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<K,V>[] 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 * The default threshold of capacity above which alternate hashing is used.
168 * Alternative hashing reduces the incidence of collisions due to weak hash
169 * code calculation.
170 * <p/>
171 * This value may be overridden by defining the system property
172 * {@code java.util.althashing.threshold}. A property value of {@code 1}
173 * forces alternative hashing to be used at all times whereas
174 * {@code 2147483648 } ({@code Integer.MAX_VALUE}) value ensures that
175 * alternative hashing is never used.
176 */
177 static final int ALTERNATE_HASHING_THRESHOLD_DEFAULT = 0;
178
179 /**
180 * holds values which can't be initialized until after VM is booted.
181 */
182 private static class Holder {
183
184 /**
185 * Table capacity above which to switch to use alternate hashing.
186 */
187 static final int ALTERNATE_HASHING_THRESHOLD;
188
189 static {
190 String altThreshold = java.security.AccessController.doPrivileged(
191 new sun.security.action.GetPropertyAction(
192 "jdk.map.althashing.threshold"));
193
194 int threshold;
195 try {
196 threshold = (null != altThreshold)
197 ? Integer.parseInt(altThreshold)
198 : 1;
199
200 if(threshold == -1) {
201 threshold = Integer.MAX_VALUE;
202 }
203
204 if(threshold < 0) {
205 throw new IllegalArgumentException("value must be positive integer.");
206 }
207 } catch(IllegalArgumentException failed) {
208 throw new Error("Illegal value for 'jdk.map.althashing.threshold'", failed);
209 }
210
211 ALTERNATE_HASHING_THRESHOLD = threshold;
212 }
213 }
214
215 /**
216 * If {@code true} then perform alternate hashing to reduce the incidence of
217 * collisions due to weak hash code calculation.
218 */
219 transient boolean useAltHashing;
220
221 // Unsafe mechanics
222 private static final sun.misc.Unsafe UNSAFE;
223 private static final long HASHSEED_OFFSET;
224
225 static {
226 try {
227 UNSAFE = sun.misc.Unsafe.getUnsafe();
228 HASHSEED_OFFSET = UNSAFE.objectFieldOffset(
229 Hashtable.class.getDeclaredField("hashSeed"));
230 } catch (NoSuchFieldException | SecurityException e) {
231 throw new Error("Failed to record hashSeed offset", e);
232 }
233 }
234
235 /**
236 * A randomizing value associated with this instance that is applied to
237 * hash code of keys to make hash collisions harder to find.
238 */
239 transient final int hashSeed = sun.misc.Hashing.randomHashSeed(this);
240
241 private int hash(Object k) {
242 if (useAltHashing) {
243 int h = hashSeed;
244 if (k.getClass() == String.class) {
245 return h ^ sun.misc.Hashing.stringHash32((String) k);
246 } else {
247 h ^= k.hashCode();
248
249 // This function ensures that hashCodes that differ only by
250 // constant multiples at each bit position have a bounded
251 // number of collisions (approximately 8 at default load factor).
252 h ^= (h >>> 20) ^ (h >>> 12);
253 return h ^ (h >>> 7) ^ (h >>> 4);
254 }
255 } else {
256 return k.hashCode();
257 }
258 }
259
260 /**
261 * Constructs a new, empty hashtable with the specified initial
262 * capacity and the specified load factor.
263 *
264 * @param initialCapacity the initial capacity of the hashtable.
265 * @param loadFactor the load factor of the hashtable.
266 * @exception IllegalArgumentException if the initial capacity is less
267 * than zero, or if the load factor is nonpositive.
268 */
269 public Hashtable(int initialCapacity, float loadFactor) {
270 if (initialCapacity < 0)
271 throw new IllegalArgumentException("Illegal Capacity: "+
272 initialCapacity);
273 if (loadFactor <= 0 || Float.isNaN(loadFactor))
274 throw new IllegalArgumentException("Illegal Load: "+loadFactor);
275
276 if (initialCapacity==0)
277 initialCapacity = 1;
278 this.loadFactor = loadFactor;
279 table = new Entry[initialCapacity];
280 threshold = (int)Math.min(initialCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
281 useAltHashing = sun.misc.VM.isBooted() &&
282 (initialCapacity >= Holder.ALTERNATE_HASHING_THRESHOLD);
283 }
284
285 /**
286 * Constructs a new, empty hashtable with the specified initial capacity
287 * and default load factor (0.75).
