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root/jsr166/jsr166/src/main/java/util/ArrayDeque.java

Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.4 by dl, Tue Mar 8 19:07:39 2005 UTC vs.
Revision 1.30 by jsr166, Sun May 18 23:47:55 2008 UTC

#	Line 18 | Line 18 | import java.io.*;
18		* <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time.
19		* Exceptions include {@link #remove(Object) remove}, {@link
20		* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
21	<	* removeLastOccurrence}, {@link #contains contains }, {@link #iterator
21	>	* removeLastOccurrence}, {@link #contains contains}, {@link #iterator
22		* iterator.remove()}, and the bulk operations, all of which run in linear
23		* time.
24		*
25		* <p>The iterators returned by this class's <tt>iterator</tt> method are
26		* <i>fail-fast</i>: If the deque is modified at any time after the iterator
27	<	* is created, in any way except through the iterator's own remove method, the
28	<	* iterator will generally throw a {@link ConcurrentModificationException}.
29	<	* Thus, in the face of concurrent modification, the iterator fails quickly
30	<	* and cleanly, rather than risking arbitrary, non-deterministic behavior at
31	<	* an undetermined time in the future.
27	>	* is created, in any way except through the iterator's own <tt>remove</tt>
28	>	* method, the iterator will generally throw a {@link
29	>	* ConcurrentModificationException}.  Thus, in the face of concurrent
30	>	* modification, the iterator fails quickly and cleanly, rather than risking
31	>	* arbitrary, non-deterministic behavior at an undetermined time in the
32	>	* future.
33		*
34		* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
35		* as it is, generally speaking, impossible to make any hard guarantees in the
36		* presence of unsynchronized concurrent modification.  Fail-fast iterators
37	<	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
37	>	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
38		* Therefore, it would be wrong to write a program that depended on this
39		* exception for its correctness: <i>the fail-fast behavior of iterators
40		* should be used only to detect bugs.</i>
41		*
42		* <p>This class and its iterator implement all of the
43	<	* optional methods of the {@link Collection} and {@link
44	<	* Iterator} interfaces.  This class is a member of the <a
45	<	* href="{@docRoot}/../guide/collections/index.html"> Java Collections
46	<	* Framework</a>.
43	>	* <em>optional</em> methods of the {@link Collection} and {@link
44	>	* Iterator} interfaces.
45	>	*
46	>	* <p>This class is a member of the
47	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
48	>	* Java Collections Framework</a>.
49		*
50		* @author  Josh Bloch and Doug Lea
51		* @since   1.6
#	Line 87 | Line 90 | public class ArrayDeque<E> extends Abstr
90		/**
91		* Allocate empty array to hold the given number of elements.
92		*
93	<	* @param numElements  the number of elements to hold.
93	>	* @param numElements  the number of elements to hold
94		*/
95	<	private void allocateElements(int numElements) {
95	>	private void allocateElements(int numElements) {
96		int initialCapacity = MIN_INITIAL_CAPACITY;
97		// Find the best power of two to hold elements.
98		// Tests "<=" because arrays aren't kept full.
#	Line 113 | Line 116 | public class ArrayDeque<E> extends Abstr
116		* when head and tail have wrapped around to become equal.
117		*/
118		private void doubleCapacity() {
119	<	assert head == tail;
119	>	assert head == tail;
120		int p = head;
121		int n = elements.length;
122		int r = n - p; // number of elements to the right of p
#	Line 129 | Line 132 | public class ArrayDeque<E> extends Abstr
132		}
133
134		/**
135	<	* Copy the elements from our element array into the specified array,
135	>	* Copies the elements from our element array into the specified array,
136		* in order (from first to last element in the deque).  It is assumed
137		* that the array is large enough to hold all elements in the deque.
138		*
#	Line 184 | Line 187 | public class ArrayDeque<E> extends Abstr
187		// terms of these.
188
189		/**
190	<	* Inserts the specified element to the front this deque.
190	>	* Inserts the specified element at the front of this deque.
