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 * A constructor chained from {@link Properties} keeps Hashtable fields
234 * uninitialized since they are not used.
235 *
236 * @param dummy a dummy parameter
237 */
238 Hashtable(Void dummy) {}
239
240 /**
241 * Returns the number of keys in this hashtable.
242 *
243 * @return the number of keys in this hashtable.
244 */
245 public synchronized int size() {
246 return count;
247 }
248
249 /**
250 * Tests if this hashtable maps no keys to values.
251 *
252 * @return <code>true</code> if this hashtable maps no keys to values;
253 * <code>false</code> otherwise.
254 */
255 public synchronized boolean isEmpty() {
256 return count == 0;
257 }
258
259 /**
260 * Returns an enumeration of the keys in this hashtable.
261 * Use the Enumeration methods on the returned object to fetch the keys
262 * sequentially. If the hashtable is structurally modified while enumerating
263 * over the keys then the results of enumerating are undefined.
264 *
265 * @return an enumeration of the keys in this hashtable.
266 * @see Enumeration
267 * @see #elements()
268 * @see #keySet()
269 * @see Map
270 */
271 public synchronized Enumeration<K> keys() {
272 return this.<K>getEnumeration(KEYS);
273 }
274
275 /**
276 * Returns an enumeration of the values in this hashtable.
277 * Use the Enumeration methods on the returned object to fetch the elements
278 * sequentially. If the hashtable is structurally modified while enumerating
279 * over the values then the results of enumerating are undefined.
280 *
281 * @return an enumeration of the values in this hashtable.
282 * @see java.util.Enumeration
283 * @see #keys()
284 * @see #values()
285 * @see Map
286 */
287 public synchronized Enumeration<V> elements() {
288 return this.<V>getEnumeration(VALUES);
289 }
290
291 /**
292 * Tests if some key maps into the specified value in this hashtable.
293 * This operation is more expensive than the {@link #containsKey
294 * containsKey} method.
295 *
296 * <p>Note that this method is identical in functionality to
297 * {@link #containsValue containsValue}, (which is part of the
298 * {@link Map} interface in the collections framework).
299 *
300 * @param value a value to search for
301 * @return <code>true</code> if and only if some key maps to the
302 * <code>value</code> argument in this hashtable as
303 * determined by the <tt>equals</tt> method;
304 * <code>false</code> otherwise.
305 * @exception NullPointerException if the value is <code>null</code>
306 */
307 public synchronized boolean contains(Object value) {
308 if (value == null) {
309 throw new NullPointerException();
310 }
311
312 Entry<?,?> tab[] = table;
313 for (int i = tab.length ; i-- > 0 ;) {
314 for (Entry<?,?> e = tab[i] ; e != null ; e = e.next) {
315 if (e.value.equals(value)) {
316 return true;
317 }
318 }
319 }
320 return false;
321 }
322
323 /**
324 * Returns true if this hashtable maps one or more keys to this value.
325 *
326 * <p>Note that this method is identical in functionality to {@link
327 * #contains contains} (which predates the {@link Map} interface).
328 *
329 * @param value value whose presence in this hashtable is to be tested
330 * @return <tt>true</tt> if this map maps one or more keys to the
331 * specified value
332 * @throws NullPointerException if the value is <code>null</code>
333 * @since 1.2
334 */
335 public boolean containsValue(Object value) {
336 return contains(value);
337 }
338
339 /**
340 * Tests if the specified object is a key in this hashtable.
341 *
342 * @param key possible key
343 * @return <code>true</code> if and only if the specified object
344 * is a key in this hashtable, as determined by the
345 * <tt>equals</tt> method; <code>false</code> otherwise.
346 * @throws NullPointerException if the key is <code>null</code>
347 * @see #contains(Object)
348 */
349 public synchronized boolean containsKey(Object key) {
350 Entry<?,?> tab[] = table;
351 int hash = key.hashCode();
352 int index = (hash & 0x7FFFFFFF) % tab.length;
353 for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
354 if ((e.hash == hash) && e.key.equals(key)) {
355 return true;
356 }
357 }
358 return false;
359 }
360
361 /**
362 * Returns the value to which the specified key is mapped,
363 * or {@code null} if this map contains no mapping for the key.
364 *
365 * <p>More formally, if this map contains a mapping from a key
366 * {@code k} to a value {@code v} such that {@code (key.equals(k))},
367 * then this method returns {@code v}; otherwise it returns
368 * {@code null}. (There can be at most one such mapping.)
369 *
370 * @param key the key whose associated value is to be returned
371 * @return the value to which the specified key is mapped, or
372 * {@code null} if this map contains no mapping for the key
373 * @throws NullPointerException if the specified key is null
374 * @see #put(Object, Object)
375 */
376 @SuppressWarnings("unchecked")
377 public synchronized V get(Object key) {
378 Entry<?,?> tab[] = table;
379 int hash = key.hashCode();
380 int index = (hash & 0x7FFFFFFF) % tab.length;
381 for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
382 if ((e.hash == hash) && e.key.equals(key)) {
383 return (V)e.value;
384 }
385 }
386 return null;
387 }
388
389 /**
390 * The maximum size of array to allocate.
