1 |
/* |
2 |
* Written by Josh Bloch of Google Inc. and released to the public domain, |
3 |
* as explained at http://creativecommons.org/licenses/publicdomain. |
4 |
*/ |
5 |
|
6 |
package java.util; |
7 |
import java.util.*; // for javadoc (till 6280605 is fixed) |
8 |
import java.io.*; |
9 |
|
10 |
/** |
11 |
* Resizable-array implementation of the {@link Deque} interface. Array |
12 |
* deques have no capacity restrictions; they grow as necessary to support |
13 |
* usage. They are not thread-safe; in the absence of external |
14 |
* synchronization, they do not support concurrent access by multiple threads. |
15 |
* Null elements are prohibited. This class is likely to be faster than |
16 |
* {@link Stack} when used as a stack, and faster than {@link LinkedList} |
17 |
* when used as a queue. |
18 |
* |
19 |
* <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time. |
20 |
* Exceptions include {@link #remove(Object) remove}, {@link |
21 |
* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence |
22 |
* removeLastOccurrence}, {@link #contains contains}, {@link #iterator |
23 |
* iterator.remove()}, and the bulk operations, all of which run in linear |
24 |
* time. |
25 |
* |
26 |
* <p>The iterators returned by this class's <tt>iterator</tt> method are |
27 |
* <i>fail-fast</i>: If the deque is modified at any time after the iterator |
28 |
* is created, in any way except through the iterator's own <tt>remove</tt> |
29 |
* method, the iterator will generally throw a {@link |
30 |
* ConcurrentModificationException}. Thus, in the face of concurrent |
31 |
* modification, the iterator fails quickly and cleanly, rather than risking |
32 |
* arbitrary, non-deterministic behavior at an undetermined time in the |
33 |
* future. |
34 |
* |
35 |
* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed |
36 |
* as it is, generally speaking, impossible to make any hard guarantees in the |
37 |
* presence of unsynchronized concurrent modification. Fail-fast iterators |
38 |
* throw <tt>ConcurrentModificationException</tt> on a best-effort basis. |
39 |
* Therefore, it would be wrong to write a program that depended on this |
40 |
* exception for its correctness: <i>the fail-fast behavior of iterators |
41 |
* should be used only to detect bugs.</i> |
42 |
* |
43 |
* <p>This class and its iterator implement all of the |
44 |
* <em>optional</em> methods of the {@link Collection} and {@link |
45 |
* Iterator} interfaces. |
46 |
* |
47 |
* <p>This class is a member of the |
48 |
* <a href="{@docRoot}/../guide/collections/index.html"> |
49 |
* Java Collections Framework</a>. |
50 |
* |
51 |
* @author Josh Bloch and Doug Lea |
52 |
* @since 1.6 |
53 |
* @param <E> the type of elements held in this collection |
54 |
*/ |
55 |
public class ArrayDeque<E> extends AbstractCollection<E> |
56 |
implements Deque<E>, Cloneable, Serializable |
57 |
{ |
58 |
/** |
59 |
* The array in which the elements of the deque are stored. |
60 |
* The capacity of the deque is the length of this array, which is |
61 |
* always a power of two. The array is never allowed to become |
62 |
* full, except transiently within an addX method where it is |
63 |
* resized (see doubleCapacity) immediately upon becoming full, |
64 |
* thus avoiding head and tail wrapping around to equal each |
65 |
* other. We also guarantee that all array cells not holding |
66 |
* deque elements are always null. |
67 |
*/ |
68 |
private transient E[] elements; |
69 |
|
70 |
/** |
71 |
* The index of the element at the head of the deque (which is the |
72 |
* element that would be removed by remove() or pop()); or an |
73 |
* arbitrary number equal to tail if the deque is empty. |
74 |
*/ |
75 |
