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

Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.3 by dl, Tue Mar 8 17:52:02 2005 UTC vs.
Revision 1.34 by jsr166, Fri Jun 10 20:58:50 2011 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Josh Bloch of Google Inc. and released to the public domain,
3	<	* as explained at http://creativecommons.org/licenses/publicdomain.
3	>	* as explained at http://creativecommons.org/publicdomain/zero/1.0/.
4		*/
5
6		package java.util;
7	–	import java.io.*;
7
8		/**
9		* Resizable-array implementation of the {@link Deque} interface.  Array
#	Line 18 | Line 17 | import java.io.*;
17		* <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time.
18		* Exceptions include {@link #remove(Object) remove}, {@link
19		* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
20	<	* removeLastOccurrence}, {@link #contains contains }, {@link #iterator
20	>	* removeLastOccurrence}, {@link #contains contains}, {@link #iterator
21		* iterator.remove()}, and the bulk operations, all of which run in linear
22		* time.
23		*
24		* <p>The iterators returned by this class's <tt>iterator</tt> method are
25		* <i>fail-fast</i>: If the deque is modified at any time after the iterator
26	<	* is created, in any way except through the iterator's own remove method, the
27	<	* iterator will generally throw a {@link ConcurrentModificationException}.
28	<	* Thus, in the face of concurrent modification, the iterator fails quickly
29	<	* and cleanly, rather than risking arbitrary, non-deterministic behavior at
30	<	* an undetermined time in the future.
26	>	* is created, in any way except through the iterator's own <tt>remove</tt>
27	>	* method, the iterator will generally throw a {@link
28	>	* ConcurrentModificationException}.  Thus, in the face of concurrent
29	>	* modification, the iterator fails quickly and cleanly, rather than risking
30	>	* arbitrary, non-deterministic behavior at an undetermined time in the
31	>	* future.
32		*
33		* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
34		* as it is, generally speaking, impossible to make any hard guarantees in the
35		* presence of unsynchronized concurrent modification.  Fail-fast iterators
36	<	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
36	>	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
37		* Therefore, it would be wrong to write a program that depended on this
38		* exception for its correctness: <i>the fail-fast behavior of iterators
39		* should be used only to detect bugs.</i>
40		*
41		* <p>This class and its iterator implement all of the
42	<	* optional methods of the {@link Collection} and {@link
43	<	* Iterator} interfaces.  This class is a member of the <a
44	<	* href="{@docRoot}/../guide/collections/index.html"> Java Collections
45	<	* Framework</a>.
42	>	* <em>optional</em> methods of the {@link Collection} and {@link
43	>	* Iterator} interfaces.
44	>	*
45	>	* <p>This class is a member of the
46	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
47	>	* Java Collections Framework</a>.
48		*
49		* @author  Josh Bloch and Doug Lea
50		* @since   1.6
51		* @param <E> the type of elements held in this collection
52		*/
53		public class ArrayDeque<E> extends AbstractCollection<E>
54	<	implements Deque<E>, Cloneable, Serializable
54	>	implements Deque<E>, Cloneable, java.io.Serializable
55		{
56		/**
57	<	* The array in which the elements of in the deque are stored.
57	>	* The array in which the elements of the deque are stored.
58		* The capacity of the deque is the length of this array, which is
59		* always a power of two. The array is never allowed to become
60		* full, except transiently within an addX method where it is
#	Line 61 | Line 63 | public class ArrayDeque<E> extends Abstr
63		* other.  We also guarantee that all array cells not holding
64		* deque elements are always null.
65		*/
66	<	private transient E[] elements;
66	>	private transient Object[] elements;
67
68		/**
69		* The index of the element at the head of the deque (which is the
#	Line 87 | Line 89 | public class ArrayDeque<E> extends Abstr
89		/**
90		* Allocate empty array to hold the given number of elements.
91		*
92	<	* @param numElements  the number of elements to hold.
92	>	* @param numElements  the number of elements to hold
93		*/
94	<	private void allocateElements(int numElements) {
94	>	private void allocateElements(int numElements) {
95		int initialCapacity = MIN_INITIAL_CAPACITY;
96		// Find the best power of two to hold elements.
