold to Integer.MAX_VALUE.
477 * This has the effect of preventing future calls.
478 *
479 * @param newCapacity the new capacity, MUST be a power of two;
480 * must be greater than current capacity unless current
481 * capacity is MAXIMUM_CAPACITY (in which case value
482 * is irrelevant).
483 */
484 void resize(int newCapacity) {
485 Entry<?,?>[] oldTable = table;
486 int oldCapacity = oldTable.length;
487 if (oldCapacity == MAXIMUM_CAPACITY) {
488 threshold = Integer.MAX_VALUE;
489 return;
490 }
491
492 Entry<?,?>[] newTable = new Entry<?,?>[newCapacity];
493 transfer(newTable);
494 table = newTable;
495 threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
496 }
497
498 /**
499 * Transfers all entries from current table to newTable.
500 */
501 @SuppressWarnings("unchecked")
502 void transfer(Entry<?,?>[] newTable) {
503 Entry<?,?>[] src = table;
504 int newCapacity = newTable.length;
505 for (int j = 0; j < src.length; j++ ) {
506 Entry<K,V> e = (Entry<K,V>) src[j];
507 while(null != e) {
508 Entry<K,V> next = e.next;
509 int i = indexFor(e.hash, newCapacity);
510 e.next = (Entry<K,V>) newTable[i];
511 newTable[i] = e;
512 e = next;
513 }
514 }
515 Arrays.fill(table, null);
516 }
517
518 /**
519 * Copies all of the mappings from the specified map to this map.
520 * These mappings will replace any mappings that this map had for
521 * any of the keys currently in the specified map.
522 *
523 * @param m mappings to be stored in this map
524 * @throws NullPointerException if the specified map is null
525 */
526 public void putAll(Map<? extends K, ? extends V> m) {
527 int numKeysToBeAdded = m.size();
528 if (numKeysToBeAdded == 0)
529 return;
530
531 /*
532 * Expand the map if the map if the number of mappings to be added
533 * is greater than or equal to threshold. This is conservative; the
534 * obvious condition is (m.size() + size) >= threshold, but this
535 * condition could result in a map with twice the appropriate capacity,
536 * if the keys to be added overlap with the keys already in this map.
537 * By using the conservative calculation, we subject ourself
538 * to at most one extra resize.
539 */
540 if (numKeysToBeAdded > threshold) {
541 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
542 if (targetCapacity > MAXIMUM_CAPACITY)
543 targetCapacity = MAXIMUM_CAPACITY;
544 int newCapacity = table.length;
545 while (newCapacity < targetCapacity)
546 newCapacity <<= 1;
547 if (newCapacity > table.length)
548 resize(newCapacity);
549 }
550
551 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
552 put(e.getKey(), e.getValue());
553 }
554
555 /**
556 * Removes the mapping for the specified key from this map if present.
557 *
558 * @param key key whose mapping is to be removed from the map
559 * @return the previous value associated with <tt>key</tt>, or
560 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
561 * (A <tt>null</tt> return can also indicate that the map
562 * previously associated <tt>null</tt> with <tt>key</tt>.)
563 */
564 public V remove(Object key) {
565 Entry<K,V> e = removeEntryForKey(key);
566 return (e == null ? null : e.value);
567 }
568
569 /**
570 * Removes and returns the entry associated with the specified key
571 * in the HashMap. Returns null if the HashMap contains no mapping
572 * for this key.
573 */
574 final Entry<K,V> removeEntryForKey(Object key) {
575 int hash = (key == null) ? 0 : hash(key);
576 int i = indexFor(hash, table.length);
577 @SuppressWarnings("unchecked")
578 Entry<K,V> prev = (Entry<K,V>)table[i];
579 Entry<K,V> e = prev;
580
581 while (e != null) {
582 Entry<K,V> next = e.next;
583 Object k;
584 if (e.hash == hash &&
585 ((k = e.key) == key || (key != null && key.equals(k)))) {
586 modCount++;
587 size--;
588 if (prev == e)
589 table[i] = next;
590 else
591 prev.next = next;
592 e.recordRemoval(this);
593 return e;
594 }
595 prev = e;
596 e = next;
597 }
598
599 return e;
600 }
601
602 /**
603 * Special version of remove for EntrySet using {@code Map.Entry.equals()}
604 * for matching.
