1 /* 2 * Copyright (c) 1994, 2008, 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 * This class implements a hash table, which maps keys to values. Any 31 * non-<code>null</code> object can be used as a key or as a value. <p> 32 * 33 * To successfully store and retrieve objects from a hashtable, the 34 * objects used as keys must implement the <code>hashCode</code> 35 * method and the <code>equals</code> method. <p> 36 * 37 * An instance of <code>Hashtable</code> has two parameters that affect its 38 * performance: <i>initial capacity</i> and <i>load factor</i>. The 39 * <i>capacity</i> is the number of <i>buckets</i> in the hash table, and the 40 * <i>initial capacity</i> is simply the capacity at the time the hash table 41 * is created. Note that the hash table is <i>open</i>: in the case of a "hash 42 * collision", a single bucket stores multiple entries, which must be searched 43 * sequentially. The <i>load factor</i> is a measure of how full the hash 44 * table is allowed to get before its capacity is automatically increased. 45 * The initial capacity and load factor parameters are merely hints to 46 * the implementation. The exact details as to when and whether the rehash 47 * method is invoked are implementation-dependent.<p> 48 * 49 * Generally, the default load factor (.75) offers a good tradeoff between 50 * time and space costs. Higher values decrease the space overhead but 51 * increase the time cost to look up an entry (which is reflected in most 52 * <tt>Hashtable</tt> operations, including <tt>get</tt> and <tt>put</tt>).<p> 53 * 54 * The initial capacity controls a tradeoff between wasted space and the 55 * need for <code>rehash</code> operations, which are time-consuming. 56 * No <code>rehash</code> operations will <i>ever</i> occur if the initial 57 * capacity is greater than the maximum number of entries the 58 * <tt>Hashtable</tt> will contain divided by its load factor. However, 59 * setting the initial capacity too high can waste space.<p> 60 * 61 * If many entries are to be made into a <code>Hashtable</code>, 62 * creating it with a sufficiently large capacity may allow the 63 * entries to be inserted more efficiently than letting it perform 64 * automatic rehashing as needed to grow the table. <p> 65 * 66 * This example creates a hashtable of numbers. It uses the names of 67 * the numbers as keys: 68 * <pre> {@code 69 * Hashtable<String, Integer> numbers 70 * = new Hashtable<String, Integer>(); 71 * numbers.put("one", 1); 72 * numbers.put("two", 2); 73 * numbers.put("three", 3);}</pre> 74 * 75 * <p>To retrieve a number, use the following code: 76 * <pre> {@code 77 * Integer n = numbers.get("two"); 78 * if (n != null) { 79 * System.out.println("two = " + n); 80 * }}</pre> 81 * 82 * <p>The iterators returned by the <tt>iterator</tt> method of the collections 83 * returned by all of this class's "collection view methods" are 84 * <em>fail-fast</em>: if the Hashtable is structurally modified at any time 85 * after the iterator is created, in any way except through the iterator's own 86 * <tt>remove</tt> method, the iterator will throw a {@link 87 * ConcurrentModificationException}. Thus, in the face of concurrent 88 * modification, the iterator fails quickly and cleanly, rather than risking 89 * arbitrary, non-deterministic behavior at an undetermined time in the future. 90 * The Enumerations returned by Hashtable's keys and elements methods are 91 * <em>not</em> fail-fast. 92 * 93 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed 94 * as it is, generally speaking, impossible to make any hard guarantees in the 95 * presence of unsynchronized concurrent modification. Fail-fast iterators 96 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. 97 * Therefore, it would be wrong to write a program that depended on this 98 * exception for its correctness: <i>the fail-fast behavior of iterators 99 * should be used only to detect bugs.</i> 100 * 101 * <p>As of the Java 2 platform v1.2, this class was retrofitted to 102 * implement the {@link Map} interface, making it a member of the 103 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 104 * 105 * Java Collections Framework</a>. Unlike the new collection 106 * implementations, {@code Hashtable} is synchronized. If a 107 * thread-safe implementation is not needed, it is recommended to use 108 * {@link HashMap} in place of {@code Hashtable}. If a thread-safe 109 * highly-concurrent implementation is desired, then it is recommended 110 * to use {@link java.util.concurrent.ConcurrentHashMap} in place of 111 * {@code Hashtable}. 