1 /* 2 * Copyright (c) 1998, 2022, 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 28 import java.lang.ref.WeakReference; 29 import java.lang.ref.ReferenceQueue; 30 import java.util.function.BiConsumer; 31 import java.util.function.BiFunction; 32 import java.util.function.Consumer; 33 34 35 /** 36 * Hash table based implementation of the {@code Map} interface, with 37 * <em>weak keys</em>. 38 * An entry in a {@code WeakHashMap} will automatically be removed when 39 * its key is no longer in ordinary use. More precisely, the presence of a 40 * mapping for a given key will not prevent the key from being discarded by the 41 * garbage collector, that is, made finalizable, finalized, and then reclaimed. 42 * When a key has been discarded its entry is effectively removed from the map, 43 * so this class behaves somewhat differently from other {@code Map} 44 * implementations. 45 * 46 * <p> Both null values and the null key are supported. This class has 47 * performance characteristics similar to those of the {@code HashMap} 48 * class, and has the same efficiency parameters of <em>initial capacity</em> 49 * and <em>load factor</em>. 50 * 51 * <p> Like most collection classes, this class is not synchronized. 52 * A synchronized {@code WeakHashMap} may be constructed using the 53 * {@link Collections#synchronizedMap Collections.synchronizedMap} 54 * method. 55 * 56 * <p> This class is intended primarily for use with key objects whose 57 * {@code equals} methods test for object identity using the 58 * {@code ==} operator. Once such a key is discarded it can never be 59 * recreated, so it is impossible to do a lookup of that key in a 60 * {@code WeakHashMap} at some later time and be surprised that its entry 61 * has been removed. This class will work perfectly well with key objects 62 * whose {@code equals} methods are not based upon object identity, such 63 * as {@code String} instances. With such recreatable key objects, 64 * however, the automatic removal of {@code WeakHashMap} entries whose 65 * keys have been discarded may prove to be confusing. 66 * 67 * <p> The behavior of the {@code WeakHashMap} class depends in part upon 68 * the actions of the garbage collector, so several familiar (though not 69 * required) {@code Map} invariants do not hold for this class. Because 70 * the garbage collector may discard keys at any time, a 71 * {@code WeakHashMap} may behave as though an unknown thread is silently 72 * removing entries. In particular, even if you synchronize on a 73 * {@code WeakHashMap} instance and invoke none of its mutator methods, it 74 * is possible for the {@code size} method to return smaller values over 75 * time, for the {@code isEmpty} method to return {@code false} and 76 * then {@code true}, for the {@code containsKey} method to return 77 * {@code true} and later {@code false} for a given key, for the 78 * {@code get} method to return a value for a given key but later return 79 * {@code null}, for the {@code put} method to return 80 * {@code null} and the {@code remove} method to return 81 * {@code false} for a key that previously appeared to be in the map, and 82 * for successive examinations of the key set, the value collection, and 83 * the entry set to yield successively smaller numbers of elements. 84 * 85 * <p> Each key object in a {@code WeakHashMap} is stored indirectly as 86 * the referent of a weak reference. Therefore a key will automatically be 87 * removed only after the weak references to it, both inside and outside of the 88 * map, have been cleared by the garbage collector. 89 * 90 * <p> <strong>Implementation note:</strong> The value objects in a 91 * {@code WeakHashMap} are held by ordinary strong references. Thus care 92 * should be taken to ensure that value objects do not strongly refer to their 93 * own keys, either directly or indirectly, since that will prevent the keys 94 * from being discarded. Note that a value object may refer indirectly to its 95 * key via the {@code WeakHashMap} itself; that is, a value object may 96 * strongly refer to some other key object whose associated value object, in 97 * turn, strongly refers to the key of the first value object. If the values 98 * in the map do not rely on the map holding strong references to them, one way 99 * to deal with this is to wrap values themselves within 100 * {@code WeakReferences} before 101 * inserting, as in: {@code m.put(key, new WeakReference(value))}, 102 * and then unwrapping upon each {@code get}. 103 * 104 * <p>The iterators returned by the {@code iterator} method of the collections 105 * returned by all of this class's "collection view methods" are 106 * <i>fail-fast</i>: if the map is structurally modified at any time after the 107 * iterator is created, in any way except through the iterator's own 108 * {@code remove} method, the iterator will throw a {@link 109 * ConcurrentModificationException}. Thus, in the face of concurrent 110 * modification, the iterator fails quickly and cleanly, rather than risking 111 * arbitrary, non-deterministic behavior at an undetermined time in the future. 112 * 113 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed 114 * as it is, generally speaking, impossible to make any hard guarantees in the 115 * presence of unsynchronized concurrent modification. Fail-fast iterators 116 * throw {@code ConcurrentModificationException} on a best-effort basis. 