J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1994-2006 Sun Microsystems, Inc. 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. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | package java.util; |
| 27 | import java.io.*; |
| 28 | |
| 29 | /** |
| 30 | * This class implements a hashtable, 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"> Java |
| 104 | * Collections Framework</a>. Unlike the new collection |
| 105 | * implementations, {@code Hashtable} is synchronized. |
| 106 | * |
| 107 | * @author Arthur van Hoff |
| 108 | * @author Josh Bloch |
| 109 | * @author Neal Gafter |
| 110 | * @see Object#equals(java.lang.Object) |
| 111 | * @see Object#hashCode() |
| 112 | * @see Hashtable#rehash() |
| 113 | * @see Collection |
| 114 | * @see Map |
| 115 | * @see HashMap |
| 116 | * @see TreeMap |
| 117 | * @since JDK1.0 |
| 118 | */ |
| 119 | public class Hashtable<K,V> |
| 120 | extends Dictionary<K,V> |
| 121 | implements Map<K,V>, Cloneable, java.io.Serializable { |
| 122 | |
| 123 | /** |
| 124 | * The hash table data. |
| 125 | */ |
| 126 | private transient Entry[] table; |
| 127 | |
| 128 | /** |
| 129 | * The total number of entries in the hash table. |
| 130 | */ |
| 131 | private transient int count; |
| 132 | |
| 133 | /** |
| 134 | * The table is rehashed when its size exceeds this threshold. (The |
| 135 | * value of this field is (int)(capacity * loadFactor).) |
| 136 | * |
| 137 | * @serial |
| 138 | */ |
| 139 | private int threshold; |
| 140 | |
| 141 | /** |
| 142 | * The load factor for the hashtable. |
| 143 | * |
| 144 | * @serial |
| 145 | */ |
| 146 | private float loadFactor; |
| 147 | |
| 148 | /** |
| 149 | * The number of times this Hashtable has been structurally modified |
| 150 | * Structural modifications are those that change the number of entries in |
| 151 | * the Hashtable or otherwise modify its internal structure (e.g., |
| 152 | * rehash). This field is used to make iterators on Collection-views of |
| 153 | * the Hashtable fail-fast. (See ConcurrentModificationException). |
| 154 | */ |
| 155 | private transient int modCount = 0; |
| 156 | |
| 157 | /** use serialVersionUID from JDK 1.0.2 for interoperability */ |
| 158 | private static final long serialVersionUID = 1421746759512286392L; |
| 159 | |
| 160 | /** |
| 161 | * Constructs a new, empty hashtable with the specified initial |
| 162 | * capacity and the specified load factor. |
| 163 | * |
| 164 | * @param initialCapacity the initial capacity of the hashtable. |
| 165 | * @param loadFactor the load factor of the hashtable. |
| 166 | * @exception IllegalArgumentException if the initial capacity is less |
| 167 | * than zero, or if the load factor is nonpositive. |
| 168 | */ |
| 169 | public Hashtable(int initialCapacity, float loadFactor) { |
| 170 | if (initialCapacity < 0) |
| 171 | throw new IllegalArgumentException("Illegal Capacity: "+ |
| 172 | initialCapacity); |
| 173 | if (loadFactor <= 0 || Float.isNaN(loadFactor)) |
| 174 | throw new IllegalArgumentException("Illegal Load: "+loadFactor); |
| 175 | |
| 176 | if (initialCapacity==0) |
| 177 | initialCapacity = 1; |
| 178 | this.loadFactor = loadFactor; |
| 179 | table = new Entry[initialCapacity]; |
| 180 | threshold = (int)(initialCapacity * loadFactor); |
| 181 | } |
| 182 | |
| 183 | /** |
| 184 | * Constructs a new, empty hashtable with the specified initial capacity |
| 185 | * and default load factor (0.75). |
| 186 | * |
| 187 | * @param initialCapacity the initial capacity of the hashtable. |
| 188 | * @exception IllegalArgumentException if the initial capacity is less |
| 189 | * than zero. |
| 190 | */ |
| 191 | public Hashtable(int initialCapacity) { |
| 192 | this(initialCapacity, 0.75f); |
| 193 | } |
| 194 | |
| 195 | /** |
| 196 | * Constructs a new, empty hashtable with a default initial capacity (11) |
| 197 | * and load factor (0.75). |
| 198 | */ |
| 199 | public Hashtable() { |
| 200 | this(11, 0.75f); |
| 201 | } |
| 202 | |
| 203 | /** |
| 204 | * Constructs a new hashtable with the same mappings as the given |
| 205 | * Map. The hashtable is created with an initial capacity sufficient to |
| 206 | * hold the mappings in the given Map and a default load factor (0.75). |
| 207 | * |
| 208 | * @param t the map whose mappings are to be placed in this map. |
| 209 | * @throws NullPointerException if the specified map is null. |
| 210 | * @since 1.2 |
| 211 | */ |
| 212 | public Hashtable(Map<? extends K, ? extends V> t) { |
