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

Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.1 by dl, Tue Dec 28 12:14:07 2004 UTC vs.
Revision 1.21 by dl, Fri Sep 16 23:17:05 2005 UTC

#	Line 4 | Line 4
4		*/
5
6		package java.util;
7	+	import java.util.*; // for javadoc (till 6280605 is fixed)
8		import java.io.*;
9
10		/**
#	Line 12 | Line 13 | import java.io.*;
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 as a stack, and faster than {@link LinkedList}
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
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 remove method, the
29	<	* iterator will generally throw a {@link ConcurrentModificationException}.
30	<	* Thus, in the face of concurrent modification, the iterator fails quickly
31	<	* and cleanly, rather than risking arbitrary, non-deterministic behavior at
32	<	* an undetermined time in the future.
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.
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	<	* optional methods of the {@link Collection} and {@link
45	<	* Iterator} interfaces.  This class is a member of the <a
46	<	* href="{@docRoot}/../guide/collections/index.html"> Java Collections
47	<	* Framework</a>.
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
#	Line 52 | Line 56 | public class ArrayDeque<E> extends Abstr
56		implements Deque<E>, Cloneable, Serializable
57		{
58		/**
59	<	* The array in which the elements of in the deque are stored.
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
#	Line 87 | Line 91 | public class ArrayDeque<E> extends Abstr
91		/**
92		* Allocate empty array to hold the given number of elements.
93		*
94	<	* @param numElements  the number of elements to hold.
94	>	* @param numElements  the number of elements to hold
95		*/
96	<	private void allocateElements(int numElements) {
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.
#	Line 113 | Line 117 | public class ArrayDeque<E> extends Abstr
117		* when head and tail have wrapped around to become equal.
118		*/
119		private void doubleCapacity() {
120	<	assert head == tail;
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
#	Line 129 | Line 133 | public class ArrayDeque<E> extends Abstr
133		}
134
135		/**
136	<	* Copy the elements from our element array into the specified array,
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		*
#	Line 147 | Line 151 | public class ArrayDeque<E> extends Abstr
151		}
152
153		/**
154	<	* Constructs an empty array deque with the an initial capacity
154	>	* Constructs an empty array deque with an initial capacity
155		* sufficient to hold 16 elements.
156		*/
157		public ArrayDeque() {
#	Line 184 | Line 188 | public class ArrayDeque<E> extends Abstr
188		// terms of these.
189
190		/**
191	<	* Inserts the specified element to the front this deque.
191	>	* Inserts the specified element at the front of this deque.
192		*
193	<	* @param e the element to insert
194	<	* @throws NullPointerException if <tt>e</tt> is null
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)
200	>	if (head == tail)
201		doubleCapacity();
202		}
203
204		/**
205	<	* Inserts the specified element to the end this deque.
206	<	* This method is equivalent to {@link Collection#add} and
207	<	* {@link #push}.
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 insert
210	<	* @throws NullPointerException if <tt>e</tt> is null
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)
#	Line 214 | Line 218 | public class ArrayDeque<E> extends Abstr
218		}
219
220		/**
221	<	* 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.
221	>	* Inserts the specified element at the front of this deque.
222		*
223	<	* @param e the element to insert
224	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst})
225	<	* @throws NullPointerException if <tt>e</tt> is null
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);
#	Line 260 | Line 230 | public class ArrayDeque<E> extends Abstr
230		}
231
232		/**
233	<	* Inserts the specified element to the end this deque.
233	>	* Inserts the specified element at the end of this deque.
234		*
235	<	* @param e the element to insert
236	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
237	<	* @throws NullPointerException if <tt>e</tt> is null
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);
#	Line 272 | Line 242 | public class ArrayDeque<E> extends Abstr
242		}
243
244		/**
245	<	* 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
245	>	* @throws NoSuchElementException {@inheritDoc}
246		*/
247		public E removeFirst() {
248		E x = pollFirst();
#	Line 287 | Line 252 | public class ArrayDeque<E> extends Abstr
252		}
253
254		/**
255	<	* 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
255	>	* @throws NoSuchElementException {@inheritDoc}
256		*/
257		public E removeLast() {
258		E x = pollLast();
#	Line 301 | Line 261 | public class ArrayDeque<E> extends Abstr
261		return x;
262		}
263
264	<	/**
265	<	* Retrieves, but does not remove, the first element of this deque,
266	<	* returning <tt>null</tt> if this deque is empty.