605 */
606 final Entry<K,V> removeMapping(Object o) {
607 if (!(o instanceof Map.Entry))
608 return null;
609
610 Map.Entry<?,?> entry = (Map.Entry<?,?>) o;
611 Object key = entry.getKey();
612 int hash = (key == null) ? 0 : hash(key.hashCode());
613 int i = indexFor(hash, table.length);
614 @SuppressWarnings("unchecked")
615 Entry<K,V> prev = (Entry<K,V>)table[i];
616 Entry<K,V> e = prev;
617
618 while (e != null) {
619 Entry<K,V> next = e.next;
620 if (e.hash == hash && e.equals(entry)) {
621 modCount++;
622 size--;
623 if (prev == e)
624 table[i] = next;
625 else
626 prev.next = next;
627 e.recordRemoval(this);
628 return e;
629 }
630 prev = e;
631 e = next;
632 }
633
634 return e;
635 }
636
637 /**
638 * Removes all of the mappings from this map.
639 * The map will be empty after this call returns.
640 */
641 public void clear() {
642 modCount++;
643 Entry<?,?>[] tab = table;
644 for (int i = 0; i < tab.length; i++)
645 tab[i] = null;
646 size = 0;
647 }
648
649 /**
650 * Returns <tt>true</tt> if this map maps one or more keys to the
651 * specified value.
652 *
653 * @param value value whose presence in this map is to be tested
654 * @return <tt>true</tt> if this map maps one or more keys to the
655 * specified value
656 */
657 public boolean containsValue(Object value) {
658 if (value == null)
659 return containsNullValue();
660
661 Entry<?,?>[] tab = table;
662 for (int i = 0; i < tab.length ; i++)
663 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next)
664 if (value.equals(e.value))
665 return true;
666 return false;
667 }
668
669 /**
670 * Special-case code for containsValue with null argument
671 */
672 private boolean containsNullValue() {
673 Entry<?,?>[] tab = table;
674 for (int i = 0; i < tab.length ; i++)
675 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next)
676 if (e.value == null)
677 return true;
678 return false;
679 }
680
681 /**
682 * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and
683 * values themselves are not cloned.
684 *
685 * @return a shallow copy of this map
686 */
687 @SuppressWarnings("unchecked")
688 public Object clone() {
689 HashMap<K,V> result = null;
690 try {
691 result = (HashMap<K,V>)super.clone();
692 } catch (CloneNotSupportedException e) {
693 // assert false;
694 }
695 result.table = new Entry<?,?>[table.length];
696 result.entrySet = null;
697 result.modCount = 0;
698 result.size = 0;
699 result.init();
700 result.putAllForCreate(this);
701
702 return result;
703 }
704
705 static class Entry<K,V> implements Map.Entry<K,V> {
706 final K key;
707 V value;
708 Entry<K,V> next;
709 final int hash;
710
711 /**
712 * Creates new entry.
