1 /*
2 * Copyright (c) 1994, 2013, 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
28 import java.io.*;
29 import java.util.concurrent.ThreadLocalRandom;
30 import java.util.function.BiConsumer;
31 import java.util.function.Function;
32 import java.util.function.BiFunction;
33
34 /**
35 * This class implements a hash table, which maps keys to values. Any
36 * non-<code>null</code> object can be used as a key or as a value. <p>
37 *
38 * To successfully store and retrieve objects from a hashtable, the
39 * objects used as keys must implement the <code>hashCode</code>
40 * method and the <code>equals</code> method. <p>
41 *
42 * An instance of <code>Hashtable</code> has two parameters that affect its
43 * performance: <i>initial capacity</i> and <i>load factor</i>. The
44 * <i>capacity</i> is the number of <i>buckets</i> in the hash table, and the
45 * <i>initial capacity</i> is simply the capacity at the time the hash table
46 * is created. Note that the hash table is <i>open</i>: in the case of a "hash
47 * collision", a single bucket stores multiple entries, which must be searched
48 * sequentially. The <i>load factor</i> is a measure of how full the hash
49 * table is allowed to get before its capacity is automatically increased.
50 * The initial capacity and load factor parameters are merely hints to
51 * the implementation. The exact details as to when and whether the rehash
52 * method is invoked are implementation-dependent.<p>
53 *
54 * Generally, the default load factor (.75) offers a good tradeoff between
55 * time and space costs. Higher values decrease the space overhead but
56 * increase the time cost to look up an entry (which is reflected in most
57 * <tt>Hashtable</tt> operations, including <tt>get</tt> and <tt>put</tt>).<p>
58 *
59 * The initial capacity controls a tradeoff between wasted space and the
60 * need for <code>rehash</code> operations, which are time-consuming.
61 * No <code>rehash</code> operations will <i>ever</i> occur if the initial
62 * capacity is greater than the maximum number of entries the
63 * <tt>Hashtable</tt> will contain divided by its load factor. However,
64 * setting the initial capacity too high can waste space.<p>
65 *
66 * If many entries are to be made into a <code>Hashtable</code>,
67 * creating it with a sufficiently large capacity may allow the
68 * entries to be inserted more efficiently than letting it perform
69 * automatic rehashing as needed to grow the table. <p>
70 *
71 * This example creates a hashtable of numbers. It uses the names of
72 * the numbers as keys:
73 * <pre> {@code
74 * Hashtable<String, Integer> numbers
75 * = new Hashtable<String, Integer>();
76 * numbers.put("one", 1);
77 * numbers.put("two", 2);
78 * numbers.put("three", 3);}</pre>
79 *
80 * <p>To retrieve a number, use the following code:
81 * <pre> {@code
82 * Integer n = numbers.get("two");
83 * if (n != null) {
84 * System.out.println("two = " + n);
85 * }}</pre>
86 *
87 * <p>The iterators returned by the <tt>iterator</tt> method of the collections
88 * returned by all of this class's "collection view methods" are
89 * <em>fail-fast</em>: if the Hashtable is structurally modified at any time
90 * after the iterator is created, in any way except through the iterator's own
91 * <tt>remove</tt> method, the iterator will throw a {@link
92 * ConcurrentModificationException}. Thus, in the face of concurrent
93 * modification, the iterator fails quickly and cleanly, rather than risking
94 * arbitrary, non-deterministic behavior at an undetermined time in the future.
95 * The Enumerations returned by Hashtable's keys and elements methods are
96 * <em>not</em> fail-fast.
97 *
98 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
99 * as it is, generally speaking, impossible to make any hard guarantees in the
100 * presence of unsynchronized concurrent modification. Fail-fast iterators
101 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
102 * Therefore, it would be wrong to write a program that depended on this
103 * exception for its correctness: <i>the fail-fast behavior of iterators
104 * should be used only to detect bugs.</i>
105 *
106 * <p>As of the Java 2 platform v1.2, this class was retrofitted to
107 * implement the {@link Map} interface, making it a member of the
108 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
109 *
110 * Java Collections Framework</a>. Unlike the new collection
111 * implementations, {@code Hashtable} is synchronized. If a
112 * thread-safe implementation is not needed, it is recommended to use
113 * {@link HashMap} in place of {@code Hashtable}. If a thread-safe
114 * highly-concurrent implementation is desired, then it is recommended
115 * to use {@link java.util.concurrent.ConcurrentHashMap} in place of
116 * {@code Hashtable}.
117 *
118 * @author Arthur van Hoff
119 * @author Josh Bloch
120 * @author Neal Gafter
121 * @see Object#equals(java.lang.Object)
122 * @see Object#hashCode()
123 * @see Hashtable#rehash()
124 * @see Collection
125 * @see Map
126 * @see HashMap
127 * @see TreeMap
128 * @since JDK1.0
129 */
130 public class Hashtable<K,V>
131 extends Dictionary<K,V>
132 implements Map<K,V>, Cloneable, java.io.Serializable {
133
134 /**
135 * The hash table data.
136 */
137 private transient Entry<?,?>[] table;
138
139 /**
140 * The total number of entries in the hash table.
141 */
142 private transient int count;
143
144 /**
145 * The table is rehashed when its size exceeds this threshold. (The
146 * value of this field is (int)(capacity * loadFactor).)
147 *
148 * @serial
149 */
150 private int threshold;
151
152 /**
153 * The load factor for the hashtable.
154 *
155 * @serial
156 */
157 private float loadFactor;
158
159 /**
160 * The number of times this Hashtable has been structurally modified
161 * Structural modifications are those that change the number of entries in
162 * the Hashtable or otherwise modify its internal structure (e.g.,
163 * rehash). This field is used to make iterators on Collection-views of
164 * the Hashtable fail-fast. (See ConcurrentModificationException).