391 * Some VMs reserve some header words in an array.
392 * Attempts to allocate larger arrays may result in
393 * OutOfMemoryError: Requested array size exceeds VM limit
394 */
395 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
396
397 /**
398 * Increases the capacity of and internally reorganizes this
399 * hashtable, in order to accommodate and access its entries more
400 * efficiently. This method is called automatically when the
401 * number of keys in the hashtable exceeds this hashtable's capacity
402 * and load factor.
403 */
404 @SuppressWarnings("unchecked")
405 protected void rehash() {
406 int oldCapacity = table.length;
407 Entry<?,?>[] oldMap = table;
408
409 // overflow-conscious code
410 int newCapacity = (oldCapacity << 1) + 1;
411 if (newCapacity - MAX_ARRAY_SIZE > 0) {
412 if (oldCapacity == MAX_ARRAY_SIZE)
413 // Keep running with MAX_ARRAY_SIZE buckets
414 return;
415 newCapacity = MAX_ARRAY_SIZE;
416 }
417 Entry<?,?>[] newMap = new Entry<?,?>[newCapacity];
418
419 modCount++;
420 threshold = (int)Math.min(newCapacity * loadFactor, MAX_ARRAY_SIZE + 1);
421 table = newMap;
422
423 for (int i = oldCapacity ; i-- > 0 ;) {
424 for (Entry<K,V> old = (Entry<K,V>)oldMap[i] ; old != null ; ) {
425 Entry<K,V> e = old;
426 old = old.next;
427
428 int index = (e.hash & 0x7FFFFFFF) % newCapacity;
429 e.next = (Entry<K,V>)newMap[index];
430 newMap[index] = e;
431 }
432 }
433 }
434
435 private void addEntry(int hash, K key, V value, int index) {
436 Entry<?,?> tab[] = table;
437 if (count >= threshold) {
438 // Rehash the table if the threshold is exceeded
439 rehash();
440
441 tab = table;
442 hash = key.hashCode();
443 index = (hash & 0x7FFFFFFF) % tab.length;
444 }
445
446 // Creates the new entry.
447 @SuppressWarnings("unchecked")
448 Entry<K,V> e = (Entry<K,V>) tab[index];
449 tab[index] = new Entry<>(hash, key, value, e);
450 count++;
451 modCount++;
452 }
453
454 /**
455 * Maps the specified <code>key</code> to the specified
456 * <code>value</code> in this hashtable. Neither the key nor the
457 * value can be <code>null</code>. <p>
458 *
459 * The value can be retrieved by calling the <code>get</code> method
460 * with a key that is equal to the original key.
461 *
462 * @param key the hashtable key
463 * @param value the value
464 * @return the previous value of the specified key in this hashtable,
465 * or <code>null</code> if it did not have one
466 * @exception NullPointerException if the key or value is
467 * <code>null</code>
468 * @see Object#equals(Object)
469 * @see #get(Object)
470 */
471 public synchronized V put(K key, V value) {
472 // Make sure the value is not null
473 if (value == null) {
474 throw new NullPointerException();
475 }
476
477 // Makes sure the key is not already in the hashtable.
478 Entry<?,?> tab[] = table;
479 int hash = key.hashCode();
480 int index = (hash & 0x7FFFFFFF) % tab.length;
481 @SuppressWarnings("unchecked")
482 Entry<K,V> entry = (Entry<K,V>)tab[index];
483 for(; entry != null ; entry = entry.next) {
484 if ((entry.hash == hash) && entry.key.equals(key)) {
485 V old = entry.value;
486 entry.value = value;
487 return old;
488 }
489 }
490
491 addEntry(hash, key, value, index);
492 return null;
493 }
494
495 /**
496 * Removes the key (and its corresponding value) from this
497 * hashtable. This method does nothing if the key is not in the hashtable.
498 *
499 * @param key the key that needs to be removed
500 * @return the value to which the key had been mapped in this hashtable,
501 * or <code>null</code> if the key did not have a mapping
502 * @throws NullPointerException if the key is <code>null</code>
503 */
504 public synchronized V remove(Object key) {
505 Entry<?,?> tab[] = table;
506 int hash = key.hashCode();
507 int index = (hash & 0x7FFFFFFF) % tab.length;
508 @SuppressWarnings("unchecked")
509 Entry<K,V> e = (Entry<K,V>)tab[index];
510 for(Entry<K,V> prev = null ; e != null ; prev = e, e = e.next) {
511 if ((e.hash == hash) && e.key.equals(key)) {
512 if (prev != null) {
513 prev.next = e.next;
514 } else {
515 tab[index] = e.next;
516 }
517 modCount++;
518 count--;
519 V oldValue = e.value;
520 e.value = null;
521 return oldValue;
522 }
523 }
524 return null;
525 }
526
527 /**
528 * Copies all of the mappings from the specified map to this hashtable.
529 * These mappings will replace any mappings that this hashtable had for any
530 * of the keys currently in the specified map.
