1 /*
2 * Copyright 1997-2007 Sun Microsystems, Inc. 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. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25
26 package java.util;
27 import java.io;
28
29 /**
30 * Hash table based implementation of the Map interface. This
31 * implementation provides all of the optional map operations, and permits
32 * null values and the null key. (The HashMap
33 * class is roughly equivalent to Hashtable, 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 * This implementation provides constant-time performance for the basic
39 * operations (get and put), 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 * HashMap 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 *
An instance of HashMap has two parameters that affect its
48 * performance: initial capacity and load factor. The
49 * capacity 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 * load factor 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 rehashed (that is, internal data
55 * structures are rebuilt) so that the hash table has approximately twice the
56 * number of buckets.
57 *
58 *
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 * HashMap class, including get and put). 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 *
If many mappings are to be stored in a HashMap 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 *
Note that this implementation is not synchronized.
74 * If multiple threads access a hash map concurrently, and at least one of
75 * the threads modifies the map structurally, it must 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:
86 * Map m = Collections.synchronizedMap(new HashMap(...));
87 *
88 * The iterators returned by all of this class's "collection view methods"
89 * are fail-fast: 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 * remove 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 *
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 ConcurrentModificationException on a best-effort basis.
101 * Therefore, it would be wrong to write a program that depended on this
102 * exception for its correctness: the fail-fast behavior of iterators
103 * should be used only to detect bugs.
104 *
105 *
This class is a member of the
106 *
107 * Java Collections Framework.
108 *
109 * @param the type of keys maintained by this map
110 * @param 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
125 extends AbstractMap
126 implements Map, 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 volatile int modCount;
177
178 /**
179 * Constructs an empty HashMap 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 HashMap 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 HashMap 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 HashMap with the same mappings as the
232 * specified Map. The HashMap is created with
233 * default load factor (0.75) and an initial capacity sufficient to
234 * hold the mappings in the specified Map.
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 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 true if this map contains no key-value mappings.
290 *
291 * @return true 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 * 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 *
A return value of {@code null} does not necessarily
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 public V get(Object key) {
315 if (key == null)
316 return getForNullKey();
317 int hash = hash(key.hashCode());
318 for (Entry e = table[indexFor(hash, table.length)];
319 e != null;
320 e = e.next) {
321 Object k;
322 if (e.hash == hash && ((k = e.key) == key || key.equals(k)))
323 return e.value;
324 }
325 return null;
326 }
327
328 /**
329 * Offloaded version of get() to look up null keys. Null keys map
330 * to index 0. This null case is split out into separate methods
331 * for the sake of performance in the two most commonly used
332 * operations (get and put), but incorporated with conditionals in
333 * others.
334 */
335 private V getForNullKey() {
336 for (Entry e = table[0]; e != null; e = e.next) {
337 if (e.key == null)
338 return e.value;
339 }
340 return null;
341 }
342
343 /**
344 * Returns true if this map contains a mapping for the
345 * specified key.
346 *
347 * @param key The key whose presence in this map is to be tested
348 * @return true if this map contains a mapping for the specified
349 * key.
350 */
351 public boolean containsKey(Object key) {
352 return getEntry(key) != null;
353 }
354
355 /**
356 * Returns the entry associated with the specified key in the
357 * HashMap. Returns null if the HashMap contains no mapping
358 * for the key.
359 */
360 final Entry getEntry(Object key) {
361 int hash = (key == null) ? 0 : hash(key.hashCode());
362 for (Entry e = table[indexFor(hash, table.length)];
363 e != null;
364 e = e.next) {
365 Object k;
366 if (e.hash == hash &&
367 ((k = e.key) == key || (key != null && key.equals(k))))
368 return e;
369 }
370 return null;
371 }
372
373
374 /**
375 * Associates the specified value with the specified key in this map.
376 * If the map previously contained a mapping for the key, the old
377 * value is replaced.
