1 /*
2 * Copyright (c) 1997, 2013, 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 * An empty table instance to share when the table is not inflated.
148 */
149 static final Entry<?,?>[] EMPTY_TABLE = {};
150
151 /**
152 * The table, resized as necessary. Length MUST Always be a power of two.
153 */
154 transient Entry<?,?>[] table = EMPTY_TABLE;
155
156 /**
157 * The number of key-value mappings contained in this map.
158 */
159 transient int size;
160
161 /**
162 * The next size value at which to resize (capacity * load factor).
163 * @serial
164 */
165 int threshold;
166
167 /**
168 * The load factor for the hash table.
169 *
170 * @serial
171 */
172 final float loadFactor;
173
174 /**
175 * The number of times this HashMap has been structurally modified
176 * Structural modifications are those that change the number of mappings in
177 * the HashMap or otherwise modify its internal structure (e.g.,
178 * rehash). This field is used to make iterators on Collection-views of
179 * the HashMap fail-fast. (See ConcurrentModificationException).
180 */
181 transient int modCount;
182
183 private static class Holder {
184 /**
185 *
186 */
187 static final sun.misc.Unsafe UNSAFE;
188
189 /**
190 * Offset of "final" hashSeed field we must set in
191 * readObject() method.
192 */
193 static final long HASHSEED_OFFSET;
194
195 /**
196 * Offset of "final" initialCapacity field we must set in
197 * readObject() method.
198 */
199 static final long INITIAL_CAPACITY_OFFSET;
200
201 static {
202 try {
203 UNSAFE = sun.misc.Unsafe.getUnsafe();
204 HASHSEED_OFFSET = UNSAFE.objectFieldOffset(
205 HashMap.class.getDeclaredField("hashSeed"));
206 INITIAL_CAPACITY_OFFSET = UNSAFE.objectFieldOffset(
207 HashMap.class.getDeclaredField("initialCapacity"));
208 } catch (NoSuchFieldException | SecurityException e) {
209 throw new InternalError("Failed to record field offset", e);
210 }
211 }
212 }
213
214 /**
215 * A randomizing value associated with this instance that is applied to
216 * hash code of keys to make hash collisions harder to find.
217 */
218 transient final int hashSeed = sun.misc.Hashing.randomHashSeed(this);
219
220 /**
221 * The requested initial capacity increased to a power of two.
222 */
223 transient final int initialCapacity;
224
225 /**
226 * Constructs an empty <tt>HashMap</tt> with the specified initial
227 * capacity and load factor.
228 *
229 * @param initialCapacity the initial capacity
230 * @param loadFactor the load factor
231 * @throws IllegalArgumentException if the initial capacity is negative
232 * or the load factor is nonpositive
233 */
234 public HashMap(int initialCapacity, float loadFactor) {
235 if (initialCapacity < 0)
236 throw new IllegalArgumentException("Illegal initial capacity: " +
237 initialCapacity);
238 if (initialCapacity > MAXIMUM_CAPACITY)
239 initialCapacity = MAXIMUM_CAPACITY;
240 if (loadFactor <= 0 || Float.isNaN(loadFactor))
241 throw new IllegalArgumentException("Illegal load factor: " +
242 loadFactor);
243
244 // Find a power of 2 >= initialCapacity
245 int capacity = (capacity = Integer.highestOneBit(initialCapacity)) != 0
246 ? capacity
247 : 1;
248 capacity <<= (Integer.bitCount(initialCapacity) > 1) ? 1 : 0;
249
250 this.loadFactor = loadFactor;
251 threshold = 0;
252 this.initialCapacity = capacity;
253 init();
254 }
255
256 /**
257 * Constructs an empty <tt>HashMap</tt> with the specified initial
258 * capacity and the default load factor (0.75).
259 *
260 * @param initialCapacity the initial capacity.
261 * @throws IllegalArgumentException if the initial capacity is negative.
