001 /*
002 * Copyright 1997-2007 Sun Microsystems, Inc. All Rights Reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation. Sun designates this
008 * particular file as subject to the "Classpath" exception as provided
009 * by Sun in the LICENSE file that accompanied this code.
010 *
011 * This code is distributed in the hope that it will be useful, but WITHOUT
012 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014 * version 2 for more details (a copy is included in the LICENSE file that
015 * accompanied this code).
016 *
017 * You should have received a copy of the GNU General Public License version
018 * 2 along with this work; if not, write to the Free Software Foundation,
019 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020 *
021 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022 * CA 95054 USA or visit www.sun.com if you need additional information or
023 * have any questions.
024 */
025
026 package java.util;
027
028 import java.util.Map.Entry;
029
030 /**
031 * This class provides a skeletal implementation of the <tt>Map</tt>
032 * interface, to minimize the effort required to implement this interface.
033 *
034 * <p>To implement an unmodifiable map, the programmer needs only to extend this
035 * class and provide an implementation for the <tt>entrySet</tt> method, which
036 * returns a set-view of the map's mappings. Typically, the returned set
037 * will, in turn, be implemented atop <tt>AbstractSet</tt>. This set should
038 * not support the <tt>add</tt> or <tt>remove</tt> methods, and its iterator
039 * should not support the <tt>remove</tt> method.
040 *
041 * <p>To implement a modifiable map, the programmer must additionally override
042 * this class's <tt>put</tt> method (which otherwise throws an
043 * <tt>UnsupportedOperationException</tt>), and the iterator returned by
044 * <tt>entrySet().iterator()</tt> must additionally implement its
045 * <tt>remove</tt> method.
046 *
047 * <p>The programmer should generally provide a void (no argument) and map
048 * constructor, as per the recommendation in the <tt>Map</tt> interface
049 * specification.
050 *
051 * <p>The documentation for each non-abstract method in this class describes its
052 * implementation in detail. Each of these methods may be overridden if the
053 * map being implemented admits a more efficient implementation.
054 *
055 * <p>This class is a member of the
056 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
057 * Java Collections Framework</a>.
058 *
059 * @param <K> the type of keys maintained by this map
060 * @param <V> the type of mapped values
061 *
062 * @author Josh Bloch
063 * @author Neal Gafter
064 * @version 1.57, 06/12/07
065 * @see Map
066 * @see Collection
067 * @since 1.2
068 */
069
070 public abstract class AbstractMap<K, V> implements Map<K, V> {
071 /**
072 * Sole constructor. (For invocation by subclass constructors, typically
073 * implicit.)
074 */
075 protected AbstractMap() {
076 }
077
078 // Query Operations
079
080 /**
081 * {@inheritDoc}
082 *
083 * <p>This implementation returns <tt>entrySet().size()</tt>.
084 */
085 public int size() {
086 return entrySet().size();
087 }
088
089 /**
090 * {@inheritDoc}
091 *
092 * <p>This implementation returns <tt>size() == 0</tt>.
093 */
094 public boolean isEmpty() {
095 return size() == 0;
096 }
097
098 /**
099 * {@inheritDoc}
100 *
101 * <p>This implementation iterates over <tt>entrySet()</tt> searching
102 * for an entry with the specified value. If such an entry is found,
103 * <tt>true</tt> is returned. If the iteration terminates without
104 * finding such an entry, <tt>false</tt> is returned. Note that this
105 * implementation requires linear time in the size of the map.
106 *
107 * @throws ClassCastException {@inheritDoc}
108 * @throws NullPointerException {@inheritDoc}
109 */
110 public boolean containsValue(Object value) {
111 Iterator<Entry<K, V>> i = entrySet().iterator();
112 if (value == null) {
113 while (i.hasNext()) {
114 Entry<K, V> e = i.next();
115 if (e.getValue() == null)
116 return true;
117 }
118 } else {
119 while (i.hasNext()) {
120 Entry<K, V> e = i.next();
121 if (value.equals(e.getValue()))
122 return true;
123 }
124 }
125 return false;
126 }
127
128 /**
129 * {@inheritDoc}
130 *
131 * <p>This implementation iterates over <tt>entrySet()</tt> searching
132 * for an entry with the specified key. If such an entry is found,
133 * <tt>true</tt> is returned. If the iteration terminates without
134 * finding such an entry, <tt>false</tt> is returned. Note that this
135 * implementation requires linear time in the size of the map; many
136 * implementations will override this method.