112 * 113 * @author Arthur van Hoff 114 * @author Josh Bloch 115 * @author Neal Gafter 116 * @see Object#equals(java.lang.Object) 117 * @see Object#hashCode() 118 * @see Hashtable#rehash() 119 * @see Collection 120 * @see Map 121 * @see HashMap 122 * @see TreeMap 123 * @since JDK1.0 124 */ 125 public class Hashtable<K,V> 126 extends Dictionary<K,V> 127 implements Map<K,V>, Cloneable, java.io.Serializable { 128 129 /** 130 * The hash table data. 131 */ 132 private transient Entry[] table; 133 134 /** 135 * The total number of entries in the hash table. 136 */ 137 private transient int count; 138 139 /** 140 * The table is rehashed when its size exceeds this threshold. (The 141 * value of this field is (int)(capacity * loadFactor).) 142 * 143 * @serial 144 */ 145 private int threshold; 146 147 /** 148 * The load factor for the hashtable. 149 * 150 * @serial 151 */ 152 private float loadFactor; 153 154 /** 155 * The number of times this Hashtable has been structurally modified 156 * Structural modifications are those that change the number of entries in 157 * the Hashtable or otherwise modify its internal structure (e.g., 158 * rehash). This field is used to make iterators on Collection-views of 159 * the Hashtable fail-fast. (See ConcurrentModificationException). 160 */ 161 private transient int modCount = 0; 162 163 /** use serialVersionUID from JDK 1.0.2 for interoperability */ 164 private static final long serialVersionUID = 1421746759512286392L; 165 166 /** 167 * Constructs a new, empty hashtable with the specified initial 168 * capacity and the specified load factor. 169 * 170 * @param initialCapacity the initial capacity of the hashtable. 171 * @param loadFactor the load factor of the hashtable. 172 * @exception IllegalArgumentException if the initial capacity is less 173 * than zero, or if the load factor is nonpositive. 174 */ 175 public Hashtable(int initialCapacity, float loadFactor) { 176 if (initialCapacity < 0) 177 throw new IllegalArgumentException("Illegal Capacity: "+ 178 initialCapacity); 179 if (loadFactor <= 0 || Float.isNaN(loadFactor)) 180 throw new IllegalArgumentException("Illegal Load: "+loadFactor); 181 182 if (initialCapacity==0) 183 initialCapacity = 1; 184 this.loadFactor = loadFactor; 185 table = new Entry[initialCapacity]; 186 threshold = (int)(initialCapacity * loadFactor); 187 } 188 189 /** 190 * Constructs a new, empty hashtable with the specified initial capacity 191 * and default load factor (0.75). 192 * 193 * @param initialCapacity the initial capacity of the hashtable. 194 * @exception IllegalArgumentException if the initial capacity is less 195 * than zero. 196 */ 197 public Hashtable(int initialCapacity) { 198 this(initialCapacity, 0.75f); 199 } 200 201 /** 202 * Constructs a new, empty hashtable with a default initial capacity (11) 203 * and load factor (0.75). 204 */ 205 public Hashtable() { 206 this(11, 0.75f); 207 } 208 209 /** 210 * Constructs a new hashtable with the same mappings as the given 211 * Map. The hashtable is created with an initial capacity sufficient to 212 * hold the mappings in the given Map and a default load factor (0.75). 213 * 214 * @param t the map whose mappings are to be placed in this map. 215 * @throws NullPointerException if the specified map is null. 216 * @since 1.2 217 */ 218 public Hashtable(Map<? extends K, ? extends V> t) { 219 this(Math.max(2*t.size(), 11), 0.75f); 220 putAll(t); 221 } 222 223 /** 224 * Returns the number of keys in this hashtable. 225 * 226 * @return the number of keys in this hashtable. 227 */ 228 public synchronized int size() { 229 return count; 230 } 231 232 /** 233 * Tests if this hashtable maps no keys to values. 234 * 235 * @return <code>true</code> if this hashtable maps no keys to values; 236 * <code>false</code> otherwise. 237 */ 238 public synchronized boolean isEmpty() { 239 return count == 0; 240 } 241 242 /** 243 * Returns an enumeration of the keys in this hashtable. 244 * 245 * @return an enumeration of the keys in this hashtable. 246 * @see Enumeration 247 * @see #elements() 248 * @see #keySet() 249 * @see Map 250 */ 251 public synchronized Enumeration<K> keys() { 252 return this.