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<?,?>[] 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 int h = hashSeed; 292 if (k instanceof String) { 293 return ((String)k).hash32(); 294 } 295 296 h ^= k.hashCode(); 297 298 // This function ensures that hashCodes that differ only by 299 // constant multiples at each bit position have a bounded 300 // number of collisions (approximately 8 at default load factor). 301 h ^= (h >>> 20) ^ (h >>> 12); 302 return h ^ (h >>> 7) ^ (h >>> 4); 303 } 304 305 /** 306 * Returns index for hash code h. 307 */ 308 static int indexFor(int h, int length) { 309 return h & (length-1); 310 } 311 312 /** 313 * Returns the number of key-value mappings in this map. 314 * 315 * @return the number of key-value mappings in this map 316 */ 317 public int size() { 318 return size; 319 } 320 321 /** 322 * Returns <tt>true</tt> if this map contains no key-value mappings. 323 * 324 * @return <tt>true</tt> if this map contains no key-value mappings 325 */ 326 public boolean isEmpty() { 327 return size == 0; 328 } 329 330 /** 331 * Returns the value to which the specified key is mapped, 332 * or {@code null} if this map contains no mapping for the key. 333 * 334 * <p>More formally, if this map contains a mapping from a key 335 * {@code k} to a value {@code v} such that {@code (key==null ? k==null : 336 * key.equals(k))}, then this method returns {@code v}; otherwise 337 * it returns {@code null}. (There can be at most one such mapping.) 338 * 339 * <p>A return value of {@code null} does not <i>necessarily</i> 340 * indicate that the map contains no mapping for the key; it's also 341 * possible that the map explicitly maps the key to {@code null}. 342 * The {@link #containsKey containsKey} operation may be used to 343 * distinguish these two cases. 344 * 345 * @see #put(Object, Object) 346 */ 347 @SuppressWarnings("unchecked") 348 public V get(Object key) { 349 Entry<K,V> entry = getEntry(key); 350 351 return null == entry ? null : entry.getValue(); 352 } 353 354 /** 355 * Returns <tt>true</tt> if this map contains a mapping for the 356 * specified key. 357 * 358 * @param key The key whose presence in this map is to be tested 359 * @return <tt>true</tt> if this map contains a mapping for the specified 360 * key. 361 */ 362 public boolean containsKey(Object key) { 363 return getEntry(key) != null; 364 } 365 366 /** 367 * Returns the entry associated with the specified key in the 368 * HashMap. Returns null if the HashMap contains no mapping 369 * for the key. 370 */ 371 @SuppressWarnings("unchecked") 372 final Entry<K,V> getEntry(Object key) { 373 int hash = (key == null) ? 0 : hash(key); 374 for (Entry<?,?> e = table[indexFor(hash, table.length)]; 375 e != null; 376 e = e.next) { 377 Object k; 378 if (e.hash == hash && 379 ((k = e.key) == key || (key != null && key.equals(k)))) 380 return (Entry<K,V>)e; 381 } 382 return null; 383 } 384 385 386 /** 387 * Associates the specified value with the specified key in this map. 388 * If the map previously contained a mapping for the key, the old 389 * value is replaced. 390 * 391 * @param key key with which the specified value is to be associated 392 * @param value value to be associated with the specified key 393 * @return the previous value associated with <tt>key</tt>, or 394 * <tt>null</tt> if there was no mapping for <tt>key</tt>. 395 * (A <tt>null</tt> return can also indicate that the map 396 * previously associated <tt>null</tt> with <tt>key</tt>.) 