165 */
166 private transient int modCount = 0;
167
168 /** use serialVersionUID from JDK 1.0.2 for interoperability */
169 private static final long serialVersionUID = 1421746759512286392L;
170
171 private static class Holder {
172 // Unsafe mechanics
173 /**
174 *
175 */
176 static final sun.misc.Unsafe UNSAFE;
177
178 /**
179 * Offset of "final" hashSeed field we must set in
180 * readObject() method.
181 */
182 static final long HASHSEED_OFFSET;
183
184 static final boolean USE_HASHSEED;
185
186 static {
187 String hashSeedProp = java.security.AccessController.doPrivileged(
188 new sun.security.action.GetPropertyAction(
189 "jdk.map.useRandomSeed"));
190 boolean localBool = (null != hashSeedProp)
191 ? Boolean.parseBoolean(hashSeedProp) : false;
192 USE_HASHSEED = localBool;
193
194 if (USE_HASHSEED) {
195 try {
196 UNSAFE = sun.misc.Unsafe.getUnsafe();
197 HASHSEED_OFFSET = UNSAFE.objectFieldOffset(
198 Hashtable.class.getDeclaredField("hashSeed"));
199 } catch (NoSuchFieldException | SecurityException e) {
200 throw new InternalError("Failed to record hashSeed offset", e);
201 }
202 } else {
203 UNSAFE = null;
204 HASHSEED_OFFSET = 0;
205 }
206 }
207 }
208
209 /**
210 * A randomizing value associated with this instance that is applied to
211 * hash code of keys to make hash collisions harder to find.
212 *
213 * Non-final so it can be set lazily, but be sure not to set more than once.
214 */
215 transient final int hashSeed;
216
217 /**
218 * Return an initial value for the hashSeed, or 0 if the random seed is not
219 * enabled.
220 */
221 final int initHashSeed() {
222 if (sun.misc.VM.isBooted() && Holder.USE_HASHSEED) {
223 int seed = ThreadLocalRandom.current().nextInt();
224 return (seed != 0) ? seed : 1;
225 }
226 return 0;
227 }
228
229 private int hash(Object k) {
230 return hashSeed ^ k.hashCode();
231 }
232
233 /**
234 * Constructs a new, empty hashtable with the specified initial
235 * capacity and the specified load factor.
236 *
237 * @param initialCapacity the initial capacity of the hashtable.
238 * @param loadFactor the load factor of the hashtable.
239 * @exception IllegalArgumentException if the initial capacity is less
240 * than zero, or if the load factor is nonpositive.
241 */
242 public Hashtable(int initialCapacity, float loadFactor) {
243 if (initialCapacity < 0)
244 throw new IllegalArgumentException("Illegal Capacity: "+
245 initialCapacity);
246 if (loadFactor <= 0 || Float.isNaN(loadFactor))
247 throw new IllegalArgumentException("Illegal Load: "+loadFactor);
248
249 if (initialCapacity==0)
250 initialCapacity = 1;
251 this.loadFactor = loadFactor;
252 table = new Entry<?,?>[initialCapacity];
253 threshold = (int)Math.min(initialCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
254 hashSeed = initHashSeed();
255 }
256
257 /**
258 * Constructs a new, empty hashtable with the specified initial capacity
259 * and default load factor (0.75).
260 *
261 * @param initialCapacity the initial capacity of the hashtable.
262 * @exception IllegalArgumentException if the initial capacity is less
263 * than zero.
264 */
265 public Hashtable(int initialCapacity) {
266 this(initialCapacity, 0.75f);
267 }
268
269 /**
270 * Constructs a new, empty hashtable with a default initial capacity (11)
271 * and load factor (0.75).
272 */
273 public Hashtable() {
274 this(11, 0.75f);
275 }
276
277 /**
278 * Constructs a new hashtable with the same mappings as the given
279 * Map. The hashtable is created with an initial capacity sufficient to
280 * hold the mappings in the given Map and a default load factor (0.75).
281 *
282 * @param t the map whose mappings are to be placed in this map.
283 * @throws NullPointerException if the specified map is null.
284 * @since 1.2
285 */
286 public Hashtable(Map<? extends K, ? extends V> t) {
287 this(Math.max(2*t.size(), 11), 0.75f);
288 putAll(t);
289 }
290
291 /**
292 * Returns the number of keys in this hashtable.
293 *
294 * @return the number of keys in this hashtable.
295 */
296 public synchronized int size() {
297 return count;
298 }
299
300 /**
301 * Tests if this hashtable maps no keys to values.
302 *
303 * @return <code>true</code> if this hashtable maps no keys to values;
304 * <code>false</code> otherwise.
305 */
306 public synchronized boolean isEmpty() {
307 return count == 0;
308 }
309
310 /**
311 * Returns an enumeration of the keys in this hashtable.
312 *
313 * @return an enumeration of the keys in this hashtable.
314 * @see Enumeration
315 * @see #elements()
316 * @see #keySet()
317 * @see Map
318 */
319 public synchronized Enumeration<K> keys() {
320 return this.<K>getEnumeration(KEYS);
321 }
322
323 /**
324 * Returns an enumeration of the values in this hashtable.
325 * Use the Enumeration methods on the returned object to fetch the elements
326 * sequentially.
327 *
328 * @return an enumeration of the values in this hashtable.
329 * @see java.util.Enumeration
330 * @see #keys()
331 * @see #values()
332 * @see Map
333 */
334 public synchronized Enumeration<V> elements() {
335 return this.<V>getEnumeration(VALUES);
336 }
337
338 /**
339 * Tests if some key maps into the specified value in this hashtable.
340 * This operation is more expensive than the {@link #containsKey
341 * containsKey} method.
342 *
343 * <p>Note that this method is identical in functionality to
344 * {@link #containsValue containsValue}, (which is part of the
345 * {@link Map} interface in the collections framework).