713 */
714 Entry(int h, K k, V v, Entry<K,V> n) {
715 value = v;
716 next = n;
717 key = k;
718 hash = h;
719 }
720
721 public final K getKey() {
722 return key;
723 }
724
725 public final V getValue() {
726 return value;
727 }
728
729 public final V setValue(V newValue) {
730 V oldValue = value;
731 value = newValue;
732 return oldValue;
733 }
734
735 public final boolean equals(Object o) {
736 if (!(o instanceof Map.Entry))
737 return false;
738 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
739 Object k1 = getKey();
740 Object k2 = e.getKey();
741 if (k1 == k2 || (k1 != null && k1.equals(k2))) {
742 Object v1 = getValue();
743 Object v2 = e.getValue();
744 if (v1 == v2 || (v1 != null && v1.equals(v2)))
745 return true;
746 }
747 return false;
748 }
749
750 public final int hashCode() {
751 return (key==null ? 0 : key.hashCode()) ^
752 (value==null ? 0 : value.hashCode());
753 }
754
755 public final String toString() {
756 return getKey() + "=" + getValue();
757 }
758
759 /**
760 * This method is invoked whenever the value in an entry is
761 * overwritten by an invocation of put(k,v) for a key k that's already
762 * in the HashMap.
763 */
764 void recordAccess(HashMap<K,V> m) {
765 }
766
767 /**
768 * This method is invoked whenever the entry is
769 * removed from the table.
770 */
771 void recordRemoval(HashMap<K,V> m) {
772 }
773 }
774
775 /**
776 * Adds a new entry with the specified key, value and hash code to
777 * the specified bucket. It is the responsibility of this
778 * method to resize the table if appropriate.
779 *
780 * Subclass overrides this to alter the behavior of put method.
781 */
782 void addEntry(int hash, K key, V value, int bucketIndex) {
783 if ((size >= threshold) && (null != table[bucketIndex])) {
784 resize(2 * table.length);
785 hash = (null != key) ? hash(key) : 0;
786 bucketIndex = indexFor(hash, table.length);
787 }
788
789 createEntry(hash, key, value, bucketIndex);
790 }
791
792 /**
793 * Like addEntry except that this version is used when creating entries
794 * as part of Map construction or "pseudo-construction" (cloning,
795 * deserialization). This version needn't worry about resizing the table.
796 *
797 * Subclass overrides this to alter the behavior of HashMap(Map),
798 * clone, and readObject.
799 */
800 void createEntry(int hash, K key, V value, int bucketIndex) {
801 @SuppressWarnings("unchecked")
802 Entry<K,V> e = (Entry<K,V>)table[bucketIndex];
803 table[bucketIndex] = new Entry<>(hash, key, value, e);
804 size++;
805 }
806
807 private abstract class HashIterator<E> implements Iterator<E> {
808 Entry<?,?> next; // next entry to return
809 int expectedModCount; // For fast-fail
810 int index; // current slot
811 Entry<?,?> current; // current entry
812
813 HashIterator() {
814 expectedModCount = modCount;
815 if (size > 0) { // advance to first entry
816 Entry<?,?>[] t = table;
817 while (index < t.length && (next = t[index++]) == null)
818 ;
819 }
820 }
821
822 public final boolean hasNext() {
823 return next != null;
824 }
825
826 @SuppressWarnings("unchecked")
827 final Entry<K,V> nextEntry() {
828 if (modCount != expectedModCount)
829 throw new ConcurrentModificationException();
830 Entry<?,?> e = next;
831 if (e == null)
832 throw new NoSuchElementException();
833
834 if ((next = e.next) == null) {
835 Entry<?,?>[] t = table;
836 while (index < t.length && (next = t[index++]) == null)
837 ;
838 }
839 current = e;
840 return (Entry<K,V>)e;
841 }
842
843 public void remove() {
844 if (current == null)
845 throw new IllegalStateException();
846 if (modCount != expectedModCount)
847 throw new ConcurrentModificationException();
848 Object k = current.key;
849 current = null;
850 HashMap.this.removeEntryForKey(k);
851 expectedModCount = modCount;
852 }
853 }
854
855 private final class ValueIterator extends HashIterator<V> {
856 public V next() {
857 return nextEntry().value;
858 }
859 }
860
861 private final class KeyIterator extends HashIterator<K> {
862 public K next() {
863 return nextEntry().getKey();
864 }
865 }
866
867 private final class EntryIterator extends HashIterator<Map.Entry<K,V>> {
868 public Map.Entry<K,V> next() {
869 return nextEntry();
870 }
871 }
872
873 // Subclass overrides these to alter behavior of views' iterator() method
874 Iterator<K> newKeyIterator() {
875 return new KeyIterator();
876 }
877 Iterator<V> newValueIterator() {
878 return new ValueIterator();
879 }
880 Iterator<Map.Entry<K,V>> newEntryIterator() {
881 return new EntryIterator();
882 }
883
884
885 // Views
886
887 private transient Set<Map.Entry<K,V>> entrySet = null;
888
889 /**
890 * Returns a {@link Set} view of the keys contained in this map.
