001 /* Hashtable.java -- a class providing a basic hashtable data structure,
002 mapping Object --> Object
003 Copyright (C) 1998, 1999, 2000, 2001, 2002, 2004, 2005, 2006
004 Free Software Foundation, Inc.
005
006 This file is part of GNU Classpath.
007
008 GNU Classpath is free software; you can redistribute it and/or modify
009 it under the terms of the GNU General Public License as published by
010 the Free Software Foundation; either version 2, or (at your option)
011 any later version.
012
013 GNU Classpath is distributed in the hope that it will be useful, but
014 WITHOUT ANY WARRANTY; without even the implied warranty of
015 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
016 General Public License for more details.
017
018 You should have received a copy of the GNU General Public License
019 along with GNU Classpath; see the file COPYING. If not, write to the
020 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
021 02110-1301 USA.
022
023 Linking this library statically or dynamically with other modules is
024 making a combined work based on this library. Thus, the terms and
025 conditions of the GNU General Public License cover the whole
026 combination.
027
028 As a special exception, the copyright holders of this library give you
029 permission to link this library with independent modules to produce an
030 executable, regardless of the license terms of these independent
031 modules, and to copy and distribute the resulting executable under
032 terms of your choice, provided that you also meet, for each linked
033 independent module, the terms and conditions of the license of that
034 module. An independent module is a module which is not derived from
035 or based on this library. If you modify this library, you may extend
036 this exception to your version of the library, but you are not
037 obligated to do so. If you do not wish to do so, delete this
038 exception statement from your version. */
039
040 package java.util;
041
042 import java.io.IOException;
043 import java.io.ObjectInputStream;
044 import java.io.ObjectOutputStream;
045 import java.io.Serializable;
046
047 // NOTE: This implementation is very similar to that of HashMap. If you fix
048 // a bug in here, chances are you should make a similar change to the HashMap
049 // code.
050
051 /**
052 * A class which implements a hashtable data structure.
053 * <p>
054 *
055 * This implementation of Hashtable uses a hash-bucket approach. That is:
056 * linear probing and rehashing is avoided; instead, each hashed value maps
057 * to a simple linked-list which, in the best case, only has one node.
058 * Assuming a large enough table, low enough load factor, and / or well
059 * implemented hashCode() methods, Hashtable should provide O(1)
060 * insertion, deletion, and searching of keys. Hashtable is O(n) in
061 * the worst case for all of these (if all keys hash to the same bucket).
062 * <p>
063 *
064 * This is a JDK-1.2 compliant implementation of Hashtable. As such, it
065 * belongs, partially, to the Collections framework (in that it implements
066 * Map). For backwards compatibility, it inherits from the obsolete and
067 * utterly useless Dictionary class.
068 * <p>
069 *
070 * Being a hybrid of old and new, Hashtable has methods which provide redundant
071 * capability, but with subtle and even crucial differences.
072 * For example, one can iterate over various aspects of a Hashtable with
073 * either an Iterator (which is the JDK-1.2 way of doing things) or with an
074 * Enumeration. The latter can end up in an undefined state if the Hashtable
075 * changes while the Enumeration is open.
076 * <p>
077 *
078 * Unlike HashMap, Hashtable does not accept `null' as a key value. Also,
079 * all accesses are synchronized: in a single thread environment, this is
080 * expensive, but in a multi-thread environment, this saves you the effort
081 * of extra synchronization. However, the old-style enumerators are not
082 * synchronized, because they can lead to unspecified behavior even if
083 * they were synchronized. You have been warned.
084 * <p>
085 *
086 * The iterators are <i>fail-fast</i>, meaning that any structural
087 * modification, except for <code>remove()</code> called on the iterator
088 * itself, cause the iterator to throw a
089 * <code>ConcurrentModificationException</code> rather than exhibit
090 * non-deterministic behavior.
091 *
092 * @author Jon Zeppieri
093 * @author Warren Levy
094 * @author Bryce McKinlay
095 * @author Eric Blake (ebb9@email.byu.edu)
096 * @see HashMap
097 * @see TreeMap
098 * @see IdentityHashMap
099 * @see LinkedHashMap
100 * @since 1.0
101 * @status updated to 1.4
102 */
103 public class Hashtable<K, V> extends Dictionary<K, V>
104 implements Map<K, V>, Cloneable, Serializable
105 {
106 // WARNING: Hashtable is a CORE class in the bootstrap cycle. See the
107 // comments in vm/reference/java/lang/Runtime for implications of this fact.
108
109 /** Default number of buckets. This is the value the JDK 1.3 uses. Some
110 * early documentation specified this value as 101. That is incorrect.
111 */
112 private static final int DEFAULT_CAPACITY = 11;
113
114 /**
115 * The default load factor; this is explicitly specified by the spec.
116 */
117 private static final float DEFAULT_LOAD_FACTOR = 0.75f;
118
119 /**
120 * Compatible with JDK 1.0+.
121 */
122 private static final long serialVersionUID = 1421746759512286392L;
123
124 /**
125 * The rounded product of the capacity and the load factor; when the number
126 * of elements exceeds the threshold, the Hashtable calls
127 * <code>rehash()</code>.
128 * @serial
129 */
130 private int threshold;
131
132 /**
133 * Load factor of this Hashtable: used in computing the threshold.
134 * @serial
135 */
136 private final float loadFactor;
137
138 /**
139 * Array containing the actual key-value mappings.