private transient int head; |
76 |
|
77 |
/** |
78 |
* The index at which the next element would be added to the tail |
79 |
* of the deque (via addLast(E), add(E), or push(E)). |
80 |
*/ |
81 |
private transient int tail; |
82 |
|
83 |
/** |
84 |
* The minimum capacity that we'll use for a newly created deque. |
85 |
* Must be a power of 2. |
86 |
*/ |
87 |
private static final int MIN_INITIAL_CAPACITY = 8; |
88 |
|
89 |
// ****** Array allocation and resizing utilities ****** |
90 |
|
91 |
/** |
92 |
* Allocate empty array to hold the given number of elements. |
93 |
* |
94 |
* @param numElements the number of elements to hold |
95 |
*/ |
96 |
private void allocateElements(int numElements) { |
97 |
int initialCapacity = MIN_INITIAL_CAPACITY; |
98 |
// Find the best power of two to hold elements. |
99 |
// Tests "<=" because arrays aren't kept full. |
100 |
if (numElements >= initialCapacity) { |
101 |
initialCapacity = numElements; |
102 |
initialCapacity |= (initialCapacity >>> 1); |
103 |
initialCapacity |= (initialCapacity >>> 2); |
104 |
initialCapacity |= (initialCapacity >>> 4); |
105 |
initialCapacity |= (initialCapacity >>> 8); |
106 |
initialCapacity |= (initialCapacity >>> 16); |
107 |
initialCapacity++; |
108 |
|
109 |
if (initialCapacity < 0) // Too many elements, must back off |
110 |
initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements |
111 |
} |
112 |
elements = (E[]) new Object[initialCapacity]; |
113 |
} |
114 |
|
115 |
/** |
116 |
* Double the capacity of this deque. Call only when full, i.e., |
117 |
* when head and tail have wrapped around to become equal. |
118 |
*/ |
119 |
private void doubleCapacity() { |
120 |
assert head == tail; |
121 |
int p = head; |
122 |
int n = elements.length; |
123 |
int r = n - p; // number of elements to the right of p |
124 |
int newCapacity = n << 1; |
125 |
if (newCapacity < 0) |
126 |
throw new IllegalStateException("Sorry, deque too big"); |
127 |
Object[] a = new Object[newCapacity]; |
128 |
System.arraycopy(elements, p, a, 0, r); |
129 |
System.arraycopy(elements, 0, a, r, p); |
130 |
elements = (E[])a; |
131 |
head = 0; |
132 |
tail = n; |
133 |
} |
134 |
|
135 |
/** |
136 |
* Copies the elements from our element array into the specified array, |
137 |
* in order (from first to last element in the deque). It is assumed |
138 |
* that the array is large enough to hold all elements in the deque. |
139 |
* |
140 |
* @return its argument |
141 |
*/ |
142 |
private <T> T[] copyElements(T[] a) { |
143 |
if (head < tail) { |
144 |
System.arraycopy(elements, head, a, 0, size()); |
145 |
} else if (head > tail) { |
146 |
int headPortionLen = elements.length - head; |
147 |
System.arraycopy(elements, head, a, 0, headPortionLen); |
148 |
System.arraycopy(elements, 0, a, headPortionLen, tail); |
149 |
} |
150 |
return a; |
151 |
} |
152 |
|
153 |
/** |
154 |
* Constructs an empty array deque with an initial capacity |
155 |
* sufficient to hold 16 elements. |
156 |
*/ |
157 |
public ArrayDeque() { |
158 |
elements = (E[]) new Object[16]; |
159 |
} |
160 |
|
161 |
/** |
162 |
* Constructs an empty array deque with an initial capacity |
163 |
* sufficient to hold the specified number of elements. |
164 |
* |
165 |
* @param numElements lower bound on initial capacity of the deque |
166 |
*/ |
167 |
public ArrayDeque(int numElements) { |
168 |
allocateElements(numElements); |
169 |
} |
170 |
|
171 |
/** |
172 |
* Constructs a deque containing the elements of the specified |
173 |
* collection, in the order they are returned by the collection's |
174 |
* iterator. (The first element returned by the collection's |
175 |
* iterator becomes the first element, or <i>front</i> of the |
176 |
* deque.) |