267	<	*
268	<	* @return the first element of this deque, or <tt>null</tt> if
269	<	*     this deque is empty
270	<	*/
271	<	public E peekFirst() {
312	<	return elements[head]; // elements[head] is null if deque empty
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	<	/**
275	<	* Retrieves, but does not remove, the last element of this deque,
276	<	* returning <tt>null</tt> if this deque is empty.
277	<	*
278	<	* @return the last element of this deque, or <tt>null</tt> if this deque
279	<	*     is empty
280	<	*/
281	<	public E peekLast() {
323	<	return elements[(tail - 1) & (elements.length - 1)];
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	<	* 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
285	>	* @throws NoSuchElementException {@inheritDoc}
286		*/
287		public E getFirst() {
288		E x = elements[head];
#	Line 339 | Line 292 | public class ArrayDeque<E> extends Abstr
292		}
293
294		/**
295	<	* 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
295	>	* @throws NoSuchElementException {@inheritDoc}
296		*/
297		public E getLast() {
298		E x = elements[(tail - 1) & (elements.length - 1)];
#	Line 353 | Line 301 | public class ArrayDeque<E> extends Abstr
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).  If the deque
315	<	* does not contain the element, it is unchanged.
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 e element to be removed from this deque, if present
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 e) {
325	<	if (e == null)
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 (e.equals(x)) {
331	>	if (o.equals(x)) {
332		delete(i);
333		return true;
334		}
#	Line 379 | Line 339 | public class ArrayDeque<E> extends Abstr
339
340		/**
341		* Removes the last occurrence of the specified element in this
342	<	* deque (when traversing the deque from head to tail).  If the deque
343	<	* does not contain the element, it is unchanged.
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 e element to be removed from this deque, if present
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 e) {
353	<	if (e == null)
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 (e.equals(x)) {
359	>	if (o.equals(x)) {
360		delete(i);
361		return true;
362		}
#	Line 404 | Line 368 | public class ArrayDeque<E> extends Abstr
368		// *** Queue methods ***
369
370		/**
371	<	* 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.
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 insert
376	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
377	<	* @throws NullPointerException if <tt>e</tt> is null
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);
#	Line 431 | Line 382 | public class ArrayDeque<E> extends Abstr
382		}
383
384		/**
385	<	* 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.
385	>	* Inserts the specified element at the end of this deque.
386		*
387	<	* <p>This method is equivalent to {@link #pollFirst}.
387	>	* <p>This method is equivalent to {@link #offerLast}.
388		*
389	<	* @return the first element of this deque, or <tt>null</tt> if
390	<	*     this deque is empty
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 E poll() {
394	<	return pollFirst();
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	<	* This method differs from the <tt>poll</tt> method in that it throws an
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 if this deque is empty
406	>	* @throws NoSuchElementException {@inheritDoc}
407		*/
408		public E remove() {
409		return removeFirst();
410		}
411
412		/**
413	<	* Retrieves, but does not remove, the head of the queue represented by
414	<	* this deque, returning <tt>null</tt> if this deque is empty.
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 #peekFirst}
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
420	>	*         <tt>null</tt> if this deque is empty
421		*/
422	<	public E peek() {
423	<	return peekFirst();
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 the <tt>peek</tt> method only in
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}
431	>	* <p>This method is equivalent to {@link #getFirst}.
432		*
433		* @return the head of the queue represented by this deque
434	<	* @throws NoSuchElementException if this deque is empty
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 to the front this deque.
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 <tt>e</tt> is null
462	>	* @throws NullPointerException if the specified element is null
463		*/
464		public void push(E e) {
465		addFirst(e);
#	Line 503 | Line 467 | public class ArrayDeque<E> extends Abstr
467
468		/**
469		* Pops an element from the stack represented by this deque.  In other
470	<	* words, removes and returns the the first element of this deque.
