1 /*
2 * Copyright (c) 1994, 2011, 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<?,?> 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<?,?> 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 @SuppressWarnings("unchecked")
356 public synchronized V get(Object key) {
357 Entry<?,?> tab[] = table;
358 int hash = key.hashCode();
359 int index = (hash & 0x7FFFFFFF) % tab.length;
360 for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
361 if ((e.hash == hash) && e.key.equals(key)) {
362 return (V)e.value;
363 }
364 }
365 return null;
366 }
367
368 /**
369 * The maximum size of array to allocate.
370 * Some VMs reserve some header words in an array.
371 * Attempts to allocate larger arrays may result in
372 * OutOfMemoryError: Requested array size exceeds VM limit
373 */
374 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
375
376 /**
377 * Increases the capacity of and internally reorganizes this
378 * hashtable, in order to accommodate and access its entries more
379 * efficiently. This method is called automatically when the
380 * number of keys in the hashtable exceeds this hashtable's capacity
381 * and load factor.
382 */
383 @SuppressWarnings("unchecked")
384 protected void rehash() {
385 int oldCapacity = table.length;
386 Entry<?,?>[] oldMap = table;
387
388 // overflow-conscious code
389 int newCapacity = (oldCapacity << 1) + 1;
390 if (newCapacity - MAX_ARRAY_SIZE > 0) {
391 if (oldCapacity == MAX_ARRAY_SIZE)
392 // Keep running with MAX_ARRAY_SIZE buckets
393 return;
394 newCapacity = MAX_ARRAY_SIZE;
395 }
396 Entry<?,?>[] newMap = new Entry<?,?>[newCapacity];
397
398 modCount++;
399 threshold = (int)(newCapacity * loadFactor);
400 table = newMap;
401
402 for (int i = oldCapacity ; i-- > 0 ;) {
403 for (Entry<K,V> old = (Entry<K,V>)oldMap[i] ; old != null ; ) {
404 Entry<K,V> e = old;
405 old = old.next;
406
407 int index = (e.hash & 0x7FFFFFFF) % newCapacity;
408 e.next = (Entry<K,V>)newMap[index];
409 newMap[index] = e;
410 }
411 }
412 }
413
414 /**
415 * Maps the specified <code>key</code> to the specified
416 * <code>value</code> in this hashtable. Neither the key nor the
417 * value can be <code>null</code>. <p>
418 *
419 * The value can be retrieved by calling the <code>get</code> method
420 * with a key that is equal to the original key.
421 *
422 * @param key the hashtable key
423 * @param value the value
424 * @return the previous value of the specified key in this hashtable,
425 * or <code>null</code> if it did not have one
426 * @exception NullPointerException if the key or value is
427 * <code>null</code>
428 * @see Object#equals(Object)
429 * @see #get(Object)
430 */
431 public synchronized V put(K key, V value) {
432 // Make sure the value is not null
433 if (value == null) {
434 throw new NullPointerException();
435 }
436
437 // Makes sure the key is not already in the hashtable.
438 Entry<?,?> tab[] = table;
439 int hash = key.hashCode();
440 int index = (hash & 0x7FFFFFFF) % tab.length;
441 @SuppressWarnings("unchecked")
442 Entry<K,V> entry = (Entry<K,V>)tab[index];
443 for(; entry != null ; entry = entry.next) {
444 if ((entry.hash == hash) && entry.key.equals(key)) {
445 V old = entry.value;
446 entry.value = value;
447 return old;
448 }
449 }
450
451 modCount++;
452 if (count >= threshold) {
453 // Rehash the table if the threshold is exceeded
454 rehash();
455
456 tab = table;
457 index = (hash & 0x7FFFFFFF) % tab.length;
458 }
459
460 // Creates the new entry.
461 @SuppressWarnings("unchecked")
462 Entry<K,V> e = (Entry<K,V>)tab[index];
463 tab[index] = new Entry<>(hash, key, value, e);
464 count++;
465 return null;
466 }
467
468 /**
469 * Removes the key (and its corresponding value) from this
470 * hashtable. This method does nothing if the key is not in the hashtable.
