1 /*
2 * Copyright (c) 1997, 2012, 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 = 1 << 4; // aka 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 // If table == EMPTY_TABLE then this is the initial capacity at which the
166 // table will be created when inflated.
167 int threshold;
168
169 /**
170 * The load factor for the hash table.
171 *
172 * @serial
173 */
174 final float loadFactor;
175
176 /**
177 * The number of times this HashMap has been structurally modified
178 * Structural modifications are those that change the number of mappings in
179 * the HashMap or otherwise modify its internal structure (e.g.,
180 * rehash). This field is used to make iterators on Collection-views of
181 * the HashMap fail-fast. (See ConcurrentModificationException).
182 */
183 transient int modCount;
184
185 private static class Holder {
186 /**
187 *
188 */
189 static final sun.misc.Unsafe UNSAFE;
190
191 /**
192 * Offset of "final" hashSeed field we must set in
193 * readObject() method.
194 */
195 static final long HASHSEED_OFFSET;
196
197 static {
198 try {
199 UNSAFE = sun.misc.Unsafe.getUnsafe();
200 HASHSEED_OFFSET = UNSAFE.objectFieldOffset(
201 HashMap.class.getDeclaredField("hashSeed"));
202 } catch (NoSuchFieldException | SecurityException e) {
203 throw new InternalError("Failed to record hashSeed offset", e);
204 }
205 }
206 }
207
208 /**
209 * A randomizing value associated with this instance that is applied to
210 * hash code of keys to make hash collisions harder to find.
211 */
212 transient final int hashSeed = sun.misc.Hashing.randomHashSeed(this);
213
214 /**
215 * Constructs an empty <tt>HashMap</tt> with the specified initial
216 * capacity and load factor.
217 *
218 * @param initialCapacity the initial capacity
219 * @param loadFactor the load factor
220 * @throws IllegalArgumentException if the initial capacity is negative
221 * or the load factor is nonpositive
222 */
223 public HashMap(int initialCapacity, float loadFactor) {
224 if (initialCapacity < 0)
225 throw new IllegalArgumentException("Illegal initial capacity: " +
226 initialCapacity);
227 if (initialCapacity > MAXIMUM_CAPACITY)
228 initialCapacity = MAXIMUM_CAPACITY;
229 if (loadFactor <= 0 || Float.isNaN(loadFactor))
230 throw new IllegalArgumentException("Illegal load factor: " +
231 loadFactor);
232
233 this.loadFactor = loadFactor;
234 threshold = initialCapacity;
235 init();
236 }
237
238 /**
239 * Constructs an empty <tt>HashMap</tt> with the specified initial
240 * capacity and the default load factor (0.75).
241 *
242 * @param initialCapacity the initial capacity.
243 * @throws IllegalArgumentException if the initial capacity is negative.
244 */
245 public HashMap(int initialCapacity) {
246 this(initialCapacity, DEFAULT_LOAD_FACTOR);
247 }
248
249 /**
250 * Constructs an empty <tt>HashMap</tt> with the default initial capacity
251 * (16) and the default load factor (0.75).
252 */
253 public HashMap() {
254 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
255 }
256
257 /**
258 * Constructs a new <tt>HashMap</tt> with the same mappings as the
259 * specified <tt>Map</tt>. The <tt>HashMap</tt> is created with
260 * default load factor (0.75) and an initial capacity sufficient to
261 * hold the mappings in the specified <tt>Map</tt>.
262 *
263 * @param m the map whose mappings are to be placed in this map
264 * @throws NullPointerException if the specified map is null
265 */
266 public HashMap(Map<? extends K, ? extends V> m) {
267 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
268 DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);
269 inflateTable(threshold);
270
271 putAllForCreate(m);
272 }
273
274 private static int roundUpToPowerOf2(int number) {
275 // assert number >= 0 : "number must be non-negative";
276 int rounded = number >= MAXIMUM_CAPACITY
277 ? MAXIMUM_CAPACITY
278 : (rounded = Integer.highestOneBit(number)) != 0
279 ? (Integer.bitCount(number) > 1) ? rounded << 1 : rounded
280 : 1;
281
282 return rounded;
283 }
284
285 /**
286 * Inflates the table.