177 |
* |
178 |
* @param c the collection whose elements are to be placed into the deque |
179 |
* @throws NullPointerException if the specified collection is null |
180 |
*/ |
181 |
public ArrayDeque(Collection<? extends E> c) { |
182 |
allocateElements(c.size()); |
183 |
addAll(c); |
184 |
} |
185 |
|
186 |
// The main insertion and extraction methods are addFirst, |
187 |
// addLast, pollFirst, pollLast. The other methods are defined in |
188 |
// terms of these. |
189 |
|
190 |
/** |
191 |
* Inserts the specified element at the front of this deque. |
192 |
* |
193 |
* @param e the element to add |
194 |
* @throws NullPointerException if the specified element is null |
195 |
*/ |
196 |
public void addFirst(E e) { |
197 |
if (e == null) |
198 |
throw new NullPointerException(); |
199 |
elements[head = (head - 1) & (elements.length - 1)] = e; |
200 |
if (head == tail) |
201 |
doubleCapacity(); |
202 |
} |
203 |
|
204 |
/** |
205 |
* Inserts the specified element at the end of this deque. |
206 |
* |
207 |
* <p>This method is equivalent to {@link #add}. |
208 |
* |
209 |
* @param e the element to add |
210 |
* @throws NullPointerException if the specified element is null |
211 |
*/ |
212 |
public void addLast(E e) { |
213 |
if (e == null) |
214 |
throw new NullPointerException(); |
215 |
elements[tail] = e; |
216 |
if ( (tail = (tail + 1) & (elements.length - 1)) == head) |
217 |
doubleCapacity(); |
218 |
} |
219 |
|
220 |
/** |
221 |
* Inserts the specified element at the front of this deque. |
222 |
* |
223 |
* @param e the element to add |
224 |
* @return <tt>true</tt> (as specified by {@link Deque#offerFirst}) |
225 |
* @throws NullPointerException if the specified element is null |
226 |
*/ |
227 |
public boolean offerFirst(E e) { |
228 |
addFirst(e); |
229 |
return true; |
230 |
} |
231 |
|
232 |
/** |
233 |
* Inserts the specified element at the end of this deque. |
234 |
* |
235 |
* @param e the element to add |
236 |
* @return <tt>true</tt> (as specified by {@link Deque#offerLast}) |
237 |
* @throws NullPointerException if the specified element is null |
238 |
*/ |
239 |
public boolean offerLast(E e) { |
240 |
addLast(e); |
241 |
return true; |
242 |
} |
243 |
|
244 |
/** |
245 |
* @throws NoSuchElementException {@inheritDoc} |
246 |
*/ |
247 |
public E removeFirst() { |
248 |
E x = pollFirst(); |
249 |
if (x == null) |
250 |
throw new NoSuchElementException(); |
251 |
return x; |
252 |
} |
253 |
|
254 |
/** |
255 |
* @throws NoSuchElementException {@inheritDoc} |
256 |
*/ |
257 |
public E removeLast() { |
258 |
E x = pollLast(); |
259 |
if (x == null) |
260 |
throw new NoSuchElementException(); |
261 |
return x; |
262 |
} |
263 |
|
264 |
public E pollFirst() { |
265 |
int h = head; |
266 |
E result = elements[h]; // 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 |
E result = elements[t]; |
277 |
if (result == null) |
278 |
return null; |
279 |
elements[t] = null; |
280 |
tail = t; |
281 |
return result; |
282 |
} |
283 |
|
284 |
/** |
285 |
* @throws NoSuchElementException {@inheritDoc} |
286 |
*/ |
287 |
public E getFirst() { |
288 |
E x = elements[head]; |
289 |
if (x == null) |
290 |
throw new NoSuchElementException(); |
291 |
return x; |
292 |
} |
293 |
|
294 |
/** |
295 |
* @throws NoSuchElementException {@inheritDoc} |
296 |
*/ |
297 |
public E getLast() { |
298 |
E x = elements[(tail - 1) & (elements.length - 1)]; |
299 |
if (x == null) |
300 |
throw new NoSuchElementException(); |
301 |
return x; |
302 |
} |
303 |
|
304 |
public E peekFirst() { |
305 |
return elements[head]; // elements[head] is null if deque empty |
306 |
} |
307 |
|
308 |
public E peekLast() { |
309 |
return elements[(tail - 1) & (elements.length - 1)]; |