471 *
472 * @param key the key that needs to be removed
473 * @return the value to which the key had been mapped in this hashtable,
474 * or <code>null</code> if the key did not have a mapping
475 * @throws NullPointerException if the key is <code>null</code>
476 */
477 public synchronized V remove(Object key) {
478 Entry<?,?> tab[] = table;
479 int hash = key.hashCode();
480 int index = (hash & 0x7FFFFFFF) % tab.length;
481 @SuppressWarnings("unchecked")
482 Entry<K,V> e = (Entry<K,V>)tab[index];
483 for(Entry<K,V> prev = null ; e != null ; prev = e, e = e.next) {
484 if ((e.hash == hash) && e.key.equals(key)) {
485 modCount++;
486 if (prev != null) {
487 prev.next = e.next;
488 } else {
489 tab[index] = e.next;
490 }
491 count--;
492 V oldValue = e.value;
493 e.value = null;
494 return oldValue;
495 }
496 }
497 return null;
498 }
499
500 /**
501 * Copies all of the mappings from the specified map to this hashtable.
502 * These mappings will replace any mappings that this hashtable had for any
503 * of the keys currently in the specified map.
504 *
505 * @param t mappings to be stored in this map
506 * @throws NullPointerException if the specified map is null
507 * @since 1.2
508 */
509 public synchronized void putAll(Map<? extends K, ? extends V> t) {
510 for (Map.Entry<? extends K, ? extends V> e : t.entrySet())
511 put(e.getKey(), e.getValue());
512 }
513
514 /**
515 * Clears this hashtable so that it contains no keys.
516 */
517 public synchronized void clear() {
518 Entry<?,?> tab[] = table;
519 modCount++;
520 for (int index = tab.length; --index >= 0; )
521 tab[index] = null;
522 count = 0;
523 }
524
525 /**
526 * Creates a shallow copy of this hashtable. All the structure of the
527 * hashtable itself is copied, but the keys and values are not cloned.
528 * This is a relatively expensive operation.
529 *
530 * @return a clone of the hashtable
531 */
532 public synchronized Object clone() {
533 try {
534 Hashtable<?,?> t = (Hashtable<?,?>)super.clone();
535 t.table = new Entry<?,?>[table.length];
536 for (int i = table.length ; i-- > 0 ; ) {
537 t.table[i] = (table[i] != null)
538 ? (Entry<?,?>) table[i].clone() : null;
539 }
540 t.keySet = null;
541 t.entrySet = null;
542 t.values = null;
543 t.modCount = 0;
544 return t;
545 } catch (CloneNotSupportedException e) {
546 // this shouldn't happen, since we are Cloneable
547 throw new InternalError(e);
548 }
549 }
550
551 /**
552 * Returns a string representation of this <tt>Hashtable</tt> object
553 * in the form of a set of entries, enclosed in braces and separated
554 * by the ASCII characters "<tt>, </tt>" (comma and space). Each
555 * entry is rendered as the key, an equals sign <tt>=</tt>, and the
556 * associated element, where the <tt>toString</tt> method is used to
557 * convert the key and element to strings.
558 *
559 * @return a string representation of this hashtable
560 */
561 public synchronized String toString() {
562 int max = size() - 1;
563 if (max == -1)
564 return "{}";
565
566 StringBuilder sb = new StringBuilder();
567 Iterator<Map.Entry<K,V>> it = entrySet().iterator();
568
569 sb.append('{');
570 for (int i = 0; ; i++) {
571 Map.Entry<K,V> e = it.next();
572 K key = e.getKey();
573 V value = e.getValue();
574 sb.append(key == this ? "(this Map)" : key.toString());
575 sb.append('=');
576 sb.append(value == this ? "(this Map)" : value.toString());
577
578 if (i == max)
579 return sb.append('}').toString();
580 sb.append(", ");
581 }
582 }
583
584
585 private <T> Enumeration<T> getEnumeration(int type) {
586 if (count == 0) {
587 return Collections.emptyEnumeration();
588 } else {
589 return new Enumerator<>(type, false);
590 }
591 }
592
593 private <T> Iterator<T> getIterator(int type) {
594 if (count == 0) {
595 return Collections.emptyIterator();
596 } else {
597 return new Enumerator<>(type, true);
598 }
599 }
600
601 // Views
602
603 /**
604 * Each of these fields are initialized to contain an instance of the
605 * appropriate view the first time this view is requested. The views are
606 * stateless, so there's no reason to create more than one of each.