97		// Tests "<=" because arrays aren't kept full.
#	Line 105 | Line 107 | public class ArrayDeque<E> extends Abstr
107		if (initialCapacity < 0)   // Too many elements, must back off
108		initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
109		}
110	<	elements = (E[]) new Object[initialCapacity];
110	>	elements = new Object[initialCapacity];
111		}
112
113		/**
#	Line 113 | Line 115 | public class ArrayDeque<E> extends Abstr
115		* when head and tail have wrapped around to become equal.
116		*/
117		private void doubleCapacity() {
118	<	assert head == tail;
118	>	assert head == tail;
119		int p = head;
120		int n = elements.length;
121		int r = n - p; // number of elements to the right of p
#	Line 123 | Line 125 | public class ArrayDeque<E> extends Abstr
125		Object[] a = new Object[newCapacity];
126		System.arraycopy(elements, p, a, 0, r);
127		System.arraycopy(elements, 0, a, r, p);
128	<	elements = (E[])a;
128	>	elements = a;
129		head = 0;
130		tail = n;
131		}
132
133		/**
134	<	* Copy the elements from our element array into the specified array,
134	>	* Copies the elements from our element array into the specified array,
135		* in order (from first to last element in the deque).  It is assumed
136		* that the array is large enough to hold all elements in the deque.
137		*
#	Line 147 | Line 149 | public class ArrayDeque<E> extends Abstr
149		}
150
151		/**
152	<	* Constructs an empty array deque with the an initial capacity
152	>	* Constructs an empty array deque with an initial capacity
153		* sufficient to hold 16 elements.
154		*/
155		public ArrayDeque() {
156	<	elements = (E[]) new Object[16];
156	>	elements = new Object[16];
157		}
158
159		/**
#	Line 184 | Line 186 | public class ArrayDeque<E> extends Abstr
186		// terms of these.
187
188		/**
189	<	* Inserts the specified element to the front this deque.
189	>	* Inserts the specified element at the front of this deque.
190		*
191	<	* @param e the element to insert
192	<	* @throws NullPointerException if <tt>e</tt> is null
191	>	* @param e the element to add
192	>	* @throws NullPointerException if the specified element is null
193		*/
194		public void addFirst(E e) {
195		if (e == null)
196		throw new NullPointerException();
197		elements[head = (head - 1) & (elements.length - 1)] = e;
198	<	if (head == tail)
198	>	if (head == tail)
199		doubleCapacity();
200		}
201
202		/**
203	<	* Inserts the specified element to the end this deque.
204	<	* This method is equivalent to {@link Collection#add} and
205	<	* {@link #push}.
203	>	* Inserts the specified element at the end of this deque.
204	>	*
205	>	* <p>This method is equivalent to {@link #add}.
206		*
207	<	* @param e the element to insert
208	<	* @throws NullPointerException if <tt>e</tt> is null
207	>	* @param e the element to add
208	>	* @throws NullPointerException if the specified element is null
209		*/
210		public void addLast(E e) {
211		if (e == null)
#	Line 214 | Line 216 | public class ArrayDeque<E> extends Abstr
216		}
217
218		/**
219	<	* 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.
219	>	* Inserts the specified element at the front of this deque.
220		*
221	<	* @return the last element of this deque, or <tt>null</tt> if
222	<	*     this deque is empty
223	<	*/
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.
252	<	*
253	<	* @param e the element to insert
254	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst})
255	<	* @throws NullPointerException if <tt>e</tt> is null
221	>	* @param e the element to add
222	>	* @return <tt>true</tt> (as specified by {@link Deque#offerFirst})
223	>	* @throws NullPointerException if the specified element is null
224		*/
225		public boolean offerFirst(E e) {
226		addFirst(e);
#	Line 260 | Line 228 | public class ArrayDeque<E> extends Abstr
228		}
229
230		/**
231	<	* Inserts the specified element to the end this deque.
231	>	* Inserts the specified element at the end of this deque.