310 |
} |
311 |
|
312 |
/** |
313 |
* Removes the first occurrence of the specified element in this |
314 |
* deque (when traversing the deque from head to tail). |
315 |
* If the deque does not contain the element, it is unchanged. |
316 |
* More formally, removes the first element <tt>e</tt> such that |
317 |
* <tt>o.equals(e)</tt> (if such an element exists). |
318 |
* Returns <tt>true</tt> if this deque contained the specified element |
319 |
* (or equivalently, if this deque changed as a result of the call). |
320 |
* |
321 |
* @param o element to be removed from this deque, if present |
322 |
* @return <tt>true</tt> if the deque contained the specified element |
323 |
*/ |
324 |
public boolean removeFirstOccurrence(Object o) { |
325 |
if (o == null) |
326 |
return false; |
327 |
int mask = elements.length - 1; |
328 |
int i = head; |
329 |
E x; |
330 |
while ( (x = elements[i]) != null) { |
331 |
if (o.equals(x)) { |
332 |
delete(i); |
333 |
return true; |
334 |
} |
335 |
i = (i + 1) & mask; |
336 |
} |
337 |
return false; |
338 |
} |
339 |
|
340 |
/** |
341 |
* Removes the last occurrence of the specified element in this |
342 |
* deque (when traversing the deque from head to tail). |
343 |
* If the deque does not contain the element, it is unchanged. |
344 |
* More formally, removes the last element <tt>e</tt> such that |
345 |
* <tt>o.equals(e)</tt> (if such an element exists). |
346 |
* Returns <tt>true</tt> if this deque contained the specified element |
347 |
* (or equivalently, if this deque changed as a result of the call). |
348 |
* |
349 |
* @param o element to be removed from this deque, if present |
350 |
* @return <tt>true</tt> if the deque contained the specified element |
351 |
*/ |
352 |
public boolean removeLastOccurrence(Object o) { |
353 |
if (o == null) |
354 |
return false; |
355 |
int mask = elements.length - 1; |
356 |
int i = (tail - 1) & mask; |
357 |
E x; |
358 |
while ( (x = elements[i]) != null) { |
359 |
if (o.equals(x)) { |
360 |
delete(i); |
361 |
return true; |
362 |
} |
363 |
i = (i - 1) & mask; |
364 |
} |
365 |
return false; |
366 |
} |
367 |
|
368 |
// *** Queue methods *** |
369 |
|
370 |
/** |
371 |
* Inserts the specified element at the end of this deque. |
372 |
* |
373 |
* <p>This method is equivalent to {@link #addLast}. |
374 |
* |
375 |
* @param e the element to add |
376 |
* @return <tt>true</tt> (as specified by {@link Collection#add}) |
377 |
* @throws NullPointerException if the specified element is null |
378 |
*/ |
379 |
public boolean add(E e) { |
380 |
addLast(e); |
381 |
return true; |
382 |
} |
383 |
|
384 |
/** |
385 |
* Inserts the specified element at the end of this deque. |
386 |
* |
387 |
* <p>This method is equivalent to {@link #offerLast}. |
388 |
* |
389 |
* @param e the element to add |
390 |
* @return <tt>true</tt> (as specified by {@link Queue#offer}) |
391 |
* @throws NullPointerException if the specified element is null |
392 |
*/ |
393 |
public boolean offer(E e) { |
394 |
return offerLast(e); |
395 |
} |
396 |
|
397 |
/** |
398 |
* Retrieves and removes the head of the queue represented by this deque. |
399 |
* |
400 |
* This method differs from {@link #poll poll} only in that it throws an |
401 |
* exception if this deque is empty. |
402 |
* |
403 |
* <p>This method is equivalent to {@link #removeFirst}. |
404 |
* |
405 |
* @return the head of the queue represented by this deque |
406 |
* @throws NoSuchElementException {@inheritDoc} |
407 |
*/ |
408 |
public E remove() { |
409 |
return removeFirst(); |
410 |
} |
411 |
|
412 |
/** |
413 |
* Retrieves and removes the head of the queue represented by this deque |
414 |
* (in other words, the first element of this deque), or returns |