262 */
263 public HashMap(int initialCapacity) {
264 this(initialCapacity, DEFAULT_LOAD_FACTOR);
265 }
266
267 /**
268 * Constructs an empty <tt>HashMap</tt> with the default initial capacity
269 * (16) and the default load factor (0.75).
270 */
271 public HashMap() {
272 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
273 }
274
275 /**
276 * Constructs a new <tt>HashMap</tt> with the same mappings as the
277 * specified <tt>Map</tt>. The <tt>HashMap</tt> is created with
278 * default load factor (0.75) and an initial capacity sufficient to
279 * hold the mappings in the specified <tt>Map</tt>.
280 *
281 * @param m the map whose mappings are to be placed in this map
282 * @throws NullPointerException if the specified map is null
283 */
284 public HashMap(Map<? extends K, ? extends V> m) {
285 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
286 DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);
287 inflateTable();
288
289 putAllForCreate(m);
290 }
291
292 /**
293 * Inflate the table
294 */
295 final void inflateTable() {
296 threshold = (int)Math.min(initialCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
297 table = new Entry[initialCapacity];
298 }
299 // internal utilities
300
301 /**
302 * Initialization hook for subclasses. This method is called
303 * in all constructors and pseudo-constructors (clone, readObject)
304 * after HashMap has been initialized but before any entries have
305 * been inserted. (In the absence of this method, readObject would
306 * require explicit knowledge of subclasses.)
307 */
308 void init() {
309 }
310
311 /**
312 * Retrieve object hash code and applies a supplemental hash function to the
313 * result hash, which defends against poor quality hash functions. This is
314 * critical because HashMap uses power-of-two length hash tables, that
315 * otherwise encounter collisions for hashCodes that do not differ
316 * in lower bits.
317 */
318 final int hash(Object k) {
319 if (k instanceof String) {
320 return ((String) k).hash32();
321 }
322
323 int h = hashSeed ^ k.hashCode();
324
325 // This function ensures that hashCodes that differ only by
326 // constant multiples at each bit position have a bounded
327 // number of collisions (approximately 8 at default load factor).
328 h ^= (h >>> 20) ^ (h >>> 12);
329 return h ^ (h >>> 7) ^ (h >>> 4);
330 }
331
332 /**
333 * Returns index for hash code h.
334 */
335 static int indexFor(int h, int length) {
336 return h & (length-1);
337 }
338
339 /**
340 * Returns the number of key-value mappings in this map.
341 *
342 * @return the number of key-value mappings in this map
343 */
344 public int size() {
345 return size;
346 }
347
348 /**
349 * Returns <tt>true</tt> if this map contains no key-value mappings.
350 *
351 * @return <tt>true</tt> if this map contains no key-value mappings
352 */
353 public boolean isEmpty() {
354 return size == 0;
355 }
356
357 /**
358 * Returns the value to which the specified key is mapped,
359 * or {@code null} if this map contains no mapping for the key.
360 *
361 * <p>More formally, if this map contains a mapping from a key
362 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
363 * key.equals(k))}, then this method returns {@code v}; otherwise
364 * it returns {@code null}. (There can be at most one such mapping.)
365 *
366 * <p>A return value of {@code null} does not <i>necessarily</i>
367 * indicate that the map contains no mapping for the key; it's also
368 * possible that the map explicitly maps the key to {@code null}.
369 * The {@link #containsKey containsKey} operation may be used to
370 * distinguish these two cases.
371 *
372 * @see #put(Object, Object)
373 */
374 @SuppressWarnings("unchecked")
375 public V get(Object key) {
376 Entry<K,V> entry = getEntry(key);
377
378 return null == entry ? null : entry.getValue();
379 }
380
381 /**
382 * Returns <tt>true</tt> if this map contains a mapping for the
383 * specified key.
384 *
385 * @param key The key whose presence in this map is to be tested
386 * @return <tt>true</tt> if this map contains a mapping for the specified
387 * key.