| 213 | this(Math.max(2*t.size(), 11), 0.75f); |
| 214 | putAll(t); |
| 215 | } |
| 216 | |
| 217 | /** |
| 218 | * Returns the number of keys in this hashtable. |
| 219 | * |
| 220 | * @return the number of keys in this hashtable. |
| 221 | */ |
| 222 | public synchronized int size() { |
| 223 | return count; |
| 224 | } |
| 225 | |
| 226 | /** |
| 227 | * Tests if this hashtable maps no keys to values. |
| 228 | * |
| 229 | * @return <code>true</code> if this hashtable maps no keys to values; |
| 230 | * <code>false</code> otherwise. |
| 231 | */ |
| 232 | public synchronized boolean isEmpty() { |
| 233 | return count == 0; |
| 234 | } |
| 235 | |
| 236 | /** |
| 237 | * Returns an enumeration of the keys in this hashtable. |
| 238 | * |
| 239 | * @return an enumeration of the keys in this hashtable. |
| 240 | * @see Enumeration |
| 241 | * @see #elements() |
| 242 | * @see #keySet() |
| 243 | * @see Map |
| 244 | */ |
| 245 | public synchronized Enumeration<K> keys() { |
| 246 | return this.<K>getEnumeration(KEYS); |
| 247 | } |
| 248 | |
| 249 | /** |
| 250 | * Returns an enumeration of the values in this hashtable. |
| 251 | * Use the Enumeration methods on the returned object to fetch the elements |
| 252 | * sequentially. |
| 253 | * |
| 254 | * @return an enumeration of the values in this hashtable. |
| 255 | * @see java.util.Enumeration |
| 256 | * @see #keys() |
| 257 | * @see #values() |
| 258 | * @see Map |
| 259 | */ |
| 260 | public synchronized Enumeration<V> elements() { |
| 261 | return this.<V>getEnumeration(VALUES); |
| 262 | } |
| 263 | |
| 264 | /** |
| 265 | * Tests if some key maps into the specified value in this hashtable. |
| 266 | * This operation is more expensive than the {@link #containsKey |
| 267 | * containsKey} method. |
| 268 | * |
| 269 | * <p>Note that this method is identical in functionality to |
| 270 | * {@link #containsValue containsValue}, (which is part of the |
| 271 | * {@link Map} interface in the collections framework). |
| 272 | * |
| 273 | * @param value a value to search for |
| 274 | * @return <code>true</code> if and only if some key maps to the |
| 275 | * <code>value</code> argument in this hashtable as |
| 276 | * determined by the <tt>equals</tt> method; |
| 277 | * <code>false</code> otherwise. |
| 278 | * @exception NullPointerException if the value is <code>null</code> |
| 279 | */ |
| 280 | public synchronized boolean contains(Object value) { |
| 281 | if (value == null) { |
| 282 | throw new NullPointerException(); |
| 283 | } |
| 284 | |
| 285 | Entry tab[] = table; |
| 286 | for (int i = tab.length ; i-- > 0 ;) { |
| 287 | for (Entry<K,V> e = tab[i] ; e != null ; e = e.next) { |
| 288 | if (e.value.equals(value)) { |
| 289 | return true; |
| 290 | } |
| 291 | } |
| 292 | } |
| 293 | return false; |
| 294 | } |
| 295 | |
| 296 | /** |
| 297 | * Returns true if this hashtable maps one or more keys to this value. |
| 298 | * |
| 299 | * <p>Note that this method is identical in functionality to {@link |
| 300 | * #contains contains} (which predates the {@link Map} interface). |
| 301 | * |
| 302 | * @param value value whose presence in this hashtable is to be tested |
| 303 | * @return <tt>true</tt> if this map maps one or more keys to the |
| 304 | * specified value |
| 305 | * @throws NullPointerException if the value is <code>null</code> |
| 306 | * @since 1.2 |
| 307 | */ |
| 308 | public boolean containsValue(Object value) { |
| 309 | return contains(value); |
| 310 | } |
| 311 | |
| 312 | /** |
| 313 | * Tests if the specified object is a key in this hashtable. |
| 314 | * |
| 315 | * @param key possible key |
| 316 | * @return <code>true</code> if and only if the specified object |
| 317 | * is a key in this hashtable, as determined by the |
| 318 | * <tt>equals</tt> method; <code>false</code> otherwise. |
| 319 | * @throws NullPointerException if the key is <code>null</code> |
| 320 | * @see #contains(Object) |
| 321 | */ |
| 322 | public synchronized boolean containsKey(Object key) { |
| 323 | Entry tab[] = table; |
| 324 | int hash = key.hashCode(); |
| 325 | int index = (hash & 0x7FFFFFFF) % tab.length; |
| 326 | for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) { |
| 327 | if ((e.hash == hash) && e.key.equals(key)) { |
| 328 | return true; |
| 329 | } |
| 330 | } |
| 331 | return false; |
| 332 | } |
| 333 | |
| 334 | /** |
| 335 | * Returns the value to which the specified key is mapped, |
| 336 | * or {@code null} if this map contains no mapping for the key. |
