1 /*
2 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.util;
27 import java.util.Map.Entry;
28
29 /**
30 * This class provides a skeletal implementation of the <tt>Map</tt>
31 * interface, to minimize the effort required to implement this interface.
32 *
33 * <p>To implement an unmodifiable map, the programmer needs only to extend this
34 * class and provide an implementation for the <tt>entrySet</tt> method, which
35 * returns a set-view of the map's mappings. Typically, the returned set
36 * will, in turn, be implemented atop <tt>AbstractSet</tt>. This set should
37 * not support the <tt>add</tt> or <tt>remove</tt> methods, and its iterator
38 * should not support the <tt>remove</tt> method.
39 *
40 * <p>To implement a modifiable map, the programmer must additionally override
41 * this class's <tt>put</tt> method (which otherwise throws an
42 * <tt>UnsupportedOperationException</tt>), and the iterator returned by
43 * <tt>entrySet().iterator()</tt> must additionally implement its
44 * <tt>remove</tt> method.
45 *
46 * <p>The programmer should generally provide a void (no argument) and map
47 * constructor, as per the recommendation in the <tt>Map</tt> interface
48 * specification.
49 *
50 * <p>The documentation for each non-abstract method in this class describes its
51 * implementation in detail. Each of these methods may be overridden if the
52 * map being implemented admits a more efficient implementation.
53 *
54 * <p>This class is a member of the
55 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
56 * Java Collections Framework</a>.
57 *
58 * @param <K> the type of keys maintained by this map
59 * @param <V> the type of mapped values
60 *
61 * @author Josh Bloch
62 * @author Neal Gafter
63 * @see Map
64 * @see Collection
65 * @since 1.2
66 */
67
68 public abstract class AbstractMap<K,V> implements Map<K,V> {
69 /**
70 * Sole constructor. (For invocation by subclass constructors, typically
71 * implicit.)
72 */
73 protected AbstractMap() {
74 }
75
76 // Query Operations
77
78 /**
79 * {@inheritDoc}
80 *
81 * @implSpec
82 * This implementation returns <tt>entrySet().size()</tt>.
83 */
84 public int size() {
85 return entrySet().size();
86 }
87
88 /**
89 * {@inheritDoc}
90 *
91 * @implSpec
92 * This implementation returns <tt>size() == 0</tt>.
93 */
94 public boolean isEmpty() {
95 return size() == 0;
96 }
97
98 /**
99 * {@inheritDoc}
100 *
101 * @implSpec
102 * This implementation iterates over <tt>entrySet()</tt> searching
103 * for an entry with the specified value. If such an entry is found,
104 * <tt>true</tt> is returned. If the iteration terminates without
105 * finding such an entry, <tt>false</tt> is returned. Note that this
106 * implementation requires linear time in the size of the map.
107 *
108 * @throws ClassCastException {@inheritDoc}
109 * @throws NullPointerException {@inheritDoc}
110 */
111 public boolean containsValue(Object value) {
112 Iterator<Entry<K,V>> i = entrySet().iterator();
113 if (value==null) {
114 while (i.hasNext()) {
115 Entry<K,V> e = i.next();
116 if (e.getValue()==null)
117 return true;
118 }
119 } else {
120 while (i.hasNext()) {
121 Entry<K,V> e = i.next();
122 if (value.equals(e.getValue()))
123 return true;
124 }
125 }
126 return false;
127 }
128
129 /**
130 * {@inheritDoc}
131 *
132 * @implSpec
133 * This implementation iterates over <tt>entrySet()</tt> searching
134 * for an entry with the specified key. If such an entry is found,
135 * <tt>true</tt> is returned. If the iteration terminates without
136 * finding such an entry, <tt>false</tt> is returned. Note that this
137 * implementation requires linear time in the size of the map; many
138 * implementations will override this method.
