1 /*
2 * Copyright (c) 2000, 2011, 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
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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 *
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20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 * questions.
24 */
25
26 package java.util;
27 import java.io.*;
28
29 /**
30 * This class implements the <tt>Map</tt> interface with a hash table, using
31 * reference-equality in place of object-equality when comparing keys (and
32 * values). In other words, in an <tt>IdentityHashMap</tt>, two keys
33 * <tt>k1</tt> and <tt>k2</tt> are considered equal if and only if
34 * <tt>(k1==k2)</tt>. (In normal <tt>Map</tt> implementations (like
35 * <tt>HashMap</tt>) two keys <tt>k1</tt> and <tt>k2</tt> are considered equal
36 * if and only if <tt>(k1==null ? k2==null : k1.equals(k2))</tt>.)
37 *
38 * <p><b>This class is <i>not</i> a general-purpose <tt>Map</tt>
39 * implementation! While this class implements the <tt>Map</tt> interface, it
40 * intentionally violates <tt>Map's</tt> general contract, which mandates the
41 * use of the <tt>equals</tt> method when comparing objects. This class is
42 * designed for use only in the rare cases wherein reference-equality
43 * semantics are required.</b>
44 *
45 * <p>A typical use of this class is <i>topology-preserving object graph
46 * transformations</i>, such as serialization or deep-copying. To perform such
47 * a transformation, a program must maintain a "node table" that keeps track
48 * of all the object references that have already been processed. The node
49 * table must not equate distinct objects even if they happen to be equal.
50 * Another typical use of this class is to maintain <i>proxy objects</i>. For
51 * example, a debugging facility might wish to maintain a proxy object for
52 * each object in the program being debugged.
53 *
54 * <p>This class provides all of the optional map operations, and permits
55 * <tt>null</tt> values and the <tt>null</tt> key. This class makes no
56 * guarantees as to the order of the map; in particular, it does not guarantee
57 * that the order will remain constant over time.
58 *
59 * <p>This class provides constant-time performance for the basic
60 * operations (<tt>get</tt> and <tt>put</tt>), assuming the system
61 * identity hash function ({@link System#identityHashCode(Object)})
62 * disperses elements properly among the buckets.
63 *
64 * <p>This class has one tuning parameter (which affects performance but not
65 * semantics): <i>expected maximum size</i>. This parameter is the maximum
66 * number of key-value mappings that the map is expected to hold. Internally,
67 * this parameter is used to determine the number of buckets initially
68 * comprising the hash table. The precise relationship between the expected
69 * maximum size and the number of buckets is unspecified.
70 *
71 * <p>If the size of the map (the number of key-value mappings) sufficiently
72 * exceeds the expected maximum size, the number of buckets is increased
73 * Increasing the number of buckets ("rehashing") may be fairly expensive, so
74 * it pays to create identity hash maps with a sufficiently large expected
75 * maximum size. On the other hand, iteration over collection views requires
76 * time proportional to the number of buckets in the hash table, so it
77 * pays not to set the expected maximum size too high if you are especially
78 * concerned with iteration performance or memory usage.
79 *
80 * <p><strong>Note that this implementation is not synchronized.</strong>
81 * If multiple threads access an identity hash map concurrently, and at
82 * least one of the threads modifies the map structurally, it <i>must</i>
83 * be synchronized externally. (A structural modification is any operation
84 * that adds or deletes one or more mappings; merely changing the value
85 * associated with a key that an instance already contains is not a
86 * structural modification.) This is typically accomplished by
87 * synchronizing on some object that naturally encapsulates the map.
88 *
89 * If no such object exists, the map should be "wrapped" using the
90 * {@link Collections#synchronizedMap Collections.synchronizedMap}
91 * method. This is best done at creation time, to prevent accidental
92 * unsynchronized access to the map:<pre>
93 * Map m = Collections.synchronizedMap(new IdentityHashMap(...));</pre>
94 *
95 * <p>The iterators returned by the <tt>iterator</tt> method of the
96 * collections returned by all of this class's "collection view
97 * methods" are <i>fail-fast</i>: if the map is structurally modified
98 * at any time after the iterator is created, in any way except
99 * through the iterator's own <tt>remove</tt> method, the iterator
100 * will throw a {@link ConcurrentModificationException}. Thus, in the
101 * face of concurrent modification, the iterator fails quickly and
102 * cleanly, rather than risking arbitrary, non-deterministic behavior
103 * at an undetermined time in the future.
104 *
105 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
106 * as it is, generally speaking, impossible to make any hard guarantees in the
107 * presence of unsynchronized concurrent modification. Fail-fast iterators
108 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
109 * Therefore, it would be wrong to write a program that depended on this
110 * exception for its correctness: <i>fail-fast iterators should be used only
111 * to detect bugs.</i>
112 *
113 * <p>Implementation note: This is a simple <i>linear-probe</i> hash table,
114 * as described for example in texts by Sedgewick and Knuth. The array
115 * alternates holding keys and values. (This has better locality for large
116 * tables than does using separate arrays.) For many JRE implementations
117 * and operation mixes, this class will yield better performance than
118 * {@link HashMap} (which uses <i>chaining</i> rather than linear-probing).
119 *
120 * <p>This class is a member of the
121 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
122 * Java Collections Framework</a>.