191		*
192	<	* @param e the element to insert
193	<	* @throws NullPointerException if <tt>e</tt> is null
192	>	* @param e the element to add
193	>	* @throws NullPointerException if the specified element is null
194		*/
195		public void addFirst(E e) {
196		if (e == null)
197		throw new NullPointerException();
198		elements[head = (head - 1) & (elements.length - 1)] = e;
199	<	if (head == tail)
199	>	if (head == tail)
200		doubleCapacity();
201		}
202
203		/**
204	<	* Inserts the specified element to the end this deque.
205	<	* This method is equivalent to {@link Collection#add} and
206	<	* {@link #push}.
204	>	* Inserts the specified element at the end of this deque.
205	>	*
206	>	* <p>This method is equivalent to {@link #add}.
207		*
208	<	* @param e the element to insert
209	<	* @throws NullPointerException if <tt>e</tt> is null
208	>	* @param e the element to add
209	>	* @throws NullPointerException if the specified element is null
210		*/
211		public void addLast(E e) {
212		if (e == null)
#	Line 214 | Line 217 | public class ArrayDeque<E> extends Abstr
217		}
218
219		/**
220	<	* Retrieves and removes the first element of this deque, or
218	<	* <tt>null</tt> if this deque is empty.
219	<	*
220	<	* @return the first element of this deque, or <tt>null</tt> if
221	<	*     this deque is empty
222	<	*/
223	<	public E pollFirst() {
224	<	int h = head;
225	<	E result = elements[h]; // Element is null if deque empty
226	<	if (result == null)
227	<	return null;
228	<	elements[h] = null;     // Must null out slot
229	<	head = (h + 1) & (elements.length - 1);
230	<	return result;
231	<	}
232	<
233	<	/**
234	<	* Retrieves and removes the last element of this deque, or
235	<	* <tt>null</tt> if this deque is empty.
236	<	*
237	<	* @return the last element of this deque, or <tt>null</tt> if
238	<	*     this deque is empty
239	<	*/
240	<	public E pollLast() {
241	<	int t = (tail - 1) & (elements.length - 1);
242	<	E result = elements[t];
243	<	if (result == null)
244	<	return null;
245	<	elements[t] = null;
246	<	tail = t;
247	<	return result;
248	<	}
249	<
250	<	/**
251	<	* Inserts the specified element to the front this deque.
220	>	* Inserts the specified element at the front of this deque.
221		*
222	<	* @param e the element to insert
223	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst})
224	<	* @throws NullPointerException if <tt>e</tt> is null
222	>	* @param e the element to add
223	>	* @return <tt>true</tt> (as specified by {@link Deque#offerFirst})
224	>	* @throws NullPointerException if the specified element is null
225		*/
226		public boolean offerFirst(E e) {
227		addFirst(e);
#	Line 260 | Line 229 | public class ArrayDeque<E> extends Abstr
229		}
230
231		/**
232	<	* Inserts the specified element to the end this deque.
232	>	* Inserts the specified element at the end of this deque.
233		*
234	<	* @param e the element to insert
235	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
236	<	* @throws NullPointerException if <tt>e</tt> is null
234	>	* @param e the element to add
235	>	* @return <tt>true</tt> (as specified by {@link Deque#offerLast})
236	>	* @throws NullPointerException if the specified element is null
237		*/
238		public boolean offerLast(E e) {
239		addLast(e);
#	Line 272 | Line 241 | public class ArrayDeque<E> extends Abstr
241		}
242
243		/**
244	<	* Retrieves and removes the first element of this deque.  This method
276	<	* differs from the <tt>pollFirst</tt> method in that it throws an
277	<	* exception if this deque is empty.
278	<	*
279	<	* @return the first element of this deque
280	<	* @throws NoSuchElementException if this deque is empty
244	>	* @throws NoSuchElementException {@inheritDoc}
245		*/
246		public E removeFirst() {
247		E x = pollFirst();
#	Line 287 | Line 251 | public class ArrayDeque<E> extends Abstr
251		}
252
253		/**
254	<	* Retrieves and removes the last element of this deque.  This method
291	<	* differs from the <tt>pollLast</tt> method in that it throws an
292	<	* exception if this deque is empty.