607 */
608 private transient volatile Set<K> keySet = null;
609 private transient volatile Set<Map.Entry<K,V>> entrySet = null;
610 private transient volatile Collection<V> values = null;
611
612 /**
613 * Returns a {@link Set} view of the keys contained in this map.
614 * The set is backed by the map, so changes to the map are
615 * reflected in the set, and vice-versa. If the map is modified
616 * while an iteration over the set is in progress (except through
617 * the iterator's own <tt>remove</tt> operation), the results of
618 * the iteration are undefined. The set supports element removal,
619 * which removes the corresponding mapping from the map, via the
620 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
621 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
622 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
623 * operations.
624 *
625 * @since 1.2
626 */
627 public Set<K> keySet() {
628 if (keySet == null)
629 keySet = Collections.synchronizedSet(new KeySet(), this);
630 return keySet;
631 }
632
633 private class KeySet extends AbstractSet<K> {
634 public Iterator<K> iterator() {
635 return getIterator(KEYS);
636 }
637 public int size() {
638 return count;
639 }
640 public boolean contains(Object o) {
641 return containsKey(o);
642 }
643 public boolean remove(Object o) {
644 return Hashtable.this.remove(o) != null;
645 }
646 public void clear() {
647 Hashtable.this.clear();
648 }
649 }
650
651 /**
652 * Returns a {@link Set} view of the mappings contained in this map.
653 * The set is backed by the map, so changes to the map are
654 * reflected in the set, and vice-versa. If the map is modified
655 * while an iteration over the set is in progress (except through
656 * the iterator's own <tt>remove</tt> operation, or through the
657 * <tt>setValue</tt> operation on a map entry returned by the
658 * iterator) the results of the iteration are undefined. The set
659 * supports element removal, which removes the corresponding
660 * mapping from the map, via the <tt>Iterator.remove</tt>,
661 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
662 * <tt>clear</tt> operations. It does not support the
663 * <tt>add</tt> or <tt>addAll</tt> operations.
664 *
665 * @since 1.2
666 */
667 public Set<Map.Entry<K,V>> entrySet() {
668 if (entrySet==null)
669 entrySet = Collections.synchronizedSet(new EntrySet(), this);
670 return entrySet;
671 }
672
673 private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
674 public Iterator<Map.Entry<K,V>> iterator() {
675 return getIterator(ENTRIES);
676 }
677
678 public boolean add(Map.Entry<K,V> o) {
679 return super.add(o);
680 }
681
682 public boolean contains(Object o) {
683 if (!(o instanceof Map.Entry))
684 return false;
685 Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
686 Object key = entry.getKey();
687 Entry<?,?>[] tab = table;
688 int hash = key.hashCode();
689 int index = (hash & 0x7FFFFFFF) % tab.length;
690
691 for (Entry<?,?> e = tab[index]; e != null; e = e.next)
692 if (e.hash==hash && e.equals(entry))
693 return true;
694 return false;
695 }
696
697 public boolean remove(Object o) {
698 if (!(o instanceof Map.Entry))
699 return false;
700 Map.Entry<?,?> entry = (Map.Entry<?,?>) o;
701 Object key = entry.getKey();
702 Entry<?,?>[] tab = table;
703 int hash = key.hashCode();
704 int index = (hash & 0x7FFFFFFF) % tab.length;
705
706 @SuppressWarnings("unchecked")
707 Entry<K,V> e = (Entry<K,V>)tab[index];
708 for(Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
709 if (e.hash==hash && e.equals(entry)) {
710 modCount++;
711 if (prev != null)
712 prev.next = e.next;
713 else
714 tab[index] = e.next;
715
716 count--;
717 e.value = null;
718 return true;
719 }
720 }
721 return false;
722 }
723
724 public int size() {
725 return count;
726 }
727
728 public void clear() {
729 Hashtable.this.clear();
730 }
731 }
732
733 /**
734 * Returns a {@link Collection} view of the values contained in this map.