415 |
* <tt>null</tt> if this deque is empty. |
416 |
* |
417 |
* <p>This method is equivalent to {@link #pollFirst}. |
418 |
* |
419 |
* @return the head of the queue represented by this deque, or |
420 |
* <tt>null</tt> if this deque is empty |
421 |
*/ |
422 |
public E poll() { |
423 |
return pollFirst(); |
424 |
} |
425 |
|
426 |
/** |
427 |
* Retrieves, but does not remove, the head of the queue represented by |
428 |
* this deque. This method differs from {@link #peek peek} only in |
429 |
* that it throws an exception if this deque is empty. |
430 |
* |
431 |
* <p>This method is equivalent to {@link #getFirst}. |
432 |
* |
433 |
* @return the head of the queue represented by this deque |
434 |
* @throws NoSuchElementException {@inheritDoc} |
435 |
*/ |
436 |
public E element() { |
437 |
return getFirst(); |
438 |
} |
439 |
|
440 |
/** |
441 |
* Retrieves, but does not remove, the head of the queue represented by |
442 |
* this deque, or returns <tt>null</tt> if this deque is empty. |
443 |
* |
444 |
* <p>This method is equivalent to {@link #peekFirst}. |
445 |
* |
446 |
* @return the head of the queue represented by this deque, or |
447 |
* <tt>null</tt> if this deque is empty |
448 |
*/ |
449 |
public E peek() { |
450 |
return peekFirst(); |
451 |
} |
452 |
|
453 |
// *** Stack methods *** |
454 |
|
455 |
/** |
456 |
* Pushes an element onto the stack represented by this deque. In other |
457 |
* words, inserts the element at the front of this deque. |
458 |
* |
459 |
* <p>This method is equivalent to {@link #addFirst}. |
460 |
* |
461 |
* @param e the element to push |
462 |
* @throws NullPointerException if the specified element is null |
463 |
*/ |
464 |
public void push(E e) { |
465 |
addFirst(e); |
466 |
} |
467 |
|
468 |
/** |
469 |
* Pops an element from the stack represented by this deque. In other |
470 |
* words, removes and returns the first element of this deque. |
471 |
* |
472 |
* <p>This method is equivalent to {@link #removeFirst()}. |
473 |
* |
474 |
* @return the element at the front of this deque (which is the top |
475 |
* of the stack represented by this deque) |
476 |
* @throws NoSuchElementException {@inheritDoc} |
477 |
*/ |
478 |
public E pop() { |
479 |
return removeFirst(); |
480 |
} |
481 |
|
482 |
/** |
483 |
* Removes the element at the specified position in the elements array, |
484 |
* adjusting head and tail as necessary. This can result in motion of |
485 |
* elements backwards or forwards in the array. |
486 |
* |
487 |
* <p>This method is called delete rather than remove to emphasize |
488 |
* that its semantics differ from those of {@link List#remove(int)}. |
489 |
* |
490 |
* @return true if elements moved backwards |
491 |
*/ |
492 |
private boolean delete(int i) { |
493 |
final E[] 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 |
private boolean xdelete(int i) { |
531 |
int mask = elements.length - 1; |
532 |
int front = (i - head) & mask; |
533 |
int back = (tail - i) & mask; |
534 |
|
535 |
// Invariant: head <= i < tail mod circularity |
536 |
if (front >= ((tail - head) & mask)) |
537 |
throw new ConcurrentModificationException(); |
538 |
|
539 |
// Optimize for least element motion |
540 |
if (front < back) { |
541 |
if (head <= i) { |
542 |
System.arraycopy(elements, head, elements, head + 1, front); |
543 |
} else { // Wrap around |
544 |
System.arraycopy(elements, 0, elements, 1, i); |
545 |
elements[0] = elements[mask]; |
546 |
System.arraycopy(elements, head, elements, head + 1, mask - head); |
547 |
} |
548 |
elements[head] = null; |
549 |
head = (head + 1) & mask; |
550 |
return false; |
551 |
} else { |
552 |
int t = tail; |
553 |
tail = (tail - 1) & mask; |