346 *
347 * @param value a value to search for
348 * @return <code>true</code> if and only if some key maps to the
349 * <code>value</code> argument in this hashtable as
350 * determined by the <tt>equals</tt> method;
351 * <code>false</code> otherwise.
352 * @exception NullPointerException if the value is <code>null</code>
353 */
354 public synchronized boolean contains(Object value) {
355 if (value == null) {
356 throw new NullPointerException();
357 }
358
359 Entry<?,?> tab[] = table;
360 for (int i = tab.length ; i-- > 0 ;) {
361 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next) {
362 if (e.value.equals(value)) {
363 return true;
364 }
365 }
366 }
367 return false;
368 }
369
370 /**
371 * Returns true if this hashtable maps one or more keys to this value.
372 *
373 * <p>Note that this method is identical in functionality to {@link
374 * #contains contains} (which predates the {@link Map} interface).
375 *
376 * @param value value whose presence in this hashtable is to be tested
377 * @return <tt>true</tt> if this map maps one or more keys to the
378 * specified value
379 * @throws NullPointerException if the value is <code>null</code>
380 * @since 1.2
381 */
382 public boolean containsValue(Object value) {
383 return contains(value);
384 }
385
386 /**
387 * Tests if the specified object is a key in this hashtable.
388 *
389 * @param key possible key
390 * @return <code>true</code> if and only if the specified object
391 * is a key in this hashtable, as determined by the
392 * <tt>equals</tt> method; <code>false</code> otherwise.
393 * @throws NullPointerException if the key is <code>null</code>
394 * @see #contains(Object)
395 */
396 public synchronized boolean containsKey(Object key) {
397 Entry<?,?> tab[] = table;
398 int hash = hash(key);
399 int index = (hash & 0x7FFFFFFF) % tab.length;
400 for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
401 if ((e.hash == hash) && e.key.equals(key)) {
402 return true;
403 }
404 }
405 return false;
406 }
407
408 /**
409 * Returns the value to which the specified key is mapped,
410 * or {@code null} if this map contains no mapping for the key.
411 *
412 * <p>More formally, if this map contains a mapping from a key
413 * {@code k} to a value {@code v} such that {@code (key.equals(k))},
414 * then this method returns {@code v}; otherwise it returns
415 * {@code null}. (There can be at most one such mapping.)
416 *
417 * @param key the key whose associated value is to be returned
418 * @return the value to which the specified key is mapped, or
419 * {@code null} if this map contains no mapping for the key
420 * @throws NullPointerException if the specified key is null
421 * @see #put(Object, Object)
422 */
423 @SuppressWarnings("unchecked")
424 public synchronized V get(Object key) {
425 Entry<?,?> tab[] = table;
426 int hash = hash(key);
427 int index = (hash & 0x7FFFFFFF) % tab.length;
428 for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
429 if ((e.hash == hash) && e.key.equals(key)) {
430 return (V)e.value;
431 }
432 }
433 return null;
434 }
435
436 /**
437 * The maximum size of array to allocate.
438 * Some VMs reserve some header words in an array.
439 * Attempts to allocate larger arrays may result in
440 * OutOfMemoryError: Requested array size exceeds VM limit
441 */
442 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
443
444 /**
445 * Increases the capacity of and internally reorganizes this
446 * hashtable, in order to accommodate and access its entries more
447 * efficiently. This method is called automatically when the
448 * number of keys in the hashtable exceeds this hashtable's capacity
449 * and load factor.
450 */
451 @SuppressWarnings("unchecked")
452 protected void rehash() {
453 int oldCapacity = table.length;
454 Entry<?,?>[] oldMap = table;
455
456 // overflow-conscious code
457 int newCapacity = (oldCapacity << 1) + 1;
458 if (newCapacity - MAX_ARRAY_SIZE > 0) {
459 if (oldCapacity == MAX_ARRAY_SIZE)
460 // Keep running with MAX_ARRAY_SIZE buckets
461 return;
462 newCapacity = MAX_ARRAY_SIZE;
463 }
464 Entry<?,?>[] newMap = new Entry<?,?>[newCapacity];
465
466 modCount++;
467 threshold = (int)Math.min(newCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
468 table = newMap;
469
470 for (int i = oldCapacity ; i-- > 0 ;) {
471 for (Entry<K,V> old = (Entry<K,V>)oldMap[i] ; old != null ; ) {
472 Entry<K,V> e = old;
473 old = old.next;
474
475 int index = (e.hash & 0x7FFFFFFF) % newCapacity;
476 e.next = (Entry<K,V>)newMap[index];
477 newMap[index] = e;
478 }
479 }
480 }
481
482 private void addEntry(int hash, K key, V value, int index) {
483 modCount++;
484
485 Entry<?,?> tab[] = table;
486 if (count >= threshold) {
487 // Rehash the table if the threshold is exceeded
488 rehash();
489
490 tab = table;
491 hash = hash(key);
492 index = (hash & 0x7FFFFFFF) % tab.length;
493 }
494
495 // Creates the new entry.
496 @SuppressWarnings("unchecked")
497 Entry<K,V> e = (Entry<K,V>) tab[index];
498 tab[index] = new Entry<>(hash, key, value, e);
499 count++;
500 }
501
502 /**
503 * Maps the specified <code>key</code> to the specified
504 * <code>value</code> in this hashtable. Neither the key nor the
505 * value can be <code>null</code>. <p>
506 *
507 * The value can be retrieved by calling the <code>get</code> method
508 * with a key that is equal to the original key.
509 *
510 * @param key the hashtable key
511 * @param value the value
512 * @return the previous value of the specified key in this hashtable,
513 * or <code>null</code> if it did not have one
514 * @exception NullPointerException if the key or value is
515 * <code>null</code>
516 * @see Object#equals(Object)
517 * @see #get(Object)
518 */
519 public synchronized V put(K key, V value) {
520 // Make sure the value is not null
521 if (value == null) {
522 throw new NullPointerException();
523 }
524
525 // Makes sure the key is not already in the hashtable.
