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 /**
188 * A random mask value that is used for hashcode values associated with this
189 * instance to make hash collisions harder to find.
190 */
191 transient final int hashMask = sun.misc.Hashing.makeHashMask(this);
192
193 @SuppressWarnings("unchecked")
194 private Entry<K,V>[] newTable(int n) {
195 return (Entry<K,V>[]) new Entry<?,?>[n];
196 }
197
198 /**
199 * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial
200 * capacity and the given load factor.
201 *
202 * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt>
203 * @param loadFactor The load factor of the <tt>WeakHashMap</tt>
204 * @throws IllegalArgumentException if the initial capacity is negative,
205 * or if the load factor is nonpositive.
206 */
207 public WeakHashMap(int initialCapacity, float loadFactor) {
208 if (initialCapacity < 0)
209 throw new IllegalArgumentException("Illegal Initial Capacity: "+
210 initialCapacity);
211 if (initialCapacity > MAXIMUM_CAPACITY)
212 initialCapacity = MAXIMUM_CAPACITY;
213
214 if (loadFactor <= 0 || Float.isNaN(loadFactor))
215 throw new IllegalArgumentException("Illegal Load factor: "+
216 loadFactor);
217 int capacity = 1;
218 while (capacity < initialCapacity)
219 capacity <<= 1;
220 table = newTable(capacity);
221 this.loadFactor = loadFactor;
222 threshold = (int)(capacity * loadFactor);
223 }
224
225 /**
226 * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial
227 * capacity and the default load factor (0.75).
228 *
229 * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt>
230 * @throws IllegalArgumentException if the initial capacity is negative
231 */
232 public WeakHashMap(int initialCapacity) {
233 this(initialCapacity, DEFAULT_LOAD_FACTOR);
234 }
235
236 /**
237 * Constructs a new, empty <tt>WeakHashMap</tt> with the default initial
238 * capacity (16) and load factor (0.75).
239 */
240 public WeakHashMap() {
241 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
242 }
243
244 /**
245 * Constructs a new <tt>WeakHashMap</tt> with the same mappings as the
246 * specified map. The <tt>WeakHashMap</tt> is created with the default
247 * load factor (0.75) and an initial capacity sufficient to hold the
248 * mappings in the specified map.
249 *
250 * @param m the map whose mappings are to be placed in this map
251 * @throws NullPointerException if the specified map is null
252 * @since 1.3
253 */
254 public WeakHashMap(Map<? extends K, ? extends V> m) {
255 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
256 DEFAULT_INITIAL_CAPACITY),
257 DEFAULT_LOAD_FACTOR);
258 putAll(m);
259 }
260
261 // internal utilities
262
263 /**
264 * Value representing null keys inside tables.
265 */
266 private static final Object NULL_KEY = new Object();
267
268 /**
269 * Use NULL_KEY for key if it is null.
270 */
271 private static Object maskNull(Object key) {
272 return (key == null) ? NULL_KEY : key;
273 }
274
275 /**
276 * Returns internal representation of null key back to caller as null.
277 */
278 static Object unmaskNull(Object key) {
279 return (key == NULL_KEY) ? null : key;
280 }
281
282 /**
283 * Checks for equality of non-null reference x and possibly-null y. By
284 * default uses Object.equals.
285 */
286 private static boolean eq(Object x, Object y) {
287 return x == y || x.equals(y);
288 }
289
290 /**
291 * Retrieve object hash code and applies a supplemental hash function to the
292 * result hash, which defends against poor quality hash functions. This is
293 * critical because HashMap uses power-of-two length hash tables, that
294 * otherwise encounter collisions for hashCodes that do not differ
295 * in lower bits. Note: Null keys always map to hash 0, thus index 0.
296 */
297 int hash(Object k) {
298 if (null == k) {
299 return 0;
300 }
301
302 int h = hashMask;
303 if (0 == hashMask) {
304 if (k instanceof Hashable32) {
305 h ^= ((Hashable32) k).hash32();
306 } else {
307 h ^= k.hashCode();
308 }
309 } else {
310 h = k.hashCode();
311 }
312
313 // This function ensures that hashCodes that differ only by
314 // constant multiples at each bit position have a bounded
315 // number of collisions (approximately 8 at default load factor).
