J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1998-2007 Sun Microsystems, Inc. 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. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | package java.util; |
| 27 | import java.lang.ref.WeakReference; |
| 28 | import java.lang.ref.ReferenceQueue; |
| 29 | |
| 30 | |
| 31 | /** |
| 32 | * A hashtable-based <tt>Map</tt> implementation with <em>weak keys</em>. |
| 33 | * An entry in a <tt>WeakHashMap</tt> will automatically be removed when |
| 34 | * its key is no longer in ordinary use. More precisely, the presence of a |
| 35 | * mapping for a given key will not prevent the key from being discarded by the |
| 36 | * garbage collector, that is, made finalizable, finalized, and then reclaimed. |
| 37 | * When a key has been discarded its entry is effectively removed from the map, |
| 38 | * so this class behaves somewhat differently from other <tt>Map</tt> |
| 39 | * implementations. |
| 40 | * |
| 41 | * <p> Both null values and the null key are supported. This class has |
| 42 | * performance characteristics similar to those of the <tt>HashMap</tt> |
| 43 | * class, and has the same efficiency parameters of <em>initial capacity</em> |
| 44 | * and <em>load factor</em>. |
| 45 | * |
| 46 | * <p> Like most collection classes, this class is not synchronized. |
| 47 | * A synchronized <tt>WeakHashMap</tt> may be constructed using the |
| 48 | * {@link Collections#synchronizedMap Collections.synchronizedMap} |
| 49 | * method. |
| 50 | * |
| 51 | * <p> This class is intended primarily for use with key objects whose |
| 52 | * <tt>equals</tt> methods test for object identity using the |
| 53 | * <tt>==</tt> operator. Once such a key is discarded it can never be |
| 54 | * recreated, so it is impossible to do a lookup of that key in a |
| 55 | * <tt>WeakHashMap</tt> at some later time and be surprised that its entry |
| 56 | * has been removed. This class will work perfectly well with key objects |
| 57 | * whose <tt>equals</tt> methods are not based upon object identity, such |
| 58 | * as <tt>String</tt> instances. With such recreatable key objects, |
| 59 | * however, the automatic removal of <tt>WeakHashMap</tt> entries whose |
| 60 | * keys have been discarded may prove to be confusing. |
| 61 | * |
| 62 | * <p> The behavior of the <tt>WeakHashMap</tt> class depends in part upon |
| 63 | * the actions of the garbage collector, so several familiar (though not |
| 64 | * required) <tt>Map</tt> invariants do not hold for this class. Because |
| 65 | * the garbage collector may discard keys at any time, a |
| 66 | * <tt>WeakHashMap</tt> may behave as though an unknown thread is silently |
| 67 | * removing entries. In particular, even if you synchronize on a |
| 68 | * <tt>WeakHashMap</tt> instance and invoke none of its mutator methods, it |
| 69 | * is possible for the <tt>size</tt> method to return smaller values over |
| 70 | * time, for the <tt>isEmpty</tt> method to return <tt>false</tt> and |
| 71 | * then <tt>true</tt>, for the <tt>containsKey</tt> method to return |
| 72 | * <tt>true</tt> and later <tt>false</tt> for a given key, for the |
| 73 | * <tt>get</tt> method to return a value for a given key but later return |
| 74 | * <tt>null</tt>, for the <tt>put</tt> method to return |
| 75 | * <tt>null</tt> and the <tt>remove</tt> method to return |
| 76 | * <tt>false</tt> for a key that previously appeared to be in the map, and |
| 77 | * for successive examinations of the key set, the value collection, and |
| 78 | * the entry set to yield successively smaller numbers of elements. |
| 79 | * |
| 80 | * <p> Each key object in a <tt>WeakHashMap</tt> is stored indirectly as |
| 81 | * the referent of a weak reference. Therefore a key will automatically be |
| 82 | * removed only after the weak references to it, both inside and outside of the |
| 83 | * map, have been cleared by the garbage collector. |
| 84 | * |
| 85 | * <p> <strong>Implementation note:</strong> The value objects in a |
| 86 | * <tt>WeakHashMap</tt> are held by ordinary strong references. Thus care |
| 87 | * should be taken to ensure that value objects do not strongly refer to their |
| 88 | * own keys, either directly or indirectly, since that will prevent the keys |
| 89 | * from being discarded. Note that a value object may refer indirectly to its |
| 90 | * key via the <tt>WeakHashMap</tt> itself; that is, a value object may |
| 91 | * strongly refer to some other key object whose associated value object, in |
