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 {@link #keys keys} and
95 * {@link #elements elements} methods are <em>not</em> fail-fast; if the
96 * Hashtable is structurally modified at any time after the enumeration is
97 * created then the results of enumerating are undefined.
98 *
99 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
100 * as it is, generally speaking, impossible to make any hard guarantees in the
101 * presence of unsynchronized concurrent modification. Fail-fast iterators
102 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
103 * Therefore, it would be wrong to write a program that depended on this
104 * exception for its correctness: <i>the fail-fast behavior of iterators
105 * should be used only to detect bugs.</i>
106 *
107 * <p>As of the Java 2 platform v1.2, this class was retrofitted to
108 * implement the {@link Map} interface, making it a member of the
109 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
110 *
111 * Java Collections Framework</a>. Unlike the new collection
112 * implementations, {@code Hashtable} is synchronized. If a
113 * thread-safe implementation is not needed, it is recommended to use
114 * {@link HashMap} in place of {@code Hashtable}. If a thread-safe
115 * highly-concurrent implementation is desired, then it is recommended
116 * to use {@link java.util.concurrent.ConcurrentHashMap} in place of
117 * {@code Hashtable}.
118 *
119 * @param <K> the type of keys maintained by this map
120 * @param <V> the type of mapped values
121 *
122 * @author Arthur van Hoff
123 * @author Josh Bloch
124 * @author Neal Gafter
125 * @see Object#equals(java.lang.Object)
126 * @see Object#hashCode()
127 * @see Hashtable#rehash()
128 * @see Collection
129 * @see Map
130 * @see HashMap
131 * @see TreeMap
132 * @since 1.0
133 */
134 public class Hashtable<K,V>
135 extends Dictionary<K,V>
136 implements Map<K,V>, Cloneable, java.io.Serializable {
137
138 /**
139 * The hash table data.
140 */
141 private transient Entry<?,?>[] table;
142
143 /**
144 * The total number of entries in the hash table.
145 */
146 private transient int count;
147
148 /**
149 * The table is rehashed when its size exceeds this threshold. (The
150 * value of this field is (int)(capacity * loadFactor).)
151 *
152 * @serial
153 */
154 private int threshold;
155
156 /**
157 * The load factor for the hashtable.
158 *
159 * @serial
160 */
161 private float loadFactor;
162
163 /**
164 * The number of times this Hashtable has been structurally modified
165 * Structural modifications are those that change the number of entries in
166 * the Hashtable or otherwise modify its internal structure (e.g.,
167 * rehash). This field is used to make iterators on Collection-views of
168 * the Hashtable fail-fast. (See ConcurrentModificationException).
169 */
170 private transient int modCount = 0;
171
172 /** use serialVersionUID from JDK 1.0.2 for interoperability */
173 private static final long serialVersionUID = 1421746759512286392L;
174
175 /**
176 * Constructs a new, empty hashtable with the specified initial
177 * capacity and the specified load factor.
178 *
179 * @param initialCapacity the initial capacity of the hashtable.
180 * @param loadFactor the load factor of the hashtable.
181 * @exception IllegalArgumentException if the initial capacity is less
182 * than zero, or if the load factor is nonpositive.
183 */
184 public Hashtable(int initialCapacity, float loadFactor) {
185 if (initialCapacity < 0)
186 throw new IllegalArgumentException("Illegal Capacity: "+
187 initialCapacity);
188 if (loadFactor <= 0 || Float.isNaN(loadFactor))
189 throw new IllegalArgumentException("Illegal Load: "+loadFactor);
190
191 if (initialCapacity==0)
192 initialCapacity = 1;
193 this.loadFactor = loadFactor;
194 table = new Entry<?,?>[initialCapacity];
195 threshold = (int)Math.min(initialCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
196 }
197
198 /**
199 * Constructs a new, empty hashtable with the specified initial capacity
200 * and default load factor (0.75).
201 *
202 * @param initialCapacity the initial capacity of the hashtable.
203 * @exception IllegalArgumentException if the initial capacity is less
204 * than zero.
205 */
206 public Hashtable(int initialCapacity) {
207 this(initialCapacity, 0.75f);
208 }
209
210 /**
211 * Constructs a new, empty hashtable with a default initial capacity (11)
212 * and load factor (0.75).
213 */
214 public Hashtable() {
215 this(11, 0.75f);
216 }
217
218 /**
219 * Constructs a new hashtable with the same mappings as the given
220 * Map. The hashtable is created with an initial capacity sufficient to
221 * hold the mappings in the given Map and a default load factor (0.75).
222 *
223 * @param t the map whose mappings are to be placed in this map.
224 * @throws NullPointerException if the specified map is null.
225 * @since 1.2
226 */
227 public Hashtable(Map<? extends K, ? extends V> t) {
228 this(Math.max(2*t.size(), 11), 0.75f);
229 putAll(t);
230 }
231
232 /**
233 * Returns the number of keys in this hashtable.
234 *
235 * @return the number of keys in this hashtable.
236 */
237 public synchronized int size() {
238 return count;
239 }
240
241 /**
242 * Tests if this hashtable maps no keys to values.
243 *
244 * @return <code>true</code> if this hashtable maps no keys to values;
245 * <code>false</code> otherwise.