531 *
532 * @param t mappings to be stored in this map
533 * @throws NullPointerException if the specified map is null
534 * @since 1.2
535 */
536 public synchronized void putAll(Map<? extends K, ? extends V> t) {
537 for (Map.Entry<? extends K, ? extends V> e : t.entrySet())
538 put(e.getKey(), e.getValue());
539 }
540
541 /**
542 * Clears this hashtable so that it contains no keys.
543 */
544 public synchronized void clear() {
545 Entry<?,?> tab[] = table;
546 for (int index = tab.length; --index >= 0; )
547 tab[index] = null;
548 modCount++;
549 count = 0;
550 }
551
552 /**
553 * Creates a shallow copy of this hashtable. All the structure of the
554 * hashtable itself is copied, but the keys and values are not cloned.
555 * This is a relatively expensive operation.
556 *
557 * @return a clone of the hashtable
558 */
559 public synchronized Object clone() {
560 Hashtable<?,?> t = cloneHashtable();
561 t.table = new Entry<?,?>[table.length];
562 for (int i = table.length ; i-- > 0 ; ) {
563 t.table[i] = (table[i] != null)
564 ? (Entry<?,?>) table[i].clone() : null;
565 }
566 t.keySet = null;
567 t.entrySet = null;
568 t.values = null;
569 t.modCount = 0;
570 return t;
571 }
572
573 /** Calls super.clone() */
574 final Hashtable<?,?> cloneHashtable() {
575 try {
576 return (Hashtable<?,?>)super.clone();
577 } catch (CloneNotSupportedException e) {
578 // this shouldn't happen, since we are Cloneable
579 throw new InternalError(e);
580 }
581 }
582
583 /**
584 * Returns a string representation of this <tt>Hashtable</tt> object
585 * in the form of a set of entries, enclosed in braces and separated
586 * by the ASCII characters "<tt>, </tt>" (comma and space). Each
587 * entry is rendered as the key, an equals sign <tt>=</tt>, and the
588 * associated element, where the <tt>toString</tt> method is used to
589 * convert the key and element to strings.
590 *
591 * @return a string representation of this hashtable
592 */
593 public synchronized String toString() {
594 int max = size() - 1;
595 if (max == -1)
596 return "{}";
597
598 StringBuilder sb = new StringBuilder();
599 Iterator<Map.Entry<K,V>> it = entrySet().iterator();
600
601 sb.append('{');
602 for (int i = 0; ; i++) {
603 Map.Entry<K,V> e = it.next();
604 K key = e.getKey();
605 V value = e.getValue();
606 sb.append(key == this ? "(this Map)" : key.toString());
607 sb.append('=');
608 sb.append(value == this ? "(this Map)" : value.toString());
609
610 if (i == max)
611 return sb.append('}').toString();
612 sb.append(", ");
613 }
614 }
615
616
617 private <T> Enumeration<T> getEnumeration(int type) {
618 if (count == 0) {
619 return Collections.emptyEnumeration();
620 } else {
621 return new Enumerator<>(type, false);
622 }
623 }
624
625 private <T> Iterator<T> getIterator(int type) {
626 if (count == 0) {
627 return Collections.emptyIterator();
628 } else {
629 return new Enumerator<>(type, true);
630 }
631 }
632
633 // Views
634
635 /**
636 * Each of these fields are initialized to contain an instance of the
637 * appropriate view the first time this view is requested. The views are
638 * stateless, so there's no reason to create more than one of each.
639 */
640 private transient volatile Set<K> keySet;
641 private transient volatile Set<Map.Entry<K,V>> entrySet;
642 private transient volatile Collection<V> values;
643
644 /**
645 * Returns a {@link Set} view of the keys contained in this map.
646 * The set is backed by the map, so changes to the map are
647 * reflected in the set, and vice-versa. If the map is modified
648 * while an iteration over the set is in progress (except through
649 * the iterator's own <tt>remove</tt> operation), the results of
650 * the iteration are undefined. The set supports element removal,
651 * which removes the corresponding mapping from the map, via the
652 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
653 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
654 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
655 * operations.
656 *
657 * @since 1.2
658 */
659 public Set<K> keySet() {
660 if (keySet == null)
661 keySet = Collections.synchronizedSet(new KeySet(), this);
662 return keySet;
663 }
664
665 private class KeySet extends AbstractSet<K> {
666 public Iterator<K> iterator() {
667 return getIterator(KEYS);
668 }
669 public int size() {
670 return count;
671 }
672 public boolean contains(Object o) {
673 return containsKey(o);
674 }
675 public boolean remove(Object o) {
676 return Hashtable.this.remove(o) != null;
677 }
678 public void clear() {
679 Hashtable.this.clear();
680 }
681 }
682
683 /**
684 * Returns a {@link Set} view of the mappings contained in this map.
685 * The set is backed by the map, so changes to the map are
686 * reflected in the set, and vice-versa. If the map is modified
687 * while an iteration over the set is in progress (except through
688 * the iterator's own <tt>remove</tt> operation, or through the
689 * <tt>setValue</tt> operation on a map entry returned by the
690 * iterator) the results of the iteration are undefined. The set
691 * supports element removal, which removes the corresponding
692 * mapping from the map, via the <tt>Iterator.remove</tt>,
693 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and
694 * <tt>clear</tt> operations. It does not support the
695 * <tt>add</tt> or <tt>addAll</tt> operations.
