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>. However, as the use of
98 * <tt>WeakReference</tt> in this manner will not prevent value objects
99 * from being GC'd, this approach is only useful when entries in the map
100 * are not relied upon for keeping the underlying value objects "live".
101 *
102 * <p>The iterators returned by the <tt>iterator</tt> method of the collections
103 * returned by all of this class's "collection view methods" are
104 * <i>fail-fast</i>: if the map is structurally modified at any time after the
105 * iterator is created, in any way except through the iterator's own
106 * <tt>remove</tt> method, the iterator will throw a {@link
107 * ConcurrentModificationException}. Thus, in the face of concurrent
108 * modification, the iterator fails quickly and cleanly, rather than risking
109 * arbitrary, non-deterministic behavior at an undetermined time in the future.
110 *
111 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
112 * as it is, generally speaking, impossible to make any hard guarantees in the
113 * presence of unsynchronized concurrent modification. Fail-fast iterators
114 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
115 * Therefore, it would be wrong to write a program that depended on this
116 * exception for its correctness: <i>the fail-fast behavior of iterators
117 * should be used only to detect bugs.</i>
118 *
119 * <p>This class is a member of the
120 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
121 * Java Collections Framework</a>.
122 *
123 * @param <K> the type of keys maintained by this map
124 * @param <V> the type of mapped values
125 *
126 * @author Doug Lea
127 * @author Josh Bloch
128 * @author Mark Reinhold
129 * @since 1.2
130 * @see java.util.HashMap
131 * @see java.lang.ref.WeakReference
132 */
133 public class WeakHashMap<K,V>
134 extends AbstractMap<K,V>
135 implements Map<K,V> {
136
137 /**
138 * The default initial capacity -- MUST be a power of two.
139 */
140 private static final int DEFAULT_INITIAL_CAPACITY = 16;
141
142 /**
143 * The maximum capacity, used if a higher value is implicitly specified
144 * by either of the constructors with arguments.
145 * MUST be a power of two <= 1<<30.
146 */
147 private static final int MAXIMUM_CAPACITY = 1 << 30;
148
149 /**
150 * The load factor used when none specified in constructor.
151 */
152 private static final float DEFAULT_LOAD_FACTOR = 0.75f;
153
154 /**
155 * The table, resized as necessary. Length MUST Always be a power of two.
156 */
157 Entry<K,V>[] table;
158
159 /**
160 * The number of key-value mappings contained in this weak hash map.
161 */
162 private int size;
163
164 /**
165 * The next size value at which to resize (capacity * load factor).
166 */
167 private int threshold;
168
169 /**
170 * The load factor for the hash table.
171 */
172 private final float loadFactor;
173
174 /**
175 * Reference queue for cleared WeakEntries
176 */
177 private final ReferenceQueue<Object> queue = new ReferenceQueue<>();
178
179 /**
180 * The number of times this WeakHashMap has been structurally modified.
181 * Structural modifications are those that change the number of
182 * mappings in the map or otherwise modify its internal structure
183 * (e.g., rehash). This field is used to make iterators on
184 * Collection-views of the map fail-fast.
185 *
186 * @see ConcurrentModificationException
187 */
188 int modCount;
189
190 @SuppressWarnings("unchecked")
191 private Entry<K,V>[] newTable(int n) {
192 return (Entry<K,V>[]) new Entry<?,?>[n];
193 }
194
195 /**
196 * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial
197 * capacity and the given load factor.
198 *
199 * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt>
200 * @param loadFactor The load factor of the <tt>WeakHashMap</tt>
201 * @throws IllegalArgumentException if the initial capacity is negative,
202 * or if the load factor is nonpositive.