123 *
124 * @see System#identityHashCode(Object)
125 * @see Object#hashCode()
126 * @see Collection
127 * @see Map
128 * @see HashMap
129 * @see TreeMap
130 * @author Doug Lea and Josh Bloch
131 * @since 1.4
132 */
133
134 public class IdentityHashMap<K,V>
135 extends AbstractMap<K,V>
136 implements Map<K,V>, java.io.Serializable, Cloneable
137 {
138 /**
139 * The initial capacity used by the no-args constructor.
140 * MUST be a power of two. The value 32 corresponds to the
141 * (specified) expected maximum size of 21, given a load factor
142 * of 2/3.
143 */
144 private static final int DEFAULT_CAPACITY = 32;
145
146 /**
147 * The minimum capacity, used if a lower value is implicitly specified
148 * by either of the constructors with arguments. The value 4 corresponds
149 * to an expected maximum size of 2, given a load factor of 2/3.
150 * MUST be a power of two.
151 */
152 private static final int MINIMUM_CAPACITY = 4;
153
154 /**
155 * The maximum capacity, used if a higher value is implicitly specified
156 * by either of the constructors with arguments.
157 * MUST be a power of two <= 1<<29.
158 */
159 private static final int MAXIMUM_CAPACITY = 1 << 29;
160
161 /**
162 * The table, resized as necessary. Length MUST always be a power of two.
163 */
164 private transient Object[] table;
165
166 /**
167 * The number of key-value mappings contained in this identity hash map.
168 *
169 * @serial
170 */
171 private int size;
172
173 /**
174 * The number of modifications, to support fast-fail iterators
175 */
176 private transient int modCount;
177
178 /**
179 * The next size value at which to resize (capacity * load factor).
180 */
181 private transient int threshold;
182
183 /**
184 * Value representing null keys inside tables.
185 */
186 private static final Object NULL_KEY = new Object();
187
188 /**
189 * Use NULL_KEY for key if it is null.
190 */
191 private static Object maskNull(Object key) {
192 return (key == null ? NULL_KEY : key);
193 }
194
195 /**
196 * Returns internal representation of null key back to caller as null.
197 */
198 private static Object unmaskNull(Object key) {
199 return (key == NULL_KEY ? null : key);
200 }
201
202 /**
203 * Constructs a new, empty identity hash map with a default expected
204 * maximum size (21).
205 */
206 public IdentityHashMap() {
207 init(DEFAULT_CAPACITY);
208 }
209
210 /**
211 * Constructs a new, empty map with the specified expected maximum size.
212 * Putting more than the expected number of key-value mappings into
213 * the map may cause the internal data structure to grow, which may be
214 * somewhat time-consuming.
215 *
216 * @param expectedMaxSize the expected maximum size of the map
217 * @throws IllegalArgumentException if <tt>expectedMaxSize</tt> is negative
218 */
219 public IdentityHashMap(int expectedMaxSize) {
220 if (expectedMaxSize < 0)
221 throw new IllegalArgumentException("expectedMaxSize is negative: "
222 + expectedMaxSize);
223 init(capacity(expectedMaxSize));
224 }
225
226 /**
227 * Returns the appropriate capacity for the specified expected maximum
228 * size. Returns the smallest power of two between MINIMUM_CAPACITY
229 * and MAXIMUM_CAPACITY, inclusive, that is greater than
230 * (3 * expectedMaxSize)/2, if such a number exists. Otherwise
231 * returns MAXIMUM_CAPACITY. If (3 * expectedMaxSize)/2 is negative, it
232 * is assumed that overflow has occurred, and MAXIMUM_CAPACITY is returned.
233 */
234 private int capacity(int expectedMaxSize) {
235 // Compute min capacity for expectedMaxSize given a load factor of 2/3
236 int minCapacity = (3 * expectedMaxSize)/2;
237
238 // Compute the appropriate capacity
239 int result;
240 if (minCapacity > MAXIMUM_CAPACITY || minCapacity < 0) {
241 result = MAXIMUM_CAPACITY;
242 } else {
243 result = MINIMUM_CAPACITY;
244 while (result < minCapacity)
245 result <<= 1;
246 }
247 return result;
248 }
249
250 /**
251 * Initializes object to be an empty map with the specified initial
252 * capacity, which is assumed to be a power of two between
253 * MINIMUM_CAPACITY and MAXIMUM_CAPACITY inclusive.
254 */
255 private void init(int initCapacity) {
256 // assert (initCapacity & -initCapacity) == initCapacity; // power of 2
257 // assert initCapacity >= MINIMUM_CAPACITY;
258 // assert initCapacity <= MAXIMUM_CAPACITY;
259
260 threshold = (initCapacity * 2)/3;
261 table = new Object[2 * initCapacity];
262 }
263
264 /**
265 * Constructs a new identity hash map containing the keys-value mappings
266 * in the specified map.
267 *
268 * @param m the map whose mappings are to be placed into this map
269 * @throws NullPointerException if the specified map is null
270 */
271 public IdentityHashMap(Map<? extends K, ? extends V> m) {
272 // Allow for a bit of growth
273 this((int) ((1 + m.size()) * 1.1));
274 putAll(m);
275 }
276
277 /**
278 * Returns the number of key-value mappings in this identity hash map.
279 *
280 * @return the number of key-value mappings in this map
281 */
282 public int size() {
283 return size;
284 }
285
286 /**
287 * Returns <tt>true</tt> if this identity hash map contains no key-value
288 * mappings.