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 if this deque is empty
475	>	*         of the stack represented by this deque)
476	>	* @throws NoSuchElementException {@inheritDoc}
477		*/
478		public E pop() {
479		return removeFirst();
480		}
481
482		/**
483	<	* Remove the element at the specified position in the elements array,
484	<	* adjusting head, tail, and size as necessary.  This can result in
485	<	* motion of elements backwards or forwards in the array.
486	<	*
487	<	* <p>This method is called delete rather than remove to emphasize the
488	<	* that that its semantics differ from those of List.remove(int).
489	<	*
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	<	// Case 1: Deque doesn't wrap
494	<	// Case 2: Deque does wrap and removed element is in the head portion
495	<	if ((head < tail || tail == 0) || i >= head) {
496	<	System.arraycopy(elements, head, elements, head + 1, i - head);
497	<	elements[head] = null;
498	<	head = (head + 1) & (elements.length - 1);
493	>	int mask = elements.length - 1;
494	>	int front = (i - head) & mask;
495	>	int back  = (tail - i) & mask;
496	>
497	>	// Invariant: head <= i < tail mod circularity
498	>	if (front >= ((tail - head) & mask))
499	>	throw new ConcurrentModificationException();
500	>
501	>	// Optimize for least element motion
502	>	if (front < back) {
503	>	if (head <= i) {
504	>	System.arraycopy(elements, head, elements, head + 1, front);
505	>	} else { // Wrap around
506	>	elements[0] = elements[mask];
507	>	System.arraycopy(elements, 0, elements, 1, i);
508	>	System.arraycopy(elements, head, elements, head + 1, mask - head);
509	>	}
510	>	elements[head] = null;
511	>	head = (head + 1) & mask;
512		return false;
513	<	}
514	<
515	<	// Case 3: Deque wraps and removed element is in the tail portion
516	<	tail--;
517	<	System.arraycopy(elements, i + 1, elements, i, tail - i);
518	<	elements[tail] = null;
519	<	return true;
513	>	} else {
514	>	int t = tail;
515	>	tail = (tail - 1) & mask;
516	>	if (i < t) { // Copy the null tail as well
517	>	System.arraycopy(elements, i + 1, elements, i, back);
518	>	} else {     // Wrap around
519	>	elements[mask] = elements[0];
520	>	System.arraycopy(elements, i + 1, elements, i, mask - i);
521	>	System.arraycopy(elements, 1, elements, 0, t);
522	>	}
523	>	return true;
524	>	}
525		}
526
527		// *** Collection Methods ***
#	Line 554 | Line 536 | public class ArrayDeque<E> extends Abstr
536		}
537
538		/**
539	<	* Returns <tt>true</tt> if this collection contains no elements.<p>
539	>	* Returns <tt>true</tt> if this deque contains no elements.
540		*
541	<	* @return <tt>true</tt> if this collection contains no elements.
541	>	* @return <tt>true</tt> if this deque contains no elements
542		*/
543		public boolean isEmpty() {
544		return head == tail;
#	Line 567 | Line 549 | public class ArrayDeque<E> extends Abstr
549		* will be ordered from first (head) to last (tail).  This is the same
550		* order that elements would be dequeued (via successive calls to
551		* {@link #remove} or popped (via successive calls to {@link #pop}).
552	<	*
553	<	* @return an <tt>Iterator</tt> over the elements in this deque
552	>	*
553	>	* @return an iterator over the elements in this deque
554		*/
555		public Iterator<E> iterator() {
556		return new DeqIterator();
557		}
558
559	+	public Iterator<E> descendingIterator() {
560	+	return new DescendingIterator();
561	+	}
562	+
563		private class DeqIterator implements Iterator<E> {
564		/**
565		* Index of element to be returned by subsequent call to next.