139 *
140 * @throws ClassCastException {@inheritDoc}
141 * @throws NullPointerException {@inheritDoc}
142 */
143 public boolean containsKey(Object key) {
144 Iterator<Map.Entry<K,V>> i = entrySet().iterator();
145 if (key==null) {
146 while (i.hasNext()) {
147 Entry<K,V> e = i.next();
148 if (e.getKey()==null)
149 return true;
150 }
151 } else {
152 while (i.hasNext()) {
153 Entry<K,V> e = i.next();
154 if (key.equals(e.getKey()))
155 return true;
156 }
157 }
158 return false;
159 }
160
161 /**
162 * {@inheritDoc}
163 *
164 * @implSpec
165 * This implementation iterates over <tt>entrySet()</tt> searching
166 * for an entry with the specified key. If such an entry is found,
167 * the entry's value is returned. If the iteration terminates without
168 * finding such an entry, <tt>null</tt> is returned. Note that this
169 * implementation requires linear time in the size of the map; many
170 * implementations will override this method.
171 *
172 * @throws ClassCastException {@inheritDoc}
173 * @throws NullPointerException {@inheritDoc}
174 */
175 public V get(Object key) {
176 Iterator<Entry<K,V>> i = entrySet().iterator();
177 if (key==null) {
178 while (i.hasNext()) {
179 Entry<K,V> e = i.next();
180 if (e.getKey()==null)
181 return e.getValue();
182 }
183 } else {
184 while (i.hasNext()) {
185 Entry<K,V> e = i.next();
186 if (key.equals(e.getKey()))
187 return e.getValue();
188 }
189 }
190 return null;
191 }
192
193
194 // Modification Operations
195
196 /**
197 * {@inheritDoc}
198 *
199 * @implSpec
200 * This implementation always throws an
201 * <tt>UnsupportedOperationException</tt>.
202 *
203 * @throws UnsupportedOperationException {@inheritDoc}
204 * @throws ClassCastException {@inheritDoc}
205 * @throws NullPointerException {@inheritDoc}
206 * @throws IllegalArgumentException {@inheritDoc}
207 */
208 public V put(K key, V value) {
209 throw new UnsupportedOperationException();
210 }
211
212 /**
213 * {@inheritDoc}
214 *
215 * @implSpec
216 * This implementation iterates over <tt>entrySet()</tt> searching for an
217 * entry with the specified key. If such an entry is found, its value is
218 * obtained with its <tt>getValue</tt> operation, the entry is removed
219 * from the collection (and the backing map) with the iterator's
220 * <tt>remove</tt> operation, and the saved value is returned. If the
221 * iteration terminates without finding such an entry, <tt>null</tt> is
222 * returned. Note that this implementation requires linear time in the
223 * size of the map; many implementations will override this method.
224 *
225 * <p>Note that this implementation throws an
226 * <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>
227 * iterator does not support the <tt>remove</tt> method and this map
228 * contains a mapping for the specified key.
229 *
230 * @throws UnsupportedOperationException {@inheritDoc}
231 * @throws ClassCastException {@inheritDoc}
232 * @throws NullPointerException {@inheritDoc}
233 */
234 public V remove(Object key) {
235 Iterator<Entry<K,V>> i = entrySet().iterator();
236 Entry<K,V> correctEntry = null;
237 if (key==null) {
238 while (correctEntry==null && i.hasNext()) {
239 Entry<K,V> e = i.next();
240 if (e.getKey()==null)
241 correctEntry = e;
242 }
243 } else {
244 while (correctEntry==null && i.hasNext()) {
245 Entry<K,V> e = i.next();
246 if (key.equals(e.getKey()))
247 correctEntry = e;
248 }
249 }
250
251 V oldValue = null;
252 if (correctEntry !=null) {
253 oldValue = correctEntry.getValue();
254 i.remove();
255 }
256 return oldValue;
257 }
258
259
260 // Bulk Operations
261
262 /**
263 * {@inheritDoc}
264 *
265 * @implSpec
266 * This implementation iterates over the specified map's
267 * <tt>entrySet()</tt> collection, and calls this map's <tt>put</tt>
268 * operation once for each entry returned by the iteration.
269 *
270 * <p>Note that this implementation throws an
271 * <tt>UnsupportedOperationException</tt> if this map does not support
272 * the <tt>put</tt> operation and the specified map is nonempty.
273 *
274 * @throws UnsupportedOperationException {@inheritDoc}
275 * @throws ClassCastException {@inheritDoc}
276 * @throws NullPointerException {@inheritDoc}
277 * @throws IllegalArgumentException {@inheritDoc}
278 */
279 public void putAll(Map<? extends K, ? extends V> m) {
280 for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
281 put(e.getKey(), e.getValue());
282 }
283
284 /**
285 * {@inheritDoc}
286 *
287 * @implSpec
288 * This implementation calls <tt>entrySet().clear()</tt>.