137 *
138 * @throws ClassCastException {@inheritDoc}
139 * @throws NullPointerException {@inheritDoc}
140 */
141 public boolean containsKey(Object key) {
142 Iterator<Map.Entry<K, V>> i = entrySet().iterator();
143 if (key == null) {
144 while (i.hasNext()) {
145 Entry<K, V> e = i.next();
146 if (e.getKey() == null)
147 return true;
148 }
149 } else {
150 while (i.hasNext()) {
151 Entry<K, V> e = i.next();
152 if (key.equals(e.getKey()))
153 return true;
154 }
155 }
156 return false;
157 }
158
159 /**
160 * {@inheritDoc}
161 *
162 * <p>This implementation iterates over <tt>entrySet()</tt> searching
163 * for an entry with the specified key. If such an entry is found,
164 * the entry's value is returned. If the iteration terminates without
165 * finding such an entry, <tt>null</tt> is returned. Note that this
166 * implementation requires linear time in the size of the map; many
167 * implementations will override this method.
168 *
169 * @throws ClassCastException {@inheritDoc}
170 * @throws NullPointerException {@inheritDoc}
171 */
172 public V get(Object key) {
173 Iterator<Entry<K, V>> i = entrySet().iterator();
174 if (key == null) {
175 while (i.hasNext()) {
176 Entry<K, V> e = i.next();
177 if (e.getKey() == null)
178 return e.getValue();
179 }
180 } else {
181 while (i.hasNext()) {
182 Entry<K, V> e = i.next();
183 if (key.equals(e.getKey()))
184 return e.getValue();
185 }
186 }
187 return null;
188 }
189
190 // Modification Operations
191
192 /**
193 * {@inheritDoc}
194 *
195 * <p>This implementation always throws an
196 * <tt>UnsupportedOperationException</tt>.
197 *
198 * @throws UnsupportedOperationException {@inheritDoc}
199 * @throws ClassCastException {@inheritDoc}
200 * @throws NullPointerException {@inheritDoc}
201 * @throws IllegalArgumentException {@inheritDoc}
202 */
203 public V put(K key, V value) {
204 throw new UnsupportedOperationException();
205 }
206
207 /**
208 * {@inheritDoc}
209 *
210 * <p>This implementation iterates over <tt>entrySet()</tt> searching for an
211 * entry with the specified key. If such an entry is found, its value is
212 * obtained with its <tt>getValue</tt> operation, the entry is removed
213 * from the collection (and the backing map) with the iterator's
214 * <tt>remove</tt> operation, and the saved value is returned. If the
215 * iteration terminates without finding such an entry, <tt>null</tt> is
216 * returned. Note that this implementation requires linear time in the
217 * size of the map; many implementations will override this method.
218 *
219 * <p>Note that this implementation throws an
220 * <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>
221 * iterator does not support the <tt>remove</tt> method and this map
222 * contains a mapping for the specified key.
223 *
224 * @throws UnsupportedOperationException {@inheritDoc}
225 * @throws ClassCastException {@inheritDoc}
226 * @throws NullPointerException {@inheritDoc}
227 */
228 public V remove(Object key) {
229 Iterator<Entry<K, V>> i = entrySet().iterator();
230 Entry<K, V> correctEntry = null;
231 if (key == null) {
232 while (correctEntry == null && i.hasNext()) {
233 Entry<K, V> e = i.next();
234 if (e.getKey() == null)
235 correctEntry = e;
236 }
237 } else {
238 while (correctEntry == null && i.hasNext()) {
239 Entry<K, V> e = i.next();
240 if (key.equals(e.getKey()))
241 correctEntry = e;
242 }
243 }
244
245 V oldValue = null;
246 if (correctEntry != null) {
247 oldValue = correctEntry.getValue();
248 i.remove();
249 }
250 return oldValue;
251 }
252
253 // Bulk Operations
254
255 /**
256 * {@inheritDoc}
257 *
258 * <p>This implementation iterates over the specified map's
259 * <tt>entrySet()</tt> collection, and calls this map's <tt>put</tt>
260 * operation once for each entry returned by the iteration.
261 *
262 * <p>Note that this implementation throws an
263 * <tt>UnsupportedOperationException</tt> if this map does not support
264 * the <tt>put</tt> operation and the specified map is nonempty.