378 *
379 * @param key key with which the specified value is to be associated
380 * @param value value to be associated with the specified key
381 * @return the previous value associated with key, or
382 * null if there was no mapping for key.
383 * (A null return can also indicate that the map
384 * previously associated null with key.)
385 */
386 public V put(K key, V value) {
387 if (key == null)
388 return putForNullKey(value);
389 int hash = hash(key.hashCode());
390 int i = indexFor(hash, table.length);
391 for (Entry e = table[i]; e != null; e = e.next) {
392 Object k;
393 if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
394 V oldValue = e.value;
395 e.value = value;
396 e.recordAccess(this);
397 return oldValue;
398 }
399 }
400
401 modCount++;
402 addEntry(hash, key, value, i);
403 return null;
404 }
405
406 /**
407 * Offloaded version of put for null keys
408 */
409 private V putForNullKey(V value) {
410 for (Entry e = table[0]; e != null; e = e.next) {
411 if (e.key == null) {
412 V oldValue = e.value;
413 e.value = value;
414 e.recordAccess(this);
415 return oldValue;
416 }
417 }
418 modCount++;
419 addEntry(0, null, value, 0);
420 return null;
421 }
422
423 /**
424 * This method is used instead of put by constructors and
425 * pseudoconstructors (clone, readObject). It does not resize the table,
426 * check for comodification, etc. It calls createEntry rather than
427 * addEntry.
428 */
429 private void putForCreate(K key, V value) {
430 int hash = (key == null) ? 0 : hash(key.hashCode());
431 int i = indexFor(hash, table.length);
432
433 /**
434 * Look for preexisting entry for key. This will never happen for
435 * clone or deserialize. It will only happen for construction if the
436 * input Map is a sorted map whose ordering is inconsistent w/ equals.
437 */
438 for (Entry e = table[i]; e != null; e = e.next) {
439 Object k;
440 if (e.hash == hash &&
441 ((k = e.key) == key || (key != null && key.equals(k)))) {
442 e.value = value;
443 return;
444 }
445 }
446
447 createEntry(hash, key, value, i);
448 }
449
450 private void putAllForCreate(Map m) {
451 for (Iterator> i = m.entrySet().iterator(); i.hasNext(); ) {
452 Map.Entry e = i.next();
453 putForCreate(e.getKey(), e.getValue());
454 }
455 }
456
457 /**
458 * Rehashes the contents of this map into a new array with a
459 * larger capacity. This method is called automatically when the
460 * number of keys in this map reaches its threshold.
461 *
462 * If current capacity is MAXIMUM_CAPACITY, this method does not
463 * resize the map, but sets threshold to Integer.MAX_VALUE.
464 * This has the effect of preventing future calls.
465 *
466 * @param newCapacity the new capacity, MUST be a power of two;
467 * must be greater than current capacity unless current
468 * capacity is MAXIMUM_CAPACITY (in which case value
469 * is irrelevant).
470 */
471 void resize(int newCapacity) {
472 Entry[] oldTable = table;
473 int oldCapacity = oldTable.length;
474 if (oldCapacity == MAXIMUM_CAPACITY) {
475 threshold = Integer.MAX_VALUE;
476 return;
477 }
478
479 Entry[] newTable = new Entry[newCapacity];
480 transfer(newTable);
481 table = newTable;
482 threshold = (int)(newCapacity * loadFactor);
483 }
484
485 /**
486 * Transfers all entries from current table to newTable.
487 */
488 void transfer(Entry[] newTable) {
489 Entry[] src = table;
490 int newCapacity = newTable.length;
491 for (int j = 0; j < src.length; j++) {
492 Entry e = src[j];
493 if (e != null) {
494 src[j] = null;
495 do {
496 Entry next = e.next;
497 int i = indexFor(e.hash, newCapacity);
498 e.next = newTable[i];
499 newTable[i] = e;
500 e = next;
501 } while (e != null);
502 }
503 }
504 }
505
506 /**
507 * Copies all of the mappings from the specified map to this map.
