1 |
/* |
2 |
* Written by Josh Bloch of Google Inc. and released to the public domain, |
3 |
* as explained at http://creativecommons.org/publicdomain/zero/1.0/. |
4 |
*/ |
5 |
|
6 |
package java.util; |
7 |
|
8 |
import java.io.Serializable; |
9 |
import java.util.function.Consumer; |
10 |
|
11 |
/** |
12 |
* Resizable-array implementation of the {@link Deque} interface. Array |
13 |
* deques have no capacity restrictions; they grow as necessary to support |
14 |
* usage. They are not thread-safe; in the absence of external |
15 |
* synchronization, they do not support concurrent access by multiple threads. |
16 |
* Null elements are prohibited. This class is likely to be faster than |
17 |
* {@link Stack} when used as a stack, and faster than {@link LinkedList} |
18 |
* when used as a queue. |
19 |
* |
20 |
* <p>Most {@code ArrayDeque} operations run in amortized constant time. |
21 |
* Exceptions include |
22 |
* {@link #remove(Object) remove}, |
23 |
* {@link #removeFirstOccurrence removeFirstOccurrence}, |
24 |
* {@link #removeLastOccurrence removeLastOccurrence}, |
25 |
* {@link #contains contains}, |
26 |
* {@link #iterator iterator.remove()}, |
27 |
* and the bulk operations, all of which run in linear time. |
28 |
* |
29 |
* <p>The iterators returned by this class's {@link #iterator() iterator} |
30 |
* method are <em>fail-fast</em>: If the deque is modified at any time after |
31 |
* the iterator is created, in any way except through the iterator's own |
32 |
* {@code remove} method, the iterator will generally throw a {@link |
33 |
* ConcurrentModificationException}. Thus, in the face of concurrent |
34 |
* modification, the iterator fails quickly and cleanly, rather than risking |
35 |
* arbitrary, non-deterministic behavior at an undetermined time in the |
36 |
* future. |
37 |
* |
38 |
* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed |
39 |
* as it is, generally speaking, impossible to make any hard guarantees in the |
40 |
* presence of unsynchronized concurrent modification. Fail-fast iterators |
41 |
* throw {@code ConcurrentModificationException} on a best-effort basis. |
42 |
* Therefore, it would be wrong to write a program that depended on this |
43 |
* exception for its correctness: <i>the fail-fast behavior of iterators |
44 |
* should be used only to detect bugs.</i> |
45 |
* |
46 |
* <p>This class and its iterator implement all of the |
47 |
* <em>optional</em> methods of the {@link Collection} and {@link |
48 |
* Iterator} interfaces. |
49 |
* |
50 |
* <p>This class is a member of the |
51 |
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
52 |
* Java Collections Framework</a>. |
53 |
* |
54 |
* @author Josh Bloch and Doug Lea |
55 |
* @since 1.6 |
56 |
* @param <E> the type of elements held in this deque |
57 |
*/ |
58 |
public class ArrayDeque<E> extends AbstractCollection<E> |
59 |
implements Deque<E>, Cloneable, Serializable |
60 |
{ |
61 |
/** |
62 |
* The array in which the elements of the deque are stored. |
63 |
* The capacity of the deque is the length of this array, which is |
64 |
* always a power of two. The array is never allowed to become |
65 |
* full, except transiently within an addX method where it is |
66 |
* resized (see doubleCapacity) immediately upon becoming full, |
67 |
* thus avoiding head and tail wrapping around to equal each |
68 |
* other. We also guarantee that all array cells not holding |
69 |
* deque elements are always null. |
70 |
*/ |
71 |
transient Object[] elements; // non-private to simplify nested class access |
72 |
|
73 |
/** |
74 |
* The index of the element at the head of the deque (which is the |
75 |
* element that would be removed by remove() or pop()); or an |
76 |
* arbitrary number equal to tail if the deque is empty. |
77 |
*/ |
78 |
transient int head; |
79 |
|
80 |
/** |
81 |
* The index at which the next element would be added to the tail |
82 |
* of the deque (via addLast(E), add(E), or push(E)). |
83 |
*/ |
84 |
transient int tail; |
85 |
|
86 |
/** |
87 |
* The minimum capacity that we'll use for a newly created deque. |
88 |
* Must be a power of 2. |
89 |
*/ |
90 |
private static final int MIN_INITIAL_CAPACITY = 8; |
91 |
|
92 |
// ****** Array allocation and resizing utilities ****** |
93 |
|