| 92 | * turn, strongly refers to the key of the first value object. One way |
| 93 | * to deal with this is to wrap values themselves within |
| 94 | * <tt>WeakReferences</tt> before |
| 95 | * inserting, as in: <tt>m.put(key, new WeakReference(value))</tt>, |
| 96 | * and then unwrapping upon each <tt>get</tt>. |
| 97 | * |
| 98 | * <p>The iterators returned by the <tt>iterator</tt> method of the collections |
| 99 | * returned by all of this class's "collection view methods" are |
| 100 | * <i>fail-fast</i>: if the map is structurally modified at any time after the |
| 101 | * iterator is created, in any way except through the iterator's own |
| 102 | * <tt>remove</tt> method, the iterator will throw a {@link |
| 103 | * ConcurrentModificationException}. Thus, in the face of concurrent |
| 104 | * modification, the iterator fails quickly and cleanly, rather than risking |
| 105 | * arbitrary, non-deterministic behavior at an undetermined time in the future. |
| 106 | * |
| 107 | * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed |
| 108 | * as it is, generally speaking, impossible to make any hard guarantees in the |
| 109 | * presence of unsynchronized concurrent modification. Fail-fast iterators |
| 110 | * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. |
| 111 | * Therefore, it would be wrong to write a program that depended on this |
| 112 | * exception for its correctness: <i>the fail-fast behavior of iterators |
| 113 | * should be used only to detect bugs.</i> |
| 114 | * |
| 115 | * <p>This class is a member of the |
| 116 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| 117 | * Java Collections Framework</a>. |
| 118 | * |
| 119 | * @param <K> the type of keys maintained by this map |
| 120 | * @param <V> the type of mapped values |
| 121 | * |
| 122 | * @author Doug Lea |
| 123 | * @author Josh Bloch |
| 124 | * @author Mark Reinhold |
| 125 | * @since 1.2 |
| 126 | * @see java.util.HashMap |
| 127 | * @see java.lang.ref.WeakReference |
| 128 | */ |
| 129 | public class WeakHashMap<K,V> |
| 130 | extends AbstractMap<K,V> |
| 131 | implements Map<K,V> { |
| 132 | |
| 133 | /** |
| 134 | * The default initial capacity -- MUST be a power of two. |
| 135 | */ |
| 136 | private static final int DEFAULT_INITIAL_CAPACITY = 16; |
| 137 | |
| 138 | /** |
| 139 | * The maximum capacity, used if a higher value is implicitly specified |
| 140 | * by either of the constructors with arguments. |
| 141 | * MUST be a power of two <= 1<<30. |
| 142 | */ |
| 143 | private static final int MAXIMUM_CAPACITY = 1 << 30; |
| 144 | |
| 145 | /** |
| 146 | * The load factor used when none specified in constructor. |
| 147 | */ |
| 148 | private static final float DEFAULT_LOAD_FACTOR = 0.75f; |
| 149 | |
| 150 | /** |
| 151 | * The table, resized as necessary. Length MUST Always be a power of two. |
| 152 | */ |
| 153 | Entry<K,V>[] table; |
| 154 | |
| 155 | /** |
| 156 | * The number of key-value mappings contained in this weak hash map. |
| 157 | */ |
| 158 | private int size; |
| 159 | |
| 160 | /** |
| 161 | * The next size value at which to resize (capacity * load factor). |
| 162 | */ |
| 163 | private int threshold; |
| 164 | |
| 165 | /** |
| 166 | * The load factor for the hash table. |
| 167 | */ |
| 168 | private final float loadFactor; |
| 169 | |
| 170 | /** |
| 171 | * Reference queue for cleared WeakEntries |
| 172 | */ |
| 173 | private final ReferenceQueue<Object> queue = new ReferenceQueue<Object>(); |
| 174 | |
| 175 | /** |
| 176 | * The number of times this WeakHashMap has been structurally modified. |
| 177 | * Structural modifications are those that change the number of |
| 178 | * mappings in the map or otherwise modify its internal structure |
| 179 | * (e.g., rehash). This field is used to make iterators on |
| 180 | * Collection-views of the map fail-fast. |
| 181 | * |
| 182 | * @see ConcurrentModificationException |
| 183 | */ |
| 184 | volatile int modCount; |
| 185 | |
| 186 | @SuppressWarnings("unchecked") |
| 187 | private Entry<K,V>[] newTable(int n) { |
| 188 | return (Entry<K,V>[]) new Entry[n]; |
| 189 | } |
| 190 | |
| 191 | /** |
| 192 | * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial |
| 193 | * capacity and the given load factor. |
| 194 | * |
| 195 | * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt> |
| 196 | * @param loadFactor The load factor of the <tt>WeakHashMap</tt> |
| 197 | * @throws IllegalArgumentException if the initial capacity is negative, |
| 198 | * or if the load factor is nonpositive. |