203 */
204 public WeakHashMap(int initialCapacity, float loadFactor) {
205 if (initialCapacity < 0)
206 throw new IllegalArgumentException("Illegal Initial Capacity: "+
207 initialCapacity);
208 if (initialCapacity > MAXIMUM_CAPACITY)
209 initialCapacity = MAXIMUM_CAPACITY;
210
211 if (loadFactor <= 0 || Float.isNaN(loadFactor))
212 throw new IllegalArgumentException("Illegal Load factor: "+
213 loadFactor);
214 int capacity = 1;
215 while (capacity < initialCapacity)
216 capacity <<= 1;
217 table = newTable(capacity);
218 this.loadFactor = loadFactor;
219 threshold = (int)(capacity * loadFactor);
220 }
221
222 /**
223 * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial
224 * capacity and the default load factor (0.75).
225 *
226 * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt>
227 * @throws IllegalArgumentException if the initial capacity is negative
228 */
229 public WeakHashMap(int initialCapacity) {
230 this(initialCapacity, DEFAULT_LOAD_FACTOR);
231 }
232
233 /**
234 * Constructs a new, empty <tt>WeakHashMap</tt> with the default initial
235 * capacity (16) and load factor (0.75).
236 */
237 public WeakHashMap() {
238 this.loadFactor = DEFAULT_LOAD_FACTOR;
239 threshold = DEFAULT_INITIAL_CAPACITY;
240 table = newTable(DEFAULT_INITIAL_CAPACITY);
241 }
242
243 /**
244 * Constructs a new <tt>WeakHashMap</tt> with the same mappings as the
245 * specified map. The <tt>WeakHashMap</tt> is created with the default
246 * load factor (0.75) and an initial capacity sufficient to hold the
247 * mappings in the specified map.
248 *
249 * @param m the map whose mappings are to be placed in this map
250 * @throws NullPointerException if the specified map is null
251 * @since 1.3
252 */
253 public WeakHashMap(Map<? extends K, ? extends V> m) {
254 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, 16),
255 DEFAULT_LOAD_FACTOR);
256 putAll(m);
257 }
258
259 // internal utilities
260
261 /**
262 * Value representing null keys inside tables.
263 */
264 private static final Object NULL_KEY = new Object();
265
266 /**
267 * Use NULL_KEY for key if it is null.
268 */
269 private static Object maskNull(Object key) {
270 return (key == null) ? NULL_KEY : key;
271 }
272
273 /**
274 * Returns internal representation of null key back to caller as null.
275 */
276 static Object unmaskNull(Object key) {
277 return (key == NULL_KEY) ? null : key;
278 }
279
280 /**
281 * Checks for equality of non-null reference x and possibly-null y. By
282 * default uses Object.equals.
283 */
284 private static boolean eq(Object x, Object y) {
285 return x == y || x.equals(y);
286 }
287
288 /**
289 * Returns index for hash code h.
290 */
291 private static int indexFor(int h, int length) {
292 return h & (length-1);
293 }
294
295 /**
296 * Expunges stale entries from the table.
297 */
298 private void expungeStaleEntries() {
299 for (Object x; (x = queue.poll()) != null; ) {
300 synchronized (queue) {
301 @SuppressWarnings("unchecked")
302 Entry<K,V> e = (Entry<K,V>) x;
303 int i = indexFor(e.hash, table.length);
304
305 Entry<K,V> prev = table[i];
306 Entry<K,V> p = prev;
307 while (p != null) {
308 Entry<K,V> next = p.next;
309 if (p == e) {
310 if (prev == e)
311 table[i] = next;
312 else
313 prev.next = next;
314 // Must not null out e.next;
315 // stale entries may be in use by a HashIterator
316 e.value = null; // Help GC
317 size--;
318 break;
319 }
320 prev = p;
321 p = next;
322 }
323 }
324 }
325 }
326
327 /**
328 * Returns the table after first expunging stale entries.
329 */
330 private Entry<K,V>[] getTable() {
331 expungeStaleEntries();
332 return table;
333 }
334
335 /**
336 * Returns the number of key-value mappings in this map.