526 Entry<?,?> tab[] = table;
527 int hash = hash(key);
528 int index = (hash & 0x7FFFFFFF) % tab.length;
529 @SuppressWarnings("unchecked")
530 Entry<K,V> entry = (Entry<K,V>)tab[index];
531 for(; entry != null ; entry = entry.next) {
532 if ((entry.hash == hash) && entry.key.equals(key)) {
533 V old = entry.value;
534 entry.value = value;
535 return old;
536 }
537 }
538
539 addEntry(hash, key, value, index);
540 return null;
541 }
542
543 /**
544 * Removes the key (and its corresponding value) from this
545 * hashtable. This method does nothing if the key is not in the hashtable.
546 *
547 * @param key the key that needs to be removed
548 * @return the value to which the key had been mapped in this hashtable,
549 * or <code>null</code> if the key did not have a mapping
550 * @throws NullPointerException if the key is <code>null</code>
551 */
552 public synchronized V remove(Object key) {
553 Entry<?,?> tab[] = table;
554 int hash = hash(key);
555 int index = (hash & 0x7FFFFFFF) % tab.length;
556 @SuppressWarnings("unchecked")
557 Entry<K,V> e = (Entry<K,V>)tab[index];
558 for(Entry<K,V> prev = null ; e != null ; prev = e, e = e.next) {
559 if ((e.hash == hash) && e.key.equals(key)) {
560 modCount++;
561 if (prev != null) {
562 prev.next = e.next;
563 } else {
564 tab[index] = e.next;
565 }
566 count--;
567 V oldValue = e.value;
568 e.value = null;
569 return oldValue;
570 }
571 }
572 return null;
573 }
574
575 /**
576 * Copies all of the mappings from the specified map to this hashtable.
577 * These mappings will replace any mappings that this hashtable had for any
578 * of the keys currently in the specified map.
579 *
580 * @param t mappings to be stored in this map
581 * @throws NullPointerException if the specified map is null
582 * @since 1.2
583 */
584 public synchronized void putAll(Map<? extends K, ? extends V> t) {
585 for (Map.Entry<? extends K, ? extends V> e : t.entrySet())
586 put(e.getKey(), e.getValue());
587 }
588
589 /**
590 * Clears this hashtable so that it contains no keys.
591 */
592 public synchronized void clear() {
593 Entry<?,?> tab[] = table;
594 modCount++;
595 for (int index = tab.length; --index >= 0; )
596 tab[index] = null;
597 count = 0;
598 }
599
600 /**
601 * Creates a shallow copy of this hashtable. All the structure of the
602 * hashtable itself is copied, but the keys and values are not cloned.
603 * This is a relatively expensive operation.
604 *
605 * @return a clone of the hashtable
606 */
607 public synchronized Object clone() {
608 try {
609 Hashtable<?,?> t = (Hashtable<?,?>)super.clone();
610 t.table = new Entry<?,?>[table.length];
611 for (int i = table.length ; i-- > 0 ; ) {
612 t.table[i] = (table[i] != null)
613 ? (Entry<?,?>) table[i].clone() : null;
614 }
615 t.keySet = null;
616 t.entrySet = null;
617 t.values = null;
618 t.modCount = 0;
619 return t;
620 } catch (CloneNotSupportedException e) {
621 // this shouldn't happen, since we are Cloneable
622 throw new InternalError(e);
623 }
624 }
625
626 /**
627 * Returns a string representation of this <tt>Hashtable</tt> object
628 * in the form of a set of entries, enclosed in braces and separated
629 * by the ASCII characters "<tt>, </tt>" (comma and space). Each
630 * entry is rendered as the key, an equals sign <tt>=</tt>, and the
631 * associated element, where the <tt>toString</tt> method is used to
632 * convert the key and element to strings.
633 *
634 * @return a string representation of this hashtable
635 */
636 public synchronized String toString() {
637 int max = size() - 1;
638 if (max == -1)
639 return "{}";
640
641 StringBuilder sb = new StringBuilder();
642 Iterator<Map.Entry<K,V>> it = entrySet().iterator();
643
644 sb.append('{');
645 for (int i = 0; ; i++) {
646 Map.Entry<K,V> e = it.next();
647 K key = e.getKey();
648 V value = e.getValue();
649 sb.append(key == this ? "(this Map)" : key.toString());
650 sb.append('=');
651 sb.append(value == this ? "(this Map)" : value.toString());
652
653 if (i == max)
654 return sb.append('}').toString();
655 sb.append(", ");
656 }
657 }
658
659
660 private <T> Enumeration<T> getEnumeration(int type) {
661 if (count == 0) {
662 return Collections.emptyEnumeration();
663 } else {
664 return new Enumerator<>(type, false);
665 }
666 }
667
668 private <T> Iterator<T> getIterator(int type) {
669 if (count == 0) {
670 return Collections.emptyIterator();
671 } else {
672 return new Enumerator<>(type, true);
673 }
674 }
675
676 // Views
677
678 /**
679 * Each of these fields are initialized to contain an instance of the
680 * appropriate view the first time this view is requested. The views are
681 * stateless, so there's no reason to create more than one of each.
682 */
683 private transient volatile Set<K> keySet = null;
684 private transient volatile Set<Map.Entry<K,V>> entrySet = null;
685 private transient volatile Collection<V> values = null;
686
687 /**
688 * Returns a {@link Set} view of the keys contained in this map.
689 * The set is backed by the map, so changes to the map are
690 * reflected in the set, and vice-versa. If the map is modified
691 * while an iteration over the set is in progress (except through
692 * the iterator's own <tt>remove</tt> operation), the results of
693 * the iteration are undefined. The set supports element removal,
694 * which removes the corresponding mapping from the map, via the
695 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
696 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
697 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
698 * operations.