289 *
290 * <p>Note that this implementation throws an
291 * <tt>UnsupportedOperationException</tt> if the <tt>entrySet</tt>
292 * does not support the <tt>clear</tt> operation.
293 *
294 * @throws UnsupportedOperationException {@inheritDoc}
295 */
296 public void clear() {
297 entrySet().clear();
298 }
299
300
301 // Views
302
303 /**
304 * Each of these fields are initialized to contain an instance of the
305 * appropriate view the first time this view is requested. The views are
306 * stateless, so there's no reason to create more than one of each.
307 */
308 transient volatile Set<K> keySet;
309 transient volatile Collection<V> values;
310
311 /**
312 * {@inheritDoc}
313 *
314 * @implSpec
315 * This implementation returns a set that subclasses {@link AbstractSet}.
316 * The subclass's iterator method returns a "wrapper object" over this
317 * map's <tt>entrySet()</tt> iterator. The <tt>size</tt> method
318 * delegates to this map's <tt>size</tt> method and the
319 * <tt>contains</tt> method delegates to this map's
320 * <tt>containsKey</tt> method.
321 *
322 * <p>The set is created the first time this method is called,
323 * and returned in response to all subsequent calls. No synchronization
324 * is performed, so there is a slight chance that multiple calls to this
325 * method will not all return the same set.
326 */
327 public Set<K> keySet() {
328 if (keySet == null) {
329 keySet = new AbstractSet<K>() {
330 public Iterator<K> iterator() {
331 return new Iterator<K>() {
332 private Iterator<Entry<K,V>> i = entrySet().iterator();
333
334 public boolean hasNext() {
335 return i.hasNext();
336 }
337
338 public K next() {
339 return i.next().getKey();
340 }
341
342 public void remove() {
343 i.remove();
344 }
345 };
346 }
347
348 public int size() {
349 return AbstractMap.this.size();
350 }
351
352 public boolean isEmpty() {
353 return AbstractMap.this.isEmpty();
354 }
355
356 public void clear() {
357 AbstractMap.this.clear();
358 }
359
360 public boolean contains(Object k) {
361 return AbstractMap.this.containsKey(k);
362 }
363 };
364 }
365 return keySet;
366 }
367
368 /**
369 * {@inheritDoc}
370 *
371 * @implSpec
372 * This implementation returns a collection that subclasses {@link
373 * AbstractCollection}. The subclass's iterator method returns a
374 * "wrapper object" over this map's <tt>entrySet()</tt> iterator.
375 * The <tt>size</tt> method delegates to this map's <tt>size</tt>
376 * method and the <tt>contains</tt> method delegates to this map's
377 * <tt>containsValue</tt> method.
378 *
379 * <p>The collection is created the first time this method is called, and
380 * returned in response to all subsequent calls. No synchronization is
381 * performed, so there is a slight chance that multiple calls to this
382 * method will not all return the same collection.
383 */
384 public Collection<V> values() {
385 if (values == null) {
386 values = new AbstractCollection<V>() {
387 public Iterator<V> iterator() {
388 return new Iterator<V>() {
389 private Iterator<Entry<K,V>> i = entrySet().iterator();
390
391 public boolean hasNext() {
392 return i.hasNext();
393 }
394
395 public V next() {
396 return i.next().getValue();
397 }
398
399 public void remove() {
400 i.remove();
401 }
402 };
403 }
404
405 public int size() {
406 return AbstractMap.this.size();
407 }
408
409 public boolean isEmpty() {
410 return AbstractMap.this.isEmpty();
411 }
412
413 public void clear() {
414 AbstractMap.this.clear();
415 }
416
417 public boolean contains(Object v) {
418 return AbstractMap.this.containsValue(v);
419 }
420 };
421 }
422 return values;
423 }
424
425 public abstract Set<Entry<K,V>> entrySet();
426
427
428 // Comparison and hashing
429
430 /**
431 * Compares the specified object with this map for equality. Returns
432 * <tt>true</tt> if the given object is also a map and the two maps
433 * represent the same mappings. More formally, two maps <tt>m1</tt> and
434 * <tt>m2</tt> represent the same mappings if
435 * <tt>m1.entrySet().equals(m2.entrySet())</tt>. This ensures that the
436 * <tt>equals</tt> method works properly across different implementations
437 * of the <tt>Map</tt> interface.