891 * The set is backed by the map, so changes to the map are
892 * reflected in the set, and vice-versa. If the map is modified
893 * while an iteration over the set is in progress (except through
894 * the iterator's own <tt>remove</tt> operation), the results of
895 * the iteration are undefined. The set supports element removal,
896 * which removes the corresponding mapping from the map, via the
897 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
898 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
899 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
900 * operations.
901 */
902 public Set<K> keySet() {
903 Set<K> ks = keySet;
904 return (ks != null ? ks : (keySet = new KeySet()));
905 }
906
907 private final class KeySet extends AbstractSet<K> {
908 public Iterator<K> iterator() {
909 return newKeyIterator();
910 }
911 public int size() {
912 return size;
913 }
914 public boolean contains(Object o) {
915 return containsKey(o);
916 }
917 public boolean remove(Object o) {
918 return HashMap.this.removeEntryForKey(o) != null;
919 }
920 public void clear() {
921 HashMap.this.clear();
922 }
923 }
924
925 /**
926 * Returns a {@link Collection} view of the values contained in this map.
927 * The collection is backed by the map, so changes to the map are
928 * reflected in the collection, and vice-versa. If the map is
929 * modified while an iteration over the collection is in progress
930 * (except through the iterator's own <tt>remove</tt> operation),
931 * the results of the iteration are undefined. The collection
932 * supports element removal, which removes the corresponding
933 * mapping from the map, via the <tt>Iterator.remove</tt>,
934 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
935 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
936 * support the <tt>add</tt> or <tt>addAll</tt> operations.
937 */
938 public Collection<V> values() {
939 Collection<V> vs = values;
940 return (vs != null ? vs : (values = new Values()));
941 }
942
943 private final class Values extends AbstractCollection<V> {
944 public Iterator<V> iterator() {
945 return newValueIterator();
946 }
947 public int size() {
948 return size;
949 }
950 public boolean contains(Object o) {
951 return containsValue(o);
952 }
953 public void clear() {
954 HashMap.this.clear();
955 }
956 }
957
958 /**
959 * Returns a {@link Set} view of the mappings contained in this map.
960 * The set is backed by the map, so changes to the map are
961 * reflected in the set, and vice-versa. If the map is modified
962 * while an iteration over the set is in progress (except through
963 * the iterator's own <tt>remove</tt> operation, or through the
964 * <tt>setValue</tt> operation on a map entry returned by the
965 * iterator) the results of the iteration are undefined. The set
966 * supports element removal, which removes the corresponding
967 * mapping from the map, via the <tt>Iterator.remove</tt>,
968 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
969 * <tt>clear</tt> operations. It does not support the
970 * <tt>add</tt> or <tt>addAll</tt> operations.
971 *
972 * @return a set view of the mappings contained in this map
973 */
974 public Set<Map.Entry<K,V>> entrySet() {
975 return entrySet0();
976 }
977
978 private Set<Map.Entry<K,V>> entrySet0() {
979 Set<Map.Entry<K,V>> es = entrySet;
980 return es != null ? es : (entrySet = new EntrySet());
981 }
982
983 private final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
984 public Iterator<Map.Entry<K,V>> iterator() {
985 return newEntryIterator();
986 }
987 public boolean contains(Object o) {
988 if (!(o instanceof Map.Entry))
989 return false;
990 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
991 Entry<K,V> candidate = getEntry(e.getKey());
992 return candidate != null && candidate.equals(e);
993 }
994 public boolean remove(Object o) {
995 return removeMapping(o) != null;
996 }
997 public int size() {
998 return size;
999 }
1000 public void clear() {
1001 HashMap.this.clear();
1002 }
1003 }
1004
1005 /**
1006 * Save the state of the <tt>HashMap</tt> instance to a stream (i.e.,
1007 * serialize it).