| 199 | */ |
| 200 | public WeakHashMap(int initialCapacity, float loadFactor) { |
| 201 | if (initialCapacity < 0) |
| 202 | throw new IllegalArgumentException("Illegal Initial Capacity: "+ |
| 203 | initialCapacity); |
| 204 | if (initialCapacity > MAXIMUM_CAPACITY) |
| 205 | initialCapacity = MAXIMUM_CAPACITY; |
| 206 | |
| 207 | if (loadFactor <= 0 || Float.isNaN(loadFactor)) |
| 208 | throw new IllegalArgumentException("Illegal Load factor: "+ |
| 209 | loadFactor); |
| 210 | int capacity = 1; |
| 211 | while (capacity < initialCapacity) |
| 212 | capacity <<= 1; |
| 213 | table = newTable(capacity); |
| 214 | this.loadFactor = loadFactor; |
| 215 | threshold = (int)(capacity * loadFactor); |
| 216 | } |
| 217 | |
| 218 | /** |
| 219 | * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial |
| 220 | * capacity and the default load factor (0.75). |
| 221 | * |
| 222 | * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt> |
| 223 | * @throws IllegalArgumentException if the initial capacity is negative |
| 224 | */ |
| 225 | public WeakHashMap(int initialCapacity) { |
| 226 | this(initialCapacity, DEFAULT_LOAD_FACTOR); |
| 227 | } |
| 228 | |
| 229 | /** |
| 230 | * Constructs a new, empty <tt>WeakHashMap</tt> with the default initial |
| 231 | * capacity (16) and load factor (0.75). |
| 232 | */ |
| 233 | public WeakHashMap() { |
| 234 | this.loadFactor = DEFAULT_LOAD_FACTOR; |
| 235 | threshold = DEFAULT_INITIAL_CAPACITY; |
| 236 | table = newTable(DEFAULT_INITIAL_CAPACITY); |
| 237 | } |
| 238 | |
| 239 | /** |
| 240 | * Constructs a new <tt>WeakHashMap</tt> with the same mappings as the |
| 241 | * specified map. The <tt>WeakHashMap</tt> is created with the default |
| 242 | * load factor (0.75) and an initial capacity sufficient to hold the |
| 243 | * mappings in the specified map. |
| 244 | * |
| 245 | * @param m the map whose mappings are to be placed in this map |
| 246 | * @throws NullPointerException if the specified map is null |
| 247 | * @since 1.3 |
| 248 | */ |
| 249 | public WeakHashMap(Map<? extends K, ? extends V> m) { |
| 250 | this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, 16), |
| 251 | DEFAULT_LOAD_FACTOR); |
| 252 | putAll(m); |
| 253 | } |
| 254 | |
| 255 | // internal utilities |
| 256 | |
| 257 | /** |
| 258 | * Value representing null keys inside tables. |
| 259 | */ |
| 260 | private static final Object NULL_KEY = new Object(); |
| 261 | |
| 262 | /** |
| 263 | * Use NULL_KEY for key if it is null. |
| 264 | */ |
| 265 | private static Object maskNull(Object key) { |
| 266 | return (key == null) ? NULL_KEY : key; |
| 267 | } |
| 268 | |
| 269 | /** |
| 270 | * Returns internal representation of null key back to caller as null. |
| 271 | */ |
| 272 | static Object unmaskNull(Object key) { |
| 273 | return (key == NULL_KEY) ? null : key; |
| 274 | } |
| 275 | |
| 276 | /** |
| 277 | * Checks for equality of non-null reference x and possibly-null y. By |
| 278 | * default uses Object.equals. |
| 279 | */ |
| 280 | private static boolean eq(Object x, Object y) { |
| 281 | return x == y || x.equals(y); |
| 282 | } |
| 283 | |
| 284 | /** |
| 285 | * Returns index for hash code h. |
| 286 | */ |
| 287 | private static int indexFor(int h, int length) { |
| 288 | return h & (length-1); |
| 289 | } |
| 290 | |
| 291 | /** |
| 292 | * Expunges stale entries from the table. |
| 293 | */ |
| 294 | private void expungeStaleEntries() { |
| 295 | for (Object x; (x = queue.poll()) != null; ) { |
| 296 | synchronized (queue) { |
| 297 | @SuppressWarnings("unchecked") |
| 298 | Entry<K,V> e = (Entry<K,V>) x; |
| 299 | int i = indexFor(e.hash, table.length); |
| 300 | |
| 301 | Entry<K,V> prev = table[i]; |
| 302 | Entry<K,V> p = prev; |
| 303 | while (p != null) { |
| 304 | Entry<K,V> next = p.next; |
| 305 | if (p == e) { |
| 306 | if (prev == e) |
| 307 | table[i] = next; |
| 308 | else |
| 309 | prev.next = next; |
| 310 | // Must not null out e.next; |
| 311 | // stale entries may be in use by a HashIterator |
| 312 | e.value = null; // Help GC |
| 313 | size--; |
| 314 | break; |
| 315 | } |
| 316 | prev = p; |
| 317 | p = next; |
| 318 | } |
| 319 | } |
| 320 | } |
| 321 | } |
| 322 | |
| 323 | /** |
| 324 | * Returns the table after first expunging stale entries. |
| 325 | */ |
| 326 | private Entry<K,V>[] getTable() { |
| 327 | expungeStaleEntries(); |
| 328 | return table; |
| 329 | } |
| 330 | |
| 331 | /** |
| 332 | * Returns the number of key-value mappings in this map. |
