1 /*
2 * Copyright (c) 1998, 2010, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.util;
27 import java.lang.ref.WeakReference;
28 import java.lang.ref.ReferenceQueue;
29
30
31 /**
32 * Hash table based implementation of the <tt>Map</tt> interface, with
33 * <em>weak keys</em>.
34 * An entry in a <tt>WeakHashMap</tt> will automatically be removed when
35 * its key is no longer in ordinary use. More precisely, the presence of a
36 * mapping for a given key will not prevent the key from being discarded by the
37 * garbage collector, that is, made finalizable, finalized, and then reclaimed.
38 * When a key has been discarded its entry is effectively removed from the map,
39 * so this class behaves somewhat differently from other <tt>Map</tt>
40 * implementations.
41 *
42 * <p> Both null values and the null key are supported. This class has
43 * performance characteristics similar to those of the <tt>HashMap</tt>
44 * class, and has the same efficiency parameters of <em>initial capacity</em>
45 * and <em>load factor</em>.
46 *
47 * <p> Like most collection classes, this class is not synchronized.
48 * A synchronized <tt>WeakHashMap</tt> may be constructed using the
49 * {@link Collections#synchronizedMap Collections.synchronizedMap}
50 * method.
51 *
52 * <p> This class is intended primarily for use with key objects whose
53 * <tt>equals</tt> methods test for object identity using the
54 * <tt>==</tt> operator. Once such a key is discarded it can never be
55 * recreated, so it is impossible to do a lookup of that key in a
56 * <tt>WeakHashMap</tt> at some later time and be surprised that its entry
57 * has been removed. This class will work perfectly well with key objects
58 * whose <tt>equals</tt> methods are not based upon object identity, such
59 * as <tt>String</tt> instances. With such recreatable key objects,
60 * however, the automatic removal of <tt>WeakHashMap</tt> entries whose
61 * keys have been discarded may prove to be confusing.
62 *
63 * <p> The behavior of the <tt>WeakHashMap</tt> class depends in part upon
64 * the actions of the garbage collector, so several familiar (though not
65 * required) <tt>Map</tt> invariants do not hold for this class. Because
66 * the garbage collector may discard keys at any time, a
67 * <tt>WeakHashMap</tt> may behave as though an unknown thread is silently
68 * removing entries. In particular, even if you synchronize on a
69 * <tt>WeakHashMap</tt> instance and invoke none of its mutator methods, it
70 * is possible for the <tt>size</tt> method to return smaller values over
71 * time, for the <tt>isEmpty</tt> method to return <tt>false</tt> and
72 * then <tt>true</tt>, for the <tt>containsKey</tt> method to return
73 * <tt>true</tt> and later <tt>false</tt> for a given key, for the
74 * <tt>get</tt> method to return a value for a given key but later return
75 * <tt>null</tt>, for the <tt>put</tt> method to return
76 * <tt>null</tt> and the <tt>remove</tt> method to return
77 * <tt>false</tt> for a key that previously appeared to be in the map, and
78 * for successive examinations of the key set, the value collection, and
79 * the entry set to yield successively smaller numbers of elements.
80 *
81 * <p> Each key object in a <tt>WeakHashMap</tt> is stored indirectly as
82 * the referent of a weak reference. Therefore a key will automatically be
83 * removed only after the weak references to it, both inside and outside of the
84 * map, have been cleared by the garbage collector.
85 *
86 * <p> <strong>Implementation note:</strong> The value objects in a
87 * <tt>WeakHashMap</tt> are held by ordinary strong references. Thus care
88 * should be taken to ensure that value objects do not strongly refer to their
89 * own keys, either directly or indirectly, since that will prevent the keys
90 * from being discarded. Note that a value object may refer indirectly to its
91 * key via the <tt>WeakHashMap</tt> itself; that is, a value object may
92 * strongly refer to some other key object whose associated value object, in
93 * turn, strongly refers to the key of the first value object. One way
94 * to deal with this is to wrap values themselves within
95 * <tt>WeakReferences</tt> before
96 * inserting, as in: <tt>m.put(key, new WeakReference(value))</tt>,
97 * and then unwrapping upon each <tt>get</tt>.