232		*
233	<	* @param e the element to insert
234	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
235	<	* @throws NullPointerException if <tt>e</tt> is null
233	>	* @param e the element to add
234	>	* @return <tt>true</tt> (as specified by {@link Deque#offerLast})
235	>	* @throws NullPointerException if the specified element is null
236		*/
237		public boolean offerLast(E e) {
238		addLast(e);
#	Line 272 | Line 240 | public class ArrayDeque<E> extends Abstr
240		}
241
242		/**
243	<	* 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
243	>	* @throws NoSuchElementException {@inheritDoc}
244		*/
245		public E removeFirst() {
246		E x = pollFirst();
#	Line 287 | Line 250 | public class ArrayDeque<E> extends Abstr
250		}
251
252		/**
253	<	* 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
253	>	* @throws NoSuchElementException {@inheritDoc}
254		*/
255		public E removeLast() {
256		E x = pollLast();
#	Line 301 | Line 259 | public class ArrayDeque<E> extends Abstr
259		return x;
260		}
261
262	<	/**
263	<	* Retrieves, but does not remove, the first element of this deque,
264	<	* returning <tt>null</tt> if this deque is empty.
265	<	*
266	<	* @return the first element of this deque, or <tt>null</tt> if
267	<	*     this deque is empty
268	<	*/
269	<	public E peekFirst() {
270	<	return elements[head]; // elements[head] is null if deque empty
262	>	public E pollFirst() {
263	>	int h = head;
264	>	@SuppressWarnings("unchecked") E result = (E) elements[h];
265	>	// 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	>	@SuppressWarnings("unchecked") E result = (E) 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];
288	<	if (x == null)
287	>	@SuppressWarnings("unchecked") E result = (E) elements[head];
288	>	if (result == null)
289		throw new NoSuchElementException();
290	<	return x;
290	>	return result;
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)];
298	<	if (x == null)
297	>	@SuppressWarnings("unchecked")
298	>	E result = (E) elements[(tail - 1) & (elements.length - 1)];
299	>	if (result == null)
300		throw new NoSuchElementException();
301	<	return x;
301	>	return result;
302	>	}
303	>
304	>	public E peekFirst() {
305	>	@SuppressWarnings("unchecked") E result = (E) elements[head];
306	>	// elements[head] is null if deque empty
307	>	return result;
308	>	}
309	>
310	>	public E peekLast() {
311	>	@SuppressWarnings("unchecked")
312	>	E result = (E) elements[(tail - 1) & (elements.length - 1)];
313	>	return result;
314		}
315
316		/**
317		* Removes the first occurrence of the specified element in this
318	<	* deque (when traversing the deque from head to tail).  If the deque
319	<	* does not contain the element, it is unchanged.
318	>	* deque (when traversing the deque from head to tail).
319	>	* If the deque does not contain the element, it is unchanged.
320	>	* More formally, removes the first element <tt>e</tt> such that
321	>	* <tt>o.equals(e)</tt> (if such an element exists).
322	>	* Returns <tt>true</tt> if this deque contained the specified element
323	>	* (or equivalently, if this deque changed as a result of the call).
324		*
325	<	* @param e element to be removed from this deque, if present
325	>	* @param o element to be removed from this deque, if present
326		* @return <tt>true</tt> if the deque contained the specified element
327		*/
328	<	public boolean removeFirstOccurrence(Object e) {
329	<	if (e == null)
328	>	public boolean removeFirstOccurrence(Object o) {
329	>	if (o == null)
330		return false;
331		int mask = elements.length - 1;
332		int i = head;
333	<	E x;
333	>	Object x;
334		while ( (x = elements[i]) != null) {
335	<	if (e.equals(x)) {
335	>	if (o.equals(x)) {
336		delete(i);
337		return true;
338		}
#	Line 379 | Line 343 | public class ArrayDeque<E> extends Abstr
343
344		/**
345		* Removes the last occurrence of the specified element in this
346	<	* deque (when traversing the deque from head to tail).  If the deque
347	<	* does not contain the element, it is unchanged.
346	>	* deque (when traversing the deque from head to tail).
