| HashMap.java |
1 /*
2 * %W% %E%
3 *
4 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
5 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6 */
7
8 package java.util;
9 import java.io.*;
10
11 /**
12 * Hash table based implementation of the <tt>Map</tt> interface. This
13 * implementation provides all of the optional map operations, and permits
14 * <tt>null</tt> values and the <tt>null</tt> key. (The <tt>HashMap</tt>
15 * class is roughly equivalent to <tt>Hashtable</tt>, except that it is
16 * unsynchronized and permits nulls.) This class makes no guarantees as to
17 * the order of the map; in particular, it does not guarantee that the order
18 * will remain constant over time.
19 *
20 * <p>This implementation provides constant-time performance for the basic
21 * operations (<tt>get</tt> and <tt>put</tt>), assuming the hash function
22 * disperses the elements properly among the buckets. Iteration over
23 * collection views requires time proportional to the "capacity" of the
24 * <tt>HashMap</tt> instance (the number of buckets) plus its size (the number
25 * of key-value mappings). Thus, it's very important not to set the initial
26 * capacity too high (or the load factor too low) if iteration performance is
27 * important.
28 *
29 * <p>An instance of <tt>HashMap</tt> has two parameters that affect its
30 * performance: <i>initial capacity</i> and <i>load factor</i>. The
31 * <i>capacity</i> is the number of buckets in the hash table, and the initial
32 * capacity is simply the capacity at the time the hash table is created. The
33 * <i>load factor</i> is a measure of how full the hash table is allowed to
34 * get before its capacity is automatically increased. When the number of
35 * entries in the hash table exceeds the product of the load factor and the
36 * current capacity, the hash table is <i>rehashed</i> (that is, internal data
37 * structures are rebuilt) so that the hash table has approximately twice the
38 * number of buckets.
39 *
40 * <p>As a general rule, the default load factor (.75) offers a good tradeoff
41 * between time and space costs. Higher values decrease the space overhead
42 * but increase the lookup cost (reflected in most of the operations of the
43 * <tt>HashMap</tt> class, including <tt>get</tt> and <tt>put</tt>). The
44 * expected number of entries in the map and its load factor should be taken
45 * into account when setting its initial capacity, so as to minimize the
46 * number of rehash operations. If the initial capacity is greater
47 * than the maximum number of entries divided by the load factor, no
48 * rehash operations will ever occur.
49 *
50 * <p>If many mappings are to be stored in a <tt>HashMap</tt> instance,
51 * creating it with a sufficiently large capacity will allow the mappings to
52 * be stored more efficiently than letting it perform automatic rehashing as
53 * needed to grow the table.
54 *
55 * <p><strong>Note that this implementation is not synchronized.</strong>
56 * If multiple threads access a hash map concurrently, and at least one of
57 * the threads modifies the map structurally, it <i>must</i> be
58 * synchronized externally. (A structural modification is any operation
59 * that adds or deletes one or more mappings; merely changing the value
60 * associated with a key that an instance already contains is not a
61 * structural modification.) This is typically accomplished by
62 * synchronizing on some object that naturally encapsulates the map.
63 *
64 * If no such object exists, the map should be "wrapped" using the
65 * {@link Collections#synchronizedMap Collections.synchronizedMap}
66 * method. This is best done at creation time, to prevent accidental
67 * unsynchronized access to the map:<pre>
68 * Map m = Collections.synchronizedMap(new HashMap(...));</pre>
69 *
70 * <p>The iterators returned by all of this class's "collection view methods"
71 * are <i>fail-fast</i>: if the map is structurally modified at any time after
72 * the iterator is created, in any way except through the iterator's own
73 * <tt>remove</tt> method, the iterator will throw a
74 * {@link ConcurrentModificationException}. Thus, in the face of concurrent
75 * modification, the iterator fails quickly and cleanly, rather than risking
76 * arbitrary, non-deterministic behavior at an undetermined time in the
77 * future.
78 *
79 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
80 * as it is, generally speaking, impossible to make any hard guarantees in the
81 * presence of unsynchronized concurrent modification. Fail-fast iterators
82 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
83 * Therefore, it would be wrong to write a program that depended on this
84 * exception for its correctness: <i>the fail-fast behavior of iterators
85 * should be used only to detect bugs.</i>
86 *
87 * <p>This class is a member of the
88 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
89 * Java Collections Framework</a>.