699 *
700 * @since 1.2
701 */
702 public Set<K> keySet() {
703 if (keySet == null)
704 keySet = Collections.synchronizedSet(new KeySet(), this);
705 return keySet;
706 }
707
708 private class KeySet extends AbstractSet<K> {
709 public Iterator<K> iterator() {
710 return getIterator(KEYS);
711 }
712 public int size() {
713 return count;
714 }
715 public boolean contains(Object o) {
716 return containsKey(o);
717 }
718 public boolean remove(Object o) {
719 return Hashtable.this.remove(o) != null;
720 }
721 public void clear() {
722 Hashtable.this.clear();
723 }
724 }
725
726 /**
727 * Returns a {@link Set} view of the mappings contained in this map.
728 * The set is backed by the map, so changes to the map are
729 * reflected in the set, and vice-versa. If the map is modified
730 * while an iteration over the set is in progress (except through
731 * the iterator's own <tt>remove</tt> operation, or through the
732 * <tt>setValue</tt> operation on a map entry returned by the
733 * iterator) the results of the iteration are undefined. The set
734 * supports element removal, which removes the corresponding
735 * mapping from the map, via the <tt>Iterator.remove</tt>,
736 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
737 * <tt>clear</tt> operations. It does not support the
738 * <tt>add</tt> or <tt>addAll</tt> operations.
739 *
740 * @since 1.2
741 */
742 public Set<Map.Entry<K,V>> entrySet() {
743 if (entrySet==null)
744 entrySet = Collections.synchronizedSet(new EntrySet(), this);
745 return entrySet;
746 }
747
748 private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
749 public Iterator<Map.Entry<K,V>> iterator() {
750 return getIterator(ENTRIES);
751 }
752
753 public boolean add(Map.Entry<K,V> o) {
754 return super.add(o);
755 }
756
757 public boolean contains(Object o) {
758 if (!(o instanceof Map.Entry))
759 return false;
760 Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
761 Object key = entry.getKey();
762 Entry<?,?>[] tab = table;
763 int hash = hash(key);
764 int index = (hash & 0x7FFFFFFF) % tab.length;
765
766 for (Entry<?,?> e = tab[index]; e != null; e = e.next)
767 if (e.hash==hash && e.equals(entry))
768 return true;
769 return false;
770 }
771
772 public boolean remove(Object o) {
773 if (!(o instanceof Map.Entry))
774 return false;
775 Map.Entry<?,?> entry = (Map.Entry<?,?>) o;
776 Object key = entry.getKey();
777 Entry<?,?>[] tab = table;
778 int hash = hash(key);
779 int index = (hash & 0x7FFFFFFF) % tab.length;
780
781 @SuppressWarnings("unchecked")
782 Entry<K,V> e = (Entry<K,V>)tab[index];
783 for(Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
784 if (e.hash==hash && e.equals(entry)) {
785 modCount++;
786 if (prev != null)
787 prev.next = e.next;
788 else
789 tab[index] = e.next;
790
791 count--;
792 e.value = null;
793 return true;
794 }
795 }
796 return false;
797 }
798
799 public int size() {
800 return count;
801 }
802
803 public void clear() {
804 Hashtable.this.clear();
805 }
806 }
807
808 /**
809 * Returns a {@link Collection} view of the values contained in this map.
810 * The collection is backed by the map, so changes to the map are
811 * reflected in the collection, and vice-versa. If the map is
812 * modified while an iteration over the collection is in progress
813 * (except through the iterator's own <tt>remove</tt> operation),
814 * the results of the iteration are undefined. The collection
815 * supports element removal, which removes the corresponding
816 * mapping from the map, via the <tt>Iterator.remove</tt>,
817 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
818 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
819 * support the <tt>add</tt> or <tt>addAll</tt> operations.
820 *
821 * @since 1.2
822 */
823 public Collection<V> values() {
824 if (values==null)
825 values = Collections.synchronizedCollection(new ValueCollection(),
826 this);
827 return values;
828 }
829
830 private class ValueCollection extends AbstractCollection<V> {
831 public Iterator<V> iterator() {
832 return getIterator(VALUES);
833 }
834 public int size() {
835 return count;
836 }
837 public boolean contains(Object o) {
838 return containsValue(o);
839 }
840 public void clear() {
841 Hashtable.this.clear();
842 }
843 }
844
845 // Comparison and hashing
846
847 /**
848 * Compares the specified Object with this Map for equality,
849 * as per the definition in the Map interface.
850 *
851 * @param o object to be compared for equality with this hashtable
852 * @return true if the specified Object is equal to this Map
853 * @see Map#equals(Object)
854 * @since 1.2
855 */
856 public synchronized boolean equals(Object o) {
857 if (o == this)
858 return true;
859
860 if (!(o instanceof Map))
861 return false;
862 Map<?,?> t = (Map<?,?>) o;
863 if (t.size() != size())
864 return false;
865
866 try {
867 Iterator<Map.Entry<K,V>> i = entrySet().iterator();
868 while (i.hasNext()) {
869 Map.Entry<K,V> e = i.next();
870 K key = e.getKey();
871 V value = e.getValue();
872 if (value == null) {
873 if (!(t.get(key)==null && t.containsKey(key)))
874 return false;
875 } else {
876 if (!value.equals(t.get(key)))
877 return false;
878 }
879 }
880 } catch (ClassCastException unused) {
881 return false;
882 } catch (NullPointerException unused) {
883 return false;
884 }
885
886 return true;
887 }
888
889 /**
890 * Returns the hash code value for this Map as per the definition in the
891 * Map interface.
892 *
893 * @see Map#hashCode()
894 * @since 1.2
895 */
896 public synchronized int hashCode() {
897 /*
898 * This code detects the recursion caused by computing the hash code
899 * of a self-referential hash table and prevents the stack overflow
900 * that would otherwise result. This allows certain 1.1-era
901 * applets with self-referential hash tables to work. This code
902 * abuses the loadFactor field to do double-duty as a hashCode
903 * in progress flag, so as not to worsen the space performance.