| 333 | * This result is a snapshot, and may not reflect unprocessed |
| 334 | * entries that will be removed before next attempted access |
| 335 | * because they are no longer referenced. |
| 336 | */ |
| 337 | public int size() { |
| 338 | if (size == 0) |
| 339 | return 0; |
| 340 | expungeStaleEntries(); |
| 341 | return size; |
| 342 | } |
| 343 | |
| 344 | /** |
| 345 | * Returns <tt>true</tt> if this map contains no key-value mappings. |
| 346 | * This result is a snapshot, and may not reflect unprocessed |
| 347 | * entries that will be removed before next attempted access |
| 348 | * because they are no longer referenced. |
| 349 | */ |
| 350 | public boolean isEmpty() { |
| 351 | return size() == 0; |
| 352 | } |
| 353 | |
| 354 | /** |
| 355 | * Returns the value to which the specified key is mapped, |
| 356 | * or {@code null} if this map contains no mapping for the key. |
| 357 | * |
| 358 | * <p>More formally, if this map contains a mapping from a key |
| 359 | * {@code k} to a value {@code v} such that {@code (key==null ? k==null : |
| 360 | * key.equals(k))}, then this method returns {@code v}; otherwise |
| 361 | * it returns {@code null}. (There can be at most one such mapping.) |
| 362 | * |
| 363 | * <p>A return value of {@code null} does not <i>necessarily</i> |
| 364 | * indicate that the map contains no mapping for the key; it's also |
| 365 | * possible that the map explicitly maps the key to {@code null}. |
| 366 | * The {@link #containsKey containsKey} operation may be used to |
| 367 | * distinguish these two cases. |
| 368 | * |
| 369 | * @see #put(Object, Object) |
| 370 | */ |
| 371 | public V get(Object key) { |
| 372 | Object k = maskNull(key); |
| 373 | int h = HashMap.hash(k.hashCode()); |
| 374 | Entry<K,V>[] tab = getTable(); |
| 375 | int index = indexFor(h, tab.length); |
| 376 | Entry<K,V> e = tab[index]; |
| 377 | while (e != null) { |
| 378 | if (e.hash == h && eq(k, e.get())) |
| 379 | return e.value; |
| 380 | e = e.next; |
| 381 | } |
| 382 | return null; |
| 383 | } |
| 384 | |
| 385 | /** |
| 386 | * Returns <tt>true</tt> if this map contains a mapping for the |
| 387 | * specified key. |
| 388 | * |
| 389 | * @param key The key whose presence in this map is to be tested |
| 390 | * @return <tt>true</tt> if there is a mapping for <tt>key</tt>; |
| 391 | * <tt>false</tt> otherwise |
| 392 | */ |
| 393 | public boolean containsKey(Object key) { |
| 394 | return getEntry(key) != null; |
| 395 | } |
| 396 | |
| 397 | /** |
| 398 | * Returns the entry associated with the specified key in this map. |
| 399 | * Returns null if the map contains no mapping for this key. |
| 400 | */ |
| 401 | Entry<K,V> getEntry(Object key) { |
| 402 | Object k = maskNull(key); |
| 403 | int h = HashMap.hash(k.hashCode()); |
| 404 | Entry<K,V>[] tab = getTable(); |
| 405 | int index = indexFor(h, tab.length); |
| 406 | Entry<K,V> e = tab[index]; |
| 407 | while (e != null && !(e.hash == h && eq(k, e.get()))) |
| 408 | e = e.next; |
| 409 | return e; |
| 410 | } |
| 411 | |
| 412 | /** |
| 413 | * Associates the specified value with the specified key in this map. |
| 414 | * If the map previously contained a mapping for this key, the old |
| 415 | * value is replaced. |
| 416 | * |
| 417 | * @param key key with which the specified value is to be associated. |
| 418 | * @param value value to be associated with the specified key. |
| 419 | * @return the previous value associated with <tt>key</tt>, or |
| 420 | * <tt>null</tt> if there was no mapping for <tt>key</tt>. |
| 421 | * (A <tt>null</tt> return can also indicate that the map |
| 422 | * previously associated <tt>null</tt> with <tt>key</tt>.) |
| 423 | */ |
| 424 | public V put(K key, V value) { |
| 425 | Object k = maskNull(key); |
| 426 | int h = HashMap.hash(k.hashCode()); |
| 427 | Entry<K,V>[] tab = getTable(); |
| 428 | int i = indexFor(h, tab.length); |
| 429 | |
| 430 | for (Entry<K,V> e = tab[i]; e != null; e = e.next) { |
| 431 | if (h == e.hash && eq(k, e.get())) { |
| 432 | V oldValue = e.value; |
| 433 | if (value != oldValue) |
| 434 | e.value = value; |
| 435 | return oldValue; |
| 436 | } |
| 437 | } |
| 438 | |
| 439 | modCount++; |
| 440 | Entry<K,V> e = tab[i]; |
| 441 | tab[i] = new Entry<K,V>(k, value, queue, h, e); |
| 442 | if (++size >= threshold) |
| 443 | resize(tab.length * 2); |
| 444 | return null; |
| 445 | } |
| 446 | |
| 447 | /** |
| 448 | * Rehashes the contents of this map into a new array with a |
| 449 | * larger capacity. This method is called automatically when the |