90 *
91 * @param <K> the type of keys maintained by this map
92 * @param <V> the type of mapped values
93 *
94 * @author Doug Lea
95 * @author Josh Bloch
96 * @author Arthur van Hoff
97 * @author Neal Gafter
98 * @version %I%, %G%
99 * @see Object#hashCode()
100 * @see Collection
101 * @see Map
102 * @see TreeMap
103 * @see Hashtable
104 * @since 1.2
105 */
106
107 public class HashMap<K,V>
108 extends AbstractMap<K,V>
109 implements Map<K,V>, Cloneable, Serializable
110 {
111
112 /**
113 * The default initial capacity - MUST be a power of two.
114 */
115 static final int DEFAULT_INITIAL_CAPACITY = 16;
116
117 /**
118 * The maximum capacity, used if a higher value is implicitly specified
119 * by either of the constructors with arguments.
120 * MUST be a power of two <= 1<<30.
121 */
122 static final int MAXIMUM_CAPACITY = 1 << 30;
123
124 /**
125 * The load factor used when none specified in constructor.
126 */
127 static final float DEFAULT_LOAD_FACTOR = 0.75f;
128
129 /**
130 * The table, resized as necessary. Length MUST Always be a power of two.
131 */
132 transient Entry[] table;
133
134 /**
135 * The number of key-value mappings contained in this map.
136 */
137 transient int size;
138
139 /**
140 * The next size value at which to resize (capacity * load factor).
141 * @serial
142 */
143 int threshold;
144
145 /**
146 * The load factor for the hash table.
147 *
148 * @serial
149 */
150 final float loadFactor;
151
152 /**
153 * The number of times this HashMap has been structurally modified
154 * Structural modifications are those that change the number of mappings in
155 * the HashMap or otherwise modify its internal structure (e.g.,
156 * rehash). This field is used to make iterators on Collection-views of
157 * the HashMap fail-fast. (See ConcurrentModificationException).
158 */
159 transient volatile int modCount;
160
161 /**
162 * Constructs an empty <tt>HashMap</tt> with the specified initial
163 * capacity and load factor.
164 *
165 * @param initialCapacity the initial capacity
166 * @param loadFactor the load factor
167 * @throws IllegalArgumentException if the initial capacity is negative
168 * or the load factor is nonpositive
169 */
170 public HashMap(int initialCapacity, float loadFactor) {
171 if (initialCapacity < 0)
172 throw new IllegalArgumentException("Illegal initial capacity: " +
173 initialCapacity);
174 if (initialCapacity > MAXIMUM_CAPACITY)
175 initialCapacity = MAXIMUM_CAPACITY;
176 if (loadFactor <= 0 || Float.isNaN(loadFactor))
177 throw new IllegalArgumentException("Illegal load factor: " +
178 loadFactor);
179
180 // Find a power of 2 >= initialCapacity
181 int capacity = 1;
182 while (capacity < initialCapacity)
183 capacity <<= 1;
184
185 this.loadFactor = loadFactor;
186 threshold = (int)(capacity * loadFactor);
187 table = new Entry[capacity];
188 init();
189 }
190
191 /**
192 * Constructs an empty <tt>HashMap</tt> with the specified initial
193 * capacity and the default load factor (0.75).
194 *
195 * @param initialCapacity the initial capacity.
196 * @throws IllegalArgumentException if the initial capacity is negative.
197 */
198 public HashMap(int initialCapacity) {
199 this(initialCapacity, DEFAULT_LOAD_FACTOR);
200 }
201
202 /**
203 * Constructs an empty <tt>HashMap</tt> with the default initial capacity
204 * (16) and the default load factor (0.75).
205 */
206 public HashMap() {
207 this.loadFactor = DEFAULT_LOAD_FACTOR;
208 threshold = (int)(DEFAULT_INITIAL_CAPACITY * DEFAULT_LOAD_FACTOR);
209 table = new Entry[DEFAULT_INITIAL_CAPACITY];
210 init();
211 }
212
213 /**
214 * Constructs a new <tt>HashMap</tt> with the same mappings as the
215 * specified <tt>Map</tt>. The <tt>HashMap</tt> is created with
216 * default load factor (0.75) and an initial capacity sufficient to
217 * hold the mappings in the specified <tt>Map</tt>.