293	<	*
294	<	* @return the last element of this deque
295	<	* @throws NoSuchElementException if this deque is empty
254	>	* @throws NoSuchElementException {@inheritDoc}
255		*/
256		public E removeLast() {
257		E x = pollLast();
#	Line 301 | Line 260 | public class ArrayDeque<E> extends Abstr
260		return x;
261		}
262
263	<	/**
264	<	* Retrieves, but does not remove, the first element of this deque,
265	<	* returning <tt>null</tt> if this deque is empty.
266	<	*
267	<	* @return the first element of this deque, or <tt>null</tt> if
268	<	*     this deque is empty
269	<	*/
270	<	public E peekFirst() {
312	<	return elements[head]; // elements[head] is null if deque empty
263	>	public E pollFirst() {
264	>	int h = head;
265	>	E result = elements[h]; // Element is null if deque empty
266	>	if (result == null)
267	>	return null;
268	>	elements[h] = null;     // Must null out slot
269	>	head = (h + 1) & (elements.length - 1);
270	>	return result;
271		}
272
273	<	/**
274	<	* Retrieves, but does not remove, the last element of this deque,
275	<	* returning <tt>null</tt> if this deque is empty.
276	<	*
277	<	* @return the last element of this deque, or <tt>null</tt> if this deque
278	<	*     is empty
279	<	*/
280	<	public E peekLast() {
323	<	return elements[(tail - 1) & (elements.length - 1)];
273	>	public E pollLast() {
274	>	int t = (tail - 1) & (elements.length - 1);
275	>	E result = elements[t];
276	>	if (result == null)
277	>	return null;
278	>	elements[t] = null;
279	>	tail = t;
280	>	return result;
281		}
282
283		/**
284	<	* Retrieves, but does not remove, the first element of this
328	<	* deque.  This method differs from the <tt>peek</tt> method only
329	<	* in that it throws an exception if this deque is empty.
330	<	*
331	<	* @return the first element of this deque
332	<	* @throws NoSuchElementException if this deque is empty
284	>	* @throws NoSuchElementException {@inheritDoc}
285		*/
286		public E getFirst() {
287		E x = elements[head];
#	Line 339 | Line 291 | public class ArrayDeque<E> extends Abstr
291		}
292
293		/**
294	<	* Retrieves, but does not remove, the last element of this
343	<	* deque.  This method differs from the <tt>peek</tt> method only
344	<	* in that it throws an exception if this deque is empty.
345	<	*
346	<	* @return the last element of this deque
347	<	* @throws NoSuchElementException if this deque is empty
294	>	* @throws NoSuchElementException {@inheritDoc}
295		*/
296		public E getLast() {
297		E x = elements[(tail - 1) & (elements.length - 1)];
#	Line 353 | Line 300 | public class ArrayDeque<E> extends Abstr
300		return x;
301		}
302
303	+	public E peekFirst() {
304	+	return elements[head]; // elements[head] is null if deque empty
305	+	}
306	+
307	+	public E peekLast() {
308	+	return elements[(tail - 1) & (elements.length - 1)];
309	+	}
310	+
311		/**
312		* Removes the first occurrence of the specified element in this
313	<	* deque (when traversing the deque from head to tail).  If the deque
314	<	* does not contain the element, it is unchanged.
313	>	* deque (when traversing the deque from head to tail).
314	>	* If the deque does not contain the element, it is unchanged.
315	>	* More formally, removes the first element <tt>e</tt> such that
316	>	* <tt>o.equals(e)</tt> (if such an element exists).
317	>	* Returns <tt>true</tt> if this deque contained the specified element
318	>	* (or equivalently, if this deque changed as a result of the call).
319		*
320	<	* @param e element to be removed from this deque, if present
320	>	* @param o element to be removed from this deque, if present
321		* @return <tt>true</tt> if the deque contained the specified element
322		*/
323	<	public boolean removeFirstOccurrence(Object e) {
324	<	if (e == null)
323	>	public boolean removeFirstOccurrence(Object o) {
324	>	if (o == null)
325		return false;
326		int mask = elements.length - 1;
327		int i = head;
328		E x;
329		while ( (x = elements[i]) != null) {
330	<	if (e.equals(x)) {
330	>	if (o.equals(x)) {
331		delete(i);
332		return true;
333		}
#	Line 379 | Line 338 | public class ArrayDeque<E> extends Abstr
338
339		/**
340		* Removes the last occurrence of the specified element in this
341	<	* deque (when traversing the deque from head to tail).  If the deque
342	<	* does not contain the element, it is unchanged.
