HashMap.java revision 46e3649f898305d185fc40bae2542e933a16b619
1/* 2 * Copyright (c) 1997, 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 26package java.util; 27import java.io.*; 28 29/** 30 * Hash table based implementation of the <tt>Map</tt> interface. This 31 * implementation provides all of the optional map operations, and permits 32 * <tt>null</tt> values and the <tt>null</tt> key. (The <tt>HashMap</tt> 33 * class is roughly equivalent to <tt>Hashtable</tt>, except that it is 34 * unsynchronized and permits nulls.) This class makes no guarantees as to 35 * the order of the map; in particular, it does not guarantee that the order 36 * will remain constant over time. 37 * 38 * <p>This implementation provides constant-time performance for the basic 39 * operations (<tt>get</tt> and <tt>put</tt>), assuming the hash function 40 * disperses the elements properly among the buckets. Iteration over 41 * collection views requires time proportional to the "capacity" of the 42 * <tt>HashMap</tt> instance (the number of buckets) plus its size (the number 43 * of key-value mappings). Thus, it's very important not to set the initial 44 * capacity too high (or the load factor too low) if iteration performance is 45 * important. 46 * 47 * <p>An instance of <tt>HashMap</tt> has two parameters that affect its 48 * performance: <i>initial capacity</i> and <i>load factor</i>. The 49 * <i>capacity</i> is the number of buckets in the hash table, and the initial 50 * capacity is simply the capacity at the time the hash table is created. The 51 * <i>load factor</i> is a measure of how full the hash table is allowed to 52 * get before its capacity is automatically increased. When the number of 53 * entries in the hash table exceeds the product of the load factor and the 54 * current capacity, the hash table is <i>rehashed</i> (that is, internal data 55 * structures are rebuilt) so that the hash table has approximately twice the 56 * number of buckets. 57 * 58 * <p>As a general rule, the default load factor (.75) offers a good tradeoff 59 * between time and space costs. Higher values decrease the space overhead 60 * but increase the lookup cost (reflected in most of the operations of the 61 * <tt>HashMap</tt> class, including <tt>get</tt> and <tt>put</tt>). The 62 * expected number of entries in the map and its load factor should be taken 63 * into account when setting its initial capacity, so as to minimize the 64 * number of rehash operations. If the initial capacity is greater 65 * than the maximum number of entries divided by the load factor, no 66 * rehash operations will ever occur. 67 * 68 * <p>If many mappings are to be stored in a <tt>HashMap</tt> instance, 69 * creating it with a sufficiently large capacity will allow the mappings to 70 * be stored more efficiently than letting it perform automatic rehashing as 71 * needed to grow the table. 72 * 73 * <p><strong>Note that this implementation is not synchronized.</strong> 74 * If multiple threads access a hash map concurrently, and at least one of 75 * the threads modifies the map structurally, it <i>must</i> be 76 * synchronized externally. (A structural modification is any operation 77 * that adds or deletes one or more mappings; merely changing the value 78 * associated with a key that an instance already contains is not a 79 * structural modification.) This is typically accomplished by 80 * synchronizing on some object that naturally encapsulates the map. 81 * 82 * If no such object exists, the map should be "wrapped" using the 83 * {@link Collections#synchronizedMap Collections.synchronizedMap} 84 * method. This is best done at creation time, to prevent accidental 85 * unsynchronized access to the map:<pre> 86 * Map m = Collections.synchronizedMap(new HashMap(...));</pre> 87 * 88 * <p>The iterators returned by all of this class's "collection view methods" 89 * are <i>fail-fast</i>: if the map is structurally modified at any time after 90 * the iterator is created, in any way except through the iterator's own 91 * <tt>remove</tt> method, the iterator will throw a 92 * {@link ConcurrentModificationException}. Thus, in the face of concurrent 93 * modification, the iterator fails quickly and cleanly, rather than risking 94 * arbitrary, non-deterministic behavior at an undetermined time in the 95 * future. 96 * 97 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed 98 * as it is, generally speaking, impossible to make any hard guarantees in the 99 * presence of unsynchronized concurrent modification. Fail-fast iterators 100 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. 