117 * Therefore, it would be wrong to write a program that depended on this 118 * exception for its correctness: <i>the fail-fast behavior of iterators 119 * should be used only to detect bugs.</i> 120 * 121 * <p>This class is a member of the 122 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> 123 * Java Collections Framework</a>. 124 * 125 * @param <K> the type of keys maintained by this map 126 * @param <V> the type of mapped values 127 * 128 * @author Doug Lea 129 * @author Josh Bloch 130 * @author Mark Reinhold 131 * @since 1.2 132 * @see java.util.HashMap 133 * @see java.lang.ref.WeakReference 134 */ 135 public class WeakHashMap<K,V> 136 extends AbstractMap<K,V> 137 implements Map<K,V> { 138 139 /** 140 * The default initial capacity -- MUST be a power of two. 141 */ 142 private static final int DEFAULT_INITIAL_CAPACITY = 16; 143 144 /** 145 * The maximum capacity, used if a higher value is implicitly specified 146 * by either of the constructors with arguments. 147 * MUST be a power of two <= 1<<30. 148 */ 149 private static final int MAXIMUM_CAPACITY = 1 << 30; 150 151 /** 152 * The load factor used when none specified in constructor. 153 */ 154 private static final float DEFAULT_LOAD_FACTOR = 0.75f; 155 156 /** 157 * The table, resized as necessary. Length MUST Always be a power of two. 158 */ 159 Entry<K,V>[] table; 160 161 /** 162 * The number of key-value mappings contained in this weak hash map. 163 */ 164 private int size; 165 166 /** 167 * The next size value at which to resize (capacity * load factor). 168 */ 169 private int threshold; 170 171 /** 172 * The load factor for the hash table. 173 */ 174 private final float loadFactor; 175 176 /** 177 * Reference queue for cleared WeakEntries 178 */ 179 private final ReferenceQueue<Object> queue = new ReferenceQueue<>(); 180 181 /** 182 * The number of times this WeakHashMap has been structurally modified. 183 * Structural modifications are those that change the number of 184 * mappings in the map or otherwise modify its internal structure 185 * (e.g., rehash). This field is used to make iterators on 186 * Collection-views of the map fail-fast. 187 * 188 * @see ConcurrentModificationException 189 */ 190 int modCount; 191 192 @SuppressWarnings("unchecked") newTable(int n)193 private Entry<K,V>[] newTable(int n) { 194 return (Entry<K,V>[]) new Entry<?,?>[n]; 195 } 196 197 /** 198 * Constructs a new, empty {@code WeakHashMap} with the given initial 199 * capacity and the given load factor. 200 * 201 * @apiNote 202 * To create a {@code WeakHashMap} with an initial capacity that accommodates 203 * an expected number of mappings, use {@link #newWeakHashMap(int) newWeakHashMap}. 204 * 205 * @param initialCapacity The initial capacity of the {@code WeakHashMap} 206 * @param loadFactor The load factor of the {@code WeakHashMap} 207 * @throws IllegalArgumentException if the initial capacity is negative, 208 * or if the load factor is nonpositive. 209 */ WeakHashMap(int initialCapacity, float loadFactor)210 public WeakHashMap(int initialCapacity, float loadFactor) { 211 if (initialCapacity < 0) 212 throw new IllegalArgumentException("Illegal Initial Capacity: "+ 213 initialCapacity); 214 if (initialCapacity > MAXIMUM_CAPACITY) 215 initialCapacity = MAXIMUM_CAPACITY; 216 217 if (loadFactor <= 0 || Float.isNaN(loadFactor)) 218 throw new IllegalArgumentException("Illegal Load factor: "+ 219 loadFactor); 220 int capacity = HashMap.tableSizeFor(initialCapacity); 221 table = newTable(capacity); 222 this.loadFactor = loadFactor; 223 threshold = (int)(capacity * loadFactor); 224 } 225 226 /** 227 * Constructs a new, empty {@code WeakHashMap} with the given initial 228 * capacity and the default load factor (0.75). 229 * 230 * @apiNote 231 * To create a {@code WeakHashMap} with an initial capacity that accommodates 232 * an expected number of mappings, use {@link #newWeakHashMap(int) newWeakHashMap}. 233 * 234 * @param initialCapacity The initial capacity of the {@code WeakHashMap} 235 * @throws IllegalArgumentException if the initial capacity is negative 236 */ WeakHashMap(int initialCapacity)237 public WeakHashMap(int initialCapacity) { 238 this(initialCapacity, DEFAULT_LOAD_FACTOR); 239 } 240 241 /** 242 * Constructs a new, empty {@code WeakHashMap} with the default initial 243 * capacity (16) and load factor (0.75). 244 */ WeakHashMap()245 public WeakHashMap() { 246 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR); 247 } 248 249 /** 250 * Constructs a new {@code WeakHashMap} with the same mappings as the 251 * specified map. The {@code WeakHashMap} is created with the default 252 * load factor (0.75) and an initial capacity sufficient to hold the 253 * mappings in the specified map. 254 * 255 * @param m the map whose mappings are to be placed in this map 256 * @throws NullPointerException if the specified map is null 257 * @since 1.3 258 */ WeakHashMap(Map<? extends K, ? extends V> m)259 public WeakHashMap(Map<? extends K, ? extends V> m) { 260 this(Math.max((int) Math.ceil(m.size() / (double)DEFAULT_LOAD_FACTOR), 261 DEFAULT_INITIAL_CAPACITY), 262 DEFAULT_LOAD_FACTOR); 263 putAll(m); 264 } 265 266 // internal utilities 267 268 /** 269 * Value representing null keys inside tables. 