<K>getEnumeration(KEYS); 253 } 254 255 /** 256 * Returns an enumeration of the values in this hashtable. 257 * Use the Enumeration methods on the returned object to fetch the elements 258 * sequentially. 259 * 260 * @return an enumeration of the values in this hashtable. 261 * @see java.util.Enumeration 262 * @see #keys() 263 * @see #values() 264 * @see Map 265 */ 266 public synchronized Enumeration<V> elements() { 267 return this.<V>getEnumeration(VALUES); 268 } 269 270 /** 271 * Tests if some key maps into the specified value in this hashtable. 272 * This operation is more expensive than the {@link #containsKey 273 * containsKey} method. 274 * 275 * <p>Note that this method is identical in functionality to 276 * {@link #containsValue containsValue}, (which is part of the 277 * {@link Map} interface in the collections framework). 278 * 279 * @param value a value to search for 280 * @return <code>true</code> if and only if some key maps to the 281 * <code>value</code> argument in this hashtable as 282 * determined by the <tt>equals</tt> method; 283 * <code>false</code> otherwise. 284 * @exception NullPointerException if the value is <code>null</code> 285 */ 286 public synchronized boolean contains(Object value) { 287 if (value == null) { 288 throw new NullPointerException(); 289 } 290 291 Entry tab[] = table; 292 for (int i = tab.length ; i-- > 0 ;) { 293 for (Entry<K,V> e = tab[i] ; e != null ; e = e.next) { 294 if (e.value.equals(value)) { 295 return true; 296 } 297 } 298 } 299 return false; 300 } 301 302 /** 303 * Returns true if this hashtable maps one or more keys to this value. 304 * 305 * <p>Note that this method is identical in functionality to {@link 306 * #contains contains} (which predates the {@link Map} interface). 307 * 308 * @param value value whose presence in this hashtable is to be tested 309 * @return <tt>true</tt> if this map maps one or more keys to the 310 * specified value 311 * @throws NullPointerException if the value is <code>null</code> 312 * @since 1.2 313 */ 314 public boolean containsValue(Object value) { 315 return contains(value); 316 } 317 318 /** 319 * Tests if the specified object is a key in this hashtable. 320 * 321 * @param key possible key 322 * @return <code>true</code> if and only if the specified object 323 * is a key in this hashtable, as determined by the 324 * <tt>equals</tt> method; <code>false</code> otherwise. 325 * @throws NullPointerException if the key is <code>null</code> 326 * @see #contains(Object) 327 */ 328 public synchronized boolean containsKey(Object key) { 329 Entry tab[] = table; 330 int hash = key.hashCode(); 331 int index = (hash & 0x7FFFFFFF) % tab.length; 332 for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) { 333 if ((e.hash == hash) && e.key.equals(key)) { 334 return true; 335 } 336 } 337 return false; 338 } 339 340 /** 341 * Returns the value to which the specified key is mapped, 342 * or {@code null} if this map contains no mapping for the key. 343 * 344 * <p>More formally, if this map contains a mapping from a key 345 * {@code k} to a value {@code v} such that {@code (key.equals(k))}, 346 * then this method returns {@code v}; otherwise it returns 347 * {@code null}. (There can be at most one such mapping.) 348 * 349 * @param key the key whose associated value is to be returned 350 * @return the value to which the specified key is mapped, or 351 * {@code null} if this map contains no mapping for the key 352 * @throws NullPointerException if the specified key is null 353 * @see #put(Object, Object) 354 */ 355 public synchronized V get(Object key) { 356 Entry tab[] = table; 357 int hash = key.hashCode(); 358 int index = (hash & 0x7FFFFFFF) % tab.length; 359 for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) { 360 if ((e.hash == hash) && e.key.equals(key)) { 361 return e.value; 362 } 363 } 364 return null; 365 } 366 367 /** 368 * The maximum size of array to allocate. 369 * Some VMs reserve some header words in an array. 370 * Attempts to allocate larger arrays may result in 371 * OutOfMemoryError: Requested array size exceeds VM limit 372 */ 373 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; 374 375 /** 376 * Increases the capacity of and internally reorganizes this 377 * hashtable, in order to accommodate and access its entries more 378 * efficiently. This method is called automatically when the 379 * number of keys in the hashtable exceeds this hashtable's capacity 380 * and load factor. 