246 */
247 public synchronized boolean isEmpty() {
248 return count == 0;
249 }
250
251 /**
252 * Returns an enumeration of the keys in this hashtable.
253 * Use the Enumeration methods on the returned object to fetch the keys
254 * sequentially. If the hashtable is structurally modified while enumerating
255 * over the keys then the results of enumerating are undefined.
256 *
257 * @return an enumeration of the keys in this hashtable.
258 * @see Enumeration
259 * @see #elements()
260 * @see #keySet()
261 * @see Map
262 */
263 public synchronized Enumeration<K> keys() {
264 return this.<K>getEnumeration(KEYS);
265 }
266
267 /**
268 * Returns an enumeration of the values in this hashtable.
269 * Use the Enumeration methods on the returned object to fetch the elements
270 * sequentially. If the hashtable is structurally modified while enumerating
271 * over the values then the results of enumerating are undefined.
272 *
273 * @return an enumeration of the values in this hashtable.
274 * @see java.util.Enumeration
275 * @see #keys()
276 * @see #values()
277 * @see Map
278 */
279 public synchronized Enumeration<V> elements() {
280 return this.<V>getEnumeration(VALUES);
281 }
282
283 /**
284 * Tests if some key maps into the specified value in this hashtable.
285 * This operation is more expensive than the {@link #containsKey
286 * containsKey} method.
287 *
288 * <p>Note that this method is identical in functionality to
289 * {@link #containsValue containsValue}, (which is part of the
290 * {@link Map} interface in the collections framework).
291 *
292 * @param value a value to search for
293 * @return <code>true</code> if and only if some key maps to the
294 * <code>value</code> argument in this hashtable as
295 * determined by the <tt>equals</tt> method;
296 * <code>false</code> otherwise.
297 * @exception NullPointerException if the value is <code>null</code>
298 */
299 public synchronized boolean contains(Object value) {
300 if (value == null) {
301 throw new NullPointerException();
302 }
303
304 Entry<?,?> tab[] = table;
305 for (int i = tab.length ; i-- > 0 ;) {
306 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next) {
307 if (e.value.equals(value)) {
308 return true;
309 }
310 }
311 }
312 return false;
313 }
314
315 /**
316 * Returns true if this hashtable maps one or more keys to this value.
317 *
318 * <p>Note that this method is identical in functionality to {@link
319 * #contains contains} (which predates the {@link Map} interface).
320 *
321 * @param value value whose presence in this hashtable is to be tested
322 * @return <tt>true</tt> if this map maps one or more keys to the
323 * specified value
324 * @throws NullPointerException if the value is <code>null</code>
325 * @since 1.2
326 */
327 public boolean containsValue(Object value) {
328 return contains(value);
329 }
330
331 /**
332 * Tests if the specified object is a key in this hashtable.
333 *
334 * @param key possible key
335 * @return <code>true</code> if and only if the specified object
336 * is a key in this hashtable, as determined by the
337 * <tt>equals</tt> method; <code>false</code> otherwise.
338 * @throws NullPointerException if the key is <code>null</code>
339 * @see #contains(Object)
340 */
341 public synchronized boolean containsKey(Object key) {
342 Entry<?,?> tab[] = table;
343 int hash = key.hashCode();
344 int index = (hash & 0x7FFFFFFF) % tab.length;
345 for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
346 if ((e.hash == hash) && e.key.equals(key)) {
347 return true;
348 }
349 }
350 return false;
351 }
352
353 /**
354 * Returns the value to which the specified key is mapped,
355 * or {@code null} if this map contains no mapping for the key.
356 *
357 * <p>More formally, if this map contains a mapping from a key
358 * {@code k} to a value {@code v} such that {@code (key.equals(k))},
359 * then this method returns {@code v}; otherwise it returns
360 * {@code null}. (There can be at most one such mapping.)
361 *
362 * @param key the key whose associated value is to be returned
363 * @return the value to which the specified key is mapped, or
364 * {@code null} if this map contains no mapping for the key
365 * @throws NullPointerException if the specified key is null
366 * @see #put(Object, Object)
367 */
368 @SuppressWarnings("unchecked")
369 public synchronized V get(Object key) {
370 Entry<?,?> tab[] = table;
371 int hash = key.hashCode();
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 (V)e.value;
376 }
377 }
378 return null;
379 }
380
381 /**
382 * The maximum size of array to allocate.
383 * Some VMs reserve some header words in an array.
384 * Attempts to allocate larger arrays may result in
385 * OutOfMemoryError: Requested array size exceeds VM limit
386 */
387 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
388
389 /**
390 * Increases the capacity of and internally reorganizes this
391 * hashtable, in order to accommodate and access its entries more
392 * efficiently. This method is called automatically when the
393 * number of keys in the hashtable exceeds this hashtable's capacity
394 * and load factor.