218 *
219 * @param m the map whose mappings are to be placed in this map
220 * @throws NullPointerException if the specified map is null
221 */
222 public HashMap(Map<? extends K, ? extends V> m) {
223 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
224 DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);
225 putAllForCreate(m);
226 }
227
228 // internal utilities
229
230 /**
231 * Initialization hook for subclasses. This method is called
232 * in all constructors and pseudo-constructors (clone, readObject)
233 * after HashMap has been initialized but before any entries have
234 * been inserted. (In the absence of this method, readObject would
235 * require explicit knowledge of subclasses.)
236 */
237 void init() {
238 }
239
240 /**
241 * Applies a supplemental hash function to a given hashCode, which
242 * defends against poor quality hash functions. This is critical
243 * because HashMap uses power-of-two length hash tables, that
244 * otherwise encounter collisions for hashCodes that do not differ
245 * in lower bits. Note: Null keys always map to hash 0, thus index 0.
246 */
247 static int hash(int h) {
248 // This function ensures that hashCodes that differ only by
249 // constant multiples at each bit position have a bounded
250 // number of collisions (approximately 8 at default load factor).
251 h ^= (h >>> 20) ^ (h >>> 12);
252 return h ^ (h >>> 7) ^ (h >>> 4);
253 }
254
255 /**
256 * Returns index for hash code h.
257 */
258 static int indexFor(int h, int length) {
259 return h & (length-1);
260 }
261
262 /**
263 * Returns the number of key-value mappings in this map.
264 *
265 * @return the number of key-value mappings in this map
266 */
267 public int size() {
268 return size;
269 }
270
271 /**
272 * Returns <tt>true</tt> if this map contains no key-value mappings.
273 *
274 * @return <tt>true</tt> if this map contains no key-value mappings
275 */
276 public boolean isEmpty() {
277 return size == 0;
278 }
279
280 /**
281 * Returns the value to which the specified key is mapped,
282 * or {@code null} if this map contains no mapping for the key.
283 *
284 * <p>More formally, if this map contains a mapping from a key
285 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
286 * key.equals(k))}, then this method returns {@code v}; otherwise
287 * it returns {@code null}. (There can be at most one such mapping.)
288 *
289 * <p>A return value of {@code null} does not <i>necessarily</i>
290 * indicate that the map contains no mapping for the key; it's also
291 * possible that the map explicitly maps the key to {@code null}.
292 * The {@link #containsKey containsKey} operation may be used to
293 * distinguish these two cases.
294 *
295 * @see #put(Object, Object)
296 */
297 public V get(Object key) {
298 if (key == null)
299 return getForNullKey();
300 int hash = hash(key.hashCode());
301 for (Entry<K,V> e = table[indexFor(hash, table.length)];
302 e != null;
303 e = e.next) {
304 Object k;
305 if (e.hash == hash && ((k = e.key) == key || key.equals(k)))
306 return e.value;
307 }
308 return null;
309 }
310
311 /**
312 * Offloaded version of get() to look up null keys. Null keys map
313 * to index 0. This null case is split out into separate methods
314 * for the sake of performance in the two most commonly used
315 * operations (get and put), but incorporated with conditionals in
316 * others.
317 */
318 private V getForNullKey() {
319 for (Entry<K,V> e = table[0]; e != null; e = e.next) {
320 if (e.key == null)
321 return e.value;
322 }
323 return null;
324 }
325
326 /**
327 * Returns <tt>true</tt> if this map contains a mapping for the
328 * specified key.
329 *
330 * @param key The key whose presence in this map is to be tested
331 * @return <tt>true</tt> if this map contains a mapping for the specified
332 * key.
333 */
334 public boolean containsKey(Object key) {
335 return getEntry(key) != null;
336 }
337
338 /**
339 * Returns the entry associated with the specified key in the
340 * HashMap. Returns null if the HashMap contains no mapping
341 * for the key.