381 */ 382 protected void rehash() { 383 int oldCapacity = table.length; 384 Entry[] oldMap = table; 385 386 // overflow-conscious code 387 int newCapacity = (oldCapacity << 1) + 1; 388 if (newCapacity - MAX_ARRAY_SIZE > 0) { 389 if (oldCapacity == MAX_ARRAY_SIZE) 390 // Keep running with MAX_ARRAY_SIZE buckets 391 return; 392 newCapacity = MAX_ARRAY_SIZE; 393 } 394 Entry[] newMap = new Entry[newCapacity]; 395 396 modCount++; 397 threshold = (int)(newCapacity * loadFactor); 398 table = newMap; 399 400 for (int i = oldCapacity ; i-- > 0 ;) { 401 for (Entry<K,V> old = oldMap[i] ; old != null ; ) { 402 Entry<K,V> e = old; 403 old = old.next; 404 405 int index = (e.hash & 0x7FFFFFFF) % newCapacity; 406 e.next = newMap[index]; 407 newMap[index] = e; 408 } 409 } 410 } 411 412 /** 413 * Maps the specified <code>key</code> to the specified 414 * <code>value</code> in this hashtable. Neither the key nor the 415 * value can be <code>null</code>. <p> 416 * 417 * The value can be retrieved by calling the <code>get</code> method 418 * with a key that is equal to the original key. 419 * 420 * @param key the hashtable key 421 * @param value the value 422 * @return the previous value of the specified key in this hashtable, 423 * or <code>null</code> if it did not have one 424 * @exception NullPointerException if the key or value is 425 * <code>null</code> 426 * @see Object#equals(Object) 427 * @see #get(Object) 428 */ 429 public synchronized V put(K key, V value) { 430 // Make sure the value is not null 431 if (value == null) { 432 throw new NullPointerException(); 433 } 434 435 // Makes sure the key is not already in the hashtable. 436 Entry tab[] = table; 437 int hash = key.hashCode(); 438 int index = (hash & 0x7FFFFFFF) % tab.length; 439 for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) { 440 if ((e.hash == hash) && e.key.equals(key)) { 441 V old = e.value; 442 e.value = value; 443 return old; 444 } 445 } 446 447 modCount++; 448 if (count >= threshold) { 449 // Rehash the table if the threshold is exceeded 450 rehash(); 451 452 tab = table; 453 index = (hash & 0x7FFFFFFF) % tab.length; 454 } 455 456 // Creates the new entry. 457 Entry<K,V> e = tab[index]; 458 tab[index] = new Entry<K,V>(hash, key, value, e); 459 count++; 460 return null; 461 } 462 463 /** 464 * Removes the key (and its corresponding value) from this 465 * hashtable. This method does nothing if the key is not in the hashtable. 466 * 467 * @param key the key that needs to be removed 468 * @return the value to which the key had been mapped in this hashtable, 469 * or <code>null</code> if the key did not have a mapping 470 * @throws NullPointerException if the key is <code>null</code> 471 */ 472 public synchronized V remove(Object key) { 473 Entry tab[] = table; 474 int hash = key.hashCode(); 475 int index = (hash & 0x7FFFFFFF) % tab.length; 476 for (Entry<K,V> e = tab[index], prev = null ; e != null ; prev = e, e = e.next) { 477 if ((e.hash == hash) && e.key.equals(key)) { 478 modCount++; 479 if (prev != null) { 480 prev.next = e.next; 481 } else { 482 tab[index] = e.next; 483 } 484 count--; 485 V oldValue = e.value; 486 e.value = null; 487 return oldValue; 488 } 489 } 490 return null; 491 } 492 493 /** 494 * Copies all of the mappings from the specified map to this hashtable. 495 * These mappings will replace any mappings that this hashtable had for any 496 * of the keys currently in the specified map. 497 * 498 * @param t mappings to be stored in this map 499 * @throws NullPointerException if the specified map is null 500 * @since 1.2 501 */ 502 public synchronized void putAll(Map<? extends K, ? extends V> t) { 503 for (Map.Entry<? extends K, ? extends V> e : t.entrySet()) 504 put(e.getKey(), e.getValue()); 505 } 506 507 /** 508 * Clears this hashtable so that it contains no keys. 509 */ 510 public synchronized void clear() { 511 Entry tab[] = table; 512 modCount++; 513 for (int index = tab.length; --index >= 0; ) 514 tab[index] = null; 515 count = 0; 516 } 517 518 /** 519 * Creates a shallow copy of this hashtable. All the structure of the 520 * hashtable itself is copied, but the keys and values are not cloned. 