347	>	* If the deque does not contain the element, it is unchanged.
348	>	* More formally, removes the last element <tt>e</tt> such that
349	>	* <tt>o.equals(e)</tt> (if such an element exists).
350	>	* Returns <tt>true</tt> if this deque contained the specified element
351	>	* (or equivalently, if this deque changed as a result of the call).
352		*
353	<	* @param e element to be removed from this deque, if present
353	>	* @param o element to be removed from this deque, if present
354		* @return <tt>true</tt> if the deque contained the specified element
355		*/
356	<	public boolean removeLastOccurrence(Object e) {
357	<	if (e == null)
356	>	public boolean removeLastOccurrence(Object o) {
357	>	if (o == null)
358		return false;
359		int mask = elements.length - 1;
360		int i = (tail - 1) & mask;
361	<	E x;
361	>	Object x;
362		while ( (x = elements[i]) != null) {
363	<	if (e.equals(x)) {
363	>	if (o.equals(x)) {
364		delete(i);
365		return true;
366		}
#	Line 404 | Line 372 | public class ArrayDeque<E> extends Abstr
372		// *** Queue methods ***
373
374		/**
375	<	* 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.
375	>	* Inserts the specified element at the end of this deque.
376		*
377		* <p>This method is equivalent to {@link #addLast}.
378		*
379	<	* @param e the element to insert
380	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
381	<	* @throws NullPointerException if <tt>e</tt> is null
379	>	* @param e the element to add
380	>	* @return <tt>true</tt> (as specified by {@link Collection#add})
381	>	* @throws NullPointerException if the specified element is null
382		*/
383		public boolean add(E e) {
384		addLast(e);
#	Line 431 | Line 386 | public class ArrayDeque<E> extends Abstr
386		}
387
388		/**
389	<	* 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.
389	>	* Inserts the specified element at the end of this deque.
390		*
391	<	* <p>This method is equivalent to {@link #pollFirst}.
391	>	* <p>This method is equivalent to {@link #offerLast}.
392		*
393	<	* @return the first element of this deque, or <tt>null</tt> if
394	<	*     this deque is empty
393	>	* @param e the element to add
394	>	* @return <tt>true</tt> (as specified by {@link Queue#offer})
395	>	* @throws NullPointerException if the specified element is null
396		*/
397	<	public E poll() {
398	<	return pollFirst();
397	>	public boolean offer(E e) {
398	>	return offerLast(e);
399		}
400
401		/**
402		* Retrieves and removes the head of the queue represented by this deque.
403	<	* This method differs from the <tt>poll</tt> method in that it throws an
403	>	*
404	>	* This method differs from {@link #poll poll} only in that it throws an
405		* exception if this deque is empty.
406		*
407		* <p>This method is equivalent to {@link #removeFirst}.
408		*
409		* @return the head of the queue represented by this deque
410	<	* @throws NoSuchElementException if this deque is empty
410	>	* @throws NoSuchElementException {@inheritDoc}
411		*/
412		public E remove() {
413		return removeFirst();
414		}
415
416		/**
417	<	* Retrieves, but does not remove, the head of the queue represented by
418	<	* this deque, returning <tt>null</tt> if this deque is empty.
417	>	* Retrieves and removes the head of the queue represented by this deque
418	>	* (in other words, the first element of this deque), or returns
419	>	* <tt>null</tt> if this deque is empty.
420		*
421	<	* <p>This method is equivalent to {@link #peekFirst}
421	>	* <p>This method is equivalent to {@link #pollFirst}.
422		*
423		* @return the head of the queue represented by this deque, or
424	<	*     <tt>null</tt> if this deque is empty
424	>	*         <tt>null</tt> if this deque is empty
425		*/
426	<	public E peek() {
427	<	return peekFirst();
426	>	public E poll() {
427	>	return pollFirst();
428		}
429
430		/**
431		* Retrieves, but does not remove, the head of the queue represented by
432	<	* this deque.  This method differs from the <tt>peek</tt> method only in
432	>	* this deque.  This method differs from {@link #peek peek} only in
433		* that it throws an exception if this deque is empty.