388 */
389 public boolean containsKey(Object key) {
390 return getEntry(key) != null;
391 }
392
393 /**
394 * Returns the entry associated with the specified key in the
395 * HashMap. Returns null if the HashMap contains no mapping
396 * for the key.
397 */
398 @SuppressWarnings("unchecked")
399 final Entry<K,V> getEntry(Object key) {
400 if (isEmpty()) {
401 return null;
402 }
403
404 int hash = (key == null) ? 0 : hash(key);
405 for (Entry<?,?> e = table[indexFor(hash, table.length)];
406 e != null;
407 e = e.next) {
408 Object k;
409 if (e.hash == hash &&
410 ((k = e.key) == key || (key != null && key.equals(k))))
411 return (Entry<K,V>)e;
412 }
413 return null;
414 }
415
416 /**
417 * Associates the specified value with the specified key in this map.
418 * If the map previously contained a mapping for the key, the old
419 * value is replaced.
420 *
421 * @param key key with which the specified value is to be associated
422 * @param value value to be associated with the specified key
423 * @return the previous value associated with <tt>key</tt>, or
424 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
425 * (A <tt>null</tt> return can also indicate that the map
426 * previously associated <tt>null</tt> with <tt>key</tt>.)
427 */
428 public V put(K key, V value) {
429 if (table == EMPTY_TABLE) {
430 inflateTable();
431 }
432 if (key == null)
433 return putForNullKey(value);
434 int hash = hash(key);
435 int i = indexFor(hash, table.length);
436 @SuppressWarnings("unchecked")
437 Entry<K,V> e = (Entry<K,V>)table[i];
438 for(; e != null; e = e.next) {
439 Object k;
440 if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
441 V oldValue = e.value;
442 e.value = value;
443 e.recordAccess(this);
444 return oldValue;
445 }
446 }
447
448 modCount++;
449 addEntry(hash, key, value, i);
450 return null;
451 }
452
453 /**
454 * Offloaded version of put for null keys
455 */
456 private V putForNullKey(V value) {
457 @SuppressWarnings("unchecked")
458 Entry<K,V> e = (Entry<K,V>)table[0];
459 for(; e != null; e = e.next) {
460 if (e.key == null) {
461 V oldValue = e.value;
462 e.value = value;
463 e.recordAccess(this);
464 return oldValue;
465 }
466 }
467 modCount++;
468 addEntry(0, null, value, 0);
469 return null;
470 }
471
472 /**
473 * This method is used instead of put by constructors and
474 * pseudoconstructors (clone, readObject). It does not resize the table,
475 * check for comodification, etc. It calls createEntry rather than
476 * addEntry.
477 */
478 private void putForCreate(K key, V value) {
479 int hash = null == key ? 0 : hash(key);
480 int i = indexFor(hash, table.length);
481
482 /**
483 * Look for preexisting entry for key. This will never happen for
484 * clone or deserialize. It will only happen for construction if the
485 * input Map is a sorted map whose ordering is inconsistent w/ equals.
486 */
487 for (@SuppressWarnings("unchecked")
488 Entry<?,V> e = (Entry<?,V>)table[i]; e != null; e = e.next) {
489 Object k;
490 if (e.hash == hash &&
491 ((k = e.key) == key || (key != null && key.equals(k)))) {
492 e.value = value;
493 return;
494 }
495 }
496
497 createEntry(hash, key, value, i);
498 }
499
500 private void putAllForCreate(Map<? extends K, ? extends V> m) {
501 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
502 putForCreate(e.getKey(), e.getValue());
503 }
504
505 /**
506 * Rehashes the contents of this map into a new array with a
507 * larger capacity. This method is called automatically when the
508 * number of keys in this map reaches its threshold.
509 *
510 * If current capacity is MAXIMUM_CAPACITY, this method does not
511 * resize the map, but sets threshold to Integer.MAX_VALUE.
512 * This has the effect of preventing future calls.
513 *
514 * @param newCapacity the new capacity, MUST be a power of two;
515 * must be greater than current capacity unless current
516 * capacity is MAXIMUM_CAPACITY (in which case value
517 * is irrelevant).