288 *
289 * @param initialCapacity the initial capacity of the hashtable.
290 * @exception IllegalArgumentException if the initial capacity is less
291 * than zero.
292 */
293 public Hashtable(int initialCapacity) {
294 this(initialCapacity, 0.75f);
295 }
296
297 /**
298 * Constructs a new, empty hashtable with a default initial capacity (11)
299 * and load factor (0.75).
300 */
301 public Hashtable() {
302 this(11, 0.75f);
303 }
304
305 /**
306 * Constructs a new hashtable with the same mappings as the given
307 * Map. The hashtable is created with an initial capacity sufficient to
308 * hold the mappings in the given Map and a default load factor (0.75).
309 *
310 * @param t the map whose mappings are to be placed in this map.
311 * @throws NullPointerException if the specified map is null.
312 * @since 1.2
313 */
314 public Hashtable(Map<? extends K, ? extends V> t) {
315 this(Math.max(2*t.size(), 11), 0.75f);
316 putAll(t);
317 }
318
319 /**
320 * Returns the number of keys in this hashtable.
321 *
322 * @return the number of keys in this hashtable.
323 */
324 public synchronized int size() {
325 return count;
326 }
327
328 /**
329 * Tests if this hashtable maps no keys to values.
330 *
331 * @return <code>true</code> if this hashtable maps no keys to values;
332 * <code>false</code> otherwise.
333 */
334 public synchronized boolean isEmpty() {
335 return count == 0;
336 }
337
338 /**
339 * Returns an enumeration of the keys in this hashtable.
340 *
341 * @return an enumeration of the keys in this hashtable.
342 * @see Enumeration
343 * @see #elements()
344 * @see #keySet()
345 * @see Map
346 */
347 public synchronized Enumeration<K> keys() {
348 return this.<K>getEnumeration(KEYS);
349 }
350
351 /**
352 * Returns an enumeration of the values in this hashtable.
353 * Use the Enumeration methods on the returned object to fetch the elements
354 * sequentially.
355 *
356 * @return an enumeration of the values in this hashtable.
357 * @see java.util.Enumeration
358 * @see #keys()
359 * @see #values()
360 * @see Map
361 */
362 public synchronized Enumeration<V> elements() {
363 return this.<V>getEnumeration(VALUES);
364 }
365
366 /**
367 * Tests if some key maps into the specified value in this hashtable.
368 * This operation is more expensive than the {@link #containsKey
369 * containsKey} method.
370 *
371 * <p>Note that this method is identical in functionality to
372 * {@link #containsValue containsValue}, (which is part of the
373 * {@link Map} interface in the collections framework).
374 *
375 * @param value a value to search for
376 * @return <code>true</code> if and only if some key maps to the
377 * <code>value</code> argument in this hashtable as
378 * determined by the <tt>equals</tt> method;
379 * <code>false</code> otherwise.
380 * @exception NullPointerException if the value is <code>null</code>
381 */
382 public synchronized boolean contains(Object value) {
383 if (value == null) {
384 throw new NullPointerException();
385 }
386
387 Entry tab[] = table;
388 for (int i = tab.length ; i-- > 0 ;) {
389 for (Entry<K,V> e = tab[i] ; e != null ; e = e.next) {
390 if (e.value.equals(value)) {
391 return true;
392 }
393 }
394 }
395 return false;
396 }
397
398 /**
399 * Returns true if this hashtable maps one or more keys to this value.
400 *
401 * <p>Note that this method is identical in functionality to {@link
402 * #contains contains} (which predates the {@link Map} interface).
403 *
404 * @param value value whose presence in this hashtable is to be tested
405 * @return <tt>true</tt> if this map maps one or more keys to the
406 * specified value
407 * @throws NullPointerException if the value is <code>null</code>
408 * @since 1.2
409 */
410 public boolean containsValue(Object value) {
411 return contains(value);
412 }
413
414 /**
415 * Tests if the specified object is a key in this hashtable.
416 *
417 * @param key possible key
418 * @return <code>true</code> if and only if the specified object
419 * is a key in this hashtable, as determined by the
420 * <tt>equals</tt> method; <code>false</code> otherwise.