696 *
697 * @since 1.2
698 */
699 public Set<Map.Entry<K,V>> entrySet() {
700 if (entrySet==null)
701 entrySet = Collections.synchronizedSet(new EntrySet(), this);
702 return entrySet;
703 }
704
705 private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
706 public Iterator<Map.Entry<K,V>> iterator() {
707 return getIterator(ENTRIES);
708 }
709
710 public boolean add(Map.Entry<K,V> o) {
711 return super.add(o);
712 }
713
714 public boolean contains(Object o) {
715 if (!(o instanceof Map.Entry))
716 return false;
717 Map.Entry<?,?> entry = (Map.Entry<?,?>)o;
718 Object key = entry.getKey();
719 Entry<?,?>[] tab = table;
720 int hash = key.hashCode();
721 int index = (hash & 0x7FFFFFFF) % tab.length;
722
723 for (Entry<?,?> e = tab[index]; e != null; e = e.next)
724 if (e.hash==hash && e.equals(entry))
725 return true;
726 return false;
727 }
728
729 public boolean remove(Object o) {
730 if (!(o instanceof Map.Entry))
731 return false;
732 Map.Entry<?,?> entry = (Map.Entry<?,?>) o;
733 Object key = entry.getKey();
734 Entry<?,?>[] tab = table;
735 int hash = key.hashCode();
736 int index = (hash & 0x7FFFFFFF) % tab.length;
737
738 @SuppressWarnings("unchecked")
739 Entry<K,V> e = (Entry<K,V>)tab[index];
740 for(Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
741 if (e.hash==hash && e.equals(entry)) {
742 if (prev != null)
743 prev.next = e.next;
744 else
745 tab[index] = e.next;
746
747 e.value = null; // clear for gc.
748 modCount++;
749 count--;
750 return true;
751 }
752 }
753 return false;
754 }
755
756 public int size() {
757 return count;
758 }
759
760 public void clear() {
761 Hashtable.this.clear();
762 }
763 }
764
765 /**
766 * Returns a {@link Collection} view of the values contained in this map.
767 * The collection is backed by the map, so changes to the map are
768 * reflected in the collection, and vice-versa. If the map is
769 * modified while an iteration over the collection is in progress
770 * (except through the iterator's own <tt>remove</tt> operation),
771 * the results of the iteration are undefined. The collection
772 * supports element removal, which removes the corresponding
773 * mapping from the map, via the <tt>Iterator.remove</tt>,
774 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
775 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not
776 * support the <tt>add</tt> or <tt>addAll</tt> operations.
777 *
778 * @since 1.2
779 */
780 public Collection<V> values() {
781 if (values==null)
782 values = Collections.synchronizedCollection(new ValueCollection(),
783 this);
784 return values;
785 }
786
787 private class ValueCollection extends AbstractCollection<V> {
788 public Iterator<V> iterator() {
789 return getIterator(VALUES);
790 }
791 public int size() {
792 return count;
793 }
794 public boolean contains(Object o) {
795 return containsValue(o);
796 }
797 public void clear() {
798 Hashtable.this.clear();
799 }
800 }
801
802 // Comparison and hashing
803
804 /**
805 * Compares the specified Object with this Map for equality,
806 * as per the definition in the Map interface.
807 *
808 * @param o object to be compared for equality with this hashtable
809 * @return true if the specified Object is equal to this Map
810 * @see Map#equals(Object)
811 * @since 1.2
812 */
813 public synchronized boolean equals(Object o) {
814 if (o == this)
815 return true;
816
817 if (!(o instanceof Map))
818 return false;
819 Map<?,?> t = (Map<?,?>) o;
820 if (t.size() != size())
821 return false;
822
823 try {
824 for (Map.Entry<K, V> e : entrySet()) {
825 K key = e.getKey();
826 V value = e.getValue();
827 if (value == null) {
828 if (!(t.get(key) == null && t.containsKey(key)))
829 return false;
830 } else {
831 if (!value.equals(t.get(key)))
832 return false;
833 }
834 }
835 } catch (ClassCastException unused) {
836 return false;
837 } catch (NullPointerException unused) {
838 return false;
839 }
840
841 return true;
842 }
843
844 /**
845 * Returns the hash code value for this Map as per the definition in the
846 * Map interface.
847 *
848 * @see Map#hashCode()
849 * @since 1.2
850 */
851 public synchronized int hashCode() {
852 /*
853 * This code detects the recursion caused by computing the hash code
854 * of a self-referential hash table and prevents the stack overflow
855 * that would otherwise result. This allows certain 1.1-era
856 * applets with self-referential hash tables to work. This code
857 * abuses the loadFactor field to do double-duty as a hashCode
858 * in progress flag, so as not to worsen the space performance.
859 * A negative load factor indicates that hash code computation is
860 * in progress.