316 h ^= (h >>> 20) ^ (h >>> 12);
317 h ^= (h >>> 7) ^ (h >>> 4);
318
319 return h;
320 }
321
322 /**
323 * Returns index for hash code h.
324 */
325 private static int indexFor(int h, int length) {
326 return h & (length-1);
327 }
328
329 /**
330 * Expunges stale entries from the table.
331 */
332 private void expungeStaleEntries() {
333 for (Object x; (x = queue.poll()) != null; ) {
334 synchronized (queue) {
335 @SuppressWarnings("unchecked")
336 Entry<K,V> e = (Entry<K,V>) x;
337 int i = indexFor(e.hash, table.length);
338
339 Entry<K,V> prev = table[i];
340 Entry<K,V> p = prev;
341 while (p != null) {
342 Entry<K,V> next = p.next;
343 if (p == e) {
344 if (prev == e)
345 table[i] = next;
346 else
347 prev.next = next;
348 // Must not null out e.next;
349 // stale entries may be in use by a HashIterator
350 e.value = null; // Help GC
351 size--;
352 break;
353 }
354 prev = p;
355 p = next;
356 }
357 }
358 }
359 }
360
361 /**
362 * Returns the table after first expunging stale entries.
363 */
364 private Entry<K,V>[] getTable() {
365 expungeStaleEntries();
366 return table;
367 }
368
369 /**
370 * Returns the number of key-value mappings in this map.
371 * This result is a snapshot, and may not reflect unprocessed
372 * entries that will be removed before next attempted access
373 * because they are no longer referenced.
374 */
375 public int size() {
376 if (size == 0)
377 return 0;
378 expungeStaleEntries();
379 return size;
380 }
381
382 /**
383 * Returns <tt>true</tt> if this map contains no key-value mappings.
384 * This result is a snapshot, and may not reflect unprocessed
385 * entries that will be removed before next attempted access
386 * because they are no longer referenced.
387 */
388 public boolean isEmpty() {
389 return size() == 0;
390 }
391
392 /**
393 * Returns the value to which the specified key is mapped,
394 * or {@code null} if this map contains no mapping for the key.
395 *
396 * <p>More formally, if this map contains a mapping from a key
397 * {@code k} to a value {@code v} such that {@code (key==null ? k==null :
398 * key.equals(k))}, then this method returns {@code v}; otherwise
399 * it returns {@code null}. (There can be at most one such mapping.)
400 *
401 * <p>A return value of {@code null} does not <i>necessarily</i>
402 * indicate that the map contains no mapping for the key; it's also
403 * possible that the map explicitly maps the key to {@code null}.
404 * The {@link #containsKey containsKey} operation may be used to
405 * distinguish these two cases.
406 *
407 * @see #put(Object, Object)
408 */
409 public V get(Object key) {
410 Object k = maskNull(key);
411 int h = hash(k);
412 Entry<K,V>[] tab = getTable();
413 int index = indexFor(h, tab.length);
414 Entry<K,V> e = tab[index];
415 while (e != null) {
416 if (e.hash == h && eq(k, e.get()))
417 return e.value;
418 e = e.next;
419 }
420 return null;
421 }
422
423 /**
424 * Returns <tt>true</tt> if this map contains a mapping for the
425 * specified key.
426 *
427 * @param key The key whose presence in this map is to be tested
428 * @return <tt>true</tt> if there is a mapping for <tt>key</tt>;
429 * <tt>false</tt> otherwise
430 */
431 public boolean containsKey(Object key) {
432 return getEntry(key) != null;
433 }
434
435 /**
436 * Returns the entry associated with the specified key in this map.
437 * Returns null if the map contains no mapping for this key.
438 */
439 Entry<K,V> getEntry(Object key) {
440 Object k = maskNull(key);
441 int h = hash(k);
442 Entry<K,V>[] tab = getTable();
443 int index = indexFor(h, tab.length);
444 Entry<K,V> e = tab[index];
445 while (e != null && !(e.hash == h && eq(k, e.get())))
446 e = e.next;
447 return e;
448 }
449
450 /**
451 * Associates the specified value with the specified key in this map.