| 450 | * number of keys in this map reaches its threshold. |
| 451 | * |
| 452 | * If current capacity is MAXIMUM_CAPACITY, this method does not |
| 453 | * resize the map, but sets threshold to Integer.MAX_VALUE. |
| 454 | * This has the effect of preventing future calls. |
| 455 | * |
| 456 | * @param newCapacity the new capacity, MUST be a power of two; |
| 457 | * must be greater than current capacity unless current |
| 458 | * capacity is MAXIMUM_CAPACITY (in which case value |
| 459 | * is irrelevant). |
| 460 | */ |
| 461 | void resize(int newCapacity) { |
| 462 | Entry<K,V>[] oldTable = getTable(); |
| 463 | int oldCapacity = oldTable.length; |
| 464 | if (oldCapacity == MAXIMUM_CAPACITY) { |
| 465 | threshold = Integer.MAX_VALUE; |
| 466 | return; |
| 467 | } |
| 468 | |
| 469 | Entry<K,V>[] newTable = newTable(newCapacity); |
| 470 | transfer(oldTable, newTable); |
| 471 | table = newTable; |
| 472 | |
| 473 | /* |
| 474 | * If ignoring null elements and processing ref queue caused massive |
| 475 | * shrinkage, then restore old table. This should be rare, but avoids |
| 476 | * unbounded expansion of garbage-filled tables. |
| 477 | */ |
| 478 | if (size >= threshold / 2) { |
| 479 | threshold = (int)(newCapacity * loadFactor); |
| 480 | } else { |
| 481 | expungeStaleEntries(); |
| 482 | transfer(newTable, oldTable); |
| 483 | table = oldTable; |
| 484 | } |
| 485 | } |
| 486 | |
| 487 | /** Transfers all entries from src to dest tables */ |
| 488 | private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest) { |
| 489 | for (int j = 0; j < src.length; ++j) { |
| 490 | Entry<K,V> e = src[j]; |
| 491 | src[j] = null; |
| 492 | while (e != null) { |
| 493 | Entry<K,V> next = e.next; |
| 494 | Object key = e.get(); |
| 495 | if (key == null) { |
| 496 | e.next = null; // Help GC |
| 497 | e.value = null; // " " |
| 498 | size--; |
| 499 | } else { |
| 500 | int i = indexFor(e.hash, dest.length); |
| 501 | e.next = dest[i]; |
| 502 | dest[i] = e; |
| 503 | } |
| 504 | e = next; |
| 505 | } |
| 506 | } |
| 507 | } |
| 508 | |
| 509 | /** |
| 510 | * Copies all of the mappings from the specified map to this map. |
| 511 | * These mappings will replace any mappings that this map had for any |
| 512 | * of the keys currently in the specified map. |
| 513 | * |
| 514 | * @param m mappings to be stored in this map. |
| 515 | * @throws NullPointerException if the specified map is null. |
| 516 | */ |
| 517 | public void putAll(Map<? extends K, ? extends V> m) { |
| 518 | int numKeysToBeAdded = m.size(); |
| 519 | if (numKeysToBeAdded == 0) |
| 520 | return; |
| 521 | |
| 522 | /* |
| 523 | * Expand the map if the map if the number of mappings to be added |
| 524 | * is greater than or equal to threshold. This is conservative; the |
| 525 | * obvious condition is (m.size() + size) >= threshold, but this |
| 526 | * condition could result in a map with twice the appropriate capacity, |
| 527 | * if the keys to be added overlap with the keys already in this map. |
| 528 | * By using the conservative calculation, we subject ourself |
| 529 | * to at most one extra resize. |
| 530 | */ |
| 531 | if (numKeysToBeAdded > threshold) { |
| 532 | int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1); |
| 533 | if (targetCapacity > MAXIMUM_CAPACITY) |
| 534 | targetCapacity = MAXIMUM_CAPACITY; |
| 535 | int newCapacity = table.length; |
| 536 | while (newCapacity < targetCapacity) |
| 537 | newCapacity <<= 1; |
| 538 | if (newCapacity > table.length) |
| 539 | resize(newCapacity); |
| 540 | } |
| 541 | |
| 542 | for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) |
| 543 | put(e.getKey(), e.getValue()); |
| 544 | } |
| 545 | |
| 546 | /** |
| 547 | * Removes the mapping for a key from this weak hash map if it is present. |
| 548 | * More formally, if this map contains a mapping from key <tt>k</tt> to |
| 549 | * value <tt>v</tt> such that <code>(key==null ? k==null : |
| 550 | * key.equals(k))</code>, that mapping is removed. (The map can contain |
| 551 | * at most one such mapping.) |
| 552 | * |
| 553 | * <p>Returns the value to which this map previously associated the key, |
| 554 | * or <tt>null</tt> if the map contained no mapping for the key. A |
| 555 | * return value of <tt>null</tt> does not <i>necessarily</i> indicate |
| 556 | * that the map contained no mapping for the key; it's also possible |
| 557 | * that the map explicitly mapped the key to <tt>null</tt>. |
| 558 | * |