94 |
/** |
95 |
* Allocates empty array to hold the given number of elements. |
96 |
* |
97 |
* @param numElements the number of elements to hold |
98 |
*/ |
99 |
private void allocateElements(int numElements) { |
100 |
int initialCapacity = MIN_INITIAL_CAPACITY; |
101 |
// Find the best power of two to hold elements. |
102 |
// Tests "<=" because arrays aren't kept full. |
103 |
if (numElements >= initialCapacity) { |
104 |
initialCapacity = numElements; |
105 |
initialCapacity |= (initialCapacity >>> 1); |
106 |
initialCapacity |= (initialCapacity >>> 2); |
107 |
initialCapacity |= (initialCapacity >>> 4); |
108 |
initialCapacity |= (initialCapacity >>> 8); |
109 |
initialCapacity |= (initialCapacity >>> 16); |
110 |
initialCapacity++; |
111 |
|
112 |
if (initialCapacity < 0) // Too many elements, must back off |
113 |
initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements |
114 |
} |
115 |
elements = new Object[initialCapacity]; |
116 |
} |
117 |
|
118 |
/** |
119 |
* Doubles the capacity of this deque. Call only when full, i.e., |
120 |
* when head and tail have wrapped around to become equal. |
121 |
*/ |
122 |
private void doubleCapacity() { |
123 |
assert head == tail; |
124 |
int p = head; |
125 |
int n = elements.length; |
126 |
int r = n - p; // number of elements to the right of p |
127 |
int newCapacity = n << 1; |
128 |
if (newCapacity < 0) |
129 |
throw new IllegalStateException("Sorry, deque too big"); |
130 |
Object[] a = new Object[newCapacity]; |
131 |
System.arraycopy(elements, p, a, 0, r); |
132 |
System.arraycopy(elements, 0, a, r, p); |
133 |
elements = a; |
134 |
head = 0; |
135 |
tail = n; |
136 |
} |
137 |
|
138 |
/** |
139 |
* Constructs an empty array deque with an initial capacity |
140 |
* sufficient to hold 16 elements. |
141 |
*/ |
142 |
public ArrayDeque() { |
143 |
elements = new Object[16]; |
144 |
} |
145 |
|
146 |
/** |
147 |
* Constructs an empty array deque with an initial capacity |
148 |
* sufficient to hold the specified number of elements. |
149 |
* |
150 |
* @param numElements lower bound on initial capacity of the deque |
151 |
*/ |
152 |
public ArrayDeque(int numElements) { |
153 |
allocateElements(numElements); |
154 |
} |
155 |
|
156 |
/** |
157 |
* Constructs a deque containing the elements of the specified |
158 |
* collection, in the order they are returned by the collection's |
159 |
* iterator. (The first element returned by the collection's |
160 |
* iterator becomes the first element, or <i>front</i> of the |
161 |
* deque.) |
162 |
* |
163 |
* @param c the collection whose elements are to be placed into the deque |
164 |
* @throws NullPointerException if the specified collection is null |
165 |
*/ |
166 |
public ArrayDeque(Collection<? extends E> c) { |
167 |
allocateElements(c.size()); |
168 |
addAll(c); |
169 |
} |
170 |
|
171 |
// The main insertion and extraction methods are addFirst, |
172 |
// addLast, pollFirst, pollLast. The other methods are defined in |
173 |
// terms of these. |
174 |
|
175 |
/** |
176 |
* Inserts the specified element at the front of this deque. |
177 |
* |
178 |
* @param e the element to add |
179 |
* @throws NullPointerException if the specified element is null |
180 |
*/ |
181 |
public void addFirst(E e) { |
182 |
if (e == null) |
183 |
throw new NullPointerException(); |
184 |
elements[head = (head - 1) & (elements.length - 1)] = e; |
185 |
if (head == tail) |
186 |
doubleCapacity(); |
187 |
} |
188 |
|
189 |
/** |
190 |
* Inserts the specified element at the end of this deque. |
191 |
* |
192 |
* <p>This method is equivalent to {@link #add}. |
193 |
* |
194 |
* @param e the element to add |
195 |
* @throws NullPointerException if the specified element is null |
196 |
*/ |
197 |
public void addLast(E e) { |
198 |
if (e == null) |
199 |
throw new NullPointerException(); |
200 |
elements[tail] = e; |
201 |
if ( (tail = (tail + 1) & (elements.length - 1)) == head) |
202 |
doubleCapacity(); |
203 |
} |
204 |
|
205 |
/** |
206 |
* Inserts the specified element at the front of this deque. |
207 |
* |
208 |
* @param e the element to add |
209 |
* @return {@code true} (as specified by {@link Deque#offerFirst}) |
210 |
* @throws NullPointerException if the specified element is null |
211 |
*/ |
212 |