341	>	* deque (when traversing the deque from head to tail).
342	>	* If the deque does not contain the element, it is unchanged.
343	>	* More formally, removes the last element <tt>e</tt> such that
344	>	* <tt>o.equals(e)</tt> (if such an element exists).
345	>	* Returns <tt>true</tt> if this deque contained the specified element
346	>	* (or equivalently, if this deque changed as a result of the call).
347		*
348	<	* @param e element to be removed from this deque, if present
348	>	* @param o element to be removed from this deque, if present
349		* @return <tt>true</tt> if the deque contained the specified element
350		*/
351	<	public boolean removeLastOccurrence(Object e) {
352	<	if (e == null)
351	>	public boolean removeLastOccurrence(Object o) {
352	>	if (o == null)
353		return false;
354		int mask = elements.length - 1;
355		int i = (tail - 1) & mask;
356		E x;
357		while ( (x = elements[i]) != null) {
358	<	if (e.equals(x)) {
358	>	if (o.equals(x)) {
359		delete(i);
360		return true;
361		}
#	Line 404 | Line 367 | public class ArrayDeque<E> extends Abstr
367		// *** Queue methods ***
368
369		/**
370	<	* Inserts the specified element to the end of this deque.
408	<	*
409	<	* <p>This method is equivalent to {@link #offerLast}.
410	<	*
411	<	* @param e the element to insert
412	<	* @return <tt>true</tt> (as per the spec for {@link Queue#offer})
413	<	* @throws NullPointerException if <tt>e</tt> is null
414	<	*/
415	<	public boolean offer(E e) {
416	<	return offerLast(e);
417	<	}
418	<
419	<	/**
420	<	* Inserts the specified element to the end of this deque.
370	>	* Inserts the specified element at the end of this deque.
371		*
372		* <p>This method is equivalent to {@link #addLast}.
373		*
374	<	* @param e the element to insert
375	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
376	<	* @throws NullPointerException if <tt>e</tt> is null
374	>	* @param e the element to add
375	>	* @return <tt>true</tt> (as specified by {@link Collection#add})
376	>	* @throws NullPointerException if the specified element is null
377		*/
378		public boolean add(E e) {
379		addLast(e);
#	Line 431 | Line 381 | public class ArrayDeque<E> extends Abstr
381		}
382
383		/**
384	<	* Retrieves and removes the head of the queue represented by
435	<	* this deque, or <tt>null</tt> if this deque is empty.  In other words,
436	<	* retrieves and removes the first element of this deque, or <tt>null</tt>
437	<	* if this deque is empty.
384	>	* Inserts the specified element at the end of this deque.
385		*
386	<	* <p>This method is equivalent to {@link #pollFirst}.
386	>	* <p>This method is equivalent to {@link #offerLast}.
387		*
388	<	* @return the first element of this deque, or <tt>null</tt> if
389	<	*     this deque is empty
388	>	* @param e the element to add
389	>	* @return <tt>true</tt> (as specified by {@link Queue#offer})
390	>	* @throws NullPointerException if the specified element is null
391		*/
392	<	public E poll() {
393	<	return pollFirst();
392	>	public boolean offer(E e) {
393	>	return offerLast(e);
394		}
395
396		/**
397		* Retrieves and removes the head of the queue represented by this deque.
398	<	* This method differs from the <tt>poll</tt> method in that it throws an
398	>	*
399	>	* This method differs from {@link #poll poll} only in that it throws an
400		* exception if this deque is empty.
401		*
402		* <p>This method is equivalent to {@link #removeFirst}.
403		*
404		* @return the head of the queue represented by this deque
405	<	* @throws NoSuchElementException if this deque is empty
405	>	* @throws NoSuchElementException {@inheritDoc}
406		*/
407		public E remove() {
408		return removeFirst();
409		}
410
411		/**
412	<	* Retrieves, but does not remove, the head of the queue represented by
413	<	* this deque, returning <tt>null</tt> if this deque is empty.