289 *
290 * @return <tt>true</tt> if this identity hash map contains no key-value
291 * mappings
292 */
293 public boolean isEmpty() {
294 return size == 0;
295 }
296
297 /**
298 * Returns index for Object x.
299 */
300 private static int hash(Object x, int length) {
301 int h = System.identityHashCode(x);
302 // Multiply by -127, and left-shift to use least bit as part of hash
303 return ((h << 1) - (h << 8)) & (length - 1);
304 }
305
306 /**
307 * Circularly traverses table of size len.
308 */
309 private static int nextKeyIndex(int i, int len) {
310 return (i + 2 < len ? i + 2 : 0);
311 }
312
313 /**
314 * Returns the value to which the specified key is mapped,
315 * or {@code null} if this map contains no mapping for the key.
316 *
317 * <p>More formally, if this map contains a mapping from a key
318 * {@code k} to a value {@code v} such that {@code (key == k)},
319 * then this method returns {@code v}; otherwise it returns
320 * {@code null}. (There can be at most one such mapping.)
321 *
322 * <p>A return value of {@code null} does not <i>necessarily</i>
323 * indicate that the map contains no mapping for the key; it's also
324 * possible that the map explicitly maps the key to {@code null}.
325 * The {@link #containsKey containsKey} operation may be used to
326 * distinguish these two cases.
327 *
328 * @see #put(Object, Object)
329 */
330 public V get(Object key) {
331 Object k = maskNull(key);
332 Object[] tab = table;
333 int len = tab.length;
334 int i = hash(k, len);
335 while (true) {
336 Object item = tab[i];
337 if (item == k)
338 return (V) tab[i + 1];
339 if (item == null)
340 return null;
341 i = nextKeyIndex(i, len);
342 }
343 }
344
345 /**
346 * Tests whether the specified object reference is a key in this identity
347 * hash map.
348 *
349 * @param key possible key
350 * @return <code>true</code> if the specified object reference is a key
351 * in this map
352 * @see #containsValue(Object)
353 */
354 public boolean containsKey(Object key) {
355 Object k = maskNull(key);
356 Object[] tab = table;
357 int len = tab.length;
358 int i = hash(k, len);
359 while (true) {
360 Object item = tab[i];
361 if (item == k)
362 return true;
363 if (item == null)
364 return false;
365 i = nextKeyIndex(i, len);
366 }
367 }
368
369 /**
370 * Tests whether the specified object reference is a value in this identity
371 * hash map.
372 *
373 * @param value value whose presence in this map is to be tested
374 * @return <tt>true</tt> if this map maps one or more keys to the
375 * specified object reference
376 * @see #containsKey(Object)
377 */
378 public boolean containsValue(Object value) {
379 Object[] tab = table;
380 for (int i = 1; i < tab.length; i += 2)
381 if (tab[i] == value && tab[i - 1] != null)
382 return true;
383
384 return false;
385 }
386
387 /**
388 * Tests if the specified key-value mapping is in the map.
389 *
390 * @param key possible key
391 * @param value possible value
392 * @return <code>true</code> if and only if the specified key-value
393 * mapping is in the map
394 */
395 private boolean containsMapping(Object key, Object value) {
396 Object k = maskNull(key);
397 Object[] tab = table;
398 int len = tab.length;
399 int i = hash(k, len);
400 while (true) {
401 Object item = tab[i];
402 if (item == k)
403 return tab[i + 1] == value;
404 if (item == null)
405 return false;
406 i = nextKeyIndex(i, len);
407 }
408 }
409
410 /**
411 * Associates the specified value with the specified key in this identity
412 * hash map. If the map previously contained a mapping for the key, the
413 * old value is replaced.
414 *
415 * @param key the key with which the specified value is to be associated
416 * @param value the value to be associated with the specified key
417 * @return the previous value associated with <tt>key</tt>, or
418 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
419 * (A <tt>null</tt> return can also indicate that the map
420 * previously associated <tt>null</tt> with <tt>key</tt>.)
421 * @see Object#equals(Object)
422 * @see #get(Object)
423 * @see #containsKey(Object)
424 */
425 public V put(K key, V value) {
426 Object k = maskNull(key);
427 Object[] tab = table;
428 int len = tab.length;
429 int i = hash(k, len);
430
431 Object item;
432 while ( (item = tab[i]) != null) {
433 if (item == k) {
434 V oldValue = (V) tab[i + 1];
435 tab[i + 1] = value;
436 return oldValue;
437 }
438 i = nextKeyIndex(i, len);
439 }
440
441 modCount++;
442 tab[i] = k;
443 tab[i + 1] = value;
444 if (++size >= threshold)
445 resize(len); // len == 2 * current capacity.
446 return null;
447 }
448
449 /**
450 * Resize the table to hold given capacity.
451 *
452 * @param newCapacity the new capacity, must be a power of two.
453 */
454 private void resize(int newCapacity) {
455 // assert (newCapacity & -newCapacity) == newCapacity; // power of 2
456 int newLength = newCapacity * 2;
457
458 Object[] oldTable = table;
459 int oldLength = oldTable.length;
460 if (oldLength == 2*MAXIMUM_CAPACITY) { // can't expand any further
461 if (threshold == MAXIMUM_CAPACITY-1)
462 throw new IllegalStateException("Capacity exhausted.");
463 threshold = MAXIMUM_CAPACITY-1; // Gigantic map!