265 *
266 * @throws UnsupportedOperationException {@inheritDoc}
267 * @throws ClassCastException {@inheritDoc}
268 * @throws NullPointerException {@inheritDoc}
269 * @throws IllegalArgumentException {@inheritDoc}
270 */
271 public void putAll(Map<? extends K, ? extends V> m) {
272 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
273 put(e.getKey(), e.getValue());
274 }
275
276 /**
277 * {@inheritDoc}
278 *
279 * <p>This implementation calls <tt>entrySet().clear()</tt>.
280 *
281 * <p>Note that this implementation throws an
282 * <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>
283 * does not support the <tt>clear</tt> operation.
284 *
285 * @throws UnsupportedOperationException {@inheritDoc}
286 */
287 public void clear() {
288 entrySet().clear();
289 }
290
291 // Views
292
293 /**
294 * Each of these fields are initialized to contain an instance of the
295 * appropriate view the first time this view is requested. The views are
296 * stateless, so there's no reason to create more than one of each.
297 */
298 transient volatile Set<K> keySet = null;
299 transient volatile Collection<V> values = null;
300
301 /**
302 * {@inheritDoc}
303 *
304 * <p>This implementation returns a set that subclasses {@link AbstractSet}.
305 * The subclass's iterator method returns a "wrapper object" over this
306 * map's <tt>entrySet()</tt> iterator. The <tt>size</tt> method
307 * delegates to this map's <tt>size</tt> method and the
308 * <tt>contains</tt> method delegates to this map's
309 * <tt>containsKey</tt> method.
310 *
311 * <p>The set is created the first time this method is called,
312 * and returned in response to all subsequent calls. No synchronization
313 * is performed, so there is a slight chance that multiple calls to this
314 * method will not all return the same set.
315 */
316 public Set<K> keySet() {
317 if (keySet == null) {
318 keySet = new AbstractSet<K>() {
319 public Iterator<K> iterator() {
320 return new Iterator<K>() {
321 private Iterator<Entry<K, V>> i = entrySet()
322 .iterator();
323
324 public boolean hasNext() {
325 return i.hasNext();
326 }
327
328 public K next() {
329 return i.next().getKey();
330 }
331
332 public void remove() {
333 i.remove();
334 }
335 };
336 }
337
338 public int size() {
339 return AbstractMap.this .size();
340 }
341
342 public boolean isEmpty() {
343 return AbstractMap.this .isEmpty();
344 }
345
346 public void clear() {
347 AbstractMap.this .clear();
348 }
349
350 public boolean contains(Object k) {
351 return AbstractMap.this .containsKey(k);
352 }
353 };
354 }
355 return keySet;
356 }
357
358 /**
359 * {@inheritDoc}
360 *
361 * <p>This implementation returns a collection that subclasses {@link
362 * AbstractCollection}. The subclass's iterator method returns a
363 * "wrapper object" over this map's <tt>entrySet()</tt> iterator.
364 * The <tt>size</tt> method delegates to this map's <tt>size</tt>
365 * method and the <tt>contains</tt> method delegates to this map's
366 * <tt>containsValue</tt> method.
367 *
368 * <p>The collection is created the first time this method is called, and
369 * returned in response to all subsequent calls. No synchronization is
370 * performed, so there is a slight chance that multiple calls to this
371 * method will not all return the same collection.
372 */
373 public Collection<V> values() {
374 if (values == null) {
375 values = new AbstractCollection<V>() {
376 public Iterator<V> iterator() {
377 return new Iterator<V>() {
378 private Iterator<Entry<K, V>> i = entrySet()
379 .iterator();
380
381 public boolean hasNext() {
382 return i.hasNext();
383 }
384
385 public V next() {
386 return i.next().getValue();
387 }
388
389 public void remove() {
390 i.remove();
391 }
392 };
393 }
394
395 public int size() {
396 return AbstractMap.this .size();
397 }
398
399 public boolean isEmpty() {
400 return AbstractMap.this .isEmpty();
401 }
402
403 public void clear() {
404 AbstractMap.this .clear();
405 }
406
407 public boolean contains(Object v) {
408 return AbstractMap.this .containsValue(v);
409 }
410 };
411 }
412 return values;
413 }
414
415 public abstract Set<Entry<K, V>> entrySet();
416
417 // Comparison and hashing
418
419 /**
420 * Compares the specified object with this map for equality. Returns
421 * <tt>true</tt> if the given object is also a map and the two maps
422 * represent the same mappings. More formally, two maps <tt>m1</tt> and
423 * <tt>m2</tt> represent the same mappings if
424 * <tt>m1.entrySet().equals(m2.entrySet())</tt>. This ensures that the
425 * <tt>equals</tt> method works properly across different implementations
426 * of the <tt>Map</tt> interface.