98 *
99 * <p>The iterators returned by the <tt>iterator</tt> method of the collections
100 * returned by all of this class's "collection view methods" are
101 * <i>fail-fast</i>: if the map is structurally modified at any time after the
102 * iterator is created, in any way except through the iterator's own
103 * <tt>remove</tt> method, the iterator will throw a {@link
104 * ConcurrentModificationException}. Thus, in the face of concurrent
105 * modification, the iterator fails quickly and cleanly, rather than risking
106 * arbitrary, non-deterministic behavior at an undetermined time in the future.
107 *
108 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
109 * as it is, generally speaking, impossible to make any hard guarantees in the
110 * presence of unsynchronized concurrent modification. Fail-fast iterators
111 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
112 * Therefore, it would be wrong to write a program that depended on this
113 * exception for its correctness: <i>the fail-fast behavior of iterators
114 * should be used only to detect bugs.</i>
115 *
116 * <p>This class is a member of the
117 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
118 * Java Collections Framework</a>.
119 *
120 * @param <K> the type of keys maintained by this map
121 * @param <V> the type of mapped values
122 *
123 * @author Doug Lea
124 * @author Josh Bloch
125 * @author Mark Reinhold
126 * @since 1.2
127 * @see java.util.HashMap
128 * @see java.lang.ref.WeakReference
129 */
130 public class WeakHashMap<K,V>
131 extends AbstractMap<K,V>
132 implements Map<K,V> {
133
134 /**
135 * The default initial capacity -- MUST be a power of two.
136 */
137 private static final int DEFAULT_INITIAL_CAPACITY = 16;
138
139 /**
140 * The maximum capacity, used if a higher value is implicitly specified
141 * by either of the constructors with arguments.
142 * MUST be a power of two <= 1<<30.
143 */
144 private static final int MAXIMUM_CAPACITY = 1 << 30;
145
146 /**
147 * The load factor used when none specified in constructor.
148 */
149 private static final float DEFAULT_LOAD_FACTOR = 0.75f;
150
151 /**
152 * The table, resized as necessary. Length MUST Always be a power of two.
153 */
154 Entry<K,V>[] table;
155
156 /**
157 * The number of key-value mappings contained in this weak hash map.
158 */
159 private int size;
160
161 /**
162 * The next size value at which to resize (capacity * load factor).
163 */
164 private int threshold;
165
166 /**
167 * The load factor for the hash table.
168 */
169 private final float loadFactor;
170
171 /**
172 * Reference queue for cleared WeakEntries
173 */
174 private final ReferenceQueue<Object> queue = new ReferenceQueue<>();
175
176 /**
177 * The number of times this WeakHashMap has been structurally modified.
178 * Structural modifications are those that change the number of
179 * mappings in the map or otherwise modify its internal structure
180 * (e.g., rehash). This field is used to make iterators on
181 * Collection-views of the map fail-fast.
182 *
183 * @see ConcurrentModificationException
184 */
185 int modCount;
186
187 @SuppressWarnings("unchecked")
188 private Entry<K,V>[] newTable(int n) {
189 return (Entry<K,V>[]) new Entry[n];
190 }
191
192 /**
193 * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial
194 * capacity and the given load factor.
195 *
196 * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt>
197 * @param loadFactor The load factor of the <tt>WeakHashMap</tt>
198 * @throws IllegalArgumentException if the initial capacity is negative,
199 * or if the load factor is nonpositive.
200 */
201 public WeakHashMap(int initialCapacity, float loadFactor) {
202 if (initialCapacity < 0)
203 throw new IllegalArgumentException("Illegal Initial Capacity: "+
204 initialCapacity);
205 if (initialCapacity > MAXIMUM_CAPACITY)
206 initialCapacity = MAXIMUM_CAPACITY;
207
208 if (loadFactor <= 0 || Float.isNaN(loadFactor))
209 throw new IllegalArgumentException("Illegal Load factor: "+
210 loadFactor);
211 int capacity = 1;
212 while (capacity < initialCapacity)
213 capacity <<= 1;
214 table = newTable(capacity);
215 this.loadFactor = loadFactor;
216 threshold = (int)(capacity * loadFactor);
217 }
218
219 /**
220 * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial
221 * capacity and the default load factor (0.75).
222 *
223 * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt>
224 * @throws IllegalArgumentException if the initial capacity is negative
225 */
226 public WeakHashMap(int initialCapacity) {
227 this(initialCapacity, DEFAULT_LOAD_FACTOR);
228 }
229
230 /**
231 * Constructs a new, empty <tt>WeakHashMap</tt> with the default initial
232 * capacity (16) and load factor (0.75).