101 * Therefore, it would be wrong to write a program that depended on this 102 * exception for its correctness: <i>the fail-fast behavior of iterators 103 * should be used only to detect bugs.</i> 104 * 105 * <p>This class is a member of the 106 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 107 * Java Collections Framework</a>. 108 * 109 * @param <K> the type of keys maintained by this map 110 * @param <V> the type of mapped values 111 * 112 * @author Doug Lea 113 * @author Josh Bloch 114 * @author Arthur van Hoff 115 * @author Neal Gafter 116 * @see Object#hashCode() 117 * @see Collection 118 * @see Map 119 * @see TreeMap 120 * @see Hashtable 121 * @since 1.2 122 */ 123 124public class HashMap<K,V> 125 extends AbstractMap<K,V> 126 implements Map<K,V>, Cloneable, Serializable 127{ 128 129 /** 130 * The default initial capacity - MUST be a power of two. 131 */ 132 static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16 133 134 /** 135 * The maximum capacity, used if a higher value is implicitly specified 136 * by either of the constructors with arguments. 137 * MUST be a power of two <= 1<<30. 138 */ 139 static final int MAXIMUM_CAPACITY = 1 << 30; 140 141 /** 142 * The load factor used when none specified in constructor. 143 */ 144 static final float DEFAULT_LOAD_FACTOR = 0.75f; 145 146 /** 147 * An empty table instance to share when the table is not inflated. 148 */ 149 static final Entry<?,?>[] EMPTY_TABLE = {}; 150 151 /** 152 * The table, resized as necessary. Length MUST Always be a power of two. 153 */ 154 transient Entry<K,V>[] table = (Entry<K,V>[]) EMPTY_TABLE; 155 156 /** 157 * The number of key-value mappings contained in this map. 158 */ 159 transient int size; 160 161 /** 162 * The next size value at which to resize (capacity * load factor). 163 * @serial 164 */ 165 // If table == EMPTY_TABLE then this is the initial capacity at which the 166 // table will be created when inflated. 167 int threshold; 168 169 /** 170 * The load factor for the hash table. 171 * 172 * @serial 173 */ 174 final float loadFactor; 175 176 /** 177 * The number of times this HashMap has been structurally modified 178 * Structural modifications are those that change the number of mappings in 179 * the HashMap or otherwise modify its internal structure (e.g., 180 * rehash). This field is used to make iterators on Collection-views of 181 * the HashMap fail-fast. (See ConcurrentModificationException). 182 */ 183 transient int modCount; 184 185 /** 186 * The default threshold of map capacity above which alternative hashing is 187 * used for String keys. Alternative hashing reduces the incidence of 188 * collisions due to weak hash code calculation for String keys. 189 * <p/> 190 * This value may be overridden by defining the system property 191 * {@code jdk.map.althashing.threshold}. A property value of {@code 1} 192 * forces alternative hashing to be used at all times whereas 193 * {@code -1} value ensures that alternative hashing is never used. 194 */ 195 static final int ALTERNATIVE_HASHING_THRESHOLD_DEFAULT = Integer.MAX_VALUE; 196 197 /** 198 * holds values which can't be initialized until after VM is booted. 199 */ 200 private static class Holder { 201 202 /** 203 * Table capacity above which to switch to use alternative hashing. 204 */ 205 static final int ALTERNATIVE_HASHING_THRESHOLD; 206 207 static { 208 String altThreshold = java.security.AccessController.doPrivileged( 209 new sun.security.action.GetPropertyAction( 210 "jdk.map.althashing.threshold")); 211 212 int threshold; 213 try { 214 threshold = (null != altThreshold) 215 ? Integer.parseInt(altThreshold) 216 : ALTERNATIVE_HASHING_THRESHOLD_DEFAULT; 217 218 // disable alternative hashing if -1 219 if (threshold == -1) { 220 threshold = Integer.MAX_VALUE; 221 } 222 223 if (threshold < 0) { 224 throw new IllegalArgumentException("value must be positive integer."); 225 } 226 } catch(IllegalArgumentException failed) { 227 throw new Error("Illegal value for 'jdk.map.althashing.threshold'", failed); 228 } 229 230 ALTERNATIVE_HASHING_THRESHOLD = threshold; 231 } 232 } 233 234 /** 235 * A randomizing value associated with this instance that is applied to 236 * hash code of keys to make hash collisions harder to find. If 0 then 237 * alternative hashing is disabled. 238 */ 239 transient int hashSeed = 0; 240 241 /** 242 * Constructs an empty <tt>HashMap</tt> with the specified initial 243 * capacity and load factor. 