427 *
428 * <p>This implementation first checks if the specified object is this map;
429 * if so it returns <tt>true</tt>. Then, it checks if the specified
430 * object is a map whose size is identical to the size of this map; if
431 * not, it returns <tt>false</tt>. If so, it iterates over this map's
432 * <tt>entrySet</tt> collection, and checks that the specified map
433 * contains each mapping that this map contains. If the specified map
434 * fails to contain such a mapping, <tt>false</tt> is returned. If the
435 * iteration completes, <tt>true</tt> is returned.
436 *
437 * @param o object to be compared for equality with this map
438 * @return <tt>true</tt> if the specified object is equal to this map
439 */
440 public boolean equals(Object o) {
441 if (o == this )
442 return true;
443
444 if (!(o instanceof Map))
445 return false;
446 Map<K, V> m = (Map<K, V>) o;
447 if (m.size() != size())
448 return false;
449
450 try {
451 Iterator<Entry<K, V>> i = entrySet().iterator();
452 while (i.hasNext()) {
453 Entry<K, V> e = i.next();
454 K key = e.getKey();
455 V value = e.getValue();
456 if (value == null) {
457 if (!(m.get(key) == null && m.containsKey(key)))
458 return false;
459 } else {
460 if (!value.equals(m.get(key)))
461 return false;
462 }
463 }
464 } catch (ClassCastException unused) {
465 return false;
466 } catch (NullPointerException unused) {
467 return false;
468 }
469
470 return true;
471 }
472
473 /**
474 * Returns the hash code value for this map. The hash code of a map is
475 * defined to be the sum of the hash codes of each entry in the map's
476 * <tt>entrySet()</tt> view. This ensures that <tt>m1.equals(m2)</tt>
477 * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps
478 * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of
479 * {@link Object#hashCode}.
480 *
481 * <p>This implementation iterates over <tt>entrySet()</tt>, calling
482 * {@link Map.Entry#hashCode hashCode()} on each element (entry) in the
483 * set, and adding up the results.
484 *
485 * @return the hash code value for this map
486 * @see Map.Entry#hashCode()
487 * @see Object#equals(Object)
488 * @see Set#equals(Object)
489 */
490 public int hashCode() {
491 int h = 0;
492 Iterator<Entry<K, V>> i = entrySet().iterator();
493 while (i.hasNext())
494 h += i.next().hashCode();
495 return h;
496 }
497
498 /**
499 * Returns a string representation of this map. The string representation
500 * consists of a list of key-value mappings in the order returned by the
501 * map's <tt>entrySet</tt> view's iterator, enclosed in braces
502 * (<tt>"{}"</tt>). Adjacent mappings are separated by the characters
503 * <tt>", "</tt> (comma and space). Each key-value mapping is rendered as
504 * the key followed by an equals sign (<tt>"="</tt>) followed by the
505 * associated value. Keys and values are converted to strings as by
506 * {@link String#valueOf(Object)}.
507 *
508 * @return a string representation of this map
509 */
510 public String toString() {
511 Iterator<Entry<K, V>> i = entrySet().iterator();
512 if (!i.hasNext())
513 return "{}";
514
515 StringBuilder sb = new StringBuilder();
516 sb.append('{');
517 for (;;) {
518 Entry<K, V> e = i.next();
519 K key = e.getKey();
520 V value = e.getValue();
521 sb.append(key == this ? "(this Map)" : key);
522 sb.append('=');
523 sb.append(value == this ? "(this Map)" : value);
524 if (!i.hasNext())
525 return sb.append('}').toString();
526 sb.append(", ");
527 }
528 }
529
530 /**
531 * Returns a shallow copy of this <tt>AbstractMap</tt> instance: the keys
532 * and values themselves are not cloned.