public boolean offerFirst(E e) { |
213 |
addFirst(e); |
214 |
return true; |
215 |
} |
216 |
|
217 |
/** |
218 |
* Inserts the specified element at the end of this deque. |
219 |
* |
220 |
* @param e the element to add |
221 |
* @return {@code true} (as specified by {@link Deque#offerLast}) |
222 |
* @throws NullPointerException if the specified element is null |
223 |
*/ |
224 |
public boolean offerLast(E e) { |
225 |
addLast(e); |
226 |
return true; |
227 |
} |
228 |
|
229 |
/** |
230 |
* @throws NoSuchElementException {@inheritDoc} |
231 |
*/ |
232 |
public E removeFirst() { |
233 |
E x = pollFirst(); |
234 |
if (x == null) |
235 |
throw new NoSuchElementException(); |
236 |
return x; |
237 |
} |
238 |
|
239 |
/** |
240 |
* @throws NoSuchElementException {@inheritDoc} |
241 |
*/ |
242 |
public E removeLast() { |
243 |
E x = pollLast(); |
244 |
if (x == null) |
245 |
throw new NoSuchElementException(); |
246 |
return x; |
247 |
} |
248 |
|
249 |
public E pollFirst() { |
250 |
final Object[] elements = this.elements; |
251 |
final int h = head; |
252 |
@SuppressWarnings("unchecked") |
253 |
E result = (E) elements[h]; |
254 |
// Element is null if deque empty |
255 |
if (result != null) { |
256 |
elements[h] = null; // Must null out slot |
257 |
head = (h + 1) & (elements.length - 1); |
258 |
} |
259 |
return result; |
260 |
} |
261 |
|
262 |
public E pollLast() { |
263 |
final Object[] elements = this.elements; |
264 |
final int t = (tail - 1) & (elements.length - 1); |
265 |
@SuppressWarnings("unchecked") |
266 |
E result = (E) elements[t]; |
267 |
if (result != null) { |
268 |
elements[t] = null; |
269 |
tail = t; |
270 |
} |
271 |
return result; |
272 |
} |
273 |
|
274 |
/** |
275 |
* @throws NoSuchElementException {@inheritDoc} |
276 |
*/ |
277 |
public E getFirst() { |
278 |
@SuppressWarnings("unchecked") |
279 |
E result = (E) elements[head]; |
280 |
if (result == null) |
281 |
throw new NoSuchElementException(); |
282 |
return result; |
283 |
} |
284 |
|
285 |
/** |
286 |
* @throws NoSuchElementException {@inheritDoc} |
287 |
*/ |
288 |
public E getLast() { |
289 |
@SuppressWarnings("unchecked") |
290 |
E result = (E) elements[(tail - 1) & (elements.length - 1)]; |
291 |
if (result == null) |
292 |
throw new NoSuchElementException(); |
293 |
return result; |
294 |
} |
295 |
|
296 |
@SuppressWarnings("unchecked") |
297 |
public E peekFirst() { |
298 |
// elements[head] is null if deque empty |
299 |
return (E) elements[head]; |
300 |
} |
301 |
|
302 |
@SuppressWarnings("unchecked") |
303 |
public E peekLast() { |
304 |
return (E) elements[(tail - 1) & (elements.length - 1)]; |
305 |
} |
306 |
|
307 |
/** |
308 |
* Removes the first occurrence of the specified element in this |
309 |
* deque (when traversing the deque from head to tail). |
310 |
* If the deque does not contain the element, it is unchanged. |
311 |
* More formally, removes the first element {@code e} such that |
312 |
* {@code o.equals(e)} (if such an element exists). |
313 |
* Returns {@code true} if this deque contained the specified element |
314 |
* (or equivalently, if this deque changed as a result of the call). |
315 |
* |
316 |
* @param o element to be removed from this deque, if present |
317 |
* @return {@code true} if the deque contained the specified element |
318 |
*/ |
319 |
public boolean removeFirstOccurrence(Object o) { |
320 |
if (o != null) { |
321 |
int mask = elements.length - 1; |
322 |
int i = head; |
323 |
for (Object x; (x = elements[i]) != null; i = (i + 1) & mask) { |
324 |
if (o.equals(x)) { |
325 |
delete(i); |
326 |
return true; |
327 |
} |
328 |
} |
329 |
} |
330 |
return false; |
331 |
} |
332 |
|
333 |
/** |
334 |
* Removes the last occurrence of the specified element in this |
335 |
* deque (when traversing the deque from head to tail). |
336 |
* If the deque does not contain the element, it is unchanged. |
337 |
* More formally, removes the last element {@code e} such that |
338 |
* {@code o.equals(e)} (if such an element exists). |
339 |
* Returns {@code true} if this deque contained the specified element |
340 |
* (or equivalently, if this deque changed as a result of the call). |
341 |
* |
342 |
* @param o element to be removed from this deque, if present |
343 |