434		*
435	<	* <p>This method is equivalent to {@link #getFirst}
435	>	* <p>This method is equivalent to {@link #getFirst}.
436		*
437		* @return the head of the queue represented by this deque
438	<	* @throws NoSuchElementException if this deque is empty
438	>	* @throws NoSuchElementException {@inheritDoc}
439		*/
440		public E element() {
441		return getFirst();
442		}
443
444	+	/**
445	+	* Retrieves, but does not remove, the head of the queue represented by
446	+	* this deque, or returns <tt>null</tt> if this deque is empty.
447	+	*
448	+	* <p>This method is equivalent to {@link #peekFirst}.
449	+	*
450	+	* @return the head of the queue represented by this deque, or
451	+	*         <tt>null</tt> if this deque is empty
452	+	*/
453	+	public E peek() {
454	+	return peekFirst();
455	+	}
456	+
457		// *** Stack methods ***
458
459		/**
460		* Pushes an element onto the stack represented by this deque.  In other
461	<	* words, inserts the element to the front this deque.
461	>	* words, inserts the element at the front of this deque.
462		*
463		* <p>This method is equivalent to {@link #addFirst}.
464		*
465		* @param e the element to push
466	<	* @throws NullPointerException if <tt>e</tt> is null
466	>	* @throws NullPointerException if the specified element is null
467		*/
468		public void push(E e) {
469		addFirst(e);
#	Line 508 | Line 476 | public class ArrayDeque<E> extends Abstr
476		* <p>This method is equivalent to {@link #removeFirst()}.
477		*
478		* @return the element at the front of this deque (which is the top
479	<	*     of the stack represented by this deque)
480	<	* @throws NoSuchElementException if this deque is empty
479	>	*         of the stack represented by this deque)
480	>	* @throws NoSuchElementException {@inheritDoc}
481		*/
482		public E pop() {
483		return removeFirst();
484		}
485
486	+	private void checkInvariants() {
487	+	assert elements[tail] == null;
488	+	assert head == tail ? elements[head] == null :
489	+	(elements[head] != null &&
490	+	elements[(tail - 1) & (elements.length - 1)] != null);
491	+	assert elements[(head - 1) & (elements.length - 1)] == null;
492	+	}
493	+
494		/**
495	<	* Remove the element at the specified position in the elements array,
496	<	* adjusting head, tail, and size as necessary.  This can result in
497	<	* motion of elements backwards or forwards in the array.
498	<	*
499	<	* <p>This method is called delete rather than remove to emphasize
500	<	* that its semantics differ from those of List.remove(int).
501	<	*
495	>	* Removes the element at the specified position in the elements array,
496	>	* adjusting head and tail as necessary.  This can result in motion of
497	>	* elements backwards or forwards in the array.
498	>	*
499	>	* <p>This method is called delete rather than remove to emphasize
500	>	* that its semantics differ from those of {@link List#remove(int)}.
501	>	*
502		* @return true if elements moved backwards
503		*/
504		private boolean delete(int i) {
505	<	// Case 1: Deque doesn't wrap
506	<	// Case 2: Deque does wrap and removed element is in the head portion
507	<	if ((head < tail || tail == 0) || i >= head) {
508	<	System.arraycopy(elements, head, elements, head + 1, i - head);
509	<	elements[head] = null;
510	<	head = (head + 1) & (elements.length - 1);
505	>	checkInvariants();
506	>	final Object[] elements = this.elements;
507	>	final int mask = elements.length - 1;
508	>	final int h = head;
509	>	final int t = tail;
510	>	final int front = (i - h) & mask;
511	>	final int back  = (t - i) & mask;
512	>
513	>	// Invariant: head <= i < tail mod circularity
514	>	if (front >= ((t - h) & mask))
515	>	throw new ConcurrentModificationException();
516	>
517	>	// Optimize for least element motion
518	>	if (front < back) {
519	>	if (h <= i) {
520	>	System.arraycopy(elements, h, elements, h + 1, front);
521	>	} else { // Wrap around
522	>	System.arraycopy(elements, 0, elements, 1, i);
523	>	elements[0] = elements[mask];
524	>	System.arraycopy(elements, h, elements, h + 1, mask - h);
525	>	}
526	>	elements[h] = null;
527	>	head = (h + 1) & mask;
528		return false;
529	+	} else {
530	+	if (i < t) { // Copy the null tail as well
531	+	System.arraycopy(elements, i + 1, elements, i, back);
532	+	tail = t - 1;
533	+	} else { // Wrap around
534	+	System.arraycopy(elements, i + 1, elements, i, mask - i);
535	+	elements[mask] = elements[0];
536	+	System.arraycopy(elements, 1, elements, 0, t);
537	+	tail = (t - 1) & mask;
538	+	}
539	+	return true;
540		}
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;
541		}
542
543		// *** Collection Methods ***
#	Line 554 | Line 552 | public class ArrayDeque<E> extends Abstr
552		}
553
554		/**
555	<	* Returns <tt>true</tt> if this collection contains no elements.<p>
555	>	* Returns <tt>true</tt> if this deque contains no elements.