412	>	* Retrieves and removes the head of the queue represented by this deque
413	>	* (in other words, the first element of this deque), or returns
414	>	* <tt>null</tt> if this deque is empty.
415		*
416	<	* <p>This method is equivalent to {@link #peekFirst}
416	>	* <p>This method is equivalent to {@link #pollFirst}.
417		*
418		* @return the head of the queue represented by this deque, or
419	<	*     <tt>null</tt> if this deque is empty
419	>	*         <tt>null</tt> if this deque is empty
420		*/
421	<	public E peek() {
422	<	return peekFirst();
421	>	public E poll() {
422	>	return pollFirst();
423		}
424
425		/**
426		* Retrieves, but does not remove, the head of the queue represented by
427	<	* this deque.  This method differs from the <tt>peek</tt> method only in
427	>	* this deque.  This method differs from {@link #peek peek} only in
428		* that it throws an exception if this deque is empty.
429		*
430	<	* <p>This method is equivalent to {@link #getFirst}
430	>	* <p>This method is equivalent to {@link #getFirst}.
431		*
432		* @return the head of the queue represented by this deque
433	<	* @throws NoSuchElementException if this deque is empty
433	>	* @throws NoSuchElementException {@inheritDoc}
434		*/
435		public E element() {
436		return getFirst();
437		}
438
439	+	/**
440	+	* Retrieves, but does not remove, the head of the queue represented by
441	+	* this deque, or returns <tt>null</tt> if this deque is empty.
442	+	*
443	+	* <p>This method is equivalent to {@link #peekFirst}.
444	+	*
445	+	* @return the head of the queue represented by this deque, or
446	+	*         <tt>null</tt> if this deque is empty
447	+	*/
448	+	public E peek() {
449	+	return peekFirst();
450	+	}
451	+
452		// *** Stack methods ***
453
454		/**
455		* Pushes an element onto the stack represented by this deque.  In other
456	<	* words, inserts the element to the front this deque.
456	>	* words, inserts the element at the front of this deque.
457		*
458		* <p>This method is equivalent to {@link #addFirst}.
459		*
460		* @param e the element to push
461	<	* @throws NullPointerException if <tt>e</tt> is null
461	>	* @throws NullPointerException if the specified element is null
462		*/
463		public void push(E e) {
464		addFirst(e);
#	Line 508 | Line 471 | public class ArrayDeque<E> extends Abstr
471		* <p>This method is equivalent to {@link #removeFirst()}.
472		*
473		* @return the element at the front of this deque (which is the top
474	<	*     of the stack represented by this deque)
475	<	* @throws NoSuchElementException if this deque is empty
474	>	*         of the stack represented by this deque)
475	>	* @throws NoSuchElementException {@inheritDoc}
476		*/
477		public E pop() {
478		return removeFirst();
479		}
480
481	+	private void checkInvariants() {
482	+	assert elements[tail] == null;
483	+	assert head == tail ? elements[head] == null :
484	+	(elements[head] != null &&
485	+	elements[(tail - 1) & (elements.length - 1)] != null);
486	+	assert elements[(head - 1) & (elements.length - 1)] == null;
487	+	}
488	+
489		/**
490	<	* Remove the element at the specified position in the elements array,
491	<	* adjusting head, tail, and size as necessary.  This can result in
492	<	* motion of elements backwards or forwards in the array.
493	<	*
494	<	* <p>This method is called delete rather than remove to emphasize
495	<	* that its semantics differ from those of List.remove(int).
496	<	*
490	>	* Removes the element at the specified position in the elements array,
491	>	* adjusting head and tail as necessary.  This can result in motion of
492	>	* elements backwards or forwards in the array.
493	>	*
494	>	* <p>This method is called delete rather than remove to emphasize
495	>	* that its semantics differ from those of {@link List#remove(int)}.