140 */
141 // Package visible for use by nested classes.
142 transient HashEntry<K, V>[] buckets;
143
144 /**
145 * Counts the number of modifications this Hashtable has undergone, used
146 * by Iterators to know when to throw ConcurrentModificationExceptions.
147 */
148 // Package visible for use by nested classes.
149 transient int modCount;
150
151 /**
152 * The size of this Hashtable: denotes the number of key-value pairs.
153 */
154 // Package visible for use by nested classes.
155 transient int size;
156
157 /**
158 * The cache for {@link #keySet()}.
159 */
160 private transient Set<K> keys;
161
162 /**
163 * The cache for {@link #values()}.
164 */
165 private transient Collection<V> values;
166
167 /**
168 * The cache for {@link #entrySet()}.
169 */
170 private transient Set<Map.Entry<K, V>> entries;
171
172 /**
173 * Class to represent an entry in the hash table. Holds a single key-value
174 * pair. A Hashtable Entry is identical to a HashMap Entry, except that
175 * `null' is not allowed for keys and values.
176 */
177 private static final class HashEntry<K, V>
178 extends AbstractMap.SimpleEntry<K, V>
179 {
180 /** The next entry in the linked list. */
181 HashEntry<K, V> next;
182
183 /**
184 * Simple constructor.
185 * @param key the key, already guaranteed non-null
186 * @param value the value, already guaranteed non-null
187 */
188 HashEntry(K key, V value)
189 {
190 super(key, value);
191 }
192
193 /**
194 * Resets the value.
195 * @param newVal the new value
196 * @return the prior value
197 * @throws NullPointerException if <code>newVal</code> is null
198 */
199 public V setValue(V newVal)
200 {
201 if (newVal == null)
202 throw new NullPointerException();
203 return super.setValue(newVal);
204 }
205 }
206
207 /**
208 * Construct a new Hashtable with the default capacity (11) and the default
209 * load factor (0.75).
210 */
211 public Hashtable()
212 {
213 this(DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR);
214 }
215
216 /**
217 * Construct a new Hashtable from the given Map, with initial capacity
218 * the greater of the size of <code>m</code> or the default of 11.
219 * <p>
220 *
221 * Every element in Map m will be put into this new Hashtable.
222 *
223 * @param m a Map whose key / value pairs will be put into
224 * the new Hashtable. <b>NOTE: key / value pairs
225 * are not cloned in this constructor.</b>
226 * @throws NullPointerException if m is null, or if m contains a mapping
227 * to or from `null'.
228 * @since 1.2
229 */
230 public Hashtable(Map<? extends K, ? extends V> m)
231 {
232 this(Math.max(m.size() * 2, DEFAULT_CAPACITY), DEFAULT_LOAD_FACTOR);
233 putAll(m);
234 }
235
236 /**
237 * Construct a new Hashtable with a specific inital capacity and
238 * default load factor of 0.75.
239 *
240 * @param initialCapacity the initial capacity of this Hashtable (>= 0)
241 * @throws IllegalArgumentException if (initialCapacity < 0)
242 */
243 public Hashtable(int initialCapacity)
244 {
245 this(initialCapacity, DEFAULT_LOAD_FACTOR);
246 }
247
248 /**
249 * Construct a new Hashtable with a specific initial capacity and
250 * load factor.
251 *
252 * @param initialCapacity the initial capacity (>= 0)
253 * @param loadFactor the load factor (> 0, not NaN)
254 * @throws IllegalArgumentException if (initialCapacity < 0) ||
255 * ! (loadFactor > 0.0)
256 */
257 public Hashtable(int initialCapacity, float loadFactor)
258 {
259 if (initialCapacity < 0)
260 throw new IllegalArgumentException("Illegal Capacity: "
261 + initialCapacity);
262 if (! (loadFactor > 0)) // check for NaN too
263 throw new IllegalArgumentException("Illegal Load: " + loadFactor);
264
265 if (initialCapacity == 0)
266 initialCapacity = 1;
267 buckets = (HashEntry<K, V>[]) new HashEntry[initialCapacity];
268 this.loadFactor = loadFactor;
269 threshold = (int) (initialCapacity * loadFactor);
270 }
271
272 /**
273 * Returns the number of key-value mappings currently in this hashtable.
274 * @return the size
275 */
276 public synchronized int size()
277 {
278 return size;
279 }
280
281 /**
282 * Returns true if there are no key-value mappings currently in this table.
283 * @return <code>size() == 0</code>
284 */
285 public synchronized boolean isEmpty()
286 {
287 return size == 0;
288 }
289
290 /**
291 * Return an enumeration of the keys of this table. There's no point
292 * in synchronizing this, as you have already been warned that the
293 * enumeration is not specified to be thread-safe.
294 *
295 * @return the keys
296 * @see #elements()
297 * @see #keySet()
298 */
299 public Enumeration<K> keys()
300 {
301 return new KeyEnumerator();
302 }
303
304 /**
305 * Return an enumeration of the values of this table. There's no point
306 * in synchronizing this, as you have already been warned that the
307 * enumeration is not specified to be thread-safe.
308 *
309 * @return the values
310 * @see #keys()
311 * @see #values()
312 */
313 public Enumeration<V> elements()
314 {
315 return new ValueEnumerator();
316 }
317
318 /**
319 * Returns true if this Hashtable contains a value <code>o</code>,
320 * such that <code>o.equals(value)</code>. This is the same as
321 * <code>containsValue()</code>, and is O(n).