337 * This result is a snapshot, and may not reflect unprocessed
338 * entries that will be removed before next attempted access
339 * because they are no longer referenced.
340 */
341 public int size() {
342 if (size == 0)
343 return 0;
344 expungeStaleEntries();
345 return size;
346 }
347
348 /**
349 * Returns <tt>true</tt> if this map contains no key-value mappings.
350 * This result is a snapshot, and may not reflect unprocessed
351 * entries that will be removed before next attempted access
352 * because they are no longer referenced.
353 */
354 public boolean isEmpty() {
355 return size() == 0;
356 }
357
358 /**
359 * Returns the value to which the specified key is mapped,
360 * or {@code null} if this map contains no mapping for the key.
361 *
362 * <p>More formally, if this map contains a mapping from a key
363 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
364 * key.equals(k))}, then this method returns {@code v}; otherwise
365 * it returns {@code null}. (There can be at most one such mapping.)
366 *
367 * <p>A return value of {@code null} does not <i>necessarily</i>
368 * indicate that the map contains no mapping for the key; it's also
369 * possible that the map explicitly maps the key to {@code null}.
370 * The {@link #containsKey containsKey} operation may be used to
371 * distinguish these two cases.
372 *
373 * @see #put(Object, Object)
374 */
375 public V get(Object key) {
376 Object k = maskNull(key);
377 int h = HashMap.hash(k.hashCode());
378 Entry<K,V>[] tab = getTable();
379 int index = indexFor(h, tab.length);
380 Entry<K,V> e = tab[index];
381 while (e != null) {
382 if (e.hash == h && eq(k, e.get()))
383 return e.value;
384 e = e.next;
385 }
386 return null;
387 }
388
389 /**
390 * Returns <tt>true</tt> if this map contains a mapping for the
391 * specified key.
392 *
393 * @param key The key whose presence in this map is to be tested
394 * @return <tt>true</tt> if there is a mapping for <tt>key</tt>;
395 * <tt>false</tt> otherwise
396 */
397 public boolean containsKey(Object key) {
398 return getEntry(key) != null;
399 }
400
401 /**
402 * Returns the entry associated with the specified key in this map.
403 * Returns null if the map contains no mapping for this key.
404 */
405 Entry<K,V> getEntry(Object key) {
406 Object k = maskNull(key);
407 int h = HashMap.hash(k.hashCode());
408 Entry<K,V>[] tab = getTable();
409 int index = indexFor(h, tab.length);
410 Entry<K,V> e = tab[index];
411 while (e != null && !(e.hash == h && eq(k, e.get())))
412 e = e.next;
413 return e;
414 }
415
416 /**
417 * Associates the specified value with the specified key in this map.
418 * If the map previously contained a mapping for this key, the old
419 * value is replaced.
420 *
421 * @param key key with which the specified value is to be associated.
422 * @param value value to be associated with the specified key.
423 * @return the previous value associated with <tt>key</tt>, or
424 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
425 * (A <tt>null</tt> return can also indicate that the map
426 * previously associated <tt>null</tt> with <tt>key</tt>.)
427 */
428 public V put(K key, V value) {
429 Object k = maskNull(key);
430 int h = HashMap.hash(k.hashCode());
431 Entry<K,V>[] tab = getTable();
432 int i = indexFor(h, tab.length);
433
434 for (Entry<K,V> e = tab[i]; e != null; e = e.next) {
435 if (h == e.hash && eq(k, e.get())) {
436 V oldValue = e.value;
437 if (value != oldValue)
438 e.value = value;
439 return oldValue;
440 }
441 }
442
443 modCount++;
444 Entry<K,V> e = tab[i];
445 tab[i] = new Entry<>(k, value, queue, h, e);
446 if (++size >= threshold)
447 resize(tab.length * 2);
448 return null;
449 }
450
451 /**
452 * Rehashes the contents of this map into a new array with a
453 * larger capacity. This method is called automatically when the
454 * number of keys in this map reaches its threshold.