| 559 | * <p>The map will not contain a mapping for the specified key once the |
| 560 | * call returns. |
| 561 | * |
| 562 | * @param key key whose mapping is to be removed from the map |
| 563 | * @return the previous value associated with <tt>key</tt>, or |
| 564 | * <tt>null</tt> if there was no mapping for <tt>key</tt> |
| 565 | */ |
| 566 | public V remove(Object key) { |
| 567 | Object k = maskNull(key); |
| 568 | int h = HashMap.hash(k.hashCode()); |
| 569 | Entry<K,V>[] tab = getTable(); |
| 570 | int i = indexFor(h, tab.length); |
| 571 | Entry<K,V> prev = tab[i]; |
| 572 | Entry<K,V> e = prev; |
| 573 | |
| 574 | while (e != null) { |
| 575 | Entry<K,V> next = e.next; |
| 576 | if (h == e.hash && eq(k, e.get())) { |
| 577 | modCount++; |
| 578 | size--; |
| 579 | if (prev == e) |
| 580 | tab[i] = next; |
| 581 | else |
| 582 | prev.next = next; |
| 583 | return e.value; |
| 584 | } |
| 585 | prev = e; |
| 586 | e = next; |
| 587 | } |
| 588 | |
| 589 | return null; |
| 590 | } |
| 591 | |
| 592 | /** Special version of remove needed by Entry set */ |
| 593 | boolean removeMapping(Object o) { |
| 594 | if (!(o instanceof Map.Entry)) |
| 595 | return false; |
| 596 | Entry<K,V>[] tab = getTable(); |
| 597 | Map.Entry<?,?> entry = (Map.Entry<?,?>)o; |
| 598 | Object k = maskNull(entry.getKey()); |
| 599 | int h = HashMap.hash(k.hashCode()); |
| 600 | int i = indexFor(h, tab.length); |
| 601 | Entry<K,V> prev = tab[i]; |
| 602 | Entry<K,V> e = prev; |
| 603 | |
| 604 | while (e != null) { |
| 605 | Entry<K,V> next = e.next; |
| 606 | if (h == e.hash && e.equals(entry)) { |
| 607 | modCount++; |
| 608 | size--; |
| 609 | if (prev == e) |
| 610 | tab[i] = next; |
| 611 | else |
| 612 | prev.next = next; |
| 613 | return true; |
| 614 | } |
| 615 | prev = e; |
| 616 | e = next; |
| 617 | } |
| 618 | |
| 619 | return false; |
| 620 | } |
| 621 | |
| 622 | /** |
| 623 | * Removes all of the mappings from this map. |
| 624 | * The map will be empty after this call returns. |
| 625 | */ |
| 626 | public void clear() { |
| 627 | // clear out ref queue. We don't need to expunge entries |
| 628 | // since table is getting cleared. |
| 629 | while (queue.poll() != null) |
| 630 | ; |
| 631 | |
| 632 | modCount++; |
| 633 | Arrays.fill(table, null); |
| 634 | size = 0; |
| 635 | |
| 636 | // Allocation of array may have caused GC, which may have caused |
| 637 | // additional entries to go stale. Removing these entries from the |
| 638 | // reference queue will make them eligible for reclamation. |
| 639 | while (queue.poll() != null) |
| 640 | ; |
| 641 | } |
| 642 | |
| 643 | /** |
| 644 | * Returns <tt>true</tt> if this map maps one or more keys to the |
| 645 | * specified value. |
| 646 | * |
| 647 | * @param value value whose presence in this map is to be tested |
| 648 | * @return <tt>true</tt> if this map maps one or more keys to the |
| 649 | * specified value |
| 650 | */ |
| 651 | public boolean containsValue(Object value) { |
| 652 | if (value==null) |
| 653 | return containsNullValue(); |
| 654 | |
| 655 | Entry<K,V>[] tab = getTable(); |
| 656 | for (int i = tab.length; i-- > 0;) |
| 657 | for (Entry<K,V> e = tab[i]; e != null; e = e.next) |
| 658 | if (value.equals(e.value)) |
| 659 | return true; |
| 660 | return false; |
| 661 | } |
| 662 | |
| 663 | /** |
| 664 | * Special-case code for containsValue with null argument |
| 665 | */ |
| 666 | private boolean containsNullValue() { |
| 667 | Entry<K,V>[] tab = getTable(); |
| 668 | for (int i = tab.length; i-- > 0;) |
| 669 | for (Entry<K,V> e = tab[i]; e != null; e = e.next) |
| 670 | if (e.value==null) |
| 671 | return true; |
| 672 | return false; |
| 673 | } |
| 674 | |
| 675 | /** |
| 676 | * The entries in this hash table extend WeakReference, using its main ref |
| 677 | * field as the key. |
| 678 | */ |
| 679 | private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> { |
| 680 | V value; |
| 681 | final int hash; |
| 682 | Entry<K,V> next; |
| 683 | |
| 684 | /** |
| 685 | * Creates new entry. |
| 686 | */ |
| 687 | Entry(Object key, V value, |
| 688 | ReferenceQueue<Object> queue, |
| 689 | int hash, Entry<K,V> next) { |
| 690 | super(key, queue); |
| 691 | this.value = value; |
| 692 | this.hash = hash; |
| 693 | this.next = next; |
| 694 | } |
| 695 | |
| 696 | @SuppressWarnings("unchecked") |
| 697 | public K getKey() { |
| 698 | return (K) WeakHashMap.unmaskNull(get()); |
| 699 | } |
| 700 | |
| 701 | public V getValue() { |
| 702 | return value; |
| 703 | } |
| 704 | |