| 337 | * |
| 338 | * <p>More formally, if this map contains a mapping from a key |
| 339 | * {@code k} to a value {@code v} such that {@code (key.equals(k))}, |
| 340 | * then this method returns {@code v}; otherwise it returns |
| 341 | * {@code null}. (There can be at most one such mapping.) |
| 342 | * |
| 343 | * @param key the key whose associated value is to be returned |
| 344 | * @return the value to which the specified key is mapped, or |
| 345 | * {@code null} if this map contains no mapping for the key |
| 346 | * @throws NullPointerException if the specified key is null |
| 347 | * @see #put(Object, Object) |
| 348 | */ |
| 349 | public synchronized V get(Object key) { |
| 350 | Entry tab[] = table; |
| 351 | int hash = key.hashCode(); |
| 352 | int index = (hash & 0x7FFFFFFF) % tab.length; |
| 353 | for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) { |
| 354 | if ((e.hash == hash) && e.key.equals(key)) { |
| 355 | return e.value; |
| 356 | } |
| 357 | } |
| 358 | return null; |
| 359 | } |
| 360 | |
| 361 | /** |
| 362 | * Increases the capacity of and internally reorganizes this |
| 363 | * hashtable, in order to accommodate and access its entries more |
| 364 | * efficiently. This method is called automatically when the |
| 365 | * number of keys in the hashtable exceeds this hashtable's capacity |
| 366 | * and load factor. |
| 367 | */ |
| 368 | protected void rehash() { |
| 369 | int oldCapacity = table.length; |
| 370 | Entry[] oldMap = table; |
| 371 | |
| 372 | int newCapacity = oldCapacity * 2 + 1; |
| 373 | Entry[] newMap = new Entry[newCapacity]; |
| 374 | |
| 375 | modCount++; |
| 376 | threshold = (int)(newCapacity * loadFactor); |
| 377 | table = newMap; |
| 378 | |
| 379 | for (int i = oldCapacity ; i-- > 0 ;) { |
| 380 | for (Entry<K,V> old = oldMap[i] ; old != null ; ) { |
| 381 | Entry<K,V> e = old; |
| 382 | old = old.next; |
| 383 | |
| 384 | int index = (e.hash & 0x7FFFFFFF) % newCapacity; |
| 385 | e.next = newMap[index]; |
| 386 | newMap[index] = e; |
| 387 | } |
| 388 | } |
| 389 | } |
| 390 | |
| 391 | /** |
| 392 | * Maps the specified <code>key</code> to the specified |
| 393 | * <code>value</code> in this hashtable. Neither the key nor the |
| 394 | * value can be <code>null</code>. <p> |
| 395 | * |
| 396 | * The value can be retrieved by calling the <code>get</code> method |
| 397 | * with a key that is equal to the original key. |
| 398 | * |
| 399 | * @param key the hashtable key |
| 400 | * @param value the value |
| 401 | * @return the previous value of the specified key in this hashtable, |
| 402 | * or <code>null</code> if it did not have one |
| 403 | * @exception NullPointerException if the key or value is |
| 404 | * <code>null</code> |
| 405 | * @see Object#equals(Object) |
| 406 | * @see #get(Object) |
| 407 | */ |
| 408 | public synchronized V put(K key, V value) { |
| 409 | // Make sure the value is not null |
| 410 | if (value == null) { |
| 411 | throw new NullPointerException(); |
| 412 | } |
| 413 | |
| 414 | // Makes sure the key is not already in the hashtable. |
| 415 | Entry tab[] = table; |
| 416 | int hash = key.hashCode(); |
| 417 | int index = (hash & 0x7FFFFFFF) % tab.length; |
| 418 | for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) { |
| 419 | if ((e.hash == hash) && e.key.equals(key)) { |
| 420 | V old = e.value; |
| 421 | e.value = value; |
| 422 | return old; |
| 423 | } |
| 424 | } |
| 425 | |
| 426 | modCount++; |
| 427 | if (count >= threshold) { |
| 428 | // Rehash the table if the threshold is exceeded |
| 429 | rehash(); |
| 430 | |
| 431 | tab = table; |
| 432 | index = (hash & 0x7FFFFFFF) % tab.length; |
| 433 | } |
| 434 | |
| 435 | // Creates the new entry. |
| 436 | Entry<K,V> e = tab[index]; |
| 437 | tab[index] = new Entry<K,V>(hash, key, value, e); |
| 438 | count++; |
| 439 | return null; |
| 440 | } |
| 441 | |
| 442 | /** |
| 443 | * Removes the key (and its corresponding value) from this |
| 444 | * hashtable. This method does nothing if the key is not in the hashtable. |
| 445 | * |
| 446 | * @param key the key that needs to be removed |
| 447 | * @return the value to which the key had been mapped in this hashtable, |
| 448 | * or <code>null</code> if the key did not have a mapping |
| 449 | * @throws NullPointerException if the key is <code>null</code> |
| 450 | */ |
| 451 | public synchronized V remove(Object key) { |
| 452 | Entry tab[] = table; |
| 453 | int hash = key.hashCode(); |