904 * A negative load factor indicates that hash code computation is
905 * in progress.
906 */
907 int h = 0;
908 if (count == 0 || loadFactor < 0)
909 return h; // Returns zero
910
911 loadFactor = -loadFactor; // Mark hashCode computation in progress
912 Entry<?,?>[] tab = table;
913 for (Entry<?,?> entry : tab) {
914 while (entry != null) {
915 h += entry.hashCode();
916 entry = entry.next;
917 }
918 }
919
920 loadFactor = -loadFactor; // Mark hashCode computation complete
921
922 return h;
923 }
924
925 @Override
926 public synchronized V getOrDefault(Object key, V defaultValue) {
927 V result = get(key);
928 return (null == result) ? defaultValue : result;
929 }
930
931 @Override
932 public synchronized void forEach(BiConsumer<? super K, ? super V> action) {
933 Objects.requireNonNull(action); // explicit check required in case
934 // table is empty.
935 Entry<?,?>[] tab = table;
936 for (Entry<?,?> entry : tab) {
937 while (entry != null) {
938 action.accept((K)entry.key, (V)entry.value);
939 entry = entry.next;
940 }
941 }
942 }
943
944 @Override
945 public synchronized void replaceAll(
946 BiFunction<? super K, ? super V, ? extends V> function) {
947 Map.super.replaceAll(function);
948 }
949
950 @Override
951 public synchronized V putIfAbsent(K key, V value) {
952 Objects.requireNonNull(value);
953
954 // Makes sure the key is not already in the hashtable.
955 Entry<?,?> tab[] = table;
956 int hash = hash(key);
957 int index = (hash & 0x7FFFFFFF) % tab.length;
958 @SuppressWarnings("unchecked")
959 Entry<K,V> entry = (Entry<K,V>)tab[index];
960 for (; entry != null; entry = entry.next) {
961 if ((entry.hash == hash) && entry.key.equals(key)) {
962 V old = entry.value;
963 if (old == null) {
964 entry.value = value;
965 }
966 return old;
967 }
968 }
969
970 addEntry(hash, key, value, index);
971 return null;
972 }
973
974 @Override
975 public synchronized boolean remove(Object key, Object value) {
976 Objects.requireNonNull(value);
977
978 Entry<?,?> tab[] = table;
979 int hash = hash(key);
980 int index = (hash & 0x7FFFFFFF) % tab.length;
981 @SuppressWarnings("unchecked")
982 Entry<K,V> e = (Entry<K,V>)tab[index];
983 for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
984 if ((e.hash == hash) && e.key.equals(key) && e.value.equals(value)) {
985 modCount++;
986 if (prev != null) {
987 prev.next = e.next;
988 } else {
989 tab[index] = e.next;
990 }
991 count--;
992 e.value = null;
993 return true;
994 }
995 }
996 return false;
997 }
998
999 @Override
1000 public synchronized boolean replace(K key, V oldValue, V newValue) {
1001 Entry<?,?> tab[] = table;
1002 int hash = hash(key);
1003 int index = (hash & 0x7FFFFFFF) % tab.length;
1004 @SuppressWarnings("unchecked")
1005 Entry<K,V> e = (Entry<K,V>)tab[index];
1006 for (; e != null; e = e.next) {
1007 if ((e.hash == hash) && e.key.equals(key)) {
1008 if (e.value.equals(oldValue)) {
1009 e.value = newValue;
1010 return true;
1011 } else {
1012 return false;
1013 }
1014 }
1015 }
1016 return false;
1017 }
1018
1019 @Override
1020 public synchronized V replace(K key, V value) {
1021 Entry<?,?> tab[] = table;
1022 int hash = hash(key);
1023 int index = (hash & 0x7FFFFFFF) % tab.length;
1024 @SuppressWarnings("unchecked")
1025 Entry<K,V> e = (Entry<K,V>)tab[index];
1026 for (; e != null; e = e.next) {
1027 if ((e.hash == hash) && e.key.equals(key)) {
1028 V oldValue = e.value;
1029 e.value = value;
1030 return oldValue;
1031 }
1032 }
1033 return null;
1034 }
1035
1036 @Override
1037 public synchronized V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
1038 Objects.requireNonNull(mappingFunction);
1039
1040 Entry<?,?> tab[] = table;
1041 int hash = hash(key);
1042 int index = (hash & 0x7FFFFFFF) % tab.length;
1043 @SuppressWarnings("unchecked")
1044 Entry<K,V> e = (Entry<K,V>)tab[index];
1045 for (; e != null; e = e.next) {
1046 if (e.hash == hash && e.key.equals(key)) {
1047 // Hashtable not accept null value
1048 return e.value;
1049 }
1050 }
1051
1052 V newValue = mappingFunction.apply(key);
1053 if (newValue != null) {
1054 addEntry(hash, key, newValue, index);
1055 }
1056
1057 return newValue;
1058 }
1059
1060 @Override
1061 public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1062 Objects.requireNonNull(remappingFunction);
1063
1064 Entry<?,?> tab[] = table;
1065 int hash = hash(key);
1066 int index = (hash & 0x7FFFFFFF) % tab.length;
1067 @SuppressWarnings("unchecked")
1068 Entry<K,V> e = (Entry<K,V>)tab[index];
1069 for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
1070 if (e.hash == hash && e.key.equals(key)) {
1071 V newValue = remappingFunction.apply(key, e.value);
1072 if (newValue == null) {
1073 modCount++;
1074 if (prev != null) {
1075 prev.next = e.next;
1076 } else {
1077 tab[index] = e.next;
1078 }
1079 count--;
1080 } else {
1081 e.value = newValue;
1082 }
1083 return newValue;
1084 }
1085 }
1086 return null;
1087 }
1088
1089 @Override
1090 public V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1091 Objects.requireNonNull(remappingFunction);
1092
1093 Entry<?,?> tab[] = table;
1094 int hash = hash(key);
1095 int index = (hash & 0x7FFFFFFF) % tab.length;
1096 @SuppressWarnings("unchecked")