| 705 | public V setValue(V newValue) { |
| 706 | V oldValue = value; |
| 707 | value = newValue; |
| 708 | return oldValue; |
| 709 | } |
| 710 | |
| 711 | public boolean equals(Object o) { |
| 712 | if (!(o instanceof Map.Entry)) |
| 713 | return false; |
| 714 | Map.Entry<?,?> e = (Map.Entry<?,?>)o; |
| 715 | K k1 = getKey(); |
| 716 | Object k2 = e.getKey(); |
| 717 | if (k1 == k2 || (k1 != null && k1.equals(k2))) { |
| 718 | V v1 = getValue(); |
| 719 | Object v2 = e.getValue(); |
| 720 | if (v1 == v2 || (v1 != null && v1.equals(v2))) |
| 721 | return true; |
| 722 | } |
| 723 | return false; |
| 724 | } |
| 725 | |
| 726 | public int hashCode() { |
| 727 | K k = getKey(); |
| 728 | V v = getValue(); |
| 729 | return ((k==null ? 0 : k.hashCode()) ^ |
| 730 | (v==null ? 0 : v.hashCode())); |
| 731 | } |
| 732 | |
| 733 | public String toString() { |
| 734 | return getKey() + "=" + getValue(); |
| 735 | } |
| 736 | } |
| 737 | |
| 738 | private abstract class HashIterator<T> implements Iterator<T> { |
| 739 | private int index; |
| 740 | private Entry<K,V> entry = null; |
| 741 | private Entry<K,V> lastReturned = null; |
| 742 | private int expectedModCount = modCount; |
| 743 | |
| 744 | /** |
| 745 | * Strong reference needed to avoid disappearance of key |
| 746 | * between hasNext and next |
| 747 | */ |
| 748 | private Object nextKey = null; |
| 749 | |
| 750 | /** |
| 751 | * Strong reference needed to avoid disappearance of key |
| 752 | * between nextEntry() and any use of the entry |
| 753 | */ |
| 754 | private Object currentKey = null; |
| 755 | |
| 756 | HashIterator() { |
| 757 | index = isEmpty() ? 0 : table.length; |
| 758 | } |
| 759 | |
| 760 | public boolean hasNext() { |
| 761 | Entry<K,V>[] t = table; |
| 762 | |
| 763 | while (nextKey == null) { |
| 764 | Entry<K,V> e = entry; |
| 765 | int i = index; |
| 766 | while (e == null && i > 0) |
| 767 | e = t[--i]; |
| 768 | entry = e; |
| 769 | index = i; |
| 770 | if (e == null) { |
| 771 | currentKey = null; |
| 772 | return false; |
| 773 | } |
| 774 | nextKey = e.get(); // hold on to key in strong ref |
| 775 | if (nextKey == null) |
| 776 | entry = entry.next; |
| 777 | } |
| 778 | return true; |
| 779 | } |
| 780 | |
| 781 | /** The common parts of next() across different types of iterators */ |
| 782 | protected Entry<K,V> nextEntry() { |
| 783 | if (modCount != expectedModCount) |
| 784 | throw new ConcurrentModificationException(); |
| 785 | if (nextKey == null && !hasNext()) |
| 786 | throw new NoSuchElementException(); |
| 787 | |
| 788 | lastReturned = entry; |
| 789 | entry = entry.next; |
| 790 | currentKey = nextKey; |
| 791 | nextKey = null; |
| 792 | return lastReturned; |
| 793 | } |
| 794 | |
| 795 | public void remove() { |
| 796 | if (lastReturned == null) |
| 797 | throw new IllegalStateException(); |
| 798 | if (modCount != expectedModCount) |
| 799 | throw new ConcurrentModificationException(); |
| 800 | |
| 801 | WeakHashMap.this.remove(currentKey); |
| 802 | expectedModCount = modCount; |
| 803 | lastReturned = null; |
| 804 | currentKey = null; |
| 805 | } |
| 806 | |
| 807 | } |
| 808 | |
| 809 | private class ValueIterator extends HashIterator<V> { |
| 810 | public V next() { |
| 811 | return nextEntry().value; |
| 812 | } |
| 813 | } |
| 814 | |
| 815 | private class KeyIterator extends HashIterator<K> { |
| 816 | public K next() { |
| 817 | return nextEntry().getKey(); |
| 818 | } |
| 819 | } |
| 820 | |
| 821 | private class EntryIterator extends HashIterator<Map.Entry<K,V>> { |
| 822 | public Map.Entry<K,V> next() { |
| 823 | return nextEntry(); |
| 824 | } |
| 825 | } |
| 826 | |
| 827 | // Views |
| 828 | |
| 829 | private transient Set<Map.Entry<K,V>> entrySet = null; |
| 830 | |
| 831 | /** |
| 832 | * Returns a {@link Set} view of the keys contained in this map. |
| 833 | * The set is backed by the map, so changes to the map are |
| 834 | * reflected in the set, and vice-versa. If the map is modified |
| 835 | * while an iteration over the set is in progress (except through |
| 836 | * the iterator's own <tt>remove</tt> operation), the results of |
| 837 | * the iteration are undefined. The set supports element removal, |
| 838 | * which removes the corresponding mapping from the map, via the |
| 839 | * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, |
| 840 | * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> |
| 841 | * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> |
| 842 | * operations. |
| 843 | */ |
| 844 | public Set<K> keySet() { |