* @return {@code true} if the deque contained the specified element |
344 |
*/ |
345 |
public boolean removeLastOccurrence(Object o) { |
346 |
if (o != null) { |
347 |
int mask = elements.length - 1; |
348 |
int i = (tail - 1) & mask; |
349 |
for (Object x; (x = elements[i]) != null; i = (i - 1) & mask) { |
350 |
if (o.equals(x)) { |
351 |
delete(i); |
352 |
return true; |
353 |
} |
354 |
} |
355 |
} |
356 |
return false; |
357 |
} |
358 |
|
359 |
// *** Queue methods *** |
360 |
|
361 |
/** |
362 |
* Inserts the specified element at the end of this deque. |
363 |
* |
364 |
* <p>This method is equivalent to {@link #addLast}. |
365 |
* |
366 |
* @param e the element to add |
367 |
* @return {@code true} (as specified by {@link Collection#add}) |
368 |
* @throws NullPointerException if the specified element is null |
369 |
*/ |
370 |
public boolean add(E e) { |
371 |
addLast(e); |
372 |
return true; |
373 |
} |
374 |
|
375 |
/** |
376 |
* Inserts the specified element at the end of this deque. |
377 |
* |
378 |
* <p>This method is equivalent to {@link #offerLast}. |
379 |
* |
380 |
* @param e the element to add |
381 |
* @return {@code true} (as specified by {@link Queue#offer}) |
382 |
* @throws NullPointerException if the specified element is null |
383 |
*/ |
384 |
public boolean offer(E e) { |
385 |
return offerLast(e); |
386 |
} |
387 |
|
388 |
/** |
389 |
* Retrieves and removes the head of the queue represented by this deque. |
390 |
* |
391 |
* This method differs from {@link #poll poll} only in that it throws an |
392 |
* exception if this deque is empty. |
393 |
* |
394 |
* <p>This method is equivalent to {@link #removeFirst}. |
395 |
* |
396 |
* @return the head of the queue represented by this deque |
397 |
* @throws NoSuchElementException {@inheritDoc} |
398 |
*/ |
399 |
public E remove() { |
400 |
return removeFirst(); |
401 |
} |
402 |
|
403 |
/** |
404 |
* Retrieves and removes the head of the queue represented by this deque |
405 |
* (in other words, the first element of this deque), or returns |
406 |
* {@code null} if this deque is empty. |
407 |
* |
408 |
* <p>This method is equivalent to {@link #pollFirst}. |
409 |
* |
410 |
* @return the head of the queue represented by this deque, or |
411 |
* {@code null} if this deque is empty |
412 |
*/ |
413 |
public E poll() { |
414 |
return pollFirst(); |
415 |
} |
416 |
|
417 |
/** |
418 |
* Retrieves, but does not remove, the head of the queue represented by |
419 |
* this deque. This method differs from {@link #peek peek} only in |
420 |
* that it throws an exception if this deque is empty. |
421 |
* |
422 |
* <p>This method is equivalent to {@link #getFirst}. |
423 |
* |
424 |
* @return the head of the queue represented by this deque |
425 |
* @throws NoSuchElementException {@inheritDoc} |
426 |
*/ |
427 |
public E element() { |
428 |
return getFirst(); |
429 |
} |
430 |
|
431 |
/** |
432 |
* Retrieves, but does not remove, the head of the queue represented by |
433 |
* this deque, or returns {@code null} if this deque is empty. |
434 |
* |
435 |
* <p>This method is equivalent to {@link #peekFirst}. |
436 |
* |
437 |
* @return the head of the queue represented by this deque, or |
438 |
* {@code null} if this deque is empty |
439 |
*/ |
440 |
public E peek() { |
441 |
return peekFirst(); |
442 |
} |
443 |
|
444 |
// *** Stack methods *** |
445 |
|
446 |
/** |
447 |
* Pushes an element onto the stack represented by this deque. In other |
448 |
* words, inserts the element at the front of this deque. |
449 |
* |
450 |
* <p>This method is equivalent to {@link #addFirst}. |
451 |
* |
452 |
* @param e the element to push |
453 |
* @throws NullPointerException if the specified element is null |
454 |
*/ |
455 |
public void push(E e) { |
456 |
addFirst(e); |
457 |
} |
458 |
|
459 |
/** |
460 |
* Pops an element from the stack represented by this deque. In other |
461 |
* words, removes and returns the first element of this deque. |
462 |
* |
463 |
* <p>This method is equivalent to {@link #removeFirst()}. |
464 |
* |
465 |
* @return the element at the front of this deque (which is the top |
466 |
* of the stack represented by this deque) |
467 |
* @throws NoSuchElementException {@inheritDoc} |
468 |
*/ |
469 |
public E pop() { |
470 |
return removeFirst(); |