322 * <p>
323 *
324 * @param value the value to search for in this Hashtable
325 * @return true if at least one key maps to the value
326 * @throws NullPointerException if <code>value</code> is null
327 * @see #containsValue(Object)
328 * @see #containsKey(Object)
329 */
330 public synchronized boolean contains(Object value)
331 {
332 if (value == null)
333 throw new NullPointerException();
334
335 for (int i = buckets.length - 1; i >= 0; i--)
336 {
337 HashEntry<K, V> e = buckets[i];
338 while (e != null)
339 {
340 if (e.value.equals(value))
341 return true;
342 e = e.next;
343 }
344 }
345
346 return false;
347 }
348
349 /**
350 * Returns true if this Hashtable contains a value <code>o</code>, such that
351 * <code>o.equals(value)</code>. This is the new API for the old
352 * <code>contains()</code>.
353 *
354 * @param value the value to search for in this Hashtable
355 * @return true if at least one key maps to the value
356 * @see #contains(Object)
357 * @see #containsKey(Object)
358 * @throws NullPointerException if <code>value</code> is null
359 * @since 1.2
360 */
361 public boolean containsValue(Object value)
362 {
363 // Delegate to older method to make sure code overriding it continues
364 // to work.
365 return contains(value);
366 }
367
368 /**
369 * Returns true if the supplied object <code>equals()</code> a key
370 * in this Hashtable.
371 *
372 * @param key the key to search for in this Hashtable
373 * @return true if the key is in the table
374 * @throws NullPointerException if key is null
375 * @see #containsValue(Object)
376 */
377 public synchronized boolean containsKey(Object key)
378 {
379 int idx = hash(key);
380 HashEntry<K, V> e = buckets[idx];
381 while (e != null)
382 {
383 if (e.key.equals(key))
384 return true;
385 e = e.next;
386 }
387 return false;
388 }
389
390 /**
391 * Return the value in this Hashtable associated with the supplied key,
392 * or <code>null</code> if the key maps to nothing.
393 *
394 * @param key the key for which to fetch an associated value
395 * @return what the key maps to, if present
396 * @throws NullPointerException if key is null
397 * @see #put(Object, Object)
398 * @see #containsKey(Object)
399 */
400 public synchronized V get(Object key)
401 {
402 int idx = hash(key);
403 HashEntry<K, V> e = buckets[idx];
404 while (e != null)
405 {
406 if (e.key.equals(key))
407 return e.value;
408 e = e.next;
409 }
410 return null;
411 }
412
413 /**
414 * Puts the supplied value into the Map, mapped by the supplied key.
415 * Neither parameter may be null. The value may be retrieved by any
416 * object which <code>equals()</code> this key.
417 *
418 * @param key the key used to locate the value
419 * @param value the value to be stored in the table
420 * @return the prior mapping of the key, or null if there was none
421 * @throws NullPointerException if key or value is null
422 * @see #get(Object)
423 * @see Object#equals(Object)
424 */
425 public synchronized V put(K key, V value)
426 {
427 int idx = hash(key);
428 HashEntry<K, V> e = buckets[idx];
429
430 // Check if value is null since it is not permitted.
431 if (value == null)
432 throw new NullPointerException();
433
434 while (e != null)
435 {
436 if (e.key.equals(key))
437 {
438 // Bypass e.setValue, since we already know value is non-null.
439 V r = e.value;
440 e.value = value;
441 return r;
442 }
443 else
444 {
445 e = e.next;
446 }
447 }
448
449 // At this point, we know we need to add a new entry.
450 modCount++;
451 if (++size > threshold)
452 {
453 rehash();
454 // Need a new hash value to suit the bigger table.
455 idx = hash(key);
456 }
457
458 e = new HashEntry<K, V>(key, value);
459
460 e.next = buckets[idx];
461 buckets[idx] = e;
462
463 return null;
464 }
465
466 /**
467 * Removes from the table and returns the value which is mapped by the
468 * supplied key. If the key maps to nothing, then the table remains
469 * unchanged, and <code>null</code> is returned.
470 *
471 * @param key the key used to locate the value to remove
472 * @return whatever the key mapped to, if present
473 */
474 public synchronized V remove(Object key)
475 {
476 int idx = hash(key);
477 HashEntry<K, V> e = buckets[idx];
478 HashEntry<K, V> last = null;
479
480 while (e != null)
481 {
482 if (e.key.equals(key))
483 {
484 modCount++;
485 if (last == null)
486 buckets[idx] = e.next;
487 else
488 last.next = e.next;
489 size--;
490 return e.value;
491 }
492 last = e;
493 e = e.next;
494 }
495 return null;
496 }
497
498 /**
499 * Copies all elements of the given map into this hashtable. However, no
500 * mapping can contain null as key or value. If this table already has
501 * a mapping for a key, the new mapping replaces the current one.
502 *
503 * @param m the map to be hashed into this
504 * @throws NullPointerException if m is null, or contains null keys or values
505 */
506 public synchronized void putAll(Map<? extends K, ? extends V> m)
507 {
508 final Map<K,V> addMap = (Map<K,V>) m;
509 final Iterator<Map.Entry<K,V>> it = addMap.entrySet().iterator();
510 while (it.hasNext())
511 {
512 final Map.Entry<K,V> e = it.next();
513 // Optimize in case the Entry is one of our own.