464 return;
465 }
466 if (oldLength >= newLength)
467 return;
468
469 Object[] newTable = new Object[newLength];
470 threshold = newLength / 3;
471
472 for (int j = 0; j < oldLength; j += 2) {
473 Object key = oldTable[j];
474 if (key != null) {
475 Object value = oldTable[j+1];
476 oldTable[j] = null;
477 oldTable[j+1] = null;
478 int i = hash(key, newLength);
479 while (newTable[i] != null)
480 i = nextKeyIndex(i, newLength);
481 newTable[i] = key;
482 newTable[i + 1] = value;
483 }
484 }
485 table = newTable;
486 }
487
488 /**
489 * Copies all of the mappings from the specified map to this map.
490 * These mappings will replace any mappings that this map had for
491 * any of the keys currently in the specified map.
492 *
493 * @param m mappings to be stored in this map
494 * @throws NullPointerException if the specified map is null
495 */
496 public void putAll(Map<? extends K, ? extends V> m) {
497 int n = m.size();
498 if (n == 0)
499 return;
500 if (n > threshold) // conservatively pre-expand
501 resize(capacity(n));
502
503 for (Entry<? extends K, ? extends V> e : m.entrySet())
504 put(e.getKey(), e.getValue());
505 }
506
507 /**
508 * Removes the mapping for this key from this map if present.
509 *
510 * @param key key whose mapping is to be removed from the map
511 * @return the previous value associated with <tt>key</tt>, or
512 * <tt>null</tt> if there was no mapping for <tt>key</tt>.
513 * (A <tt>null</tt> return can also indicate that the map
514 * previously associated <tt>null</tt> with <tt>key</tt>.)
515 */
516 public V remove(Object key) {
517 Object k = maskNull(key);
518 Object[] tab = table;
519 int len = tab.length;
520 int i = hash(k, len);
521
522 while (true) {
523 Object item = tab[i];
524 if (item == k) {
525 modCount++;
526 size--;
527 V oldValue = (V) tab[i + 1];
528 tab[i + 1] = null;
529 tab[i] = null;
530 closeDeletion(i);
531 return oldValue;
532 }
533 if (item == null)
534 return null;
535 i = nextKeyIndex(i, len);
536 }
537
538 }
539
540 /**
541 * Removes the specified key-value mapping from the map if it is present.
542 *
543 * @param key possible key
544 * @param value possible value
545 * @return <code>true</code> if and only if the specified key-value
546 * mapping was in the map
547 */
548 private boolean removeMapping(Object key, Object value) {
549 Object k = maskNull(key);
550 Object[] tab = table;
551 int len = tab.length;
552 int i = hash(k, len);
553
554 while (true) {
555 Object item = tab[i];
556 if (item == k) {
557 if (tab[i + 1] != value)
558 return false;
559 modCount++;
560 size--;
561 tab[i] = null;
562 tab[i + 1] = null;
563 closeDeletion(i);
564 return true;
565 }
566 if (item == null)
567 return false;
568 i = nextKeyIndex(i, len);
569 }
570 }
571
572 /**
573 * Rehash all possibly-colliding entries following a
574 * deletion. This preserves the linear-probe
575 * collision properties required by get, put, etc.
576 *
577 * @param d the index of a newly empty deleted slot
578 */
579 private void closeDeletion(int d) {
580 // Adapted from Knuth Section 6.4 Algorithm R
581 Object[] tab = table;
582 int len = tab.length;
583
584 // Look for items to swap into newly vacated slot
585 // starting at index immediately following deletion,
586 // and continuing until a null slot is seen, indicating
587 // the end of a run of possibly-colliding keys.
588 Object item;
589 for (int i = nextKeyIndex(d, len); (item = tab[i]) != null;
590 i = nextKeyIndex(i, len) ) {
591 // The following test triggers if the item at slot i (which
592 // hashes to be at slot r) should take the spot vacated by d.
593 // If so, we swap it in, and then continue with d now at the
594 // newly vacated i. This process will terminate when we hit
595 // the null slot at the end of this run.
596 // The test is messy because we are using a circular table.
597 int r = hash(item, len);
598 if ((i < r && (r <= d || d <= i)) || (r <= d && d <= i)) {
599 tab[d] = item;
600 tab[d + 1] = tab[i + 1];
601 tab[i] = null;
602 tab[i + 1] = null;
603 d = i;
604 }
605 }
606 }
607
608 /**
609 * Removes all of the mappings from this map.
610 * The map will be empty after this call returns.
611 */
612 public void clear() {
613 modCount++;
614 Object[] tab = table;
615 for (int i = 0; i < tab.length; i++)
616 tab[i] = null;
617 size = 0;
618 }
619
620 /**
621 * Compares the specified object with this map for equality. Returns
622 * <tt>true</tt> if the given object is also a map and the two maps
623 * represent identical object-reference mappings. More formally, this
624 * map is equal to another map <tt>m</tt> if and only if
625 * <tt>this.entrySet().equals(m.entrySet())</tt>.