556		*
557	<	* @return <tt>true</tt> if this collection contains no elements.
557	>	* @return <tt>true</tt> if this deque contains no elements
558		*/
559		public boolean isEmpty() {
560		return head == tail;
#	Line 567 | Line 565 | public class ArrayDeque<E> extends Abstr
565		* will be ordered from first (head) to last (tail).  This is the same
566		* order that elements would be dequeued (via successive calls to
567		* {@link #remove} or popped (via successive calls to {@link #pop}).
568	<	*
569	<	* @return an <tt>Iterator</tt> over the elements in this deque
568	>	*
569	>	* @return an iterator over the elements in this deque
570		*/
571		public Iterator<E> iterator() {
572		return new DeqIterator();
573		}
574
575	+	public Iterator<E> descendingIterator() {
576	+	return new DescendingIterator();
577	+	}
578	+
579		private class DeqIterator implements Iterator<E> {
580		/**
581		* Index of element to be returned by subsequent call to next.
#	Line 597 | Line 599 | public class ArrayDeque<E> extends Abstr
599		}
600
601		public E next() {
600	–	E result;
602		if (cursor == fence)
603		throw new NoSuchElementException();
604	+	@SuppressWarnings("unchecked") E result = (E) elements[cursor];
605		// This check doesn't catch all possible comodifications,
606		// but does catch the ones that corrupt traversal
607	<	if (tail != fence || (result = elements[cursor]) == null)
607	>	if (tail != fence || result == null)
608		throw new ConcurrentModificationException();
609		lastRet = cursor;
610		cursor = (cursor + 1) & (elements.length - 1);
#	Line 612 | Line 614 | public class ArrayDeque<E> extends Abstr
614		public void remove() {
615		if (lastRet < 0)
616		throw new IllegalStateException();
617	<	if (delete(lastRet))
618	<	cursor--;
617	>	if (delete(lastRet)) { // if left-shifted, undo increment in next()
618	>	cursor = (cursor - 1) & (elements.length - 1);
619	>	fence = tail;
620	>	}
621	>	lastRet = -1;
622	>	}
623	>	}
624	>
625	>	private class DescendingIterator implements Iterator<E> {
626	>	/*
627	>	* This class is nearly a mirror-image of DeqIterator, using
628	>	* tail instead of head for initial cursor, and head instead of
629	>	* tail for fence.
630	>	*/
631	>	private int cursor = tail;
632	>	private int fence = head;
633	>	private int lastRet = -1;
634	>
635	>	public boolean hasNext() {
636	>	return cursor != fence;
637	>	}
638	>
639	>	public E next() {
640	>	if (cursor == fence)
641	>	throw new NoSuchElementException();
642	>	cursor = (cursor - 1) & (elements.length - 1);
643	>	@SuppressWarnings("unchecked") E result = (E) elements[cursor];
644	>	if (head != fence || result == null)
645	>	throw new ConcurrentModificationException();
646	>	lastRet = cursor;
647	>	return result;
648	>	}
649	>
650	>	public void remove() {
651	>	if (lastRet < 0)
652	>	throw new IllegalStateException();
653	>	if (!delete(lastRet)) {
654	>	cursor = (cursor + 1) & (elements.length - 1);
655	>	fence = head;
656	>	}
657		lastRet = -1;
618	–	fence = tail;
658		}
659		}
660
661		/**
662	<	* Returns <tt>true</tt> if this deque contains the specified
663	<	* element.  More formally, returns <tt>true</tt> if and only if this
664	<	* deque contains at least one element <tt>e</tt> such that
626	<	* <tt>e.equals(o)</tt>.