395 */
396 @SuppressWarnings("unchecked")
397 protected void rehash() {
398 int oldCapacity = table.length;
399 Entry<?,?>[] oldMap = table;
400
401 // overflow-conscious code
402 int newCapacity = (oldCapacity << 1) + 1;
403 if (newCapacity - MAX_ARRAY_SIZE > 0) {
404 if (oldCapacity == MAX_ARRAY_SIZE)
405 // Keep running with MAX_ARRAY_SIZE buckets
406 return;
407 newCapacity = MAX_ARRAY_SIZE;
408 }
409 Entry<?,?>[] newMap = new Entry<?,?>[newCapacity];
410
411 modCount++;
412 threshold = (int)Math.min(newCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
413 table = newMap;
414
415 for (int i = oldCapacity ; i-- > 0 ;) {
416 for (Entry<K,V> old = (Entry<K,V>)oldMap[i] ; old != null ; ) {
417 Entry<K,V> e = old;
418 old = old.next;
419
420 int index = (e.hash & 0x7FFFFFFF) % newCapacity;
421 e.next = (Entry<K,V>)newMap[index];
422 newMap[index] = e;
423 }
424 }
425 }
426
427 private void addEntry(int hash, K key, V value, int index) {
428 Entry<?,?> tab[] = table;
429 if (count >= threshold) {
430 // Rehash the table if the threshold is exceeded
431 rehash();
432
433 tab = table;
434 hash = key.hashCode();
435 index = (hash & 0x7FFFFFFF) % tab.length;
436 }
437
438 // Creates the new entry.
439 @SuppressWarnings("unchecked")
440 Entry<K,V> e = (Entry<K,V>) tab[index];
441 tab[index] = new Entry<>(hash, key, value, e);
442 count++;
443 modCount++;
444 }
445
446 /**
447 * Maps the specified <code>key</code> to the specified
448 * <code>value</code> in this hashtable. Neither the key nor the
449 * value can be <code>null</code>. <p>
450 *
451 * The value can be retrieved by calling the <code>get</code> method
452 * with a key that is equal to the original key.
453 *
454 * @param key the hashtable key
455 * @param value the value
456 * @return the previous value of the specified key in this hashtable,
457 * or <code>null</code> if it did not have one
458 * @exception NullPointerException if the key or value is
459 * <code>null</code>
460 * @see Object#equals(Object)
461 * @see #get(Object)
462 */
463 public synchronized V put(K key, V value) {
464 // Make sure the value is not null
465 if (value == null) {
466 throw new NullPointerException();
467 }
468
469 // Makes sure the key is not already in the hashtable.
470 Entry<?,?> tab[] = table;
471 int hash = key.hashCode();
472 int index = (hash & 0x7FFFFFFF) % tab.length;
473 @SuppressWarnings("unchecked")
474 Entry<K,V> entry = (Entry<K,V>)tab[index];
475 for(; entry != null ; entry = entry.next) {
476 if ((entry.hash == hash) && entry.key.equals(key)) {
477 V old = entry.value;
478 entry.value = value;
479 return old;
480 }
481 }
482
483 addEntry(hash, key, value, index);
484 return null;
485 }
486
487 /**
488 * Removes the key (and its corresponding value) from this
489 * hashtable. This method does nothing if the key is not in the hashtable.
490 *
491 * @param key the key that needs to be removed
492 * @return the value to which the key had been mapped in this hashtable,
493 * or <code>null</code> if the key did not have a mapping
494 * @throws NullPointerException if the key is <code>null</code>
495 */
496 public synchronized V remove(Object key) {
497 Entry<?,?> tab[] = table;
498 int hash = key.hashCode();
499 int index = (hash & 0x7FFFFFFF) % tab.length;
500 @SuppressWarnings("unchecked")
501 Entry<K,V> e = (Entry<K,V>)tab[index];
502 for(Entry<K,V> prev = null ; e != null ; prev = e, e = e.next) {
503 if ((e.hash == hash) && e.key.equals(key)) {
504 if (prev != null) {
505 prev.next = e.next;
506 } else {
507 tab[index] = e.next;
508 }
509 modCount++;
510 count--;
511 V oldValue = e.value;
512 e.value = null;
513 return oldValue;
514 }
515 }
516 return null;
517 }
518
519 /**
520 * Copies all of the mappings from the specified map to this hashtable.
521 * These mappings will replace any mappings that this hashtable had for any
522 * of the keys currently in the specified map.
523 *
524 * @param t mappings to be stored in this map
525 * @throws NullPointerException if the specified map is null
526 * @since 1.2
527 */
528 public synchronized void putAll(Map<? extends K, ? extends V> t) {
529 for (Map.Entry<? extends K, ? extends V> e : t.entrySet())
530 put(e.getKey(), e.getValue());
531 }
532
533 /**
534 * Clears this hashtable so that it contains no keys.
535 */
536 public synchronized void clear() {
537 Entry<?,?> tab[] = table;
538 for (int index = tab.length; --index >= 0; )
539 tab[index] = null;
540 modCount++;
541 count = 0;
542 }
543
544 /**
545 * Creates a shallow copy of this hashtable. All the structure of the
546 * hashtable itself is copied, but the keys and values are not cloned.
547 * This is a relatively expensive operation.
548 *
549 * @return a clone of the hashtable
550 */
551 public synchronized Object clone() {
552 try {
553 Hashtable<?,?> t = (Hashtable<?,?>)super.clone();
554 t.table = new Entry<?,?>[table.length];
555 for (int i = table.length ; i-- > 0 ; ) {
556 t.table[i] = (table[i] != null)
557 ? (Entry<?,?>) table[i].clone() : null;
558 }
559 t.keySet = null;
560 t.entrySet = null;
561 t.values = null;
562 t.modCount = 0;
563 return t;
564 } catch (CloneNotSupportedException e) {
565 // this shouldn't happen, since we are Cloneable
566 throw new InternalError(e);
567 }
568 }
569
570 /**
571 * Returns a string representation of this <tt>Hashtable</tt> object
572 * in the form of a set of entries, enclosed in braces and separated
573 * by the ASCII characters "<tt>, </tt>" (comma and space). Each
574 * entry is rendered as the key, an equals sign <tt>=</tt>, and the
575 * associated element, where the <tt>toString</tt> method is used to
576 * convert the key and element to strings.
