1 /* 2 * Copyright (c) 1997, 2012, 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<?,?>[] 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 private static class Holder { 179 /** 180 * 181 */ 182 static final sun.misc.Unsafe UNSAFE; 183 184 /** 185 * Offset of "final" hashSeed field we must set in 186 * readObject() method. 187 */ 188 static final long HASHSEED_OFFSET; 189 190 static { 191 try { 192 UNSAFE = sun.misc.Unsafe.getUnsafe(); 193 HASHSEED_OFFSET = UNSAFE.objectFieldOffset( 194 HashMap.class.getDeclaredField("hashSeed")); 195 } catch (NoSuchFieldException | SecurityException e) { 196 throw new InternalError("Failed to record hashSeed offset", e); 197 } 198 } 199 } 200 201 /** 202 * A randomizing value associated with this instance that is applied to 203 * hash code of keys to make hash collisions harder to find. 204 */ 205 transient final int hashSeed = sun.misc.Hashing.randomHashSeed(this); 206 207 /** 208 * Constructs an empty <tt>HashMap</tt> with the specified initial 209 * capacity and load factor. 210 * 211 * @param initialCapacity the initial capacity 212 * @param loadFactor the load factor 213 * @throws IllegalArgumentException if the initial capacity is negative 214 * or the load factor is nonpositive 215 */ 216 public HashMap(int initialCapacity, float loadFactor) { 217 if (initialCapacity < 0) 218 throw new IllegalArgumentException("Illegal initial capacity: " + 219 initialCapacity); 220 if (initialCapacity > MAXIMUM_CAPACITY) 221 initialCapacity = MAXIMUM_CAPACITY; 222 if (loadFactor <= 0 || Float.isNaN(loadFactor)) 223 throw new IllegalArgumentException("Illegal load factor: " + 224 loadFactor); 225 226 // Find a power of 2 >= initialCapacity 227 int capacity = 1; 228 while (capacity < initialCapacity) 229 capacity <<= 1; 230 231 this.loadFactor = loadFactor; 232 threshold = (int)Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1); 233 table = new Entry<?,?>[capacity]; 234 init(); 235 } 236 237 /** 238 * Constructs an empty <tt>HashMap</tt> with the specified initial 239 * capacity and the default load factor (0.75). 240 * 241 * @param initialCapacity the initial capacity. 242 * @throws IllegalArgumentException if the initial capacity is negative. 243 */ 244 public HashMap(int initialCapacity) { 245 this(initialCapacity, DEFAULT_LOAD_FACTOR); 246 } 247 248 /** 249 * Constructs an empty <tt>HashMap</tt> with the default initial capacity 250 * (16) and the default load factor (0.75). 251 */ 252 public HashMap() { 253 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR); 254 } 255 256 /** 257 * Constructs a new <tt>HashMap</tt> with the same mappings as the 258 * specified <tt>Map</tt>. The <tt>HashMap</tt> is created with 259 * default load factor (0.75) and an initial capacity sufficient to 260 * hold the mappings in the specified <tt>Map</tt>. 261 * 262 * @param m the map whose mappings are to be placed in this map 263 * @throws NullPointerException if the specified map is null 264 */ 265 public HashMap(Map<? extends K, ? extends V> m) { 266 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, 267 DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR); 268 putAllForCreate(m); 269 } 270 271 // internal utilities 272 273 /** 274 * Initialization hook for subclasses. This method is called 275 * in all constructors and pseudo-constructors (clone, readObject) 276 * after HashMap has been initialized but before any entries have 277 * been inserted. (In the absence of this method, readObject would 278 * require explicit knowledge of subclasses.) 279 */ 280 void init() { 281 } 282 283 /** 284 * Retrieve object hash code and applies a supplemental hash function to the 285 * result hash, which defends against poor quality hash functions. This is 286 * critical because HashMap uses power-of-two length hash tables, that 287 * otherwise encounter collisions for hashCodes that do not differ 288 * in lower bits. 289 */ 290 final int hash(Object k) { 291 if (k instanceof String) { 292 return ((String) k).hash32(); 293 } 294 295 int h = hashSeed ^ k.hashCode(); 296 297 // This function ensures that hashCodes that differ only by 298 // constant multiples at each bit position have a bounded 299 // number of collisions (approximately 8 at default load factor). 