518 */
519 void resize(int newCapacity) {
520 Entry<?,?>[] oldTable = table;
521 int oldCapacity = oldTable.length;
522 if (oldCapacity == MAXIMUM_CAPACITY) {
523 threshold = Integer.MAX_VALUE;
524 return;
525 }
526
527 Entry<?,?>[] newTable = new Entry<?,?>[newCapacity];
528 transfer(newTable);
529 table = newTable;
530 threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
531 }
532
533 /**
534 * Transfers all entries from current table to newTable.
535 */
536 @SuppressWarnings("unchecked")
537 void transfer(Entry<?,?>[] newTable) {
538 Entry<?,?>[] src = table;
539 int newCapacity = newTable.length;
540 for (int j = 0; j < src.length; j++ ) {
541 Entry<K,V> e = (Entry<K,V>) src[j];
542 while(null != e) {
543 Entry<K,V> next = e.next;
544 int i = indexFor(e.hash, newCapacity);
545 e.next = (Entry<K,V>) newTable[i];
546 newTable[i] = e;
547 e = next;
548 }
549 }
550 Arrays.fill(table, null);
551 }
552
553 /**
554 * Copies all of the mappings from the specified map to this map.
555 * These mappings will replace any mappings that this map had for
556 * any of the keys currently in the specified map.
557 *
558 * @param m mappings to be stored in this map
559 * @throws NullPointerException if the specified map is null
560 */
561 public void putAll(Map<? extends K, ? extends V> m) {
562 int numKeysToBeAdded = m.size();
563 if (numKeysToBeAdded == 0)
564 return;
565
566 if (table == EMPTY_TABLE) {
567 inflateTable();
568 }
569
570 /*
571 * Expand the map if the map if the number of mappings to be added
572 * is greater than or equal to threshold. This is conservative; the
573 * obvious condition is (m.size() + size) >= threshold, but this
574 * condition could result in a map with twice the appropriate capacity,
575 * if the keys to be added overlap with the keys already in this map.
576 * By using the conservative calculation, we subject ourself
577 * to at most one extra resize.
578 */
579 if (numKeysToBeAdded > threshold) {
580 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
581 if (targetCapacity > MAXIMUM_CAPACITY)
582 targetCapacity = MAXIMUM_CAPACITY;
583 int newCapacity = table.length;
584 while (newCapacity < targetCapacity)
585 newCapacity <<= 1;
586 if (newCapacity > table.length)
587 resize(newCapacity);
588 }
589
590 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
591 put(e.getKey(), e.getValue());
592 }
593
594 /**
595 * Removes the mapping for the specified key from this map if present.
596 *
597 * @param key key whose mapping is to be removed from the map
598 * @return the previous value associated with <tt>key</tt>, or
599 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
600 * (A <tt>null</tt> return can also indicate that the map
601 * previously associated <tt>null</tt> with <tt>key</tt>.)
602 */
603 public V remove(Object key) {
604 if(isEmpty()) {
605 return null;
606 }
607 Entry<K,V> e = removeEntryForKey(key);
608 return (e == null ? null : e.value);
609 }
610
611 /**
612 * Removes and returns the entry associated with the specified key
613 * in the HashMap. Returns null if the HashMap contains no mapping
614 * for this key.
615 */
616 final Entry<K,V> removeEntryForKey(Object key) {
617 int hash = (key == null) ? 0 : hash(key);
618 int i = indexFor(hash, table.length);
619 @SuppressWarnings("unchecked")
620 Entry<K,V> prev = (Entry<K,V>)table[i];
621 Entry<K,V> e = prev;
622
623 while (e != null) {
624 Entry<K,V> next = e.next;
625 Object k;
626 if (e.hash == hash &&
627 ((k = e.key) == key || (key != null && key.equals(k)))) {
628 modCount++;
629 size--;
630 if (prev == e)
631 table[i] = next;
632 else
633 prev.next = next;
634 e.recordRemoval(this);
635 return e;
636 }
637 prev = e;
638 e = next;
639 }
640
641 return e;
642 }
643
644 /**
645 * Special version of remove for EntrySet using {@code Map.Entry.equals()}
646 * for matching.