270 */ 271 private static final Object NULL_KEY = new Object(); 272 273 /** 274 * Use NULL_KEY for key if it is null. 275 */ maskNull(Object key)276 private static Object maskNull(Object key) { 277 return (key == null) ? NULL_KEY : key; 278 } 279 280 /** 281 * Returns internal representation of null key back to caller as null. 282 */ unmaskNull(Object key)283 static Object unmaskNull(Object key) { 284 return (key == NULL_KEY) ? null : key; 285 } 286 287 /** 288 * Checks for equality of non-null reference x and possibly-null y. By 289 * default uses Object.equals. 290 */ matchesKey(Entry<K,V> e, Object key)291 private boolean matchesKey(Entry<K,V> e, Object key) { 292 // check if the given entry refers to the given key without 293 // keeping a strong reference to the entry's referent 294 if (e.refersTo(key)) return true; 295 296 // then check for equality if the referent is not cleared 297 Object k = e.get(); 298 return k != null && key.equals(k); 299 } 300 301 /** 302 * Retrieve object hash code and applies a supplemental hash function to the 303 * result hash, which defends against poor quality hash functions. This is 304 * critical because HashMap uses power-of-two length hash tables, that 305 * otherwise encounter collisions for hashCodes that do not differ 306 * in lower bits. 307 */ hash(Object k)308 final int hash(Object k) { 309 int h = k.hashCode(); 310 311 // This function ensures that hashCodes that differ only by 312 // constant multiples at each bit position have a bounded 313 // number of collisions (approximately 8 at default load factor). 314 h ^= (h >>> 20) ^ (h >>> 12); 315 return h ^ (h >>> 7) ^ (h >>> 4); 316 } 317 318 /** 319 * Returns index for hash code h. 320 */ indexFor(int h, int length)321 private static int indexFor(int h, int length) { 322 return h & (length-1); 323 } 324 325 /** 326 * Expunges stale entries from the table. 327 */ expungeStaleEntries()328 private void expungeStaleEntries() { 329 for (Object x; (x = queue.poll()) != null; ) { 330 synchronized (queue) { 331 @SuppressWarnings("unchecked") 332 Entry<K,V> e = (Entry<K,V>) x; 333 int i = indexFor(e.hash, table.length); 334 335 Entry<K,V> prev = table[i]; 336 Entry<K,V> p = prev; 337 while (p != null) { 338 Entry<K,V> next = p.next; 339 if (p == e) { 340 if (prev == e) 341 table[i] = next; 342 else 343 prev.next = next; 344 // Must not null out e.next; 345 // stale entries may be in use by a HashIterator 346 e.value = null; // Help GC 347 size--; 348 break; 349 } 350 prev = p; 351 p = next; 352 } 353 } 354 } 355 } 356 357 /** 358 * Returns the table after first expunging stale entries. 359 */ getTable()360 private Entry<K,V>[] getTable() { 361 expungeStaleEntries(); 362 return table; 363 } 364 365 /** 366 * Returns the number of key-value mappings in this map. 367 * This result is a snapshot, and may not reflect unprocessed 368 * entries that will be removed before next attempted access 369 * because they are no longer referenced. 370 */ size()371 public int size() { 372 if (size == 0) 373 return 0; 374 expungeStaleEntries(); 375 return size; 376 } 377 378 /** 379 * Returns {@code true} if this map contains no key-value mappings. 380 * This result is a snapshot, and may not reflect unprocessed 381 * entries that will be removed before next attempted access 382 * because they are no longer referenced. 383 */ isEmpty()384 public boolean isEmpty() { 385 return size() == 0; 386 } 387 388 /** 389 * Returns the value to which the specified key is mapped, 390 * or {@code null} if this map contains no mapping for the key. 391 * 392 * <p>More formally, if this map contains a mapping from a key 393 * {@code k} to a value {@code v} such that 394 * {@code Objects.equals(key, k)}, 395 * then this method returns {@code v}; otherwise 396 * it returns {@code null}. (There can be at most one such mapping.) 397 * 398 * <p>A return value of {@code null} does not <i>necessarily</i> 399 * indicate that the map contains no mapping for the key; it's also 400 * possible that the map explicitly maps the key to {@code null}. 401 * The {@link #containsKey containsKey} operation may be used to 402 * distinguish these two cases. 403 * 404 * @see #put(Object, Object) 405 */ get(Object key)406 public V get(Object key) { 407 Object k = maskNull(key); 408 int h = hash(k); 409 Entry<K,V>[] tab = getTable(); 410 int index = indexFor(h, tab.length); 411 Entry<K,V> e = tab[index]; 412 while (e != null) { 413 if (e.hash == h && matchesKey(e, k)) 414 return e.value; 415 e = e.next; 416 } 417 return null; 418 } 419 420 /** 421 * Returns {@code true} if this map contains a mapping for the 422 * specified key. 423 * 424 * @param key The key whose presence in this map is to be tested 425 * @return {@code true} if there is a mapping for {@code key}; 426 * {@code false} otherwise 427 */ containsKey(Object key)428 public boolean containsKey(Object key) { 429 return getEntry(key) != null; 430 } 431 432 /** 433 * Returns the entry associated with the specified key in this map. 434 * Returns null if the map contains no mapping for this key. 435 */ getEntry(Object key)436 Entry<K,V> getEntry(Object key) { 437 Object k = maskNull(key); 438 int h = hash(k); 439 Entry<K,V>[] tab = getTable(); 440 int index = indexFor(h, tab.length); 441 Entry<K,V> e = tab[index]; 442 while (e != null && !(e.hash == h && matchesKey(e, k))) 443 e = e.next; 444 return e; 445 } 446 447 /** 448 * Associates the specified value with the specified key in this map. 449 * If the map previously contained a mapping for this key, the old 450 * value is replaced. 451 * 452 * @param key key with which the specified value is to be associated. 