508 * These mappings will replace any mappings that this map had for
509 * any of the keys currently in the specified map.
510 *
511 * @param m mappings to be stored in this map
512 * @throws NullPointerException if the specified map is null
513 */
514 public void putAll(Map m) {
515 int numKeysToBeAdded = m.size();
516 if (numKeysToBeAdded == 0)
517 return;
518
519 /*
520 * Expand the map if the map if the number of mappings to be added
521 * is greater than or equal to threshold. This is conservative; the
522 * obvious condition is (m.size() + size) >= threshold, but this
523 * condition could result in a map with twice the appropriate capacity,
524 * if the keys to be added overlap with the keys already in this map.
525 * By using the conservative calculation, we subject ourself
526 * to at most one extra resize.
527 */
528 if (numKeysToBeAdded > threshold) {
529 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
530 if (targetCapacity > MAXIMUM_CAPACITY)
531 targetCapacity = MAXIMUM_CAPACITY;
532 int newCapacity = table.length;
533 while (newCapacity < targetCapacity)
534 newCapacity <<= 1;
535 if (newCapacity > table.length)
536 resize(newCapacity);
537 }
538
539 for (Iterator> i = m.entrySet().iterator(); i.hasNext(); ) {
540 Map.Entry e = i.next();
541 put(e.getKey(), e.getValue());
542 }
543 }
544
545 /**
546 * Removes the mapping for the specified key from this map if present.
547 *
548 * @param key key whose mapping is to be removed from the map
549 * @return the previous value associated with key, or
550 * null if there was no mapping for key.
551 * (A null return can also indicate that the map
552 * previously associated null with key.)
553 */
554 public V remove(Object key) {
555 Entry e = removeEntryForKey(key);
556 return (e == null ? null : e.value);
557 }
558
559 /**
560 * Removes and returns the entry associated with the specified key
561 * in the HashMap. Returns null if the HashMap contains no mapping
562 * for this key.
563 */
564 final Entry removeEntryForKey(Object key) {
565 int hash = (key == null) ? 0 : hash(key.hashCode());
566 int i = indexFor(hash, table.length);
567 Entry prev = table[i];
568 Entry e = prev;
569
570 while (e != null) {
571 Entry next = e.next;
572 Object k;
573 if (e.hash == hash &&
574 ((k = e.key) == key || (key != null && key.equals(k)))) {
575 modCount++;
576 size--;
577 if (prev == e)
578 table[i] = next;
579 else
580 prev.next = next;
581 e.recordRemoval(this);
582 return e;
583 }
584 prev = e;
585 e = next;
586 }
587
588 return e;
589 }
590
591 /**
592 * Special version of remove for EntrySet.
593 */
594 final Entry removeMapping(Object o) {
595 if (!(o instanceof Map.Entry))
596 return null;
597
598 Map.Entry entry = (Map.Entry) o;
599 Object key = entry.getKey();
600 int hash = (key == null) ? 0 : hash(key.hashCode());
601 int i = indexFor(hash, table.length);
602 Entry prev = table[i];
603 Entry e = prev;
604
605 while (e != null) {
606 Entry next = e.next;
607 if (e.hash == hash && e.equals(entry)) {
608 modCount++;
609 size--;
610 if (prev == e)
611 table[i] = next;
612 else
613 prev.next = next;
614 e.recordRemoval(this);
615 return e;
616 }
617 prev = e;
618 e = next;
619 }
620
621 return e;
622 }
623
624 /**
625 * Removes all of the mappings from this map.
626 * The map will be empty after this call returns.
627 */
628 public void clear() {
629 modCount++;
630 Entry[] tab = table;
631 for (int i = 0; i < tab.length; i++)
632 tab[i] = null;
633 size = 0;
634 }
635
636 /**
637 * Returns true if this map maps one or more keys to the
638 * specified value.