244 * 245 * @param initialCapacity the initial capacity 246 * @param loadFactor the load factor 247 * @throws IllegalArgumentException if the initial capacity is negative 248 * or the load factor is nonpositive 249 */ 250 public HashMap(int initialCapacity, float loadFactor) { 251 if (initialCapacity < 0) 252 throw new IllegalArgumentException("Illegal initial capacity: " + 253 initialCapacity); 254 if (initialCapacity > MAXIMUM_CAPACITY) 255 initialCapacity = MAXIMUM_CAPACITY; 256 if (loadFactor <= 0 || Float.isNaN(loadFactor)) 257 throw new IllegalArgumentException("Illegal load factor: " + 258 loadFactor); 259 260 this.loadFactor = loadFactor; 261 if (initialCapacity < 2) { 262 initialCapacity = 2; 263 } 264 threshold = initialCapacity; 265 init(); 266 } 267 268 /** 269 * Constructs an empty <tt>HashMap</tt> with the specified initial 270 * capacity and the default load factor (0.75). 271 * 272 * @param initialCapacity the initial capacity. 273 * @throws IllegalArgumentException if the initial capacity is negative. 274 */ 275 public HashMap(int initialCapacity) { 276 this(initialCapacity, DEFAULT_LOAD_FACTOR); 277 } 278 279 /** 280 * Constructs an empty <tt>HashMap</tt> with the default initial capacity 281 * (16) and the default load factor (0.75). 282 */ 283 public HashMap() { 284 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR); 285 } 286 287 /** 288 * Constructs a new <tt>HashMap</tt> with the same mappings as the 289 * specified <tt>Map</tt>. The <tt>HashMap</tt> is created with 290 * default load factor (0.75) and an initial capacity sufficient to 291 * hold the mappings in the specified <tt>Map</tt>. 292 * 293 * @param m the map whose mappings are to be placed in this map 294 * @throws NullPointerException if the specified map is null 295 */ 296 public HashMap(Map<? extends K, ? extends V> m) { 297 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, 298 DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR); 299 inflateTable(threshold); 300 301 putAllForCreate(m); 302 } 303 304 private static int roundUpToPowerOf2(int number) { 305 // assert number >= 0 : "number must be non-negative"; 306 int rounded = number >= MAXIMUM_CAPACITY 307 ? MAXIMUM_CAPACITY 308 : (rounded = Integer.highestOneBit(number)) != 0 309 ? (Integer.bitCount(number) > 1) ? rounded << 1 : rounded 310 : 1; 311 312 return rounded; 313 } 314 315 /** 316 * Inflates the table. 317 */ 318 private void inflateTable(int toSize) { 319 int capacity = (int) (roundUpToPowerOf2(toSize) * loadFactor); 320 threshold = (capacity <= MAXIMUM_CAPACITY + 1) ? capacity : MAXIMUM_CAPACITY + 1; 321 322 table = new Entry[capacity]; 323 initHashSeedAsNeeded(capacity); 324 } 325 326 // internal utilities 327 328 /** 329 * Initialization hook for subclasses. This method is called 330 * in all constructors and pseudo-constructors (clone, readObject) 331 * after HashMap has been initialized but before any entries have 332 * been inserted. (In the absence of this method, readObject would 333 * require explicit knowledge of subclasses.) 334 */ 335 void init() { 336 } 337 338 /** 339 * Initialize the hashing mask value. We defer initialization until we 340 * really need it. 341 */ 342 final boolean initHashSeedAsNeeded(int capacity) { 343 boolean currentAltHashing = hashSeed != 0; 344 boolean useAltHashing = sun.misc.VM.isBooted() && 345 (capacity >= Holder.ALTERNATIVE_HASHING_THRESHOLD); 346 boolean switching = currentAltHashing ^ useAltHashing; 347 if (switching) { 348 hashSeed = useAltHashing 349 ? sun.misc.Hashing.randomHashSeed(this) 350 : 0; 351 } 352 return switching; 353 } 354 355 /** 356 * Retrieve object hash code and applies a supplemental hash function to the 357 * result hash, which defends against poor quality hash functions. This is 358 * critical because HashMap uses power-of-two length hash tables, that 359 * otherwise encounter collisions for hashCodes that do not differ 360 * in lower bits. Note: Null keys always map to hash 0, thus index 0. 361 */ 362 final int hash(Object k) { 363 int h = hashSeed; 364 if (0 != h && k instanceof String) { 365 return sun.misc.Hashing.stringHash32((String) k); 366 } 367 368 h ^= k.hashCode(); 369 370 // This function ensures that hashCodes that differ only by 371 // constant multiples at each bit position have a bounded 372 // number of collisions (approximately 8 at default load factor). 373 h ^= (h >>> 20) ^ (h >>> 12); 374 return h ^ (h >>> 7) ^ (h >>> 4); 375 } 376 377 /** 378 * Returns index for hash code h. 379 */ 380 static int indexFor(int h, int length) { 381 // assert Integer.bitCount(length) == 1 : "length must be a non-zero power of 2"; 382 return h & (length-1); 383 } 384 385 /** 386 * Returns the number of key-value mappings in this map. 387 * 388 * @return the number of key-value mappings in this map 389 */ 390 public int size() { 391 return size; 392 } 393 394 /** 395 * Returns <tt>true</tt> if this map contains no key-value mappings. 