453 * @param value value to be associated with the specified key. 454 * @return the previous value associated with {@code key}, or 455 * {@code null} if there was no mapping for {@code key}. 456 * (A {@code null} return can also indicate that the map 457 * previously associated {@code null} with {@code key}.) 458 */ put(K key, V value)459 public V put(K key, V value) { 460 Object k = maskNull(key); 461 int h = hash(k); 462 Entry<K,V>[] tab = getTable(); 463 int i = indexFor(h, tab.length); 464 465 for (Entry<K,V> e = tab[i]; e != null; e = e.next) { 466 if (h == e.hash && matchesKey(e, k)) { 467 V oldValue = e.value; 468 if (value != oldValue) 469 e.value = value; 470 return oldValue; 471 } 472 } 473 474 modCount++; 475 Entry<K,V> e = tab[i]; 476 tab[i] = new Entry<>(k, value, queue, h, e); 477 if (++size > threshold) 478 resize(tab.length * 2); 479 return null; 480 } 481 482 /** 483 * Rehashes the contents of this map into a new array with a 484 * larger capacity. This method is called automatically when the 485 * number of keys in this map reaches its threshold. 486 * 487 * If current capacity is MAXIMUM_CAPACITY, this method does not 488 * resize the map, but sets threshold to Integer.MAX_VALUE. 489 * This has the effect of preventing future calls. 490 * 491 * @param newCapacity the new capacity, MUST be a power of two; 492 * must be greater than current capacity unless current 493 * capacity is MAXIMUM_CAPACITY (in which case value 494 * is irrelevant). 495 */ resize(int newCapacity)496 void resize(int newCapacity) { 497 Entry<K,V>[] oldTable = getTable(); 498 int oldCapacity = oldTable.length; 499 if (oldCapacity == MAXIMUM_CAPACITY) { 500 threshold = Integer.MAX_VALUE; 501 return; 502 } 503 504 Entry<K,V>[] newTable = newTable(newCapacity); 505 transfer(oldTable, newTable); 506 table = newTable; 507 508 /* 509 * If ignoring null elements and processing ref queue caused massive 510 * shrinkage, then restore old table. This should be rare, but avoids 511 * unbounded expansion of garbage-filled tables. 512 */ 513 if (size >= threshold / 2) { 514 threshold = (int)(newCapacity * loadFactor); 515 } else { 516 expungeStaleEntries(); 517 transfer(newTable, oldTable); 518 table = oldTable; 519 } 520 } 521 522 /** Transfers all entries from src to dest tables */ transfer(Entry<K,V>[] src, Entry<K,V>[] dest)523 private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest) { 524 for (int j = 0; j < src.length; ++j) { 525 Entry<K,V> e = src[j]; 526 src[j] = null; 527 while (e != null) { 528 Entry<K,V> next = e.next; 529 if (e.refersTo(null)) { 530 e.next = null; // Help GC 531 e.value = null; // " " 532 size--; 533 } else { 534 int i = indexFor(e.hash, dest.length); 535 e.next = dest[i]; 536 dest[i] = e; 537 } 538 e = next; 539 } 540 } 541 } 542 543 /** 544 * Copies all of the mappings from the specified map to this map. 545 * These mappings will replace any mappings that this map had for any 546 * of the keys currently in the specified map. 547 * 548 * @param m mappings to be stored in this map. 549 * @throws NullPointerException if the specified map is null. 550 */ putAll(Map<? extends K, ? extends V> m)551 public void putAll(Map<? extends K, ? extends V> m) { 552 int numKeysToBeAdded = m.size(); 553 if (numKeysToBeAdded == 0) 554 return; 555 556 /* 557 * Expand the map if the map if the number of mappings to be added 558 * is greater than or equal to threshold. This is conservative; the 559 * obvious condition is (m.size() + size) >= threshold, but this 560 * condition could result in a map with twice the appropriate capacity, 561 * if the keys to be added overlap with the keys already in this map. 562 * By using the conservative calculation, we subject ourself 563 * to at most one extra resize. 564 */ 565 if (numKeysToBeAdded > threshold) { 566 int targetCapacity = (int)Math.ceil(numKeysToBeAdded / (double)loadFactor); 567 if (targetCapacity > MAXIMUM_CAPACITY) 568 targetCapacity = MAXIMUM_CAPACITY; 569 int newCapacity = table.length; 570 while (newCapacity < targetCapacity) 571 newCapacity <<= 1; 572 if (newCapacity > table.length) 573 resize(newCapacity); 574 } 575 576 for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) 577 put(e.getKey(), e.getValue()); 578 } 579 580 /** 581 * Removes the mapping for a key from this weak hash map if it is present. 582 * More formally, if this map contains a mapping from key {@code k} to 583 * value {@code v} such that <code>(key==null ? k==null : 584 * key.equals(k))</code>, that mapping is removed. (The map can contain 585 * at most one such mapping.) 586 * 587 * <p>Returns the value to which this map previously associated the key, 588 * or {@code null} if the map contained no mapping for the key. A 589 * return value of {@code null} does not <i>necessarily</i> indicate 590 * that the map contained no mapping for the key; it's also possible 591 * that the map explicitly mapped the key to {@code null}. 592 * 593 * <p>The map will not contain a mapping for the specified key once the 594 * call returns. 595 * 596 * @param key key whose mapping is to be removed from the map 597 * @return the previous value associated with {@code key}, or 598 * {@code null} if there was no mapping for {@code key} 599 */ remove(Object key)600 public V remove(Object key) { 601 Object k = maskNull(key); 602 int h = hash(k); 603 Entry<K,V>[] tab = getTable(); 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 && matchesKey(e, k)) { 611 modCount++; 612 size--; 613 if (prev == e) 614 tab[i] = next; 615 else 616 prev.next = next; 617 return e.value; 618 } 619 prev = e; 620 e = next; 621 } 622 623 return null; 624 } 625 626 /** Special version of remove needed by Entry set */ removeMapping(Object o)627 boolean removeMapping(Object o) { 628 if (!