639 *
640 * @param value value whose presence in this map is to be tested
641 * @return true if this map maps one or more keys to the
642 * specified value
643 */
644 public boolean containsValue(Object value) {
645 if (value == null)
646 return containsNullValue();
647
648 Entry[] tab = table;
649 for (int i = 0; i < tab.length ; i++)
650 for (Entry e = tab[i] ; e != null ; e = e.next)
651 if (value.equals(e.value))
652 return true;
653 return false;
654 }
655
656 /**
657 * Special-case code for containsValue with null argument
658 */
659 private boolean containsNullValue() {
660 Entry[] tab = table;
661 for (int i = 0; i < tab.length ; i++)
662 for (Entry e = tab[i] ; e != null ; e = e.next)
663 if (e.value == null)
664 return true;
665 return false;
666 }
667
668 /**
669 * Returns a shallow copy of this HashMap instance: the keys and
670 * values themselves are not cloned.
671 *
672 * @return a shallow copy of this map
673 */
674 public Object clone() {
675 HashMap result = null;
676 try {
677 result = (HashMap)super.clone();
678 } catch (CloneNotSupportedException e) {
679 // assert false;
680 }
681 result.table = new Entry[table.length];
682 result.entrySet = null;
683 result.modCount = 0;
684 result.size = 0;
685 result.init();
686 result.putAllForCreate(this);
687
688 return result;
689 }
690
691 static class Entry implements Map.Entry {
692 final K key;
693 V value;
694 Entry next;
695 final int hash;
696
697 /**
698 * Creates new entry.
699 */
700 Entry(int h, K k, V v, Entry n) {
701 value = v;
702 next = n;
703 key = k;
704 hash = h;
705 }
706
707 public final K getKey() {
708 return key;
709 }
710
711 public final V getValue() {
712 return value;
713 }
714
715 public final V setValue(V newValue) {
716 V oldValue = value;
717 value = newValue;
718 return oldValue;
719 }
720
721 public final boolean equals(Object o) {
722 if (!(o instanceof Map.Entry))
723 return false;
724 Map.Entry e = (Map.Entry)o;
725 Object k1 = getKey();
726 Object k2 = e.getKey();
727 if (k1 == k2 || (k1 != null && k1.equals(k2))) {
728 Object v1 = getValue();
729 Object v2 = e.getValue();
730 if (v1 == v2 || (v1 != null && v1.equals(v2)))
731 return true;
732 }
733 return false;
734 }
735
736 public final int hashCode() {
737 return (key==null ? 0 : key.hashCode()) ^
738 (value==null ? 0 : value.hashCode());
739 }
740
741 public final String toString() {
742 return getKey() + "=" + getValue();
743 }
744
745 /**
746 * This method is invoked whenever the value in an entry is
747 * overwritten by an invocation of put(k,v) for a key k that's already
748 * in the HashMap.
749 */
750 void recordAccess(HashMap m) {
751 }
752
753 /**
754 * This method is invoked whenever the entry is
755 * removed from the table.
756 */
757 void recordRemoval(HashMap m) {
758 }
759 }
760
761 /**
762 * Adds a new entry with the specified key, value and hash code to
763 * the specified bucket. It is the responsibility of this
764 * method to resize the table if appropriate.
765 *
766 * Subclass overrides this to alter the behavior of put method.
767 */
768 void addEntry(int hash, K key, V value, int bucketIndex) {
769 Entry e = table[bucketIndex];
770 table[bucketIndex] = new Entry(hash, key, value, e);
771 if (size++ >= threshold)
772 resize(2 * table.length);
773 }
774
775 /**
776 * Like addEntry except that this version is used when creating entries
777 * as part of Map construction or "pseudo-construction" (cloning,
778 * deserialization). This version needn't worry about resizing the table.
779 *
780 * Subclass overrides this to alter the behavior of HashMap(Map),
781 * clone, and readObject.