| 454 | int index = (hash & 0x7FFFFFFF) % tab.length; |
| 455 | for (Entry<K,V> e = tab[index], prev = null ; e != null ; prev = e, e = e.next) { |
| 456 | if ((e.hash == hash) && e.key.equals(key)) { |
| 457 | modCount++; |
| 458 | if (prev != null) { |
| 459 | prev.next = e.next; |
| 460 | } else { |
| 461 | tab[index] = e.next; |
| 462 | } |
| 463 | count--; |
| 464 | V oldValue = e.value; |
| 465 | e.value = null; |
| 466 | return oldValue; |
| 467 | } |
| 468 | } |
| 469 | return null; |
| 470 | } |
| 471 | |
| 472 | /** |
| 473 | * Copies all of the mappings from the specified map to this hashtable. |
| 474 | * These mappings will replace any mappings that this hashtable had for any |
| 475 | * of the keys currently in the specified map. |
| 476 | * |
| 477 | * @param t mappings to be stored in this map |
| 478 | * @throws NullPointerException if the specified map is null |
| 479 | * @since 1.2 |
| 480 | */ |
| 481 | public synchronized void putAll(Map<? extends K, ? extends V> t) { |
| 482 | for (Map.Entry<? extends K, ? extends V> e : t.entrySet()) |
| 483 | put(e.getKey(), e.getValue()); |
| 484 | } |
| 485 | |
| 486 | /** |
| 487 | * Clears this hashtable so that it contains no keys. |
| 488 | */ |
| 489 | public synchronized void clear() { |
| 490 | Entry tab[] = table; |
| 491 | modCount++; |
| 492 | for (int index = tab.length; --index >= 0; ) |
| 493 | tab[index] = null; |
| 494 | count = 0; |
| 495 | } |
| 496 | |
| 497 | /** |
| 498 | * Creates a shallow copy of this hashtable. All the structure of the |
| 499 | * hashtable itself is copied, but the keys and values are not cloned. |
| 500 | * This is a relatively expensive operation. |
| 501 | * |
| 502 | * @return a clone of the hashtable |
| 503 | */ |
| 504 | public synchronized Object clone() { |
| 505 | try { |
| 506 | Hashtable<K,V> t = (Hashtable<K,V>) super.clone(); |
| 507 | t.table = new Entry[table.length]; |
| 508 | for (int i = table.length ; i-- > 0 ; ) { |
| 509 | t.table[i] = (table[i] != null) |
| 510 | ? (Entry<K,V>) table[i].clone() : null; |
| 511 | } |
| 512 | t.keySet = null; |
| 513 | t.entrySet = null; |
| 514 | t.values = null; |
| 515 | t.modCount = 0; |
| 516 | return t; |
| 517 | } catch (CloneNotSupportedException e) { |
| 518 | // this shouldn't happen, since we are Cloneable |
| 519 | throw new InternalError(); |
| 520 | } |
| 521 | } |
| 522 | |
| 523 | /** |
| 524 | * Returns a string representation of this <tt>Hashtable</tt> object |
| 525 | * in the form of a set of entries, enclosed in braces and separated |
| 526 | * by the ASCII characters "<tt>, </tt>" (comma and space). Each |
| 527 | * entry is rendered as the key, an equals sign <tt>=</tt>, and the |
| 528 | * associated element, where the <tt>toString</tt> method is used to |
| 529 | * convert the key and element to strings. |
| 530 | * |
| 531 | * @return a string representation of this hashtable |
| 532 | */ |
| 533 | public synchronized String toString() { |
| 534 | int max = size() - 1; |
| 535 | if (max == -1) |
| 536 | return "{}"; |
| 537 | |
| 538 | StringBuilder sb = new StringBuilder(); |
| 539 | Iterator<Map.Entry<K,V>> it = entrySet().iterator(); |
| 540 | |
| 541 | sb.append('{'); |
| 542 | for (int i = 0; ; i++) { |
| 543 | Map.Entry<K,V> e = it.next(); |
| 544 | K key = e.getKey(); |
| 545 | V value = e.getValue(); |
| 546 | sb.append(key == this ? "(this Map)" : key.toString()); |
| 547 | sb.append('='); |
| 548 | sb.append(value == this ? "(this Map)" : value.toString()); |
| 549 | |
| 550 | if (i == max) |
| 551 | return sb.append('}').toString(); |
| 552 | sb.append(", "); |
| 553 | } |
| 554 | } |
| 555 | |
| 556 | |
| 557 | private <T> Enumeration<T> getEnumeration(int type) { |
| 558 | if (count == 0) { |
| 559 | return Collections.emptyEnumeration(); |
| 560 | } else { |
| 561 | return new Enumerator<T>(type, false); |
| 562 | } |
| 563 | } |
| 564 | |
| 565 | private <T> Iterator<T> getIterator(int type) { |
| 566 | if (count == 0) { |
| 567 | return Collections.emptyIterator(); |
| 568 | } else { |
| 569 | return new Enumerator<T>(type, true); |
| 570 | } |
| 571 | } |
| 572 | |
| 573 | // Views |
| 574 | |
| 575 | /** |
| 576 | * Each of these fields are initialized to contain an instance of the |
| 577 | * appropriate view the first time this view is requested. The views are |
| 578 | * stateless, so there's no reason to create more than one of each. |
| 579 | */ |
| 580 | private transient volatile Set<K> keySet = null; |