577 *
578 * @return a string representation of this hashtable
579 */
580 public synchronized String toString() {
581 int max = size() - 1;
582 if (max == -1)
583 return "{}";
584
585 StringBuilder sb = new StringBuilder();
586 Iterator<Map.Entry<K,V>> it = entrySet().iterator();
587
588 sb.append('{');
589 for (int i = 0; ; i++) {
590 Map.Entry<K,V> e = it.next();
591 K key = e.getKey();
592 V value = e.getValue();
593 sb.append(key == this ? "(this Map)" : key.toString());
594 sb.append('=');
595 sb.append(value == this ? "(this Map)" : value.toString());
596
597 if (i == max)
598 return sb.append('}').toString();
599 sb.append(", ");
600 }
601 }
602
603
604 private <T> Enumeration<T> getEnumeration(int type) {
605 if (count == 0) {
606 return Collections.emptyEnumeration();
607 } else {
608 return new Enumerator<>(type, false);
609 }
610 }
611
612 private <T> Iterator<T> getIterator(int type) {
613 if (count == 0) {
614 return Collections.emptyIterator();
615 } else {
616 return new Enumerator<>(type, true);
617 }
618 }
619
620 // Views
621
622 /**
623 * Each of these fields are initialized to contain an instance of the
624 * appropriate view the first time this view is requested. The views are
625 * stateless, so there's no reason to create more than one of each.
626 */
627 private transient volatile Set<K> keySet;
628 private transient volatile Set<Map.Entry<K,V>> entrySet;
629 private transient volatile Collection<V> values;
630
631 /**
632 * Returns a {@link Set} view of the keys contained in this map.
633 * The set is backed by the map, so changes to the map are
634 * reflected in the set, and vice-versa. If the map is modified
635 * while an iteration over the set is in progress (except through
636 * the iterator's own <tt>remove</tt> operation), the results of
637 * the iteration are undefined. The set supports element removal,
638 * which removes the corresponding mapping from the map, via the
639 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
640 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
641 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
642 * operations.
643 *
644 * @since 1.2
645 */
646 public Set<K> keySet() {
647 if (keySet == null)
648 keySet = Collections.synchronizedSet(new KeySet(), this);
649 return keySet;
650 }
651
652 private class KeySet extends AbstractSet<K> {
653 public Iterator<K> iterator() {
654 return getIterator(KEYS);
655 }
656 public int size() {
657 return count;
658 }
659 public boolean contains(Object o) {
660 return containsKey(o);
661 }
662 public boolean remove(Object o) {
663 return Hashtable.this.remove(o) != null;
664 }
665 public void clear() {
666 Hashtable.this.clear();
667 }
668 }
669
670 /**
671 * Returns a {@link Set} view of the mappings contained in this map.
672 * The set is backed by the map, so changes to the map are
673 * reflected in the set, and vice-versa. If the map is modified
674 * while an iteration over the set is in progress (except through
675 * the iterator's own <tt>remove</tt> operation, or through the
676 * <tt>setValue</tt> operation on a map entry returned by the
677 * iterator) the results of the iteration are undefined. The set
678 * supports element removal, which removes the corresponding
679 * mapping from the map, via the <tt>Iterator.remove</tt>,
680 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
681 * <tt>clear</tt> operations. It does not support the
682 * <tt>add</tt> or <tt>addAll</tt> operations.
683 *
684 * @since 1.2
685 */
686 public Set<Map.Entry<K,V>> entrySet() {
687 if (entrySet==null)
688 entrySet = Collections.synchronizedSet(new EntrySet(), this);
689 return entrySet;
690 }
691
692 private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
693 public Iterator<Map.Entry<K,V>> iterator() {
694 return getIterator(ENTRIES);
695 }
696
697 public boolean add(Map.Entry<K,V> o) {
698 return super.add(o);
699 }
700
701 public boolean contains(Object o) {
702 if (!(o instanceof Map.Entry))
703 return false;
704 Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
705 Object key = entry.getKey();
706 Entry<?,?>[] tab = table;
707 int hash = key.hashCode();
708 int index = (hash & 0x7FFFFFFF) % tab.length;
709
710 for (Entry<?,?> e = tab[index]; e != null; e = e.next)
711 if (e.hash==hash && e.equals(entry))
712 return true;
713 return false;
714 }
715
716 public boolean remove(Object o) {
717 if (!(o instanceof Map.Entry))
718 return false;
719 Map.Entry<?,?> entry = (Map.Entry<?,?>) o;
720 Object key = entry.getKey();
721 Entry<?,?>[] tab = table;
722 int hash = key.hashCode();
723 int index = (hash & 0x7FFFFFFF) % tab.length;
724
725 @SuppressWarnings("unchecked")
726 Entry<K,V> e = (Entry<K,V>)tab[index];
727 for(Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
728 if (e.hash==hash && e.equals(entry)) {
729 if (prev != null)
730 prev.next = e.next;
731 else
732 tab[index] = e.next;
733
734 e.value = null; // clear for gc.