496	>	*
497		* @return true if elements moved backwards
498		*/
499		private boolean delete(int i) {
500	<	// Case 1: Deque doesn't wrap
501	<	// Case 2: Deque does wrap and removed element is in the head portion
502	<	if ((head < tail || tail == 0) || i >= head) {
503	<	System.arraycopy(elements, head, elements, head + 1, i - head);
504	<	elements[head] = null;
505	<	head = (head + 1) & (elements.length - 1);
500	>	checkInvariants();
501	>	final E[] elements = this.elements;
502	>	final int mask = elements.length - 1;
503	>	final int h = head;
504	>	final int t = tail;
505	>	final int front = (i - h) & mask;
506	>	final int back  = (t - i) & mask;
507	>
508	>	// Invariant: head <= i < tail mod circularity
509	>	if (front >= ((t - h) & mask))
510	>	throw new ConcurrentModificationException();
511	>
512	>	// Optimize for least element motion
513	>	if (front < back) {
514	>	if (h <= i) {
515	>	System.arraycopy(elements, h, elements, h + 1, front);
516	>	} else { // Wrap around
517	>	System.arraycopy(elements, 0, elements, 1, i);
518	>	elements[0] = elements[mask];
519	>	System.arraycopy(elements, h, elements, h + 1, mask - h);
520	>	}
521	>	elements[h] = null;
522	>	head = (h + 1) & mask;
523		return false;
524	+	} else {
525	+	if (i < t) { // Copy the null tail as well
526	+	System.arraycopy(elements, i + 1, elements, i, back);
527	+	tail = t - 1;
528	+	} else { // Wrap around
529	+	System.arraycopy(elements, i + 1, elements, i, mask - i);
530	+	elements[mask] = elements[0];
531	+	System.arraycopy(elements, 1, elements, 0, t);
532	+	tail = (t - 1) & mask;
533	+	}
534	+	return true;
535		}
537	–
538	–	// Case 3: Deque wraps and removed element is in the tail portion
539	–	tail--;
540	–	System.arraycopy(elements, i + 1, elements, i, tail - i);
541	–	elements[tail] = null;
542	–	return true;
536		}
537
538		// *** Collection Methods ***
#	Line 554 | Line 547 | public class ArrayDeque<E> extends Abstr
547		}
548
549		/**
550	<	* Returns <tt>true</tt> if this collection contains no elements.<p>
550	>	* Returns <tt>true</tt> if this deque contains no elements.
551		*
552	<	* @return <tt>true</tt> if this collection contains no elements.
552	>	* @return <tt>true</tt> if this deque contains no elements
553		*/
554		public boolean isEmpty() {
555		return head == tail;
#	Line 567 | Line 560 | public class ArrayDeque<E> extends Abstr
560		* will be ordered from first (head) to last (tail).  This is the same
561		* order that elements would be dequeued (via successive calls to
562		* {@link #remove} or popped (via successive calls to {@link #pop}).
563	<	*
564	<	* @return an <tt>Iterator</tt> over the elements in this deque
563	>	*
564	>	* @return an iterator over the elements in this deque
565		*/
566		public Iterator<E> iterator() {
567		return new DeqIterator();
568		}
569
570	+	public Iterator<E> descendingIterator() {
571	+	return new DescendingIterator();
572	+	}
573	+
574		private class DeqIterator implements Iterator<E> {
575		/**
576		* Index of element to be returned by subsequent call to next.
#	Line 597 | Line 594 | public class ArrayDeque<E> extends Abstr
594		}
595
596		public E next() {
600	–	E result;
597		if (cursor == fence)
598		throw new NoSuchElementException();
599	+	E result = elements[cursor];
600		// This check doesn't catch all possible comodifications,
601		// but does catch the ones that corrupt traversal
602	<	if (tail != fence || (result = elements[cursor]) == null)
602	>	if (tail != fence || result == null)
603		throw new ConcurrentModificationException();
604		lastRet = cursor;
605		cursor = (cursor + 1) & (elements.length - 1);
#	Line 612 | Line 609 | public class ArrayDeque<E> extends Abstr
609		public void remove() {
610		if (lastRet < 0)
611		throw new IllegalStateException();
612	<	if (delete(lastRet))
613	<	cursor--;
612	>	if (delete(lastRet)) { // if left-shifted, undo increment in next()
613	>	cursor = (cursor - 1) & (elements.length - 1);
614	>	fence = tail;
615	>	}
616	>	lastRet = -1;
617	>	}
618	>	}
619	>
620	>	private class DescendingIterator implements Iterator<E> {
621	>	/*
622	>	* This class is nearly a mirror-image of DeqIterator, using
623	>	* tail instead of head for initial cursor, and head instead of
624	>	* tail for fence.