396 * 397 * @return <tt>true</tt> if this map contains no key-value mappings 398 */ 399 public boolean isEmpty() { 400 return size == 0; 401 } 402 403 /** 404 * Returns the value to which the specified key is mapped, 405 * or {@code null} if this map contains no mapping for the key. 406 * 407 * <p>More formally, if this map contains a mapping from a key 408 * {@code k} to a value {@code v} such that {@code (key==null ? k==null : 409 * key.equals(k))}, then this method returns {@code v}; otherwise 410 * it returns {@code null}. (There can be at most one such mapping.) 411 * 412 * <p>A return value of {@code null} does not <i>necessarily</i> 413 * indicate that the map contains no mapping for the key; it's also 414 * possible that the map explicitly maps the key to {@code null}. 415 * The {@link #containsKey containsKey} operation may be used to 416 * distinguish these two cases. 417 * 418 * @see #put(Object, Object) 419 */ 420 public V get(Object key) { 421 if (key == null) 422 return getForNullKey(); 423 Entry<K,V> entry = getEntry(key); 424 425 return null == entry ? null : entry.getValue(); 426 } 427 428 /** 429 * Offloaded version of get() to look up null keys. Null keys map 430 * to index 0. This null case is split out into separate methods 431 * for the sake of performance in the two most commonly used 432 * operations (get and put), but incorporated with conditionals in 433 * others. 434 */ 435 private V getForNullKey() { 436 if (size == 0) { 437 return null; 438 } 439 for (Entry<K,V> e = table[0]; e != null; e = e.next) { 440 if (e.key == null) 441 return e.value; 442 } 443 return null; 444 } 445 446 /** 447 * Returns <tt>true</tt> if this map contains a mapping for the 448 * specified key. 449 * 450 * @param key The key whose presence in this map is to be tested 451 * @return <tt>true</tt> if this map contains a mapping for the specified 452 * key. 453 */ 454 public boolean containsKey(Object key) { 455 return getEntry(key) != null; 456 } 457 458 /** 459 * Returns the entry associated with the specified key in the 460 * HashMap. Returns null if the HashMap contains no mapping 461 * for the key. 462 */ 463 final Entry<K,V> getEntry(Object key) { 464 if (size == 0) { 465 return null; 466 } 467 468 int hash = (key == null) ? 0 : hash(key); 469 for (Entry<K,V> e = table[indexFor(hash, table.length)]; 470 e != null; 471 e = e.next) { 472 Object k; 473 if (e.hash == hash && 474 ((k = e.key) == key || (key != null && key.equals(k)))) 475 return e; 476 } 477 return null; 478 } 479 480 /** 481 * Associates the specified value with the specified key in this map. 482 * If the map previously contained a mapping for the key, the old 483 * value is replaced. 484 * 485 * @param key key with which the specified value is to be associated 486 * @param value value to be associated with the specified key 487 * @return the previous value associated with <tt>key</tt>, or 488 * <tt>null</tt> if there was no mapping for <tt>key</tt>. 489 * (A <tt>null</tt> return can also indicate that the map 490 * previously associated <tt>null</tt> with <tt>key</tt>.) 491 */ 492 public V put(K key, V value) { 493 if (table == EMPTY_TABLE) { 494 inflateTable(threshold); 495 } 496 if (key == null) 497 return putForNullKey(value); 498 int hash = hash(key); 499 int i = indexFor(hash, table.length); 500 for (Entry<K,V> e = table[i]; e != null; e = e.next) { 501 Object k; 502 if (e.hash == hash && ((k = e.key) == key || key.equals(k))) { 503 V oldValue = e.value; 504 e.value = value; 505 e.recordAccess(this); 506 return oldValue; 507 } 508 } 509 510 modCount++; 511 addEntry(hash, key, value, i); 512 return null; 513 } 514 515 /** 516 * Offloaded version of put for null keys 517 */ 518 private V putForNullKey(V value) { 519 for (Entry<K,V> e = table[0]; e != null; e = e.next) { 520 if (e.key == null) { 521 V oldValue = e.value; 522 e.value = value; 523 e.recordAccess(this); 524 return oldValue; 525 } 526 } 527 modCount++; 528 addEntry(0, null, value, 0); 529 return null; 530 } 531 532 /** 533 * This method is used instead of put by constructors and 534 * pseudoconstructors (clone, readObject). It does not resize the table, 535 * check for comodification, etc. It calls createEntry rather than 536 * addEntry. 537 */ 538 private void putForCreate(K key, V value) { 539 int hash = null == key ? 0 : hash(key); 540 int i = indexFor(hash, table.length); 541 542 /** 543 * Look for preexisting entry for key. This will never happen for 544 * clone or deserialize. It will only happen for construction if the 545 * input Map is a sorted map whose ordering is inconsistent w/ equals. 