452 * If the map previously contained a mapping for this key, the old
453 * value is replaced.
454 *
455 * @param key key with which the specified value is to be associated.
456 * @param value value to be associated with the specified key.
457 * @return the previous value associated with <tt>key</tt>, or
458 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
459 * (A <tt>null</tt> return can also indicate that the map
460 * previously associated <tt>null</tt> with <tt>key</tt>.)
461 */
462 public V put(K key, V value) {
463 Object k = maskNull(key);
464 int h = hash(k);
465 Entry<K,V>[] tab = getTable();
466 int i = indexFor(h, tab.length);
467
468 for (Entry<K,V> e = tab[i]; e != null; e = e.next) {
469 if (h == e.hash && eq(k, e.get())) {
470 V oldValue = e.value;
471 if (value != oldValue)
472 e.value = value;
473 return oldValue;
474 }
475 }
476
477 modCount++;
478 Entry<K,V> e = tab[i];
479 tab[i] = new Entry<>(k, value, queue, h, e);
480 if (++size >= threshold)
481 resize(tab.length * 2);
482 return null;
483 }
484
485 /**
486 * Rehashes the contents of this map into a new array with a
487 * larger capacity. This method is called automatically when the
488 * number of keys in this map reaches its threshold.
489 *
490 * If current capacity is MAXIMUM_CAPACITY, this method does not
491 * resize the map, but sets threshold to Integer.MAX_VALUE.
492 * This has the effect of preventing future calls.
493 *
494 * @param newCapacity the new capacity, MUST be a power of two;
495 * must be greater than current capacity unless current
496 * capacity is MAXIMUM_CAPACITY (in which case value
497 * is irrelevant).
498 */
499 void resize(int newCapacity) {
500 Entry<K,V>[] oldTable = getTable();
501 int oldCapacity = oldTable.length;
502 if (oldCapacity == MAXIMUM_CAPACITY) {
503 threshold = Integer.MAX_VALUE;
504 return;
505 }
506
507 Entry<K,V>[] newTable = newTable(newCapacity);
508 transfer(oldTable, newTable);
509 table = newTable;
510
511 /*
512 * If ignoring null elements and processing ref queue caused massive
513 * shrinkage, then restore old table. This should be rare, but avoids
514 * unbounded expansion of garbage-filled tables.
515 */
516 if (size >= threshold / 2) {
517 threshold = (int)(newCapacity * loadFactor);
518 } else {
519 expungeStaleEntries();
520 transfer(newTable, oldTable);
521 table = oldTable;
522 }
523 }
524
525 /** Transfers all entries from src to dest tables */
526 private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest) {
527 for (int j = 0; j < src.length; ++j) {
528 Entry<K,V> e = src[j];
529 src[j] = null;
530 while (e != null) {
531 Entry<K,V> next = e.next;
532 Object key = e.get();
533 if (key == null) {
534 e.next = null; // Help GC
535 e.value = null; // " "
536 size--;
537 } else {
538 int i = indexFor(e.hash, dest.length);
539 e.next = dest[i];
540 dest[i] = e;
541 }
542 e = next;
543 }
544 }
545 }
546
547 /**
548 * Copies all of the mappings from the specified map to this map.
549 * These mappings will replace any mappings that this map had for any
550 * of the keys currently in the specified map.
551 *
552 * @param m mappings to be stored in this map.
553 * @throws NullPointerException if the specified map is null.
554 */
555 public void putAll(Map<? extends K, ? extends V> m) {
556 int numKeysToBeAdded = m.size();
557 if (numKeysToBeAdded == 0)
558 return;
559
560 /*
561 * Expand the map if the map if the number of mappings to be added
562 * is greater than or equal to threshold. This is conservative; the
563 * obvious condition is (m.size() + size) >= threshold, but this
564 * condition could result in a map with twice the appropriate capacity,
565 * if the keys to be added overlap with the keys already in this map.
566 * By using the conservative calculation, we subject ourself
567 * to at most one extra resize.