735 * The collection is backed by the map, so changes to the map are
736 * reflected in the collection, and vice-versa. If the map is
737 * modified while an iteration over the collection is in progress
738 * (except through the iterator's own <tt>remove</tt> operation),
739 * the results of the iteration are undefined. The collection
740 * supports element removal, which removes the corresponding
741 * mapping from the map, via the <tt>Iterator.remove</tt>,
742 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
743 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
744 * support the <tt>add</tt> or <tt>addAll</tt> operations.
745 *
746 * @since 1.2
747 */
748 public Collection<V> values() {
749 if (values==null)
750 values = Collections.synchronizedCollection(new ValueCollection(),
751 this);
752 return values;
753 }
754
755 private class ValueCollection extends AbstractCollection<V> {
756 public Iterator<V> iterator() {
757 return getIterator(VALUES);
758 }
759 public int size() {
760 return count;
761 }
762 public boolean contains(Object o) {
763 return containsValue(o);
764 }
765 public void clear() {
766 Hashtable.this.clear();
767 }
768 }
769
770 // Comparison and hashing
771
772 /**
773 * Compares the specified Object with this Map for equality,
774 * as per the definition in the Map interface.
775 *
776 * @param o object to be compared for equality with this hashtable
777 * @return true if the specified Object is equal to this Map
778 * @see Map#equals(Object)
779 * @since 1.2
780 */
781 public synchronized boolean equals(Object o) {
782 if (o == this)
783 return true;
784
785 if (!(o instanceof Map))
786 return false;
787 Map<?,?> t = (Map<?,?>) o;
788 if (t.size() != size())
789 return false;
790
791 try {
792 Iterator<Map.Entry<K,V>> i = entrySet().iterator();
793 while (i.hasNext()) {
794 Map.Entry<K,V> e = i.next();
795 K key = e.getKey();
796 V value = e.getValue();
797 if (value == null) {
798 if (!(t.get(key)==null && t.containsKey(key)))
799 return false;
800 } else {
801 if (!value.equals(t.get(key)))
802 return false;
803 }
804 }
805 } catch (ClassCastException unused) {
806 return false;
807 } catch (NullPointerException unused) {
808 return false;
809 }
810
811 return true;
812 }
813
814 /**
815 * Returns the hash code value for this Map as per the definition in the
816 * Map interface.
817 *
818 * @see Map#hashCode()
819 * @since 1.2
820 */
821 public synchronized int hashCode() {
822 /*
823 * This code detects the recursion caused by computing the hash code
824 * of a self-referential hash table and prevents the stack overflow
825 * that would otherwise result. This allows certain 1.1-era
826 * applets with self-referential hash tables to work. This code
827 * abuses the loadFactor field to do double-duty as a hashCode
828 * in progress flag, so as not to worsen the space performance.
829 * A negative load factor indicates that hash code computation is
830 * in progress.
831 */
832 int h = 0;
833 if (count == 0 || loadFactor < 0)
834 return h; // Returns zero
835
836 loadFactor = -loadFactor; // Mark hashCode computation in progress
837 Entry<?,?>[] tab = table;
838 for (int i = 0; i < tab.length; i++)
839 for (Entry<?,?> e = tab[i]; e != null; e = e.next)
840 h += e.key.hashCode() ^ e.value.hashCode();
841 loadFactor = -loadFactor; // Mark hashCode computation complete
842
843 return h;
844 }
845
846 /**
847 * Save the state of the Hashtable to a stream (i.e., serialize it).
848 *
849 * @serialData The <i>capacity</i> of the Hashtable (the length of the
850 * bucket array) is emitted (int), followed by the
851 * <i>size</i> of the Hashtable (the number of key-value
852 * mappings), followed by the key (Object) and value (Object)
853 * for each key-value mapping represented by the Hashtable
854 * The key-value mappings are emitted in no particular order.