647 */
648 final Entry<K,V> removeMapping(Object o) {
649 if (!(o instanceof Map.Entry))
650 return null;
651 if(isEmpty()) {
652 return null;
653 }
654
655 Map.Entry<?,?> entry = (Map.Entry<?,?>) o;
656 Object key = entry.getKey();
657 int hash = (key == null) ? 0 : hash(key);
658 int i = indexFor(hash, table.length);
659 @SuppressWarnings("unchecked")
660 Entry<K,V> prev = (Entry<K,V>)table[i];
661 Entry<K,V> e = prev;
662
663 while (e != null) {
664 Entry<K,V> next = e.next;
665 if (e.hash == hash && e.equals(entry)) {
666 modCount++;
667 size--;
668 if (prev == e)
669 table[i] = next;
670 else
671 prev.next = next;
672 e.recordRemoval(this);
673 return e;
674 }
675 prev = e;
676 e = next;
677 }
678
679 return e;
680 }
681
682 /**
683 * Removes all of the mappings from this map.
684 * The map will be empty after this call returns.
685 */
686 public void clear() {
687 modCount++;
688 Arrays.fill(table, null);
689 size = 0;
690 }
691
692 /**
693 * Returns <tt>true</tt> if this map maps one or more keys to the
694 * specified value.
695 *
696 * @param value value whose presence in this map is to be tested
697 * @return <tt>true</tt> if this map maps one or more keys to the
698 * specified value
699 */
700 public boolean containsValue(Object value) {
701 if(isEmpty()) {
702 return false;
703 }
704
705 if (value == null)
706 return containsNullValue();
707
708 Entry<?,?>[] tab = table;
709 for (int i = 0; i < tab.length ; i++)
710 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next)
711 if (value.equals(e.value))
712 return true;
713 return false;
714 }
715
716 /**
717 * Special-case code for containsValue with null argument
718 */
719 private boolean containsNullValue() {
720 Entry<?,?>[] tab = table;
721 for (int i = 0; i < tab.length ; i++)
722 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next)
723 if (e.value == null)
724 return true;
725 return false;
726 }
727
728 /**
729 * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and
730 * values themselves are not cloned.
731 *
732 * @return a shallow copy of this map
733 */
734 @SuppressWarnings("unchecked")
735 public Object clone() {
736 HashMap<K,V> result = null;
737 try {
738 result = (HashMap<K,V>)super.clone();
739 } catch (CloneNotSupportedException e) {
740 // assert false;
741 }
742 result.table = (table == EMPTY_TABLE)
743 ? EMPTY_TABLE
744 : new Entry<?,?>[table.length];
745 result.entrySet = null;
746 result.modCount = 0;
747 result.size = 0;
748 result.init();
749 result.putAllForCreate(this);
750
751 return result;
752 }
753
754 static class Entry<K,V> implements Map.Entry<K,V> {
755 final K key;
756 V value;
757 Entry<K,V> next;
758 final int hash;
759
760 /**
761 * Creates new entry.
762 */
763 Entry(int h, K k, V v, Entry<K,V> n) {
764 value = v;
765 next = n;
766 key = k;
767 hash = h;
768 }
769
770 public final K getKey() {
771 return key;
772 }
773
774 public final V getValue() {
775 return value;
776 }
777
778 public final V setValue(V newValue) {
779 V oldValue = value;
780 value = newValue;
781 return oldValue;
782 }
783
784 public final boolean equals(Object o) {
785 if (!(o instanceof Map.Entry))
786 return false;
787 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
788 Object k1 = getKey();
789 Object k2 = e.getKey();
790 if (k1 == k2 || (k1 != null && k1.equals(k2))) {
791 Object v1 = getValue();
792 Object v2 = e.getValue();
793 if (v1 == v2 || (v1 != null && v1.equals(v2)))
794 return true;
795 }
796 return false;
797 }
798
799 public final int hashCode() {
800 return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
801 }
802
803 public final String toString() {
804 return getKey() + "=" + getValue();
805 }
806
807 /**
808 * This method is invoked whenever the value in an entry is
809 * overwritten by an invocation of put(k,v) for a key k that's already
810 * in the HashMap.
