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