546 */ 547 for (Entry<K,V> e = table[i]; e != null; e = e.next) { 548 Object k; 549 if (e.hash == hash && 550 ((k = e.key) == key || (key != null && key.equals(k)))) { 551 e.value = value; 552 return; 553 } 554 } 555 556 createEntry(hash, key, value, i); 557 } 558 559 private void putAllForCreate(Map<? extends K, ? extends V> m) { 560 for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) 561 putForCreate(e.getKey(), e.getValue()); 562 } 563 564 /** 565 * Rehashes the contents of this map into a new array with a 566 * larger capacity. This method is called automatically when the 567 * number of keys in this map reaches its threshold. 568 * 569 * If current capacity is MAXIMUM_CAPACITY, this method does not 570 * resize the map, but sets threshold to Integer.MAX_VALUE. 571 * This has the effect of preventing future calls. 572 * 573 * @param newCapacity the new capacity, MUST be a power of two; 574 * must be greater than current capacity unless current 575 * capacity is MAXIMUM_CAPACITY (in which case value 576 * is irrelevant). 577 */ 578 void resize(int newCapacity) { 579 Entry[] oldTable = table; 580 int oldCapacity = oldTable.length; 581 if (oldCapacity == MAXIMUM_CAPACITY) { 582 threshold = Integer.MAX_VALUE; 583 return; 584 } 585 586 Entry[] newTable = new Entry[newCapacity]; 587 transfer(newTable, initHashSeedAsNeeded(newCapacity)); 588 table = newTable; 589 threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1); 590 } 591 592 /** 593 * Transfers all entries from current table to newTable. 594 */ 595 void transfer(Entry[] newTable, boolean rehash) { 596 int newCapacity = newTable.length; 597 for (Entry<K,V> e : table) { 598 while(null != e) { 599 Entry<K,V> next = e.next; 600 if (rehash) { 601 e.hash = null == e.key ? 0 : hash(e.key); 602 } 603 int i = indexFor(e.hash, newCapacity); 604 e.next = newTable[i]; 605 newTable[i] = e; 606 e = next; 607 } 608 } 609 } 610 611 /** 612 * Copies all of the mappings from the specified map to this map. 613 * These mappings will replace any mappings that this map had for 614 * any of the keys currently in the specified map. 615 * 616 * @param m mappings to be stored in this map 617 * @throws NullPointerException if the specified map is null 618 */ 619 public void putAll(Map<? extends K, ? extends V> m) { 620 int numKeysToBeAdded = m.size(); 621 if (numKeysToBeAdded == 0) 622 return; 623 624 if (table == EMPTY_TABLE) { 625 inflateTable((int) Math.max(numKeysToBeAdded * loadFactor, threshold)); 626 } 627 628 /* 629 * Expand the map if the map if the number of mappings to be added 630 * is greater than or equal to threshold. This is conservative; the 631 * obvious condition is (m.size() + size) >= threshold, but this 632 * condition could result in a map with twice the appropriate capacity, 633 * if the keys to be added overlap with the keys already in this map. 634 * By using the conservative calculation, we subject ourself 635 * to at most one extra resize. 636 */ 637 if (numKeysToBeAdded > threshold) { 638 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1); 639 if (targetCapacity > MAXIMUM_CAPACITY) 640 targetCapacity = MAXIMUM_CAPACITY; 641 int newCapacity = table.length; 642 while (newCapacity < targetCapacity) 643 newCapacity <<= 1; 644 if (newCapacity > table.length) 645 resize(newCapacity); 646 } 647 648 for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) 649 put(e.getKey(), e.getValue()); 650 } 651 652 /** 653 * Removes the mapping for the specified key from this map if present. 654 * 655 * @param key key whose mapping is to be removed from the map 656 * @return the previous value associated with <tt>key</tt>, or 657 * <tt>null</tt> if there was no mapping for <tt>key</tt>. 658 * (A <tt>null</tt> return can also indicate that the map 659 * previously associated <tt>null</tt> with <tt>key</tt>.) 660 */ 661 public V remove(Object key) { 662 Entry<K,V> e = removeEntryForKey(key); 663 return (e == null ? null : e.value); 664 } 665 666 /** 667 * Removes and returns the entry associated with the specified key 668 * in the HashMap. Returns null if the HashMap contains no mapping 669 * for this key. 670 */ 671 final Entry<K,V> removeEntryForKey(Object key) { 672 if (size == 0) { 673 return null; 674 } 675 int hash = (key == null) ? 0 : hash(key); 676 int i = indexFor(hash, table.length); 677 Entry<K,V> prev = table[i]; 678 Entry<K,V> e = prev; 679 680 while (e != null) { 681 Entry<K,V> next = e.next; 682 Object k; 683 if (e.hash == hash && 684 ((k = e.key) == key || (key != null && key.equals(k)))) { 685 modCount++; 686 size--; 687 if (prev == e) 688 table[i] = next; 689 else 690 prev.next = next; 691 e.recordRemoval(this); 692 return e; 693 } 694 prev = e; 695 e = next; 696 } 697 698 return e; 699 } 700 701 /** 702 * Special version of remove for EntrySet using {@code Map.Entry.equals()} 703 * for matching. 