625	>	*/
626	>	private int cursor = tail;
627	>	private int fence = head;
628	>	private int lastRet = -1;
629	>
630	>	public boolean hasNext() {
631	>	return cursor != fence;
632	>	}
633	>
634	>	public E next() {
635	>	if (cursor == fence)
636	>	throw new NoSuchElementException();
637	>	cursor = (cursor - 1) & (elements.length - 1);
638	>	E result = elements[cursor];
639	>	if (head != fence || result == null)
640	>	throw new ConcurrentModificationException();
641	>	lastRet = cursor;
642	>	return result;
643	>	}
644	>
645	>	public void remove() {
646	>	if (lastRet < 0)
647	>	throw new IllegalStateException();
648	>	if (!delete(lastRet)) {
649	>	cursor = (cursor + 1) & (elements.length - 1);
650	>	fence = head;
651	>	}
652		lastRet = -1;
618	–	fence = tail;
653		}
654		}
655
656		/**
657	<	* Returns <tt>true</tt> if this deque contains the specified
658	<	* element.  More formally, returns <tt>true</tt> if and only if this
659	<	* deque contains at least one element <tt>e</tt> such that
626	<	* <tt>e.equals(o)</tt>.
657	>	* Returns <tt>true</tt> if this deque contains the specified element.
658	>	* More formally, returns <tt>true</tt> if and only if this deque contains
659	>	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
660		*
661		* @param o object to be checked for containment in this deque
662		* @return <tt>true</tt> if this deque contains the specified element
#	Line 644 | Line 677 | public class ArrayDeque<E> extends Abstr
677
678		/**
679		* Removes a single instance of the specified element from this deque.
680	<	* This method is equivalent to {@link #removeFirstOccurrence}.
680	>	* If the deque does not contain the element, it is unchanged.
681	>	* More formally, removes the first element <tt>e</tt> such that
682	>	* <tt>o.equals(e)</tt> (if such an element exists).
683	>	* Returns <tt>true</tt> if this deque contained the specified element
684	>	* (or equivalently, if this deque changed as a result of the call).
685	>	*
686	>	* <p>This method is equivalent to {@link #removeFirstOccurrence}.
687		*
688	<	* @param e element to be removed from this deque, if present
688	>	* @param o element to be removed from this deque, if present
689		* @return <tt>true</tt> if this deque contained the specified element
690		*/
691	<	public boolean remove(Object e) {
692	<	return removeFirstOccurrence(e);
691	>	public boolean remove(Object o) {
692	>	return removeFirstOccurrence(o);
693		}
694
695		/**
696		* Removes all of the elements from this deque.
697	+	* The deque will be empty after this call returns.
698		*/
699		public void clear() {
700		int h = head;
#	Line 666 | Line 706 | public class ArrayDeque<E> extends Abstr
706		do {
707		elements[i] = null;
708		i = (i + 1) & mask;
709	<	} while(i != t);
709	>	} while (i != t);
710		}
711		}
712
713		/**
714	<	* Returns an array containing all of the elements in this list
715	<	* in the correct order.
714	>	* Returns an array containing all of the elements in this deque
715	>	* in proper sequence (from first to last element).
716	>	*
717	>	* <p>The returned array will be "safe" in that no references to it are
718	>	* maintained by this deque.  (In other words, this method must allocate
719	>	* a new array).  The caller is thus free to modify the returned array.
720	>	*
721	>	* <p>This method acts as bridge between array-based and collection-based
722	>	* APIs.
723		*
724	<	* @return an array containing all of the elements in this list
678	<	*         in the correct order
724	>	* @return an array containing all of the elements in this deque
725		*/
726		public Object[] toArray() {
727	<	return copyElements(new Object[size()]);
727	>	return copyElements(new Object[size()]);
728		}
729
730		/**
731	<	* Returns an array containing all of the elements in this deque in the
732	<	* correct order; the runtime type of the returned array is that of the
733	<	* specified array.  If the deque fits in the specified array, it is
734	<	* returned therein.  Otherwise, a new array is allocated with the runtime
735	<	* type of the specified array and the size of this deque.