514 if (e instanceof AbstractMap.SimpleEntry)
515 {
516 AbstractMap.SimpleEntry<? extends K, ? extends V> entry
517 = (AbstractMap.SimpleEntry<? extends K, ? extends V>) e;
518 put(entry.key, entry.value);
519 }
520 else
521 {
522 put(e.getKey(), e.getValue());
523 }
524 }
525 }
526
527 /**
528 * Clears the hashtable so it has no keys. This is O(1).
529 */
530 public synchronized void clear()
531 {
532 if (size > 0)
533 {
534 modCount++;
535 Arrays.fill(buckets, null);
536 size = 0;
537 }
538 }
539
540 /**
541 * Returns a shallow clone of this Hashtable. The Map itself is cloned,
542 * but its contents are not. This is O(n).
543 *
544 * @return the clone
545 */
546 public synchronized Object clone()
547 {
548 Hashtable<K, V> copy = null;
549 try
550 {
551 copy = (Hashtable<K, V>) super.clone();
552 }
553 catch (CloneNotSupportedException x)
554 {
555 // This is impossible.
556 }
557 copy.buckets = (HashEntry<K, V>[]) new HashEntry[buckets.length];
558 copy.putAllInternal(this);
559 // Clear the caches.
560 copy.keys = null;
561 copy.values = null;
562 copy.entries = null;
563 return copy;
564 }
565
566 /**
567 * Converts this Hashtable to a String, surrounded by braces, and with
568 * key/value pairs listed with an equals sign between, separated by a
569 * comma and space. For example, <code>"{a=1, b=2}"</code>.<p>
570 *
571 * NOTE: if the <code>toString()</code> method of any key or value
572 * throws an exception, this will fail for the same reason.
573 *
574 * @return the string representation
575 */
576 public synchronized String toString()
577 {
578 // Since we are already synchronized, and entrySet().iterator()
579 // would repeatedly re-lock/release the monitor, we directly use the
580 // unsynchronized EntryIterator instead.
581 Iterator<Map.Entry<K, V>> entries = new EntryIterator();
582 StringBuffer r = new StringBuffer("{");
583 for (int pos = size; pos > 0; pos--)
584 {
585 r.append(entries.next());
586 if (pos > 1)
587 r.append(", ");
588 }
589 r.append("}");
590 return r.toString();
591 }
592
593 /**
594 * Returns a "set view" of this Hashtable's keys. The set is backed by
595 * the hashtable, so changes in one show up in the other. The set supports
596 * element removal, but not element addition. The set is properly
597 * synchronized on the original hashtable. Sun has not documented the
598 * proper interaction of null with this set, but has inconsistent behavior
599 * in the JDK. Therefore, in this implementation, contains, remove,
600 * containsAll, retainAll, removeAll, and equals just ignore a null key
601 * rather than throwing a {@link NullPointerException}.
602 *
603 * @return a set view of the keys
604 * @see #values()
605 * @see #entrySet()
606 * @since 1.2
607 */
608 public Set<K> keySet()
609 {
610 if (keys == null)
611 {
612 // Create a synchronized AbstractSet with custom implementations of
613 // those methods that can be overridden easily and efficiently.
614 Set<K> r = new AbstractSet<K>()
615 {
616 public int size()
617 {
618 return size;
619 }
620
621 public Iterator<K> iterator()
622 {
623 return new KeyIterator();
624 }
625
626 public void clear()
627 {
628 Hashtable.this.clear();
629 }
630
631 public boolean contains(Object o)
632 {
633 if (o == null)
634 return false;
635 return containsKey(o);
636 }
637
638 public boolean remove(Object o)
639 {
640 return Hashtable.this.remove(o) != null;
641 }
642 };
643 // We must specify the correct object to synchronize upon, hence the
644 // use of a non-public API
645 keys = new Collections.SynchronizedSet<K>(this, r);
646 }
647 return keys;
648 }
649
650 /**
651 * Returns a "collection view" (or "bag view") of this Hashtable's values.
652 * The collection is backed by the hashtable, so changes in one show up
653 * in the other. The collection supports element removal, but not element
654 * addition. The collection is properly synchronized on the original
655 * hashtable. Sun has not documented the proper interaction of null with
656 * this set, but has inconsistent behavior in the JDK. Therefore, in this
657 * implementation, contains, remove, containsAll, retainAll, removeAll, and
658 * equals just ignore a null value rather than throwing a
659 * {@link NullPointerException}.
660 *
661 * @return a bag view of the values
662 * @see #keySet()
663 * @see #entrySet()
664 * @since 1.2
665 */
666 public Collection<V> values()
667 {
668 if (values == null)
669 {
670 // We don't bother overriding many of the optional methods, as doing so
671 // wouldn't provide any significant performance advantage.