704 */ 705 final Entry<K,V> removeMapping(Object o) { 706 if (size == 0 || !(o instanceof Map.Entry)) 707 return null; 708 709 Map.Entry<K,V> entry = (Map.Entry<K,V>) o; 710 Object key = entry.getKey(); 711 int hash = (key == null) ? 0 : hash(key); 712 int i = indexFor(hash, table.length); 713 Entry<K,V> prev = table[i]; 714 Entry<K,V> e = prev; 715 716 while (e != null) { 717 Entry<K,V> next = e.next; 718 if (e.hash == hash && e.equals(entry)) { 719 modCount++; 720 size--; 721 if (prev == e) 722 table[i] = next; 723 else 724 prev.next = next; 725 e.recordRemoval(this); 726 return e; 727 } 728 prev = e; 729 e = next; 730 } 731 732 return e; 733 } 734 735 /** 736 * Removes all of the mappings from this map. 737 * The map will be empty after this call returns. 738 */ 739 public void clear() { 740 modCount++; 741 Arrays.fill(table, null); 742 size = 0; 743 } 744 745 /** 746 * Returns <tt>true</tt> if this map maps one or more keys to the 747 * specified value. 748 * 749 * @param value value whose presence in this map is to be tested 750 * @return <tt>true</tt> if this map maps one or more keys to the 751 * specified value 752 */ 753 public boolean containsValue(Object value) { 754 if (value == null) 755 return containsNullValue(); 756 757 Entry[] tab = table; 758 for (int i = 0; i < tab.length ; i++) 759 for (Entry e = tab[i] ; e != null ; e = e.next) 760 if (value.equals(e.value)) 761 return true; 762 return false; 763 } 764 765 /** 766 * Special-case code for containsValue with null argument 767 */ 768 private boolean containsNullValue() { 769 Entry[] tab = table; 770 for (int i = 0; i < tab.length ; i++) 771 for (Entry e = tab[i] ; e != null ; e = e.next) 772 if (e.value == null) 773 return true; 774 return false; 775 } 776 777 /** 778 * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and 779 * values themselves are not cloned. 780 * 781 * @return a shallow copy of this map 782 */ 783 public Object clone() { 784 HashMap<K,V> result = null; 785 try { 786 result = (HashMap<K,V>)super.clone(); 787 } catch (CloneNotSupportedException e) { 788 // assert false; 789 } 790 result.table = new Entry[table.length]; 791 result.entrySet = null; 792 result.modCount = 0; 793 result.size = 0; 794 result.init(); 795 result.putAllForCreate(this); 796 797 return result; 798 } 799 800 // Android-changed: Make HashMap.Entry public. 801 public static class Entry<K,V> implements Map.Entry<K,V> { 802 final K key; 803 V value; 804 Entry<K,V> next; 805 int hash; 806 807 /** 808 * Creates new entry. 809 */ 810 Entry(int h, K k, V v, Entry<K,V> n) { 811 value = v; 812 next = n; 813 key = k; 814 hash = h; 815 } 816 817 public final K getKey() { 818 return key; 819 } 820 821 public final V getValue() { 822 return value; 823 } 824 825 public final V setValue(V newValue) { 826 V oldValue = value; 827 value = newValue; 828 return oldValue; 829 } 830 831 public final boolean equals(Object o) { 832 if (!(o instanceof Map.Entry)) 833 return false; 834 Map.Entry e = (Map.Entry)o; 835 Object k1 = getKey(); 836 Object k2 = e.getKey(); 837 if (k1 == k2 || (k1 != null && k1.equals(k2))) { 838 Object v1 = getValue(); 839 Object v2 = e.getValue(); 840 if (v1 == v2 || (v1 != null && v1.equals(v2))) 841 return true; 842 } 843 return false; 844 } 845 846 public final int hashCode() { 847 return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue()); 848 } 849 850 public final String toString() { 851 return getKey() + "=" + getValue(); 852 } 853 854 /** 855 * This method is invoked whenever the value in an entry is 856 * overwritten by an invocation of put(k,v) for a key k that's already 857 * in the HashMap. 858 */ 859 void recordAccess(HashMap<K,V> m) { 860 } 861 862 /** 863 * This method is invoked whenever the entry is 864 * removed from the table. 865 */ 866 void recordRemoval(HashMap<K,V> m) { 867 } 868 } 869 870 /** 871 * Adds a new entry with the specified key, value and hash code to 872 * the specified bucket. It is the responsibility of this 873 * method to resize the table if appropriate. 874 * 875 * Subclass overrides this to alter the behavior of put method. 876 */ 877 void addEntry(int hash, K key, V value, int bucketIndex) { 878 if ((size >= threshold) && (null != table[bucketIndex])) { 879 resize(2 * table.length); 880 hash = (null != key) ? hash(key) : 0; 881 bucketIndex = indexFor(hash, table.length); 882 } 883 884 createEntry(hash, key, value, bucketIndex); 885 } 886 887 /** 888 * Like addEntry except that this version is used when creating entries 889 * as part of Map construction or "pseudo-construction" (cloning, 890 * deserialization). This version needn't worry about resizing the table. 