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