233 */
234 public WeakHashMap() {
235 this.loadFactor = DEFAULT_LOAD_FACTOR;
236 threshold = DEFAULT_INITIAL_CAPACITY;
237 table = newTable(DEFAULT_INITIAL_CAPACITY);
238 }
239
240 /**
241 * Constructs a new <tt>WeakHashMap</tt> with the same mappings as the
242 * specified map. The <tt>WeakHashMap</tt> is created with the default
243 * load factor (0.75) and an initial capacity sufficient to hold the
244 * mappings in the specified map.
245 *
246 * @param m the map whose mappings are to be placed in this map
247 * @throws NullPointerException if the specified map is null
248 * @since 1.3
249 */
250 public WeakHashMap(Map<? extends K, ? extends V> m) {
251 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, 16),
252 DEFAULT_LOAD_FACTOR);
253 putAll(m);
254 }
255
256 // internal utilities
257
258 /**
259 * Value representing null keys inside tables.
260 */
261 private static final Object NULL_KEY = new Object();
262
263 /**
264 * Use NULL_KEY for key if it is null.
265 */
266 private static Object maskNull(Object key) {
267 return (key == null) ? NULL_KEY : key;
268 }
269
270 /**
271 * Returns internal representation of null key back to caller as null.
272 */
273 static Object unmaskNull(Object key) {
274 return (key == NULL_KEY) ? null : key;
275 }
276
277 /**
278 * Checks for equality of non-null reference x and possibly-null y. By
279 * default uses Object.equals.
280 */
281 private static boolean eq(Object x, Object y) {
282 return x == y || x.equals(y);
283 }
284
285 /**
286 * Returns index for hash code h.
287 */
288 private static int indexFor(int h, int length) {
289 return h & (length-1);
290 }
291
292 /**
293 * Expunges stale entries from the table.
294 */
295 private void expungeStaleEntries() {
296 for (Object x; (x = queue.poll()) != null; ) {
297 synchronized (queue) {
298 @SuppressWarnings("unchecked")
299 Entry<K,V> e = (Entry<K,V>) x;
300 int i = indexFor(e.hash, table.length);
301
302 Entry<K,V> prev = table[i];
303 Entry<K,V> p = prev;
304 while (p != null) {
305 Entry<K,V> next = p.next;
306 if (p == e) {
307 if (prev == e)
308 table[i] = next;
309 else
310 prev.next = next;
311 // Must not null out e.next;
312 // stale entries may be in use by a HashIterator
313 e.value = null; // Help GC
314 size--;
315 break;
316 }
317 prev = p;
318 p = next;
319 }
320 }
321 }
322 }
323
324 /**
325 * Returns the table after first expunging stale entries.
326 */
327 private Entry<K,V>[] getTable() {
328 expungeStaleEntries();
329 return table;
330 }
331
332 /**
333 * Returns the number of key-value mappings in this map.
334 * This result is a snapshot, and may not reflect unprocessed
335 * entries that will be removed before next attempted access
336 * because they are no longer referenced.
337 */
338 public int size() {
339 if (size == 0)
340 return 0;
341 expungeStaleEntries();
342 return size;
343 }
344
345 /**
346 * Returns <tt>true</tt> if this map contains no key-value mappings.
347 * This result is a snapshot, and may not reflect unprocessed
348 * entries that will be removed before next attempted access
349 * because they are no longer referenced.
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 public V get(Object key) {
373 Object k = maskNull(key);
374 int h = HashMap.hash(k.hashCode());
375 Entry<K,V>[] tab = getTable();
376 int index = indexFor(h, tab.length);
377 Entry<K,V> e = tab[index];
378 while (e != null) {
379 if (e.hash == h && eq(k, e.get()))
380 return e.value;
381 e = e.next;
382 }
383 return null;
384 }
385
386 /**
387 * Returns <tt>true</tt> if this map contains a mapping for the
388 * specified key.
389 *
390 * @param key The key whose presence in this map is to be tested
391 * @return <tt>true</tt> if there is a mapping for <tt>key</tt>;
392 * <tt>false</tt> otherwise
393 */
394 public boolean containsKey(Object key) {
395 return getEntry(key) != null;
396 }
397
398 /**
399 * Returns the entry associated with the specified key in this map.