438 *
439 * @implSpec
440 * This implementation first checks if the specified object is this map;
441 * if so it returns <tt>true</tt>. Then, it checks if the specified
442 * object is a map whose size is identical to the size of this map; if
443 * not, it returns <tt>false</tt>. If so, it iterates over this map's
444 * <tt>entrySet</tt> collection, and checks that the specified map
445 * contains each mapping that this map contains. If the specified map
446 * fails to contain such a mapping, <tt>false</tt> is returned. If the
447 * iteration completes, <tt>true</tt> is returned.
448 *
449 * @param o object to be compared for equality with this map
450 * @return <tt>true</tt> if the specified object is equal to this map
451 */
452 public boolean equals(Object o) {
453 if (o == this)
454 return true;
455
456 if (!(o instanceof Map))
457 return false;
458 Map<?,?> m = (Map<?,?>) o;
459 if (m.size() != size())
460 return false;
461
462 try {
463 for (Entry<K, V> e : entrySet()) {
464 K key = e.getKey();
465 V value = e.getValue();
466 if (value == null) {
467 if (!(m.get(key) == null && m.containsKey(key)))
468 return false;
469 } else {
470 if (!value.equals(m.get(key)))
471 return false;
472 }
473 }
474 } catch (ClassCastException unused) {
475 return false;
476 } catch (NullPointerException unused) {
477 return false;
478 }
479
480 return true;
481 }
482
483 /**
484 * Returns the hash code value for this map. The hash code of a map is
485 * defined to be the sum of the hash codes of each entry in the map's
486 * <tt>entrySet()</tt> view. This ensures that <tt>m1.equals(m2)</tt>
487 * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps
488 * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of
489 * {@link Object#hashCode}.
490 *
491 * @implSpec
492 * This implementation iterates over <tt>entrySet()</tt>, calling
493 * {@link Map.Entry#hashCode hashCode()} on each element (entry) in the
494 * set, and adding up the results.
495 *
496 * @return the hash code value for this map
497 * @see Map.Entry#hashCode()
498 * @see Object#equals(Object)
499 * @see Set#equals(Object)
500 */
501 public int hashCode() {
502 int h = 0;
503 for (Entry<K, V> entry : entrySet())
504 h += entry.hashCode();
505 return h;
506 }
507
508 /**
509 * Returns a string representation of this map. The string representation
510 * consists of a list of key-value mappings in the order returned by the
511 * map's <tt>entrySet</tt> view's iterator, enclosed in braces
512 * (<tt>"{}"</tt>). Adjacent mappings are separated by the characters
513 * <tt>", "</tt> (comma and space). Each key-value mapping is rendered as
514 * the key followed by an equals sign (<tt>"="</tt>) followed by the
515 * associated value. Keys and values are converted to strings as by
516 * {@link String#valueOf(Object)}.
517 *
518 * @return a string representation of this map
519 */
520 public String toString() {
521 Iterator<Entry<K,V>> i = entrySet().iterator();
522 if (! i.hasNext())
523 return "{}";
524
525 StringBuilder sb = new StringBuilder();
526 sb.append('{');
527 for (;;) {
528 Entry<K,V> e = i.next();
529 K key = e.getKey();
530 V value = e.getValue();
531 sb.append(key == this ? "(this Map)" : key);
532 sb.append('=');
533 sb.append(value == this ? "(this Map)" : value);
534 if (! i.hasNext())
535 return sb.append('}').toString();
536 sb.append(',').append(' ');
537 }
538 }
539
540 /**
541 * Returns a shallow copy of this <tt>AbstractMap</tt> instance: the keys
542 * and values themselves are not cloned.
543 *
544 * @return a shallow copy of this map
545 */
546 protected Object clone() throws CloneNotSupportedException {
547 AbstractMap<?,?> result = (AbstractMap<?,?>)super.clone();
548 result.keySet = null;
549 result.values = null;
550 return result;
551 }
552
553 /**
554 * Utility method for SimpleEntry and SimpleImmutableEntry.
555 * Test for equality, checking for nulls.