554 |
if (i < t) { // Copy the null tail as well |
555 |
System.arraycopy(elements, i + 1, elements, i, back); |
556 |
} else { // Wrap around |
557 |
System.arraycopy(elements, i + 1, elements, i, mask - i); |
558 |
elements[mask] = elements[0]; |
559 |
System.arraycopy(elements, 1, elements, 0, t); |
560 |
} |
561 |
return true; |
562 |
} |
563 |
} |
564 |
|
565 |
// *** Collection Methods *** |
566 |
|
567 |
/** |
568 |
* Returns the number of elements in this deque. |
569 |
* |
570 |
* @return the number of elements in this deque |
571 |
*/ |
572 |
public int size() { |
573 |
return (tail - head) & (elements.length - 1); |
574 |
} |
575 |
|
576 |
/** |
577 |
* Returns <tt>true</tt> if this deque contains no elements. |
578 |
* |
579 |
* @return <tt>true</tt> if this deque contains no elements |
580 |
*/ |
581 |
public boolean isEmpty() { |
582 |
return head == tail; |
583 |
} |
584 |
|
585 |
/** |
586 |
* Returns an iterator over the elements in this deque. The elements |
587 |
* will be ordered from first (head) to last (tail). This is the same |
588 |
* order that elements would be dequeued (via successive calls to |
589 |
* {@link #remove} or popped (via successive calls to {@link #pop}). |
590 |
* |
591 |
* @return an iterator over the elements in this deque |
592 |
*/ |
593 |
public Iterator<E> iterator() { |
594 |
return new DeqIterator(); |
595 |
} |
596 |
|
597 |
public Iterator<E> descendingIterator() { |
598 |
return new DescendingIterator(); |
599 |
} |
600 |
|
601 |
private class DeqIterator implements Iterator<E> { |
602 |
/** |
603 |
* Index of element to be returned by subsequent call to next. |
604 |
*/ |
605 |
private int cursor = head; |
606 |
|
607 |
/** |
608 |
* Tail recorded at construction (also in remove), to stop |
609 |
* iterator and also to check for comodification. |
610 |
*/ |
611 |
private int fence = tail; |
612 |
|
613 |
/** |
614 |
* Index of element returned by most recent call to next. |
615 |
* Reset to -1 if element is deleted by a call to remove. |
616 |
*/ |
617 |
private int lastRet = -1; |
618 |
|
619 |
public boolean hasNext() { |
620 |
return cursor != fence; |
621 |
} |
622 |
|
623 |
public E next() { |
624 |
E result; |
625 |
if (cursor == fence) |
626 |
throw new NoSuchElementException(); |
627 |
// This check doesn't catch all possible comodifications, |
628 |
// but does catch the ones that corrupt traversal |
629 |
if (tail != fence || (result = elements[cursor]) == null) |
630 |
throw new ConcurrentModificationException(); |
631 |
lastRet = cursor; |
632 |
cursor = (cursor + 1) & (elements.length - 1); |
633 |
return result; |
634 |
} |
635 |
|
636 |
public void remove() { |
637 |
if (lastRet < 0) |
638 |
throw new IllegalStateException(); |
639 |
if (delete(lastRet)) // if left-shifted, undo increment in next() |
640 |
cursor = (cursor - 1) & (elements.length - 1); |
641 |
lastRet = -1; |
642 |
fence = tail; |
643 |
} |
644 |
} |
645 |
|
646 |
|
647 |
private class DescendingIterator implements Iterator<E> { |
648 |
/* |
649 |
* This class is nearly a mirror-image of DeqIterator, using |
650 |
* (tail-1) instead of head for initial cursor, (head-1) |
651 |
* instead of tail for fence, and elements.length instead of -1 |
652 |
* for sentinel. It shares the same structure, but not many |
653 |
* actual lines of code. |
654 |
*/ |
655 |
private int cursor = (tail - 1) & (elements.length - 1); |
656 |
private int fence = (head - 1) & (elements.length - 1); |
657 |
private int lastRet = elements.length; |
658 |
|
659 |
public boolean hasNext() { |
660 |
return cursor != fence; |
661 |
} |
662 |
|
663 |
public E next() { |
664 |
E result; |
665 |
if (cursor == fence) |
666 |