471 |
} |
472 |
|
473 |
private void checkInvariants() { |
474 |
assert elements[tail] == null; |
475 |
assert head == tail ? elements[head] == null : |
476 |
(elements[head] != null && |
477 |
elements[(tail - 1) & (elements.length - 1)] != null); |
478 |
assert elements[(head - 1) & (elements.length - 1)] == null; |
479 |
} |
480 |
|
481 |
/** |
482 |
* Removes the element at the specified position in the elements array, |
483 |
* adjusting head and tail as necessary. This can result in motion of |
484 |
* elements backwards or forwards in the array. |
485 |
* |
486 |
* <p>This method is called delete rather than remove to emphasize |
487 |
* that its semantics differ from those of {@link List#remove(int)}. |
488 |
* |
489 |
* @return true if elements moved backwards |
490 |
*/ |
491 |
private boolean delete(int i) { |
492 |
checkInvariants(); |
493 |
final Object[] elements = this.elements; |
494 |
final int mask = elements.length - 1; |
495 |
final int h = head; |
496 |
final int t = tail; |
497 |
final int front = (i - h) & mask; |
498 |
final int back = (t - i) & mask; |
499 |
|
500 |
// Invariant: head <= i < tail mod circularity |
501 |
if (front >= ((t - h) & mask)) |
502 |
throw new ConcurrentModificationException(); |
503 |
|
504 |
// Optimize for least element motion |
505 |
if (front < back) { |
506 |
if (h <= i) { |
507 |
System.arraycopy(elements, h, elements, h + 1, front); |
508 |
} else { // Wrap around |
509 |
System.arraycopy(elements, 0, elements, 1, i); |
510 |
elements[0] = elements[mask]; |
511 |
System.arraycopy(elements, h, elements, h + 1, mask - h); |
512 |
} |
513 |
elements[h] = null; |
514 |
head = (h + 1) & mask; |
515 |
return false; |
516 |
} else { |
517 |
if (i < t) { // Copy the null tail as well |
518 |
System.arraycopy(elements, i + 1, elements, i, back); |
519 |
tail = t - 1; |
520 |
} else { // Wrap around |
521 |
System.arraycopy(elements, i + 1, elements, i, mask - i); |
522 |
elements[mask] = elements[0]; |
523 |
System.arraycopy(elements, 1, elements, 0, t); |
524 |
tail = (t - 1) & mask; |
525 |
} |
526 |
return true; |
527 |
} |
528 |
} |
529 |
|
530 |
// *** Collection Methods *** |
531 |
|
532 |
/** |
533 |
* Returns the number of elements in this deque. |
534 |
* |
535 |
* @return the number of elements in this deque |
536 |
*/ |
537 |
public int size() { |
538 |
return (tail - head) & (elements.length - 1); |
539 |
} |
540 |
|
541 |
/** |
542 |
* Returns {@code true} if this deque contains no elements. |
543 |
* |
544 |
* @return {@code true} if this deque contains no elements |
545 |
*/ |
546 |
public boolean isEmpty() { |
547 |
return head == tail; |
548 |
} |
549 |
|
550 |
/** |
551 |
* Returns an iterator over the elements in this deque. The elements |
552 |
* will be ordered from first (head) to last (tail). This is the same |
553 |
* order that elements would be dequeued (via successive calls to |
554 |
* {@link #remove} or popped (via successive calls to {@link #pop}). |
555 |
* |
556 |
* @return an iterator over the elements in this deque |
557 |
*/ |
558 |
public Iterator<E> iterator() { |
559 |
return new DeqIterator(); |
560 |
} |
561 |
|
562 |
public Iterator<E> descendingIterator() { |
563 |
return new DescendingIterator(); |
564 |
} |
565 |
|
566 |
private class DeqIterator implements Iterator<E> { |
567 |
/** |
568 |
* Index of element to be returned by subsequent call to next. |
569 |
*/ |
570 |
private int cursor = head; |
571 |
|
572 |
/** |
573 |
* Tail recorded at construction (also in remove), to stop |
574 |
* iterator and also to check for comodification. |
575 |
*/ |
576 |
private int fence = tail; |
577 |
|
578 |
/** |
579 |
* Index of element returned by most recent call to next. |
580 |
* Reset to -1 if element is deleted by a call to remove. |
581 |
*/ |
582 |
private int lastRet = -1; |
583 |
|
584 |
public boolean hasNext() { |
585 |
return cursor != fence; |
586 |
} |
587 |
|
588 |
public E next() { |
589 |
if (cursor == fence) |
590 |
throw new NoSuchElementException(); |
591 |
@SuppressWarnings("unchecked") |
592 |
E result = (E) elements[cursor]; |
593 |
// This check doesn't catch all possible comodifications, |
594 |
// but does catch the ones that corrupt traversal |
595 |
if (tail != fence || result == null) |