521 * This is a relatively expensive operation. 522 * 523 * @return a clone of the hashtable 524 */ 525 public synchronized Object clone() { 526 try { 527 Hashtable<K,V> t = (Hashtable<K,V>) super.clone(); 528 t.table = new Entry[table.length]; 529 for (int i = table.length ; i-- > 0 ; ) { 530 t.table[i] = (table[i] != null) 531 ? (Entry<K,V>) table[i].clone() : null; 532 } 533 t.keySet = null; 534 t.entrySet = null; 535 t.values = null; 536 t.modCount = 0; 537 return t; 538 } catch (CloneNotSupportedException e) { 539 // this shouldn't happen, since we are Cloneable 540 throw new InternalError(); 541 } 542 } 543 544 /** 545 * Returns a string representation of this <tt>Hashtable</tt> object 546 * in the form of a set of entries, enclosed in braces and separated 547 * by the ASCII characters "<tt>, </tt>" (comma and space). Each 548 * entry is rendered as the key, an equals sign <tt>=</tt>, and the 549 * associated element, where the <tt>toString</tt> method is used to 550 * convert the key and element to strings. 551 * 552 * @return a string representation of this hashtable 553 */ 554 public synchronized String toString() { 555 int max = size() - 1; 556 if (max == -1) 557 return "{}"; 558 559 StringBuilder sb = new StringBuilder(); 560 Iterator<Map.Entry<K,V>> it = entrySet().iterator(); 561 562 sb.append('{'); 563 for (int i = 0; ; i++) { 564 Map.Entry<K,V> e = it.next(); 565 K key = e.getKey(); 566 V value = e.getValue(); 567 sb.append(key == this ? "(this Map)" : key.toString()); 568 sb.append('='); 569 sb.append(value == this ? "(this Map)" : value.toString()); 570 571 if (i == max) 572 return sb.append('}').toString(); 573 sb.append(", "); 574 } 575 } 576 577 578 private <T> Enumeration<T> getEnumeration(int type) { 579 if (count == 0) { 580 return Collections.emptyEnumeration(); 581 } else { 582 return new Enumerator<T>(type, false); 583 } 584 } 585 586 private <T> Iterator<T> getIterator(int type) { 587 if (count == 0) { 588 return Collections.emptyIterator(); 589 } else { 590 return new Enumerator<T>(type, true); 591 } 592 } 593 594 // Views 595 596 /** 597 * Each of these fields are initialized to contain an instance of the 598 * appropriate view the first time this view is requested. The views are 599 * stateless, so there's no reason to create more than one of each. 600 */ 601 private transient volatile Set<K> keySet = null; 602 private transient volatile Set<Map.Entry<K,V>> entrySet = null; 603 private transient volatile Collection<V> values = null; 604 605 /** 606 * Returns a {@link Set} view of the keys contained in this map. 607 * The set is backed by the map, so changes to the map are 608 * reflected in the set, and vice-versa. If the map is modified 609 * while an iteration over the set is in progress (except through 610 * the iterator's own <tt>remove</tt> operation), the results of 611 * the iteration are undefined. The set supports element removal, 612 * which removes the corresponding mapping from the map, via the 613 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, 614 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> 615 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> 616 * operations. 617 * 618 * @since 1.2 619 */ 620 public Set<K> keySet() { 621 if (keySet == null) 622 keySet = Collections.synchronizedSet(new KeySet(), this); 623 return keySet; 624 } 625 626 private class KeySet extends AbstractSet<K> { 627 public Iterator<K> iterator() { 628 return getIterator(KEYS); 629 } 630 public int size() { 631 return count; 632 } 633 public boolean contains(Object o) { 634 return containsKey(o); 635 } 636 public boolean remove(Object o) { 637 return Hashtable.this.remove(o) != null; 638 } 639 public void clear() { 640 Hashtable.this.clear(); 641 } 642 } 643 644 /** 645 * Returns a {@link Set} view of the mappings contained in this map. 646 * The set is backed by the map, so changes to the map are 647 * reflected in the set, and vice-versa. If the map is modified 648 * while an iteration over the set is in progress (except through 649 * the iterator's own <tt>remove</tt> operation, or through the 650 * <tt>setValue</tt> operation on a map entry returned by the 651 * iterator) the results of the iteration are undefined. The set 652 * supports element removal, which removes the corresponding 653 * mapping from the map, via the <tt>Iterator.remove</tt>, 654 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and 655 * <tt>clear</tt> operations. It does not support the 656 * <tt>add</tt> or <tt>addAll</tt> operations. 