626 *
627 * <p><b>Owing to the reference-equality-based semantics of this map it is
628 * possible that the symmetry and transitivity requirements of the
629 * <tt>Object.equals</tt> contract may be violated if this map is compared
630 * to a normal map. However, the <tt>Object.equals</tt> contract is
631 * guaranteed to hold among <tt>IdentityHashMap</tt> instances.</b>
632 *
633 * @param o object to be compared for equality with this map
634 * @return <tt>true</tt> if the specified object is equal to this map
635 * @see Object#equals(Object)
636 */
637 public boolean equals(Object o) {
638 if (o == this) {
639 return true;
640 } else if (o instanceof IdentityHashMap) {
641 IdentityHashMap m = (IdentityHashMap) o;
642 if (m.size() != size)
643 return false;
644
645 Object[] tab = m.table;
646 for (int i = 0; i < tab.length; i+=2) {
647 Object k = tab[i];
648 if (k != null && !containsMapping(k, tab[i + 1]))
649 return false;
650 }
651 return true;
652 } else if (o instanceof Map) {
653 Map m = (Map)o;
654 return entrySet().equals(m.entrySet());
655 } else {
656 return false; // o is not a Map
657 }
658 }
659
660 /**
661 * Returns the hash code value for this map. The hash code of a map is
662 * defined to be the sum of the hash codes of each entry in the map's
663 * <tt>entrySet()</tt> view. This ensures that <tt>m1.equals(m2)</tt>
664 * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two
665 * <tt>IdentityHashMap</tt> instances <tt>m1</tt> and <tt>m2</tt>, as
666 * required by the general contract of {@link Object#hashCode}.
667 *
668 * <p><b>Owing to the reference-equality-based semantics of the
669 * <tt>Map.Entry</tt> instances in the set returned by this map's
670 * <tt>entrySet</tt> method, it is possible that the contractual
671 * requirement of <tt>Object.hashCode</tt> mentioned in the previous
672 * paragraph will be violated if one of the two objects being compared is
673 * an <tt>IdentityHashMap</tt> instance and the other is a normal map.</b>
674 *
675 * @return the hash code value for this map
676 * @see Object#equals(Object)
677 * @see #equals(Object)
678 */
679 public int hashCode() {
680 int result = 0;
681 Object[] tab = table;
682 for (int i = 0; i < tab.length; i +=2) {
683 Object key = tab[i];
684 if (key != null) {
685 Object k = unmaskNull(key);
686 result += System.identityHashCode(k) ^
687 System.identityHashCode(tab[i + 1]);
688 }
689 }
690 return result;
691 }
692
693 /**
694 * Returns a shallow copy of this identity hash map: the keys and values
695 * themselves are not cloned.
696 *
697 * @return a shallow copy of this map
698 */
699 public Object clone() {
700 try {
701 IdentityHashMap<K,V> m = (IdentityHashMap<K,V>) super.clone();
702 m.entrySet = null;
703 m.table = table.clone();
704 return m;
705 } catch (CloneNotSupportedException e) {
706 throw new InternalError();
707 }
708 }
709
710 private abstract class IdentityHashMapIterator<T> implements Iterator<T> {
711 int index = (size != 0 ? 0 : table.length); // current slot.
712 int expectedModCount = modCount; // to support fast-fail
713 int lastReturnedIndex = -1; // to allow remove()
714 boolean indexValid; // To avoid unnecessary next computation
715 Object[] traversalTable = table; // reference to main table or copy
716
717 public boolean hasNext() {
718 Object[] tab = traversalTable;
719 for (int i = index; i < tab.length; i+=2) {
720 Object key = tab[i];
721 if (key != null) {
722 index = i;
723 return indexValid = true;
724 }
725 }
726 index = tab.length;
727 return false;
728 }
729
730 protected int nextIndex() {
731 if (modCount != expectedModCount)
732 throw new ConcurrentModificationException();
733 if (!indexValid && !hasNext())
734 throw new NoSuchElementException();
735
736 indexValid = false;
737 lastReturnedIndex = index;
738 index += 2;
739 return lastReturnedIndex;
740 }
741
742 public void remove() {
743 if (lastReturnedIndex == -1)
744 throw new IllegalStateException();
745 if (modCount != expectedModCount)
746 throw new ConcurrentModificationException();
747
748 expectedModCount = ++modCount;
749 int deletedSlot = lastReturnedIndex;
750 lastReturnedIndex = -1;
751 // back up index to revisit new contents after deletion
752 index = deletedSlot;
753 indexValid = false;
754
755 // Removal code proceeds as in closeDeletion except that
756 // it must catch the rare case where an element already
757 // seen is swapped into a vacant slot that will be later
758 // traversed by this iterator. We cannot allow future
759 // next() calls to return it again. The likelihood of
760 // this occurring under 2/3 load factor is very slim, but
761 // when it does happen, we must make a copy of the rest of
762 // the table to use for the rest of the traversal. Since
763 // this can only happen when we are near the end of the table,
764 // even in these rare cases, this is not very expensive in
765 // time or space.
766
767 Object[] tab = traversalTable;
768 int len = tab.length;
769
770 int d = deletedSlot;
771 K key = (K) tab[d];
772 tab[d] = null; // vacate the slot
773 tab[d + 1] = null;
774
775 // If traversing a copy, remove in real table.
776 // We can skip gap-closure on copy.
777 if (tab != IdentityHashMap.this.table) {
778 IdentityHashMap.this.remove(key);
779 expectedModCount = modCount;
780 return;
781 }
782
783 size--;
784
785 Object item;
786 for (int i = nextKeyIndex(d, len); (item = tab[i]) != null;
787 i = nextKeyIndex(i, len)) {
788 int r = hash(item, len);
789 // See closeDeletion for explanation of this conditional
790 if ((i < r && (r <= d || d <= i)) ||
791 (r <= d && d <= i)) {
792
793 // If we are about to swap an already-seen element
794 // into a slot that may later be returned by next(),
795 // then clone the rest of table for use in future
796 // next() calls. It is OK that our copy will have
797 // a gap in the "wrong" place, since it will never
798 // be used for searching anyway.