596 |
throw new ConcurrentModificationException(); |
597 |
lastRet = cursor; |
598 |
cursor = (cursor + 1) & (elements.length - 1); |
599 |
return result; |
600 |
} |
601 |
|
602 |
public void remove() { |
603 |
if (lastRet < 0) |
604 |
throw new IllegalStateException(); |
605 |
if (delete(lastRet)) { // if left-shifted, undo increment in next() |
606 |
cursor = (cursor - 1) & (elements.length - 1); |
607 |
fence = tail; |
608 |
} |
609 |
lastRet = -1; |
610 |
} |
611 |
|
612 |
public void forEachRemaining(Consumer<? super E> action) { |
613 |
Objects.requireNonNull(action); |
614 |
Object[] a = elements; |
615 |
int m = a.length - 1, f = fence, i = cursor; |
616 |
cursor = f; |
617 |
while (i != f) { |
618 |
@SuppressWarnings("unchecked") E e = (E)a[i]; |
619 |
i = (i + 1) & m; |
620 |
if (e == null) |
621 |
throw new ConcurrentModificationException(); |
622 |
action.accept(e); |
623 |
} |
624 |
} |
625 |
} |
626 |
|
627 |
/** |
628 |
* This class is nearly a mirror-image of DeqIterator, using tail |
629 |
* instead of head for initial cursor, and head instead of tail |
630 |
* for fence. |
631 |
*/ |
632 |
private class DescendingIterator implements Iterator<E> { |
633 |
private int cursor = tail; |
634 |
private int fence = head; |
635 |
private int lastRet = -1; |
636 |
|
637 |
public boolean hasNext() { |
638 |
return cursor != fence; |
639 |
} |
640 |
|
641 |
public E next() { |
642 |
if (cursor == fence) |
643 |
throw new NoSuchElementException(); |
644 |
cursor = (cursor - 1) & (elements.length - 1); |
645 |
@SuppressWarnings("unchecked") |
646 |
E result = (E) elements[cursor]; |
647 |
if (head != fence || result == null) |
648 |
throw new ConcurrentModificationException(); |
649 |
lastRet = cursor; |
650 |
return result; |
651 |
} |
652 |
|
653 |
public void remove() { |
654 |
if (lastRet < 0) |
655 |
throw new IllegalStateException(); |
656 |
if (!delete(lastRet)) { |
657 |
cursor = (cursor + 1) & (elements.length - 1); |
658 |
fence = head; |
659 |
} |
660 |
lastRet = -1; |
661 |
} |
662 |
} |
663 |
|
664 |
/** |
665 |
* Returns {@code true} if this deque contains the specified element. |
666 |
* More formally, returns {@code true} if and only if this deque contains |
667 |
* at least one element {@code e} such that {@code o.equals(e)}. |
668 |
* |
669 |
* @param o object to be checked for containment in this deque |
670 |
* @return {@code true} if this deque contains the specified element |
671 |
*/ |
672 |
public boolean contains(Object o) { |
673 |
if (o != null) { |
674 |
int mask = elements.length - 1; |
675 |
int i = head; |
676 |
for (Object x; (x = elements[i]) != null; i = (i + 1) & mask) { |
677 |
if (o.equals(x)) |
678 |
return true; |
679 |
} |
680 |
} |
681 |
return false; |
682 |
} |
683 |
|
684 |
/** |
685 |
* Removes a single instance of the specified element from this deque. |
686 |
* If the deque does not contain the element, it is unchanged. |
687 |
* More formally, removes the first element {@code e} such that |
688 |
* {@code o.equals(e)} (if such an element exists). |
689 |
* Returns {@code true} if this deque contained the specified element |
690 |
* (or equivalently, if this deque changed as a result of the call). |
691 |
* |
692 |
* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}. |
693 |
* |
694 |
* @param o element to be removed from this deque, if present |
695 |
* @return {@code true} if this deque contained the specified element |
696 |
*/ |
697 |
public boolean remove(Object o) { |
698 |
return removeFirstOccurrence(o); |
699 |
} |
700 |
|
701 |
/** |
702 |
* Removes all of the elements from this deque. |
703 |
* The deque will be empty after this call returns. |
704 |
*/ |
705 |
public void clear() { |
706 |
int h = head; |
707 |
int t = tail; |
708 |
if (h != t) { // clear all cells |
709 |
head = tail = 0; |
710 |
int i = h; |
711 |
int mask = elements.length - 1; |
712 |
do { |
713 |
elements[i] = null; |
714 |
i = (i + 1) & mask; |
715 |
} while (i != t); |
716 |
} |
717 |
} |
718 |
|
719 |
/** |
720 |
* Returns an array containing all of the elements in this deque |
721 |
* in proper sequence (from first to last element). |
722 |
* |
723 |
* <p>The returned array will be "safe" in that no references to it are |
724 |