568 */
569 if (numKeysToBeAdded > threshold) {
570 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
571 if (targetCapacity > MAXIMUM_CAPACITY)
572 targetCapacity = MAXIMUM_CAPACITY;
573 int newCapacity = table.length;
574 while (newCapacity < targetCapacity)
575 newCapacity <<= 1;
576 if (newCapacity > table.length)
577 resize(newCapacity);
578 }
579
580 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
581 put(e.getKey(), e.getValue());
582 }
583
584 /**
585 * Removes the mapping for a key from this weak hash map if it is present.
586 * More formally, if this map contains a mapping from key <tt>k</tt> to
587 * value <tt>v</tt> such that <code>(key==null ? k==null :
588 * key.equals(k))</code>, that mapping is removed. (The map can contain
589 * at most one such mapping.)
590 *
591 * <p>Returns the value to which this map previously associated the key,
592 * or <tt>null</tt> if the map contained no mapping for the key. A
593 * return value of <tt>null</tt> does not <i>necessarily</i> indicate
594 * that the map contained no mapping for the key; it's also possible
595 * that the map explicitly mapped the key to <tt>null</tt>.
596 *
597 * <p>The map will not contain a mapping for the specified key once the
598 * call returns.
599 *
600 * @param key key whose mapping is to be removed from the map
601 * @return the previous value associated with <tt>key</tt>, or
602 * <tt>null</tt> if there was no mapping for <tt>key</tt>
603 */
604 public V remove(Object key) {
605 Object k = maskNull(key);
606 int h = hash(k);
607 Entry<K,V>[] tab = getTable();
608 int i = indexFor(h, tab.length);
609 Entry<K,V> prev = tab[i];
610 Entry<K,V> e = prev;
611
612 while (e != null) {
613 Entry<K,V> next = e.next;
614 if (h == e.hash && eq(k, e.get())) {
615 modCount++;
616 size--;
617 if (prev == e)
618 tab[i] = next;
619 else
620 prev.next = next;
621 return e.value;
622 }
623 prev = e;
624 e = next;
625 }
626
627 return null;
628 }
629
630 /** Special version of remove needed by Entry set */
631 boolean removeMapping(Object o) {
632 if (!(o instanceof Map.Entry))
633 return false;
634 Entry<K,V>[] tab = getTable();
635 Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
636 Object k = maskNull(entry.getKey());
637 int h = hash(k);
638 int i = indexFor(h, tab.length);
639 Entry<K,V> prev = tab[i];
640 Entry<K,V> e = prev;
641
642 while (e != null) {
643 Entry<K,V> next = e.next;
644 if (h == e.hash && e.equals(entry)) {
645 modCount++;
646 size--;
647 if (prev == e)
648 tab[i] = next;
649 else
650 prev.next = next;
651 return true;
652 }
653 prev = e;
654 e = next;
655 }
656
657 return false;
658 }
659
660 /**
661 * Removes all of the mappings from this map.
662 * The map will be empty after this call returns.
663 */
664 public void clear() {
665 // clear out ref queue. We don't need to expunge entries
666 // since table is getting cleared.
667 while (queue.poll() != null)
668 ;
669
670 modCount++;
671 Arrays.fill(table, null);
672 size = 0;
673
674 // Allocation of array may have caused GC, which may have caused
675 // additional entries to go stale. Removing these entries from the
676 // reference queue will make them eligible for reclamation.
677 while (queue.poll() != null)
678 ;
679 }
680
681 /**
682 * Returns <tt>true</tt> if this map maps one or more keys to the
683 * specified value.
684 *
685 * @param value value whose presence in this map is to be tested
686 * @return <tt>true</tt> if this map maps one or more keys to the
687 * specified value
688 */
689 public boolean containsValue(Object value) {
690 if (value==null)
691 return containsNullValue();
692
693 Entry<K,V>[] tab = getTable();
694 for (int i = tab.length; i-- > 0;)
695 for (Entry<K,V> e = tab[i]; e != null; e = e.next)
696 if (value.equals(e.value))
697 return true;
698 return false;
699 }
700
701 /**
702 * Special-case code for containsValue with null argument
703 */
704 private boolean containsNullValue() {
705 Entry<K,V>[] tab = getTable();
706 for (int i = tab.length; i-- > 0;)
707 for (Entry<K,V> e = tab[i]; e != null; e = e.next)
708 if (e.value==null)
709 return true;
710 return false;
711 }
712
713 /**
714 * The entries in this hash table extend WeakReference, using its main ref
715 * field as the key.