400 * Returns null if the map contains no mapping for this key.
401 */
402 Entry<K,V> getEntry(Object key) {
403 Object k = maskNull(key);
404 int h = HashMap.hash(k.hashCode());
405 Entry<K,V>[] tab = getTable();
406 int index = indexFor(h, tab.length);
407 Entry<K,V> e = tab[index];
408 while (e != null && !(e.hash == h && eq(k, e.get())))
409 e = e.next;
410 return e;
411 }
412
413 /**
414 * Associates the specified value with the specified key in this map.
415 * If the map previously contained a mapping for this key, the old
416 * value is replaced.
417 *
418 * @param key key with which the specified value is to be associated.
419 * @param value value to be associated with the specified key.
420 * @return the previous value associated with <tt>key</tt>, or
421 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
422 * (A <tt>null</tt> return can also indicate that the map
423 * previously associated <tt>null</tt> with <tt>key</tt>.)
424 */
425 public V put(K key, V value) {
426 Object k = maskNull(key);
427 int h = HashMap.hash(k.hashCode());
428 Entry<K,V>[] tab = getTable();
429 int i = indexFor(h, tab.length);
430
431 for (Entry<K,V> e = tab[i]; e != null; e = e.next) {
432 if (h == e.hash && eq(k, e.get())) {
433 V oldValue = e.value;
434 if (value != oldValue)
435 e.value = value;
436 return oldValue;
437 }
438 }
439
440 modCount++;
441 Entry<K,V> e = tab[i];
442 tab[i] = new Entry<>(k, value, queue, h, e);
443 if (++size >= threshold)
444 resize(tab.length * 2);
445 return null;
446 }
447
448 /**
449 * Rehashes the contents of this map into a new array with a
450 * larger capacity. This method is called automatically when the
451 * number of keys in this map reaches its threshold.
452 *
453 * If current capacity is MAXIMUM_CAPACITY, this method does not
454 * resize the map, but sets threshold to Integer.MAX_VALUE.
455 * This has the effect of preventing future calls.
456 *
457 * @param newCapacity the new capacity, MUST be a power of two;
458 * must be greater than current capacity unless current
459 * capacity is MAXIMUM_CAPACITY (in which case value
460 * is irrelevant).
461 */
462 void resize(int newCapacity) {
463 Entry<K,V>[] oldTable = getTable();
464 int oldCapacity = oldTable.length;
465 if (oldCapacity == MAXIMUM_CAPACITY) {
466 threshold = Integer.MAX_VALUE;
467 return;
468 }
469
470 Entry<K,V>[] newTable = newTable(newCapacity);
471 transfer(oldTable, newTable);
472 table = newTable;
473
474 /*
475 * If ignoring null elements and processing ref queue caused massive
476 * shrinkage, then restore old table. This should be rare, but avoids
477 * unbounded expansion of garbage-filled tables.
478 */
479 if (size >= threshold / 2) {
480 threshold = (int)(newCapacity * loadFactor);
481 } else {
482 expungeStaleEntries();
483 transfer(newTable, oldTable);
484 table = oldTable;
485 }
486 }
487
488 /** Transfers all entries from src to dest tables */
489 private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest) {
490 for (int j = 0; j < src.length; ++j) {
491 Entry<K,V> e = src[j];
492 src[j] = null;
493 while (e != null) {
494 Entry<K,V> next = e.next;
495 Object key = e.get();
496 if (key == null) {
497 e.next = null; // Help GC
498 e.value = null; // " "
499 size--;
500 } else {
501 int i = indexFor(e.hash, dest.length);
502 e.next = dest[i];
503 dest[i] = e;
504 }
505 e = next;
506 }
507 }
508 }
509
510 /**
511 * Copies all of the mappings from the specified map to this map.
512 * These mappings will replace any mappings that this map had for any
513 * of the keys currently in the specified map.
514 *
515 * @param m mappings to be stored in this map.
516 * @throws NullPointerException if the specified map is null.
517 */
518 public void putAll(Map<? extends K, ? extends V> m) {
519 int numKeysToBeAdded = m.size();
520 if (numKeysToBeAdded == 0)
521 return;
522
523 /*
524 * Expand the map if the map if the number of mappings to be added
525 * is greater than or equal to threshold. This is conservative; the
526 * obvious condition is (m.size() + size) >= threshold, but this
527 * condition could result in a map with twice the appropriate capacity,
528 * if the keys to be added overlap with the keys already in this map.