342 */
343 final Entry<K,V> getEntry(Object key) {
344 int hash = (key == null) ? 0 : hash(key.hashCode());
345 for (Entry<K,V> e = table[indexFor(hash, table.length)];
346 e != null;
347 e = e.next) {
348 Object k;
349 if (e.hash == hash &&
350 ((k = e.key) == key || (key != null && key.equals(k))))
351 return e;
352 }
353 return null;
354 }
355
356
357 /**
358 * Associates the specified value with the specified key in this map.
359 * If the map previously contained a mapping for the key, the old
360 * value is replaced.
361 *
362 * @param key key with which the specified value is to be associated
363 * @param value value to be associated with the specified key
364 * @return the previous value associated with <tt>key</tt>, or
365 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
366 * (A <tt>null</tt> return can also indicate that the map
367 * previously associated <tt>null</tt> with <tt>key</tt>.)
368 */
369 public V put(K key, V value) {
370 if (key == null)
371 return putForNullKey(value);
372 int hash = hash(key.hashCode());
373 int i = indexFor(hash, table.length);
374 for (Entry<K,V> e = table[i]; e != null; e = e.next) {
375 Object k;
376 if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
377 V oldValue = e.value;
378 e.value = value;
379 e.recordAccess(this);
380 return oldValue;
381 }
382 }
383
384 modCount++;
385 addEntry(hash, key, value, i);
386 return null;
387 }
388
389 /**
390 * Offloaded version of put for null keys
391 */
392 private V putForNullKey(V value) {
393 for (Entry<K,V> e = table[0]; e != null; e = e.next) {
394 if (e.key == null) {
395 V oldValue = e.value;
396 e.value = value;
397 e.recordAccess(this);
398 return oldValue;
399 }
400 }
401 modCount++;
402 addEntry(0, null, value, 0);
403 return null;
404 }
405
406 /**
407 * This method is used instead of put by constructors and
408 * pseudoconstructors (clone, readObject). It does not resize the table,
409 * check for comodification, etc. It calls createEntry rather than
410 * addEntry.
411 */
412 private void putForCreate(K key, V value) {
413 int hash = (key == null) ? 0 : hash(key.hashCode());
414 int i = indexFor(hash, table.length);
415
416 /**
417 * Look for preexisting entry for key. This will never happen for
418 * clone or deserialize. It will only happen for construction if the
419 * input Map is a sorted map whose ordering is inconsistent w/ equals.
420 */
421 for (Entry<K,V> e = table[i]; e != null; e = e.next) {
422 Object k;
423 if (e.hash == hash &&
424 ((k = e.key) == key || (key != null && key.equals(k)))) {
425 e.value = value;
426 return;
427 }
428 }
429
430 createEntry(hash, key, value, i);
431 }
432
433 private void putAllForCreate(Map<? extends K, ? extends V> m) {
434 for (Iterator<? extends Map.Entry<? extends K, ? extends V>> i = m.entrySet().iterator(); i.hasNext(); ) {
435 Map.Entry<? extends K, ? extends V> e = i.next();
436 putForCreate(e.getKey(), e.getValue());
437 }
438 }
439
440 /**
441 * Rehashes the contents of this map into a new array with a
442 * larger capacity. This method is called automatically when the
443 * number of keys in this map reaches its threshold.
444 *
445 * If current capacity is MAXIMUM_CAPACITY, this method does not
446 * resize the map, but sets threshold to Integer.MAX_VALUE.
447 * This has the effect of preventing future calls.
448 *
449 * @param newCapacity the new capacity, MUST be a power of two;
450 * must be greater than current capacity unless current
451 * capacity is MAXIMUM_CAPACITY (in which case value
452 * is irrelevant).
453 */
454 void resize(int newCapacity) {
455 Entry[] oldTable = table;
456 int oldCapacity = oldTable.length;
457 if (oldCapacity == MAXIMUM_CAPACITY) {
458 threshold = Integer.MAX_VALUE;
459 return;
460 }
461
462 Entry[] newTable = new Entry[newCapacity];
463 transfer(newTable);
464 table = newTable;
465 threshold = (int)(newCapacity * loadFactor);
466 }
467
468 /**
469 * Transfers all entries from current table to newTable.