300 h ^= (h >>> 20) ^ (h >>> 12); 301 return h ^ (h >>> 7) ^ (h >>> 4); 302 } 303 304 /** 305 * Returns index for hash code h. 306 */ 307 static int indexFor(int h, int length) { 308 return h & (length-1); 309 } 310 311 /** 312 * Returns the number of key-value mappings in this map. 313 * 314 * @return the number of key-value mappings in this map 315 */ 316 public int size() { 317 return size; 318 } 319 320 /** 321 * Returns <tt>true</tt> if this map contains no key-value mappings. 322 * 323 * @return <tt>true</tt> if this map contains no key-value mappings 324 */ 325 public boolean isEmpty() { 326 return size == 0; 327 } 328 329 /** 330 * Returns the value to which the specified key is mapped, 331 * or {@code null} if this map contains no mapping for the key. 332 * 333 * <p>More formally, if this map contains a mapping from a key 334 * {@code k} to a value {@code v} such that {@code (key==null ? k==null : 335 * key.equals(k))}, then this method returns {@code v}; otherwise 336 * it returns {@code null}. (There can be at most one such mapping.) 337 * 338 * <p>A return value of {@code null} does not <i>necessarily</i> 339 * indicate that the map contains no mapping for the key; it's also 340 * possible that the map explicitly maps the key to {@code null}. 341 * The {@link #containsKey containsKey} operation may be used to 342 * distinguish these two cases. 343 * 344 * @see #put(Object, Object) 345 */ 346 @SuppressWarnings("unchecked") 347 public V get(Object key) { 348 Entry<K,V> entry = getEntry(key); 349 350 return null == entry ? null : entry.getValue(); 351 } 352 353 /** 354 * Returns <tt>true</tt> if this map contains a mapping for the 355 * specified key. 356 * 357 * @param key The key whose presence in this map is to be tested 358 * @return <tt>true</tt> if this map contains a mapping for the specified 359 * key. 360 */ 361 public boolean containsKey(Object key) { 362 return getEntry(key) != null; 363 } 364 365 /** 366 * Returns the entry associated with the specified key in the 367 * HashMap. Returns null if the HashMap contains no mapping 368 * for the key. 369 */ 370 @SuppressWarnings("unchecked") 371 final Entry<K,V> getEntry(Object key) { 372 int hash = (key == null) ? 0 : hash(key); 373 for (Entry<?,?> e = table[indexFor(hash, table.length)]; 374 e != null; 375 e = e.next) { 376 Object k; 377 if (e.hash == hash && 378 ((k = e.key) == key || (key != null && key.equals(k)))) 379 return (Entry<K,V>)e; 380 } 381 return null; 382 } 383 384 385 /** 386 * Associates the specified value with the specified key in this map. 387 * If the map previously contained a mapping for the key, the old 388 * value is replaced. 389 * 390 * @param key key with which the specified value is to be associated 391 * @param value value to be associated with the specified key 392 * @return the previous value associated with <tt>key</tt>, or 393 * <tt>null</tt> if there was no mapping for <tt>key</tt>. 394 * (A <tt>null</tt> return can also indicate that the map 395 * previously associated <tt>null</tt> with <tt>key</tt>.) 396 */ 397 public V put(K key, V value) { 398 if (key == null) 399 return putForNullKey(value); 400 int hash = hash(key); 401 int i = indexFor(hash, table.length); 402 @SuppressWarnings("unchecked") 403 Entry<K,V> e = (Entry<K,V>)table[i]; 404 for(; e != null; e = e.next) { 405 Object k; 406 if (e.hash == hash && ((k = e.key) == key || key.equals(k))) { 407 V oldValue = e.value; 408 e.value = value; 409 e.recordAccess(this); 410 return oldValue; 411 } 412 } 413 414 modCount++; 415 addEntry(hash, key, value, i); 416 return null; 417 } 418 419 /** 420 * Offloaded version of put for null keys 421 */ 422 private V putForNullKey(V value) { 423 @SuppressWarnings("unchecked") 424 Entry<K,V> e = (Entry<K,V>)table[0]; 425 for(; e != null; e = e.next) { 426 if (e.key == null) { 427 V oldValue = e.value; 428 e.value = value; 429 e.recordAccess(this); 430 return oldValue; 431 } 432 } 433 modCount++; 434 addEntry(0, null, value, 0); 435 return null; 436 } 437 438 /** 439 * This method is used instead of put by constructors and 440 * pseudoconstructors (clone, readObject). It does not resize the table, 441 * check for comodification, etc. It calls createEntry rather than 442 * addEntry. 