(o instanceof Map.Entry<?, ?> entry)) 629 return false; 630 Entry<K,V>[] tab = getTable(); 631 Object k = maskNull(entry.getKey()); 632 int h = hash(k); 633 int i = indexFor(h, tab.length); 634 Entry<K,V> prev = tab[i]; 635 Entry<K,V> e = prev; 636 637 while (e != null) { 638 Entry<K,V> next = e.next; 639 if (h == e.hash && e.equals(entry)) { 640 modCount++; 641 size--; 642 if (prev == e) 643 tab[i] = next; 644 else 645 prev.next = next; 646 return true; 647 } 648 prev = e; 649 e = next; 650 } 651 652 return false; 653 } 654 655 /** 656 * Removes all of the mappings from this map. 657 * The map will be empty after this call returns. 658 */ clear()659 public void clear() { 660 // clear out ref queue. We don't need to expunge entries 661 // since table is getting cleared. 662 while (queue.poll() != null) 663 ; 664 665 modCount++; 666 Arrays.fill(table, null); 667 size = 0; 668 669 // Allocation of array may have caused GC, which may have caused 670 // additional entries to go stale. Removing these entries from the 671 // reference queue will make them eligible for reclamation. 672 while (queue.poll() != null) 673 ; 674 } 675 676 /** 677 * Returns {@code true} if this map maps one or more keys to the 678 * specified value. 679 * 680 * @param value value whose presence in this map is to be tested 681 * @return {@code true} if this map maps one or more keys to the 682 * specified value 683 */ containsValue(Object value)684 public boolean containsValue(Object value) { 685 if (value==null) 686 return containsNullValue(); 687 688 Entry<K,V>[] tab = getTable(); 689 for (int i = tab.length; i-- > 0;) 690 for (Entry<K,V> e = tab[i]; e != null; e = e.next) 691 if (value.equals(e.value)) 692 return true; 693 return false; 694 } 695 696 /** 697 * Special-case code for containsValue with null argument 698 */ containsNullValue()699 private boolean containsNullValue() { 700 Entry<K,V>[] tab = getTable(); 701 for (int i = tab.length; i-- > 0;) 702 for (Entry<K,V> e = tab[i]; e != null; e = e.next) 703 if (e.value==null) 704 return true; 705 return false; 706 } 707 708 /** 709 * The entries in this hash table extend WeakReference, using its main ref 710 * field as the key. 711 */ 712 private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> { 713 V value; 714 final int hash; 715 Entry<K,V> next; 716 717 /** 718 * Creates new entry. 719 */ Entry(Object key, V value, ReferenceQueue<Object> queue, int hash, Entry<K,V> next)720 Entry(Object key, V value, 721 ReferenceQueue<Object> queue, 722 int hash, Entry<K,V> next) { 723 super(key, queue); 724 this.value = value; 725 this.hash = hash; 726 this.next = next; 727 } 728 729 @SuppressWarnings("unchecked") getKey()730 public K getKey() { 731 return (K) WeakHashMap.unmaskNull(get()); 732 } 733 getValue()734 public V getValue() { 735 return value; 736 } 737 setValue(V newValue)738 public V setValue(V newValue) { 739 V oldValue = value; 740 value = newValue; 741 return oldValue; 742 } 743 equals(Object o)744 public boolean equals(Object o) { 745 if (!(o instanceof Map.Entry<?, ?> e)) 746 return false; 747 K k1 = getKey(); 748 Object k2 = e.getKey(); 749 if (k1 == k2 || (k1 != null && k1.equals(k2))) { 750 V v1 = getValue(); 751 Object v2 = e.getValue(); 752 if (v1 == v2 || (v1 != null && v1.equals(v2))) 753 return true; 754 } 755 return false; 756 } 757 hashCode()758 public int hashCode() { 759 K k = getKey(); 760 V v = getValue(); 761 return Objects.hashCode(k) ^ Objects.hashCode(v); 762 } 763 toString()764 public String toString() { 765 return getKey() + "=" + getValue(); 766 } 767 } 768 769 private abstract class HashIterator<T> implements Iterator<T> { 770 private int index; 771 private Entry<K,V> entry; 772 private Entry<K,V> lastReturned; 773 private int expectedModCount = modCount; 774 775 /** 776 * Strong reference needed to avoid disappearance of key 777 * between hasNext and next 778 */ 779 private Object nextKey; 780 781 /** 782 * Strong reference needed to avoid disappearance of key 783 * between nextEntry() and any use of the entry 784 */ 785 private Object currentKey; 786 HashIterator()787 HashIterator() { 788 index = isEmpty() ? 0 : table.length; 789 } 790 hasNext()791 public boolean hasNext() { 792 Entry<K,V>[] t = table; 793 794 while (nextKey == null) { 795 Entry<K,V> e = entry; 796 int i = index; 797 while (e == null && i > 0) 798 e = t[--i]; 799 entry = e; 800 index = i; 801 if (e == null) { 802 currentKey = null; 803 return false; 804 } 805 nextKey = e.get(); // hold on to key in strong ref 806 if (nextKey == null) 807 entry = entry.next; 808 } 809 return true; 810 } 811 812 /** The common parts of next() across different types of iterators */ nextEntry()813 protected Entry<K,V> nextEntry() { 814 if (modCount != expectedModCount) 815 throw new ConcurrentModificationException(); 816 if (nextKey == null && !hasNext()) 817 throw new NoSuchElementException(); 818 819 lastReturned = entry; 820 entry = entry.next; 821 currentKey = nextKey; 822 nextKey = null; 823 return lastReturned; 824 } 825 remove()826 public void remove() { 827 if (lastReturned == null) 828 throw new IllegalStateException(); 829 if (modCount != expectedModCount) 830 throw new ConcurrentModificationException(); 831 