| 581 | private transient volatile Set<Map.Entry<K,V>> entrySet = null; |
| 582 | private transient volatile Collection<V> values = null; |
| 583 | |
| 584 | /** |
| 585 | * Returns a {@link Set} view of the keys contained in this map. |
| 586 | * The set is backed by the map, so changes to the map are |
| 587 | * reflected in the set, and vice-versa. If the map is modified |
| 588 | * while an iteration over the set is in progress (except through |
| 589 | * the iterator's own <tt>remove</tt> operation), the results of |
| 590 | * the iteration are undefined. The set supports element removal, |
| 591 | * which removes the corresponding mapping from the map, via the |
| 592 | * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, |
| 593 | * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> |
| 594 | * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> |
| 595 | * operations. |
| 596 | * |
| 597 | * @since 1.2 |
| 598 | */ |
| 599 | public Set<K> keySet() { |
| 600 | if (keySet == null) |
| 601 | keySet = Collections.synchronizedSet(new KeySet(), this); |
| 602 | return keySet; |
| 603 | } |
| 604 | |
| 605 | private class KeySet extends AbstractSet<K> { |
| 606 | public Iterator<K> iterator() { |
| 607 | return getIterator(KEYS); |
| 608 | } |
| 609 | public int size() { |
| 610 | return count; |
| 611 | } |
| 612 | public boolean contains(Object o) { |
| 613 | return containsKey(o); |
| 614 | } |
| 615 | public boolean remove(Object o) { |
| 616 | return Hashtable.this.remove(o) != null; |
| 617 | } |
| 618 | public void clear() { |
| 619 | Hashtable.this.clear(); |
| 620 | } |
| 621 | } |
| 622 | |
| 623 | /** |
| 624 | * Returns a {@link Set} view of the mappings contained in this map. |
| 625 | * The set is backed by the map, so changes to the map are |
| 626 | * reflected in the set, and vice-versa. If the map is modified |
| 627 | * while an iteration over the set is in progress (except through |
| 628 | * the iterator's own <tt>remove</tt> operation, or through the |
| 629 | * <tt>setValue</tt> operation on a map entry returned by the |
| 630 | * iterator) the results of the iteration are undefined. The set |
| 631 | * supports element removal, which removes the corresponding |
| 632 | * mapping from the map, via the <tt>Iterator.remove</tt>, |
| 633 | * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and |
| 634 | * <tt>clear</tt> operations. It does not support the |
| 635 | * <tt>add</tt> or <tt>addAll</tt> operations. |
| 636 | * |
| 637 | * @since 1.2 |
| 638 | */ |
| 639 | public Set<Map.Entry<K,V>> entrySet() { |
| 640 | if (entrySet==null) |
| 641 | entrySet = Collections.synchronizedSet(new EntrySet(), this); |
| 642 | return entrySet; |
| 643 | } |
| 644 | |
| 645 | private class EntrySet extends AbstractSet<Map.Entry<K,V>> { |
| 646 | public Iterator<Map.Entry<K,V>> iterator() { |
| 647 | return getIterator(ENTRIES); |
| 648 | } |
| 649 | |
| 650 | public boolean add(Map.Entry<K,V> o) { |
| 651 | return super.add(o); |
| 652 | } |
| 653 | |
| 654 | public boolean contains(Object o) { |
| 655 | if (!(o instanceof Map.Entry)) |
| 656 | return false; |
| 657 | Map.Entry entry = (Map.Entry)o; |
| 658 | Object key = entry.getKey(); |
| 659 | Entry[] tab = table; |
| 660 | int hash = key.hashCode(); |
| 661 | int index = (hash & 0x7FFFFFFF) % tab.length; |
| 662 | |
| 663 | for (Entry e = tab[index]; e != null; e = e.next) |
| 664 | if (e.hash==hash && e.equals(entry)) |
| 665 | return true; |
| 666 | return false; |
| 667 | } |
| 668 | |
| 669 | public boolean remove(Object o) { |
| 670 | if (!(o instanceof Map.Entry)) |
| 671 | return false; |
| 672 | Map.Entry<K,V> entry = (Map.Entry<K,V>) o; |
| 673 | K key = entry.getKey(); |
| 674 | Entry[] tab = table; |
| 675 | int hash = key.hashCode(); |
| 676 | int index = (hash & 0x7FFFFFFF) % tab.length; |
| 677 | |
| 678 | for (Entry<K,V> e = tab[index], prev = null; e != null; |
| 679 | prev = e, e = e.next) { |
| 680 | if (e.hash==hash && e.equals(entry)) { |
| 681 | modCount++; |
| 682 | if (prev != null) |
| 683 | prev.next = e.next; |
| 684 | else |
| 685 | tab[index] = e.next; |
| 686 | |
| 687 | count--; |
| 688 | e.value = null; |
| 689 | return true; |
| 690 | } |
| 691 | } |
| 692 | return false; |
| 693 | } |
| 694 | |
| 695 | public int size() { |
| 696 | return count; |
| 697 | } |
| 698 | |
| 699 | public void clear() { |
| 700 | Hashtable.this.clear(); |
| 701 | } |
| 702 | } |
| 703 | |
| 704 | /** |