455 *
456 * If current capacity is MAXIMUM_CAPACITY, this method does not
457 * resize the map, but sets threshold to Integer.MAX_VALUE.
458 * This has the effect of preventing future calls.
459 *
460 * @param newCapacity the new capacity, MUST be a power of two;
461 * must be greater than current capacity unless current
462 * capacity is MAXIMUM_CAPACITY (in which case value
463 * is irrelevant).
464 */
465 void resize(int newCapacity) {
466 Entry<K,V>[] oldTable = getTable();
467 int oldCapacity = oldTable.length;
468 if (oldCapacity == MAXIMUM_CAPACITY) {
469 threshold = Integer.MAX_VALUE;
470 return;
471 }
472
473 Entry<K,V>[] newTable = newTable(newCapacity);
474 transfer(oldTable, newTable);
475 table = newTable;
476
477 /*
478 * If ignoring null elements and processing ref queue caused massive
479 * shrinkage, then restore old table. This should be rare, but avoids
480 * unbounded expansion of garbage-filled tables.
481 */
482 if (size >= threshold / 2) {
483 threshold = (int)(newCapacity * loadFactor);
484 } else {
485 expungeStaleEntries();
486 transfer(newTable, oldTable);
487 table = oldTable;
488 }
489 }
490
491 /** Transfers all entries from src to dest tables */
492 private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest) {
493 for (int j = 0; j < src.length; ++j) {
494 Entry<K,V> e = src[j];
495 src[j] = null;
496 while (e != null) {
497 Entry<K,V> next = e.next;
498 Object key = e.get();
499 if (key == null) {
500 e.next = null; // Help GC
501 e.value = null; // " "
502 size--;
503 } else {
504 int i = indexFor(e.hash, dest.length);
505 e.next = dest[i];
506 dest[i] = e;
507 }
508 e = next;
509 }
510 }
511 }
512
513 /**
514 * Copies all of the mappings from the specified map to this map.
515 * These mappings will replace any mappings that this map had for any
516 * of the keys currently in the specified map.
517 *
518 * @param m mappings to be stored in this map.
519 * @throws NullPointerException if the specified map is null.
520 */
521 public void putAll(Map<? extends K, ? extends V> m) {
522 int numKeysToBeAdded = m.size();
523 if (numKeysToBeAdded == 0)
524 return;
525
526 /*
527 * Expand the map if the map if the number of mappings to be added
528 * is greater than or equal to threshold. This is conservative; the
529 * obvious condition is (m.size() + size) >= threshold, but this
530 * condition could result in a map with twice the appropriate capacity,
531 * if the keys to be added overlap with the keys already in this map.
532 * By using the conservative calculation, we subject ourself
533 * to at most one extra resize.
534 */
535 if (numKeysToBeAdded > threshold) {
536 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
537 if (targetCapacity > MAXIMUM_CAPACITY)
538 targetCapacity = MAXIMUM_CAPACITY;
539 int newCapacity = table.length;
540 while (newCapacity < targetCapacity)
541 newCapacity <<= 1;
542 if (newCapacity > table.length)
543 resize(newCapacity);
544 }
545
546 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
547 put(e.getKey(), e.getValue());
548 }
549
550 /**
551 * Removes the mapping for a key from this weak hash map if it is present.
552 * More formally, if this map contains a mapping from key <tt>k</tt> to
553 * value <tt>v</tt> such that <code>(key==null ? k==null :
554 * key.equals(k))</code>, that mapping is removed. (The map can contain
555 * at most one such mapping.)
556 *
557 * <p>Returns the value to which this map previously associated the key,
558 * or <tt>null</tt> if the map contained no mapping for the key. A
559 * return value of <tt>null</tt> does not <i>necessarily</i> indicate
560 * that the map contained no mapping for the key; it's also possible
561 * that the map explicitly mapped the key to <tt>null</tt>.