397 */ 398 public V put(K key, V value) { 399 if (key == null) 400 return putForNullKey(value); 401 int hash = hash(key); 402 int i = indexFor(hash, table.length); 403 @SuppressWarnings("unchecked") 404 Entry<K,V> e = (Entry<K,V>)table[i]; 405 for(; e != null; e = e.next) { 406 Object k; 407 if (e.hash == hash && ((k = e.key) == key || key.equals(k))) { 408 V oldValue = e.value; 409 e.value = value; 410 e.recordAccess(this); 411 return oldValue; 412 } 413 } 414 415 modCount++; 416 addEntry(hash, key, value, i); 417 return null; 418 } 419 420 /** 421 * Offloaded version of put for null keys 422 */ 423 private V putForNullKey(V value) { 424 @SuppressWarnings("unchecked") 425 Entry<K,V> e = (Entry<K,V>)table[0]; 426 for(; e != null; e = e.next) { 427 if (e.key == null) { 428 V oldValue = e.value; 429 e.value = value; 430 e.recordAccess(this); 431 return oldValue; 432 } 433 } 434 modCount++; 435 addEntry(0, null, value, 0); 436 return null; 437 } 438 439 /** 440 * This method is used instead of put by constructors and 441 * pseudoconstructors (clone, readObject). It does not resize the table, 442 * check for comodification, etc. It calls createEntry rather than 443 * addEntry. 444 */ 445 private void putForCreate(K key, V value) { 446 int hash = null == key ? 0 : hash(key); 447 int i = indexFor(hash, table.length); 448 449 /** 450 * Look for preexisting entry for key. This will never happen for 451 * clone or deserialize. It will only happen for construction if the 452 * input Map is a sorted map whose ordering is inconsistent w/ equals. 453 */ 454 for (@SuppressWarnings("unchecked") 455 Entry<?,V> e = (Entry<?,V>)table[i]; e != null; e = e.next) { 456 Object k; 457 if (e.hash == hash && 458 ((k = e.key) == key || (key != null && key.equals(k)))) { 459 e.value = value; 460 return; 461 } 462 } 463 464 createEntry(hash, key, value, i); 465 } 466 467 private void putAllForCreate(Map<? extends K, ? extends V> m) { 468 for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) 469 putForCreate(e.getKey(), e.getValue()); 470 } 471 472 /** 473 * Rehashes the contents of this map into a new array with a 474 * larger capacity. This method is called automatically when the 475 * number of keys in this map reaches its threshold. 476 * 477 * If current capacity is MAXIMUM_CAPACITY, this method does not 478 * resize the map, but sets threshold to Integer.MAX_VALUE. 479 * This has the effect of preventing future calls. 480 * 481 * @param newCapacity the new capacity, MUST be a power of two; 482 * must be greater than current capacity unless current 483 * capacity is MAXIMUM_CAPACITY (in which case value 484 * is irrelevant). 485 */ 486 void resize(int newCapacity) { 487 Entry<?,?>[] oldTable = table; 488 int oldCapacity = oldTable.length; 489 if (oldCapacity == MAXIMUM_CAPACITY) { 490 threshold = Integer.MAX_VALUE; 491 return; 492 } 493 494 Entry<?,?>[] newTable = new Entry<?,?>[newCapacity]; 495 transfer(newTable); 496 table = newTable; 497 threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1); 498 } 499 500 /** 501 * Transfers all entries from current table to newTable. 502 */ 503 @SuppressWarnings("unchecked") 504 void transfer(Entry<?,?>[] newTable) { 505 Entry<?,?>[] src = table; 506 int newCapacity = newTable.length; 507 for (int j = 0; j < src.length; j++ ) { 508 Entry<K,V> e = (Entry<K,V>) src[j]; 509 while(null != e) { 510 Entry<K,V> next = e.next; 511 int i = indexFor(e.hash, newCapacity); 512 e.next = (Entry<K,V>) newTable[i]; 513 newTable[i] = e; 514 e = next; 515 } 516 } 517 Arrays.fill(table, null); 518 } 519 520 /** 521 * Copies all of the mappings from the specified map to this map. 522 * These mappings will replace any mappings that this map had for 523 * any of the keys currently in the specified map. 524 * 525 * @param m mappings to be stored in this map 526 * @throws NullPointerException if the specified map is null 527 */ 528 public void putAll(Map<? extends K, ? extends V> m) { 529 int numKeysToBeAdded = m.size(); 530 if (numKeysToBeAdded == 0) 531 return; 532 533 /* 534 * Expand the map if the map if the number of mappings to be added 535 * is greater than or equal to threshold. This is conservative; the 536 * obvious condition is (m.size() + size) >= threshold, but this 537 * condition could result in a map with twice the appropriate capacity, 538 * if the keys to be added overlap with the keys already in this map. 539 * By using the conservative calculation, we subject ourself 540 * to at most one extra resize. 