| 705 | * Returns a {@link Collection} view of the values contained in this map. |
| 706 | * The collection is backed by the map, so changes to the map are |
| 707 | * reflected in the collection, and vice-versa. If the map is |
| 708 | * modified while an iteration over the collection is in progress |
| 709 | * (except through the iterator's own <tt>remove</tt> operation), |
| 710 | * the results of the iteration are undefined. The collection |
| 711 | * supports element removal, which removes the corresponding |
| 712 | * mapping from the map, via the <tt>Iterator.remove</tt>, |
| 713 | * <tt>Collection.remove</tt>, <tt>removeAll</tt>, |
| 714 | * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not |
| 715 | * support the <tt>add</tt> or <tt>addAll</tt> operations. |
| 716 | * |
| 717 | * @since 1.2 |
| 718 | */ |
| 719 | public Collection<V> values() { |
| 720 | if (values==null) |
| 721 | values = Collections.synchronizedCollection(new ValueCollection(), |
| 722 | this); |
| 723 | return values; |
| 724 | } |
| 725 | |
| 726 | private class ValueCollection extends AbstractCollection<V> { |
| 727 | public Iterator<V> iterator() { |
| 728 | return getIterator(VALUES); |
| 729 | } |
| 730 | public int size() { |
| 731 | return count; |
| 732 | } |
| 733 | public boolean contains(Object o) { |
| 734 | return containsValue(o); |
| 735 | } |
| 736 | public void clear() { |
| 737 | Hashtable.this.clear(); |
| 738 | } |
| 739 | } |
| 740 | |
| 741 | // Comparison and hashing |
| 742 | |
| 743 | /** |
| 744 | * Compares the specified Object with this Map for equality, |
| 745 | * as per the definition in the Map interface. |
| 746 | * |
| 747 | * @param o object to be compared for equality with this hashtable |
| 748 | * @return true if the specified Object is equal to this Map |
| 749 | * @see Map#equals(Object) |
| 750 | * @since 1.2 |
| 751 | */ |
| 752 | public synchronized boolean equals(Object o) { |
| 753 | if (o == this) |
| 754 | return true; |
| 755 | |
| 756 | if (!(o instanceof Map)) |
| 757 | return false; |
| 758 | Map<K,V> t = (Map<K,V>) o; |
| 759 | if (t.size() != size()) |
| 760 | return false; |
| 761 | |
| 762 | try { |
| 763 | Iterator<Map.Entry<K,V>> i = entrySet().iterator(); |
| 764 | while (i.hasNext()) { |
| 765 | Map.Entry<K,V> e = i.next(); |
| 766 | K key = e.getKey(); |
| 767 | V value = e.getValue(); |
| 768 | if (value == null) { |
| 769 | if (!(t.get(key)==null && t.containsKey(key))) |
| 770 | return false; |
| 771 | } else { |
| 772 | if (!value.equals(t.get(key))) |
| 773 | return false; |
| 774 | } |
| 775 | } |
| 776 | } catch (ClassCastException unused) { |
| 777 | return false; |
| 778 | } catch (NullPointerException unused) { |
| 779 | return false; |
| 780 | } |
| 781 | |
| 782 | return true; |
| 783 | } |
| 784 | |
| 785 | /** |
| 786 | * Returns the hash code value for this Map as per the definition in the |
| 787 | * Map interface. |
| 788 | * |
| 789 | * @see Map#hashCode() |
| 790 | * @since 1.2 |
| 791 | */ |
| 792 | public synchronized int hashCode() { |
| 793 | /* |
| 794 | * This code detects the recursion caused by computing the hash code |
| 795 | * of a self-referential hash table and prevents the stack overflow |
| 796 | * that would otherwise result. This allows certain 1.1-era |
| 797 | * applets with self-referential hash tables to work. This code |
| 798 | * abuses the loadFactor field to do double-duty as a hashCode |
| 799 | * in progress flag, so as not to worsen the space performance. |
| 800 | * A negative load factor indicates that hash code computation is |
| 801 | * in progress. |
| 802 | */ |
| 803 | int h = 0; |
| 804 | if (count == 0 || loadFactor < 0) |
| 805 | return h; // Returns zero |
| 806 | |
| 807 | loadFactor = -loadFactor; // Mark hashCode computation in progress |
| 808 | Entry[] tab = table; |
| 809 | for (int i = 0; i < tab.length; i++) |
| 810 | for (Entry e = tab[i]; e != null; e = e.next) |
| 811 | h += e.key.hashCode() ^ e.value.hashCode(); |
| 812 | loadFactor = -loadFactor; // Mark hashCode computation complete |
| 813 | |
| 814 | return h; |
| 815 | } |
| 816 | |
| 817 | /** |
| 818 | * Save the state of the Hashtable to a stream (i.e., serialize it). |
| 819 | * |
| 820 | * @serialData The <i>capacity</i> of the Hashtable (the length of the |
| 821 | * bucket array) is emitted (int), followed by the |
| 822 | * <i>size</i> of the Hashtable (the number of key-value |
| 823 | * mappings), followed by the key (Object) and value (Object) |