556 *
557 * NB: Do not replace with Object.equals until JDK-8015417 is resolved.
558 */
559 private static boolean eq(Object o1, Object o2) {
560 return o1 == null ? o2 == null : o1.equals(o2);
561 }
562
563 // Implementation Note: SimpleEntry and SimpleImmutableEntry
564 // are distinct unrelated classes, even though they share
565 // some code. Since you can't add or subtract final-ness
566 // of a field in a subclass, they can't share representations,
567 // and the amount of duplicated code is too small to warrant
568 // exposing a common abstract class.
569
570
571 /**
572 * An Entry maintaining a key and a value. The value may be
573 * changed using the <tt>setValue</tt> method. This class
574 * facilitates the process of building custom map
575 * implementations. For example, it may be convenient to return
576 * arrays of <tt>SimpleEntry</tt> instances in method
577 * <tt>Map.entrySet().toArray</tt>.
578 *
579 * @since 1.6
580 */
581 public static class SimpleEntry<K,V>
582 implements Entry<K,V>, java.io.Serializable
583 {
584 private static final long serialVersionUID = -8499721149061103585L;
585
586 private final K key;
587 private V value;
588
589 /**
590 * Creates an entry representing a mapping from the specified
591 * key to the specified value.
592 *
593 * @param key the key represented by this entry
594 * @param value the value represented by this entry
595 */
596 public SimpleEntry(K key, V value) {
597 this.key = key;
598 this.value = value;
599 }
600
601 /**
602 * Creates an entry representing the same mapping as the
603 * specified entry.
604 *
605 * @param entry the entry to copy
606 */
607 public SimpleEntry(Entry<? extends K, ? extends V> entry) {
608 this.key = entry.getKey();
609 this.value = entry.getValue();
610 }
611
612 /**
613 * Returns the key corresponding to this entry.
614 *
615 * @return the key corresponding to this entry
616 */
617 public K getKey() {
618 return key;
619 }
620
621 /**
622 * Returns the value corresponding to this entry.
623 *
624 * @return the value corresponding to this entry
625 */
626 public V getValue() {
627 return value;
628 }
629
630 /**
631 * Replaces the value corresponding to this entry with the specified
632 * value.
633 *
634 * @param value new value to be stored in this entry
635 * @return the old value corresponding to the entry
636 */
637 public V setValue(V value) {
638 V oldValue = this.value;
639 this.value = value;
640 return oldValue;
641 }
642
643 /**
644 * Compares the specified object with this entry for equality.
645 * Returns {@code true} if the given object is also a map entry and
646 * the two entries represent the same mapping. More formally, two
647 * entries {@code e1} and {@code e2} represent the same mapping
648 * if<pre>
649 * (e1.getKey()==null ?
650 * e2.getKey()==null :
651 * e1.getKey().equals(e2.getKey()))
652 * &&
653 * (e1.getValue()==null ?
654 * e2.getValue()==null :
655 * e1.getValue().equals(e2.getValue()))</pre>
656 * This ensures that the {@code equals} method works properly across
657 * different implementations of the {@code Map.Entry} interface.
658 *
659 * @param o object to be compared for equality with this map entry
660 * @return {@code true} if the specified object is equal to this map
661 * entry
662 * @see #hashCode
663 */
664 public boolean equals(Object o) {
665 if (!(o instanceof Map.Entry))
666 return false;
667 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
668 return eq(key, e.getKey()) && eq(value, e.getValue());
669 }
670
671 /**
672 * Returns the hash code value for this map entry. The hash code
673 * of a map entry {@code e} is defined to be: <pre>
674 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
675 * (e.getValue()==null ? 0 : e.getValue().hashCode())</pre>
676 * This ensures that {@code e1.equals(e2)} implies that
677 * {@code e1.hashCode()==e2.hashCode()} for any two Entries
678 * {@code e1} and {@code e2}, as required by the general
679 * contract of {@link Object#hashCode}.
680 *
681 * @return the hash code value for this map entry
682 * @see #equals
683 */
684 public int hashCode() {
685 return (key == null ? 0 : key.hashCode()) ^
686 (value == null ? 0 : value.hashCode());
687 }
688
689 /**
690 * Returns a String representation of this map entry. This
691 * implementation returns the string representation of this
692 * entry's key followed by the equals character ("<tt>=</tt>")
693 * followed by the string representation of this entry's value.