562 *
563 * <p>The map will not contain a mapping for the specified key once the
564 * call returns.
565 *
566 * @param key key whose mapping is to be removed from the map
567 * @return the previous value associated with <tt>key</tt>, or
568 * <tt>null</tt> if there was no mapping for <tt>key</tt>
569 */
570 public V remove(Object key) {
571 Object k = maskNull(key);
572 int h = HashMap.hash(k.hashCode());
573 Entry<K,V>[] tab = getTable();
574 int i = indexFor(h, tab.length);
575 Entry<K,V> prev = tab[i];
576 Entry<K,V> e = prev;
577
578 while (e != null) {
579 Entry<K,V> next = e.next;
580 if (h == e.hash && eq(k, e.get())) {
581 modCount++;
582 size--;
583 if (prev == e)
584 tab[i] = next;
585 else
586 prev.next = next;
587 return e.value;
588 }
589 prev = e;
590 e = next;
591 }
592
593 return null;
594 }
595
596 /** Special version of remove needed by Entry set */
597 boolean removeMapping(Object o) {
598 if (!(o instanceof Map.Entry))
599 return false;
600 Entry<K,V>[] tab = getTable();
601 Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
602 Object k = maskNull(entry.getKey());
603 int h = HashMap.hash(k.hashCode());
604 int i = indexFor(h, tab.length);
605 Entry<K,V> prev = tab[i];
606 Entry<K,V> e = prev;
607
608 while (e != null) {
609 Entry<K,V> next = e.next;
610 if (h == e.hash && e.equals(entry)) {
611 modCount++;
612 size--;
613 if (prev == e)
614 tab[i] = next;
615 else
616 prev.next = next;
617 return true;
618 }
619 prev = e;
620 e = next;
621 }
622
623 return false;
624 }
625
626 /**
627 * Removes all of the mappings from this map.
628 * The map will be empty after this call returns.
629 */
630 public void clear() {
631 // clear out ref queue. We don't need to expunge entries
632 // since table is getting cleared.
633 while (queue.poll() != null)
634 ;
635
636 modCount++;
637 Arrays.fill(table, null);
638 size = 0;
639
640 // Allocation of array may have caused GC, which may have caused
641 // additional entries to go stale. Removing these entries from the
642 // reference queue will make them eligible for reclamation.
643 while (queue.poll() != null)
644 ;
645 }
646
647 /**
648 * Returns <tt>true</tt> if this map maps one or more keys to the
649 * specified value.
650 *
651 * @param value value whose presence in this map is to be tested
652 * @return <tt>true</tt> if this map maps one or more keys to the
653 * specified value
654 */
655 public boolean containsValue(Object value) {
656 if (value==null)
657 return containsNullValue();
658
659 Entry<K,V>[] tab = getTable();
660 for (int i = tab.length; i-- > 0;)
661 for (Entry<K,V> e = tab[i]; e != null; e = e.next)
662 if (value.equals(e.value))
663 return true;
664 return false;
665 }
666
667 /**
668 * Special-case code for containsValue with null argument
669 */
670 private boolean containsNullValue() {
671 Entry<K,V>[] tab = getTable();
672 for (int i = tab.length; i-- > 0;)
673 for (Entry<K,V> e = tab[i]; e != null; e = e.next)
674 if (e.value==null)
675 return true;
676 return false;
677 }
678
679 /**
680 * The entries in this hash table extend WeakReference, using its main ref
681 * field as the key.
682 */
683 private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> {
684 V value;
685 final int hash;
686 Entry<K,V> next;
687
688 /**
689 * Creates new entry.
