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