832 WeakHashMap.this.remove(currentKey); 833 expectedModCount = modCount; 834 lastReturned = null; 835 currentKey = null; 836 } 837 838 } 839 840 private class ValueIterator extends HashIterator<V> { next()841 public V next() { 842 return nextEntry().value; 843 } 844 } 845 846 private class KeyIterator extends HashIterator<K> { next()847 public K next() { 848 return nextEntry().getKey(); 849 } 850 } 851 852 private class EntryIterator extends HashIterator<Map.Entry<K,V>> { next()853 public Map.Entry<K,V> next() { 854 return nextEntry(); 855 } 856 } 857 858 // Views 859 860 private transient Set<Map.Entry<K,V>> entrySet; 861 862 /** 863 * Returns a {@link Set} view of the keys contained in this map. 864 * The set is backed by the map, so changes to the map are 865 * reflected in the set, and vice-versa. If the map is modified 866 * while an iteration over the set is in progress (except through 867 * the iterator's own {@code remove} operation), the results of 868 * the iteration are undefined. The set supports element removal, 869 * which removes the corresponding mapping from the map, via the 870 * {@code Iterator.remove}, {@code Set.remove}, 871 * {@code removeAll}, {@code retainAll}, and {@code clear} 872 * operations. It does not support the {@code add} or {@code addAll} 873 * operations. 874 */ keySet()875 public Set<K> keySet() { 876 Set<K> ks = keySet; 877 if (ks == null) { 878 ks = new KeySet(); 879 keySet = ks; 880 } 881 return ks; 882 } 883 884 private class KeySet extends AbstractSet<K> { iterator()885 public Iterator<K> iterator() { 886 return new KeyIterator(); 887 } 888 size()889 public int size() { 890 return WeakHashMap.this.size(); 891 } 892 contains(Object o)893 public boolean contains(Object o) { 894 return containsKey(o); 895 } 896 remove(Object o)897 public boolean remove(Object o) { 898 if (containsKey(o)) { 899 WeakHashMap.this.remove(o); 900 return true; 901 } 902 else 903 return false; 904 } 905 clear()906 public void clear() { 907 WeakHashMap.this.clear(); 908 } 909 spliterator()910 public Spliterator<K> spliterator() { 911 return new KeySpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 912 } 913 } 914 915 /** 916 * Returns a {@link Collection} view of the values contained in this map. 917 * The collection is backed by the map, so changes to the map are 918 * reflected in the collection, and vice-versa. If the map is 919 * modified while an iteration over the collection is in progress 920 * (except through the iterator's own {@code remove} operation), 921 * the results of the iteration are undefined. The collection 922 * supports element removal, which removes the corresponding 923 * mapping from the map, via the {@code Iterator.remove}, 924 * {@code Collection.remove}, {@code removeAll}, 925 * {@code retainAll} and {@code clear} operations. It does not 926 * support the {@code add} or {@code addAll} operations. 927 */ values()928 public Collection<V> values() { 929 Collection<V> vs = values; 930 if (vs == null) { 931 vs = new Values(); 932 values = vs; 933 } 934 return vs; 935 } 936 937 private class Values extends AbstractCollection<V> { iterator()938 public Iterator<V> iterator() { 939 return new ValueIterator(); 940 } 941 size()942 public int size() { 943 return WeakHashMap.this.size(); 944 } 945 contains(Object o)946 public boolean contains(Object o) { 947 return containsValue(o); 948 } 949 clear()950 public void clear() { 951 WeakHashMap.this.clear(); 952 } 953 spliterator()954 public Spliterator<V> spliterator() { 955 return new ValueSpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 956 } 957 } 958 959 /** 960 * Returns a {@link Set} view of the mappings contained in this map. 961 * The set is backed by the map, so changes to the map are 962 * reflected in the set, and vice-versa. If the map is modified 963 * while an iteration over the set is in progress (except through 964 * the iterator's own {@code remove} operation, or through the 965 * {@code setValue} operation on a map entry returned by the 966 * iterator) the results of the iteration are undefined. The set 967 * supports element removal, which removes the corresponding 968 * mapping from the map, via the {@code Iterator.remove}, 969 * {@code Set.remove}, {@code removeAll}, {@code retainAll} and 970 * {@code clear} operations. It does not support the 971 * {@code add} or {@code addAll} operations. 972 */ entrySet()973 public Set<Map.Entry<K,V>> entrySet() { 974 Set<Map.Entry<K,V>> es = entrySet; 975 return es != null ? es : (entrySet = new EntrySet()); 976 } 977 978 private class EntrySet extends AbstractSet<Map.Entry<K,V>> { iterator()979 public Iterator<Map.Entry<K,V>> iterator() { 980 return new EntryIterator(); 981 } 982 contains(Object o)983 public boolean contains(Object o) { 984 return o instanceof Map.Entry<?, ?