529 * By using the conservative calculation, we subject ourself
530 * to at most one extra resize.
531 */
532 if (numKeysToBeAdded > threshold) {
533 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
534 if (targetCapacity > MAXIMUM_CAPACITY)
535 targetCapacity = MAXIMUM_CAPACITY;
536 int newCapacity = table.length;
537 while (newCapacity < targetCapacity)
538 newCapacity <<= 1;
539 if (newCapacity > table.length)
540 resize(newCapacity);
541 }
542
543 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
544 put(e.getKey(), e.getValue());
545 }
546
547 /**
548 * Removes the mapping for a key from this weak hash map if it is present.
549 * More formally, if this map contains a mapping from key <tt>k</tt> to
550 * value <tt>v</tt> such that <code>(key==null ? k==null :
551 * key.equals(k))</code>, that mapping is removed. (The map can contain
552 * at most one such mapping.)
553 *
554 * <p>Returns the value to which this map previously associated the key,
555 * or <tt>null</tt> if the map contained no mapping for the key. A
556 * return value of <tt>null</tt> does not <i>necessarily</i> indicate
557 * that the map contained no mapping for the key; it's also possible
558 * that the map explicitly mapped the key to <tt>null</tt>.
559 *
560 * <p>The map will not contain a mapping for the specified key once the
561 * call returns.
562 *
563 * @param key key whose mapping is to be removed from the map
564 * @return the previous value associated with <tt>key</tt>, or
565 * <tt>null</tt> if there was no mapping for <tt>key</tt>
566 */
567 public V remove(Object key) {
568 Object k = maskNull(key);
569 int h = HashMap.hash(k.hashCode());
570 Entry<K,V>[] tab = getTable();
571 int i = indexFor(h, tab.length);
572 Entry<K,V> prev = tab[i];
573 Entry<K,V> e = prev;
574
575 while (e != null) {
576 Entry<K,V> next = e.next;
577 if (h == e.hash && eq(k, e.get())) {
578 modCount++;
579 size--;
580 if (prev == e)
581 tab[i] = next;
582 else
583 prev.next = next;
584 return e.value;
585 }
586 prev = e;
587 e = next;
588 }
589
590 return null;
591 }
592
593 /** Special version of remove needed by Entry set */
594 boolean removeMapping(Object o) {
595 if (!(o instanceof Map.Entry))
596 return false;
597 Entry<K,V>[] tab = getTable();
598 Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
599 Object k = maskNull(entry.getKey());
600 int h = HashMap.hash(k.hashCode());
601 int i = indexFor(h, tab.length);
602 Entry<K,V> prev = tab[i];
603 Entry<K,V> e = prev;
604
605 while (e != null) {
606 Entry<K,V> next = e.next;
607 if (h == e.hash && e.equals(entry)) {
608 modCount++;
609 size--;
610 if (prev == e)
611 tab[i] = next;
612 else
613 prev.next = next;
614 return true;
615 }
616 prev = e;
617 e = next;
618 }
619
620 return false;
621 }
622
623 /**
624 * Removes all of the mappings from this map.
625 * The map will be empty after this call returns.
626 */
627 public void clear() {
628 // clear out ref queue. We don't need to expunge entries
629 // since table is getting cleared.
630 while (queue.poll() != null)
631 ;
632
633 modCount++;
634 Arrays.fill(table, null);
635 size = 0;
636
637 // Allocation of array may have caused GC, which may have caused
638 // additional entries to go stale. Removing these entries from the
639 // reference queue will make them eligible for reclamation.
640 while (queue.poll() != null)
641 ;
642 }
643
644 /**
645 * Returns <tt>true</tt> if this map maps one or more keys to the
646 * specified value.