throw new NoSuchElementException(); |
667 |
if (((head - 1) & (elements.length - 1)) != fence || |
668 |
(result = elements[cursor]) == null) |
669 |
throw new ConcurrentModificationException(); |
670 |
lastRet = cursor; |
671 |
cursor = (cursor - 1) & (elements.length - 1); |
672 |
return result; |
673 |
} |
674 |
|
675 |
public void remove() { |
676 |
if (lastRet >= elements.length) |
677 |
throw new IllegalStateException(); |
678 |
if (!delete(lastRet)) |
679 |
cursor = (cursor + 1) & (elements.length - 1); |
680 |
lastRet = elements.length; |
681 |
fence = (head - 1) & (elements.length - 1); |
682 |
} |
683 |
} |
684 |
|
685 |
/** |
686 |
* Returns <tt>true</tt> if this deque contains the specified element. |
687 |
* More formally, returns <tt>true</tt> if and only if this deque contains |
688 |
* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>. |
689 |
* |
690 |
* @param o object to be checked for containment in this deque |
691 |
* @return <tt>true</tt> if this deque contains the specified element |
692 |
*/ |
693 |
public boolean contains(Object o) { |
694 |
if (o == null) |
695 |
return false; |
696 |
int mask = elements.length - 1; |
697 |
int i = head; |
698 |
E x; |
699 |
while ( (x = elements[i]) != null) { |
700 |
if (o.equals(x)) |
701 |
return true; |
702 |
i = (i + 1) & mask; |
703 |
} |
704 |
return false; |
705 |
} |
706 |
|
707 |
/** |
708 |
* Removes a single instance of the specified element from this deque. |
709 |
* If the deque does not contain the element, it is unchanged. |
710 |
* More formally, removes the first element <tt>e</tt> such that |
711 |
* <tt>o.equals(e)</tt> (if such an element exists). |
712 |
* Returns <tt>true</tt> if this deque contained the specified element |
713 |
* (or equivalently, if this deque changed as a result of the call). |
714 |
* |
715 |
* <p>This method is equivalent to {@link #removeFirstOccurrence}. |
716 |
* |
717 |
* @param o element to be removed from this deque, if present |
718 |
* @return <tt>true</tt> if this deque contained the specified element |
719 |
*/ |
720 |
public boolean remove(Object o) { |
721 |
return removeFirstOccurrence(o); |
722 |
} |
723 |
|
724 |
/** |
725 |
* Removes all of the elements from this deque. |
726 |
* The deque will be empty after this call returns. |
727 |
*/ |
728 |
public void clear() { |
729 |
int h = head; |
730 |
int t = tail; |
731 |
if (h != t) { // clear all cells |
732 |
head = tail = 0; |
733 |
int i = h; |
734 |
int mask = elements.length - 1; |
735 |
do { |
736 |
elements[i] = null; |
737 |
i = (i + 1) & mask; |
738 |
} while (i != t); |
739 |
} |
740 |
} |
741 |
|
742 |
/** |
743 |
* Returns an array containing all of the elements in this deque |
744 |
* in proper sequence (from first to last element). |
745 |
* |
746 |
* <p>The returned array will be "safe" in that no references to it are |
747 |
* maintained by this deque. (In other words, this method must allocate |
748 |
* a new array). The caller is thus free to modify the returned array. |
749 |
* |
750 |
* <p>This method acts as bridge between array-based and collection-based |
751 |
* APIs. |
752 |
* |
753 |
* @return an array containing all of the elements in this deque |
754 |
*/ |
755 |
public Object[] toArray() { |
756 |
return copyElements(new Object[size()]); |
757 |
} |
758 |
|
759 |
/** |
760 |
* Returns an array containing all of the elements in this deque in |
761 |
* proper sequence (from first to last element); the runtime type of the |
762 |
* returned array is that of the specified array. If the deque fits in |
763 |
* the specified array, it is returned therein. Otherwise, a new array |
764 |
* is allocated with the runtime type of the specified array and the |