#	Line 612 | Line 598 | public class ArrayDeque<E> extends Abstr
598		public void remove() {
599		if (lastRet < 0)
600		throw new IllegalStateException();
601	<	if (delete(lastRet))
602	<	cursor--;
601	>	if (delete(lastRet)) // if left-shifted, undo increment in next()
602	>	cursor = (cursor - 1) & (elements.length - 1);
603		lastRet = -1;
604		fence = tail;
605		}
606		}
607
608	+
609	+	private class DescendingIterator implements Iterator<E> {
610	+	/*
611	+	* This class is nearly a mirror-image of DeqIterator, using
612	+	* (tail-1) instead of head for initial cursor, (head-1)
613	+	* instead of tail for fence, and elements.length instead of -1
614	+	* for sentinel. It shares the same structure, but not many
615	+	* actual lines of code.
616	+	*/
617	+	private int cursor = (tail - 1) & (elements.length - 1);
618	+	private int fence =  (head - 1) & (elements.length - 1);
619	+	private int lastRet = elements.length;
620	+
621	+	public boolean hasNext() {
622	+	return cursor != fence;
623	+	}
624	+
625	+	public E next() {
626	+	E result;
627	+	if (cursor == fence)
628	+	throw new NoSuchElementException();
629	+	if (((head - 1) & (elements.length - 1)) != fence ||
630	+	(result = elements[cursor]) == null)
631	+	throw new ConcurrentModificationException();
632	+	lastRet = cursor;
633	+	cursor = (cursor - 1) & (elements.length - 1);
634	+	return result;
635	+	}
636	+
637	+	public void remove() {
638	+	if (lastRet >= elements.length)
639	+	throw new IllegalStateException();
640	+	if (!delete(lastRet))
641	+	cursor = (cursor + 1) & (elements.length - 1);
642	+	lastRet = elements.length;
643	+	fence = (head - 1) & (elements.length - 1);
644	+	}
645	+	}
646	+
647		/**
648	<	* Returns <tt>true</tt> if this deque contains the specified
649	<	* element.  More formally, returns <tt>true</tt> if and only if this
650	<	* deque contains at least one element <tt>e</tt> such that
626	<	* <tt>e.equals(o)</tt>.
648	>	* Returns <tt>true</tt> if this deque contains the specified element.
649	>	* More formally, returns <tt>true</tt> if and only if this deque contains
650	>	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
651		*
652		* @param o object to be checked for containment in this deque
653		* @return <tt>true</tt> if this deque contains the specified element
#	Line 644 | Line 668 | public class ArrayDeque<E> extends Abstr
668
669		/**
670		* Removes a single instance of the specified element from this deque.
671	<	* This method is equivalent to {@link #removeFirstOccurrence}.
671	>	* If the deque does not contain the element, it is unchanged.
672	>	* More formally, removes the first element <tt>e</tt> such that
673	>	* <tt>o.equals(e)</tt> (if such an element exists).
674	>	* Returns <tt>true</tt> if this deque contained the specified element
675	>	* (or equivalently, if this deque changed as a result of the call).
676		*
677	<	* @param e element to be removed from this deque, if present
677	>	* <p>This method is equivalent to {@link #removeFirstOccurrence}.
678	>	*
679	>	* @param o element to be removed from this deque, if present
680		* @return <tt>true</tt> if this deque contained the specified element
681		*/
682	<	public boolean remove(Object e) {
683	<	return removeFirstOccurrence(e);
682	>	public boolean remove(Object o) {
683	>	return removeFirstOccurrence(o);
684		}
685
686		/**
687		* Removes all of the elements from this deque.
688	+	* The deque will be empty after this call returns.
689		*/
690		public void clear() {
691		int h = head;
#	Line 666 | Line 697 | public class ArrayDeque<E> extends Abstr
697		do {
698		elements[i] = null;
699		i = (i + 1) & mask;
700	<	} while(i != t);
700	>	} while (i != t);
701		}
702		}
703
704		/**
705	<	* Returns an array containing all of the elements in this list
706	<	* in the correct order.
705	>	* Returns an array containing all of the elements in this deque
706	>	* in proper sequence (from first to last element).