| 824 | * for each key-value mapping represented by the Hashtable |
| 825 | * The key-value mappings are emitted in no particular order. |
| 826 | */ |
| 827 | private synchronized void writeObject(java.io.ObjectOutputStream s) |
| 828 | throws IOException |
| 829 | { |
| 830 | // Write out the length, threshold, loadfactor |
| 831 | s.defaultWriteObject(); |
| 832 | |
| 833 | // Write out length, count of elements and then the key/value objects |
| 834 | s.writeInt(table.length); |
| 835 | s.writeInt(count); |
| 836 | for (int index = table.length-1; index >= 0; index--) { |
| 837 | Entry entry = table[index]; |
| 838 | |
| 839 | while (entry != null) { |
| 840 | s.writeObject(entry.key); |
| 841 | s.writeObject(entry.value); |
| 842 | entry = entry.next; |
| 843 | } |
| 844 | } |
| 845 | } |
| 846 | |
| 847 | /** |
| 848 | * Reconstitute the Hashtable from a stream (i.e., deserialize it). |
| 849 | */ |
| 850 | private void readObject(java.io.ObjectInputStream s) |
| 851 | throws IOException, ClassNotFoundException |
| 852 | { |
| 853 | // Read in the length, threshold, and loadfactor |
| 854 | s.defaultReadObject(); |
| 855 | |
| 856 | // Read the original length of the array and number of elements |
| 857 | int origlength = s.readInt(); |
| 858 | int elements = s.readInt(); |
| 859 | |
| 860 | // Compute new size with a bit of room 5% to grow but |
| 861 | // no larger than the original size. Make the length |
| 862 | // odd if it's large enough, this helps distribute the entries. |
| 863 | // Guard against the length ending up zero, that's not valid. |
| 864 | int length = (int)(elements * loadFactor) + (elements / 20) + 3; |
| 865 | if (length > elements && (length & 1) == 0) |
| 866 | length--; |
| 867 | if (origlength > 0 && length > origlength) |
| 868 | length = origlength; |
| 869 | |
| 870 | Entry[] table = new Entry[length]; |
| 871 | count = 0; |
| 872 | |
| 873 | // Read the number of elements and then all the key/value objects |
| 874 | for (; elements > 0; elements--) { |
| 875 | K key = (K)s.readObject(); |
| 876 | V value = (V)s.readObject(); |
| 877 | // synch could be eliminated for performance |
| 878 | reconstitutionPut(table, key, value); |
| 879 | } |
| 880 | this.table = table; |
| 881 | } |
| 882 | |
| 883 | /** |
| 884 | * The put method used by readObject. This is provided because put |
| 885 | * is overridable and should not be called in readObject since the |
| 886 | * subclass will not yet be initialized. |
| 887 | * |
| 888 | * <p>This differs from the regular put method in several ways. No |
| 889 | * checking for rehashing is necessary since the number of elements |
| 890 | * initially in the table is known. The modCount is not incremented |
| 891 | * because we are creating a new instance. Also, no return value |
| 892 | * is needed. |
| 893 | */ |
| 894 | private void reconstitutionPut(Entry[] tab, K key, V value) |
| 895 | throws StreamCorruptedException |
| 896 | { |
| 897 | if (value == null) { |
| 898 | throw new java.io.StreamCorruptedException(); |
| 899 | } |
| 900 | // Makes sure the key is not already in the hashtable. |
| 901 | // This should not happen in deserialized version. |
| 902 | int hash = key.hashCode(); |
| 903 | int index = (hash & 0x7FFFFFFF) % tab.length; |
| 904 | for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) { |
| 905 | if ((e.hash == hash) && e.key.equals(key)) { |
| 906 | throw new java.io.StreamCorruptedException(); |
| 907 | } |
| 908 | } |
| 909 | // Creates the new entry. |
| 910 | Entry<K,V> e = tab[index]; |
| 911 | tab[index] = new Entry<K,V>(hash, key, value, e); |
| 912 | count++; |
| 913 | } |
| 914 | |
| 915 | /** |
| 916 | * Hashtable collision list. |
| 917 | */ |
| 918 | private static class Entry<K,V> implements Map.Entry<K,V> { |
| 919 | int hash; |
| 920 | K key; |
| 921 | V value; |
| 922 | Entry<K,V> next; |
| 923 | |
| 924 | protected Entry(int hash, K key, V value, Entry<K,V> next) { |
| 925 | this.hash = hash; |
| 926 | this.key = key; |
| 927 | this.value = value; |
| 928 | this.next = next; |
| 929 | } |
| 930 | |
| 931 | protected Object clone() { |
| 932 | return new Entry<K,V>(hash, key, value, |
| 933 | (next==null ? null : (Entry<K,V>) next.clone())); |
| 934 | } |
| 935 | |
| 936 | // Map.Entry Ops |
| 937 | |
| 938 | public K getKey() { |
| 939 | return key; |
| 940 | } |
| 941 | |
| 942 | public V getValue() { |
| 943 | return value; |
| 944 | } |
| 945 | |
| 946 | public V setValue(V value) { |
| 947 | if (value == null) |