861 */
862 int h = 0;
863 if (count == 0 || loadFactor < 0)
864 return h; // Returns zero
865
866 loadFactor = -loadFactor; // Mark hashCode computation in progress
867 Entry<?,?>[] tab = table;
868 for (Entry<?,?> entry : tab) {
869 while (entry != null) {
870 h += entry.hashCode();
871 entry = entry.next;
872 }
873 }
874
875 loadFactor = -loadFactor; // Mark hashCode computation complete
876
877 return h;
878 }
879
880 @Override
881 public synchronized V getOrDefault(Object key, V defaultValue) {
882 V result = get(key);
883 return (null == result) ? defaultValue : result;
884 }
885
886 @SuppressWarnings("unchecked")
887 @Override
888 public synchronized void forEach(BiConsumer<? super K, ? super V> action) {
889 Objects.requireNonNull(action); // explicit check required in case
890 // table is empty.
891 final int expectedModCount = modCount;
892
893 Entry<?, ?>[] tab = table;
894 for (Entry<?, ?> entry : tab) {
895 while (entry != null) {
896 action.accept((K)entry.key, (V)entry.value);
897 entry = entry.next;
898
899 if (expectedModCount != modCount) {
900 throw new ConcurrentModificationException();
901 }
902 }
903 }
904 }
905
906 @SuppressWarnings("unchecked")
907 @Override
908 public synchronized void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
909 Objects.requireNonNull(function); // explicit check required in case
910 // table is empty.
911 final int expectedModCount = modCount;
912
913 Entry<K, V>[] tab = (Entry<K, V>[])table;
914 for (Entry<K, V> entry : tab) {
915 while (entry != null) {
916 entry.value = Objects.requireNonNull(
917 function.apply(entry.key, entry.value));
918 entry = entry.next;
919
920 if (expectedModCount != modCount) {
921 throw new ConcurrentModificationException();
922 }
923 }
924 }
925 }
926
927 @Override
928 public synchronized V putIfAbsent(K key, V value) {
929 Objects.requireNonNull(value);
930
931 // Makes sure the key is not already in the hashtable.
932 Entry<?,?> tab[] = table;
933 int hash = key.hashCode();
934 int index = (hash & 0x7FFFFFFF) % tab.length;
935 @SuppressWarnings("unchecked")
936 Entry<K,V> entry = (Entry<K,V>)tab[index];
937 for (; entry != null; entry = entry.next) {
938 if ((entry.hash == hash) && entry.key.equals(key)) {
939 V old = entry.value;
940 if (old == null) {
941 entry.value = value;
942 }
943 return old;
944 }
945 }
946
947 addEntry(hash, key, value, index);
948 return null;
949 }
950
951 @Override
952 public synchronized boolean remove(Object key, Object value) {
953 Objects.requireNonNull(value);
954
955 Entry<?,?> tab[] = table;
956 int hash = key.hashCode();
957 int index = (hash & 0x7FFFFFFF) % tab.length;
958 @SuppressWarnings("unchecked")
959 Entry<K,V> e = (Entry<K,V>)tab[index];
960 for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
961 if ((e.hash == hash) && e.key.equals(key) && e.value.equals(value)) {
962 if (prev != null) {
963 prev.next = e.next;
964 } else {
965 tab[index] = e.next;
966 }
967 e.value = null; // clear for gc
968 modCount++;
969 count--;
970 return true;
971 }
972 }
973 return false;
974 }
975
976 @Override
977 public synchronized boolean replace(K key, V oldValue, V newValue) {
978 Objects.requireNonNull(oldValue);
979 Objects.requireNonNull(newValue);
980 Entry<?,?> tab[] = table;
981 int hash = key.hashCode();
982 int index = (hash & 0x7FFFFFFF) % tab.length;
983 @SuppressWarnings("unchecked")
984 Entry<K,V> e = (Entry<K,V>)tab[index];
985 for (; e != null; e = e.next) {
986 if ((e.hash == hash) && e.key.equals(key)) {
987 if (e.value.equals(oldValue)) {
988 e.value = newValue;
989 return true;
990 } else {
991 return false;
992 }
993 }
994 }
995 return false;
996 }
997
998 @Override
999 public synchronized V replace(K key, V value) {
1000 Objects.requireNonNull(value);
1001 Entry<?,?> tab[] = table;
1002 int hash = key.hashCode();
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 V oldValue = e.value;
1009 e.value = value;
1010 return oldValue;
1011 }
1012 }
1013 return null;
1014 }
1015
1016 /**
1017 * {@inheritDoc}
1018 *
1019 * <p>This method will, on a best-effort basis, throw a
1020 * {@link java.util.ConcurrentModificationException} if the mapping
1021 * function modified this map during computation.
1022 *
1023 * @throws ConcurrentModificationException if it is detected that the
1024 * mapping function modified this map
1025 */
1026 @Override
1027 public synchronized V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
1028 Objects.requireNonNull(mappingFunction);
1029
1030 Entry<?,?> tab[] = table;
1031 int hash = key.hashCode();
1032 int index = (hash & 0x7FFFFFFF) % tab.length;
1033 @SuppressWarnings("unchecked")
1034 Entry<K,V> e = (Entry<K,V>)tab[index];
1035 for (; e != null; e = e.next) {
1036 if (e.hash == hash && e.key.equals(key)) {
1037 // Hashtable not accept null value
1038 return e.value;
1039 }
1040 }
1041
1042 int mc = modCount;
1043 V newValue = mappingFunction.apply(key);
1044 if (mc != modCount) { throw new ConcurrentModificationException(); }
1045 if (newValue != null) {
1046 addEntry(hash, key, newValue, index);
1047 }
1048
1049 return newValue;
1050 }
1051
1052 /**
1053 * {@inheritDoc}
1054 *
1055 * <p>This method will, on a best-effort basis, throw a
1056 * {@link java.util.ConcurrentModificationException} if the remapping
1057 * function modified this map during computation.