* maintained by this deque. (In other words, this method must allocate |
725 |
* a new array). The caller is thus free to modify the returned array. |
726 |
* |
727 |
* <p>This method acts as bridge between array-based and collection-based |
728 |
* APIs. |
729 |
* |
730 |
* @return an array containing all of the elements in this deque |
731 |
*/ |
732 |
public Object[] toArray() { |
733 |
final int head = this.head; |
734 |
final int tail = this.tail; |
735 |
boolean wrap = (tail < head); |
736 |
int end = wrap ? tail + elements.length : tail; |
737 |
Object[] a = Arrays.copyOfRange(elements, head, end); |
738 |
if (wrap) |
739 |
System.arraycopy(elements, 0, a, elements.length - head, tail); |
740 |
return a; |
741 |
} |
742 |
|
743 |
/** |
744 |
* Returns an array containing all of the elements in this deque in |
745 |
* proper sequence (from first to last element); the runtime type of the |
746 |
* returned array is that of the specified array. If the deque fits in |
747 |
* the specified array, it is returned therein. Otherwise, a new array |
748 |
* is allocated with the runtime type of the specified array and the |
749 |
* size of this deque. |
750 |
* |
751 |
* <p>If this deque fits in the specified array with room to spare |
752 |
* (i.e., the array has more elements than this deque), the element in |
753 |
* the array immediately following the end of the deque is set to |
754 |
* {@code null}. |
755 |
* |
756 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
757 |
* array-based and collection-based APIs. Further, this method allows |
758 |
* precise control over the runtime type of the output array, and may, |
759 |
* under certain circumstances, be used to save allocation costs. |
760 |
* |
761 |
* <p>Suppose {@code x} is a deque known to contain only strings. |
762 |
* The following code can be used to dump the deque into a newly |
763 |
* allocated array of {@code String}: |
764 |
* |
765 |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
766 |
* |
767 |
* Note that {@code toArray(new Object[0])} is identical in function to |
768 |
* {@code toArray()}. |
769 |
* |
770 |
* @param a the array into which the elements of the deque are to |
771 |
* be stored, if it is big enough; otherwise, a new array of the |
772 |
* same runtime type is allocated for this purpose |
773 |
* @return an array containing all of the elements in this deque |
774 |
* @throws ArrayStoreException if the runtime type of the specified array |
775 |
* is not a supertype of the runtime type of every element in |
776 |
* this deque |
777 |
* @throws NullPointerException if the specified array is null |
778 |
*/ |
779 |
@SuppressWarnings("unchecked") |
780 |
public <T> T[] toArray(T[] a) { |
781 |
final int head = this.head; |
782 |
final int tail = this.tail; |
783 |
boolean wrap = (tail < head); |
784 |
int size = (tail - head) + (wrap ? elements.length : 0); |
785 |
int firstLeg = size - (wrap ? tail : 0); |
786 |
int len = a.length; |
787 |
if (size > len) { |
788 |
a = (T[]) Arrays.copyOfRange(elements, head, head + size, |
789 |
a.getClass()); |
790 |
} else { |
791 |
System.arraycopy(elements, head, a, 0, firstLeg); |
792 |
if (size < len) |
793 |
a[size] = null; |
794 |
} |
795 |
if (wrap) |
796 |
System.arraycopy(elements, 0, a, firstLeg, tail); |
797 |
return a; |
798 |
} |
799 |
|
800 |
// *** Object methods *** |
801 |
|
802 |
/** |
803 |
* Returns a copy of this deque. |
804 |
* |
805 |
* @return a copy of this deque |
806 |
*/ |
807 |
public ArrayDeque<E> clone() { |
808 |
try { |
809 |
@SuppressWarnings("unchecked") |
810 |
ArrayDeque<E> result = (ArrayDeque<E>) super.clone(); |
811 |
result.elements = Arrays.copyOf(elements, elements.length); |
812 |
return result; |
813 |
} catch (CloneNotSupportedException e) { |
814 |
throw new AssertionError(); |
815 |
} |
816 |
} |
817 |
|
818 |
private static final long serialVersionUID = 2340985798034038923L; |
819 |
|
820 |
/** |
821 |
* Saves this deque to a stream (that is, serializes it). |
822 |
* |
823 |
* @param s the stream |
824 |
* @throws java.io.IOException if an I/O error occurs |
825 |
* @serialData The current size ({@code int}) of the deque, |
826 |
* followed by all of its elements (each an object reference) in |
827 |
* first-to-last order. |