| 948 | throw new NullPointerException(); |
| 949 | |
| 950 | V oldValue = this.value; |
| 951 | this.value = value; |
| 952 | return oldValue; |
| 953 | } |
| 954 | |
| 955 | public boolean equals(Object o) { |
| 956 | if (!(o instanceof Map.Entry)) |
| 957 | return false; |
| 958 | Map.Entry e = (Map.Entry)o; |
| 959 | |
| 960 | return (key==null ? e.getKey()==null : key.equals(e.getKey())) && |
| 961 | (value==null ? e.getValue()==null : value.equals(e.getValue())); |
| 962 | } |
| 963 | |
| 964 | public int hashCode() { |
| 965 | return hash ^ (value==null ? 0 : value.hashCode()); |
| 966 | } |
| 967 | |
| 968 | public String toString() { |
| 969 | return key.toString()+"="+value.toString(); |
| 970 | } |
| 971 | } |
| 972 | |
| 973 | // Types of Enumerations/Iterations |
| 974 | private static final int KEYS = 0; |
| 975 | private static final int VALUES = 1; |
| 976 | private static final int ENTRIES = 2; |
| 977 | |
| 978 | /** |
| 979 | * A hashtable enumerator class. This class implements both the |
| 980 | * Enumeration and Iterator interfaces, but individual instances |
| 981 | * can be created with the Iterator methods disabled. This is necessary |
| 982 | * to avoid unintentionally increasing the capabilities granted a user |
| 983 | * by passing an Enumeration. |
| 984 | */ |
| 985 | private class Enumerator<T> implements Enumeration<T>, Iterator<T> { |
| 986 | Entry[] table = Hashtable.this.table; |
| 987 | int index = table.length; |
| 988 | Entry<K,V> entry = null; |
| 989 | Entry<K,V> lastReturned = null; |
| 990 | int type; |
| 991 | |
| 992 | /** |
| 993 | * Indicates whether this Enumerator is serving as an Iterator |
| 994 | * or an Enumeration. (true -> Iterator). |
| 995 | */ |
| 996 | boolean iterator; |
| 997 | |
| 998 | /** |
| 999 | * The modCount value that the iterator believes that the backing |
| 1000 | * Hashtable should have. If this expectation is violated, the iterator |
| 1001 | * has detected concurrent modification. |
| 1002 | */ |
| 1003 | protected int expectedModCount = modCount; |
| 1004 | |
| 1005 | Enumerator(int type, boolean iterator) { |
| 1006 | this.type = type; |
| 1007 | this.iterator = iterator; |
| 1008 | } |
| 1009 | |
| 1010 | public boolean hasMoreElements() { |
| 1011 | Entry<K,V> e = entry; |
| 1012 | int i = index; |
| 1013 | Entry[] t = table; |
| 1014 | /* Use locals for faster loop iteration */ |
| 1015 | while (e == null && i > 0) { |
| 1016 | e = t[--i]; |
| 1017 | } |
| 1018 | entry = e; |
| 1019 | index = i; |
| 1020 | return e != null; |
| 1021 | } |
| 1022 | |
| 1023 | public T nextElement() { |
| 1024 | Entry<K,V> et = entry; |
| 1025 | int i = index; |
| 1026 | Entry[] t = table; |
| 1027 | /* Use locals for faster loop iteration */ |
| 1028 | while (et == null && i > 0) { |
| 1029 | et = t[--i]; |
| 1030 | } |
| 1031 | entry = et; |
| 1032 | index = i; |
| 1033 | if (et != null) { |
| 1034 | Entry<K,V> e = lastReturned = entry; |
| 1035 | entry = e.next; |
| 1036 | return type == KEYS ? (T)e.key : (type == VALUES ? (T)e.value : (T)e); |
| 1037 | } |
| 1038 | throw new NoSuchElementException("Hashtable Enumerator"); |
| 1039 | } |
| 1040 | |
| 1041 | // Iterator methods |
| 1042 | public boolean hasNext() { |
| 1043 | return hasMoreElements(); |
| 1044 | } |
| 1045 | |
| 1046 | public T next() { |
| 1047 | if (modCount != expectedModCount) |
| 1048 | throw new ConcurrentModificationException(); |
| 1049 | return nextElement(); |
| 1050 | } |
| 1051 | |
| 1052 | public void remove() { |
| 1053 | if (!iterator) |
| 1054 | throw new UnsupportedOperationException(); |
| 1055 | if (lastReturned == null) |
| 1056 | throw new IllegalStateException("Hashtable Enumerator"); |
| 1057 | if (modCount != expectedModCount) |
| 1058 | throw new ConcurrentModificationException(); |
| 1059 | |
| 1060 | synchronized(Hashtable.this) { |
| 1061 | Entry[] tab = Hashtable.this.table; |
| 1062 | int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length; |
| 1063 | |
| 1064 | for (Entry<K,V> e = tab[index], prev = null; e != null; |
| 1065 | prev = e, e = e.next) { |
| 1066 | if (e == lastReturned) { |
| 1067 | modCount++; |
| 1068 | expectedModCount++; |
| 1069 | if (prev == null) |
| 1070 | tab[index] = e.next; |
| 1071 | else |
| 1072 | prev.next = e.next; |
| 1073 | count--; |
| 1074 | lastReturned = null; |
| 1075 | return; |
| 1076 | } |
| 1077 | } |
| 1078 | throw new ConcurrentModificationException(); |
| 1079 | } |
| 1080 | } |
| 1081 | } |
| 1082 | } |