533 *
534 * @return a shallow copy of this map
535 */
536 protected Object clone() throws CloneNotSupportedException {
537 AbstractMap<K, V> result = (AbstractMap<K, V>) super .clone();
538 result.keySet = null;
539 result.values = null;
540 return result;
541 }
542
543 /**
544 * Utility method for SimpleEntry and SimpleImmutableEntry.
545 * Test for equality, checking for nulls.
546 */
547 private static boolean eq(Object o1, Object o2) {
548 return o1 == null ? o2 == null : o1.equals(o2);
549 }
550
551 // Implementation Note: SimpleEntry and SimpleImmutableEntry
552 // are distinct unrelated classes, even though they share
553 // some code. Since you can't add or subtract final-ness
554 // of a field in a subclass, they can't share representations,
555 // and the amount of duplicated code is too small to warrant
556 // exposing a common abstract class.
557
558 /**
559 * An Entry maintaining a key and a value. The value may be
560 * changed using the <tt>setValue</tt> method. This class
561 * facilitates the process of building custom map
562 * implementations. For example, it may be convenient to return
563 * arrays of <tt>SimpleEntry</tt> instances in method
564 * <tt>Map.entrySet().toArray</tt>.
565 *
566 * @since 1.6
567 */
568 public static class SimpleEntry<K, V> implements Entry<K, V>,
569 java.io.Serializable {
570 private static final long serialVersionUID = -8499721149061103585L;
571
572 private final K key;
573 private V value;
574
575 /**
576 * Creates an entry representing a mapping from the specified
577 * key to the specified value.
578 *
579 * @param key the key represented by this entry
580 * @param value the value represented by this entry
581 */
582 public SimpleEntry(K key, V value) {
583 this .key = key;
584 this .value = value;
585 }
586
587 /**
588 * Creates an entry representing the same mapping as the
589 * specified entry.
590 *
591 * @param entry the entry to copy
592 */
593 public SimpleEntry(Entry<? extends K, ? extends V> entry) {
594 this .key = entry.getKey();
595 this .value = entry.getValue();
596 }
597
598 /**
599 * Returns the key corresponding to this entry.
600 *
601 * @return the key corresponding to this entry
602 */
603 public K getKey() {
604 return key;
605 }
606
607 /**
608 * Returns the value corresponding to this entry.
609 *
610 * @return the value corresponding to this entry
611 */
612 public V getValue() {
613 return value;
614 }
615
616 /**
617 * Replaces the value corresponding to this entry with the specified
618 * value.
619 *
620 * @param value new value to be stored in this entry
621 * @return the old value corresponding to the entry
622 */
623 public V setValue(V value) {
624 V oldValue = this .value;
625 this .value = value;
626 return oldValue;
627 }
628
629 /**
630 * Compares the specified object with this entry for equality.
631 * Returns {@code true} if the given object is also a map entry and
632 * the two entries represent the same mapping. More formally, two
633 * entries {@code e1} and {@code e2} represent the same mapping
634 * if<pre>
635 * (e1.getKey()==null ?
636 * e2.getKey()==null :
637 * e1.getKey().equals(e2.getKey()))
638 * &&
639 * (e1.getValue()==null ?
640 * e2.getValue()==null :
641 * e1.getValue().equals(e2.getValue()))</pre>
642 * This ensures that the {@code equals} method works properly across
643 * different implementations of the {@code Map.Entry} interface.
644 *
645 * @param o object to be compared for equality with this map entry
646 * @return {@code true} if the specified object is equal to this map
647 * entry
648 * @see #hashCode
649 */
650 public boolean equals(Object o) {
651 if (!(o instanceof Map.Entry))
652 return false;
653 Map.Entry e = (Map.Entry) o;
654 return eq(key, e.getKey()) && eq(value, e.getValue());
655 }
656
657 /**
658 * Returns the hash code value for this map entry. The hash code
659 * of a map entry {@code e} is defined to be: <pre>
660 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
661 * (e.getValue()==null ? 0 : e.getValue().hashCode())</pre>
662 * This ensures that {@code e1.equals(e2)} implies that
663 * {@code e1.hashCode()==e2.hashCode()} for any two Entries
664 * {@code e1} and {@code e2}, as required by the general
665 * contract of {@link Object#hashCode}.
666 *
667 * @return the hash code value for this map entry
668 * @see #equals
669 */
670 public int hashCode() {
671 return (key == null ? 0 : key.hashCode())
672 ^ (value == null ? 0 : value.hashCode());
673 }
674
675 /**
676 * Returns a String representation of this map entry. This
677 * implementation returns the string representation of this
678 * entry's key followed by the equals character ("<tt>=</tt>")
679 * followed by the string representation of this entry's value.