782 */
783 void createEntry(int hash, K key, V value, int bucketIndex) {
784 Entry e = table[bucketIndex];
785 table[bucketIndex] = new Entry(hash, key, value, e);
786 size++;
787 }
788
789 private abstract class HashIterator implements Iterator {
790 Entry next; // next entry to return
791 int expectedModCount; // For fast-fail
792 int index; // current slot
793 Entry current; // current entry
794
795 HashIterator() {
796 expectedModCount = modCount;
797 if (size > 0) { // advance to first entry
798 Entry[] t = table;
799 while (index < t.length && (next = t[index++]) == null)
800 ;
801 }
802 }
803
804 public final boolean hasNext() {
805 return next != null;
806 }
807
808 final Entry nextEntry() {
809 if (modCount != expectedModCount)
810 throw new ConcurrentModificationException();
811 Entry e = next;
812 if (e == null)
813 throw new NoSuchElementException();
814
815 if ((next = e.next) == null) {
816 Entry[] t = table;
817 while (index < t.length && (next = t[index++]) == null)
818 ;
819 }
820 current = e;
821 return e;
822 }
823
824 public void remove() {
825 if (current == null)
826 throw new IllegalStateException();
827 if (modCount != expectedModCount)
828 throw new ConcurrentModificationException();
829 Object k = current.key;
830 current = null;
831 HashMap.this.removeEntryForKey(k);
832 expectedModCount = modCount;
833 }
834
835 }
836
837 private final class ValueIterator extends HashIterator {
838 public V next() {
839 return nextEntry().value;
840 }
841 }
842
843 private final class KeyIterator extends HashIterator {
844 public K next() {
845 return nextEntry().getKey();
846 }
847 }
848
849 private final class EntryIterator extends HashIterator> {
850 public Map.Entry next() {
851 return nextEntry();
852 }
853 }
854
855 // Subclass overrides these to alter behavior of views' iterator() method
856 Iterator newKeyIterator() {
857 return new KeyIterator();
858 }
859 Iterator newValueIterator() {
860 return new ValueIterator();
861 }
862 Iterator> newEntryIterator() {
863 return new EntryIterator();
864 }
865
866
867 // Views
868
869 private transient Set> entrySet = null;
870
871 /**
872 * Returns a {@link Set} view of the keys contained in this map.
873 * The set is backed by the map, so changes to the map are
874 * reflected in the set, and vice-versa. If the map is modified
875 * while an iteration over the set is in progress (except through
876 * the iterator's own remove operation), the results of
877 * the iteration are undefined. The set supports element removal,
878 * which removes the corresponding mapping from the map, via the
879 * Iterator.remove, Set.remove,
880 * removeAll, retainAll, and clear
881 * operations. It does not support the add or addAll
882 * operations.
883 */
884 public Set keySet() {
885 Set ks = keySet;
886 return (ks != null ? ks : (keySet = new KeySet()));
887 }
888
889 private final class KeySet extends AbstractSet {
890 public Iterator iterator() {
891 return newKeyIterator();
892 }
893 public int size() {
894 return size;
895 }
896 public boolean contains(Object o) {
897 return containsKey(o);
898 }
899 public boolean remove(Object o) {
900 return HashMap.this.removeEntryForKey(o) != null;
901 }
902 public void clear() {
903 HashMap.this.clear();
904 }
905 }
906
907 /**
908 * Returns a {@link Collection} view of the values contained in this map.
909 * The collection is backed by the map, so changes to the map are
910 * reflected in the collection, and vice-versa. If the map is
911 * modified while an iteration over the collection is in progress
912 * (except through the iterator's own remove operation),
913 * the results of the iteration are undefined. The collection
914 * supports element removal, which removes the corresponding
915 * mapping from the map, via the Iterator.remove,
916 * Collection.remove, removeAll,
917 * retainAll and clear operations. It does not
918 * support the add or addAll operations.