647 *
648 * @param value value whose presence in this map is to be tested
649 * @return <tt>true</tt> if this map maps one or more keys to the
650 * specified value
651 */
652 public boolean containsValue(Object value) {
653 if (value==null)
654 return containsNullValue();
655
656 Entry<K,V>[] tab = getTable();
657 for (int i = tab.length; i-- > 0;)
658 for (Entry<K,V> e = tab[i]; e != null; e = e.next)
659 if (value.equals(e.value))
660 return true;
661 return false;
662 }
663
664 /**
665 * Special-case code for containsValue with null argument
666 */
667 private boolean containsNullValue() {
668 Entry<K,V>[] tab = getTable();
669 for (int i = tab.length; i-- > 0;)
670 for (Entry<K,V> e = tab[i]; e != null; e = e.next)
671 if (e.value==null)
672 return true;
673 return false;
674 }
675
676 /**
677 * The entries in this hash table extend WeakReference, using its main ref
678 * field as the key.
679 */
680 private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> {
681 V value;
682 final int hash;
683 Entry<K,V> next;
684
685 /**
686 * Creates new entry.
687 */
688 Entry(Object key, V value,
689 ReferenceQueue<Object> queue,
690 int hash, Entry<K,V> next) {
691 super(key, queue);
692 this.value = value;
693 this.hash = hash;
694 this.next = next;
695 }
696
697 @SuppressWarnings("unchecked")
698 public K getKey() {
699 return (K) WeakHashMap.unmaskNull(get());
700 }
701
702 public V getValue() {
703 return value;
704 }
705
706 public V setValue(V newValue) {
707 V oldValue = value;
708 value = newValue;
709 return oldValue;
710 }
711
712 public boolean equals(Object o) {
713 if (!(o instanceof Map.Entry))
714 return false;
715 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
716 K k1 = getKey();
717 Object k2 = e.getKey();
718 if (k1 == k2 || (k1 != null && k1.equals(k2))) {
719 V v1 = getValue();
720 Object v2 = e.getValue();
721 if (v1 == v2 || (v1 != null && v1.equals(v2)))
722 return true;
723 }
724 return false;
725 }
726
727 public int hashCode() {
728 K k = getKey();
729 V v = getValue();
730 return ((k==null ? 0 : k.hashCode()) ^
731 (v==null ? 0 : v.hashCode()));
732 }
733
734 public String toString() {
735 return getKey() + "=" + getValue();
736 }
737 }
738
739 private abstract class HashIterator<T> implements Iterator<T> {
740 private int index;
741 private Entry<K,V> entry = null;
742 private Entry<K,V> lastReturned = null;
743 private int expectedModCount = modCount;
744
745 /**
746 * Strong reference needed to avoid disappearance of key
747 * between hasNext and next
748 */
749 private Object nextKey = null;
750
751 /**
752 * Strong reference needed to avoid disappearance of key
753 * between nextEntry() and any use of the entry
754 */
755 private Object currentKey = null;
756
757 HashIterator() {
758 index = isEmpty() ? 0 : table.length;
759 }
760
761 public boolean hasNext() {
762 Entry<K,V>[] t = table;
763
764 while (nextKey == null) {
765 Entry<K,V> e = entry;
766 int i = index;
767 while (e == null && i > 0)
768 e = t[--i];
769 entry = e;
770 index = i;
771 if (e == null) {
772 currentKey = null;
773 return false;
774 }
775 nextKey = e.get(); // hold on to key in strong ref
776 if (nextKey == null)
777 entry = entry.next;
778 }
779 return true;
780 }
781
782 /** The common parts of next() across different types of iterators */
783 protected Entry<K,V> nextEntry() {
784 if (modCount != expectedModCount)
785 throw new ConcurrentModificationException();
786 if (nextKey == null && !hasNext())
787 throw new NoSuchElementException();
788
789 lastReturned = entry;
790 entry = entry.next;
791 currentKey = nextKey;
792 nextKey = null;
793 return lastReturned;
794 }
795
796 public void remove() {
797 if (lastReturned == null)
798 throw new IllegalStateException();
799 if (modCount != expectedModCount)
800 throw new ConcurrentModificationException();
801
802 WeakHashMap.this.remove(currentKey);
803 expectedModCount = modCount;
804 lastReturned = null;
805 currentKey = null;
806 }
807
808 }
809
810 private class ValueIterator extends HashIterator<V> {
811 public V next() {
812 return nextEntry().value;
813 }
814 }
815
816 private class KeyIterator extends HashIterator<K> {
817 public K next() {
818 return nextEntry().getKey();
819 }
820 }
821
822 private class EntryIterator extends HashIterator<Map.Entry<K,V>> {
823 public Map.Entry<K,V> next() {
824 return nextEntry();
825 }
826 }
827
828 // Views
829
830 private transient Set<Map.Entry<K,V>> entrySet = null;
831
832 /**
833 * Returns a {@link Set} view of the keys contained in this map.