1097 Entry<K,V> e = (Entry<K,V>)tab[index];
1098 for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
1099 if (e.hash == hash && Objects.equals(e.key, key)) {
1100 V newValue = remappingFunction.apply(key, e.value);
1101 if (newValue == null) {
1102 modCount++;
1103 if (prev != null) {
1104 prev.next = e.next;
1105 } else {
1106 tab[index] = e.next;
1107 }
1108 count--;
1109 } else {
1110 e.value = newValue;
1111 }
1112 return newValue;
1113 }
1114 }
1115
1116 V newValue = remappingFunction.apply(key, null);
1117 if (newValue != null) {
1118 addEntry(hash, key, newValue, index);
1119 }
1120
1121 return newValue;
1122 }
1123
1124 @Override
1125 public V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
1126 Objects.requireNonNull(remappingFunction);
1127
1128 Entry<?,?> tab[] = table;
1129 int hash = hash(key);
1130 int index = (hash & 0x7FFFFFFF) % tab.length;
1131 @SuppressWarnings("unchecked")
1132 Entry<K,V> e = (Entry<K,V>)tab[index];
1133 for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
1134 if (e.hash == hash && e.key.equals(key)) {
1135 V newValue = remappingFunction.apply(e.value, value);
1136 if (newValue == null) {
1137 modCount++;
1138 if (prev != null) {
1139 prev.next = e.next;
1140 } else {
1141 tab[index] = e.next;
1142 }
1143 count--;
1144 } else {
1145 e.value = newValue;
1146 }
1147 return newValue;
1148 }
1149 }
1150
1151 if (value != null) {
1152 addEntry(hash, key, value, index);
1153 }
1154
1155 return value;
1156 }
1157
1158 /**
1159 * Save the state of the Hashtable to a stream (i.e., serialize it).
1160 *
1161 * @serialData The <i>capacity</i> of the Hashtable (the length of the
1162 * bucket array) is emitted (int), followed by the
1163 * <i>size</i> of the Hashtable (the number of key-value
1164 * mappings), followed by the key (Object) and value (Object)
1165 * for each key-value mapping represented by the Hashtable
1166 * The key-value mappings are emitted in no particular order.
1167 */
1168 private void writeObject(java.io.ObjectOutputStream s)
1169 throws IOException {
1170 Entry<Object, Object> entryStack = null;
1171
1172 synchronized (this) {
1173 // Write out the length, threshold, loadfactor
1174 s.defaultWriteObject();
1175
1176 // Write out length, count of elements
1177 s.writeInt(table.length);
1178 s.writeInt(count);
1179
1180 // Stack copies of the entries in the table
1181 for (int index = 0; index < table.length; index++) {
1182 Entry<?,?> entry = table[index];
1183
1184 while (entry != null) {
1185 entryStack =
1186 new Entry<>(0, entry.key, entry.value, entryStack);
1187 entry = entry.next;
1188 }
1189 }
1190 }
1191
1192 // Write out the key/value objects from the stacked entries
1193 while (entryStack != null) {
1194 s.writeObject(entryStack.key);
1195 s.writeObject(entryStack.value);
1196 entryStack = entryStack.next;
1197 }
1198 }
1199
1200 /**
1201 * Reconstitute the Hashtable from a stream (i.e., deserialize it).
1202 */
1203 private void readObject(java.io.ObjectInputStream s)
1204 throws IOException, ClassNotFoundException
1205 {
1206 // Read in the length, threshold, and loadfactor
1207 s.defaultReadObject();
1208
1209 // set hashMask
1210 if (Holder.USE_HASHSEED) {
1211 int seed = ThreadLocalRandom.current().nextInt();
1212 Holder.UNSAFE.putIntVolatile(this, Holder.HASHSEED_OFFSET,
1213 (seed != 0) ? seed : 1);
1214 }
1215
1216 // Read the original length of the array and number of elements
1217 int origlength = s.readInt();
1218 int elements = s.readInt();
1219
1220 // Compute new size with a bit of room 5% to grow but
1221 // no larger than the original size. Make the length
1222 // odd if it's large enough, this helps distribute the entries.
1223 // Guard against the length ending up zero, that's not valid.
1224 int length = (int)(elements * loadFactor) + (elements / 20) + 3;
1225 if (length > elements && (length & 1) == 0)
1226 length--;
1227 if (origlength > 0 && length > origlength)
1228 length = origlength;
1229 table = new Entry<?,?>[length];
1230 threshold = (int)Math.min(length * loadFactor, MAX_ARRAY_SIZE + 1);
1231 count = 0;
1232
1233 // Read the number of elements and then all the key/value objects
1234 for (; elements > 0; elements--) {
1235 @SuppressWarnings("unchecked")
1236 K key = (K)s.readObject();
1237 @SuppressWarnings("unchecked")
1238 V value = (V)s.readObject();
1239 // synch could be eliminated for performance
1240 reconstitutionPut(table, key, value);
1241 }
1242 }
1243
1244 /**
1245 * The put method used by readObject. This is provided because put
1246 * is overridable and should not be called in readObject since the
1247 * subclass will not yet be initialized.
1248 *
1249 * <p>This differs from the regular put method in several ways. No
1250 * checking for rehashing is necessary since the number of elements
1251 * initially in the table is known. The modCount is not incremented
1252 * because we are creating a new instance. Also, no return value
1253 * is needed.
1254 */
1255 private void reconstitutionPut(Entry<?,?>[] tab, K key, V value)
1256 throws StreamCorruptedException
1257 {
1258 if (value == null) {
1259 throw new java.io.StreamCorruptedException();
1260 }
1261 // Makes sure the key is not already in the hashtable.