828 |
*/ |
829 |
private void writeObject(java.io.ObjectOutputStream s) |
830 |
throws java.io.IOException { |
831 |
s.defaultWriteObject(); |
832 |
|
833 |
// Write out size |
834 |
s.writeInt(size()); |
835 |
|
836 |
// Write out elements in order. |
837 |
int mask = elements.length - 1; |
838 |
for (int i = head; i != tail; i = (i + 1) & mask) |
839 |
s.writeObject(elements[i]); |
840 |
} |
841 |
|
842 |
/** |
843 |
* Reconstitutes this deque from a stream (that is, deserializes it). |
844 |
* @param s the stream |
845 |
* @throws ClassNotFoundException if the class of a serialized object |
846 |
* could not be found |
847 |
* @throws java.io.IOException if an I/O error occurs |
848 |
*/ |
849 |
private void readObject(java.io.ObjectInputStream s) |
850 |
throws java.io.IOException, ClassNotFoundException { |
851 |
s.defaultReadObject(); |
852 |
|
853 |
// Read in size and allocate array |
854 |
int size = s.readInt(); |
855 |
allocateElements(size); |
856 |
head = 0; |
857 |
tail = size; |
858 |
|
859 |
// Read in all elements in the proper order. |
860 |
for (int i = 0; i < size; i++) |
861 |
elements[i] = s.readObject(); |
862 |
} |
863 |
|
864 |
/** |
865 |
* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em> |
866 |
* and <em>fail-fast</em> {@link Spliterator} over the elements in this |
867 |
* deque. |
868 |
* |
869 |
* <p>The {@code Spliterator} reports {@link Spliterator#SIZED}, |
870 |
* {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and |
871 |
* {@link Spliterator#NONNULL}. Overriding implementations should document |
872 |
* the reporting of additional characteristic values. |
873 |
* |
874 |
* @return a {@code Spliterator} over the elements in this deque |
875 |
* @since 1.8 |
876 |
*/ |
877 |
public Spliterator<E> spliterator() { |
878 |
return new DeqSpliterator<>(this, -1, -1); |
879 |
} |
880 |
|
881 |
static final class DeqSpliterator<E> implements Spliterator<E> { |
882 |
private final ArrayDeque<E> deq; |
883 |
private int fence; // -1 until first use |
884 |
private int index; // current index, modified on traverse/split |
885 |
|
886 |
/** Creates new spliterator covering the given array and range */ |
887 |
DeqSpliterator(ArrayDeque<E> deq, int origin, int fence) { |
888 |
this.deq = deq; |
889 |
this.index = origin; |
890 |
this.fence = fence; |
891 |
} |
892 |
|
893 |
private int getFence() { // force initialization |
894 |
int t; |
895 |
if ((t = fence) < 0) { |
896 |
t = fence = deq.tail; |
897 |
index = deq.head; |
898 |
} |
899 |
return t; |
900 |
} |
901 |
|
902 |
public Spliterator<E> trySplit() { |
903 |
int t = getFence(), h = index, n = deq.elements.length; |
904 |
if (h != t && ((h + 1) & (n - 1)) != t) { |
905 |
if (h > t) |
906 |
t += n; |
907 |
int m = ((h + t) >>> 1) & (n - 1); |
908 |
return new DeqSpliterator<>(deq, h, index = m); |
909 |
} |
910 |
return null; |
911 |
} |
912 |
|
913 |
public void forEachRemaining(Consumer<? super E> consumer) { |
914 |
if (consumer == null) |
915 |
throw new NullPointerException(); |
916 |
Object[] a = deq.elements; |
917 |
int m = a.length - 1, f = getFence(), i = index; |
918 |
index = f; |
919 |
while (i != f) { |
920 |
@SuppressWarnings("unchecked") E e = (E)a[i]; |
921 |
i = (i + 1) & m; |
922 |
if (e == null) |
923 |
throw new ConcurrentModificationException(); |
924 |
consumer.accept(e); |
925 |
} |
926 |
} |
927 |
|
928 |
public boolean tryAdvance(Consumer<? super E> consumer) { |
929 |
if (consumer == null) |
930 |
throw new NullPointerException(); |
931 |
Object[] a = deq.elements; |
932 |
int m = a.length - 1, f = getFence(), i = index; |
933 |
if (i != f) { |
934 |
@SuppressWarnings("unchecked") E e = (E)a[i]; |
935 |
index = (i + 1) & m; |
936 |
if (e == null) |
937 |
throw new ConcurrentModificationException(); |
938 |
consumer.accept(e); |
939 |
return true; |
940 |
} |
941 |
return false; |
942 |
} |
943 |
|
944 |
public long estimateSize() { |
945 |
int n = getFence() - index; |
946 |
if (n < 0) |
947 |
n += deq.elements.length; |
948 |
return (long) n; |
949 |
} |
950 |
|
951 |
@Override |
952 |
public int characteristics() { |
953 |
return Spliterator.ORDERED | Spliterator.SIZED | |
954 |
Spliterator.NONNULL | Spliterator.SUBSIZED; |
955 |
} |
956 |
} |
957 |
|
958 |
} |