694 *
695 * @return a String representation of this map entry
696 */
697 public String toString() {
698 return key + "=" + value;
699 }
700
701 }
702
703 /**
704 * An Entry maintaining an immutable key and value. This class
705 * does not support method <tt>setValue</tt>. This class may be
706 * convenient in methods that return thread-safe snapshots of
707 * key-value mappings.
708 *
709 * @since 1.6
710 */
711 public static class SimpleImmutableEntry<K,V>
712 implements Entry<K,V>, java.io.Serializable
713 {
714 private static final long serialVersionUID = 7138329143949025153L;
715
716 private final K key;
717 private final V value;
718
719 /**
720 * Creates an entry representing a mapping from the specified
721 * key to the specified value.
722 *
723 * @param key the key represented by this entry
724 * @param value the value represented by this entry
725 */
726 public SimpleImmutableEntry(K key, V value) {
727 this.key = key;
728 this.value = value;
729 }
730
731 /**
732 * Creates an entry representing the same mapping as the
733 * specified entry.
734 *
735 * @param entry the entry to copy
736 */
737 public SimpleImmutableEntry(Entry<? extends K, ? extends V> entry) {
738 this.key = entry.getKey();
739 this.value = entry.getValue();
740 }
741
742 /**
743 * Returns the key corresponding to this entry.
744 *
745 * @return the key corresponding to this entry
746 */
747 public K getKey() {
748 return key;
749 }
750
751 /**
752 * Returns the value corresponding to this entry.
753 *
754 * @return the value corresponding to this entry
755 */
756 public V getValue() {
757 return value;
758 }
759
760 /**
761 * Replaces the value corresponding to this entry with the specified
762 * value (optional operation). This implementation simply throws
763 * <tt>UnsupportedOperationException</tt>, as this class implements
764 * an <i>immutable</i> map entry.
765 *
766 * @param value new value to be stored in this entry
767 * @return (Does not return)
768 * @throws UnsupportedOperationException always
769 */
770 public V setValue(V value) {
771 throw new UnsupportedOperationException();
772 }
773
774 /**
775 * Compares the specified object with this entry for equality.
776 * Returns {@code true} if the given object is also a map entry and
777 * the two entries represent the same mapping. More formally, two
778 * entries {@code e1} and {@code e2} represent the same mapping
779 * if<pre>
780 * (e1.getKey()==null ?
781 * e2.getKey()==null :
782 * e1.getKey().equals(e2.getKey()))
783 * &&
784 * (e1.getValue()==null ?
785 * e2.getValue()==null :
786 * e1.getValue().equals(e2.getValue()))</pre>
787 * This ensures that the {@code equals} method works properly across
788 * different implementations of the {@code Map.Entry} interface.
789 *
790 * @param o object to be compared for equality with this map entry
791 * @return {@code true} if the specified object is equal to this map
792 * entry
793 * @see #hashCode
794 */
795 public boolean equals(Object o) {
796 if (!(o instanceof Map.Entry))
797 return false;
798 Map.Entry<?,?> e = (Map.Entry<?,?>)o;
799 return eq(key, e.getKey()) && eq(value, e.getValue());
800 }
801
802 /**
803 * Returns the hash code value for this map entry. The hash code
804 * of a map entry {@code e} is defined to be: <pre>
805 * (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
806 * (e.getValue()==null ? 0 : e.getValue().hashCode())</pre>
807 * This ensures that {@code e1.equals(e2)} implies that
808 * {@code e1.hashCode()==e2.hashCode()} for any two Entries
809 * {@code e1} and {@code e2}, as required by the general
810 * contract of {@link Object#hashCode}.
811 *
812 * @return the hash code value for this map entry
813 * @see #equals
814 */
815 public int hashCode() {
816 return (key == null ? 0 : key.hashCode()) ^
817 (value == null ? 0 : value.hashCode());
818 }
819
820 /**
821 * Returns a String representation of this map entry. This
822 * implementation returns the string representation of this
823 * entry's key followed by the equals character ("<tt>=</tt>")
824 * followed by the string representation of this entry's value.
825 *
826 * @return a String representation of this map entry
827 */
828 public String toString() {
829 return key + "=" + value;
830 }
831
832 }
833
834 }