672 Collection<V> r = new AbstractCollection<V>()
673 {
674 public int size()
675 {
676 return size;
677 }
678
679 public Iterator<V> iterator()
680 {
681 return new ValueIterator();
682 }
683
684 public void clear()
685 {
686 Hashtable.this.clear();
687 }
688 };
689 // We must specify the correct object to synchronize upon, hence the
690 // use of a non-public API
691 values = new Collections.SynchronizedCollection<V>(this, r);
692 }
693 return values;
694 }
695
696 /**
697 * Returns a "set view" of this Hashtable's entries. The set is backed by
698 * the hashtable, so changes in one show up in the other. The set supports
699 * element removal, but not element addition. The set is properly
700 * synchronized on the original hashtable. Sun has not documented the
701 * proper interaction of null with this set, but has inconsistent behavior
702 * in the JDK. Therefore, in this implementation, contains, remove,
703 * containsAll, retainAll, removeAll, and equals just ignore a null entry,
704 * or an entry with a null key or value, rather than throwing a
705 * {@link NullPointerException}. However, calling entry.setValue(null)
706 * will fail.
707 * <p>
708 *
709 * Note that the iterators for all three views, from keySet(), entrySet(),
710 * and values(), traverse the hashtable in the same sequence.
711 *
712 * @return a set view of the entries
713 * @see #keySet()
714 * @see #values()
715 * @see Map.Entry
716 * @since 1.2
717 */
718 public Set<Map.Entry<K, V>> entrySet()
719 {
720 if (entries == null)
721 {
722 // Create an AbstractSet with custom implementations of those methods
723 // that can be overridden easily and efficiently.
724 Set<Map.Entry<K, V>> r = new AbstractSet<Map.Entry<K, V>>()
725 {
726 public int size()
727 {
728 return size;
729 }
730
731 public Iterator<Map.Entry<K, V>> iterator()
732 {
733 return new EntryIterator();
734 }
735
736 public void clear()
737 {
738 Hashtable.this.clear();
739 }
740
741 public boolean contains(Object o)
742 {
743 return getEntry(o) != null;
744 }
745
746 public boolean remove(Object o)
747 {
748 HashEntry<K, V> e = getEntry(o);
749 if (e != null)
750 {
751 Hashtable.this.remove(e.key);
752 return true;
753 }
754 return false;
755 }
756 };
757 // We must specify the correct object to synchronize upon, hence the
758 // use of a non-public API
759 entries = new Collections.SynchronizedSet<Map.Entry<K, V>>(this, r);
760 }
761 return entries;
762 }
763
764 /**
765 * Returns true if this Hashtable equals the supplied Object <code>o</code>.
766 * As specified by Map, this is:
767 * <code>
768 * (o instanceof Map) && entrySet().equals(((Map) o).entrySet());
769 * </code>
770 *
771 * @param o the object to compare to
772 * @return true if o is an equal map
773 * @since 1.2
774 */
775 public boolean equals(Object o)
776 {
777 // no need to synchronize, entrySet().equals() does that.
778 if (o == this)
779 return true;
780 if (!(o instanceof Map))
781 return false;
782
783 return entrySet().equals(((Map) o).entrySet());
784 }
785
786 /**
787 * Returns the hashCode for this Hashtable. As specified by Map, this is
788 * the sum of the hashCodes of all of its Map.Entry objects
789 *
790 * @return the sum of the hashcodes of the entries
791 * @since 1.2
792 */
793 public synchronized int hashCode()
794 {
795 // Since we are already synchronized, and entrySet().iterator()
796 // would repeatedly re-lock/release the monitor, we directly use the
797 // unsynchronized EntryIterator instead.
798 Iterator<Map.Entry<K, V>> itr = new EntryIterator();
799 int hashcode = 0;
800 for (int pos = size; pos > 0; pos--)
801 hashcode += itr.next().hashCode();
802
803 return hashcode;
804 }
805
806 /**
807 * Helper method that returns an index in the buckets array for `key'
808 * based on its hashCode().
809 *
810 * @param key the key
811 * @return the bucket number
812 * @throws NullPointerException if key is null
813 */
814 private int hash(Object key)
815 {
816 // Note: Inline Math.abs here, for less method overhead, and to avoid
817 // a bootstrap dependency, since Math relies on native methods.
818 int hash = key.hashCode() % buckets.length;
819 return hash < 0 ? -hash : hash;
820 }
821
822 /**
823 * Helper method for entrySet(), which matches both key and value
824 * simultaneously. Ignores null, as mentioned in entrySet().
825 *
826 * @param o the entry to match
827 * @return the matching entry, if found, or null
828 * @see #entrySet()
829 */
830 // Package visible, for use in nested classes.
831 HashEntry<K, V> getEntry(Object o)
832 {
833 if (! (o instanceof Map.Entry))
834 return null;
835 K key = ((Map.Entry<K, V>) o).getKey();
836 if (key == null)
837 return null;
838
839 int idx = hash(key);
840 HashEntry<K, V> e = buckets[idx];
841 while (e != null)
842 {
843 if (e.equals(o))
844 return e;
845 e = e.next;
846 }
847 return null;
848 }
849
850 /**
851 * A simplified, more efficient internal implementation of putAll(). clone()
852 * should not call putAll or put, in order to be compatible with the JDK
853 * implementation with respect to subclasses.
854 *
855 * @param m the map to initialize this from
856 */
857 void putAllInternal(Map<? extends K, ? extends V> m)
858 {
859 final Map<K,V> addMap = (Map<K,V>) m;
860 final Iterator<Map.Entry<K,V>> it = addMap.entrySet().iterator();
861 size = 0;
862 while (it.hasNext())
863 {
864 final Map.Entry<K,V> e = it.next();
865 size++;
866 K key = e.getKey();
867 int idx = hash(key);
868 HashEntry<K, V> he = new HashEntry<K, V>(key, e.getValue());
869 he.next = buckets[idx];
870 buckets[idx] = he;
871 }
872 }
873
874 /**
875 * Increases the size of the Hashtable and rehashes all keys to new array
876 * indices; this is called when the addition of a new value would cause
877 * size() > threshold. Note that the existing Entry objects are reused in
878 * the new hash table.