765 |
* size of this deque. |
766 |
* |
767 |
* <p>If this deque fits in the specified array with room to spare |
768 |
* (i.e., the array has more elements than this deque), the element in |
769 |
* the array immediately following the end of the deque is set to |
770 |
* <tt>null</tt>. |
771 |
* |
772 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
773 |
* array-based and collection-based APIs. Further, this method allows |
774 |
* precise control over the runtime type of the output array, and may, |
775 |
* under certain circumstances, be used to save allocation costs. |
776 |
* |
777 |
* <p>Suppose <tt>x</tt> is a deque known to contain only strings. |
778 |
* The following code can be used to dump the deque into a newly |
779 |
* allocated array of <tt>String</tt>: |
780 |
* |
781 |
* <pre> |
782 |
* String[] y = x.toArray(new String[0]);</pre> |
783 |
* |
784 |
* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
785 |
* <tt>toArray()</tt>. |
786 |
* |
787 |
* @param a the array into which the elements of the deque are to |
788 |
* be stored, if it is big enough; otherwise, a new array of the |
789 |
* same runtime type is allocated for this purpose |
790 |
* @return an array containing all of the elements in this deque |
791 |
* @throws ArrayStoreException if the runtime type of the specified array |
792 |
* is not a supertype of the runtime type of every element in |
793 |
* this deque |
794 |
* @throws NullPointerException if the specified array is null |
795 |
*/ |
796 |
public <T> T[] toArray(T[] a) { |
797 |
int size = size(); |
798 |
if (a.length < size) |
799 |
a = (T[])java.lang.reflect.Array.newInstance( |
800 |
a.getClass().getComponentType(), size); |
801 |
copyElements(a); |
802 |
if (a.length > size) |
803 |
a[size] = null; |
804 |
return a; |
805 |
} |
806 |
|
807 |
// *** Object methods *** |
808 |
|
809 |
/** |
810 |
* Returns a copy of this deque. |
811 |
* |
812 |
* @return a copy of this deque |
813 |
*/ |
814 |
public ArrayDeque<E> clone() { |
815 |
try { |
816 |
ArrayDeque<E> result = (ArrayDeque<E>) super.clone(); |
817 |
// These two lines are currently faster than cloning the array: |
818 |
result.elements = (E[]) new Object[elements.length]; |
819 |
System.arraycopy(elements, 0, result.elements, 0, elements.length); |
820 |
return result; |
821 |
|
822 |
} catch (CloneNotSupportedException e) { |
823 |
throw new AssertionError(); |
824 |
} |
825 |
} |
826 |
|
827 |
/** |
828 |
* Appease the serialization gods. |
829 |
*/ |
830 |
private static final long serialVersionUID = 2340985798034038923L; |
831 |
|
832 |
/** |
833 |
* Serialize this deque. |
834 |
* |
835 |
* @serialData The current size (<tt>int</tt>) of the deque, |
836 |
* followed by all of its elements (each an object reference) in |
837 |
* first-to-last order. |
838 |
*/ |
839 |
private void writeObject(ObjectOutputStream s) throws IOException { |
840 |
s.defaultWriteObject(); |
841 |
|
842 |
// Write out size |
843 |
s.writeInt(size()); |
844 |
|
845 |
// Write out elements in order. |
846 |
int mask = elements.length - 1; |
847 |
for (int i = head; i != tail; i = (i + 1) & mask) |
848 |
s.writeObject(elements[i]); |
849 |
} |
850 |
|
851 |
/** |
852 |
* Deserialize this deque. |
853 |
*/ |
854 |
private void readObject(ObjectInputStream s) |
855 |
throws IOException, ClassNotFoundException { |
856 |
s.defaultReadObject(); |
857 |
|
858 |
// Read in size and allocate array |
859 |
int size = s.readInt(); |
860 |
allocateElements(size); |
861 |
head = 0; |
862 |
tail = size; |
863 |
|
864 |
// Read in all elements in the proper order. |
865 |
for (int i = 0; i < size; i++) |
866 |
elements[i] = (E)s.readObject(); |
867 |
|
868 |
} |
869 |
} |