1058 *
1059 * @throws ConcurrentModificationException if it is detected that the
1060 * remapping function modified this map
1061 */
1062 @Override
1063 public synchronized V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1064 Objects.requireNonNull(remappingFunction);
1065
1066 Entry<?,?> tab[] = table;
1067 int hash = key.hashCode();
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 && e.key.equals(key)) {
1073 int mc = modCount;
1074 V newValue = remappingFunction.apply(key, e.value);
1075 if (mc != modCount) {
1076 throw new ConcurrentModificationException();
1077 }
1078 if (newValue == null) {
1079 if (prev != null) {
1080 prev.next = e.next;
1081 } else {
1082 tab[index] = e.next;
1083 }
1084 modCount = mc + 1;
1085 count--;
1086 } else {
1087 e.value = newValue;
1088 }
1089 return newValue;
1090 }
1091 }
1092 return null;
1093 }
1094 /**
1095 * {@inheritDoc}
1096 *
1097 * <p>This method will, on a best-effort basis, throw a
1098 * {@link java.util.ConcurrentModificationException} if the remapping
1099 * function modified this map during computation.
1100 *
1101 * @throws ConcurrentModificationException if it is detected that the
1102 * remapping function modified this map
1103 */
1104 @Override
1105 public synchronized V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
1106 Objects.requireNonNull(remappingFunction);
1107
1108 Entry<?,?> tab[] = table;
1109 int hash = key.hashCode();
1110 int index = (hash & 0x7FFFFFFF) % tab.length;
1111 @SuppressWarnings("unchecked")
1112 Entry<K,V> e = (Entry<K,V>)tab[index];
1113 for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
1114 if (e.hash == hash && Objects.equals(e.key, key)) {
1115 int mc = modCount;
1116 V newValue = remappingFunction.apply(key, e.value);
1117 if (mc != modCount) {
1118 throw new ConcurrentModificationException();
1119 }
1120 if (newValue == null) {
1121 if (prev != null) {
1122 prev.next = e.next;
1123 } else {
1124 tab[index] = e.next;
1125 }
1126 modCount = mc + 1;
1127 count--;
1128 } else {
1129 e.value = newValue;
1130 }
1131 return newValue;
1132 }
1133 }
1134
1135 int mc = modCount;
1136 V newValue = remappingFunction.apply(key, null);
1137 if (mc != modCount) { throw new ConcurrentModificationException(); }
1138 if (newValue != null) {
1139 addEntry(hash, key, newValue, index);
1140 }
1141
1142 return newValue;
1143 }
1144
1145 /**
1146 * {@inheritDoc}
1147 *
1148 * <p>This method will, on a best-effort basis, throw a
1149 * {@link java.util.ConcurrentModificationException} if the remapping
1150 * function modified this map during computation.
1151 *
1152 * @throws ConcurrentModificationException if it is detected that the
1153 * remapping function modified this map
1154 */
1155 @Override
1156 public synchronized V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
1157 Objects.requireNonNull(remappingFunction);
1158
1159 Entry<?,?> tab[] = table;
1160 int hash = key.hashCode();
1161 int index = (hash & 0x7FFFFFFF) % tab.length;
1162 @SuppressWarnings("unchecked")
1163 Entry<K,V> e = (Entry<K,V>)tab[index];
1164 for (Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
1165 if (e.hash == hash && e.key.equals(key)) {
1166 int mc = modCount;
1167 V newValue = remappingFunction.apply(e.value, value);
1168 if (mc != modCount) {
1169 throw new ConcurrentModificationException();
1170 }
1171 if (newValue == null) {
1172 if (prev != null) {
1173 prev.next = e.next;
1174 } else {
1175 tab[index] = e.next;
1176 }
1177 modCount = mc + 1;
1178 count--;
1179 } else {
1180 e.value = newValue;
1181 }
1182 return newValue;
1183 }
1184 }
1185
1186 if (value != null) {
1187 addEntry(hash, key, value, index);
1188 }
1189
1190 return value;
1191 }
1192
1193 /**
1194 * Save the state of the Hashtable to a stream (i.e., serialize it).
1195 *
1196 * @serialData The <i>capacity</i> of the Hashtable (the length of the
1197 * bucket array) is emitted (int), followed by the
1198 * <i>size</i> of the Hashtable (the number of key-value
1199 * mappings), followed by the key (Object) and value (Object)
1200 * for each key-value mapping represented by the Hashtable
1201 * The key-value mappings are emitted in no particular order.