287 */
288 private void inflateTable(int toSize) {
289 // Find a power of 2 >= toSize
290 int capacity = roundUpToPowerOf2(toSize);
291
292 threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
293 table = new Entry[capacity];
294 }
295
296 // internal utilities
297
298 /**
299 * Initialization hook for subclasses. This method is called
300 * in all constructors and pseudo-constructors (clone, readObject)
301 * after HashMap has been initialized but before any entries have
302 * been inserted. (In the absence of this method, readObject would
303 * require explicit knowledge of subclasses.)
304 */
305 void init() {
306 }
307
308 /**
309 * Retrieve object hash code and applies a supplemental hash function to the
310 * result hash, which defends against poor quality hash functions. This is
311 * critical because HashMap uses power-of-two length hash tables, that
312 * otherwise encounter collisions for hashCodes that do not differ
313 * in lower bits.
314 */
315 final int hash(Object k) {
316 if (k instanceof String) {
317 return ((String) k).hash32();
318 }
319
320 int h = hashSeed ^ k.hashCode();
321
322 // This function ensures that hashCodes that differ only by
323 // constant multiples at each bit position have a bounded
324 // number of collisions (approximately 8 at default load factor).
325 h ^= (h >>> 20) ^ (h >>> 12);
326 return h ^ (h >>> 7) ^ (h >>> 4);
327 }
328
329 /**
330 * Returns index for hash code h.
331 */
332 static int indexFor(int h, int length) {
333 // assert Integer.bitCount(length) == 1 : "length must be a non-zero power of 2";
334 return h & (length-1);
335 }
336
337 /**
338 * Returns the number of key-value mappings in this map.
339 *
340 * @return the number of key-value mappings in this map
341 */
342 public int size() {
343 return size;
344 }
345
346 /**
347 * Returns <tt>true</tt> if this map contains no key-value mappings.
348 *
349 * @return <tt>true</tt> if this map contains no key-value mappings
350 */
351 public boolean isEmpty() {
352 return size == 0;
353 }
354
355 /**
356 * Returns the value to which the specified key is mapped,
357 * or {@code null} if this map contains no mapping for the key.
358 *
359 * <p>More formally, if this map contains a mapping from a key
360 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
361 * key.equals(k))}, then this method returns {@code v}; otherwise
362 * it returns {@code null}. (There can be at most one such mapping.)
363 *
364 * <p>A return value of {@code null} does not <i>necessarily</i>
365 * indicate that the map contains no mapping for the key; it's also
366 * possible that the map explicitly maps the key to {@code null}.
367 * The {@link #containsKey containsKey} operation may be used to
368 * distinguish these two cases.
369 *
370 * @see #put(Object, Object)
371 */
372 @SuppressWarnings("unchecked")
373 public V get(Object key) {
374 Entry<K,V> entry = getEntry(key);
375
376 return null == entry ? null : entry.getValue();
377 }
378
379 /**
380 * Returns <tt>true</tt> if this map contains a mapping for the
381 * specified key.
382 *
383 * @param key The key whose presence in this map is to be tested
384 * @return <tt>true</tt> if this map contains a mapping for the specified
385 * key.
386 */
387 public boolean containsKey(Object key) {
388 return getEntry(key) != null;
389 }
390
391 /**
392 * Returns the entry associated with the specified key in the
393 * HashMap. Returns null if the HashMap contains no mapping
394 * for the key.