855 */
856 private void writeObject(java.io.ObjectOutputStream s)
857 throws IOException {
858 Entry<Object, Object> entryStack = null;
859
860 synchronized (this) {
861 // Write out the length, threshold, loadfactor
862 s.defaultWriteObject();
863
864 // Write out length, count of elements
865 s.writeInt(table.length);
866 s.writeInt(count);
867
868 // Stack copies of the entries in the table
869 for (int index = 0; index < table.length; index++) {
870 Entry<?,?> entry = table[index];
871
872 while (entry != null) {
873 entryStack =
874 new Entry<>(0, entry.key, entry.value, entryStack);
875 entry = entry.next;
876 }
877 }
878 }
879
880 // Write out the key/value objects from the stacked entries
881 while (entryStack != null) {
882 s.writeObject(entryStack.key);
883 s.writeObject(entryStack.value);
884 entryStack = entryStack.next;
885 }
886 }
887
888 /**
889 * Reconstitute the Hashtable from a stream (i.e., deserialize it).
890 */
891 private void readObject(java.io.ObjectInputStream s)
892 throws IOException, ClassNotFoundException
893 {
894 // Read in the length, threshold, and loadfactor
895 s.defaultReadObject();
896
897 // Read the original length of the array and number of elements
898 int origlength = s.readInt();
899 int elements = s.readInt();
900
901 // Compute new size with a bit of room 5% to grow but
902 // no larger than the original size. Make the length
903 // odd if it's large enough, this helps distribute the entries.
904 // Guard against the length ending up zero, that's not valid.
905 int length = (int)(elements * loadFactor) + (elements / 20) + 3;
906 if (length > elements && (length & 1) == 0)
907 length--;
908 if (origlength > 0 && length > origlength)
909 length = origlength;
910 Entry<?,?>[] table = new Entry<?,?>[length];
911 count = 0;
912
913 // Read the number of elements and then all the key/value objects
914 for (; elements > 0; elements--) {
915 @SuppressWarnings("unchecked")
916 K key = (K)s.readObject();
917 @SuppressWarnings("unchecked")
918 V value = (V)s.readObject();
919 // synch could be eliminated for performance
920 reconstitutionPut(table, key, value);
921 }
922 this.table = table;
923 }
924
925 /**
926 * The put method used by readObject. This is provided because put
927 * is overridable and should not be called in readObject since the
928 * subclass will not yet be initialized.
929 *
930 * <p>This differs from the regular put method in several ways. No
931 * checking for rehashing is necessary since the number of elements
932 * initially in the table is known. The modCount is not incremented
933 * because we are creating a new instance. Also, no return value
934 * is needed.
935 */
936 private void reconstitutionPut(Entry<?,?>[] tab, K key, V value)
937 throws StreamCorruptedException
938 {
939 if (value == null) {
940 throw new java.io.StreamCorruptedException();
941 }
942 // Makes sure the key is not already in the hashtable.
943 // This should not happen in deserialized version.
944 int hash = key.hashCode();
945 int index = (hash & 0x7FFFFFFF) % tab.length;
946 for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
947 if ((e.hash == hash) && e.key.equals(key)) {
948 throw new java.io.StreamCorruptedException();
949 }
950 }
951 // Creates the new entry.
952 @SuppressWarnings("unchecked")
953 Entry<K,V> e = (Entry<K,V>)tab[index];
954 tab[index] = new Entry<>(hash, key, value, e);
955 count++;
956 }
957
958 /**
959 * Hashtable collision list.