680 *
681 * @return a String representation of this map entry
682 */
683 public String toString() {
684 return key + "=" + value;
685 }
686
687 }
688
689 /**
690 * An Entry maintaining an immutable key and value. This class
691 * does not support method <tt>setValue</tt>. This class may be
692 * convenient in methods that return thread-safe snapshots of
693 * key-value mappings.
694 *
695 * @since 1.6
696 */
697 public static class SimpleImmutableEntry<K, V> implements
698 Entry<K, V>, java.io.Serializable {
699 private static final long serialVersionUID = 7138329143949025153L;
700
701 private final K key;
702 private final V value;
703
704 /**
705 * Creates an entry representing a mapping from the specified
706 * key to the specified value.
707 *
708 * @param key the key represented by this entry
709 * @param value the value represented by this entry
710 */
711 public SimpleImmutableEntry(K key, V value) {
712 this .key = key;
713 this .value = value;
714 }
715
716 /**
717 * Creates an entry representing the same mapping as the
718 * specified entry.
719 *
720 * @param entry the entry to copy
721 */
722 public SimpleImmutableEntry(
723 Entry<? extends K, ? extends V> entry) {
724 this .key = entry.getKey();
725 this .value = entry.getValue();
726 }
727
728 /**
729 * Returns the key corresponding to this entry.
730 *
731 * @return the key corresponding to this entry
732 */
733 public K getKey() {
734 return key;
735 }
736
737 /**
738 * Returns the value corresponding to this entry.
739 *
740 * @return the value corresponding to this entry
741 */
742 public V getValue() {
743 return value;
744 }
745
746 /**
747 * Replaces the value corresponding to this entry with the specified
748 * value (optional operation). This implementation simply throws
749 * <tt>UnsupportedOperationException</tt>, as this class implements
750 * an <i>immutable</i> map entry.
751 *
752 * @param value new value to be stored in this entry
753 * @return (Does not return)
754 * @throws UnsupportedOperationException always
755 */
756 public V setValue(V value) {
757 throw new UnsupportedOperationException();
758 }
759
760 /**
761 * Compares the specified object with this entry for equality.
762 * Returns {@code true} if the given object is also a map entry and
763 * the two entries represent the same mapping. More formally, two
764 * entries {@code e1} and {@code e2} represent the same mapping
765 * if<pre>
766 * (e1.getKey()==null ?
767 * e2.getKey()==null :
768 * e1.getKey().equals(e2.getKey()))
769 * &&
770 * (e1.getValue()==null ?
771 * e2.getValue()==null :
772 * e1.getValue().equals(e2.getValue()))</pre>
773 * This ensures that the {@code equals} method works properly across
774 * different implementations of the {@code Map.Entry} interface.
775 *
776 * @param o object to be compared for equality with this map entry
777 * @return {@code true} if the specified object is equal to this map
778 * entry
779 * @see #hashCode
780 */
781 public boolean equals(Object o) {
782 if (!(o instanceof Map.Entry))
783 return false;
784 Map.Entry e = (Map.Entry) o;
785 return eq(key, e.getKey()) && eq(value, e.getValue());
786 }
787
788 /**
789 * Returns the hash code value for this map entry. The hash code
790 * of a map entry {@code e} is defined to be: <pre>
791 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
792 * (e.getValue()==null ? 0 : e.getValue().hashCode())</pre>
793 * This ensures that {@code e1.equals(e2)} implies that
794 * {@code e1.hashCode()==e2.hashCode()} for any two Entries
795 * {@code e1} and {@code e2}, as required by the general
796 * contract of {@link Object#hashCode}.
797 *
798 * @return the hash code value for this map entry
799 * @see #equals
800 */
801 public int hashCode() {
802 return (key == null ? 0 : key.hashCode())
803 ^ (value == null ? 0 : value.hashCode());
804 }
805
806 /**
807 * Returns a String representation of this map entry. This
808 * implementation returns the string representation of this
809 * entry's key followed by the equals character ("<tt>=</tt>")
810 * followed by the string representation of this entry's value.
811 *
812 * @return a String representation of this map entry
813 */
814 public String toString() {
815 return key + "=" + value;
816 }
817
818 }
819
820 }
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