879 * <p>
880 *
881 * This is not specified, but the new size is twice the current size plus
882 * one; this number is not always prime, unfortunately. This implementation
883 * is not synchronized, as it is only invoked from synchronized methods.
884 */
885 protected void rehash()
886 {
887 HashEntry<K, V>[] oldBuckets = buckets;
888
889 int newcapacity = (buckets.length * 2) + 1;
890 threshold = (int) (newcapacity * loadFactor);
891 buckets = (HashEntry<K, V>[]) new HashEntry[newcapacity];
892
893 for (int i = oldBuckets.length - 1; i >= 0; i--)
894 {
895 HashEntry<K, V> e = oldBuckets[i];
896 while (e != null)
897 {
898 int idx = hash(e.key);
899 HashEntry<K, V> dest = buckets[idx];
900
901 if (dest != null)
902 {
903 HashEntry next = dest.next;
904 while (next != null)
905 {
906 dest = next;
907 next = dest.next;
908 }
909 dest.next = e;
910 }
911 else
912 {
913 buckets[idx] = e;
914 }
915
916 HashEntry<K, V> next = e.next;
917 e.next = null;
918 e = next;
919 }
920 }
921 }
922
923 /**
924 * Serializes this object to the given stream.
925 *
926 * @param s the stream to write to
927 * @throws IOException if the underlying stream fails
928 * @serialData the <i>capacity</i> (int) that is the length of the
929 * bucket array, the <i>size</i> (int) of the hash map
930 * are emitted first. They are followed by size entries,
931 * each consisting of a key (Object) and a value (Object).
932 */
933 private synchronized void writeObject(ObjectOutputStream s)
934 throws IOException
935 {
936 // Write the threshold and loadFactor fields.
937 s.defaultWriteObject();
938
939 s.writeInt(buckets.length);
940 s.writeInt(size);
941 // Since we are already synchronized, and entrySet().iterator()
942 // would repeatedly re-lock/release the monitor, we directly use the
943 // unsynchronized EntryIterator instead.
944 Iterator<Map.Entry<K, V>> it = new EntryIterator();
945 while (it.hasNext())
946 {
947 HashEntry<K, V> entry = (HashEntry<K, V>) it.next();
948 s.writeObject(entry.key);
949 s.writeObject(entry.value);
950 }
951 }
952
953 /**
954 * Deserializes this object from the given stream.
955 *
956 * @param s the stream to read from
957 * @throws ClassNotFoundException if the underlying stream fails
958 * @throws IOException if the underlying stream fails
959 * @serialData the <i>capacity</i> (int) that is the length of the
960 * bucket array, the <i>size</i> (int) of the hash map
961 * are emitted first. They are followed by size entries,
962 * each consisting of a key (Object) and a value (Object).
963 */
964 private void readObject(ObjectInputStream s)
965 throws IOException, ClassNotFoundException
966 {
967 // Read the threshold and loadFactor fields.
968 s.defaultReadObject();
969
970 // Read and use capacity.
971 buckets = (HashEntry<K, V>[]) new HashEntry[s.readInt()];
972 int len = s.readInt();
973
974 // Read and use key/value pairs.
975 // TODO: should we be defensive programmers, and check for illegal nulls?
976 while (--len >= 0)
977 put((K) s.readObject(), (V) s.readObject());
978 }
979
980 /**
981 * A class which implements the Iterator interface and is used for
982 * iterating over Hashtables.
983 * This implementation iterates entries. Subclasses are used to
984 * iterate key and values. It also allows the removal of elements,
985 * as per the Javasoft spec. Note that it is not synchronized; this
986 * is a performance enhancer since it is never exposed externally
987 * and is only used within synchronized blocks above.
988 *
989 * @author Jon Zeppieri
990 * @author Fridjof Siebert
991 */
992 private class EntryIterator
993 implements Iterator<Entry<K,V>>
994 {
995 /**
996 * The number of modifications to the backing Hashtable that we know about.
997 */
998 int knownMod = modCount;
999 /** The number of elements remaining to be returned by next(). */
1000 int count = size;
1001 /** Current index in the physical hash table. */
1002 int idx = buckets.length;
1003 /** The last Entry returned by a next() call. */
1004 HashEntry<K, V> last;
1005 /**
1006 * The next entry that should be returned by next(). It is set to something
1007 * if we're iterating through a bucket that contains multiple linked
1008 * entries. It is null if next() needs to find a new bucket.
1009 */
1010 HashEntry<K, V> next;
1011
1012 /**
1013 * Construct a new EntryIterator
1014 */
1015 EntryIterator()
1016 {
1017 }
1018
1019
1020 /**
1021 * Returns true if the Iterator has more elements.
1022 * @return true if there are more elements
1023 */
1024 public boolean hasNext()
1025 {
1026 return count > 0;
1027 }
1028
1029 /**
1030 * Returns the next element in the Iterator's sequential view.