470 */
471 void transfer(Entry[] newTable) {
472 Entry[] src = table;
473 int newCapacity = newTable.length;
474 for (int j = 0; j < src.length; j++) {
475 Entry<K,V> e = src[j];
476 if (e != null) {
477 src[j] = null;
478 do {
479 Entry<K,V> next = e.next;
480 int i = indexFor(e.hash, newCapacity);
481 e.next = newTable[i];
482 newTable[i] = e;
483 e = next;
484 } while (e != null);
485 }
486 }
487 }
488
489 /**
490 * Copies all of the mappings from the specified map to this map.
491 * These mappings will replace any mappings that this map had for
492 * any of the keys currently in the specified map.
493 *
494 * @param m mappings to be stored in this map
495 * @throws NullPointerException if the specified map is null
496 */
497 public void putAll(Map<? extends K, ? extends V> m) {
498 int numKeysToBeAdded = m.size();
499 if (numKeysToBeAdded == 0)
500 return;
501
502 /*
503 * Expand the map if the map if the number of mappings to be added
504 * is greater than or equal to threshold. This is conservative; the
505 * obvious condition is (m.size() + size) >= threshold, but this
506 * condition could result in a map with twice the appropriate capacity,
507 * if the keys to be added overlap with the keys already in this map.
508 * By using the conservative calculation, we subject ourself
509 * to at most one extra resize.
510 */
511 if (numKeysToBeAdded > threshold) {
512 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
513 if (targetCapacity > MAXIMUM_CAPACITY)
514 targetCapacity = MAXIMUM_CAPACITY;
515 int newCapacity = table.length;
516 while (newCapacity < targetCapacity)
517 newCapacity <<= 1;
518 if (newCapacity > table.length)
519 resize(newCapacity);
520 }
521
522 for (Iterator<? extends Map.Entry<? extends K, ? extends V>> i = m.entrySet().iterator(); i.hasNext(); ) {
523 Map.Entry<? extends K, ? extends V> e = i.next();
524 put(e.getKey(), e.getValue());
525 }
526 }
527
528 /**
529 * Removes the mapping for the specified key from this map if present.
530 *
531 * @param key key whose mapping is to be removed from the map
532 * @return the previous value associated with <tt>key</tt>, or
533 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
534 * (A <tt>null</tt> return can also indicate that the map
535 * previously associated <tt>null</tt> with <tt>key</tt>.)
536 */
537 public V remove(Object key) {
538 Entry<K,V> e = removeEntryForKey(key);
539 return (e == null ? null : e.value);
540 }
541
542 /**
543 * Removes and returns the entry associated with the specified key
544 * in the HashMap. Returns null if the HashMap contains no mapping
545 * for this key.
546 */
547 final Entry<K,V> removeEntryForKey(Object key) {
548 int hash = (key == null) ? 0 : hash(key.hashCode());
549 int i = indexFor(hash, table.length);
550 Entry<K,V> prev = table[i];
551 Entry<K,V> e = prev;
552
553 while (e != null) {
554 Entry<K,V> next = e.next;
555 Object k;
556 if (e.hash == hash &&
557 ((k = e.key) == key || (key != null && key.equals(k)))) {
558 modCount++;
559 size--;
560 if (prev == e)
561 table[i] = next;
562 else
563 prev.next = next;
564 e.recordRemoval(this);
565 return e;
566 }
567 prev = e;
568 e = next;
569 }
570
571 return e;
572 }
573
574 /**
575 * Special version of remove for EntrySet.
576 */
577 final Entry<K,V> removeMapping(Object o) {
578 if (!(o instanceof Map.Entry))
579 return null;
580
581 Map.Entry<K,V> entry = (Map.Entry<K,V>) o;
582 Object key = entry.getKey();
583 int hash = (key == null) ? 0 : hash(key.hashCode());
584 int i = indexFor(hash, table.length);
585 Entry<K,V> prev = table[i];
586 Entry<K,V> e = prev;
587
588 while (e != null) {
589 Entry<K,V> next = e.next;
590 if (e.hash == hash && e.equals(entry)) {
591 modCount++;
592 size--;
593 if (prev == e)
594 table[i] = next;
595 else
596 prev.next = next;
597 e.recordRemoval(this);
598 return e;
599 }
600 prev = e;
601 e = next;
602 }
603
604 return e;
605 }
606
607 /**
608 * Removes all of the mappings from this map.
609 * The map will be empty after this call returns.
