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
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 }
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))},
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 }
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());
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))
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 }
|
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} 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}
39 * method and the {@code equals} method. <p>
40 *
41 * An instance of {@code Hashtable} 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 * {@code Hashtable} operations, including {@code get} and {@code put}).<p>
57 *
58 * The initial capacity controls a tradeoff between wasted space and the
59 * need for {@code rehash} operations, which are time-consuming.
60 * No {@code rehash} operations will <i>ever</i> occur if the initial
61 * capacity is greater than the maximum number of entries the
62 * {@code Hashtable} 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},
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 {@code iterator} 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 * {@code remove} 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 {@code ConcurrentModificationException} 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
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} if this hashtable maps no keys to values;
245 * {@code false} 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 }
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} if and only if some key maps to the
294 * {@code value} argument in this hashtable as
295 * determined by the {@code equals} method;
296 * {@code false} otherwise.
297 * @exception NullPointerException if the value is {@code null}
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 {@code true} if this map maps one or more keys to the
323 * specified value
324 * @throws NullPointerException if the value is {@code null}
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} if and only if the specified object
336 * is a key in this hashtable, as determined by the
337 * {@code equals} method; {@code false} otherwise.
338 * @throws NullPointerException if the key is {@code null}
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))},
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} to the specified
448 * {@code value} in this hashtable. Neither the key nor the
449 * value can be {@code null}. <p>
450 *
451 * The value can be retrieved by calling the {@code get} 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} if it did not have one
458 * @exception NullPointerException if the key or value is
459 * {@code null}
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} if the key did not have a mapping
494 * @throws NullPointerException if the key is {@code null}
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 }
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 {@code Hashtable} object
572 * in the form of a set of entries, enclosed in braces and separated
573 * by the ASCII characters "<code> , </code>" (comma and space). Each
574 * entry is rendered as the key, an equals sign {@code =}, and the
575 * associated element, where the {@code toString} 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());
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 {@code remove} 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 * {@code Iterator.remove}, {@code Set.remove},
640 * {@code removeAll}, {@code retainAll}, and {@code clear}
641 * operations. It does not support the {@code add} or {@code addAll}
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 {@code remove} operation, or through the
676 * {@code setValue} 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 {@code Iterator.remove},
680 * {@code Set.remove}, {@code removeAll}, {@code retainAll} and
681 * {@code clear} operations. It does not support the
682 * {@code add} or {@code addAll} 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))
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 {@code remove} 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 {@code Iterator.remove},
761 * {@code Collection.remove}, {@code removeAll},
762 * {@code retainAll} and {@code clear} operations. It does not
763 * support the {@code add} or {@code addAll} 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 }
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