395 */
396 @SuppressWarnings("unchecked")
397 final Entry<K,V> getEntry(Object key) {
398 if (isEmpty()) {
399 return null;
400 }
401
402 int hash = (key == null) ? 0 : hash(key);
403 for (Entry<?,?> e = table[indexFor(hash, table.length)];
404 e != null;
405 e = e.next) {
406 Object k;
407 if (e.hash == hash &&
408 ((k = e.key) == key || (key != null && key.equals(k))))
409 return (Entry<K,V>)e;
410 }
411 return null;
412 }
413
414 /**
415 * Associates the specified value with the specified key in this map.
416 * If the map previously contained a mapping for the key, the old
417 * value is replaced.
418 *
419 * @param key key with which the specified value is to be associated
420 * @param value value to be associated with the specified key
421 * @return the previous value associated with <tt>key</tt>, or
422 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
423 * (A <tt>null</tt> return can also indicate that the map
424 * previously associated <tt>null</tt> with <tt>key</tt>.)
425 */
426 public V put(K key, V value) {
427 if (table == EMPTY_TABLE) {
428 inflateTable(threshold);
429 }
430 if (key == null)
431 return putForNullKey(value);
432 int hash = hash(key);
433 int i = indexFor(hash, table.length);
434 @SuppressWarnings("unchecked")
435 Entry<K,V> e = (Entry<K,V>)table[i];
436 for(; e != null; e = e.next) {
437 Object k;
438 if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
439 V oldValue = e.value;
440 e.value = value;
441 e.recordAccess(this);
442 return oldValue;
443 }
444 }
445
446 modCount++;
447 addEntry(hash, key, value, i);
448 return null;
449 }
450
451 /**
452 * Offloaded version of put for null keys
453 */
454 private V putForNullKey(V value) {
455 @SuppressWarnings("unchecked")
456 Entry<K,V> e = (Entry<K,V>)table[0];
457 for(; e != null; e = e.next) {
458 if (e.key == null) {
459 V oldValue = e.value;
460 e.value = value;
461 e.recordAccess(this);
462 return oldValue;
463 }
464 }
465 modCount++;
466 addEntry(0, null, value, 0);
467 return null;
468 }
469
470 /**
471 * This method is used instead of put by constructors and
472 * pseudoconstructors (clone, readObject). It does not resize the table,
473 * check for comodification, etc. It calls createEntry rather than
474 * addEntry.
475 */
476 private void putForCreate(K key, V value) {
477 int hash = null == key ? 0 : hash(key);
478 int i = indexFor(hash, table.length);
479
480 /**
481 * Look for preexisting entry for key. This will never happen for
482 * clone or deserialize. It will only happen for construction if the
483 * input Map is a sorted map whose ordering is inconsistent w/ equals.
484 */
485 for (@SuppressWarnings("unchecked")
486 Entry<?,V> e = (Entry<?,V>)table[i]; e != null; e = e.next) {
487 Object k;
488 if (e.hash == hash &&
489 ((k = e.key) == key || (key != null && key.equals(k)))) {
490 e.value = value;
491 return;
492 }
493 }
494
495 createEntry(hash, key, value, i);
496 }
497
498 private void putAllForCreate(Map<? extends K, ? extends V> m) {
499 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
500 putForCreate(e.getKey(), e.getValue());
501 }
502
503 /**
504 * Rehashes the contents of this map into a new array with a
505 * larger capacity. This method is called automatically when the
506 * number of keys in this map reaches its threshold.
507 *
508 * If current capacity is MAXIMUM_CAPACITY, this method does not
509 * resize the map, but sets threshold to Integer.MAX_VALUE.
510 * This has the effect of preventing future calls.
511 *
512 * @param newCapacity the new capacity, MUST be a power of two;
513 * must be greater than current capacity unless current
514 * capacity is MAXIMUM_CAPACITY (in which case value
515 * is irrelevant).