735 modCount++;
736 count--;
737 return true;
738 }
739 }
740 return false;
741 }
742
743 public int size() {
744 return count;
745 }
746
747 public void clear() {
748 Hashtable.this.clear();
749 }
750 }
751
752 /**
753 * Returns a {@link Collection} view of the values contained in this map.
754 * The collection is backed by the map, so changes to the map are
755 * reflected in the collection, and vice-versa. If the map is
756 * modified while an iteration over the collection is in progress
757 * (except through the iterator's own <tt>remove</tt> operation),
758 * the results of the iteration are undefined. The collection
759 * supports element removal, which removes the corresponding
760 * mapping from the map, via the <tt>Iterator.remove</tt>,
761 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
762 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
763 * support the <tt>add</tt> or <tt>addAll</tt> operations.
764 *
765 * @since 1.2
766 */
767 public Collection<V> values() {
768 if (values==null)
769 values = Collections.synchronizedCollection(new ValueCollection(),
770 this);
771 return values;
772 }
773
774 private class ValueCollection extends AbstractCollection<V> {
775 public Iterator<V> iterator() {
776 return getIterator(VALUES);
777 }
778 public int size() {
779 return count;
780 }
781 public boolean contains(Object o) {
782 return containsValue(o);
783 }
784 public void clear() {
785 Hashtable.this.clear();
786 }
787 }
788
789 // Comparison and hashing
790
791 /**
792 * Compares the specified Object with this Map for equality,
793 * as per the definition in the Map interface.
794 *
795 * @param o object to be compared for equality with this hashtable
796 * @return true if the specified Object is equal to this Map
797 * @see Map#equals(Object)
798 * @since 1.2
799 */
800 public synchronized boolean equals(Object o) {
801 if (o == this)
802 return true;
803
804 if (!(o instanceof Map))
805 return false;
806 Map<?,?> t = (Map<?,?>) o;
807 if (t.size() != size())
808 return false;
809
810 try {
811 for (Map.Entry<K, V> e : entrySet()) {
812 K key = e.getKey();
813 V value = e.getValue();
814 if (value == null) {
815 if (!(t.get(key) == null && t.containsKey(key)))
816 return false;
817 } else {
818 if (!value.equals(t.get(key)))
819 return false;
820 }
821 }
822 } catch (ClassCastException unused) {
823 return false;
824 } catch (NullPointerException unused) {
825 return false;
826 }
827
828 return true;
829 }
830
831 /**
832 * Returns the hash code value for this Map as per the definition in the
833 * Map interface.
834 *
835 * @see Map#hashCode()
836 * @since 1.2
837 */
838 public synchronized int hashCode() {
839 /*
840 * This code detects the recursion caused by computing the hash code
841 * of a self-referential hash table and prevents the stack overflow
842 * that would otherwise result. This allows certain 1.1-era
843 * applets with self-referential hash tables to work. This code
844 * abuses the loadFactor field to do double-duty as a hashCode
845 * in progress flag, so as not to worsen the space performance.
846 * A negative load factor indicates that hash code computation is
847 * in progress.
848 */
849 int h = 0;
850 if (count == 0 || loadFactor < 0)
851 return h; // Returns zero
852
853 loadFactor = -loadFactor; // Mark hashCode computation in progress
854 Entry<?,?>[] tab = table;
855 for (Entry<?,?> entry : tab) {
856 while (entry != null) {
857 h += entry.hashCode();
858 entry = entry.next;
859 }
860 }
861
862 loadFactor = -loadFactor; // Mark hashCode computation complete
863
864 return h;
865 }
866
867 @Override
868 public synchronized V getOrDefault(Object key, V defaultValue) {
869 V result = get(key);
870 return (null == result) ? defaultValue : result;
871 }
872
873 @SuppressWarnings("unchecked")
874 @Override
875 public synchronized void forEach(BiConsumer<? super K, ? super V> action) {
876 Objects.requireNonNull(action); // explicit check required in case
877 // table is empty.
878 final int expectedModCount = modCount;
879
880 Entry<?, ?>[] tab = table;
881 for (Entry<?, ?> entry : tab) {
882 while (entry != null) {
883 action.accept((K)entry.key, (V)entry.value);
884 entry = entry.next;
885
886 if (expectedModCount != modCount) {
887 throw new ConcurrentModificationException();
888 }
889 }
890 }
891 }
892
893 @SuppressWarnings("unchecked")
894 @Override
895 public synchronized void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
896 Objects.requireNonNull(function); // explicit check required in case
897 // table is empty.
898 final int expectedModCount = modCount;
899
900 Entry<K, V>[] tab = (Entry<K, V>[])table;
901 for (Entry<K, V> entry : tab) {
902 while (entry != null) {
903 entry.value = Objects.requireNonNull(
904 function.apply(entry.key, entry.value));
905 entry = entry.next;
906
907 if (expectedModCount != modCount) {
908 throw new ConcurrentModificationException();
909 }
910 }
911 }
912 }
913
914 @Override
915 public synchronized V putIfAbsent(K key, V value) {
916 Objects.requireNonNull(value);
917
918 // Makes sure the key is not already in the hashtable.