811 */
812 void recordAccess(HashMap<K,V> m) {
813 }
814
815 /**
816 * This method is invoked whenever the entry is
817 * removed from the table.
818 */
819 void recordRemoval(HashMap<K,V> m) {
820 }
821 }
822
823 /**
824 * Adds a new entry with the specified key, value and hash code to
825 * the specified bucket. It is the responsibility of this
826 * method to resize the table if appropriate.
827 *
828 * Subclass overrides this to alter the behavior of put method.
829 */
830 void addEntry(int hash, K key, V value, int bucketIndex) {
831 if ((size >= threshold) && (null != table[bucketIndex])) {
832 resize(2 * table.length);
833 hash = (null != key) ? hash(key) : 0;
834 bucketIndex = indexFor(hash, table.length);
835 }
836
837 createEntry(hash, key, value, bucketIndex);
838 }
839
840 /**
841 * Like addEntry except that this version is used when creating entries
842 * as part of Map construction or "pseudo-construction" (cloning,
843 * deserialization). This version needn't worry about resizing the table.
844 *
845 * Subclass overrides this to alter the behavior of HashMap(Map),
846 * clone, and readObject.
847 */
848 void createEntry(int hash, K key, V value, int bucketIndex) {
849 @SuppressWarnings("unchecked")
850 Entry<K,V> e = (Entry<K,V>)table[bucketIndex];
851 table[bucketIndex] = new Entry<>(hash, key, value, e);
852 size++;
853 }
854
855 private abstract class HashIterator<E> implements Iterator<E> {
856 Entry<?,?> next; // next entry to return
857 int expectedModCount; // For fast-fail
858 int index; // current slot
859 Entry<?,?> current; // current entry
860
861 HashIterator() {
862 expectedModCount = modCount;
863 if (size > 0) { // advance to first entry
864 Entry<?,?>[] t = table;
865 while (index < t.length && (next = t[index++]) == null)
866 ;
867 }
868 }
869
870 public final boolean hasNext() {
871 return next != null;
872 }
873
874 @SuppressWarnings("unchecked")
875 final Entry<K,V> nextEntry() {
876 if (modCount != expectedModCount)
877 throw new ConcurrentModificationException();
878 Entry<?,?> e = next;
879 if (e == null)
880 throw new NoSuchElementException();
881
882 if ((next = e.next) == null) {
883 Entry<?,?>[] t = table;
884 while (index < t.length && (next = t[index++]) == null)
885 ;
886 }
887 current = e;
888 return (Entry<K,V>)e;
889 }
890
891 public void remove() {
892 if (current == null)
893 throw new IllegalStateException();
894 if (modCount != expectedModCount)
895 throw new ConcurrentModificationException();
896 Object k = current.key;
897 current = null;
898 HashMap.this.removeEntryForKey(k);
899 expectedModCount = modCount;
900 }
901 }
902
903 private final class ValueIterator extends HashIterator<V> {
904 public V next() {
905 return nextEntry().value;
906 }
907 }
908
909 private final class KeyIterator extends HashIterator<K> {
910 public K next() {
911 return nextEntry().getKey();
912 }
913 }
914
915 private final class EntryIterator extends HashIterator<Map.Entry<K,V>> {
916 public Map.Entry<K,V> next() {
917 return nextEntry();
918 }
919 }
920
921 // Subclass overrides these to alter behavior of views' iterator() method
922 Iterator<K> newKeyIterator() {
923 return new KeyIterator();
924 }
925 Iterator<V> newValueIterator() {
926 return new ValueIterator();
927 }
928 Iterator<Map.Entry<K,V>> newEntryIterator() {
929 return new EntryIterator();
930 }
931
932
933 // Views
934
935 private transient Set<Map.Entry<K,V>> entrySet = null;
936
937 /**
938 * Returns a {@link Set} view of the keys contained in this map.