707	>	*
708	>	* <p>The returned array will be "safe" in that no references to it are
709	>	* maintained by this deque.  (In other words, this method must allocate
710	>	* a new array).  The caller is thus free to modify the returned array.
711	>	*
712	>	* <p>This method acts as bridge between array-based and collection-based
713	>	* APIs.
714		*
715	<	* @return an array containing all of the elements in this list
678	<	*         in the correct order
715	>	* @return an array containing all of the elements in this deque
716		*/
717		public Object[] toArray() {
718		return copyElements(new Object[size()]);
719		}
720
721		/**
722	<	* Returns an array containing all of the elements in this deque in the
723	<	* correct order; the runtime type of the returned array is that of the
724	<	* specified array.  If the deque fits in the specified array, it is
725	<	* returned therein.  Otherwise, a new array is allocated with the runtime
726	<	* type of the specified array and the size of this deque.
727	<	*
728	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
729	<	* the array has more elements than the deque), the element in the array
730	<	* immediately following the end of the collection is set to <tt>null</tt>.
722	>	* Returns an array containing all of the elements in this deque in
723	>	* proper sequence (from first to last element); the runtime type of the
724	>	* returned array is that of the specified array.  If the deque fits in
725	>	* the specified array, it is returned therein.  Otherwise, a new array
726	>	* is allocated with the runtime type of the specified array and the
727	>	* size of this deque.
728	>	*
729	>	* <p>If this deque fits in the specified array with room to spare
730	>	* (i.e., the array has more elements than this deque), the element in
731	>	* the array immediately following the end of the deque is set to
732	>	* <tt>null</tt>.
733	>	*
734	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
735	>	* array-based and collection-based APIs.  Further, this method allows
736	>	* precise control over the runtime type of the output array, and may,
737	>	* under certain circumstances, be used to save allocation costs.
738	>	*
739	>	* <p>Suppose <tt>x</tt> is a deque known to contain only strings.
740	>	* The following code can be used to dump the deque into a newly
741	>	* allocated array of <tt>String</tt>:
742	>	*
743	>	* <pre>
744	>	*     String[] y = x.toArray(new String[0]);</pre>
745	>	*
746	>	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
747	>	* <tt>toArray()</tt>.
748		*
749		* @param a the array into which the elements of the deque are to
750	<	*          be stored, if it is big enough; otherwise, a new array of the
751	<	*          same runtime type is allocated for this purpose
752	<	* @return an array containing the elements of the deque
753	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
754	<	*         of the runtime type of every element in this deque
750	>	*          be stored, if it is big enough; otherwise, a new array of the
751	>	*          same runtime type is allocated for this purpose
752	>	* @return an array containing all of the elements in this deque
753	>	* @throws ArrayStoreException if the runtime type of the specified array
754	>	*         is not a supertype of the runtime type of every element in
755	>	*         this deque
756	>	* @throws NullPointerException if the specified array is null
757		*/
758		public <T> T[] toArray(T[] a) {
759		int size = size();
#	Line 718 | Line 774 | public class ArrayDeque<E> extends Abstr
774		* @return a copy of this deque
775		*/
776		public ArrayDeque<E> clone() {
777	<	try {
777	>	try {
778		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
779		// These two lines are currently faster than cloning the array:
780		result.elements = (E[]) new Object[elements.length];
781		System.arraycopy(elements, 0, result.elements, 0, elements.length);
782		return result;
783
784	<	} catch (CloneNotSupportedException e) {
784	>	} catch (CloneNotSupportedException e) {
785		throw new AssertionError();
786		}
787		}
#	Line 746 | Line 802 | public class ArrayDeque<E> extends Abstr
802		s.defaultWriteObject();
803
804		// Write out size
805	<	int size = size();
750	<	s.writeInt(size);
805	>	s.writeInt(size());
806
807		// Write out elements in order.
753	–	int i = head;
808		int mask = elements.length - 1;
809	<	for (int j = 0; j < size; j++) {
809	>	for (int i = head; i != tail; i = (i + 1) & mask)
810		s.writeObject(elements[i]);
757	–	i = (i + 1) & mask;
758	–	}
811		}
812
813		/**

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