516 */
517 void resize(int newCapacity) {
518 Entry<?,?>[] oldTable = table;
519 int oldCapacity = oldTable.length;
520 if (oldCapacity == MAXIMUM_CAPACITY) {
521 threshold = Integer.MAX_VALUE;
522 return;
523 }
524
525 Entry<?,?>[] newTable = new Entry<?,?>[newCapacity];
526 transfer(newTable);
527 table = newTable;
528 threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
529 }
530
531 /**
532 * Transfers all entries from current table to newTable.
533 */
534 @SuppressWarnings("unchecked")
535 void transfer(Entry<?,?>[] newTable) {
536 Entry<?,?>[] src = table;
537 int newCapacity = newTable.length;
538 for (int j = 0; j < src.length; j++ ) {
539 Entry<K,V> e = (Entry<K,V>) src[j];
540 while(null != e) {
541 Entry<K,V> next = e.next;
542 int i = indexFor(e.hash, newCapacity);
543 e.next = (Entry<K,V>) newTable[i];
544 newTable[i] = e;
545 e = next;
546 }
547 }
548 Arrays.fill(table, null);
549 }
550
551 /**
552 * Copies all of the mappings from the specified map to this map.
553 * These mappings will replace any mappings that this map had for
554 * any of the keys currently in the specified map.
555 *
556 * @param m mappings to be stored in this map
557 * @throws NullPointerException if the specified map is null
558 */
559 public void putAll(Map<? extends K, ? extends V> m) {
560 int numKeysToBeAdded = m.size();
561 if (numKeysToBeAdded == 0)
562 return;
563
564 if (table == EMPTY_TABLE) {
565 inflateTable((int) Math.max(numKeysToBeAdded * loadFactor, threshold));
566 }
567
568 /*
569 * Expand the map if the map if the number of mappings to be added
570 * is greater than or equal to threshold. This is conservative; the
571 * obvious condition is (m.size() + size) >= threshold, but this
572 * condition could result in a map with twice the appropriate capacity,
573 * if the keys to be added overlap with the keys already in this map.
574 * By using the conservative calculation, we subject ourself
575 * to at most one extra resize.
576 */
577 if (numKeysToBeAdded > threshold) {
578 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
579 if (targetCapacity > MAXIMUM_CAPACITY)
580 targetCapacity = MAXIMUM_CAPACITY;
581 int newCapacity = table.length;
582 while (newCapacity < targetCapacity)
583 newCapacity <<= 1;
584 if (newCapacity > table.length)
585 resize(newCapacity);
586 }
587
588 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
589 put(e.getKey(), e.getValue());
590 }
591
592 /**
593 * Removes the mapping for the specified key from this map if present.
594 *
595 * @param key key whose mapping is to be removed from the map
596 * @return the previous value associated with <tt>key</tt>, or
597 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
598 * (A <tt>null</tt> return can also indicate that the map
599 * previously associated <tt>null</tt> with <tt>key</tt>.)
600 */
601 public V remove(Object key) {
602 Entry<K,V> e = removeEntryForKey(key);
603 return (e == null ? null : e.value);
604 }
605
606 /**
607 * Removes and returns the entry associated with the specified key
608 * in the HashMap. Returns null if the HashMap contains no mapping
609 * for this key.
610 */
611 final Entry<K,V> removeEntryForKey(Object key) {
612 if (isEmpty()) {
613 return null;
614 }
615 int hash = (key == null) ? 0 : hash(key);
616 int i = indexFor(hash, table.length);
617 @SuppressWarnings("unchecked")
618 Entry<K,V> prev = (Entry<K,V>)table[i];
619 Entry<K,V> e = prev;
620
621 while (e != null) {
622 Entry<K,V> next = e.next;
623 Object k;
624 if (e.hash == hash &&
625 ((k = e.key) == key || (key != null && key.equals(k)))) {
626 modCount++;
627 size--;
628 if (prev == e)
629 table[i] = next;
630 else
631 prev.next = next;
632 e.recordRemoval(this);
633 return e;
634 }
635 prev = e;
636 e = next;
637 }
638
639 return e;
640 }
641
642 /**
643 * Special version of remove for EntrySet using {@code Map.Entry.equals()}
644 * for matching.