1262 // This should not happen in deserialized version.
1263 int hash = hash(key);
1264 int index = (hash & 0x7FFFFFFF) % tab.length;
1265 for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
1266 if ((e.hash == hash) && e.key.equals(key)) {
1267 throw new java.io.StreamCorruptedException();
1268 }
1269 }
1270 // Creates the new entry.
1271 @SuppressWarnings("unchecked")
1272 Entry<K,V> e = (Entry<K,V>)tab[index];
1273 tab[index] = new Entry<>(hash, key, value, e);
1274 count++;
1275 }
1276
1277 /**
1278 * Hashtable bucket collision list entry
1279 */
1280 private static class Entry<K,V> implements Map.Entry<K,V> {
1281 final int hash;
1282 final K key;
1283 V value;
1284 Entry<K,V> next;
1285
1286 protected Entry(int hash, K key, V value, Entry<K,V> next) {
1287 this.hash = hash;
1288 this.key = key;
1289 this.value = value;
1290 this.next = next;
1291 }
1292
1293 @SuppressWarnings("unchecked")
1294 protected Object clone() {
1295 return new Entry<>(hash, key, value,
1296 (next==null ? null : (Entry<K,V>) next.clone()));
1297 }
1298
1299 // Map.Entry Ops
1300
1301 public K getKey() {
1302 return key;
1303 }
1304
1305 public V getValue() {
1306 return value;
1307 }
1308
1309 public V setValue(V value) {
1310 if (value == null)
1311 throw new NullPointerException();
1312
1313 V oldValue = this.value;
1314 this.value = value;
1315 return oldValue;
1316 }
1317
1318 public boolean equals(Object o) {
1319 if (!(o instanceof Map.Entry))
1320 return false;
1321 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
1322
1323 return (key==null ? e.getKey()==null : key.equals(e.getKey())) &&
1324 (value==null ? e.getValue()==null : value.equals(e.getValue()));
1325 }
1326
1327 public int hashCode() {
1328 return (Objects.hashCode(key) ^ Objects.hashCode(value));
1329 }
1330
1331 public String toString() {
1332 return key.toString()+"="+value.toString();
1333 }
1334 }
1335
1336 // Types of Enumerations/Iterations
1337 private static final int KEYS = 0;
1338 private static final int VALUES = 1;
1339 private static final int ENTRIES = 2;
1340
1341 /**
1342 * A hashtable enumerator class. This class implements both the
1343 * Enumeration and Iterator interfaces, but individual instances
1344 * can be created with the Iterator methods disabled. This is necessary
1345 * to avoid unintentionally increasing the capabilities granted a user
1346 * by passing an Enumeration.
1347 */
1348 private class Enumerator<T> implements Enumeration<T>, Iterator<T> {
1349 Entry<?,?>[] table = Hashtable.this.table;
1350 int index = table.length;
1351 Entry<?,?> entry = null;
1352 Entry<?,?> lastReturned = null;
1353 int type;
1354
1355 /**
1356 * Indicates whether this Enumerator is serving as an Iterator
1357 * or an Enumeration. (true -> Iterator).
1358 */
1359 boolean iterator;
1360
1361 /**
1362 * The modCount value that the iterator believes that the backing
1363 * Hashtable should have. If this expectation is violated, the iterator
1364 * has detected concurrent modification.
1365 */
1366 protected int expectedModCount = modCount;
1367
1368 Enumerator(int type, boolean iterator) {
1369 this.type = type;
1370 this.iterator = iterator;
1371 }
1372
1373 public boolean hasMoreElements() {
1374 Entry<?,?> e = entry;
1375 int i = index;
1376 Entry<?,?>[] t = table;
1377 /* Use locals for faster loop iteration */
1378 while (e == null && i > 0) {
1379 e = t[--i];
1380 }
1381 entry = e;
1382 index = i;
1383 return e != null;
1384 }
1385
1386 @SuppressWarnings("unchecked")
1387 public T nextElement() {
1388 Entry<?,?> et = entry;
1389 int i = index;
1390 Entry<?,?>[] t = table;
1391 /* Use locals for faster loop iteration */
1392 while (et == null && i > 0) {
1393 et = t[--i];
1394 }
1395 entry = et;
1396 index = i;
1397 if (et != null) {
1398 Entry<?,?> e = lastReturned = entry;
1399 entry = e.next;
1400 return type == KEYS ? (T)e.key : (type == VALUES ? (T)e.value : (T)e);
1401 }
1402 throw new NoSuchElementException("Hashtable Enumerator");
1403 }
1404
1405 // Iterator methods
1406 public boolean hasNext() {
1407 return hasMoreElements();
1408 }
1409
1410 public T next() {
1411 if (modCount != expectedModCount)
1412 throw new ConcurrentModificationException();
1413 return nextElement();
1414 }
1415
1416 public void remove() {
1417 if (!iterator)
1418 throw new UnsupportedOperationException();
1419 if (lastReturned == null)
1420 throw new IllegalStateException("Hashtable Enumerator");
1421 if (modCount != expectedModCount)
1422 throw new ConcurrentModificationException();
1423
1424 synchronized(Hashtable.this) {
1425 Entry<?,?>[] tab = Hashtable.this.table;
1426 int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length;
1427
1428 @SuppressWarnings("unchecked")
1429 Entry<K,V> e = (Entry<K,V>)tab[index];
1430 for(Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
1431 if (e == lastReturned) {
1432 modCount++;
1433 expectedModCount++;
1434 if (prev == null)
1435 tab[index] = e.next;
1436 else
1437 prev.next = e.next;
1438 count--;
1439 lastReturned = null;
1440 return;
1441 }
1442 }
1443 throw new ConcurrentModificationException();
1444 }
1445 }
1446 }
1447 }