799
800 if (i < deletedSlot && d >= deletedSlot &&
801 traversalTable == IdentityHashMap.this.table) {
802 int remaining = len - deletedSlot;
803 Object[] newTable = new Object[remaining];
804 System.arraycopy(tab, deletedSlot,
805 newTable, 0, remaining);
806 traversalTable = newTable;
807 index = 0;
808 }
809
810 tab[d] = item;
811 tab[d + 1] = tab[i + 1];
812 tab[i] = null;
813 tab[i + 1] = null;
814 d = i;
815 }
816 }
817 }
818 }
819
820 private class KeyIterator extends IdentityHashMapIterator<K> {
821 public K next() {
822 return (K) unmaskNull(traversalTable[nextIndex()]);
823 }
824 }
825
826 private class ValueIterator extends IdentityHashMapIterator<V> {
827 public V next() {
828 return (V) traversalTable[nextIndex() + 1];
829 }
830 }
831
832 private class EntryIterator
833 extends IdentityHashMapIterator<Map.Entry<K,V>>
834 {
835 private Entry lastReturnedEntry = null;
836
837 public Map.Entry<K,V> next() {
838 lastReturnedEntry = new Entry(nextIndex());
839 return lastReturnedEntry;
840 }
841
842 public void remove() {
843 lastReturnedIndex =
844 ((null == lastReturnedEntry) ? -1 : lastReturnedEntry.index);
845 super.remove();
846 lastReturnedEntry.index = lastReturnedIndex;
847 lastReturnedEntry = null;
848 }
849
850 private class Entry implements Map.Entry<K,V> {
851 private int index;
852
853 private Entry(int index) {
854 this.index = index;
855 }
856
857 public K getKey() {
858 checkIndexForEntryUse();
859 return (K) unmaskNull(traversalTable[index]);
860 }
861
862 public V getValue() {
863 checkIndexForEntryUse();
864 return (V) traversalTable[index+1];
865 }
866
867 public V setValue(V value) {
868 checkIndexForEntryUse();
869 V oldValue = (V) traversalTable[index+1];
870 traversalTable[index+1] = value;
871 // if shadowing, force into main table
872 if (traversalTable != IdentityHashMap.this.table)
873 put((K) traversalTable[index], value);
874 return oldValue;
875 }
876
877 public boolean equals(Object o) {
878 if (index < 0)
879 return super.equals(o);
880
881 if (!(o instanceof Map.Entry))
882 return false;
883 Map.Entry e = (Map.Entry)o;
884 return (e.getKey() == unmaskNull(traversalTable[index]) &&
885 e.getValue() == traversalTable[index+1]);
886 }
887
888 public int hashCode() {
889 if (lastReturnedIndex < 0)
890 return super.hashCode();
891
892 return (System.identityHashCode(unmaskNull(traversalTable[index])) ^
893 System.identityHashCode(traversalTable[index+1]));
894 }
895
896 public String toString() {
897 if (index < 0)
898 return super.toString();
899
900 return (unmaskNull(traversalTable[index]) + "="
901 + traversalTable[index+1]);
902 }
903
904 private void checkIndexForEntryUse() {
905 if (index < 0)
906 throw new IllegalStateException("Entry was removed");
907 }
908 }
909 }
910
911 // Views
912
913 /**
914 * This field is initialized to contain an instance of the entry set
915 * view the first time this view is requested. The view is stateless,
916 * so there's no reason to create more than one.
917 */
918 private transient Set<Map.Entry<K,V>> entrySet = null;
919
920 /**
921 * Returns an identity-based set view of the keys contained in this map.
922 * The set is backed by the map, so changes to the map are reflected in
923 * the set, and vice-versa. If the map is modified while an iteration
924 * over the set is in progress, the results of the iteration are
925 * undefined. The set supports element removal, which removes the
926 * corresponding mapping from the map, via the <tt>Iterator.remove</tt>,
927 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and
928 * <tt>clear</tt> methods. It does not support the <tt>add</tt> or
929 * <tt>addAll</tt> methods.
930 *
931 * <p><b>While the object returned by this method implements the
932 * <tt>Set</tt> interface, it does <i>not</i> obey <tt>Set's</tt> general
933 * contract. Like its backing map, the set returned by this method
934 * defines element equality as reference-equality rather than
935 * object-equality. This affects the behavior of its <tt>contains</tt>,
936 * <tt>remove</tt>, <tt>containsAll</tt>, <tt>equals</tt>, and
937 * <tt>hashCode</tt> methods.</b>
938 *
939 * <p><b>The <tt>equals</tt> method of the returned set returns <tt>true</tt>
940 * only if the specified object is a set containing exactly the same
941 * object references as the returned set. The symmetry and transitivity
942 * requirements of the <tt>Object.equals</tt> contract may be violated if
943 * the set returned by this method is compared to a normal set. However,
944 * the <tt>Object.equals</tt> contract is guaranteed to hold among sets
945 * returned by this method.</b>
946 *
947 * <p>The <tt>hashCode</tt> method of the returned set returns the sum of
948 * the <i>identity hashcodes</i> of the elements in the set, rather than
949 * the sum of their hashcodes. This is mandated by the change in the
950 * semantics of the <tt>equals</tt> method, in order to enforce the
951 * general contract of the <tt>Object.hashCode</tt> method among sets
952 * returned by this method.