834 * The set is backed by the map, so changes to the map are
835 * reflected in the set, and vice-versa. If the map is modified
836 * while an iteration over the set is in progress (except through
837 * the iterator's own <tt>remove</tt> operation), the results of
838 * the iteration are undefined. The set supports element removal,
839 * which removes the corresponding mapping from the map, via the
840 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
841 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
842 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
843 * operations.
844 */
845 public Set<K> keySet() {
846 Set<K> ks = keySet;
847 return (ks != null ? ks : (keySet = new KeySet()));
848 }
849
850 private class KeySet extends AbstractSet<K> {
851 public Iterator<K> iterator() {
852 return new KeyIterator();
853 }
854
855 public int size() {
856 return WeakHashMap.this.size();
857 }
858
859 public boolean contains(Object o) {
860 return containsKey(o);
861 }
862
863 public boolean remove(Object o) {
864 if (containsKey(o)) {
865 WeakHashMap.this.remove(o);
866 return true;
867 }
868 else
869 return false;
870 }
871
872 public void clear() {
873 WeakHashMap.this.clear();
874 }
875 }
876
877 /**
878 * Returns a {@link Collection} view of the values contained in this map.
879 * The collection is backed by the map, so changes to the map are
880 * reflected in the collection, and vice-versa. If the map is
881 * modified while an iteration over the collection is in progress
882 * (except through the iterator's own <tt>remove</tt> operation),
883 * the results of the iteration are undefined. The collection
884 * supports element removal, which removes the corresponding
885 * mapping from the map, via the <tt>Iterator.remove</tt>,
886 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
887 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
888 * support the <tt>add</tt> or <tt>addAll</tt> operations.
889 */
890 public Collection<V> values() {
891 Collection<V> vs = values;
892 return (vs != null) ? vs : (values = new Values());
893 }
894
895 private class Values extends AbstractCollection<V> {
896 public Iterator<V> iterator() {
897 return new ValueIterator();
898 }
899
900 public int size() {
901 return WeakHashMap.this.size();
902 }
903
904 public boolean contains(Object o) {
905 return containsValue(o);
906 }
907
908 public void clear() {
909 WeakHashMap.this.clear();
910 }
911 }
912
913 /**
914 * Returns a {@link Set} view of the mappings contained in this map.
915 * The set is backed by the map, so changes to the map are
916 * reflected in the set, and vice-versa. If the map is modified
917 * while an iteration over the set is in progress (except through
918 * the iterator's own <tt>remove</tt> operation, or through the
919 * <tt>setValue</tt> operation on a map entry returned by the
920 * iterator) the results of the iteration are undefined. The set
921 * supports element removal, which removes the corresponding
922 * mapping from the map, via the <tt>Iterator.remove</tt>,
923 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
924 * <tt>clear</tt> operations. It does not support the
925 * <tt>add</tt> or <tt>addAll</tt> operations.
926 */
927 public Set<Map.Entry<K,V>> entrySet() {
928 Set<Map.Entry<K,V>> es = entrySet;
929 return es != null ? es : (entrySet = new EntrySet());
930 }
931
932 private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
933 public Iterator<Map.Entry<K,V>> iterator() {
934 return new EntryIterator();
935 }
936
937 public boolean contains(Object o) {
938 if (!(o instanceof Map.Entry))
939 return false;
940 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
941 Entry<K,V> candidate = getEntry(e.getKey());
942 return candidate != null && candidate.equals(e);
943 }
944
945 public boolean remove(Object o) {
946 return removeMapping(o);
947 }
948
949 public int size() {
950 return WeakHashMap.this.size();
951 }
952
953 public void clear() {
954 WeakHashMap.this.clear();
955 }
956
957 private List<Map.Entry<K,V>> deepCopy() {
958 List<Map.Entry<K,V>> list = new ArrayList<>(size());
959 for (Map.Entry<K,V> e : this)
960 list.add(new AbstractMap.SimpleEntry<>(e));
961 return list;
962 }
963
964 public Object[] toArray() {
965 return deepCopy().toArray();
966 }
967
968 public <T> T[] toArray(T[] a) {
969 return deepCopy().toArray(a);
970 }
971 }
972 }