421 * @throws NullPointerException if the key is <code>null</code>
422 * @see #contains(Object)
423 */
424 public synchronized boolean containsKey(Object key) {
425 Entry tab[] = table;
426 int hash = hash(key);
427 int index = (hash & 0x7FFFFFFF) % tab.length;
428 for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) {
429 if ((e.hash == hash) && e.key.equals(key)) {
430 return true;
431 }
432 }
433 return false;
434 }
435
436 /**
437 * Returns the value to which the specified key is mapped,
438 * or {@code null} if this map contains no mapping for the key.
439 *
440 * <p>More formally, if this map contains a mapping from a key
441 * {@code k} to a value {@code v} such that {@code (key.equals(k))},
442 * then this method returns {@code v}; otherwise it returns
443 * {@code null}. (There can be at most one such mapping.)
444 *
445 * @param key the key whose associated value is to be returned
446 * @return the value to which the specified key is mapped, or
447 * {@code null} if this map contains no mapping for the key
448 * @throws NullPointerException if the specified key is null
449 * @see #put(Object, Object)
450 */
451 public synchronized V get(Object key) {
452 Entry tab[] = table;
453 int hash = hash(key);
454 int index = (hash & 0x7FFFFFFF) % tab.length;
455 for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) {
456 if ((e.hash == hash) && e.key.equals(key)) {
457 return e.value;
458 }
459 }
460 return null;
461 }
462
463 /**
464 * The maximum size of array to allocate.
465 * Some VMs reserve some header words in an array.
466 * Attempts to allocate larger arrays may result in
467 * OutOfMemoryError: Requested array size exceeds VM limit
468 */
469 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
470
471 /**
472 * Increases the capacity of and internally reorganizes this
473 * hashtable, in order to accommodate and access its entries more
474 * efficiently. This method is called automatically when the
475 * number of keys in the hashtable exceeds this hashtable's capacity
476 * and load factor.
477 */
478 protected void rehash() {
479 int oldCapacity = table.length;
480 Entry<K,V>[] oldMap = table;
481
482 // overflow-conscious code
483 int newCapacity = (oldCapacity << 1) + 1;
484 if (newCapacity - MAX_ARRAY_SIZE > 0) {
485 if (oldCapacity == MAX_ARRAY_SIZE)
486 // Keep running with MAX_ARRAY_SIZE buckets
487 return;
488 newCapacity = MAX_ARRAY_SIZE;
489 }
490 Entry<K,V>[] newMap = new Entry[newCapacity];
491
492 modCount++;
493 threshold = (int)Math.min(newCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
494 boolean currentAltHashing = useAltHashing;
495 useAltHashing = sun.misc.VM.isBooted() &&
496 (newCapacity >= Holder.ALTERNATE_HASHING_THRESHOLD);
497 boolean rehash = currentAltHashing ^ useAltHashing;
498
499 table = newMap;
500
501 for (int i = oldCapacity ; i-- > 0 ;) {
502 for (Entry<K,V> old = oldMap[i] ; old != null ; ) {
503 Entry<K,V> e = old;
504 old = old.next;
505
506 if(rehash) {
507 e.hash = hash(e.key);
508 }
509 int index = (e.hash & 0x7FFFFFFF) % newCapacity;
510 e.next = newMap[index];
511 newMap[index] = e;
512 }
513 }
514 }
515
516 /**
517 * Maps the specified <code>key</code> to the specified
518 * <code>value</code> in this hashtable. Neither the key nor the
519 * value can be <code>null</code>. <p>
520 *
521 * The value can be retrieved by calling the <code>get</code> method
522 * with a key that is equal to the original key.
523 *
524 * @param key the hashtable key
525 * @param value the value
526 * @return the previous value of the specified key in this hashtable,
527 * or <code>null</code> if it did not have one
528 * @exception NullPointerException if the key or value is
529 * <code>null</code>
530 * @see Object#equals(Object)
531 * @see #get(Object)
532 */
533 public synchronized V put(K key, V value) {
534 // Make sure the value is not null
535 if (value == null) {
536 throw new NullPointerException();
537 }
538
539 // Makes sure the key is not already in the hashtable.