443 */ 444 private void putForCreate(K key, V value) { 445 int hash = null == key ? 0 : hash(key); 446 int i = indexFor(hash, table.length); 447 448 /** 449 * Look for preexisting entry for key. This will never happen for 450 * clone or deserialize. It will only happen for construction if the 451 * input Map is a sorted map whose ordering is inconsistent w/ equals. 452 */ 453 for (@SuppressWarnings("unchecked") 454 Entry<?,V> e = (Entry<?,V>)table[i]; e != null; e = e.next) { 455 Object k; 456 if (e.hash == hash && 457 ((k = e.key) == key || (key != null && key.equals(k)))) { 458 e.value = value; 459 return; 460 } 461 } 462 463 createEntry(hash, key, value, i); 464 } 465 466 private void putAllForCreate(Map<? extends K, ? extends V> m) { 467 for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) 468 putForCreate(e.getKey(), e.getValue()); 469 } 470 471 /** 472 * Rehashes the contents of this map into a new array with a 473 * larger capacity. This method is called automatically when the 474 * number of keys in this map reaches its threshold. 475 * 476 * If current capacity is MAXIMUM_CAPACITY, this method does not 477 * resize the map, but sets threshold to Integer.MAX_VALUE. 478 * This has the effect of preventing future calls. 479 * 480 * @param newCapacity the new capacity, MUST be a power of two; 481 * must be greater than current capacity unless current 482 * capacity is MAXIMUM_CAPACITY (in which case value 483 * is irrelevant). 484 */ 485 void resize(int newCapacity) { 486 Entry<?,?>[] oldTable = table; 487 int oldCapacity = oldTable.length; 488 if (oldCapacity == MAXIMUM_CAPACITY) { 489 threshold = Integer.MAX_VALUE; 490 return; 491 } 492 493 Entry<?,?>[] newTable = new Entry<?,?>[newCapacity]; 494 transfer(newTable); 495 table = newTable; 496 threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1); 497 } 498 499 /** 500 * Transfers all entries from current table to newTable. 501 */ 502 @SuppressWarnings("unchecked") 503 void transfer(Entry<?,?>[] newTable) { 504 Entry<?,?>[] src = table; 505 int newCapacity = newTable.length; 506 for (int j = 0; j < src.length; j++ ) { 507 Entry<K,V> e = (Entry<K,V>) src[j]; 508 while(null != e) { 509 Entry<K,V> next = e.next; 510 int i = indexFor(e.hash, newCapacity); 511 e.next = (Entry<K,V>) newTable[i]; 512 newTable[i] = e; 513 e = next; 514 } 515 } 516 Arrays.fill(table, null); 517 } 518 519 /** 520 * Copies all of the mappings from the specified map to this map. 521 * These mappings will replace any mappings that this map had for 522 * any of the keys currently in the specified map. 523 * 524 * @param m mappings to be stored in this map 525 * @throws NullPointerException if the specified map is null 526 */ 527 public void putAll(Map<? extends K, ? extends V> m) { 528 int numKeysToBeAdded = m.size(); 529 if (numKeysToBeAdded == 0) 530 return; 531 532 /* 533 * Expand the map if the map if the number of mappings to be added 534 * is greater than or equal to threshold. This is conservative; the 535 * obvious condition is (m.size() + size) >= threshold, but this 536 * condition could result in a map with twice the appropriate capacity, 537 * if the keys to be added overlap with the keys already in this map. 538 * By using the conservative calculation, we subject ourself 539 * to at most one extra resize. 