919 Entry<?,?> tab[] = table;
920 int hash = key.hashCode();
921 int index = (hash & 0x7FFFFFFF) % tab.length;
922 @SuppressWarnings("unchecked")
923 Entry<K,V> entry = (Entry<K,V>)tab[index];
924 for (; entry != null; entry = entry.next) {
925 if ((entry.hash == hash) && entry.key.equals(key)) {
926 V old = entry.value;
927 if (old == null) {
928 entry.value = value;
929 }
930 return old;
931 }
932 }
933
934 addEntry(hash, key, value, index);
935 return null;
936 }
937
938 @Override
939 public synchronized boolean remove(Object key, Object value) {
940 Objects.requireNonNull(value);
941
942 Entry<?,?> tab[] = table;
943 int hash = key.hashCode();
944 int index = (hash & 0x7FFFFFFF) % tab.length;
945 @SuppressWarnings("unchecked")
946 Entry<K,V> e = (Entry<K,V>)tab[index];
947 for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
948 if ((e.hash == hash) && e.key.equals(key) && e.value.equals(value)) {
949 if (prev != null) {
950 prev.next = e.next;
951 } else {
952 tab[index] = e.next;
953 }
954 e.value = null; // clear for gc
955 modCount++;
956 count--;
957 return true;
958 }
959 }
960 return false;
961 }
962
963 @Override
964 public synchronized boolean replace(K key, V oldValue, V newValue) {
965 Objects.requireNonNull(oldValue);
966 Objects.requireNonNull(newValue);
967 Entry<?,?> tab[] = table;
968 int hash = key.hashCode();
969 int index = (hash & 0x7FFFFFFF) % tab.length;
970 @SuppressWarnings("unchecked")
971 Entry<K,V> e = (Entry<K,V>)tab[index];
972 for (; e != null; e = e.next) {
973 if ((e.hash == hash) && e.key.equals(key)) {
974 if (e.value.equals(oldValue)) {
975 e.value = newValue;
976 return true;
977 } else {
978 return false;
979 }
980 }
981 }
982 return false;
983 }
984
985 @Override
986 public synchronized V replace(K key, V value) {
987 Objects.requireNonNull(value);
988 Entry<?,?> tab[] = table;
989 int hash = key.hashCode();
990 int index = (hash & 0x7FFFFFFF) % tab.length;
991 @SuppressWarnings("unchecked")
992 Entry<K,V> e = (Entry<K,V>)tab[index];
993 for (; e != null; e = e.next) {
994 if ((e.hash == hash) && e.key.equals(key)) {
995 V oldValue = e.value;
996 e.value = value;
997 return oldValue;
998 }
999 }
1000 return null;
1001 }
1002
1003 @Override
1004 public synchronized V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
1005 Objects.requireNonNull(mappingFunction);
1006
1007 Entry<?,?> tab[] = table;
1008 int hash = key.hashCode();
1009 int index = (hash & 0x7FFFFFFF) % tab.length;
1010 @SuppressWarnings("unchecked")
1011 Entry<K,V> e = (Entry<K,V>)tab[index];
1012 for (; e != null; e = e.next) {
1013 if (e.hash == hash && e.key.equals(key)) {
1014 // Hashtable not accept null value
1015 return e.value;
1016 }
1017 }
1018
1019 V newValue = mappingFunction.apply(key);
1020 if (newValue != null) {
1021 addEntry(hash, key, newValue, index);
1022 }
1023
1024 return newValue;
1025 }
1026
1027 @Override
1028 public synchronized V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1029 Objects.requireNonNull(remappingFunction);
1030
1031 Entry<?,?> tab[] = table;
1032 int hash = key.hashCode();
1033 int index = (hash & 0x7FFFFFFF) % tab.length;
1034 @SuppressWarnings("unchecked")
1035 Entry<K,V> e = (Entry<K,V>)tab[index];
1036 for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
1037 if (e.hash == hash && e.key.equals(key)) {
1038 V newValue = remappingFunction.apply(key, e.value);
1039 if (newValue == null) {
1040 if (prev != null) {
1041 prev.next = e.next;
1042 } else {
1043 tab[index] = e.next;
1044 }
1045 modCount++;
1046 count--;
1047 } else {
1048 e.value = newValue;
1049 }
1050 return newValue;
1051 }
1052 }
1053 return null;
1054 }
1055
1056 @Override
1057 public synchronized V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1058 Objects.requireNonNull(remappingFunction);
1059
1060 Entry<?,?> tab[] = table;
1061 int hash = key.hashCode();
1062 int index = (hash & 0x7FFFFFFF) % tab.length;
1063 @SuppressWarnings("unchecked")
1064 Entry<K,V> e = (Entry<K,V>)tab[index];
1065 for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
1066 if (e.hash == hash && Objects.equals(e.key, key)) {
1067 V newValue = remappingFunction.apply(key, e.value);
1068 if (newValue == null) {
1069 if (prev != null) {
1070 prev.next = e.next;
1071 } else {
1072 tab[index] = e.next;
1073 }
1074 modCount++;
1075 count--;
1076 } else {
1077 e.value = newValue;
1078 }
1079 return newValue;
1080 }
1081 }
1082
1083 V newValue = remappingFunction.apply(key, null);
1084 if (newValue != null) {
1085 addEntry(hash, key, newValue, index);
1086 }
1087
1088 return newValue;
1089 }
1090
1091 @Override
1092 public synchronized V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
1093 Objects.requireNonNull(remappingFunction);
1094
1095 Entry<?,?> tab[] = table;
1096 int hash = key.hashCode();
1097 int index = (hash & 0x7FFFFFFF) % tab.length;
1098 @SuppressWarnings("unchecked")
1099 Entry<K,V> e = (Entry<K,V>)tab[index];
1100 for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
1101 if (e.hash == hash && e.key.equals(key)) {
1102 V newValue = remappingFunction.apply(e.value, value);
1103 if (newValue == null) {
1104 if (prev != null) {
1105 prev.next = e.next;
1106 } else {
1107 tab[index] = e.next;
1108 }
1109 modCount++;
1110 count--;
1111 } else {
1112 e.value = newValue;
1113 }
1114 return newValue;
1115 }
1116 }
1117
1118 if (value != null) {
1119 addEntry(hash, key, value, index);
1120 }
1121
1122 return value;
1123 }
1124
1125 /**
1126 * Save the state of the Hashtable to a stream (i.e., serialize it).