690 */
691 Entry(Object key, V value,
692 ReferenceQueue<Object> queue,
693 int hash, Entry<K,V> next) {
694 super(key, queue);
695 this.value = value;
696 this.hash = hash;
697 this.next = next;
698 }
699
700 @SuppressWarnings("unchecked")
701 public K getKey() {
702 return (K) WeakHashMap.unmaskNull(get());
703 }
704
705 public V getValue() {
706 return value;
707 }
708
709 public V setValue(V newValue) {
710 V oldValue = value;
711 value = newValue;
712 return oldValue;
713 }
714
715 public boolean equals(Object o) {
716 if (!(o instanceof Map.Entry))
717 return false;
718 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
719 K k1 = getKey();
720 Object k2 = e.getKey();
721 if (k1 == k2 || (k1 != null && k1.equals(k2))) {
722 V v1 = getValue();
723 Object v2 = e.getValue();
724 if (v1 == v2 || (v1 != null && v1.equals(v2)))
725 return true;
726 }
727 return false;
728 }
729
730 public int hashCode() {
731 K k = getKey();
732 V v = getValue();
733 return ((k==null ? 0 : k.hashCode()) ^
734 (v==null ? 0 : v.hashCode()));
735 }
736
737 public String toString() {
738 return getKey() + "=" + getValue();
739 }
740 }
741
742 private abstract class HashIterator<T> implements Iterator<T> {
743 private int index;
744 private Entry<K,V> entry = null;
745 private Entry<K,V> lastReturned = null;
746 private int expectedModCount = modCount;
747
748 /**
749 * Strong reference needed to avoid disappearance of key
750 * between hasNext and next
751 */
752 private Object nextKey = null;
753
754 /**
755 * Strong reference needed to avoid disappearance of key
756 * between nextEntry() and any use of the entry
757 */
758 private Object currentKey = null;
759
760 HashIterator() {
761 index = isEmpty() ? 0 : table.length;
762 }
763
764 public boolean hasNext() {
765 Entry<K,V>[] t = table;
766
767 while (nextKey == null) {
768 Entry<K,V> e = entry;
769 int i = index;
770 while (e == null && i > 0)
771 e = t[--i];
772 entry = e;
773 index = i;
774 if (e == null) {
775 currentKey = null;
776 return false;
777 }
778 nextKey = e.get(); // hold on to key in strong ref
779 if (nextKey == null)
780 entry = entry.next;
781 }
782 return true;
783 }
784
785 /** The common parts of next() across different types of iterators */
786 protected Entry<K,V> nextEntry() {
787 if (modCount != expectedModCount)
788 throw new ConcurrentModificationException();
789 if (nextKey == null && !hasNext())
790 throw new NoSuchElementException();
791
792 lastReturned = entry;
793 entry = entry.next;
794 currentKey = nextKey;
795 nextKey = null;
796 return lastReturned;
797 }
798
799 public void remove() {
800 if (lastReturned == null)
801 throw new IllegalStateException();
802 if (modCount != expectedModCount)
803 throw new ConcurrentModificationException();
804
805 WeakHashMap.this.remove(currentKey);
806 expectedModCount = modCount;
807 lastReturned = null;
808 currentKey = null;
809 }
810
811 }
812
813 private class ValueIterator extends HashIterator<V> {
814 public V next() {
815 return nextEntry().value;
816 }
817 }
818
819 private class KeyIterator extends HashIterator<K> {
820 public K next() {
821 return nextEntry().getKey();
822 }
823 }
824
825 private class EntryIterator extends HashIterator<Map.Entry<K,V>> {
826 public Map.Entry<K,V> next() {
827 return nextEntry();
828 }
829 }
830
831 // Views
832
833 private transient Set<Map.Entry<K,V>> entrySet = null;
834
835 /**
836 * Returns a {@link Set} view of the keys contained in this map.
837 * The set is backed by the map, so changes to the map are
838 * reflected in the set, and vice-versa. If the map is modified
839 * while an iteration over the set is in progress (except through
840 * the iterator's own <tt>remove</tt> operation), the results of
841 * the iteration are undefined. The set supports element removal,
842 * which removes the corresponding mapping from the map, via the
843 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
844 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
845 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
846 * operations.