716 */
717 private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> {
718 V value;
719 int hash;
720 Entry<K,V> next;
721
722 /**
723 * Creates new entry.
724 */
725 Entry(Object key, V value,
726 ReferenceQueue<Object> queue,
727 int hash, Entry<K,V> next) {
728 super(key, queue);
729 this.value = value;
730 this.hash = hash;
731 this.next = next;
732 }
733
734 @SuppressWarnings("unchecked")
735 public K getKey() {
736 return (K) WeakHashMap.unmaskNull(get());
737 }
738
739 public V getValue() {
740 return value;
741 }
742
743 public V setValue(V newValue) {
744 V oldValue = value;
745 value = newValue;
746 return oldValue;
747 }
748
749 public boolean equals(Object o) {
750 if (!(o instanceof Map.Entry))
751 return false;
752 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
753 K k1 = getKey();
754 Object k2 = e.getKey();
755 if (k1 == k2 || (k1 != null && k1.equals(k2))) {
756 V v1 = getValue();
757 Object v2 = e.getValue();
758 if (v1 == v2 || (v1 != null && v1.equals(v2)))
759 return true;
760 }
761 return false;
762 }
763
764 public int hashCode() {
765 K k = getKey();
766 V v = getValue();
767 return ((k==null ? 0 : k.hashCode()) ^
768 (v==null ? 0 : v.hashCode()));
769 }
770
771 public String toString() {
772 return getKey() + "=" + getValue();
773 }
774 }
775
776 private abstract class HashIterator<T> implements Iterator<T> {
777 private int index;
778 private Entry<K,V> entry = null;
779 private Entry<K,V> lastReturned = null;
780 private int expectedModCount = modCount;
781
782 /**
783 * Strong reference needed to avoid disappearance of key
784 * between hasNext and next
785 */
786 private Object nextKey = null;
787
788 /**
789 * Strong reference needed to avoid disappearance of key
790 * between nextEntry() and any use of the entry
791 */
792 private Object currentKey = null;
793
794 HashIterator() {
795 index = isEmpty() ? 0 : table.length;
796 }
797
798 public boolean hasNext() {
799 Entry<K,V>[] t = table;
800
801 while (nextKey == null) {
802 Entry<K,V> e = entry;
803 int i = index;
804 while (e == null && i > 0)
805 e = t[--i];
806 entry = e;
807 index = i;
808 if (e == null) {
809 currentKey = null;
810 return false;
811 }
812 nextKey = e.get(); // hold on to key in strong ref
813 if (nextKey == null)
814 entry = entry.next;
815 }
816 return true;
817 }
818
819 /** The common parts of next() across different types of iterators */
820 protected Entry<K,V> nextEntry() {
821 if (modCount != expectedModCount)
822 throw new ConcurrentModificationException();
823 if (nextKey == null && !hasNext())
824 throw new NoSuchElementException();
825
826 lastReturned = entry;
827 entry = entry.next;
828 currentKey = nextKey;
829 nextKey = null;
830 return lastReturned;
831 }
832
833 public void remove() {
834 if (lastReturned == null)
835 throw new IllegalStateException();
836 if (modCount != expectedModCount)
837 throw new ConcurrentModificationException();
838
839 WeakHashMap.this.remove(currentKey);
840 expectedModCount = modCount;
841 lastReturned = null;
842 currentKey = null;
843 }
844
845 }
846
847 private class ValueIterator extends HashIterator<V> {
848 public V next() {
849 return nextEntry().value;
850 }
851 }
852
853 private class KeyIterator extends HashIterator<K> {
854 public K next() {
855 return nextEntry().getKey();
856 }
857 }
858
859 private class EntryIterator extends HashIterator<Map.Entry<K,V>> {
860 public Map.Entry<K,V> next() {
861 return nextEntry();
862 }
863 }
864
865 // Views
866
867 private transient Set<Map.Entry<K,V>> entrySet = null;
868
869 /**
870 * Returns a {@link Set} view of the keys contained in this map.