1202 */
1203 private void writeObject(java.io.ObjectOutputStream s)
1204 throws IOException {
1205 writeHashtable(s);
1206 }
1207
1208 void writeHashtable(java.io.ObjectOutputStream s)
1209 throws IOException {
1210 Entry<Object, Object> entryStack = null;
1211
1212 synchronized (this) {
1213 // Write out the threshold and loadFactor
1214 s.defaultWriteObject();
1215
1216 // Write out the length and count of elements
1217 s.writeInt(table.length);
1218 s.writeInt(count);
1219
1220 // Stack copies of the entries in the table
1221 for (Entry<?, ?> entry : table) {
1222
1223 while (entry != null) {
1224 entryStack =
1225 new Entry<>(0, entry.key, entry.value, entryStack);
1226 entry = entry.next;
1227 }
1228 }
1229 }
1230
1231 // Write out the key/value objects from the stacked entries
1232 while (entryStack != null) {
1233 s.writeObject(entryStack.key);
1234 s.writeObject(entryStack.value);
1235 entryStack = entryStack.next;
1236 }
1237 }
1238
1239 /**
1240 * Write out the simulated threshold, loadfactor
1241 * Called by Properties
1242 */
1243 final void defaultWriteHashtable(java.io.ObjectOutputStream s, int length,
1244 float loadFactor) throws IOException {
1245 this.threshold = (int)Math.min(length * loadFactor, MAX_ARRAY_SIZE + 1);
1246 this.loadFactor = loadFactor;
1247 s.defaultWriteObject();
1248 }
1249
1250 /**
1251 * Reconstitute the Hashtable from a stream (i.e., deserialize it).
1252 */
1253 private void readObject(java.io.ObjectInputStream s)
1254 throws IOException, ClassNotFoundException {
1255 readHashtable(s);
1256 }
1257
1258 void readHashtable(java.io.ObjectInputStream s)
1259 throws IOException, ClassNotFoundException {
1260 // Read in the threshold and loadFactor
1261 s.defaultReadObject();
1262
1263 // Validate loadFactor (ignore threshold - it will be re-computed)
1264 if (loadFactor <= 0 || Float.isNaN(loadFactor))
1265 throw new StreamCorruptedException("Illegal Load: " + loadFactor);
1266
1267 // Read the original length of the array and number of elements
1268 int origlength = s.readInt();
1269 int elements = s.readInt();
1270
1271 // Validate # of elements
1272 if (elements < 0)
1273 throw new StreamCorruptedException("Illegal # of Elements: " + elements);
1274
1275 // Clamp original length to be more than elements / loadFactor
1276 // (this is the invariant enforced with auto-growth)
1277 origlength = Math.max(origlength, (int)(elements / loadFactor) + 1);
1278
1279 // Compute new length with a bit of room 5% + 3 to grow but
1280 // no larger than the clamped original length. Make the length
1281 // odd if it's large enough, this helps distribute the entries.
1282 // Guard against the length ending up zero, that's not valid.
1283 int length = (int)((elements + elements / 20) / loadFactor) + 3;
1284 if (length > elements && (length & 1) == 0)
1285 length--;
1286 length = Math.min(length, origlength);
1287 table = new Entry<?,?>[length];
1288 threshold = (int)Math.min(length * loadFactor, MAX_ARRAY_SIZE + 1);
1289 count = 0;
1290
1291 // Read the number of elements and then all the key/value objects
1292 for (; elements > 0; elements--) {
1293 @SuppressWarnings("unchecked")
1294 K key = (K)s.readObject();
1295 @SuppressWarnings("unchecked")
1296 V value = (V)s.readObject();
1297 // sync is eliminated for performance
1298 reconstitutionPut(table, key, value);
1299 }
1300 }
1301
1302 /**
1303 * The put method used by readObject. This is provided because put
1304 * is overridable and should not be called in readObject since the
1305 * subclass will not yet be initialized.
1306 *
1307 * <p>This differs from the regular put method in several ways. No
1308 * checking for rehashing is necessary since the number of elements
1309 * initially in the table is known. The modCount is not incremented and
1310 * there's no synchronization because we are creating a new instance.
1311 * Also, no return value is needed.
1312 */
1313 private void reconstitutionPut(Entry<?,?>[] tab, K key, V value)
1314 throws StreamCorruptedException
1315 {
1316 if (value == null) {
1317 throw new java.io.StreamCorruptedException();
1318 }
1319 // Makes sure the key is not already in the hashtable.
1320 // This should not happen in deserialized version.
1321 int hash = key.hashCode();
1322 int index = (hash & 0x7FFFFFFF) % tab.length;
1323 for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
1324 if ((e.hash == hash) && e.key.equals(key)) {
1325 throw new java.io.StreamCorruptedException();
1326 }
1327 }
1328 // Creates the new entry.