| 845 | Set<K> ks = keySet; |
| 846 | return (ks != null ? ks : (keySet = new KeySet())); |
| 847 | } |
| 848 | |
| 849 | private class KeySet extends AbstractSet<K> { |
| 850 | public Iterator<K> iterator() { |
| 851 | return new KeyIterator(); |
| 852 | } |
| 853 | |
| 854 | public int size() { |
| 855 | return WeakHashMap.this.size(); |
| 856 | } |
| 857 | |
| 858 | public boolean contains(Object o) { |
| 859 | return containsKey(o); |
| 860 | } |
| 861 | |
| 862 | public boolean remove(Object o) { |
| 863 | if (containsKey(o)) { |
| 864 | WeakHashMap.this.remove(o); |
| 865 | return true; |
| 866 | } |
| 867 | else |
| 868 | return false; |
| 869 | } |
| 870 | |
| 871 | public void clear() { |
| 872 | WeakHashMap.this.clear(); |
| 873 | } |
| 874 | } |
| 875 | |
| 876 | /** |
| 877 | * Returns a {@link Collection} view of the values contained in this map. |
| 878 | * The collection is backed by the map, so changes to the map are |
| 879 | * reflected in the collection, and vice-versa. If the map is |
| 880 | * modified while an iteration over the collection is in progress |
| 881 | * (except through the iterator's own <tt>remove</tt> operation), |
| 882 | * the results of the iteration are undefined. The collection |
| 883 | * supports element removal, which removes the corresponding |
| 884 | * mapping from the map, via the <tt>Iterator.remove</tt>, |
| 885 | * <tt>Collection.remove</tt>, <tt>removeAll</tt>, |
| 886 | * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not |
| 887 | * support the <tt>add</tt> or <tt>addAll</tt> operations. |
| 888 | */ |
| 889 | public Collection<V> values() { |
| 890 | Collection<V> vs = values; |
| 891 | return (vs != null) ? vs : (values = new Values()); |
| 892 | } |
| 893 | |
| 894 | private class Values extends AbstractCollection<V> { |
| 895 | public Iterator<V> iterator() { |
| 896 | return new ValueIterator(); |
| 897 | } |
| 898 | |
| 899 | public int size() { |
| 900 | return WeakHashMap.this.size(); |
| 901 | } |
| 902 | |
| 903 | public boolean contains(Object o) { |
| 904 | return containsValue(o); |
| 905 | } |
| 906 | |
| 907 | public void clear() { |
| 908 | WeakHashMap.this.clear(); |
| 909 | } |
| 910 | } |
| 911 | |
| 912 | /** |
| 913 | * Returns a {@link Set} view of the mappings contained in this map. |
| 914 | * The set is backed by the map, so changes to the map are |
| 915 | * reflected in the set, and vice-versa. If the map is modified |
| 916 | * while an iteration over the set is in progress (except through |
| 917 | * the iterator's own <tt>remove</tt> operation, or through the |
| 918 | * <tt>setValue</tt> operation on a map entry returned by the |
| 919 | * iterator) the results of the iteration are undefined. The set |
| 920 | * supports element removal, which removes the corresponding |
| 921 | * mapping from the map, via the <tt>Iterator.remove</tt>, |
| 922 | * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and |
| 923 | * <tt>clear</tt> operations. It does not support the |
| 924 | * <tt>add</tt> or <tt>addAll</tt> operations. |
| 925 | */ |
| 926 | public Set<Map.Entry<K,V>> entrySet() { |
| 927 | Set<Map.Entry<K,V>> es = entrySet; |
| 928 | return es != null ? es : (entrySet = new EntrySet()); |
| 929 | } |
| 930 | |
| 931 | private class EntrySet extends AbstractSet<Map.Entry<K,V>> { |
| 932 | public Iterator<Map.Entry<K,V>> iterator() { |
| 933 | return new EntryIterator(); |
| 934 | } |
| 935 | |
| 936 | public boolean contains(Object o) { |
| 937 | if (!(o instanceof Map.Entry)) |
| 938 | return false; |
| 939 | Map.Entry<?,?> e = (Map.Entry<?,?>)o; |
| 940 | Entry<K,V> candidate = getEntry(e.getKey()); |
| 941 | return candidate != null && candidate.equals(e); |
| 942 | } |
| 943 | |
| 944 | public boolean remove(Object o) { |
| 945 | return removeMapping(o); |
| 946 | } |
| 947 | |
| 948 | public int size() { |
| 949 | return WeakHashMap.this.size(); |
| 950 | } |
| 951 | |
| 952 | public void clear() { |
| 953 | WeakHashMap.this.clear(); |
| 954 | } |
| 955 | |
| 956 | private List<Map.Entry<K,V>> deepCopy() { |
| 957 | List<Map.Entry<K,V>> list = |
| 958 | new ArrayList<Map.Entry<K,V>>(size()); |
| 959 | for (Map.Entry<K,V> e : this) |
| 960 | list.add(new AbstractMap.SimpleEntry<K,V>(e)); |
| 961 | return list; |
| 962 | } |
| 963 | |
| 964 | public Object[] toArray() { |
| 965 | return deepCopy().toArray(); |
| 966 | } |
| 967 | |
| 968 | public <T> T[] toArray(T[] a) { |
| 969 | return deepCopy().toArray(a); |
| 970 | } |
| 971 | } |
| 972 | } |