610 */
611 public void clear() {
612 modCount++;
613 Entry[] tab = table;
614 for (int i = 0; i < tab.length; i++)
615 tab[i] = null;
616 size = 0;
617 }
618
619 /**
620 * Returns <tt>true</tt> if this map maps one or more keys to the
621 * specified value.
622 *
623 * @param value value whose presence in this map is to be tested
624 * @return <tt>true</tt> if this map maps one or more keys to the
625 * specified value
626 */
627 public boolean containsValue(Object value) {
628 if (value == null)
629 return containsNullValue();
630
631 Entry[] tab = table;
632 for (int i = 0; i < tab.length ; i++)
633 for (Entry e = tab[i] ; e != null ; e = e.next)
634 if (value.equals(e.value))
635 return true;
636 return false;
637 }
638
639 /**
640 * Special-case code for containsValue with null argument
641 */
642 private boolean containsNullValue() {
643 Entry[] tab = table;
644 for (int i = 0; i < tab.length ; i++)
645 for (Entry e = tab[i] ; e != null ; e = e.next)
646 if (e.value == null)
647 return true;
648 return false;
649 }
650
651 /**
652 * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and
653 * values themselves are not cloned.
654 *
655 * @return a shallow copy of this map
656 */
657 public Object clone() {
658 HashMap<K,V> result = null;
659 try {
660 result = (HashMap<K,V>)super.clone();
661 } catch (CloneNotSupportedException e) {
662 // assert false;
663 }
664 result.table = new Entry[table.length];
665 result.entrySet = null;
666 result.modCount = 0;
667 result.size = 0;
668 result.init();
669 result.putAllForCreate(this);
670
671 return result;
672 }
673
674 static class Entry<K,V> implements Map.Entry<K,V> {
675 final K key;
676 V value;
677 Entry<K,V> next;
678 final int hash;
679
680 /**
681 * Creates new entry.
682 */
683 Entry(int h, K k, V v, Entry<K,V> n) {
684 value = v;
685 next = n;
686 key = k;
687 hash = h;
688 }
689
690 public final K getKey() {
691 return key;
692 }
693
694 public final V getValue() {
695 return value;
696 }
697
698 public final V setValue(V newValue) {
699 V oldValue = value;
700 value = newValue;
701 return oldValue;
702 }
703
704 public final boolean equals(Object o) {
705 if (!(o instanceof Map.Entry))
706 return false;
707 Map.Entry e = (Map.Entry)o;
708 Object k1 = getKey();
709 Object k2 = e.getKey();
710 if (k1 == k2 || (k1 != null && k1.equals(k2))) {
711 Object v1 = getValue();
712 Object v2 = e.getValue();
713 if (v1 == v2 || (v1 != null && v1.equals(v2)))
714 return true;
715 }
716 return false;
717 }
718
719 public final int hashCode() {
720 return (key==null ? 0 : key.hashCode()) ^
721 (value==null ? 0 : value.hashCode());
722 }
723
724 public final String toString() {
725 return getKey() + "=" + getValue();
726 }
727
728 /**
729 * This method is invoked whenever the value in an entry is
730 * overwritten by an invocation of put(k,v) for a key k that's already
731 * in the HashMap.
732 */
733 void recordAccess(HashMap<K,V> m) {
734 }
735
736 /**
737 * This method is invoked whenever the entry is
738 * removed from the table.
739 */
740 void recordRemoval(HashMap<K,V> m) {
741 }
742 }
743
744 /**
745 * Adds a new entry with the specified key, value and hash code to
746 * the specified bucket. It is the responsibility of this
747 * method to resize the table if appropriate.
748 *
749 * Subclass overrides this to alter the behavior of put method.
750 */
751 void addEntry(int hash, K key, V value, int bucketIndex) {
752 Entry<K,V> e = table[bucketIndex];
753 table[bucketIndex] = new Entry<K,V>(hash, key, value, e);
754 if (size++ >= threshold)
755 resize(2 * table.length);
756 }
757
758 /**
759 * Like addEntry except that this version is used when creating entries
760 * as part of Map construction or "pseudo-construction" (cloning,
761 * deserialization). This version needn't worry about resizing the table.
762 *
763 * Subclass overrides this to alter the behavior of HashMap(Map),
764 * clone, and readObject.