1127 *
1128 * @serialData The <i>capacity</i> of the Hashtable (the length of the
1129 * bucket array) is emitted (int), followed by the
1130 * <i>size</i> of the Hashtable (the number of key-value
1131 * mappings), followed by the key (Object) and value (Object)
1132 * for each key-value mapping represented by the Hashtable
1133 * The key-value mappings are emitted in no particular order.
1134 */
1135 private void writeObject(java.io.ObjectOutputStream s)
1136 throws IOException {
1137 Entry<Object, Object> entryStack = null;
1138
1139 synchronized (this) {
1140 // Write out the threshold and loadFactor
1141 s.defaultWriteObject();
1142
1143 // Write out length and count of elements
1144 s.writeInt(table.length);
1145 s.writeInt(count);
1146
1147 // Stack copies of the entries in the table
1148 for (Entry<?, ?> entry : table) {
1149
1150 while (entry != null) {
1151 entryStack =
1152 new Entry<>(0, entry.key, entry.value, entryStack);
1153 entry = entry.next;
1154 }
1155 }
1156 }
1157
1158 // Write out the key/value objects from the stacked entries
1159 while (entryStack != null) {
1160 s.writeObject(entryStack.key);
1161 s.writeObject(entryStack.value);
1162 entryStack = entryStack.next;
1163 }
1164 }
1165
1166 /**
1167 * Reconstitute the Hashtable from a stream (i.e., deserialize it).
1168 */
1169 private void readObject(java.io.ObjectInputStream s)
1170 throws IOException, ClassNotFoundException
1171 {
1172 // Read in the threshold and loadFactor
1173 s.defaultReadObject();
1174
1175 // Read the original length of the array and number of elements
1176 int origlength = s.readInt();
1177 int elements = s.readInt();
1178
1179 // Compute new length with a bit of room 5% to grow but
1180 // no larger than the original length. Make the length
1181 // odd if it's large enough, this helps distribute the entries.
1182 // Guard against the length ending up zero, that's not valid.
1183 int length = (int)(elements / loadFactor) + (elements / 20) + 3;
1184 if (length > elements && (length & 1) == 0)
1185 length--;
1186 if (origlength > 0 && length > origlength)
1187 length = origlength;
1188 table = new Entry<?,?>[length];
1189 threshold = (int)Math.min(length * loadFactor, MAX_ARRAY_SIZE + 1);
1190 count = 0;
1191
1192 // Read the number of elements and then all the key/value objects
1193 for (; elements > 0; elements--) {
1194 @SuppressWarnings("unchecked")
1195 K key = (K)s.readObject();
1196 @SuppressWarnings("unchecked")
1197 V value = (V)s.readObject();
1198 // sync is eliminated for performance
1199 reconstitutionPut(table, key, value);
1200 }
1201 }
1202
1203 /**
1204 * The put method used by readObject. This is provided because put
1205 * is overridable and should not be called in readObject since the
1206 * subclass will not yet be initialized.
1207 *
1208 * <p>This differs from the regular put method in several ways. No
1209 * checking for rehashing is necessary since the number of elements
1210 * initially in the table is known. The modCount is not incremented and
1211 * there's no synchronization because we are creating a new instance.
1212 * Also, no return value is needed.
1213 */
1214 private void reconstitutionPut(Entry<?,?>[] tab, K key, V value)
1215 throws StreamCorruptedException
1216 {
1217 if (value == null) {
1218 throw new java.io.StreamCorruptedException();
1219 }
1220 // Makes sure the key is not already in the hashtable.
1221 // This should not happen in deserialized version.
1222 int hash = key.hashCode();
1223 int index = (hash & 0x7FFFFFFF) % tab.length;
1224 for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
1225 if ((e.hash == hash) && e.key.equals(key)) {
1226 throw new java.io.StreamCorruptedException();
1227 }
1228 }
1229 // Creates the new entry.