540 Entry tab[] = table;
541 int hash = hash(key);
542 int index = (hash & 0x7FFFFFFF) % tab.length;
543 for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) {
544 if ((e.hash == hash) && e.key.equals(key)) {
545 V old = e.value;
546 e.value = value;
547 return old;
548 }
549 }
550
551 modCount++;
552 if (count >= threshold) {
553 // Rehash the table if the threshold is exceeded
554 rehash();
555
556 tab = table;
557 hash = hash(key);
558 index = (hash & 0x7FFFFFFF) % tab.length;
559 }
560
561 // Creates the new entry.
562 Entry<K,V> e = tab[index];
563 tab[index] = new Entry<>(hash, key, value, e);
564 count++;
565 return null;
566 }
567
568 /**
569 * Removes the key (and its corresponding value) from this
570 * hashtable. This method does nothing if the key is not in the hashtable.
571 *
572 * @param key the key that needs to be removed
573 * @return the value to which the key had been mapped in this hashtable,
574 * or <code>null</code> if the key did not have a mapping
575 * @throws NullPointerException if the key is <code>null</code>
576 */
577 public synchronized V remove(Object key) {
578 Entry tab[] = table;
579 int hash = hash(key);
580 int index = (hash & 0x7FFFFFFF) % tab.length;
581 for (Entry<K,V> e = tab[index], prev = null ; e != null ; prev = e, e = e.next) {
582 if ((e.hash == hash) && e.key.equals(key)) {
583 modCount++;
584 if (prev != null) {
585 prev.next = e.next;
586 } else {
587 tab[index] = e.next;
588 }
589 count--;
590 V oldValue = e.value;
591 e.value = null;
592 return oldValue;
593 }
594 }
595 return null;
596 }
597
598 /**
599 * Copies all of the mappings from the specified map to this hashtable.
600 * These mappings will replace any mappings that this hashtable had for any
601 * of the keys currently in the specified map.
602 *
603 * @param t mappings to be stored in this map
604 * @throws NullPointerException if the specified map is null
605 * @since 1.2
606 */
607 public synchronized void putAll(Map<? extends K, ? extends V> t) {
608 for (Map.Entry<? extends K, ? extends V> e : t.entrySet())
609 put(e.getKey(), e.getValue());
610 }
611
612 /**
613 * Clears this hashtable so that it contains no keys.
614 */
615 public synchronized void clear() {
616 Entry tab[] = table;
617 modCount++;
618 for (int index = tab.length; --index >= 0; )
619 tab[index] = null;
620 count = 0;
621 }
622
623 /**
624 * Creates a shallow copy of this hashtable. All the structure of the
625 * hashtable itself is copied, but the keys and values are not cloned.
626 * This is a relatively expensive operation.
627 *
628 * @return a clone of the hashtable
629 */
630 public synchronized Object clone() {
631 try {
632 Hashtable<K,V> t = (Hashtable<K,V>) super.clone();
633 t.table = new Entry[table.length];
634 for (int i = table.length ; i-- > 0 ; ) {
635 t.table[i] = (table[i] != null)
636 ? (Entry<K,V>) table[i].clone() : null;
637 }
638 t.keySet = null;
639 t.entrySet = null;
640 t.values = null;
641 t.modCount = 0;
642 return t;
643 } catch (CloneNotSupportedException e) {
644 // this shouldn't happen, since we are Cloneable
645 throw new InternalError();
646 }
647 }
648
649 /**
650 * Returns a string representation of this <tt>Hashtable</tt> object
651 * in the form of a set of entries, enclosed in braces and separated
652 * by the ASCII characters "<tt>, </tt>" (comma and space). Each
653 * entry is rendered as the key, an equals sign <tt>=</tt>, and the
654 * associated element, where the <tt>toString</tt> method is used to
655 * convert the key and element to strings.