> e 985 && getEntry(e.getKey()) != null 986 && getEntry(e.getKey()).equals(e); 987 } 988 remove(Object o)989 public boolean remove(Object o) { 990 return removeMapping(o); 991 } 992 size()993 public int size() { 994 return WeakHashMap.this.size(); 995 } 996 clear()997 public void clear() { 998 WeakHashMap.this.clear(); 999 } 1000 deepCopy()1001 private List<Map.Entry<K,V>> deepCopy() { 1002 List<Map.Entry<K,V>> list = new ArrayList<>(size()); 1003 for (Map.Entry<K,V> e : this) 1004 list.add(new AbstractMap.SimpleEntry<>(e)); 1005 return list; 1006 } 1007 toArray()1008 public Object[] toArray() { 1009 return deepCopy().toArray(); 1010 } 1011 toArray(T[] a)1012 public <T> T[] toArray(T[] a) { 1013 return deepCopy().toArray(a); 1014 } 1015 spliterator()1016 public Spliterator<Map.Entry<K,V>> spliterator() { 1017 return new EntrySpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 1018 } 1019 } 1020 1021 @SuppressWarnings("unchecked") 1022 @Override forEach(BiConsumer<? super K, ? super V> action)1023 public void forEach(BiConsumer<? super K, ? super V> action) { 1024 Objects.requireNonNull(action); 1025 int expectedModCount = modCount; 1026 1027 Entry<K, V>[] tab = getTable(); 1028 for (Entry<K, V> entry : tab) { 1029 while (entry != null) { 1030 Object key = entry.get(); 1031 if (key != null) { 1032 action.accept((K)WeakHashMap.unmaskNull(key), entry.value); 1033 } 1034 entry = entry.next; 1035 1036 if (expectedModCount != modCount) { 1037 throw new ConcurrentModificationException(); 1038 } 1039 } 1040 } 1041 } 1042 1043 @SuppressWarnings("unchecked") 1044 @Override replaceAll(BiFunction<? super K, ? super V, ? extends V> function)1045 public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { 1046 Objects.requireNonNull(function); 1047 int expectedModCount = modCount; 1048 1049 Entry<K, V>[] tab = getTable(); 1050 for (Entry<K, V> entry : tab) { 1051 while (entry != null) { 1052 Object key = entry.get(); 1053 if (key != null) { 1054 entry.value = function.apply((K)WeakHashMap.unmaskNull(key), entry.value); 1055 } 1056 entry = entry.next; 1057 1058 if (expectedModCount != modCount) { 1059 throw new ConcurrentModificationException(); 1060 } 1061 } 1062 } 1063 } 1064 1065 /** 1066 * Similar form as other hash Spliterators, but skips dead 1067 * elements. 1068 */ 1069 static class WeakHashMapSpliterator<K,V> { 1070 final WeakHashMap<K,V> map; 1071 WeakHashMap.Entry<K,V> current; // current node 1072 int index; // current index, modified on advance/split 1073 int fence; // -1 until first use; then one past last index 1074 int est; // size estimate 1075 int expectedModCount; // for comodification checks 1076 WeakHashMapSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1077 WeakHashMapSpliterator(WeakHashMap<K,V> m, int origin, 1078 int fence, int est, 1079 int expectedModCount) { 1080 this.map = m; 1081 this.index = origin; 1082 this.fence = fence; 1083 this.est = est; 1084 this.expectedModCount = expectedModCount; 1085 } 1086 getFence()1087 final int getFence() { // initialize fence and size on first use 1088 int hi; 1089 if ((hi = fence) < 0) { 1090 WeakHashMap<K,V> m = map; 1091 est = m.size(); 1092 expectedModCount = m.modCount; 1093 hi = fence = m.table.length; 1094 } 1095 return hi; 1096 } 1097 estimateSize()1098 public final long estimateSize() { 1099 getFence(); // force init 1100 return (long) est; 1101 } 1102 } 1103 1104 static final class KeySpliterator<K,V> 1105 extends WeakHashMapSpliterator<K,V> 1106 implements Spliterator<K> { KeySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1107 KeySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1108 int expectedModCount) { 1109 super(m, origin, fence, est, expectedModCount); 1110 } 1111 trySplit()1112 public KeySpliterator<K,V> trySplit() { 1113 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1114 return (lo >= mid) ? null : 1115 new KeySpliterator<>(map, lo, index = mid, est >>>= 1, 1116 expectedModCount); 1117 } 1118 forEachRemaining(Consumer<? super K> action)1119 public void forEachRemaining(Consumer<? super K> action) { 1120 int i, hi, mc; 1121 if (action == null) 1122 throw new NullPointerException(); 1123 WeakHashMap<K,V> m = map; 1124 WeakHashMap.Entry<K,V>[] tab = m.table; 1125 if ((hi = fence) < 0) { 1126 mc = expectedModCount = m.modCount; 1127 hi = fence = tab.length; 1128 } 1129 else 1130 mc = expectedModCount; 1131 if (tab.length >= hi && (i = index) >= 0 && 1132 (i < (index = hi) || current != null)) { 1133 WeakHashMap.Entry<K,V> p = current; 1134 current = null; // exhaust 1135 do { 1136 if (p == null) 1137 p = tab[i++]; 1138 else { 1139 Object x = p.get(); 1140 p = p.next; 1141 if (x != null) { 1142 @SuppressWarnings("unchecked") K k = 1143 (K) WeakHashMap.unmaskNull(x); 1144 action.accept(k); 1145 } 1146 } 1147 } while (p != null || i < hi); 1148 } 1149 if (m.modCount != mc) 1150 throw new ConcurrentModificationException(); 1151 } 1152 tryAdvance(Consumer<? super K> action)1153 public boolean tryAdvance(Consumer<? super K> action) { 1154 int hi; 1155 if (action == null) 1156 throw new NullPointerException(); 1157 WeakHashMap.Entry<K,V>[] tab = map.table; 1158 if (tab.length >= (hi = getFence()) && index >= 0) { 1159 while (current != null || index < hi) { 1160 if (current == null) 1161 current = tab[index++]; 1162 else { 1163 Object x = current.get(); 1164 current = current.next; 1165 if (x != null) { 1166 @SuppressWarnings("unchecked") K k = 1167 (K) WeakHashMap.unmaskNull(x); 1168 action.accept(k); 1169 if (map.modCount != expectedModCount) 1170 throw new ConcurrentModificationException(); 1171 return true; 1172 } 1173 } 1174 } 1175 } 1176 return false; 1177 } 1178 characteristics()1179 public int characteristics() { 1180 return Spliterator.DISTINCT; 1181 } 1182 } 1183 1184 static final class ValueSpliterator<K,V> 1185 extends WeakHashMapSpliterator<K,V> 1186 implements Spliterator<V> { ValueSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1187 ValueSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1188 int expectedModCount) { 1189 super(m, origin, fence, est, expectedModCount); 1190 } 1191 