1329 @SuppressWarnings("unchecked")
1330 Entry<K,V> e = (Entry<K,V>)tab[index];
1331 tab[index] = new Entry<>(hash, key, value, e);
1332 count++;
1333 }
1334
1335 /**
1336 * Hashtable bucket collision list entry
1337 */
1338 private static class Entry<K,V> implements Map.Entry<K,V> {
1339 final int hash;
1340 final K key;
1341 V value;
1342 Entry<K,V> next;
1343
1344 protected Entry(int hash, K key, V value, Entry<K,V> next) {
1345 this.hash = hash;
1346 this.key = key;
1347 this.value = value;
1348 this.next = next;
1349 }
1350
1351 @SuppressWarnings("unchecked")
1352 protected Object clone() {
1353 return new Entry<>(hash, key, value,
1354 (next==null ? null : (Entry<K,V>) next.clone()));
1355 }
1356
1357 // Map.Entry Ops
1358
1359 public K getKey() {
1360 return key;
1361 }
1362
1363 public V getValue() {
1364 return value;
1365 }
1366
1367 public V setValue(V value) {
1368 if (value == null)
1369 throw new NullPointerException();
1370
1371 V oldValue = this.value;
1372 this.value = value;
1373 return oldValue;
1374 }
1375
1376 public boolean equals(Object o) {
1377 if (!(o instanceof Map.Entry))
1378 return false;
1379 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
1380
1381 return (key==null ? e.getKey()==null : key.equals(e.getKey())) &&
1382 (value==null ? e.getValue()==null : value.equals(e.getValue()));
1383 }
1384
1385 public int hashCode() {
1386 return hash ^ Objects.hashCode(value);
1387 }
1388
1389 public String toString() {
1390 return key.toString()+"="+value.toString();
1391 }
1392 }
1393
1394 // Types of Enumerations/Iterations
1395 private static final int KEYS = 0;
1396 private static final int VALUES = 1;
1397 private static final int ENTRIES = 2;
1398
1399 /**
1400 * A hashtable enumerator class. This class implements both the
1401 * Enumeration and Iterator interfaces, but individual instances
1402 * can be created with the Iterator methods disabled. This is necessary
1403 * to avoid unintentionally increasing the capabilities granted a user
1404 * by passing an Enumeration.
1405 */
1406 private class Enumerator<T> implements Enumeration<T>, Iterator<T> {
1407 final Entry<?,?>[] table = Hashtable.this.table;
1408 int index = table.length;
1409 Entry<?,?> entry;
1410 Entry<?,?> lastReturned;
1411 final int type;
1412
1413 /**
1414 * Indicates whether this Enumerator is serving as an Iterator
1415 * or an Enumeration. (true -> Iterator).
1416 */
1417 final boolean iterator;
1418
1419 /**
1420 * The modCount value that the iterator believes that the backing
1421 * Hashtable should have. If this expectation is violated, the iterator
1422 * has detected concurrent modification.
1423 */
1424 protected int expectedModCount = Hashtable.this.modCount;
1425
1426 Enumerator(int type, boolean iterator) {
1427 this.type = type;
1428 this.iterator = iterator;
1429 }
1430
1431 public boolean hasMoreElements() {
1432 Entry<?,?> e = entry;
1433 int i = index;
1434 Entry<?,?>[] t = table;
1435 /* Use locals for faster loop iteration */
1436 while (e == null && i > 0) {
1437 e = t[--i];
1438 }
1439 entry = e;
1440 index = i;
1441 return e != null;
1442 }
1443
1444 @SuppressWarnings("unchecked")
1445 public T nextElement() {
1446 Entry<?,?> et = entry;
1447 int i = index;
1448 Entry<?,?>[] t = table;
1449 /* Use locals for faster loop iteration */
1450 while (et == null && i > 0) {
1451 et = t[--i];
1452 }
1453 entry = et;
1454 index = i;
1455 if (et != null) {
1456 Entry<?,?> e = lastReturned = entry;
1457 entry = e.next;
1458 return type == KEYS ? (T)e.key : (type == VALUES ? (T)e.value : (T)e);
1459 }
1460 throw new NoSuchElementException("Hashtable Enumerator");
1461 }
1462
1463 // Iterator methods
1464 public boolean hasNext() {
1465 return hasMoreElements();
1466 }
1467
1468 public T next() {
1469 if (Hashtable.this.modCount != expectedModCount)
1470 throw new ConcurrentModificationException();
1471 return nextElement();
1472 }
1473
1474 public void remove() {
1475 if (!iterator)
1476 throw new UnsupportedOperationException();
1477 if (lastReturned == null)
1478 throw new IllegalStateException("Hashtable Enumerator");
1479 if (modCount != expectedModCount)
1480 throw new ConcurrentModificationException();
1481
1482 synchronized(Hashtable.this) {
1483 Entry<?,?>[] tab = Hashtable.this.table;
1484 int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length;
1485
1486 @SuppressWarnings("unchecked")
1487 Entry<K,V> e = (Entry<K,V>)tab[index];
1488 for(Entry<K,V> prev = null; e != null; prev = e, e = e.next) {
1489 if (e == lastReturned) {
1490 if (prev == null)
1491 tab[index] = e.next;
1492 else
1493 prev.next = e.next;
1494 expectedModCount++;
1495 lastReturned = null;
1496 Hashtable.this.modCount++;
1497 Hashtable.this.count--;
1498 return;
1499 }
1500 }
1501 throw new ConcurrentModificationException();
1502 }
1503 }
1504 }
1505 }