765 */
766 void createEntry(int hash, K key, V value, int bucketIndex) {
767 Entry<K,V> e = table[bucketIndex];
768 table[bucketIndex] = new Entry<K,V>(hash, key, value, e);
769 size++;
770 }
771
772 private abstract class HashIterator<E> implements Iterator<E> {
773 Entry<K,V> next; // next entry to return
774 int expectedModCount; // For fast-fail
775 int index; // current slot
776 Entry<K,V> current; // current entry
777
778 HashIterator() {
779 expectedModCount = modCount;
780 if (size > 0) { // advance to first entry
781 Entry[] t = table;
782 while (index < t.length && (next = t[index++]) == null)
783 ;
784 }
785 }
786
787 public final boolean hasNext() {
788 return next != null;
789 }
790
791 final Entry<K,V> nextEntry() {
792 if (modCount != expectedModCount)
793 throw new ConcurrentModificationException();
794 Entry<K,V> e = next;
795 if (e == null)
796 throw new NoSuchElementException();
797
798 if ((next = e.next) == null) {
799 Entry[] t = table;
800 while (index < t.length && (next = t[index++]) == null)
801 ;
802 }
803 current = e;
804 return e;
805 }
806
807 public void remove() {
808 if (current == null)
809 throw new IllegalStateException();
810 if (modCount != expectedModCount)
811 throw new ConcurrentModificationException();
812 Object k = current.key;
813 current = null;
814 HashMap.this.removeEntryForKey(k);
815 expectedModCount = modCount;
816 }
817
818 }
819
820 private final class ValueIterator extends HashIterator<V> {
821 public V next() {
822 return nextEntry().value;
823 }
824 }
825
826 private final class KeyIterator extends HashIterator<K> {
827 public K next() {
828 return nextEntry().getKey();
829 }
830 }
831
832 private final class EntryIterator extends HashIterator<Map.Entry<K,V>> {
833 public Map.Entry<K,V> next() {
834 return nextEntry();
835 }
836 }
837
838 // Subclass overrides these to alter behavior of views' iterator() method
839 Iterator<K> newKeyIterator() {
840 return new KeyIterator();
841 }
842 Iterator<V> newValueIterator() {
843 return new ValueIterator();
844 }
845 Iterator<Map.Entry<K,V>> newEntryIterator() {
846 return new EntryIterator();
847 }
848
849
850 // Views
851
852 private transient Set<Map.Entry<K,V>> entrySet = null;
853
854 /**
855 * Returns a {@link Set} view of the keys contained in this map.
856 * The set is backed by the map, so changes to the map are
857 * reflected in the set, and vice-versa. If the map is modified
858 * while an iteration over the set is in progress (except through
859 * the iterator's own <tt>remove</tt> operation), the results of
860 * the iteration are undefined. The set supports element removal,
861 * which removes the corresponding mapping from the map, via the
862 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
863 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
864 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
865 * operations.
866 */
867 public Set<K> keySet() {
868 Set<K> ks = keySet;
869 return (ks != null ? ks : (keySet = new KeySet()));
870 }
871
872 private final class KeySet extends AbstractSet<K> {
873 public Iterator<K> iterator() {
874 return newKeyIterator();
875 }
876 public int size() {
877 return size;
878 }
879 public boolean contains(Object o) {
880 return containsKey(o);
881 }
882 public boolean remove(Object o) {
883 return HashMap.this.removeEntryForKey(o) != null;
884 }
885 public void clear() {
886 HashMap.this.clear();
887 }
888 }
889
890 /**
891 * Returns a {@link Collection} view of the values contained in this map.
892 * The collection is backed by the map, so changes to the map are
893 * reflected in the collection, and vice-versa. If the map is
894 * modified while an iteration over the collection is in progress
895 * (except through the iterator's own <tt>remove</tt> operation),
896 * the results of the iteration are undefined. The collection
897 * supports element removal, which removes the corresponding
898 * mapping from the map, via the <tt>Iterator.remove</tt>,
899 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
900 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
901 * support the <tt>add</tt> or <tt>addAll</tt> operations.