847 */
848 public Set<K> keySet() {
849 Set<K> ks = keySet;
850 return (ks != null ? ks : (keySet = new KeySet()));
851 }
852
853 private class KeySet extends AbstractSet<K> {
854 public Iterator<K> iterator() {
855 return new KeyIterator();
856 }
857
858 public int size() {
859 return WeakHashMap.this.size();
860 }
861
862 public boolean contains(Object o) {
863 return containsKey(o);
864 }
865
866 public boolean remove(Object o) {
867 if (containsKey(o)) {
868 WeakHashMap.this.remove(o);
869 return true;
870 }
871 else
872 return false;
873 }
874
875 public void clear() {
876 WeakHashMap.this.clear();
877 }
878 }
879
880 /**
881 * Returns a {@link Collection} view of the values contained in this map.
882 * The collection is backed by the map, so changes to the map are
883 * reflected in the collection, and vice-versa. If the map is
884 * modified while an iteration over the collection is in progress
885 * (except through the iterator's own <tt>remove</tt> operation),
886 * the results of the iteration are undefined. The collection
887 * supports element removal, which removes the corresponding
888 * mapping from the map, via the <tt>Iterator.remove</tt>,
889 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
890 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
891 * support the <tt>add</tt> or <tt>addAll</tt> operations.
892 */
893 public Collection<V> values() {
894 Collection<V> vs = values;
895 return (vs != null) ? vs : (values = new Values());
896 }
897
898 private class Values extends AbstractCollection<V> {
899 public Iterator<V> iterator() {
900 return new ValueIterator();
901 }
902
903 public int size() {
904 return WeakHashMap.this.size();
905 }
906
907 public boolean contains(Object o) {
908 return containsValue(o);
909 }
910
911 public void clear() {
912 WeakHashMap.this.clear();
913 }
914 }
915
916 /**
917 * Returns a {@link Set} view of the mappings contained in this map.
918 * The set is backed by the map, so changes to the map are
919 * reflected in the set, and vice-versa. If the map is modified
920 * while an iteration over the set is in progress (except through
921 * the iterator's own <tt>remove</tt> operation, or through the
922 * <tt>setValue</tt> operation on a map entry returned by the
923 * iterator) the results of the iteration are undefined. The set
924 * supports element removal, which removes the corresponding
925 * mapping from the map, via the <tt>Iterator.remove</tt>,
926 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
927 * <tt>clear</tt> operations. It does not support the
928 * <tt>add</tt> or <tt>addAll</tt> operations.
929 */
930 public Set<Map.Entry<K,V>> entrySet() {
931 Set<Map.Entry<K,V>> es = entrySet;
932 return es != null ? es : (entrySet = new EntrySet());
933 }
934
935 private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
936 public Iterator<Map.Entry<K,V>> iterator() {
937 return new EntryIterator();
938 }
939
940 public boolean contains(Object o) {
941 if (!(o instanceof Map.Entry))
942 return false;
943 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
944 Entry<K,V> candidate = getEntry(e.getKey());
945 return candidate != null && candidate.equals(e);
946 }
947
948 public boolean remove(Object o) {
949 return removeMapping(o);
950 }
951
952 public int size() {
953 return WeakHashMap.this.size();
954 }
955
956 public void clear() {
957 WeakHashMap.this.clear();
958 }
959
960 private List<Map.Entry<K,V>> deepCopy() {
961 List<Map.Entry<K,V>> list = new ArrayList<>(size());
962 for (Map.Entry<K,V> e : this)
963 list.add(new AbstractMap.SimpleEntry<>(e));
964 return list;
965 }
966
967 public Object[] toArray() {
968 return deepCopy().toArray();
969 }
970
971 public <T> T[] toArray(T[] a) {
972 return deepCopy().toArray(a);
973 }
974 }
975 }