871 * The set is backed by the map, so changes to the map are
872 * reflected in the set, and vice-versa. If the map is modified
873 * while an iteration over the set is in progress (except through
874 * the iterator's own <tt>remove</tt> operation), the results of
875 * the iteration are undefined. The set supports element removal,
876 * which removes the corresponding mapping from the map, via the
877 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
878 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
879 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
880 * operations.
881 */
882 public Set<K> keySet() {
883 Set<K> ks = keySet;
884 return (ks != null ? ks : (keySet = new KeySet()));
885 }
886
887 private class KeySet extends AbstractSet<K> {
888 public Iterator<K> iterator() {
889 return new KeyIterator();
890 }
891
892 public int size() {
893 return WeakHashMap.this.size();
894 }
895
896 public boolean contains(Object o) {
897 return containsKey(o);
898 }
899
900 public boolean remove(Object o) {
901 if (containsKey(o)) {
902 WeakHashMap.this.remove(o);
903 return true;
904 }
905 else
906 return false;
907 }
908
909 public void clear() {
910 WeakHashMap.this.clear();
911 }
912 }
913
914 /**
915 * Returns a {@link Collection} view of the values contained in this map.
916 * The collection is backed by the map, so changes to the map are
917 * reflected in the collection, and vice-versa. If the map is
918 * modified while an iteration over the collection is in progress
919 * (except through the iterator's own <tt>remove</tt> operation),
920 * the results of the iteration are undefined. The collection
921 * supports element removal, which removes the corresponding
922 * mapping from the map, via the <tt>Iterator.remove</tt>,
923 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
924 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
925 * support the <tt>add</tt> or <tt>addAll</tt> operations.
926 */
927 public Collection<V> values() {
928 Collection<V> vs = values;
929 return (vs != null) ? vs : (values = new Values());
930 }
931
932 private class Values extends AbstractCollection<V> {
933 public Iterator<V> iterator() {
934 return new ValueIterator();
935 }
936
937 public int size() {
938 return WeakHashMap.this.size();
939 }
940
941 public boolean contains(Object o) {
942 return containsValue(o);
943 }
944
945 public void clear() {
946 WeakHashMap.this.clear();
947 }
948 }
949
950 /**
951 * Returns a {@link Set} view of the mappings contained in this map.
952 * The set is backed by the map, so changes to the map are
953 * reflected in the set, and vice-versa. If the map is modified
954 * while an iteration over the set is in progress (except through
955 * the iterator's own <tt>remove</tt> operation, or through the
956 * <tt>setValue</tt> operation on a map entry returned by the
957 * iterator) the results of the iteration are undefined. The set
958 * supports element removal, which removes the corresponding
959 * mapping from the map, via the <tt>Iterator.remove</tt>,
960 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
961 * <tt>clear</tt> operations. It does not support the
962 * <tt>add</tt> or <tt>addAll</tt> operations.
963 */
964 public Set<Map.Entry<K,V>> entrySet() {
965 Set<Map.Entry<K,V>> es = entrySet;
966 return es != null ? es : (entrySet = new EntrySet());
967 }
968
969 private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
970 public Iterator<Map.Entry<K,V>> iterator() {
971 return new EntryIterator();
972 }
973
974 public boolean contains(Object o) {
975 if (!(o instanceof Map.Entry))
976 return false;
977 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
978 Entry<K,V> candidate = getEntry(e.getKey());
979 return candidate != null && candidate.equals(e);
980 }
981
982 public boolean remove(Object o) {
983 return removeMapping(o);
984 }
985
986 public int size() {
987 return WeakHashMap.this.size();
988 }
989
990 public void clear() {
991 WeakHashMap.this.clear();
992 }
993
994 private List<Map.Entry<K,V>> deepCopy() {
995 List<Map.Entry<K,V>> list = new ArrayList<>(size());
996 for (Map.Entry<K,V> e : this)
997 list.add(new AbstractMap.SimpleEntry<>(e));
998 return list;
999 }
1000
1001 public Object[] toArray() {
1002 return deepCopy().toArray();
1003 }
1004
1005 public <T> T[] toArray(T[] a) {
1006 return deepCopy().toArray(a);
1007 }
1008 }
1009 }