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