540 */ 541 if (numKeysToBeAdded > threshold) { 542 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1); 543 if (targetCapacity > MAXIMUM_CAPACITY) 544 targetCapacity = MAXIMUM_CAPACITY; 545 int newCapacity = table.length; 546 while (newCapacity < targetCapacity) 547 newCapacity <<= 1; 548 if (newCapacity > table.length) 549 resize(newCapacity); 550 } 551 552 for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) 553 put(e.getKey(), e.getValue()); 554 } 555 556 /** 557 * Removes the mapping for the specified key from this map if present. 558 * 559 * @param key key whose mapping is to be removed from the map 560 * @return the previous value associated with <tt>key</tt>, or 561 * <tt>null</tt> if there was no mapping for <tt>key</tt>. 562 * (A <tt>null</tt> return can also indicate that the map 563 * previously associated <tt>null</tt> with <tt>key</tt>.) 564 */ 565 public V remove(Object key) { 566 Entry<K,V> e = removeEntryForKey(key); 567 return (e == null ? null : e.value); 568 } 569 570 /** 571 * Removes and returns the entry associated with the specified key 572 * in the HashMap. Returns null if the HashMap contains no mapping 573 * for this key. 574 */ 575 final Entry<K,V> removeEntryForKey(Object key) { 576 int hash = (key == null) ? 0 : hash(key); 577 int i = indexFor(hash, table.length); 578 @SuppressWarnings("unchecked") 579 Entry<K,V> prev = (Entry<K,V>)table[i]; 580 Entry<K,V> e = prev; 581 582 while (e != null) { 583 Entry<K,V> next = e.next; 584 Object k; 585 if (e.hash == hash && 586 ((k = e.key) == key || (key != null && key.equals(k)))) { 587 modCount++; 588 size--; 589 if (prev == e) 590 table[i] = next; 591 else 592 prev.next = next; 593 e.recordRemoval(this); 594 return e; 595 } 596 prev = e; 597 e = next; 598 } 599 600 return e; 601 } 602 603 /** 604 * Special version of remove for EntrySet using {@code Map.Entry.equals()} 605 * for matching. 606 */ 607 final Entry<K,V> removeMapping(Object o) { 608 if (!(o instanceof Map.Entry)) 609 return null; 610 611 Map.Entry<?,?> entry = (Map.Entry<?,?>) o; 612 Object key = entry.getKey(); 613 int hash = (key == null) ? 0 : hash(key); 614 int i = indexFor(hash, table.length); 615 @SuppressWarnings("unchecked") 616 Entry<K,V> prev = (Entry<K,V>)table[i]; 617 Entry<K,V> e = prev; 618 619 while (e != null) { 620 Entry<K,V> next = e.next; 621 if (e.hash == hash && e.equals(entry)) { 622 modCount++; 623 size--; 624 if (prev == e) 625 table[i] = next; 626 else 627 prev.next = next; 628 e.recordRemoval(this); 629 return e; 630 } 631 prev = e; 632 e = next; 633 } 634 635 return e; 636 } 637 638 /** 639 * Removes all of the mappings from this map. 640 * The map will be empty after this call returns. 641 */ 642 public void clear() { 643 modCount++; 644 Entry<?,?>[] tab = table; 645 for (int i = 0; i < tab.length; i++) 646 tab[i] = null; 647 size = 0; 648 } 649 650 /** 651 * Returns <tt>true</tt> if this map maps one or more keys to the 652 * specified value. 653 * 654 * @param value value whose presence in this map is to be tested 655 * @return <tt>true</tt> if this map maps one or more keys to the 656 * specified value 657 */ 658 public boolean containsValue(Object value) { 659 if (value == null) 660 return containsNullValue(); 661 662 Entry<?,?>[] tab = table; 663 for (int i = 0; i < tab.length ; i++) 664 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next) 665 if (value.equals(e.value)) 666 return true; 667 return false; 668 } 669 670 /** 671 * Special-case code for containsValue with null argument 672 */ 673 private boolean containsNullValue() { 674 Entry<?,?>[] tab = table; 675 for (int i = 0; i < tab.length ; i++) 676 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next) 677 if (e.value == null) 678 return true; 679 return false; 680 } 681 682 /** 683 * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and 684 * values themselves are not cloned. 685 * 686 * @return a shallow copy of this map 687 */ 688 @SuppressWarnings("unchecked") 689 public Object clone() { 690 HashMap<K,V> result = null; 691 try { 692 result = (HashMap<K,V>)super.clone(); 693 } catch (CloneNotSupportedException e) { 694 // assert false; 695 } 696 result.table = new Entry<?,?