953 *
954 * @return an identity-based set view of the keys contained in this map
955 * @see Object#equals(Object)
956 * @see System#identityHashCode(Object)
957 */
958 public Set<K> keySet() {
959 Set<K> ks = keySet;
960 if (ks != null)
961 return ks;
962 else
963 return keySet = new KeySet();
964 }
965
966 private class KeySet extends AbstractSet<K> {
967 public Iterator<K> iterator() {
968 return new KeyIterator();
969 }
970 public int size() {
971 return size;
972 }
973 public boolean contains(Object o) {
974 return containsKey(o);
975 }
976 public boolean remove(Object o) {
977 int oldSize = size;
978 IdentityHashMap.this.remove(o);
979 return size != oldSize;
980 }
981 /*
982 * Must revert from AbstractSet's impl to AbstractCollection's, as
983 * the former contains an optimization that results in incorrect
984 * behavior when c is a smaller "normal" (non-identity-based) Set.
985 */
986 public boolean removeAll(Collection<?> c) {
987 boolean modified = false;
988 for (Iterator<K> i = iterator(); i.hasNext(); ) {
989 if (c.contains(i.next())) {
990 i.remove();
991 modified = true;
992 }
993 }
994 return modified;
995 }
996 public void clear() {
997 IdentityHashMap.this.clear();
998 }
999 public int hashCode() {
1000 int result = 0;
1001 for (K key : this)
1002 result += System.identityHashCode(key);
1003 return result;
1004 }
1005 }
1006
1007 /**
1008 * Returns a {@link Collection} view of the values contained in this map.
1009 * The collection is backed by the map, so changes to the map are
1010 * reflected in the collection, and vice-versa. If the map is
1011 * modified while an iteration over the collection is in progress,
1012 * the results of the iteration are undefined. The collection
1013 * supports element removal, which removes the corresponding
1014 * mapping from the map, via the <tt>Iterator.remove</tt>,
1015 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
1016 * <tt>retainAll</tt> and <tt>clear</tt> methods. It does not
1017 * support the <tt>add</tt> or <tt>addAll</tt> methods.
1018 *
1019 * <p><b>While the object returned by this method implements the
1020 * <tt>Collection</tt> interface, it does <i>not</i> obey
1021 * <tt>Collection's</tt> general contract. Like its backing map,
1022 * the collection returned by this method defines element equality as
1023 * reference-equality rather than object-equality. This affects the
1024 * behavior of its <tt>contains</tt>, <tt>remove</tt> and
1025 * <tt>containsAll</tt> methods.</b>
1026 */
1027 public Collection<V> values() {
1028 Collection<V> vs = values;
1029 if (vs != null)
1030 return vs;
1031 else
1032 return values = new Values();
1033 }
1034
1035 private class Values extends AbstractCollection<V> {
1036 public Iterator<V> iterator() {
1037 return new ValueIterator();
1038 }
1039 public int size() {
1040 return size;
1041 }
1042 public boolean contains(Object o) {
1043 return containsValue(o);
1044 }
1045 public boolean remove(Object o) {
1046 for (Iterator<V> i = iterator(); i.hasNext(); ) {
1047 if (i.next() == o) {
1048 i.remove();
1049 return true;
1050 }
1051 }
1052 return false;
1053 }
1054 public void clear() {
1055 IdentityHashMap.this.clear();
1056 }
1057 }
1058
1059 /**
1060 * Returns a {@link Set} view of the mappings contained in this map.
1061 * Each element in the returned set is a reference-equality-based
1062 * <tt>Map.Entry</tt>. The set is backed by the map, so changes
1063 * to the map are reflected in the set, and vice-versa. If the
1064 * map is modified while an iteration over the set is in progress,
1065 * the results of the iteration are undefined. The set supports
1066 * element removal, which removes the corresponding mapping from
1067 * the map, via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
1068 * <tt>removeAll</tt>, <tt>retainAll</tt> and <tt>clear</tt>
1069 * methods. It does not support the <tt>add</tt> or
1070 * <tt>addAll</tt> methods.
1071 *
1072 * <p>Like the backing map, the <tt>Map.Entry</tt> objects in the set
1073 * returned by this method define key and value equality as
1074 * reference-equality rather than object-equality. This affects the
1075 * behavior of the <tt>equals</tt> and <tt>hashCode</tt> methods of these
1076 * <tt>Map.Entry</tt> objects. A reference-equality based <tt>Map.Entry
1077 * e</tt> is equal to an object <tt>o</tt> if and only if <tt>o</tt> is a
1078 * <tt>Map.Entry</tt> and <tt>e.getKey()==o.getKey() &&
1079 * e.getValue()==o.getValue()</tt>. To accommodate these equals
1080 * semantics, the <tt>hashCode</tt> method returns
1081 * <tt>System.identityHashCode(e.getKey()) ^
1082 * System.identityHashCode(e.getValue())</tt>.
1083 *
1084 * <p><b>Owing to the reference-equality-based semantics of the
1085 * <tt>Map.Entry</tt> instances in the set returned by this method,
1086 * it is possible that the symmetry and transitivity requirements of
1087 * the {@link Object#equals(Object)} contract may be violated if any of
1088 * the entries in the set is compared to a normal map entry, or if
1089 * the set returned by this method is compared to a set of normal map
1090 * entries (such as would be returned by a call to this method on a normal
1091 * map). However, the <tt>Object.equals</tt> contract is guaranteed to
1092 * hold among identity-based map entries, and among sets of such entries.