657 * 658 * @since 1.2 659 */ 660 public Set<Map.Entry<K,V>> entrySet() { 661 if (entrySet==null) 662 entrySet = Collections.synchronizedSet(new EntrySet(), this); 663 return entrySet; 664 } 665 666 private class EntrySet extends AbstractSet<Map.Entry<K,V>> { 667 public Iterator<Map.Entry<K,V>> iterator() { 668 return getIterator(ENTRIES); 669 } 670 671 public boolean add(Map.Entry<K,V> o) { 672 return super.add(o); 673 } 674 675 public boolean contains(Object o) { 676 if (!(o instanceof Map.Entry)) 677 return false; 678 Map.Entry entry = (Map.Entry)o; 679 Object key = entry.getKey(); 680 Entry[] tab = table; 681 int hash = key.hashCode(); 682 int index = (hash & 0x7FFFFFFF) % tab.length; 683 684 for (Entry e = tab[index]; e != null; e = e.next) 685 if (e.hash==hash && e.equals(entry)) 686 return true; 687 return false; 688 } 689 690 public boolean remove(Object o) { 691 if (!(o instanceof Map.Entry)) 692 return false; 693 Map.Entry<K,V> entry = (Map.Entry<K,V>) o; 694 K key = entry.getKey(); 695 Entry[] tab = table; 696 int hash = key.hashCode(); 697 int index = (hash & 0x7FFFFFFF) % tab.length; 698 699 for (Entry<K,V> e = tab[index], prev = null; e != null; 700 prev = e, e = e.next) { 701 if (e.hash==hash && e.equals(entry)) { 702 modCount++; 703 if (prev != null) 704 prev.next = e.next; 705 else 706 tab[index] = e.next; 707 708 count--; 709 e.value = null; 710 return true; 711 } 712 } 713 return false; 714 } 715 716 public int size() { 717 return count; 718 } 719 720 public void clear() { 721 Hashtable.this.clear(); 722 } 723 } 724 725 /** 726 * Returns a {@link Collection} view of the values contained in this map. 727 * The collection is backed by the map, so changes to the map are 728 * reflected in the collection, and vice-versa. If the map is 729 * modified while an iteration over the collection is in progress 730 * (except through the iterator's own <tt>remove</tt> operation), 731 * the results of the iteration are undefined. The collection 732 * supports element removal, which removes the corresponding 733 * mapping from the map, via the <tt>Iterator.remove</tt>, 734 * <tt>Collection.remove</tt>, <tt>removeAll</tt>, 735 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not 736 * support the <tt>add</tt> or <tt>addAll</tt> operations. 737 * 738 * @since 1.2 739 */ 740 public Collection<V> values() { 741 if (values==null) 742 values = Collections.synchronizedCollection(new ValueCollection(), 743 this); 744 return values; 745 } 746 747 private class ValueCollection extends AbstractCollection<V> { 748 public Iterator<V> iterator() { 749 return getIterator(VALUES); 750 } 751 public int size() { 752 return count; 753 } 754 public boolean contains(Object o) { 755 return containsValue(o); 756 } 757 public void clear() { 758 Hashtable.this.clear(); 759 } 760 } 761 762 // Comparison and hashing 763 764 /** 765 * Compares the specified Object with this Map for equality, 766 * as per the definition in the Map interface. 767 * 768 * @param o object to be compared for equality with this hashtable 769 * @return true if the specified Object is equal to this Map 770 * @see Map#equals(Object) 771 * @since 1.2 772 */ 773 public synchronized boolean equals(Object o) { 774 if (o == this) 775 return true; 776 777 if (!(o instanceof Map)) 778 return false; 779 Map<K,V> t = (Map<K,V>) o; 780 if (t.size() != size()) 781 return false; 782 783 try { 784 Iterator<Map.Entry<K,V>> i = entrySet().iterator(); 785 while (i.hasNext()) { 786 Map.Entry<K,V> e = i.next(); 787 K key = e.getKey(); 788 V value = e.getValue(); 789 if (value == null) { 790 if (!(t.get(key)==null && t.containsKey(key))) 791 return false; 792 } else { 793 if (!value.equals(t.get(key))) 794 return false; 795 } 796 } 797 } catch (ClassCastException unused) { 798 return false; 799 } catch (NullPointerException unused) { 800 return false; 801 } 802 803 return true; 804 } 805 806 /** 807 * Returns the hash code value for this Map as per the definition in the 808 * Map interface. 