662	>	* Returns <tt>true</tt> if this deque contains the specified element.
663	>	* More formally, returns <tt>true</tt> if and only if this deque contains
664	>	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
665		*
666		* @param o object to be checked for containment in this deque
667		* @return <tt>true</tt> if this deque contains the specified element
#	Line 633 | Line 671 | public class ArrayDeque<E> extends Abstr
671		return false;
672		int mask = elements.length - 1;
673		int i = head;
674	<	E x;
674	>	Object x;
675		while ( (x = elements[i]) != null) {
676		if (o.equals(x))
677		return true;
#	Line 644 | Line 682 | public class ArrayDeque<E> extends Abstr
682
683		/**
684		* Removes a single instance of the specified element from this deque.
685	<	* This method is equivalent to {@link #removeFirstOccurrence}.
685	>	* If the deque does not contain the element, it is unchanged.
686	>	* More formally, removes the first element <tt>e</tt> such that
687	>	* <tt>o.equals(e)</tt> (if such an element exists).
688	>	* Returns <tt>true</tt> if this deque contained the specified element
689	>	* (or equivalently, if this deque changed as a result of the call).
690	>	*
691	>	* <p>This method is equivalent to {@link #removeFirstOccurrence}.
692		*
693	<	* @param e element to be removed from this deque, if present
693	>	* @param o element to be removed from this deque, if present
694		* @return <tt>true</tt> if this deque contained the specified element
695		*/
696	<	public boolean remove(Object e) {
697	<	return removeFirstOccurrence(e);
696	>	public boolean remove(Object o) {
697	>	return removeFirstOccurrence(o);
698		}
699
700		/**
701		* Removes all of the elements from this deque.
702	+	* The deque will be empty after this call returns.
703		*/
704		public void clear() {
705		int h = head;
#	Line 666 | Line 711 | public class ArrayDeque<E> extends Abstr
711		do {
712		elements[i] = null;
713		i = (i + 1) & mask;
714	<	} while(i != t);
714	>	} while (i != t);
715		}
716		}
717
718		/**
719	<	* Returns an array containing all of the elements in this list
720	<	* in the correct order.
719	>	* Returns an array containing all of the elements in this deque
720	>	* in proper sequence (from first to last element).
721	>	*
722	>	* <p>The returned array will be "safe" in that no references to it are
723	>	* maintained by this deque.  (In other words, this method must allocate
724	>	* a new array).  The caller is thus free to modify the returned array.
725	>	*
726	>	* <p>This method acts as bridge between array-based and collection-based
727	>	* APIs.
728		*
729	<	* @return an array containing all of the elements in this list
678	<	*         in the correct order
729	>	* @return an array containing all of the elements in this deque
730		*/
731		public Object[] toArray() {
732	<	return copyElements(new Object[size()]);
732	>	return copyElements(new Object[size()]);
733		}
734
735		/**
736	<	* Returns an array containing all of the elements in this deque in the
737	<	* correct order; the runtime type of the returned array is that of the
738	<	* specified array.  If the deque fits in the specified array, it is
739	<	* returned therein.  Otherwise, a new array is allocated with the runtime
740	<	* type of the specified array and the size of this deque.
736	>	* Returns an array containing all of the elements in this deque in
737	>	* proper sequence (from first to last element); the runtime type of the
738	>	* returned array is that of the specified array.  If the deque fits in
739	>	* the specified array, it is returned therein.  Otherwise, a new array
740	>	* is allocated with the runtime type of the specified array and the
741	>	* size of this deque.