645 */
646 final Entry<K,V> removeMapping(Object o) {
647 if (isEmpty() || !(o instanceof Map.Entry))
648 return null;
649
650 Map.Entry<?,?> entry = (Map.Entry<?,?>) o;
651 Object key = entry.getKey();
652 int hash = (key == null) ? 0 : hash(key);
653 int i = indexFor(hash, table.length);
654 @SuppressWarnings("unchecked")
655 Entry<K,V> prev = (Entry<K,V>)table[i];
656 Entry<K,V> e = prev;
657
658 while (e != null) {
659 Entry<K,V> next = e.next;
660 if (e.hash == hash && e.equals(entry)) {
661 modCount++;
662 size--;
663 if (prev == e)
664 table[i] = next;
665 else
666 prev.next = next;
667 e.recordRemoval(this);
668 return e;
669 }
670 prev = e;
671 e = next;
672 }
673
674 return e;
675 }
676
677 /**
678 * Removes all of the mappings from this map.
679 * The map will be empty after this call returns.
680 */
681 public void clear() {
682 modCount++;
683 Arrays.fill(table, null);
684 size = 0;
685 }
686
687 /**
688 * Returns <tt>true</tt> if this map maps one or more keys to the
689 * specified value.
690 *
691 * @param value value whose presence in this map is to be tested
692 * @return <tt>true</tt> if this map maps one or more keys to the
693 * specified value
694 */
695 public boolean containsValue(Object value) {
696 if (value == null)
697 return containsNullValue();
698
699 Entry<?,?>[] tab = table;
700 for (int i = 0; i < tab.length ; i++)
701 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next)
702 if (value.equals(e.value))
703 return true;
704 return false;
705 }
706
707 /**
708 * Special-case code for containsValue with null argument
709 */
710 private boolean containsNullValue() {
711 Entry<?,?>[] tab = table;
712 for (int i = 0; i < tab.length ; i++)
713 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next)
714 if (e.value == null)
715 return true;
716 return false;
717 }
718
719 /**
720 * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and
721 * values themselves are not cloned.
722 *
723 * @return a shallow copy of this map
724 */
725 @SuppressWarnings("unchecked")
726 public Object clone() {
727 HashMap<K,V> result = null;
728 try {
729 result = (HashMap<K,V>)super.clone();
730 } catch (CloneNotSupportedException e) {
731 // assert false;
732 }
733 if (result.table != EMPTY_TABLE) {
734 result.inflateTable(Math.min(
735 (int) Math.min(
736 size * Math.min(1 / loadFactor, 4.0f),
737 // we have limits...
738 HashMap.MAXIMUM_CAPACITY),
739 table.length));
740 }
741 result.entrySet = null;
742 result.modCount = 0;
743 result.size = 0;
744 result.init();
745 result.putAllForCreate(this);
746
747 return result;
748 }
749
750 static class Entry<K,V> implements Map.Entry<K,V> {
751 final K key;
752 V value;
753 Entry<K,V> next;
754 final int hash;
755
756 /**
757 * Creates new entry.
758 */
759 Entry(int h, K k, V v, Entry<K,V> n) {
760 value = v;
761 next = n;
762 key = k;
763 hash = h;
764 }
765
766 public final K getKey() {
767 return key;
768 }
769
770 public final V getValue() {
771 return value;
772 }
773
774 public final V setValue(V newValue) {
775 V oldValue = value;
776 value = newValue;
777 return oldValue;
778 }
779
780 public final boolean equals(Object o) {
781 if (!(o instanceof Map.Entry))
782 return false;
783 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
784 Object k1 = getKey();
785 Object k2 = e.getKey();
786 if (k1 == k2 || (k1 != null && k1.equals(k2))) {
787 Object v1 = getValue();
788 Object v2 = e.getValue();
789 if (v1 == v2 || (v1 != null && v1.equals(v2)))
790 return true;
791 }
792 return false;
793 }
794
795 public final int hashCode() {
796 return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
797 }
798
799 public final String toString() {
800 return getKey() + "=" + getValue();
801 }
802
803 /**
804 * This method is invoked whenever the value in an entry is
805 * overwritten by an invocation of put(k,v) for a key k that's already
806 * in the HashMap.