656 *
657 * @return a string representation of this hashtable
658 */
659 public synchronized String toString() {
660 int max = size() - 1;
661 if (max == -1)
662 return "{}";
663
664 StringBuilder sb = new StringBuilder();
665 Iterator<Map.Entry<K,V>> it = entrySet().iterator();
666
667 sb.append('{');
668 for (int i = 0; ; i++) {
669 Map.Entry<K,V> e = it.next();
670 K key = e.getKey();
671 V value = e.getValue();
672 sb.append(key == this ? "(this Map)" : key.toString());
673 sb.append('=');
674 sb.append(value == this ? "(this Map)" : value.toString());
675
676 if (i == max)
677 return sb.append('}').toString();
678 sb.append(", ");
679 }
680 }
681
682
683 private <T> Enumeration<T> getEnumeration(int type) {
684 if (count == 0) {
685 return Collections.emptyEnumeration();
686 } else {
687 return new Enumerator<>(type, false);
688 }
689 }
690
691 private <T> Iterator<T> getIterator(int type) {
692 if (count == 0) {
693 return Collections.emptyIterator();
694 } else {
695 return new Enumerator<>(type, true);
696 }
697 }
698
699 // Views
700
701 /**
702 * Each of these fields are initialized to contain an instance of the
703 * appropriate view the first time this view is requested. The views are
704 * stateless, so there's no reason to create more than one of each.
705 */
706 private transient volatile Set<K> keySet = null;
707 private transient volatile Set<Map.Entry<K,V>> entrySet = null;
708 private transient volatile Collection<V> values = null;
709
710 /**
711 * Returns a {@link Set} view of the keys contained in this map.
712 * The set is backed by the map, so changes to the map are
713 * reflected in the set, and vice-versa. If the map is modified
714 * while an iteration over the set is in progress (except through
715 * the iterator's own <tt>remove</tt> operation), the results of
716 * the iteration are undefined. The set supports element removal,
717 * which removes the corresponding mapping from the map, via the
718 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
719 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
720 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
721 * operations.
722 *
723 * @since 1.2
724 */
725 public Set<K> keySet() {
726 if (keySet == null)
727 keySet = Collections.synchronizedSet(new KeySet(), this);
728 return keySet;
729 }
730
731 private class KeySet extends AbstractSet<K> {
732 public Iterator<K> iterator() {
733 return getIterator(KEYS);
734 }
735 public int size() {
736 return count;
737 }
738 public boolean contains(Object o) {
739 return containsKey(o);
740 }
741 public boolean remove(Object o) {
742 return Hashtable.this.remove(o) != null;
743 }
744 public void clear() {
745 Hashtable.this.clear();
746 }
747 }
748
749 /**
750 * Returns a {@link Set} view of the mappings contained in this map.
751 * The set is backed by the map, so changes to the map are
752 * reflected in the set, and vice-versa. If the map is modified
753 * while an iteration over the set is in progress (except through
754 * the iterator's own <tt>remove</tt> operation, or through the
755 * <tt>setValue</tt> operation on a map entry returned by the
756 * iterator) the results of the iteration are undefined. The set
757 * supports element removal, which removes the corresponding
758 * mapping from the map, via the <tt>Iterator.remove</tt>,
759 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
760 * <tt>clear</tt> operations. It does not support the
761 * <tt>add</tt> or <tt>addAll</tt> operations.
762 *
763 * @since 1.2
764 */
765 public Set<Map.Entry<K,V>> entrySet() {
766 if (entrySet==null)
767 entrySet = Collections.synchronizedSet(new EntrySet(), this);
768 return entrySet;
769 }
770
771 private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
772 public Iterator<Map.Entry<K,V>> iterator() {
773 return getIterator(ENTRIES);
774 }
775
776 public boolean add(Map.Entry<K,V> o) {
777 return super.add(o);
778 }
779
780 public boolean contains(Object o) {
781 if (!(o instanceof Map.Entry))
782 return false;
783 Map.Entry entry = (Map.Entry)o;
784 Object key = entry.getKey();
785 Entry[] tab = table;
786 int hash = hash(key);
787 int index = (hash & 0x7FFFFFFF) % tab.length;
788
789 for (Entry e = tab[index]; e != null; e = e.next)
790 if (e.hash==hash && e.equals(entry))
791 return true;
792 return false;
793 }
794
795 public boolean remove(Object o) {
796 if (!(o instanceof Map.Entry))
797 return false;
798 Map.Entry<K,V> entry = (Map.Entry<K,V>) o;
799 K key = entry.getKey();
800 Entry[] tab = table;
801 int hash = hash(key);
802 int index = (hash & 0x7FFFFFFF) % tab.length;
803
804 for (Entry<K,V> e = tab[index], prev = null; e != null;
805 prev = e, e = e.next) {
806 if (e.hash==hash && e.equals(entry)) {
807 modCount++;
808 if (prev != null)
809 prev.next = e.next;
810 else
811 tab[index] = e.next;
812
813 count--;
814 e.value = null;
815 return true;
816 }
817 }
818 return false;
819 }
820
821 public int size() {
822 return count;
823 }
824
825 public void clear() {
826 Hashtable.this.clear();
827 }
828 }
829
830 /**
831 * Returns a {@link Collection} view of the values contained in this map.