>[table.length]; 697 result.entrySet = null; 698 result.modCount = 0; 699 result.size = 0; 700 result.init(); 701 result.putAllForCreate(this); 702 703 return result; 704 } 705 706 static class Entry<K,V> implements Map.Entry<K,V> { 707 final K key; 708 V value; 709 Entry<K,V> next; 710 final int hash; 711 712 /** 713 * Creates new entry. 714 */ 715 Entry(int h, K k, V v, Entry<K,V> n) { 716 value = v; 717 next = n; 718 key = k; 719 hash = h; 720 } 721 722 public final K getKey() { 723 return key; 724 } 725 726 public final V getValue() { 727 return value; 728 } 729 730 public final V setValue(V newValue) { 731 V oldValue = value; 732 value = newValue; 733 return oldValue; 734 } 735 736 public final boolean equals(Object o) { 737 if (!(o instanceof Map.Entry)) 738 return false; 739 Map.Entry<?,?> e = (Map.Entry<?,?>)o; 740 Object k1 = getKey(); 741 Object k2 = e.getKey(); 742 if (k1 == k2 || (k1 != null && k1.equals(k2))) { 743 Object v1 = getValue(); 744 Object v2 = e.getValue(); 745 if (v1 == v2 || (v1 != null && v1.equals(v2))) 746 return true; 747 } 748 return false; 749 } 750 751 public final int hashCode() { 752 return (key==null ? 0 : key.hashCode()) ^ 753 (value==null ? 0 : value.hashCode()); 754 } 755 756 public final String toString() { 757 return getKey() + "=" + getValue(); 758 } 759 760 /** 761 * This method is invoked whenever the value in an entry is 762 * overwritten by an invocation of put(k,v) for a key k that's already 763 * in the HashMap. 764 */ 765 void recordAccess(HashMap<K,V> m) { 766 } 767 768 /** 769 * This method is invoked whenever the entry is 770 * removed from the table. 771 */ 772 void recordRemoval(HashMap<K,V> m) { 773 } 774 } 775 776 /** 777 * Adds a new entry with the specified key, value and hash code to 778 * the specified bucket. It is the responsibility of this 779 * method to resize the table if appropriate. 780 * 781 * Subclass overrides this to alter the behavior of put method. 782 */ 783 void addEntry(int hash, K key, V value, int bucketIndex) { 784 if ((size >= threshold) && (null != table[bucketIndex])) { 785 resize(2 * table.length); 786 hash = (null != key) ? hash(key) : 0; 787 bucketIndex = indexFor(hash, table.length); 788 } 789 790 createEntry(hash, key, value, bucketIndex); 791 } 792 793 /** 794 * Like addEntry except that this version is used when creating entries 795 * as part of Map construction or "pseudo-construction" (cloning, 796 * deserialization). This version needn't worry about resizing the table. 797 * 798 * Subclass overrides this to alter the behavior of HashMap(Map), 799 * clone, and readObject. 800 */ 801 void createEntry(int hash, K key, V value, int bucketIndex) { 802 @SuppressWarnings("unchecked") 803 Entry<K,V> e = (Entry<K,V>)table[bucketIndex]; 804 table[bucketIndex] = new Entry<>(hash, key, value, e); 805 size++; 806 } 807 808 private abstract class HashIterator<E> implements Iterator<E> { 809 Entry<?,?> next; // next entry to return 810 int expectedModCount; // For fast-fail 811 int index; // current slot 812 Entry<?,?> current; // current entry 813 814 HashIterator() { 815 expectedModCount = modCount; 816 if (size > 0) { // advance to first entry 817 Entry<?,?>[] t = table; 818 while (index < t.length && (next = t[index++]) == null) 819 ; 820 } 821 } 822 823 public final boolean hasNext() { 824 return next != null; 825 } 826 827 @SuppressWarnings("unchecked") 828 final Entry<K,V> nextEntry() { 829 if (modCount != expectedModCount) 830 throw new ConcurrentModificationException(); 831 Entry<?,?> e = next; 832 if (e == null) 833 throw new NoSuchElementException(); 834 835 if ((next = e.next) == null) { 836 Entry<?,?