1031 * @return the next element
1032 * @throws ConcurrentModificationException if the hashtable was modified
1033 * @throws NoSuchElementException if there is none
1034 */
1035 public Map.Entry<K,V> next()
1036 {
1037 if (knownMod != modCount)
1038 throw new ConcurrentModificationException();
1039 if (count == 0)
1040 throw new NoSuchElementException();
1041 count--;
1042 HashEntry<K, V> e = next;
1043
1044 while (e == null)
1045 if (idx <= 0)
1046 return null;
1047 else
1048 e = buckets[--idx];
1049
1050 next = e.next;
1051 last = e;
1052 return e;
1053 }
1054
1055 /**
1056 * Removes from the backing Hashtable the last element which was fetched
1057 * with the <code>next()</code> method.
1058 * @throws ConcurrentModificationException if the hashtable was modified
1059 * @throws IllegalStateException if called when there is no last element
1060 */
1061 public void remove()
1062 {
1063 if (knownMod != modCount)
1064 throw new ConcurrentModificationException();
1065 if (last == null)
1066 throw new IllegalStateException();
1067
1068 Hashtable.this.remove(last.key);
1069 last = null;
1070 knownMod++;
1071 }
1072 } // class EntryIterator
1073
1074 /**
1075 * A class which implements the Iterator interface and is used for
1076 * iterating over keys in Hashtables. This class uses an
1077 * <code>EntryIterator</code> to obtain the keys of each entry.
1078 *
1079 * @author Fridtjof Siebert
1080 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
1081 */
1082 private class KeyIterator
1083 implements Iterator<K>
1084 {
1085
1086 /**
1087 * This entry iterator is used for most operations. Only
1088 * <code>next()</code> gives a different result, by returning just
1089 * the key rather than the whole element.
1090 */
1091 private EntryIterator iterator;
1092
1093 /**
1094 * Construct a new KeyIterator
1095 */
1096 KeyIterator()
1097 {
1098 iterator = new EntryIterator();
1099 }
1100
1101
1102 /**
1103 * Returns true if the entry iterator has more elements.
1104 *
1105 * @return true if there are more elements
1106 * @throws ConcurrentModificationException if the hashtable was modified
1107 */
1108 public boolean hasNext()
1109 {
1110 return iterator.hasNext();
1111 }
1112
1113 /**
1114 * Returns the next element in the Iterator's sequential view.
1115 *
1116 * @return the next element
1117 *
1118 * @throws ConcurrentModificationException if the hashtable was modified
1119 * @throws NoSuchElementException if there is none
1120 */
1121 public K next()
1122 {
1123 return ((HashEntry<K,V>) iterator.next()).key;
1124 }
1125
1126 /**
1127 * Removes the last element used by the <code>next()</code> method
1128 * using the entry iterator.
1129 *
1130 * @throws ConcurrentModificationException if the hashtable was modified
1131 * @throws IllegalStateException if called when there is no last element
1132 */
1133 public void remove()
1134 {
1135 iterator.remove();
1136 }
1137 } // class KeyIterator
1138
1139 /**
1140 * A class which implements the Iterator interface and is used for
1141 * iterating over values in Hashtables. This class uses an
1142 * <code>EntryIterator</code> to obtain the values of each entry.
1143 *
1144 * @author Fridtjof Siebert
1145 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
1146 */
1147 private class ValueIterator
1148 implements Iterator<V>
1149 {
1150
1151 /**
1152 * This entry iterator is used for most operations. Only
1153 * <code>next()</code> gives a different result, by returning just
1154 * the value rather than the whole element.
1155 */
1156 private EntryIterator iterator;
1157
1158 /**
1159 * Construct a new KeyIterator
1160 */
1161 ValueIterator()
1162 {
1163 iterator = new EntryIterator();
1164 }
1165
1166
1167 /**
1168 * Returns true if the entry iterator has more elements.
1169 *
1170 * @return true if there are more elements
1171 * @throws ConcurrentModificationException if the hashtable was modified
1172 */
1173 public boolean hasNext()
1174 {
1175 return iterator.hasNext();
1176 }
1177
1178 /**
1179 * Returns the value of the next element in the iterator's sequential view.
1180 *
1181 * @return the next value
1182 *
1183 * @throws ConcurrentModificationException if the hashtable was modified
1184 * @throws NoSuchElementException if there is none
1185 */
1186 public V next()
1187 {
1188 return ((HashEntry<K,V>) iterator.next()).value;
1189 }
1190
1191 /**
1192 * Removes the last element used by the <code>next()</code> method
1193 * using the entry iterator.
1194 *
1195 * @throws ConcurrentModificationException if the hashtable was modified
1196 * @throws IllegalStateException if called when there is no last element
1197 */
1198 public void remove()
1199 {
1200 iterator.remove();
1201 }
1202
1203 } // class ValueIterator
1204
1205 /**
1206 * Enumeration view of the entries in this Hashtable, providing
1207 * sequential access to its elements.
1208 *
1209 * <b>NOTE</b>: Enumeration is not safe if new elements are put in the table
1210 * as this could cause a rehash and we'd completely lose our place. Even
1211 * without a rehash, it is undetermined if a new element added would
1212 * appear in the enumeration. The spec says nothing about this, but
1213 * the "Java Class Libraries" book implies that modifications to the
1214 * hashtable during enumeration causes indeterminate results. Don't do it!