807 */
808 void recordAccess(HashMap<K,V> m) {
809 }
810
811 /**
812 * This method is invoked whenever the entry is
813 * removed from the table.
814 */
815 void recordRemoval(HashMap<K,V> m) {
816 }
817 }
818
819 /**
820 * Adds a new entry with the specified key, value and hash code to
821 * the specified bucket. It is the responsibility of this
822 * method to resize the table if appropriate.
823 *
824 * Subclass overrides this to alter the behavior of put method.
825 */
826 void addEntry(int hash, K key, V value, int bucketIndex) {
827 if ((size >= threshold) && (null != table[bucketIndex])) {
828 resize(2 * table.length);
829 hash = (null != key) ? hash(key) : 0;
830 bucketIndex = indexFor(hash, table.length);
831 }
832
833 createEntry(hash, key, value, bucketIndex);
834 }
835
836 /**
837 * Like addEntry except that this version is used when creating entries
838 * as part of Map construction or "pseudo-construction" (cloning,
839 * deserialization). This version needn't worry about resizing the table.
840 *
841 * Subclass overrides this to alter the behavior of HashMap(Map),
842 * clone, and readObject.
843 */
844 void createEntry(int hash, K key, V value, int bucketIndex) {
845 @SuppressWarnings("unchecked")
846 Entry<K,V> e = (Entry<K,V>)table[bucketIndex];
847 table[bucketIndex] = new Entry<>(hash, key, value, e);
848 size++;
849 }
850
851 private abstract class HashIterator<E> implements Iterator<E> {
852 Entry<?,?> next; // next entry to return
853 int expectedModCount; // For fast-fail
854 int index; // current slot
855 Entry<?,?> current; // current entry
856
857 HashIterator() {
858 expectedModCount = modCount;
859 if (size > 0) { // advance to first entry
860 Entry<?,?>[] t = table;
861 while (index < t.length && (next = t[index++]) == null)
862 ;
863 }
864 }
865
866 public final boolean hasNext() {
867 return next != null;
868 }
869
870 @SuppressWarnings("unchecked")
871 final Entry<K,V> nextEntry() {
872 if (modCount != expectedModCount)
873 throw new ConcurrentModificationException();
874 Entry<?,?> e = next;
875 if (e == null)
876 throw new NoSuchElementException();
877
878 if ((next = e.next) == null) {
879 Entry<?,?>[] t = table;
880 while (index < t.length && (next = t[index++]) == null)
881 ;
882 }
883 current = e;
884 return (Entry<K,V>)e;
885 }
886
887 public void remove() {
888 if (current == null)
889 throw new IllegalStateException();
890 if (modCount != expectedModCount)
891 throw new ConcurrentModificationException();
892 Object k = current.key;
893 current = null;
894 HashMap.this.removeEntryForKey(k);
895 expectedModCount = modCount;
896 }
897 }
898
899 private final class ValueIterator extends HashIterator<V> {
900 public V next() {
901 return nextEntry().value;
902 }
903 }
904
905 private final class KeyIterator extends HashIterator<K> {
906 public K next() {
907 return nextEntry().getKey();
908 }
909 }
910
911 private final class EntryIterator extends HashIterator<Map.Entry<K,V>> {
912 public Map.Entry<K,V> next() {
913 return nextEntry();
914 }
915 }
916
917 // Subclass overrides these to alter behavior of views' iterator() method
918 Iterator<K> newKeyIterator() {
919 return new KeyIterator();
920 }
921 Iterator<V> newValueIterator() {
922 return new ValueIterator();
923 }
924 Iterator<Map.Entry<K,V>> newEntryIterator() {
925 return new EntryIterator();
926 }
927
928
929 // Views
930
931 private transient Set<Map.Entry<K,V>> entrySet = null;
932
933 /**
934 * Returns a {@link Set} view of the keys contained in this map.