919 */
920 public Collection values() {
921 Collection vs = values;
922 return (vs != null ? vs : (values = new Values()));
923 }
924
925 private final class Values extends AbstractCollection {
926 public Iterator iterator() {
927 return newValueIterator();
928 }
929 public int size() {
930 return size;
931 }
932 public boolean contains(Object o) {
933 return containsValue(o);
934 }
935 public void clear() {
936 HashMap.this.clear();
937 }
938 }
939
940 /**
941 * Returns a {@link Set} view of the mappings contained in this map.
942 * The set is backed by the map, so changes to the map are
943 * reflected in the set, and vice-versa. If the map is modified
944 * while an iteration over the set is in progress (except through
945 * the iterator's own remove operation, or through the
946 * setValue operation on a map entry returned by the
947 * iterator) the results of the iteration are undefined. The set
948 * supports element removal, which removes the corresponding
949 * mapping from the map, via the Iterator.remove,
950 * Set.remove, removeAll, retainAll and
951 * clear operations. It does not support the
952 * add or addAll operations.
953 *
954 * @return a set view of the mappings contained in this map
955 */
956 public Set> entrySet() {
957 return entrySet0();
958 }
959
960 private Set> entrySet0() {
961 Set> es = entrySet;
962 return es != null ? es : (entrySet = new EntrySet());
963 }
964
965 private final class EntrySet extends AbstractSet> {
966 public Iterator> iterator() {
967 return newEntryIterator();
968 }
969 public boolean contains(Object o) {
970 if (!(o instanceof Map.Entry))
971 return false;
972 Map.Entry e = (Map.Entry) o;
973 Entry candidate = getEntry(e.getKey());
974 return candidate != null && candidate.equals(e);
975 }
976 public boolean remove(Object o) {
977 return removeMapping(o) != null;
978 }
979 public int size() {
980 return size;
981 }
982 public void clear() {
983 HashMap.this.clear();
984 }
985 }
986
987 /**
988 * Save the state of the HashMap instance to a stream (i.e.,
989 * serialize it).
990 *
991 * @serialData The capacity of the HashMap (the length of the
992 * bucket array) is emitted (int), followed by the
993 * size (an int, the number of key-value
994 * mappings), followed by the key (Object) and value (Object)
995 * for each key-value mapping. The key-value mappings are
996 * emitted in no particular order.
997 */
998 private void writeObject(java.io.ObjectOutputStream s)
999 throws IOException
1000 {
1001 Iterator> i =
1002 (size > 0) ? entrySet0().iterator() : null;
1003
1004 // Write out the threshold, loadfactor, and any hidden stuff
1005 s.defaultWriteObject();
1006
1007 // Write out number of buckets
1008 s.writeInt(table.length);
1009
1010 // Write out size (number of Mappings)
1011 s.writeInt(size);
1012
1013 // Write out keys and values (alternating)
1014 if (i != null) {
1015 while (i.hasNext()) {
1016 Map.Entry e = i.next();
1017 s.writeObject(e.getKey());
1018 s.writeObject(e.getValue());
1019 }
1020 }
1021 }
1022
1023 private static final long serialVersionUID = 362498820763181265L;
1024
1025 /**
1026 * Reconstitute the HashMap instance from a stream (i.e.,
1027 * deserialize it).
1028 */
1029 private void readObject(java.io.ObjectInputStream s)
1030 throws IOException, ClassNotFoundException
1031 {
1032 // Read in the threshold, loadfactor, and any hidden stuff
1033 s.defaultReadObject();
1034
1035 // Read in number of buckets and allocate the bucket array;
1036 int numBuckets = s.readInt();
1037 table = new Entry[numBuckets];
1038
1039 init(); // Give subclass a chance to do its thing.
1040
1041 // Read in size (number of Mappings)
1042 int size = s.readInt();
1043
1044 // Read the keys and values, and put the mappings in the HashMap
1045 for (int i=0; i