742		*
743	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
744	<	* the array has more elements than the deque), the element in the array
745	<	* immediately following the end of the collection is set to <tt>null</tt>.
743	>	* <p>If this deque fits in the specified array with room to spare
744	>	* (i.e., the array has more elements than this deque), the element in
745	>	* the array immediately following the end of the deque is set to
746	>	* <tt>null</tt>.
747	>	*
748	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
749	>	* array-based and collection-based APIs.  Further, this method allows
750	>	* precise control over the runtime type of the output array, and may,
751	>	* under certain circumstances, be used to save allocation costs.
752	>	*
753	>	* <p>Suppose <tt>x</tt> is a deque known to contain only strings.
754	>	* The following code can be used to dump the deque into a newly
755	>	* allocated array of <tt>String</tt>:
756	>	*
757	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
758	>	*
759	>	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
760	>	* <tt>toArray()</tt>.
761		*
762		* @param a the array into which the elements of the deque are to
763	<	*          be stored, if it is big enough; otherwise, a new array of the
764	<	*          same runtime type is allocated for this purpose
765	<	* @return an array containing the elements of the deque
766	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
767	<	*         of the runtime type of every element in this deque
763	>	*          be stored, if it is big enough; otherwise, a new array of the
764	>	*          same runtime type is allocated for this purpose
765	>	* @return an array containing all of the elements in this deque
766	>	* @throws ArrayStoreException if the runtime type of the specified array
767	>	*         is not a supertype of the runtime type of every element in
768	>	*         this deque
769	>	* @throws NullPointerException if the specified array is null
770		*/
771	+	@SuppressWarnings("unchecked")
772		public <T> T[] toArray(T[] a) {
773		int size = size();
774		if (a.length < size)
775		a = (T[])java.lang.reflect.Array.newInstance(
776		a.getClass().getComponentType(), size);
777	<	copyElements(a);
777	>	copyElements(a);
778		if (a.length > size)
779		a[size] = null;
780		return a;
#	Line 718 | Line 788 | public class ArrayDeque<E> extends Abstr
788		* @return a copy of this deque
789		*/
790		public ArrayDeque<E> clone() {
791	<	try {
791	>	try {
792	>	@SuppressWarnings("unchecked")
793		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
794	<	// 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);
794	>	result.elements = Arrays.copyOf(elements, elements.length);
795		return result;
796
797	<	} catch (CloneNotSupportedException e) {
797	>	} catch (CloneNotSupportedException e) {
798		throw new AssertionError();
799		}
800		}
#	Line 742 | Line 811 | public class ArrayDeque<E> extends Abstr
811		* followed by all of its elements (each an object reference) in
812		* first-to-last order.
813		*/
814	<	private void writeObject(ObjectOutputStream s) throws IOException {
814	>	private void writeObject(java.io.ObjectOutputStream s)
815	>	throws java.io.IOException {
816		s.defaultWriteObject();
817
818		// Write out size
819	<	int size = size();
750	<	s.writeInt(size);
819	>	s.writeInt(size());
820
821		// Write out elements in order.
753	–	int i = head;
822		int mask = elements.length - 1;
823	<	for (int j = 0; j < size; j++) {
823	>	for (int i = head; i != tail; i = (i + 1) & mask)
824		s.writeObject(elements[i]);
757	–	i = (i + 1) & mask;
758	–	}
825		}
826
827		/**
828		* Deserialize this deque.
829		*/
830	<	private void readObject(ObjectInputStream s)
831	<	throws IOException, ClassNotFoundException {
830	>	private void readObject(java.io.ObjectInputStream s)
831	>	throws java.io.IOException, ClassNotFoundException {
832		s.defaultReadObject();
833
834		// Read in size and allocate array
#	Line 773 | Line 839 | public class ArrayDeque<E> extends Abstr
839
840		// Read in all elements in the proper order.
841		for (int i = 0; i < size; i++)
842	<	elements[i] = (E)s.readObject();
777	<
842	>	elements[i] = s.readObject();
843		}
844		}

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