trySplit()1192 public ValueSpliterator<K,V> trySplit() { 1193 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1194 return (lo >= mid) ? null : 1195 new ValueSpliterator<>(map, lo, index = mid, est >>>= 1, 1196 expectedModCount); 1197 } 1198 forEachRemaining(Consumer<? super V> action)1199 public void forEachRemaining(Consumer<? super V> action) { 1200 int i, hi, mc; 1201 if (action == null) 1202 throw new NullPointerException(); 1203 WeakHashMap<K,V> m = map; 1204 WeakHashMap.Entry<K,V>[] tab = m.table; 1205 if ((hi = fence) < 0) { 1206 mc = expectedModCount = m.modCount; 1207 hi = fence = tab.length; 1208 } 1209 else 1210 mc = expectedModCount; 1211 if (tab.length >= hi && (i = index) >= 0 && 1212 (i < (index = hi) || current != null)) { 1213 WeakHashMap.Entry<K,V> p = current; 1214 current = null; // exhaust 1215 do { 1216 if (p == null) 1217 p = tab[i++]; 1218 else { 1219 Object x = p.get(); 1220 V v = p.value; 1221 p = p.next; 1222 if (x != null) 1223 action.accept(v); 1224 } 1225 } while (p != null || i < hi); 1226 } 1227 if (m.modCount != mc) 1228 throw new ConcurrentModificationException(); 1229 } 1230 tryAdvance(Consumer<? super V> action)1231 public boolean tryAdvance(Consumer<? super V> action) { 1232 int hi; 1233 if (action == null) 1234 throw new NullPointerException(); 1235 WeakHashMap.Entry<K,V>[] tab = map.table; 1236 if (tab.length >= (hi = getFence()) && index >= 0) { 1237 while (current != null || index < hi) { 1238 if (current == null) 1239 current = tab[index++]; 1240 else { 1241 Object x = current.get(); 1242 V v = current.value; 1243 current = current.next; 1244 if (x != null) { 1245 action.accept(v); 1246 if (map.modCount != expectedModCount) 1247 throw new ConcurrentModificationException(); 1248 return true; 1249 } 1250 } 1251 } 1252 } 1253 return false; 1254 } 1255 characteristics()1256 public int characteristics() { 1257 return 0; 1258 } 1259 } 1260 1261 static final class EntrySpliterator<K,V> 1262 extends WeakHashMapSpliterator<K,V> 1263 implements Spliterator<Map.Entry<K,V>> { EntrySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, int expectedModCount)1264 EntrySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1265 int expectedModCount) { 1266 super(m, origin, fence, est, expectedModCount); 1267 } 1268 trySplit()1269 public EntrySpliterator<K,V> trySplit() { 1270 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1271 return (lo >= mid) ? null : 1272 new EntrySpliterator<>(map, lo, index = mid, est >>>= 1, 1273 expectedModCount); 1274 } 1275 1276 forEachRemaining(Consumer<? super Map.Entry<K, V>> action)1277 public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) { 1278 int i, hi, mc; 1279 if (action == null) 1280 throw new NullPointerException(); 1281 WeakHashMap<K,V> m = map; 1282 WeakHashMap.Entry<K,V>[] tab = m.table; 1283 if ((hi = fence) < 0) { 1284 mc = expectedModCount = m.modCount; 1285 hi = fence = tab.length; 1286 } 1287 else 1288 mc = expectedModCount; 1289 if (tab.length >= hi && (i = index) >= 0 && 1290 (i < (index = hi) || current != null)) { 1291 WeakHashMap.Entry<K,V> p = current; 1292 current = null; // exhaust 1293 do { 1294 if (p == null) 1295 p = tab[i++]; 1296 else { 1297 Object x = p.get(); 1298 V v = p.value; 1299 p = p.next; 1300 if (x != null) { 1301 @SuppressWarnings("unchecked") K k = 1302 (K) WeakHashMap.unmaskNull(x); 1303 action.accept 1304 (new AbstractMap.SimpleImmutableEntry<>(k, v)); 1305 } 1306 } 1307 } while (p != null || i < hi); 1308 } 1309 if (m.modCount != mc) 1310 throw new ConcurrentModificationException(); 1311 } 1312 tryAdvance(Consumer<? super Map.Entry<K,V>> action)1313 public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) { 1314 int hi; 1315 if (action == null) 1316 throw new NullPointerException(); 1317 WeakHashMap.Entry<K,V>[] tab = map.table; 1318 if (tab.length >= (hi = getFence()) && index >= 0) { 1319 while (current != null || index < hi) { 1320 if (current == null) 1321 current = tab[index++]; 1322 else { 1323 Object x = current.get(); 1324 V v = current.value; 1325 current = current.next; 1326 if (x != null) { 1327 @SuppressWarnings("unchecked") K k = 1328 (K) WeakHashMap.unmaskNull(x); 1329 action.accept 1330 (new AbstractMap.SimpleImmutableEntry<>(k, v)); 1331 if (map.modCount != expectedModCount) 1332 throw new ConcurrentModificationException(); 1333 return true; 1334 } 1335 } 1336 } 1337 } 1338 return false; 1339 } 1340 characteristics()1341 public int characteristics() { 1342 return Spliterator.DISTINCT; 1343 } 1344 } 1345 1346 /** 1347 * Creates a new, empty WeakHashMap suitable for the expected number of mappings. 1348 * The returned map uses the default load factor of 0.75, and its initial capacity is 1349 * generally large enough so that the expected number of mappings can be added 1350 * without resizing the map. 1351 * 1352 * @param numMappings the expected number of mappings 1353 * @param <K> the type of keys maintained by the new map 1354 * @param <V> the type of mapped values 1355 * @return the newly created map 1356 * @throws IllegalArgumentException if numMappings is negative 1357 * @since 19 1358 */ newWeakHashMap(int numMappings)1359 public static <K, V> WeakHashMap<K, V> newWeakHashMap(int numMappings) { 1360 if (numMappings < 0) { 1361 throw new IllegalArgumentException("Negative number of mappings: " + numMappings); 1362 } 1363 return new WeakHashMap<>(HashMap.calculateHashMapCapacity(numMappings)); 1364 } 1365 1366 } 1367