935 * The set is backed by the map, so changes to the map are
936 * reflected in the set, and vice-versa. If the map is modified
937 * while an iteration over the set is in progress (except through
938 * the iterator's own <tt>remove</tt> operation), the results of
939 * the iteration are undefined. The set supports element removal,
940 * which removes the corresponding mapping from the map, via the
941 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
942 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
943 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
944 * operations.
945 */
946 public Set<K> keySet() {
947 Set<K> ks = keySet;
948 return (ks != null ? ks : (keySet = new KeySet()));
949 }
950
951 private final class KeySet extends AbstractSet<K> {
952 public Iterator<K> iterator() {
953 return newKeyIterator();
954 }
955 public int size() {
956 return size;
957 }
958 public boolean contains(Object o) {
959 return containsKey(o);
960 }
961 public boolean remove(Object o) {
962 return HashMap.this.removeEntryForKey(o) != null;
963 }
964 public void clear() {
965 HashMap.this.clear();
966 }
967 }
968
969 /**
970 * Returns a {@link Collection} view of the values contained in this map.
971 * The collection is backed by the map, so changes to the map are
972 * reflected in the collection, and vice-versa. If the map is
973 * modified while an iteration over the collection is in progress
974 * (except through the iterator's own <tt>remove</tt> operation),
975 * the results of the iteration are undefined. The collection
976 * supports element removal, which removes the corresponding
977 * mapping from the map, via the <tt>Iterator.remove</tt>,
978 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
979 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
980 * support the <tt>add</tt> or <tt>addAll</tt> operations.
981 */
982 public Collection<V> values() {
983 Collection<V> vs = values;
984 return (vs != null ? vs : (values = new Values()));
985 }
986
987 private final class Values extends AbstractCollection<V> {
988 public Iterator<V> iterator() {
989 return newValueIterator();
990 }
991 public int size() {
992 return size;
993 }
994 public boolean contains(Object o) {
995 return containsValue(o);
996 }
997 public void clear() {
998 HashMap.this.clear();
999 }
1000 }
1001
1002 /**
1003 * Returns a {@link Set} view of the mappings contained in this map.
1004 * The set is backed by the map, so changes to the map are
1005 * reflected in the set, and vice-versa. If the map is modified
1006 * while an iteration over the set is in progress (except through
1007 * the iterator's own <tt>remove</tt> operation, or through the
1008 * <tt>setValue</tt> operation on a map entry returned by the
1009 * iterator) the results of the iteration are undefined. The set
1010 * supports element removal, which removes the corresponding
1011 * mapping from the map, via the <tt>Iterator.remove</tt>,
1012 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
1013 * <tt>clear</tt> operations. It does not support the
1014 * <tt>add</tt> or <tt>addAll</tt> operations.
1015 *
1016 * @return a set view of the mappings contained in this map
1017 */
1018 public Set<Map.Entry<K,V>> entrySet() {
1019 return entrySet0();
1020 }
1021
1022 private Set<Map.Entry<K,V>> entrySet0() {
1023 Set<Map.Entry<K,V>> es = entrySet;
1024 return es != null ? es : (entrySet = new EntrySet());
1025 }
1026
1027 private final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
1028 public Iterator<Map.Entry<K,V>> iterator() {
1029 return newEntryIterator();
1030 }
1031 public boolean contains(Object o) {
1032 if (!(o instanceof Map.Entry))
1033 return false;
1034 Map.Entry<?,?> e = (Map.Entry<?,?>) o;
1035 Entry<K,V> candidate = getEntry(e.getKey());
1036 return candidate != null && candidate.equals(e);
1037 }
1038 public boolean remove(Object o) {
1039 return removeMapping(o) != null;
1040 }
1041 public int size() {
1042 return size;
1043 }
1044 public void clear() {
1045 HashMap.this.clear();
1046 }
1047 }
1048
1049 /**
1050 * Save the state of the <tt>HashMap</tt> instance to a stream (i.e.,
1051 * serialize it).