960 */
961 private static class Entry<K,V> implements Map.Entry<K,V> {
962 int hash;
963 K key;
964 V value;
965 Entry<K,V> next;
966
967 protected Entry(int hash, K key, V value, Entry<K,V> next) {
968 this.hash = hash;
969 this.key = key;
970 this.value = value;
971 this.next = next;
972 }
973
974 @SuppressWarnings("unchecked")
975 protected Object clone() {
976 return new Entry<>(hash, key, value,
977 (next==null ? null : (Entry<K,V>) next.clone()));
978 }
979
980 // Map.Entry Ops
981
982 public K getKey() {
983 return key;
984 }
985
986 public V getValue() {
987 return value;
988 }
989
990 public V setValue(V value) {
991 if (value == null)
992 throw new NullPointerException();
993
994 V oldValue = this.value;
995 this.value = value;
996 return oldValue;
997 }
998
999 public boolean equals(Object o) {
1000 if (!(o instanceof Map.Entry))
1001 return false;
1002 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
1003
1004 return (key==null ? e.getKey()==null : key.equals(e.getKey())) &&
1005 (value==null ? e.getValue()==null : value.equals(e.getValue()));
1006 }
1007
1008 public int hashCode() {
1009 return hash ^ (value==null ? 0 : value.hashCode());
1010 }
1011
1012 public String toString() {
1013 return key.toString()+"="+value.toString();
1014 }
1015 }
1016
1017 // Types of Enumerations/Iterations
1018 private static final int KEYS = 0;
1019 private static final int VALUES = 1;
1020 private static final int ENTRIES = 2;
1021
1022 /**
1023 * A hashtable enumerator class. This class implements both the
1024 * Enumeration and Iterator interfaces, but individual instances
1025 * can be created with the Iterator methods disabled. This is necessary
1026 * to avoid unintentionally increasing the capabilities granted a user
1027 * by passing an Enumeration.
1028 */
1029 private class Enumerator<T> implements Enumeration<T>, Iterator<T> {
1030 Entry<?,?>[] table = Hashtable.this.table;
1031 int index = table.length;
1032 Entry<?,?> entry = null;
1033 Entry<?,?> lastReturned = null;
1034 int type;
1035
1036 /**
1037 * Indicates whether this Enumerator is serving as an Iterator
1038 * or an Enumeration. (true -> Iterator).
1039 */
1040 boolean iterator;
1041
1042 /**
1043 * The modCount value that the iterator believes that the backing
1044 * Hashtable should have. If this expectation is violated, the iterator
1045 * has detected concurrent modification.
1046 */
1047 protected int expectedModCount = modCount;
1048
1049 Enumerator(int type, boolean iterator) {
1050 this.type = type;
1051 this.iterator = iterator;
1052 }
1053
1054 public boolean hasMoreElements() {
1055 Entry<?,?> e = entry;
1056 int i = index;
1057 Entry<?,?>[] t = table;
1058 /* Use locals for faster loop iteration */
1059 while (e == null && i > 0) {
1060 e = t[--i];
1061 }
1062 entry = e;
1063 index = i;
1064 return e != null;
1065 }
1066
1067 @SuppressWarnings("unchecked")
1068 public T nextElement() {
1069 Entry<?,?> et = entry;
1070 int i = index;
1071 Entry<?,?>[] t = table;
1072 /* Use locals for faster loop iteration */
1073 while (et == null && i > 0) {
1074 et = t[--i];
1075 }
1076 entry = et;
1077 index = i;
1078 if (et != null) {
1079 Entry<?,?> e = lastReturned = entry;
1080 entry = e.next;
1081 return type == KEYS ? (T)e.key : (type == VALUES ? (T)e.value : (T)e);
1082 }
1083 throw new NoSuchElementException("Hashtable Enumerator");
1084 }
1085
1086 // Iterator methods
1087 public boolean hasNext() {
1088 return hasMoreElements();
1089 }
1090
1091 public T next() {
1092 if (modCount != expectedModCount)
1093 throw new ConcurrentModificationException();
1094 return nextElement();
1095 }
1096
1097 public void remove() {
1098 if (!iterator)
1099 throw new UnsupportedOperationException();
1100 if (lastReturned == null)
1101 throw new IllegalStateException("Hashtable Enumerator");
1102 if (modCount != expectedModCount)
1103 throw new ConcurrentModificationException();
1104
1105 synchronized(Hashtable.this) {
1106 Entry<?,?>[] tab = Hashtable.this.table;
1107 int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length;
1108
1109 @SuppressWarnings("unchecked")
1110 Entry<K,V> e = (Entry<K,V>)tab[index];
1111 for(Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
1112 if (e == lastReturned) {
1113 modCount++;
1114 expectedModCount++;
1115 if (prev == null)
1116 tab[index] = e.next;
1117 else
1118 prev.next = e.next;
1119 count--;
1120 lastReturned = null;
1121 return;
1122 }
1123 }
1124 throw new ConcurrentModificationException();
1125 }
1126 }
1127 }
1128 }