902 */
903 public Collection<V> values() {
904 Collection<V> vs = values;
905 return (vs != null ? vs : (values = new Values()));
906 }
907
908 private final class Values extends AbstractCollection<V> {
909 public Iterator<V> iterator() {
910 return newValueIterator();
911 }
912 public int size() {
913 return size;
914 }
915 public boolean contains(Object o) {
916 return containsValue(o);
917 }
918 public void clear() {
919 HashMap.this.clear();
920 }
921 }
922
923 /**
924 * Returns a {@link Set} view of the mappings contained in this map.
925 * The set is backed by the map, so changes to the map are
926 * reflected in the set, and vice-versa. If the map is modified
927 * while an iteration over the set is in progress (except through
928 * the iterator's own <tt>remove</tt> operation, or through the
929 * <tt>setValue</tt> operation on a map entry returned by the
930 * iterator) the results of the iteration are undefined. The set
931 * supports element removal, which removes the corresponding
932 * mapping from the map, via the <tt>Iterator.remove</tt>,
933 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
934 * <tt>clear</tt> operations. It does not support the
935 * <tt>add</tt> or <tt>addAll</tt> operations.
936 *
937 * @return a set view of the mappings contained in this map
938 */
939 public Set<Map.Entry<K,V>> entrySet() {
940 return entrySet0();
941 }
942
943 private Set<Map.Entry<K,V>> entrySet0() {
944 Set<Map.Entry<K,V>> es = entrySet;
945 return es != null ? es : (entrySet = new EntrySet());
946 }
947
948 private final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
949 public Iterator<Map.Entry<K,V>> iterator() {
950 return newEntryIterator();
951 }
952 public boolean contains(Object o) {
953 if (!(o instanceof Map.Entry))
954 return false;
955 Map.Entry<K,V> e = (Map.Entry<K,V>) o;
956 Entry<K,V> candidate = getEntry(e.getKey());
957 return candidate != null && candidate.equals(e);
958 }
959 public boolean remove(Object o) {
960 return removeMapping(o) != null;
961 }
962 public int size() {
963 return size;
964 }
965 public void clear() {
966 HashMap.this.clear();
967 }
968 }
969
970 /**
971 * Save the state of the <tt>HashMap</tt> instance to a stream (i.e.,
972 * serialize it).
973 *
974 * @serialData The <i>capacity</i> of the HashMap (the length of the
975 * bucket array) is emitted (int), followed by the
976 * <i>size</i> (an int, the number of key-value
977 * mappings), followed by the key (Object) and value (Object)
978 * for each key-value mapping. The key-value mappings are
979 * emitted in no particular order.
980 */
981 private void writeObject(java.io.ObjectOutputStream s)
982 throws IOException
983 {
984 Iterator<Map.Entry<K,V>> i =
985 (size > 0) ? entrySet0().iterator() : null;
986
987 // Write out the threshold, loadfactor, and any hidden stuff
988 s.defaultWriteObject();
989
990 // Write out number of buckets
991 s.writeInt(table.length);
992
993 // Write out size (number of Mappings)
994 s.writeInt(size);
995
996 // Write out keys and values (alternating)
997 if (i != null) {
998 while (i.hasNext()) {
999 Map.Entry<K,V> e = i.next();
1000 s.writeObject(e.getKey());
1001 s.writeObject(e.getValue());
1002 }
1003 }
1004 }
1005
1006 private static final long serialVersionUID = 362498820763181265L;
1007
1008 /**
1009 * Reconstitute the <tt>HashMap</tt> instance from a stream (i.e.,
1010 * deserialize it).
1011 */
1012 private void readObject(java.io.ObjectInputStream s)
1013 throws IOException, ClassNotFoundException
1014 {
1015 // Read in the threshold, loadfactor, and any hidden stuff
1016 s.defaultReadObject();
1017
1018 // Read in number of buckets and allocate the bucket array;
1019 int numBuckets = s.readInt();
1020 table = new Entry[numBuckets];
1021
1022 init(); // Give subclass a chance to do its thing.
1023
1024 // Read in size (number of Mappings)
1025 int size = s.readInt();
1026
1027 // Read the keys and values, and put the mappings in the HashMap
1028 for (int i=0; i<size; i++) {
1029 K key = (K) s.readObject();
1030 V value = (V) s.readObject();
1031 putForCreate(key, value);
1032 }
1033 }
1034
1035 // These methods are used when serializing HashSets
1036 int capacity() { return table.length; }
1037 float loadFactor() { return loadFactor; }
1038}
1039