832 * The collection is backed by the map, so changes to the map are
833 * reflected in the collection, and vice-versa. If the map is
834 * modified while an iteration over the collection is in progress
835 * (except through the iterator's own <tt>remove</tt> operation),
836 * the results of the iteration are undefined. The collection
837 * supports element removal, which removes the corresponding
838 * mapping from the map, via the <tt>Iterator.remove</tt>,
839 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
840 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
841 * support the <tt>add</tt> or <tt>addAll</tt> operations.
842 *
843 * @since 1.2
844 */
845 public Collection<V> values() {
846 if (values==null)
847 values = Collections.synchronizedCollection(new ValueCollection(),
848 this);
849 return values;
850 }
851
852 private class ValueCollection extends AbstractCollection<V> {
853 public Iterator<V> iterator() {
854 return getIterator(VALUES);
855 }
856 public int size() {
857 return count;
858 }
859 public boolean contains(Object o) {
860 return containsValue(o);
861 }
862 public void clear() {
863 Hashtable.this.clear();
864 }
865 }
866
867 // Comparison and hashing
868
869 /**
870 * Compares the specified Object with this Map for equality,
871 * as per the definition in the Map interface.
872 *
873 * @param o object to be compared for equality with this hashtable
874 * @return true if the specified Object is equal to this Map
875 * @see Map#equals(Object)
876 * @since 1.2
877 */
878 public synchronized boolean equals(Object o) {
879 if (o == this)
880 return true;
881
882 if (!(o instanceof Map))
883 return false;
884 Map<K,V> t = (Map<K,V>) o;
885 if (t.size() != size())
886 return false;
887
888 try {
889 Iterator<Map.Entry<K,V>> i = entrySet().iterator();
890 while (i.hasNext()) {
891 Map.Entry<K,V> e = i.next();
892 K key = e.getKey();
893 V value = e.getValue();
894 if (value == null) {
895 if (!(t.get(key)==null && t.containsKey(key)))
896 return false;
897 } else {
898 if (!value.equals(t.get(key)))
899 return false;
900 }
901 }
902 } catch (ClassCastException unused) {
903 return false;
904 } catch (NullPointerException unused) {
905 return false;
906 }
907
908 return true;
909 }
910
911 /**
912 * Returns the hash code value for this Map as per the definition in the
913 * Map interface.
914 *
915 * @see Map#hashCode()
916 * @since 1.2
917 */
918 public synchronized int hashCode() {
919 /*
920 * This code detects the recursion caused by computing the hash code
921 * of a self-referential hash table and prevents the stack overflow
922 * that would otherwise result. This allows certain 1.1-era
923 * applets with self-referential hash tables to work. This code
924 * abuses the loadFactor field to do double-duty as a hashCode
925 * in progress flag, so as not to worsen the space performance.
926 * A negative load factor indicates that hash code computation is
927 * in progress.
928 */
929 int h = 0;
930 if (count == 0 || loadFactor < 0)
931 return h; // Returns zero
932
933 loadFactor = -loadFactor; // Mark hashCode computation in progress
934 Entry[] tab = table;
935 for (Entry<K,V> entry : tab)
936 while (entry != null) {
937 h += entry.hashCode();
938 entry = entry.next;
939 }
940 loadFactor = -loadFactor; // Mark hashCode computation complete
941
942 return h;
943 }
944
945 /**
946 * Save the state of the Hashtable to a stream (i.e., serialize it).
947 *
948 * @serialData The <i>capacity</i> of the Hashtable (the length of the
949 * bucket array) is emitted (int), followed by the
950 * <i>size</i> of the Hashtable (the number of key-value
951 * mappings), followed by the key (Object) and value (Object)
952 * for each key-value mapping represented by the Hashtable
953 * The key-value mappings are emitted in no particular order.