541 */ 542 if (numKeysToBeAdded > threshold) { 543 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1); 544 if (targetCapacity > MAXIMUM_CAPACITY) 545 targetCapacity = MAXIMUM_CAPACITY; 546 int newCapacity = table.length; 547 while (newCapacity < targetCapacity) 548 newCapacity <<= 1; 549 if (newCapacity > table.length) 550 resize(newCapacity); 551 } 552 553 for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) 554 put(e.getKey(), e.getValue()); 555 } 556 557 /** 558 * Removes the mapping for the specified key from this map if present. 559 * 560 * @param key key whose mapping is to be removed from the map 561 * @return the previous value associated with <tt>key</tt>, or 562 * <tt>null</tt> if there was no mapping for <tt>key</tt>. 563 * (A <tt>null</tt> return can also indicate that the map 564 * previously associated <tt>null</tt> with <tt>key</tt>.) 565 */ 566 public V remove(Object key) { 567 Entry<K,V> e = removeEntryForKey(key); 568 return (e == null ? null : e.value); 569 } 570 571 /** 572 * Removes and returns the entry associated with the specified key 573 * in the HashMap. Returns null if the HashMap contains no mapping 574 * for this key. 575 */ 576 final Entry<K,V> removeEntryForKey(Object key) { 577 int hash = (key == null) ? 0 : hash(key); 578 int i = indexFor(hash, table.length); 579 @SuppressWarnings("unchecked") 580 Entry<K,V> prev = (Entry<K,V>)table[i]; 581 Entry<K,V> e = prev; 582 583 while (e != null) { 584 Entry<K,V> next = e.next; 585 Object k; 586 if (e.hash == hash && 587 ((k = e.key) == key || (key != null && key.equals(k)))) { 588 modCount++; 589 size--; 590 if (prev == e) 591 table[i] = next; 592 else 593 prev.next = next; 594 e.recordRemoval(this); 595 return e; 596 } 597 prev = e; 598 e = next; 599 } 600 601 return e; 602 } 603 604 /** 605 * Special version of remove for EntrySet using {@code Map.Entry.equals()} 606 * for matching. 607 */ 608 final Entry<K,V> removeMapping(Object o) { 609 if (!(o instanceof Map.Entry)) 610 return null; 611 612 Map.Entry<?,?> entry = (Map.Entry<?,?>) o; 613 Object key = entry.getKey(); 614 int hash = (key == null) ? 0 : hash(key.hashCode()); 615 int i = indexFor(hash, table.length); 616 @SuppressWarnings("unchecked") 617 Entry<K,V> prev = (Entry<K,V>)table[i]; 618 Entry<K,V> e = prev; 619 620 while (e != null) { 621 Entry<K,V> next = e.next; 622 if (e.hash == hash && e.equals(entry)) { 623 modCount++; 624 size--; 625 if (prev == e) 626 table[i] = next; 627 else 628 prev.next = next; 629 e.recordRemoval(this); 630 return e; 631 } 632 prev = e; 633 e = next; 634 } 635 636 return e; 637 } 638 639 /** 640 * Removes all of the mappings from this map. 641 * The map will be empty after this call returns. 642 */ 643 public void clear() { 644 modCount++; 645 Entry<?,?>[] tab = table; 646 for (int i = 0; i < tab.length; i++) 647 tab[i] = null; 648 size = 0; 649 } 650 651 /** 652 * Returns <tt>true</tt> if this map maps one or more keys to the 653 * specified value. 654 * 655 * @param value value whose presence in this map is to be tested 656 * @return <tt>true</tt> if this map maps one or more keys to the 657 * specified value 658 */ 659 public boolean containsValue(Object value) { 660 if (value == null) 661 return containsNullValue(); 662 663 Entry<?,?>[] tab = table; 664 for (int i = 0; i < tab.length ; i++) 665 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next) 666 if (value.equals(e.value)) 667 return true; 668 return false; 669 } 670 671 /** 672 * Special-case code for containsValue with null argument 673 */ 674 private boolean containsNullValue() { 675 Entry<?,?>[] tab = table; 676 for (int i = 0; i < tab.length ; i++) 677 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next) 678 if (e.value == null) 679 return true; 680 return false; 681 } 682 683 /** 684 * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and 685 * values themselves are not cloned. 686 * 687 * @return a shallow copy of this map 688 */ 689 @SuppressWarnings("unchecked") 690 public Object clone() { 691 HashMap<K,V> result = null; 692 try { 693 result = (HashMap<K,V>)super.clone(); 694 } catch (CloneNotSupportedException e) { 695 // assert false; 696 } 697 result.table = new Entry<?,?