891 * 892 * Subclass overrides this to alter the behavior of HashMap(Map), 893 * clone, and readObject. 894 */ 895 void createEntry(int hash, K key, V value, int bucketIndex) { 896 Entry<K,V> e = table[bucketIndex]; 897 table[bucketIndex] = new Entry<>(hash, key, value, e); 898 size++; 899 } 900 901 private abstract class HashIterator<E> implements Iterator<E> { 902 Entry<K,V> next; // next entry to return 903 int expectedModCount; // For fast-fail 904 int index; // current slot 905 Entry<K,V> current; // current entry 906 907 HashIterator() { 908 expectedModCount = modCount; 909 if (size > 0) { // advance to first entry 910 Entry[] t = table; 911 while (index < t.length && (next = t[index++]) == null) 912 ; 913 } 914 } 915 916 public final boolean hasNext() { 917 return next != null; 918 } 919 920 final Entry<K,V> nextEntry() { 921 if (modCount != expectedModCount) 922 throw new ConcurrentModificationException(); 923 Entry<K,V> e = next; 924 if (e == null) 925 throw new NoSuchElementException(); 926 927 if ((next = e.next) == null) { 928 Entry[] t = table; 929 while (index < t.length && (next = t[index++]) == null) 930 ; 931 } 932 current = e; 933 return e; 934 } 935 936 public void remove() { 937 if (current == null) 938 throw new IllegalStateException(); 939 if (modCount != expectedModCount) 940 throw new ConcurrentModificationException(); 941 Object k = current.key; 942 current = null; 943 HashMap.this.removeEntryForKey(k); 944 expectedModCount = modCount; 945 } 946 } 947 948 private final class ValueIterator extends HashIterator<V> { 949 public V next() { 950 return nextEntry().value; 951 } 952 } 953 954 private final class KeyIterator extends HashIterator<K> { 955 public K next() { 956 return nextEntry().getKey(); 957 } 958 } 959 960 private final class EntryIterator extends HashIterator<Map.Entry<K,V>> { 961 public Map.Entry<K,V> next() { 962 return nextEntry(); 963 } 964 } 965 966 // Subclass overrides these to alter behavior of views' iterator() method 967 Iterator<K> newKeyIterator() { 968 return new KeyIterator(); 969 } 970 Iterator<V> newValueIterator() { 971 return new ValueIterator(); 972 } 973 Iterator<Map.Entry<K,V>> newEntryIterator() { 974 return new EntryIterator(); 975 } 976 977 978 // Views 979 980 private transient Set<Map.Entry<K,V>> entrySet = null; 981 982 /** 983 * Returns a {@link Set} view of the keys contained in this map. 984 * The set is backed by the map, so changes to the map are 985 * reflected in the set, and vice-versa. If the map is modified 986 * while an iteration over the set is in progress (except through 987 * the iterator's own <tt>remove</tt> operation), the results of 988 * the iteration are undefined. The set supports element removal, 989 * which removes the corresponding mapping from the map, via the 990 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, 991 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> 992 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> 993 * operations. 994 */ 995 public Set<K> keySet() { 996 Set<K> ks = keySet; 997 return (ks != null ? ks : (keySet = new KeySet())); 998 } 999 1000 private final class KeySet extends AbstractSet<K> { 1001 public Iterator<K> iterator() { 1002 return newKeyIterator(); 1003 } 1004 public int size() { 1005 return size; 1006 } 1007 public boolean contains(Object o) { 1008 return containsKey(o); 1009 } 1010 public boolean remove(Object o) { 1011 return HashMap.this.removeEntryForKey(o) != null; 1012 } 1013 public void clear() { 1014 HashMap.this.clear(); 1015 } 1016 } 1017 1018 /** 1019 * Returns a {@link Collection} view of the values contained in this map. 1020 * The collection is backed by the map, so changes to the map are 1021 * reflected in the collection, and vice-versa. If the map is 1022 * modified while an iteration over the collection is in progress 1023 * (except through the iterator's own <tt>remove</tt> operation), 1024 * the results of the iteration are undefined. The collection 1025 * supports element removal, which removes the corresponding 1026 * mapping from the map, via the <tt>Iterator.remove</tt>, 1027 * <tt>Collection.remove</tt>, <tt>removeAll</tt>, 1028 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not 1029 * support the <tt>add</tt> or <tt>addAll</tt> operations. 