954 */
955 private void writeObject(java.io.ObjectOutputStream s)
956 throws IOException {
957 Entry<K, V> entryStack = null;
958
959 synchronized (this) {
960 // Write out the length, threshold, loadfactor
961 s.defaultWriteObject();
962
963 // Write out length, count of elements
964 s.writeInt(table.length);
965 s.writeInt(count);
966
967 // Stack copies of the entries in the table
968 for (int index = 0; index < table.length; index++) {
969 Entry<K,V> entry = table[index];
970
971 while (entry != null) {
972 entryStack =
973 new Entry<>(0, entry.key, entry.value, entryStack);
974 entry = entry.next;
975 }
976 }
977 }
978
979 // Write out the key/value objects from the stacked entries
980 while (entryStack != null) {
981 s.writeObject(entryStack.key);
982 s.writeObject(entryStack.value);
983 entryStack = entryStack.next;
984 }
985 }
986
987 /**
988 * Reconstitute the Hashtable from a stream (i.e., deserialize it).
989 */
990 private void readObject(java.io.ObjectInputStream s)
991 throws IOException, ClassNotFoundException
992 {
993 // Read in the length, threshold, and loadfactor
994 s.defaultReadObject();
995
996 // set hashSeed
997 UNSAFE.putIntVolatile(this, HASHSEED_OFFSET,
998 sun.misc.Hashing.randomHashSeed(this));
999
1000 // Read the original length of the array and number of elements
1001 int origlength = s.readInt();
1002 int elements = s.readInt();
1003
1004 // Compute new size with a bit of room 5% to grow but
1005 // no larger than the original size. Make the length
1006 // odd if it's large enough, this helps distribute the entries.
1007 // Guard against the length ending up zero, that's not valid.
1008 int length = (int)(elements * loadFactor) + (elements / 20) + 3;
1009 if (length > elements && (length & 1) == 0)
1010 length--;
1011 if (origlength > 0 && length > origlength)
1012 length = origlength;
1013
1014 Entry<K,V>[] table = new Entry[length];
1015 threshold = (int) Math.min(length * loadFactor, MAX_ARRAY_SIZE + 1);
1016 count = 0;
1017 useAltHashing = sun.misc.VM.isBooted() &&
1018 (length >= Holder.ALTERNATE_HASHING_THRESHOLD);
1019
1020 // Read the number of elements and then all the key/value objects
1021 for (; elements > 0; elements--) {
1022 K key = (K)s.readObject();
1023 V value = (V)s.readObject();
1024 // synch could be eliminated for performance
1025 reconstitutionPut(table, key, value);
1026 }
1027 this.table = table;
1028 }
1029
1030 /**
1031 * The put method used by readObject. This is provided because put
1032 * is overridable and should not be called in readObject since the
1033 * subclass will not yet be initialized.
1034 *
1035 * <p>This differs from the regular put method in several ways. No
1036 * checking for rehashing is necessary since the number of elements
1037 * initially in the table is known. The modCount is not incremented
1038 * because we are creating a new instance. Also, no return value
1039 * is needed.
1040 */
1041 private void reconstitutionPut(Entry<K,V>[] tab, K key, V value)
1042 throws StreamCorruptedException
1043 {
1044 if (value == null) {
1045 throw new java.io.StreamCorruptedException();
1046 }
1047 // Makes sure the key is not already in the hashtable.
1048 // This should not happen in deserialized version.
1049 int hash = hash(key);
1050 int index = (hash & 0x7FFFFFFF) % tab.length;
1051 for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) {
1052 if ((e.hash == hash) && e.key.equals(key)) {
1053 throw new java.io.StreamCorruptedException();
1054 }
1055 }
1056 // Creates the new entry.