>[table.length]; 698 result.entrySet = null; 699 result.modCount = 0; 700 result.size = 0; 701 result.init(); 702 result.putAllForCreate(this); 703 704 return result; 705 } 706 707 static class Entry<K,V> implements Map.Entry<K,V> { 708 final K key; 709 V value; 710 Entry<K,V> next; 711 final int hash; 712 713 /** 714 * Creates new entry. 715 */ 716 Entry(int h, K k, V v, Entry<K,V> n) { 717 value = v; 718 next = n; 719 key = k; 720 hash = h; 721 } 722 723 public final K getKey() { 724 return key; 725 } 726 727 public final V getValue() { 728 return value; 729 } 730 731 public final V setValue(V newValue) { 732 V oldValue = value; 733 value = newValue; 734 return oldValue; 735 } 736 737 public final boolean equals(Object o) { 738 if (!(o instanceof Map.Entry)) 739 return false; 740 Map.Entry<?,?> e = (Map.Entry<?,?>)o; 741 Object k1 = getKey(); 742 Object k2 = e.getKey(); 743 if (k1 == k2 || (k1 != null && k1.equals(k2))) { 744 Object v1 = getValue(); 745 Object v2 = e.getValue(); 746 if (v1 == v2 || (v1 != null && v1.equals(v2))) 747 return true; 748 } 749 return false; 750 } 751 752 public final int hashCode() { 753 return (key==null ? 0 : key.hashCode()) ^ 754 (value==null ? 0 : value.hashCode()); 755 } 756 757 public final String toString() { 758 return getKey() + "=" + getValue(); 759 } 760 761 /** 762 * This method is invoked whenever the value in an entry is 763 * overwritten by an invocation of put(k,v) for a key k that's already 764 * in the HashMap. 765 */ 766 void recordAccess(HashMap<K,V> m) { 767 } 768 769 /** 770 * This method is invoked whenever the entry is 771 * removed from the table. 772 */ 773 void recordRemoval(HashMap<K,V> m) { 774 } 775 } 776 777 /** 778 * Adds a new entry with the specified key, value and hash code to 779 * the specified bucket. It is the responsibility of this 780 * method to resize the table if appropriate. 781 * 782 * Subclass overrides this to alter the behavior of put method. 783 */ 784 void addEntry(int hash, K key, V value, int bucketIndex) { 785 if ((size >= threshold) && (null != table[bucketIndex])) { 786 resize(2 * table.length); 787 hash = (null != key) ? hash(key) : 0; 788 bucketIndex = indexFor(hash, table.length); 789 } 790 791 createEntry(hash, key, value, bucketIndex); 792 } 793 794 /** 795 * Like addEntry except that this version is used when creating entries 796 * as part of Map construction or "pseudo-construction" (cloning, 797 * deserialization). This version needn't worry about resizing the table. 798 * 799 * Subclass overrides this to alter the behavior of HashMap(Map), 800 * clone, and readObject. 801 */ 802 void createEntry(int hash, K key, V value, int bucketIndex) { 803 @SuppressWarnings("unchecked") 804 Entry<K,V> e = (Entry<K,V>)table[bucketIndex]; 805 table[bucketIndex] = new Entry<>(hash, key, value, e); 806 size++; 807 } 808 809 private abstract class HashIterator<E> implements Iterator<E> { 810 Entry<?,?> next; // next entry to return 811 int expectedModCount; // For fast-fail 812 int index; // current slot 813 Entry<?,?> current; // current entry 814 815 HashIterator() { 816 expectedModCount = modCount; 817 if (size > 0) { // advance to first entry 818 Entry<?,?>[] t = table; 819 while (index < t.length && (next = t[index++]) == null) 820 ; 821 } 822 } 823 824 public final boolean hasNext() { 825 return next != null; 826 } 827 828 @SuppressWarnings("unchecked") 829 final Entry<K,V> nextEntry() { 830 if (modCount != expectedModCount) 831 throw new ConcurrentModificationException(); 832 Entry<?,?> e = next; 833 if (e == null) 834 throw new NoSuchElementException(); 835 836 if ((next = e.next) == null) { 837 Entry<?,?