1093 * </b>
1094 *
1095 * @return a set view of the identity-mappings contained in this map
1096 */
1097 public Set<Map.Entry<K,V>> entrySet() {
1098 Set<Map.Entry<K,V>> es = entrySet;
1099 if (es != null)
1100 return es;
1101 else
1102 return entrySet = new EntrySet();
1103 }
1104
1105 private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
1106 public Iterator<Map.Entry<K,V>> iterator() {
1107 return new EntryIterator();
1108 }
1109 public boolean contains(Object o) {
1110 if (!(o instanceof Map.Entry))
1111 return false;
1112 Map.Entry entry = (Map.Entry)o;
1113 return containsMapping(entry.getKey(), entry.getValue());
1114 }
1115 public boolean remove(Object o) {
1116 if (!(o instanceof Map.Entry))
1117 return false;
1118 Map.Entry entry = (Map.Entry)o;
1119 return removeMapping(entry.getKey(), entry.getValue());
1120 }
1121 public int size() {
1122 return size;
1123 }
1124 public void clear() {
1125 IdentityHashMap.this.clear();
1126 }
1127 /*
1128 * Must revert from AbstractSet's impl to AbstractCollection's, as
1129 * the former contains an optimization that results in incorrect
1130 * behavior when c is a smaller "normal" (non-identity-based) Set.
1131 */
1132 public boolean removeAll(Collection<?> c) {
1133 boolean modified = false;
1134 for (Iterator<Map.Entry<K,V>> i = iterator(); i.hasNext(); ) {
1135 if (c.contains(i.next())) {
1136 i.remove();
1137 modified = true;
1138 }
1139 }
1140 return modified;
1141 }
1142
1143 public Object[] toArray() {
1144 int size = size();
1145 Object[] result = new Object[size];
1146 Iterator<Map.Entry<K,V>> it = iterator();
1147 for (int i = 0; i < size; i++)
1148 result[i] = new AbstractMap.SimpleEntry<>(it.next());
1149 return result;
1150 }
1151
1152 @SuppressWarnings("unchecked")
1153 public <T> T[] toArray(T[] a) {
1154 int size = size();
1155 if (a.length < size)
1156 a = (T[])java.lang.reflect.Array
1157 .newInstance(a.getClass().getComponentType(), size);
1158 Iterator<Map.Entry<K,V>> it = iterator();
1159 for (int i = 0; i < size; i++)
1160 a[i] = (T) new AbstractMap.SimpleEntry<>(it.next());
1161 if (a.length > size)
1162 a[size] = null;
1163 return a;
1164 }
1165 }
1166
1167
1168 private static final long serialVersionUID = 8188218128353913216L;
1169
1170 /**
1171 * Save the state of the <tt>IdentityHashMap</tt> instance to a stream
1172 * (i.e., serialize it).
1173 *
1174 * @serialData The <i>size</i> of the HashMap (the number of key-value
1175 * mappings) (<tt>int</tt>), followed by the key (Object) and
1176 * value (Object) for each key-value mapping represented by the
1177 * IdentityHashMap. The key-value mappings are emitted in no
1178 * particular order.
1179 */
1180 private void writeObject(java.io.ObjectOutputStream s)
1181 throws java.io.IOException {
1182 // Write out and any hidden stuff
1183 s.defaultWriteObject();
1184
1185 // Write out size (number of Mappings)
1186 s.writeInt(size);
1187
1188 // Write out keys and values (alternating)
1189 Object[] tab = table;
1190 for (int i = 0; i < tab.length; i += 2) {
1191 Object key = tab[i];
1192 if (key != null) {
1193 s.writeObject(unmaskNull(key));
1194 s.writeObject(tab[i + 1]);
1195 }
1196 }
1197 }
1198
1199 /**
1200 * Reconstitute the <tt>IdentityHashMap</tt> instance from a stream (i.e.,
1201 * deserialize it).
1202 */
1203 private void readObject(java.io.ObjectInputStream s)
1204 throws java.io.IOException, ClassNotFoundException {
1205 // Read in any hidden stuff
1206 s.defaultReadObject();
1207
1208 // Read in size (number of Mappings)
1209 int size = s.readInt();
1210
1211 // Allow for 33% growth (i.e., capacity is >= 2* size()).
1212 init(capacity((size*4)/3));
1213
1214 // Read the keys and values, and put the mappings in the table
1215 for (int i=0; i<size; i++) {
1216 K key = (K) s.readObject();
1217 V value = (V) s.readObject();
1218 putForCreate(key, value);
1219 }
1220 }
1221
1222 /**
1223 * The put method for readObject. It does not resize the table,
1224 * update modCount, etc.
1225 */
1226 private void putForCreate(K key, V value)
1227 throws IOException
1228 {
1229 K k = (K)maskNull(key);
1230 Object[] tab = table;
1231 int len = tab.length;
1232 int i = hash(k, len);
1233
1234 Object item;
1235 while ( (item = tab[i]) != null) {
1236 if (item == k)
1237 throw new java.io.StreamCorruptedException();
1238 i = nextKeyIndex(i, len);
1239 }
1240 tab[i] = k;
1241 tab[i + 1] = value;
1242 }
1243 }