1052 *
1053 * @serialData The <i>capacity</i> of the HashMap (the length of the
1054 * bucket array) is emitted (int), followed by the
1055 * <i>size</i> (an int, the number of key-value
1056 * mappings), followed by the key (Object) and value (Object)
1057 * for each key-value mapping. The key-value mappings are
1058 * emitted in no particular order.
1059 */
1060 private void writeObject(java.io.ObjectOutputStream s)
1061 throws IOException
1062 {
1063 // Write out the threshold, loadfactor, and any hidden stuff
1064 s.defaultWriteObject();
1065
1066 // Write out number of buckets
1067 if (table==EMPTY_TABLE) {
1068 s.writeInt(roundUpToPowerOf2(threshold));
1069 } else {
1070 s.writeInt(table.length);
1071 }
1072
1073 // Write out size (number of Mappings)
1074 s.writeInt(size);
1075
1076 // Write out keys and values (alternating)
1077 if (size > 0) {
1078 for(Map.Entry<K,V> e : entrySet0()) {
1079 s.writeObject(e.getKey());
1080 s.writeObject(e.getValue());
1081 }
1082 }
1083 }
1084
1085 private static final long serialVersionUID = 362498820763181265L;
1086
1087 /**
1088 * Reconstitute the {@code HashMap} instance from a stream (i.e.,
1089 * deserialize it).
1090 */
1091 private void readObject(java.io.ObjectInputStream s)
1092 throws IOException, ClassNotFoundException
1093 {
1094 // Read in the threshold (ignored), loadfactor, and any hidden stuff
1095 s.defaultReadObject();
1096 if (loadFactor <= 0 || Float.isNaN(loadFactor)) {
1097 throw new InvalidObjectException("Illegal load factor: " +
1098 loadFactor);
1099 }
1100
1101 // set other fields that need values
1102 Holder.UNSAFE.putIntVolatile(this, Holder.HASHSEED_OFFSET,
1103 sun.misc.Hashing.randomHashSeed(this));
1104 table = EMPTY_TABLE;
1105
1106 // Read in number of buckets
1107 s.readInt(); // ignored.
1108
1109 // Read number of mappings
1110 int mappings = s.readInt();
1111 if (mappings < 0)
1112 throw new InvalidObjectException("Illegal mappings count: " +
1113 mappings);
1114
1115 // capacity chosen by number of mappings and desired load (if >= 0.25)
1116 int capacity = (int) Math.min(
1117 mappings * Math.min(1 / loadFactor, 4.0f),
1118 // we have limits...
1119 HashMap.MAXIMUM_CAPACITY);
1120
1121 // allocate the bucket array;
1122 if (mappings > 0) {
1123 inflateTable(capacity);
1124 } else {
1125 threshold = capacity;
1126 }
1127
1128 init(); // Give subclass a chance to do its thing.
1129
1130 // Read the keys and values, and put the mappings in the HashMap
1131 for (int i=0; i<mappings; i++) {
1132 @SuppressWarnings("unchecked")
1133 K key = (K) s.readObject();
1134 @SuppressWarnings("unchecked")
1135 V value = (V) s.readObject();
1136 putForCreate(key, value);
1137 }
1138 }
1139
1140 // These methods are used when serializing HashSets
1141 int capacity() { return table.length; }
1142 float loadFactor() { return loadFactor; }
1143 }