1030 */ 1031 public Collection<V> values() { 1032 Collection<V> vs = values; 1033 return (vs != null ? vs : (values = new Values())); 1034 } 1035 1036 private final class Values extends AbstractCollection<V> { 1037 public Iterator<V> iterator() { 1038 return newValueIterator(); 1039 } 1040 public int size() { 1041 return size; 1042 } 1043 public boolean contains(Object o) { 1044 return containsValue(o); 1045 } 1046 public void clear() { 1047 HashMap.this.clear(); 1048 } 1049 } 1050 1051 /** 1052 * Returns a {@link Set} view of the mappings contained in this map. 1053 * The set is backed by the map, so changes to the map are 1054 * reflected in the set, and vice-versa. If the map is modified 1055 * while an iteration over the set is in progress (except through 1056 * the iterator's own <tt>remove</tt> operation, or through the 1057 * <tt>setValue</tt> operation on a map entry returned by the 1058 * iterator) the results of the iteration are undefined. The set 1059 * supports element removal, which removes the corresponding 1060 * mapping from the map, via the <tt>Iterator.remove</tt>, 1061 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and 1062 * <tt>clear</tt> operations. It does not support the 1063 * <tt>add</tt> or <tt>addAll</tt> operations. 1064 * 1065 * @return a set view of the mappings contained in this map 1066 */ 1067 // Android-changed: Changed type parameter from <? extends Entry<K, V> 1068 // to a Map.Entry<K, V>. 1069 public Set<Map.Entry<K,V>> entrySet() { 1070 return entrySet0(); 1071 } 1072 1073 private Set<Map.Entry<K,V>> entrySet0() { 1074 Set<Map.Entry<K,V>> es = entrySet; 1075 return es != null ? es : (entrySet = new EntrySet()); 1076 } 1077 1078 private final class EntrySet extends AbstractSet<Map.Entry<K,V>> { 1079 public Iterator<Map.Entry<K,V>> iterator() { 1080 return newEntryIterator(); 1081 } 1082 public boolean contains(Object o) { 1083 if (!(o instanceof Map.Entry)) 1084 return false; 1085 Map.Entry<K,V> e = (Map.Entry<K,V>) o; 1086 Entry<K,V> candidate = getEntry(e.getKey()); 1087 return candidate != null && candidate.equals(e); 1088 } 1089 public boolean remove(Object o) { 1090 return removeMapping(o) != null; 1091 } 1092 public int size() { 1093 return size; 1094 } 1095 public void clear() { 1096 HashMap.this.clear(); 1097 } 1098 } 1099 1100 /** 1101 * Save the state of the <tt>HashMap</tt> instance to a stream (i.e., 1102 * serialize it). 1103 * 1104 * @serialData The <i>capacity</i> of the HashMap (the length of the 1105 * bucket array) is emitted (int), followed by the 1106 * <i>size</i> (an int, the number of key-value 1107 * mappings), followed by the key (Object) and value (Object) 1108 * for each key-value mapping. The key-value mappings are 1109 * emitted in no particular order. 1110 */ 1111 private void writeObject(java.io.ObjectOutputStream s) 1112 throws IOException 1113 { 1114 // Write out the threshold, loadfactor, and any hidden stuff 1115 s.defaultWriteObject(); 1116 1117 // Write out number of buckets 1118 if (table==EMPTY_TABLE) { 1119 s.writeInt(roundUpToPowerOf2(threshold)); 1120 } else { 1121 s.writeInt(table.length); 1122 } 1123 1124 // Write out size (number of Mappings) 1125 s.writeInt(size); 1126 1127 // Write out keys and values (alternating) 1128 if (size > 0) { 1129 for(Map.Entry<K,V> e : entrySet0()) { 1130 s.writeObject(e.getKey()); 1131 s.writeObject(e.getValue()); 1132 } 1133 } 1134 } 1135 1136 private static final long serialVersionUID = 362498820763181265L; 1137 1138 /** 1139 * Reconstitute the {@code HashMap} instance from a stream (i.e., 1140 * deserialize it). 1141 */ 1142 private void readObject(java.io.ObjectInputStream s) 1143 throws IOException, ClassNotFoundException 1144 { 1145 // Read in the threshold (ignored), loadfactor, and any hidden stuff 1146 s.defaultReadObject(); 1147 if (loadFactor <= 0 || Float.isNaN(loadFactor)) { 1148 throw new InvalidObjectException("Illegal load factor: " + 1149 loadFactor); 1150 } 1151 1152 // set other fields that need values 1153 table = (Entry<K,V>[]) EMPTY_TABLE; 1154 1155 // Read in number of buckets 1156 s.readInt(); // ignored. 1157 1158 // Read number of mappings 1159 int mappings = s.readInt(); 1160 if (mappings < 0) 1161 throw new InvalidObjectException("Illegal mappings count: " + 1162 mappings); 1163 1164 // capacity chosen by number of mappings and desired load (if >= 0.25) 1165 int capacity = (int) Math.min( 1166 mappings * Math.min(1 / loadFactor, 4.0f), 1167 // we have limits... 1168 HashMap.MAXIMUM_CAPACITY); 1169 1170 // allocate the bucket array; 1171 if (mappings > 0) { 1172 inflateTable(capacity); 1173 } else { 1174 threshold = capacity; 1175 } 1176 1177 init(); // Give subclass a chance to do its thing. 1178 1179 // Read the keys and values, and put the mappings in the HashMap 1180 for (int i = 0; i < mappings; i++) { 1181 K key = (K) s.readObject(); 1182 V value = (V) s.readObject(); 1183 putForCreate(key, value); 1184 } 1185 } 1186 1187 // These methods are used when serializing HashSets 1188 int capacity() { return table.length; } 1189 float loadFactor() { return loadFactor; } 1190} 1191