731	>	* Returns an array containing all of the elements in this deque in
732	>	* proper sequence (from first to last element); the runtime type of the
733	>	* returned array is that of the specified array.  If the deque fits in
734	>	* the specified array, it is returned therein.  Otherwise, a new array
735	>	* is allocated with the runtime type of the specified array and the
736	>	* size of this deque.
737		*
738	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
739	<	* the array has more elements than the deque), the element in the array
740	<	* immediately following the end of the collection is set to <tt>null</tt>.
738	>	* <p>If this deque fits in the specified array with room to spare
739	>	* (i.e., the array has more elements than this deque), the element in
740	>	* the array immediately following the end of the deque is set to
741	>	* <tt>null</tt>.
742	>	*
743	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
744	>	* array-based and collection-based APIs.  Further, this method allows
745	>	* precise control over the runtime type of the output array, and may,
746	>	* under certain circumstances, be used to save allocation costs.
747	>	*
748	>	* <p>Suppose <tt>x</tt> is a deque known to contain only strings.
749	>	* The following code can be used to dump the deque into a newly
750	>	* allocated array of <tt>String</tt>:
751	>	*
752	>	* <pre>
753	>	*     String[] y = x.toArray(new String[0]);</pre>
754	>	*
755	>	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
756	>	* <tt>toArray()</tt>.
757		*
758		* @param a the array into which the elements of the deque are to
759	<	*          be stored, if it is big enough; otherwise, a new array of the
760	<	*          same runtime type is allocated for this purpose
761	<	* @return an array containing the elements of the deque
762	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
763	<	*         of the runtime type of every element in this deque
759	>	*          be stored, if it is big enough; otherwise, a new array of the
760	>	*          same runtime type is allocated for this purpose
761	>	* @return an array containing all of the elements in this deque
762	>	* @throws ArrayStoreException if the runtime type of the specified array
763	>	*         is not a supertype of the runtime type of every element in
764	>	*         this deque
765	>	* @throws NullPointerException if the specified array is null
766		*/
767		public <T> T[] toArray(T[] a) {
768		int size = size();
769		if (a.length < size)
770		a = (T[])java.lang.reflect.Array.newInstance(
771		a.getClass().getComponentType(), size);
772	<	copyElements(a);
772	>	copyElements(a);
773		if (a.length > size)
774		a[size] = null;
775		return a;
#	Line 718 | Line 783 | public class ArrayDeque<E> extends Abstr
783		* @return a copy of this deque
784		*/
785		public ArrayDeque<E> clone() {
786	<	try {
786	>	try {
787		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
788	<	// These two lines are currently faster than cloning the array:
724	<	result.elements = (E[]) new Object[elements.length];
725	<	System.arraycopy(elements, 0, result.elements, 0, elements.length);
788	>	result.elements = Arrays.copyOf(elements, elements.length);
789		return result;
790
791	<	} catch (CloneNotSupportedException e) {
791	>	} catch (CloneNotSupportedException e) {
792		throw new AssertionError();
793		}
794		}
#	Line 746 | Line 809 | public class ArrayDeque<E> extends Abstr
809		s.defaultWriteObject();
810
811		// Write out size
812	<	int size = size();
750	<	s.writeInt(size);
812	>	s.writeInt(size());
813
814		// Write out elements in order.
753	–	int i = head;
815		int mask = elements.length - 1;
816	<	for (int j = 0; j < size; j++) {
816	>	for (int i = head; i != tail; i = (i + 1) & mask)
817		s.writeObject(elements[i]);
757	–	i = (i + 1) & mask;
758	–	}
818		}
819
820		/**
#	Line 774 | Line 833 | public class ArrayDeque<E> extends Abstr
833		// Read in all elements in the proper order.
834		for (int i = 0; i < size; i++)
835		elements[i] = (E)s.readObject();
777	–
836		}
837		}

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