809 * 810 * @see Map#hashCode() 811 * @since 1.2 812 */ 813 public synchronized int hashCode() { 814 /* 815 * This code detects the recursion caused by computing the hash code 816 * of a self-referential hash table and prevents the stack overflow 817 * that would otherwise result. This allows certain 1.1-era 818 * applets with self-referential hash tables to work. This code 819 * abuses the loadFactor field to do double-duty as a hashCode 820 * in progress flag, so as not to worsen the space performance. 821 * A negative load factor indicates that hash code computation is 822 * in progress. 823 */ 824 int h = 0; 825 if (count == 0 || loadFactor < 0) 826 return h; // Returns zero 827 828 loadFactor = -loadFactor; // Mark hashCode computation in progress 829 Entry[] tab = table; 830 for (int i = 0; i < tab.length; i++) 831 for (Entry e = tab[i]; e != null; e = e.next) 832 h += e.key.hashCode() ^ e.value.hashCode(); 833 loadFactor = -loadFactor; // Mark hashCode computation complete 834 835 return h; 836 } 837 838 /** 839 * Save the state of the Hashtable to a stream (i.e., serialize it). 840 * 841 * @serialData The <i>capacity</i> of the Hashtable (the length of the 842 * bucket array) is emitted (int), followed by the 843 * <i>size</i> of the Hashtable (the number of key-value 844 * mappings), followed by the key (Object) and value (Object) 845 * for each key-value mapping represented by the Hashtable 846 * The key-value mappings are emitted in no particular order. 847 */ 848 private synchronized void writeObject(java.io.ObjectOutputStream s) 849 throws IOException 850 { 851 // Write out the length, threshold, loadfactor 852 s.defaultWriteObject(); 853 854 // Write out length, count of elements and then the key/value objects 855 s.writeInt(table.length); 856 s.writeInt(count); 857 for (int index = table.length-1; index >= 0; index--) { 858 Entry entry = table[index]; 859 860 while (entry != null) { 861 s.writeObject(entry.key); 862 s.writeObject(entry.value); 863 entry = entry.next; 864 } 865 } 866 } 867 868 /** 869 * Reconstitute the Hashtable from a stream (i.e., deserialize it). 870 */ 871 private void readObject(java.io.ObjectInputStream s) 872 throws IOException, ClassNotFoundException 873 { 874 // Read in the length, threshold, and loadfactor 875 s.defaultReadObject(); 876 877 // Read the original length of the array and number of elements 878 int origlength = s.readInt(); 879 int elements = s.readInt(); 880 881 // Compute new size with a bit of room 5% to grow but 882 // no larger than the original size. Make the length 883 // odd if it's large enough, this helps distribute the entries. 884 // Guard against the length ending up zero, that's not valid. 885 int length = (int)(elements * loadFactor) + (elements / 20) + 3; 886 if (length > elements && (length & 1) == 0) 887 length--; 888 if (origlength > 0 && length > origlength) 889 length = origlength; 890 891 Entry[] table = new Entry[length]; 892 count = 0; 893 894 // Read the number of elements and then all the key/value objects 895 for (; elements > 0; elements--) { 896 K key = (K)s.readObject(); 897 V value = (V)s.readObject(); 898 // synch could be eliminated for performance 899 reconstitutionPut(table, key, value); 900 } 901 this.table = table; 902 } 903 904 /** 905 * The put method used by readObject. This is provided because put 906 * is overridable and should not be called in readObject since the 907 * subclass will not yet be initialized. 908 * 909 * <p>This differs from the regular put method in several ways. No 910 * checking for rehashing is necessary since the number of elements 911 * initially in the table is known. The modCount is not incremented 912 * because we are creating a new instance. Also, no return value 913 * is needed. 914 */ 915 private void reconstitutionPut(Entry[] tab, K key, V value) 916 throws StreamCorruptedException 917 { 918 if (value == null) { 919 throw new java.io.StreamCorruptedException(); 920 } 921 // Makes sure the key is not already in the hashtable. 922 // This should not happen in deserialized version. 923 int hash = key.hashCode(); 924 int index = (hash & 0x7FFFFFFF) % tab.length; 925 for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) { 926 if ((e.hash == hash) && e.key.equals(key)) { 927 throw new java.io.StreamCorruptedException(); 928 } 929 } 930 // Creates the new entry. 