>[] t = table; 837 while (index < t.length && (next = t[index++]) == null) 838 ; 839 } 840 current = e; 841 return (Entry<K,V>)e; 842 } 843 844 public void remove() { 845 if (current == null) 846 throw new IllegalStateException(); 847 if (modCount != expectedModCount) 848 throw new ConcurrentModificationException(); 849 Object k = current.key; 850 current = null; 851 HashMap.this.removeEntryForKey(k); 852 expectedModCount = modCount; 853 } 854 } 855 856 private final class ValueIterator extends HashIterator<V> { 857 public V next() { 858 return nextEntry().value; 859 } 860 } 861 862 private final class KeyIterator extends HashIterator<K> { 863 public K next() { 864 return nextEntry().getKey(); 865 } 866 } 867 868 private final class EntryIterator extends HashIterator<Map.Entry<K,V>> { 869 public Map.Entry<K,V> next() { 870 return nextEntry(); 871 } 872 } 873 874 // Subclass overrides these to alter behavior of views' iterator() method 875 Iterator<K> newKeyIterator() { 876 return new KeyIterator(); 877 } 878 Iterator<V> newValueIterator() { 879 return new ValueIterator(); 880 } 881 Iterator<Map.Entry<K,V>> newEntryIterator() { 882 return new EntryIterator(); 883 } 884 885 886 // Views 887 888 private transient Set<Map.Entry<K,V>> entrySet = null; 889 890 /** 891 * Returns a {@link Set} view of the keys contained in this map. 892 * The set is backed by the map, so changes to the map are 893 * reflected in the set, and vice-versa. If the map is modified 894 * while an iteration over the set is in progress (except through 895 * the iterator's own <tt>remove</tt> operation), the results of 896 * the iteration are undefined. The set supports element removal, 897 * which removes the corresponding mapping from the map, via the 898 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, 899 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> 900 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> 901 * operations. 902 */ 903 public Set<K> keySet() { 904 Set<K> ks = keySet; 905 return (ks != null ? ks : (keySet = new KeySet())); 906 } 907 908 private final class KeySet extends AbstractSet<K> { 909 public Iterator<K> iterator() { 910 return newKeyIterator(); 911 } 912 public int size() { 913 return size; 914 } 915 public boolean contains(Object o) { 916 return containsKey(o); 917 } 918 public boolean remove(Object o) { 919 return HashMap.this.removeEntryForKey(o) != null; 920 } 921 public void clear() { 922 HashMap.this.clear(); 923 } 924 } 925 926 /** 927 * Returns a {@link Collection} view of the values contained in this map. 928 * The collection is backed by the map, so changes to the map are 929 * reflected in the collection, and vice-versa. If the map is 930 * modified while an iteration over the collection is in progress 931 * (except through the iterator's own <tt>remove</tt> operation), 932 * the results of the iteration are undefined. The collection 933 * supports element removal, which removes the corresponding 934 * mapping from the map, via the <tt>Iterator.remove</tt>, 935 * <tt>Collection.remove</tt>, <tt>removeAll</tt>, 936 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not 937 * support the <tt>add</tt> or <tt>addAll</tt> operations. 938 */ 939 public Collection<V> values() { 940 Collection<V> vs = values; 941 return (vs != null ? vs : (values = new Values())); 942 } 943 944 private final class Values extends AbstractCollection<V> { 945 public Iterator<V> iterator() { 946 return newValueIterator(); 947 } 948 public int size() { 949 return size; 950 } 951 public boolean contains(Object o) { 952 return containsValue(o); 953 } 954 public void clear() { 955 HashMap.this.clear(); 956 } 957 } 958 959 /** 960 * Returns a {@link Set} view of the mappings contained in this map. 961 * The set is backed by the map, so changes to the map are 962 * reflected in the set, and vice-versa. If the map is modified 963 * while an iteration over the set is in progress (except through 964 * the iterator's own <tt>remove</tt> operation, or through the 965 * <tt>setValue</tt> operation on a map entry returned by the 966 * iterator) the results of the iteration are undefined. The set 967 * supports element removal, which removes the corresponding 968 * mapping from the map, via the <tt>Iterator.remove</tt>, 969 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and 970 * <tt>clear</tt> operations. It does not support the 971 * <tt>add</tt> or <tt>addAll</tt> operations. 