939 * The set is backed by the map, so changes to the map are
940 * reflected in the set, and vice-versa. If the map is modified
941 * while an iteration over the set is in progress (except through
942 * the iterator's own <tt>remove</tt> operation), the results of
943 * the iteration are undefined. The set supports element removal,
944 * which removes the corresponding mapping from the map, via the
945 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
946 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
947 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
948 * operations.
949 */
950 public Set<K> keySet() {
951 Set<K> ks = keySet;
952 return (ks != null ? ks : (keySet = new KeySet()));
953 }
954
955 private final class KeySet extends AbstractSet<K> {
956 public Iterator<K> iterator() {
957 return newKeyIterator();
958 }
959 public int size() {
960 return size;
961 }
962 public boolean contains(Object o) {
963 return containsKey(o);
964 }
965 public boolean remove(Object o) {
966 return HashMap.this.removeEntryForKey(o) != null;
967 }
968 public void clear() {
969 HashMap.this.clear();
970 }
971 }
972
973 /**
974 * Returns a {@link Collection} view of the values contained in this map.
975 * The collection is backed by the map, so changes to the map are
976 * reflected in the collection, and vice-versa. If the map is
977 * modified while an iteration over the collection is in progress
978 * (except through the iterator's own <tt>remove</tt> operation),
979 * the results of the iteration are undefined. The collection
980 * supports element removal, which removes the corresponding
981 * mapping from the map, via the <tt>Iterator.remove</tt>,
982 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
983 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
984 * support the <tt>add</tt> or <tt>addAll</tt> operations.
985 */
986 public Collection<V> values() {
987 Collection<V> vs = values;
988 return (vs != null ? vs : (values = new Values()));
989 }
990
991 private final class Values extends AbstractCollection<V> {
992 public Iterator<V> iterator() {
993 return newValueIterator();
994 }
995 public int size() {
996 return size;
997 }
998 public boolean contains(Object o) {
999 return containsValue(o);
1000 }
1001 public void clear() {
1002 HashMap.this.clear();
1003 }
1004 }
1005
1006 /**
1007 * Returns a {@link Set} view of the mappings contained in this map.
1008 * The set is backed by the map, so changes to the map are
1009 * reflected in the set, and vice-versa. If the map is modified
1010 * while an iteration over the set is in progress (except through
1011 * the iterator's own <tt>remove</tt> operation, or through the
1012 * <tt>setValue</tt> operation on a map entry returned by the
1013 * iterator) the results of the iteration are undefined. The set
1014 * supports element removal, which removes the corresponding
1015 * mapping from the map, via the <tt>Iterator.remove</tt>,
1016 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
1017 * <tt>clear</tt> operations. It does not support the
1018 * <tt>add</tt> or <tt>addAll</tt> operations.
1019 *
1020 * @return a set view of the mappings contained in this map
1021 */
1022 public Set<Map.Entry<K,V>> entrySet() {
1023 return entrySet0();
1024 }
1025
1026 private Set<Map.Entry<K,V>> entrySet0() {
1027 Set<Map.Entry<K,V>> es = entrySet;
1028 return es != null ? es : (entrySet = new EntrySet());
1029 }
1030
1031 private final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
1032 public Iterator<Map.Entry<K,V>> iterator() {
1033 return newEntryIterator();
1034 }
1035 public boolean contains(Object o) {
1036 if (!(o instanceof Map.Entry))
1037 return false;
1038 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
1039 Entry<K,V> candidate = getEntry(e.getKey());
1040 return candidate != null && candidate.equals(e);
1041 }
1042 public boolean remove(Object o) {
1043 return removeMapping(o) != null;
1044 }
1045 public int size() {
1046 return size;
1047 }
1048 public void clear() {
1049 HashMap.this.clear();
1050 }
1051 }
1052
1053 /**
1054 * Save the state of the <tt>HashMap</tt> instance to a stream (i.e.,
1055 * serialize it).