931 Entry<K,V> e = tab[index]; 932 tab[index] = new Entry<K,V>(hash, key, value, e); 933 count++; 934 } 935 936 /** 937 * Hashtable collision list. 938 */ 939 private static class Entry<K,V> implements Map.Entry<K,V> { 940 int hash; 941 K key; 942 V value; 943 Entry<K,V> next; 944 945 protected Entry(int hash, K key, V value, Entry<K,V> next) { 946 this.hash = hash; 947 this.key = key; 948 this.value = value; 949 this.next = next; 950 } 951 952 protected Object clone() { 953 return new Entry<K,V>(hash, key, value, 954 (next==null ? null : (Entry<K,V>) next.clone())); 955 } 956 957 // Map.Entry Ops 958 959 public K getKey() { 960 return key; 961 } 962 963 public V getValue() { 964 return value; 965 } 966 967 public V setValue(V value) { 968 if (value == null) 969 throw new NullPointerException(); 970 971 V oldValue = this.value; 972 this.value = value; 973 return oldValue; 974 } 975 976 public boolean equals(Object o) { 977 if (!(o instanceof Map.Entry)) 978 return false; 979 Map.Entry e = (Map.Entry)o; 980 981 return (key==null ? e.getKey()==null : key.equals(e.getKey())) && 982 (value==null ? e.getValue()==null : value.equals(e.getValue())); 983 } 984 985 public int hashCode() { 986 return hash ^ (value==null ? 0 : value.hashCode()); 987 } 988 989 public String toString() { 990 return key.toString()+"="+value.toString(); 991 } 992 } 993 994 // Types of Enumerations/Iterations 995 private static final int KEYS = 0; 996 private static final int VALUES = 1; 997 private static final int ENTRIES = 2; 998 999 /** 1000 * A hashtable enumerator class. This class implements both the 1001 * Enumeration and Iterator interfaces, but individual instances 1002 * can be created with the Iterator methods disabled. This is necessary 1003 * to avoid unintentionally increasing the capabilities granted a user 1004 * by passing an Enumeration. 1005 */ 1006 private class Enumerator<T> implements Enumeration<T>, Iterator<T> { 1007 Entry[] table = Hashtable.this.table; 1008 int index = table.length; 1009 Entry<K,V> entry = null; 1010 Entry<K,V> lastReturned = null; 1011 int type; 1012 1013 /** 1014 * Indicates whether this Enumerator is serving as an Iterator 1015 * or an Enumeration. (true -> Iterator). 1016 */ 1017 boolean iterator; 1018 1019 /** 1020 * The modCount value that the iterator believes that the backing 1021 * Hashtable should have. If this expectation is violated, the iterator 1022 * has detected concurrent modification. 1023 */ 1024 protected int expectedModCount = modCount; 1025 1026 Enumerator(int type, boolean iterator) { 1027 this.type = type; 1028 this.iterator = iterator; 1029 } 1030 1031 public boolean hasMoreElements() { 1032 Entry<K,V> e = entry; 1033 int i = index; 1034 Entry[] t = table; 1035 /* Use locals for faster loop iteration */ 1036 while (e == null && i > 0) { 1037 e = t[--i]; 1038 } 1039 entry = e; 1040 index = i; 1041 return e != null; 1042 } 1043 1044 public T nextElement() { 1045 Entry<K,V> et = entry; 1046 int i = index; 1047 Entry[] t = table; 1048 /* Use locals for faster loop iteration */ 1049 while (et == null && i > 0) { 1050 et = t[--i]; 1051 } 1052 entry = et; 1053 index = i; 1054 if (et != null) { 1055 Entry<K,V> e = lastReturned = entry; 1056 entry = e.next; 1057 return type == KEYS ? (T)e.key : (type == VALUES ? (T)e.value : (T)e); 1058 } 1059 throw new NoSuchElementException("Hashtable Enumerator"); 1060 } 1061 1062 // Iterator methods 1063 public boolean hasNext() { 1064 return hasMoreElements(); 1065 } 1066 1067 public T next() { 1068 if (modCount != expectedModCount) 1069 throw new ConcurrentModificationException(); 1070 return nextElement(); 1071 } 1072 1073 public void remove() { 1074 if (!iterator) 1075 throw new UnsupportedOperationException(); 1076 if (lastReturned == null) 1077 throw new IllegalStateException("Hashtable Enumerator"); 1078 if (modCount != expectedModCount) 1079 throw new ConcurrentModificationException(); 1080 1081 synchronized(Hashtable.this) { 1082 Entry[] tab = Hashtable.this.table; 1083 int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length; 1084 1085 for (Entry<K,V> e = tab[index], prev = null; e != null; 1086 prev = e, e = e.next) { 1087 if (e == lastReturned) { 1088 modCount++; 1089 expectedModCount++; 1090 if (prev == null) 1091 tab[index] = e.next; 1092 else 1093 prev.next = e.next; 1094 count--; 1095 lastReturned = null; 1096 return; 1097 } 1098 } 1099 throw new ConcurrentModificationException(); 1100 } 1101 } 1102 } 1103 }