1008 *
1009 * @serialData The <i>capacity</i> of the HashMap (the length of the
1010 * bucket array) is emitted (int), followed by the
1011 * <i>size</i> (an int, the number of key-value
1012 * mappings), followed by the key (Object) and value (Object)
1013 * for each key-value mapping. The key-value mappings are
1014 * emitted in no particular order.
1015 */
1016 private void writeObject(java.io.ObjectOutputStream s)
1017 throws IOException
1018 {
1019 Iterator<Map.Entry<K,V>> i =
1020 (size > 0) ? entrySet0().iterator() : null;
1021
1022 // Write out the threshold, loadfactor, and any hidden stuff
1023 s.defaultWriteObject();
1024
1025 // Write out number of buckets
1026 s.writeInt(table.length);
1027
1028 // Write out size (number of Mappings)
1029 s.writeInt(size);
1030
1031 // Write out keys and values (alternating)
1032 if (size > 0) {
1033 for(Map.Entry<K,V> e : entrySet0()) {
1034 s.writeObject(e.getKey());
1035 s.writeObject(e.getValue());
1036 }
1037 }
1038 }
1039
1040 private static final long serialVersionUID = 362498820763181265L;
1041
1042 /**
1043 * Reconstitute the {@code HashMap} instance from a stream (i.e.,
1044 * deserialize it).
1045 */
1046 private void readObject(java.io.ObjectInputStream s)
1047 throws IOException, ClassNotFoundException
1048 {
1049 // Read in the threshold (ignored), loadfactor, and any hidden stuff
1050 s.defaultReadObject();
1051 if (loadFactor <= 0 || Float.isNaN(loadFactor))
1052 throw new InvalidObjectException("Illegal load factor: " +
1053 loadFactor);
1054
1055 // set hashMask
1056 Holder.UNSAFE.putIntVolatile(this, Holder.HASHSEED_OFFSET,
1057 sun.misc.Hashing.randomHashSeed(this));
1058
1059 // Read in number of buckets and allocate the bucket array;
1060 s.readInt(); // ignored
1061
1062 // Read number of mappings
1063 int mappings = s.readInt();
1064 if (mappings < 0)
1065 throw new InvalidObjectException("Illegal mappings count: " +
1066 mappings);
1067
1068 int initialCapacity = (int) Math.min(
1069 // capacity chosen by number of mappings
1070 // and desired load (if >= 0.25)
1071 mappings * Math.min(1 / loadFactor, 4.0f),
1072 // we have limits...
1073 HashMap.MAXIMUM_CAPACITY);
1074 int capacity = 1;
1075 // find smallest power of two which holds all mappings
1076 while (capacity < initialCapacity) {
1077 capacity <<= 1;
1078 }
1079
1080 table = new Entry[capacity];
1081 threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
1082 init(); // Give subclass a chance to do its thing.
1083
1084
1085 // Read the keys and values, and put the mappings in the HashMap
1086 for (int i=0; i<mappings; i++) {
1087 @SuppressWarnings("unchecked")
1088 K key = (K) s.readObject();
1089 @SuppressWarnings("unchecked")
1090 V value = (V) s.readObject();
1091 putForCreate(key, value);
1092 }
1093 }
1094
1095 // These methods are used when serializing HashSets
1096 int capacity() { return table.length; }
1097 float loadFactor() { return loadFactor; }
1098 }