1057 Entry<K,V> e = tab[index];
1058 tab[index] = new Entry<>(hash, key, value, e);
1059 count++;
1060 }
1061
1062 /**
1063 * Hashtable bucket collision list entry
1064 */
1065 private static class Entry<K,V> implements Map.Entry<K,V> {
1066 int hash;
1067 K key;
1068 V value;
1069 Entry<K,V> next;
1070
1071 protected Entry(int hash, K key, V value, Entry<K,V> next) {
1072 this.hash = hash;
1073 this.key = key;
1074 this.value = value;
1075 this.next = next;
1076 }
1077
1078 protected Object clone() {
1079 return new Entry<>(hash, key, value,
1080 (next==null ? null : (Entry<K,V>) next.clone()));
1081 }
1082
1083 // Map.Entry Ops
1084
1085 public K getKey() {
1086 return key;
1087 }
1088
1089 public V getValue() {
1090 return value;
1091 }
1092
1093 public V setValue(V value) {
1094 if (value == null)
1095 throw new NullPointerException();
1096
1097 V oldValue = this.value;
1098 this.value = value;
1099 return oldValue;
1100 }
1101
1102 public boolean equals(Object o) {
1103 if (!(o instanceof Map.Entry))
1104 return false;
1105 Map.Entry<?,?> e = (Map.Entry)o;
1106
1107 return key.equals(e.getKey()) && value.equals(e.getValue());
1108 }
1109
1110 public int hashCode() {
1111 return hash ^ value.hashCode();
1112 }
1113
1114 public String toString() {
1115 return key.toString()+"="+value.toString();
1116 }
1117 }
1118
1119 // Types of Enumerations/Iterations
1120 private static final int KEYS = 0;
1121 private static final int VALUES = 1;
1122 private static final int ENTRIES = 2;
1123
1124 /**
1125 * A hashtable enumerator class. This class implements both the
1126 * Enumeration and Iterator interfaces, but individual instances
1127 * can be created with the Iterator methods disabled. This is necessary
1128 * to avoid unintentionally increasing the capabilities granted a user
1129 * by passing an Enumeration.
1130 */
1131 private class Enumerator<T> implements Enumeration<T>, Iterator<T> {
1132 Entry[] table = Hashtable.this.table;
1133 int index = table.length;
1134 Entry<K,V> entry = null;
1135 Entry<K,V> lastReturned = null;
1136 int type;
1137
1138 /**
1139 * Indicates whether this Enumerator is serving as an Iterator
1140 * or an Enumeration. (true -> Iterator).
1141 */
1142 boolean iterator;
1143
1144 /**
1145 * The modCount value that the iterator believes that the backing
1146 * Hashtable should have. If this expectation is violated, the iterator
1147 * has detected concurrent modification.
1148 */
1149 protected int expectedModCount = modCount;
1150
1151 Enumerator(int type, boolean iterator) {
1152 this.type = type;
1153 this.iterator = iterator;
1154 }
1155
1156 public boolean hasMoreElements() {
1157 Entry<K,V> e = entry;
1158 int i = index;
1159 Entry[] t = table;
1160 /* Use locals for faster loop iteration */
1161 while (e == null && i > 0) {
1162 e = t[--i];
1163 }
1164 entry = e;
1165 index = i;
1166 return e != null;
1167 }
1168
1169 public T nextElement() {
1170 Entry<K,V> et = entry;
1171 int i = index;
1172 Entry[] t = table;
1173 /* Use locals for faster loop iteration */
1174 while (et == null && i > 0) {
1175 et = t[--i];
1176 }
1177 entry = et;
1178 index = i;
1179 if (et != null) {
1180 Entry<K,V> e = lastReturned = entry;
1181 entry = e.next;
1182 return type == KEYS ? (T)e.key : (type == VALUES ? (T)e.value : (T)e);
1183 }
1184 throw new NoSuchElementException("Hashtable Enumerator");
1185 }
1186
1187 // Iterator methods
1188 public boolean hasNext() {
1189 return hasMoreElements();
1190 }
1191
1192 public T next() {
1193 if (modCount != expectedModCount)
1194 throw new ConcurrentModificationException();
1195 return nextElement();
1196 }
1197
1198 public void remove() {
1199 if (!iterator)
1200 throw new UnsupportedOperationException();
1201 if (lastReturned == null)
1202 throw new IllegalStateException("Hashtable Enumerator");
1203 if (modCount != expectedModCount)
1204 throw new ConcurrentModificationException();
1205
1206 synchronized(Hashtable.this) {
1207 Entry[] tab = Hashtable.this.table;
1208 int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length;
1209
1210 for (Entry<K,V> e = tab[index], prev = null; e != null;
1211 prev = e, e = e.next) {
1212 if (e == lastReturned) {
1213 modCount++;
1214 expectedModCount++;
1215 if (prev == null)
1216 tab[index] = e.next;
1217 else
1218 prev.next = e.next;
1219 count--;
1220 lastReturned = null;
1221 return;
1222 }
1223 }
1224 throw new ConcurrentModificationException();
1225 }
1226 }
1227 }
1228 }