1230 @SuppressWarnings("unchecked")
1231 Entry<K,V> e = (Entry<K,V>)tab[index];
1232 tab[index] = new Entry<>(hash, key, value, e);
1233 count++;
1234 }
1235
1236 /**
1237 * Hashtable bucket collision list entry
1238 */
1239 private static class Entry<K,V> implements Map.Entry<K,V> {
1240 final int hash;
1241 final K key;
1242 V value;
1243 Entry<K,V> next;
1244
1245 protected Entry(int hash, K key, V value, Entry<K,V> next) {
1246 this.hash = hash;
1247 this.key = key;
1248 this.value = value;
1249 this.next = next;
1250 }
1251
1252 @SuppressWarnings("unchecked")
1253 protected Object clone() {
1254 return new Entry<>(hash, key, value,
1255 (next==null ? null : (Entry<K,V>) next.clone()));
1256 }
1257
1258 // Map.Entry Ops
1259
1260 public K getKey() {
1261 return key;
1262 }
1263
1264 public V getValue() {
1265 return value;
1266 }
1267
1268 public V setValue(V value) {
1269 if (value == null)
1270 throw new NullPointerException();
1271
1272 V oldValue = this.value;
1273 this.value = value;
1274 return oldValue;
1275 }
1276
1277 public boolean equals(Object o) {
1278 if (!(o instanceof Map.Entry))
1279 return false;
1280 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
1281
1282 return (key==null ? e.getKey()==null : key.equals(e.getKey())) &&
1283 (value==null ? e.getValue()==null : value.equals(e.getValue()));
1284 }
1285
1286 public int hashCode() {
1287 return hash ^ Objects.hashCode(value);
1288 }
1289
1290 public String toString() {
1291 return key.toString()+"="+value.toString();
1292 }
1293 }
1294
1295 // Types of Enumerations/Iterations
1296 private static final int KEYS = 0;
1297 private static final int VALUES = 1;
1298 private static final int ENTRIES = 2;
1299
1300 /**
1301 * A hashtable enumerator class. This class implements both the
1302 * Enumeration and Iterator interfaces, but individual instances
1303 * can be created with the Iterator methods disabled. This is necessary
1304 * to avoid unintentionally increasing the capabilities granted a user
1305 * by passing an Enumeration.
1306 */
1307 private class Enumerator<T> implements Enumeration<T>, Iterator<T> {
1308 final Entry<?,?>[] table = Hashtable.this.table;
1309 int index = table.length;
1310 Entry<?,?> entry;
1311 Entry<?,?> lastReturned;
1312 final int type;
1313
1314 /**
1315 * Indicates whether this Enumerator is serving as an Iterator
1316 * or an Enumeration. (true -> Iterator).
1317 */
1318 final boolean iterator;
1319
1320 /**
1321 * The modCount value that the iterator believes that the backing
1322 * Hashtable should have. If this expectation is violated, the iterator
1323 * has detected concurrent modification.
1324 */
1325 protected int expectedModCount = Hashtable.this.modCount;
1326
1327 Enumerator(int type, boolean iterator) {
1328 this.type = type;
1329 this.iterator = iterator;
1330 }
1331
1332 public boolean hasMoreElements() {
1333 Entry<?,?> e = entry;
1334 int i = index;
1335 Entry<?,?>[] t = table;
1336 /* Use locals for faster loop iteration */
1337 while (e == null && i > 0) {
1338 e = t[--i];
1339 }
1340 entry = e;
1341 index = i;
1342 return e != null;
1343 }
1344
1345 @SuppressWarnings("unchecked")
1346 public T nextElement() {
1347 Entry<?,?> et = entry;
1348 int i = index;
1349 Entry<?,?>[] t = table;
1350 /* Use locals for faster loop iteration */
1351 while (et == null && i > 0) {
1352 et = t[--i];
1353 }
1354 entry = et;
1355 index = i;
1356 if (et != null) {
1357 Entry<?,?> e = lastReturned = entry;
1358 entry = e.next;
1359 return type == KEYS ? (T)e.key : (type == VALUES ? (T)e.value : (T)e);
1360 }
1361 throw new NoSuchElementException("Hashtable Enumerator");
1362 }
1363
1364 // Iterator methods
1365 public boolean hasNext() {
1366 return hasMoreElements();
1367 }
1368
1369 public T next() {
1370 if (Hashtable.this.modCount != expectedModCount)
1371 throw new ConcurrentModificationException();
1372 return nextElement();
1373 }
1374
1375 public void remove() {
1376 if (!iterator)
1377 throw new UnsupportedOperationException();
1378 if (lastReturned == null)
1379 throw new IllegalStateException("Hashtable Enumerator");
1380 if (modCount != expectedModCount)
1381 throw new ConcurrentModificationException();
1382
1383 synchronized(Hashtable.this) {
1384 Entry<?,?>[] tab = Hashtable.this.table;
1385 int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length;
1386
1387 @SuppressWarnings("unchecked")
1388 Entry<K,V> e = (Entry<K,V>)tab[index];
1389 for(Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
1390 if (e == lastReturned) {
1391 if (prev == null)
1392 tab[index] = e.next;
1393 else
1394 prev.next = e.next;
1395 expectedModCount++;
1396 lastReturned = null;
1397 Hashtable.this.modCount++;
1398 Hashtable.this.count--;
1399 return;
1400 }
1401 }
1402 throw new ConcurrentModificationException();
1403 }
1404 }
1405 }
1406 }