1215 *
1216 * @author Jon Zeppieri
1217 * @author Fridjof Siebert
1218 */
1219 private class EntryEnumerator
1220 implements Enumeration<Entry<K,V>>
1221 {
1222 /** The number of elements remaining to be returned by next(). */
1223 int count = size;
1224 /** Current index in the physical hash table. */
1225 int idx = buckets.length;
1226 /**
1227 * Entry which will be returned by the next nextElement() call. It is
1228 * set if we are iterating through a bucket with multiple entries, or null
1229 * if we must look in the next bucket.
1230 */
1231 HashEntry<K, V> next;
1232
1233 /**
1234 * Construct the enumeration.
1235 */
1236 EntryEnumerator()
1237 {
1238 // Nothing to do here.
1239 }
1240
1241 /**
1242 * Checks whether more elements remain in the enumeration.
1243 * @return true if nextElement() will not fail.
1244 */
1245 public boolean hasMoreElements()
1246 {
1247 return count > 0;
1248 }
1249
1250 /**
1251 * Returns the next element.
1252 * @return the next element
1253 * @throws NoSuchElementException if there is none.
1254 */
1255 public Map.Entry<K,V> nextElement()
1256 {
1257 if (count == 0)
1258 throw new NoSuchElementException("Hashtable Enumerator");
1259 count--;
1260 HashEntry<K, V> e = next;
1261
1262 while (e == null)
1263 if (idx <= 0)
1264 return null;
1265 else
1266 e = buckets[--idx];
1267
1268 next = e.next;
1269 return e;
1270 }
1271 } // class EntryEnumerator
1272
1273
1274 /**
1275 * Enumeration view of this Hashtable, providing sequential access to its
1276 * elements.
1277 *
1278 * <b>NOTE</b>: Enumeration is not safe if new elements are put in the table
1279 * as this could cause a rehash and we'd completely lose our place. Even
1280 * without a rehash, it is undetermined if a new element added would
1281 * appear in the enumeration. The spec says nothing about this, but
1282 * the "Java Class Libraries" book implies that modifications to the
1283 * hashtable during enumeration causes indeterminate results. Don't do it!
1284 *
1285 * @author Jon Zeppieri
1286 * @author Fridjof Siebert
1287 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
1288 */
1289 private final class KeyEnumerator
1290 implements Enumeration<K>
1291 {
1292 /**
1293 * This entry enumerator is used for most operations. Only
1294 * <code>nextElement()</code> gives a different result, by returning just
1295 * the key rather than the whole element.
1296 */
1297 private EntryEnumerator enumerator;
1298
1299 /**
1300 * Construct a new KeyEnumerator
1301 */
1302 KeyEnumerator()
1303 {
1304 enumerator = new EntryEnumerator();
1305 }
1306
1307
1308 /**
1309 * Returns true if the entry enumerator has more elements.
1310 *
1311 * @return true if there are more elements
1312 * @throws ConcurrentModificationException if the hashtable was modified
1313 */
1314 public boolean hasMoreElements()
1315 {
1316 return enumerator.hasMoreElements();
1317 }
1318
1319 /**
1320 * Returns the next element.
1321 * @return the next element
1322 * @throws NoSuchElementException if there is none.
1323 */
1324 public K nextElement()
1325 {
1326 HashEntry<K,V> entry = (HashEntry<K,V>) enumerator.nextElement();
1327 K retVal = null;
1328 if (entry != null)
1329 retVal = entry.key;
1330 return retVal;
1331 }
1332 } // class KeyEnumerator
1333
1334
1335 /**
1336 * Enumeration view of this Hashtable, providing sequential access to its
1337 * values.
1338 *
1339 * <b>NOTE</b>: Enumeration is not safe if new elements are put in the table
1340 * as this could cause a rehash and we'd completely lose our place. Even
1341 * without a rehash, it is undetermined if a new element added would
1342 * appear in the enumeration. The spec says nothing about this, but
1343 * the "Java Class Libraries" book implies that modifications to the
1344 * hashtable during enumeration causes indeterminate results. Don't do it!
1345 *
1346 * @author Jon Zeppieri
1347 * @author Fridjof Siebert
1348 * @author Andrew John Hughes (gnu_andrew@member.fsf.org)
1349 */
1350 private final class ValueEnumerator
1351 implements Enumeration<V>
1352 {
1353 /**
1354 * This entry enumerator is used for most operations. Only
1355 * <code>nextElement()</code> gives a different result, by returning just
1356 * the value rather than the whole element.
1357 */
1358 private EntryEnumerator enumerator;
1359
1360 /**
1361 * Construct a new ValueEnumerator
1362 */
1363 ValueEnumerator()
1364 {
1365 enumerator = new EntryEnumerator();
1366 }
1367
1368
1369 /**
1370 * Returns true if the entry enumerator has more elements.
1371 *
1372 * @return true if there are more elements
1373 * @throws ConcurrentModificationException if the hashtable was modified
1374 */
1375 public boolean hasMoreElements()
1376 {
1377 return enumerator.hasMoreElements();
1378 }
1379
1380 /**
1381 * Returns the next element.
1382 * @return the next element
1383 * @throws NoSuchElementException if there is none.
1384 */
1385 public V nextElement()
1386 {
1387 HashEntry<K,V> entry = (HashEntry<K,V>) enumerator.nextElement();
1388 V retVal = null;
1389 if (entry != null)
1390 retVal = entry.value;
1391 return retVal;
1392 }
1393 } // class ValueEnumerator
1394
1395 } // class Hashtable