972 * 973 * @return a set view of the mappings contained in this map 974 */ 975 public Set<Map.Entry<K,V>> entrySet() { 976 return entrySet0(); 977 } 978 979 private Set<Map.Entry<K,V>> entrySet0() { 980 Set<Map.Entry<K,V>> es = entrySet; 981 return es != null ? es : (entrySet = new EntrySet()); 982 } 983 984 private final class EntrySet extends AbstractSet<Map.Entry<K,V>> { 985 public Iterator<Map.Entry<K,V>> iterator() { 986 return newEntryIterator(); 987 } 988 public boolean contains(Object o) { 989 if (!(o instanceof Map.Entry)) 990 return false; 991 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 992 Entry<K,V> candidate = getEntry(e.getKey()); 993 return candidate != null && candidate.equals(e); 994 } 995 public boolean remove(Object o) { 996 return removeMapping(o) != null; 997 } 998 public int size() { 999 return size; 1000 } 1001 public void clear() { 1002 HashMap.this.clear(); 1003 } 1004 } 1005 1006 /** 1007 * Save the state of the <tt>HashMap</tt> instance to a stream (i.e., 1008 * serialize it). 1009 * 1010 * @serialData The <i>capacity</i> of the HashMap (the length of the 1011 * bucket array) is emitted (int), followed by the 1012 * <i>size</i> (an int, the number of key-value 1013 * mappings), followed by the key (Object) and value (Object) 1014 * for each key-value mapping. The key-value mappings are 1015 * emitted in no particular order. 1016 */ 1017 private void writeObject(java.io.ObjectOutputStream s) 1018 throws IOException 1019 { 1020 Iterator<Map.Entry<K,V>> i = 1021 (size > 0) ? entrySet0().iterator() : null; 1022 1023 // Write out the threshold, loadfactor, and any hidden stuff 1024 s.defaultWriteObject(); 1025 1026 // Write out number of buckets 1027 s.writeInt(table.length); 1028 1029 // Write out size (number of Mappings) 1030 s.writeInt(size); 1031 1032 // Write out keys and values (alternating) 1033 if (size > 0) { 1034 for(Map.Entry<K,V> e : entrySet0()) { 1035 s.writeObject(e.getKey()); 1036 s.writeObject(e.getValue()); 1037 } 1038 } 1039 } 1040 1041 private static final long serialVersionUID = 362498820763181265L; 1042 1043 /** 1044 * Reconstitute the {@code HashMap} instance from a stream (i.e., 1045 * deserialize it). 1046 */ 1047 private void readObject(java.io.ObjectInputStream s) 1048 throws IOException, ClassNotFoundException 1049 { 1050 // Read in the threshold (ignored), loadfactor, and any hidden stuff 1051 s.defaultReadObject(); 1052 if (loadFactor <= 0 || Float.isNaN(loadFactor)) 1053 throw new InvalidObjectException("Illegal load factor: " + 1054 loadFactor); 1055 1056 // set hashMask 1057 Holder.UNSAFE.putIntVolatile(this, Holder.HASHSEED_OFFSET, 1058 sun.misc.Hashing.randomHashSeed(this)); 1059 1060 // Read in number of buckets and allocate the bucket array; 1061 s.readInt(); // ignored 1062 1063 // Read number of mappings 1064 int mappings = s.readInt(); 1065 if (mappings < 0) 1066 throw new InvalidObjectException("Illegal mappings count: " + 1067 mappings); 1068 1069 int initialCapacity = (int) Math.min( 1070 // capacity chosen by number of mappings 1071 // and desired load (if >= 0.25) 1072 mappings * Math.min(1 / loadFactor, 4.0f), 1073 // we have limits... 1074 HashMap.MAXIMUM_CAPACITY); 1075 int capacity = 1; 1076 // find smallest power of two which holds all mappings 1077 while (capacity < initialCapacity) { 1078 capacity <<= 1; 1079 } 1080 1081 table = new Entry<?,?>[capacity]; 1082 threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1); 1083 init(); // Give subclass a chance to do its thing. 1084 1085 1086 // Read the keys and values, and put the mappings in the HashMap 1087 for (int i=0; i<mappings; i++) { 1088 @SuppressWarnings("unchecked") 1089 K key = (K) s.readObject(); 1090 @SuppressWarnings("unchecked") 1091 V value = (V) s.readObject(); 1092 putForCreate(key, value); 1093 } 1094 } 1095 1096 // These methods are used when serializing HashSets 1097 int capacity() { return table.length; } 1098 float loadFactor() { return loadFactor; } 1099 }