1056 *
1057 * @serialData The <i>capacity</i> of the HashMap (the length of the
1058 * bucket array) is emitted (int), followed by the
1059 * <i>size</i> (an int, the number of key-value
1060 * mappings), followed by the key (Object) and value (Object)
1061 * for each key-value mapping. The key-value mappings are
1062 * emitted in no particular order.
1063 */
1064 private void writeObject(java.io.ObjectOutputStream s)
1065 throws IOException
1066 {
1067 // Write out the threshold, loadfactor, and any hidden stuff
1068 s.defaultWriteObject();
1069
1070 // Write out number of buckets
1071 if (table==EMPTY_TABLE)
1072 s.writeInt(initialCapacity); // power of 2.
1073 else
1074 s.writeInt(table.length);
1075
1076 // Write out size (number of Mappings)
1077 s.writeInt(size);
1078
1079 // Write out keys and values (alternating)
1080 if (size > 0) {
1081 for(Map.Entry<K,V> e : entrySet0()) {
1082 s.writeObject(e.getKey());
1083 s.writeObject(e.getValue());
1084 }
1085 }
1086 }
1087
1088 private static final long serialVersionUID = 362498820763181265L;
1089
1090 /**
1091 * Reconstitute the {@code HashMap} instance from a stream (i.e.,
1092 * deserialize it).
1093 */
1094 private void readObject(java.io.ObjectInputStream s)
1095 throws IOException, ClassNotFoundException
1096 {
1097 // Read in the threshold (ignored), loadfactor, and any hidden stuff
1098 s.defaultReadObject();
1099 if (loadFactor <= 0 || Float.isNaN(loadFactor))
1100 throw new InvalidObjectException("Illegal load factor: " +
1101 loadFactor);
1102
1103 // set hashMask
1104 Holder.UNSAFE.putIntVolatile(this, Holder.HASHSEED_OFFSET,
1105 sun.misc.Hashing.randomHashSeed(this));
1106
1107 // Read in number of buckets and allocate the bucket array;
1108 s.readInt(); // ignored
1109
1110 // Read number of mappings
1111 int mappings = s.readInt();
1112 if (mappings < 0)
1113 throw new InvalidObjectException("Illegal mappings count: " +
1114 mappings);
1115
1116 int mappingsCapacity = Math.max((int) Math.min(
1117 // capacity chosen by number of mappings
1118 // and desired load (if >= 0.25)
1119 mappings * Math.min(1 / loadFactor, 4.0f),
1120 // we have limits...
1121 HashMap.MAXIMUM_CAPACITY), 0);
1122 // Find a power of 2 >= mappingCapacity
1123 int capacity = (capacity = Integer.highestOneBit(mappingsCapacity)) != 0
1124 ? capacity
1125 : 1;
1126 capacity <<= (Integer.bitCount(mappingsCapacity) > 1) ? 1 : 0;
1127 Holder.UNSAFE.putIntVolatile(this, Holder.INITIAL_CAPACITY_OFFSET,
1128 capacity);
1129
1130 if(mappings > 0) {
1131 inflateTable();
1132 } else {
1133 table = EMPTY_TABLE;
1134 threshold = 0;
1135 }
1136
1137 init(); // Give subclass a chance to do its thing.
1138
1139 // Read the keys and values, and put the mappings in the HashMap
1140 for (int i=0; i<mappings; i++) {
1141 @SuppressWarnings("unchecked")
1142 K key = (K) s.readObject();
1143 @SuppressWarnings("unchecked")
1144 V value = (V) s.readObject();
1145 putForCreate(key, value);
1146 }
1147 }
1148
1149 // These methods are used when serializing HashSets
1150 int capacity() { return table.length; }
1151 float loadFactor() { return loadFactor; }
1152 }