>[] t = table; 838 while (index < t.length && (next = t[index++]) == null) 839 ; 840 } 841 current = e; 842 return (Entry<K,V>)e; 843 } 844 845 public void remove() { 846 if (current == null) 847 throw new IllegalStateException(); 848 if (modCount != expectedModCount) 849 throw new ConcurrentModificationException(); 850 Object k = current.key; 851 current = null; 852 HashMap.this.removeEntryForKey(k); 853 expectedModCount = modCount; 854 } 855 } 856 857 private final class ValueIterator extends HashIterator<V> { 858 public V next() { 859 return nextEntry().value; 860 } 861 } 862 863 private final class KeyIterator extends HashIterator<K> { 864 public K next() { 865 return nextEntry().getKey(); 866 } 867 } 868 869 private final class EntryIterator extends HashIterator<Map.Entry<K,V>> { 870 public Map.Entry<K,V> next() { 871 return nextEntry(); 872 } 873 } 874 875 // Subclass overrides these to alter behavior of views' iterator() method 876 Iterator<K> newKeyIterator() { 877 return new KeyIterator(); 878 } 879 Iterator<V> newValueIterator() { 880 return new ValueIterator(); 881 } 882 Iterator<Map.Entry<K,V>> newEntryIterator() { 883 return new EntryIterator(); 884 } 885 886 887 // Views 888 889 private transient Set<Map.Entry<K,V>> entrySet = null; 890 891 /** 892 * Returns a {@link Set} view of the keys contained in this map. 893 * The set is backed by the map, so changes to the map are 894 * reflected in the set, and vice-versa. If the map is modified 895 * while an iteration over the set is in progress (except through 896 * the iterator's own <tt>remove</tt> operation), the results of 897 * the iteration are undefined. The set supports element removal, 898 * which removes the corresponding mapping from the map, via the 899 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, 900 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> 901 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> 902 * operations. 903 */ 904 public Set<K> keySet() { 905 Set<K> ks = keySet; 906 return (ks != null ? ks : (keySet = new KeySet())); 907 } 908 909 private final class KeySet extends AbstractSet<K> { 910 public Iterator<K> iterator() { 911 return newKeyIterator(); 912 } 913 public int size() { 914 return size; 915 } 916 public boolean contains(Object o) { 917 return containsKey(o); 918 } 919 public boolean remove(Object o) { 920 return HashMap.this.removeEntryForKey(o) != null; 921 } 922 public void clear() { 923 HashMap.this.clear(); 924 } 925 } 926 927 /** 928 * Returns a {@link Collection} view of the values contained in this map. 929 * The collection is backed by the map, so changes to the map are 930 * reflected in the collection, and vice-versa. If the map is 931 * modified while an iteration over the collection is in progress 932 * (except through the iterator's own <tt>remove</tt> operation), 933 * the results of the iteration are undefined. The collection 934 * supports element removal, which removes the corresponding 935 * mapping from the map, via the <tt>Iterator.remove</tt>, 936 * <tt>Collection.remove</tt>, <tt>removeAll</tt>, 937 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not 938 * support the <tt>add</tt> or <tt>addAll</tt> operations. 939 */ 940 public Collection<V> values() { 941 Collection<V> vs = values; 942 return (vs != null ? vs : (values = new Values())); 943 } 944 945 private final class Values extends AbstractCollection<V> { 946 public Iterator<V> iterator() { 947 return newValueIterator(); 948 } 949 public int size() { 950 return size; 951 } 952 public boolean contains(Object o) { 953 return containsValue(o); 954 } 955 public void clear() { 956 HashMap.this.clear(); 957 } 958 } 959 960 /** 961 * Returns a {@link Set} view of the mappings contained in this map. 962 * The set is backed by the map, so changes to the map are 963 * reflected in the set, and vice-versa. If the map is modified 964 * while an iteration over the set is in progress (except through 965 * the iterator's own <tt>remove</tt> operation, or through the 966 * <tt>setValue</tt> operation on a map entry returned by the 967 * iterator) the results of the iteration are undefined. The set 968 * supports element removal, which removes the corresponding 969 * mapping from the map, via the <tt>Iterator.remove</tt>, 970 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and 971 * <tt>clear</tt> operations. It does not support the 972 * <tt>add</tt> or <tt>addAll</tt> operations. 973 * 974 * @return a set view of the mappings contained in this map 975 */ 976 public Set<Map.Entry<K,V>> entrySet() { 977 return entrySet0(); 978 } 979 980 private Set<Map.Entry<K,V>> entrySet0() { 981 Set<Map.Entry<K,V>> es = entrySet; 982 return es != null ? es : (entrySet = new EntrySet()); 983 } 984 985 private final class EntrySet extends AbstractSet<Map.Entry<K,V>> { 986 public Iterator<Map.Entry<K,V>> iterator() { 987 return newEntryIterator(); 988 } 989 public boolean contains(Object o) { 990 if (!(o instanceof Map.Entry)) 991 return false; 992 Map.Entry<?,?> e = (Map.Entry<?,?>) o; 993 Entry<K,V> candidate = getEntry(e.getKey()); 994 return candidate != null && candidate.equals(e); 995 } 996 public boolean remove(Object o) { 997 return removeMapping(o) != null; 998 } 999 public int size() { 1000 return size; 1001 } 1002 public void clear() { 1003 HashMap.this.clear(); 1004 } 1005 } 1006 1007 /** 1008 * Save the state of the <tt>HashMap</tt> instance to a stream (i.e., 1009 * serialize it). 1010 * 1011 * @serialData The <i>capacity</i> of the HashMap (the length of the 1012 * bucket array) is emitted (int), followed by the 1013 * <i>size</i> (an int, the number of key-value 1014 * mappings), followed by the key (Object) and value (Object) 1015 * for each key-value mapping. The key-value mappings are 1016 * emitted in no particular order. 1017 */ 1018 private void writeObject(java.io.ObjectOutputStream s) 1019 throws IOException 1020 { 1021 Iterator<Map.Entry<K,V>> i = 1022 (size > 0) ? entrySet0().iterator() : null; 1023 1024 // Write out the threshold, loadfactor, and any hidden stuff 1025 s.defaultWriteObject(); 1026 1027 // Write out number of buckets 1028 s.writeInt(table.length); 1029 1030 // Write out size (number of Mappings) 1031 s.writeInt(size); 1032 1033 // Write out keys and values (alternating) 1034 if (size > 0) { 1035 for(Map.Entry<K,V> e : entrySet0()) { 1036 s.writeObject(e.getKey()); 1037 s.writeObject(e.getValue()); 1038 } 1039 } 1040 } 1041 1042 private static final long serialVersionUID = 362498820763181265L; 1043 1044 /** 1045 * Reconstitute the {@code HashMap} instance from a stream (i.e., 1046 * deserialize it). 1047 */ 1048 private void readObject(java.io.ObjectInputStream s) 1049 throws IOException, ClassNotFoundException 1050 { 1051 // Read in the threshold (ignored), loadfactor, and any hidden stuff 1052 s.defaultReadObject(); 1053 if (loadFactor <= 0 || Float.isNaN(loadFactor)) 1054 throw new InvalidObjectException("Illegal load factor: " + 1055 loadFactor); 1056 1057 // set hashMask 1058 Holder.UNSAFE.putIntVolatile(this, Holder.HASHSEED_OFFSET, 1059 sun.misc.Hashing.randomHashSeed(this)); 1060 1061 // Read in number of buckets and allocate the bucket array; 1062 s.readInt(); // ignored 1063 1064 // Read number of mappings 1065 int mappings = s.readInt(); 1066 if (mappings < 0) 1067 throw new InvalidObjectException("Illegal mappings count: " + 1068 mappings); 1069 1070 int initialCapacity = (int) Math.min( 1071 // capacity chosen by number of mappings 1072 // and desired load (if >= 0.25) 1073 mappings * Math.min(1 / loadFactor, 4.0f), 1074 // we have limits... 1075 HashMap.MAXIMUM_CAPACITY); 1076 int capacity = 1; 1077 // find smallest power of two which holds all mappings 1078 while (capacity < initialCapacity) { 1079 capacity <<= 1; 1080 } 1081 1082 table = new Entry[capacity]; 1083 threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1); 1084 init(); // Give subclass a chance to do its thing. 1085 1086 1087 // Read the keys and values, and put the mappings in the HashMap 1088 for (int i=0; i<mappings; i++) { 1089 @SuppressWarnings("unchecked") 1090 K key = (K) s.readObject(); 1091 @SuppressWarnings("unchecked") 1092 V value = (V) s.readObject(); 1093 putForCreate(key, value); 1094 } 1095 } 1096 1097 // These methods are used when serializing HashSets 1098 int capacity() { return table.length; } 1099 float loadFactor() { return loadFactor; } 1100 }