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

Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.2 by dl, Tue Mar 8 12:27:06 2005 UTC vs.
Revision 1.35 by jsr166, Fri Dec 2 15:47:22 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	>	@SuppressWarnings("unchecked")
305	>	public E peekFirst() {
306	>	// elements[head] is null if deque empty
307	>	return (E) elements[head];
308	>	}
309	>
310	>	@SuppressWarnings("unchecked")
311	>	public E peekLast() {
312	>	return (E) elements[(tail - 1) & (elements.length - 1)];
313		}
314
315		/**
316		* Removes the first occurrence of the specified element in this
317	<	* deque (when traversing the deque from head to tail).  If the deque
318	<	* does not contain the element, it is unchanged.
317	>	* deque (when traversing the deque from head to tail).
318	>	* If the deque does not contain the element, it is unchanged.
319	>	* More formally, removes the first element <tt>e</tt> such that
320	>	* <tt>o.equals(e)</tt> (if such an element exists).
321	>	* Returns <tt>true</tt> if this deque contained the specified element
322	>	* (or equivalently, if this deque changed as a result of the call).
323		*
324	<	* @param e element to be removed from this deque, if present
324	>	* @param o element to be removed from this deque, if present
325		* @return <tt>true</tt> if the deque contained the specified element
326		*/
327	<	public boolean removeFirstOccurrence(Object e) {
328	<	if (e == null)
327	>	public boolean removeFirstOccurrence(Object o) {
328	>	if (o == null)
329		return false;
330		int mask = elements.length - 1;
331		int i = head;
332	<	E x;
332	>	Object x;
333		while ( (x = elements[i]) != null) {
334	<	if (e.equals(x)) {
334	>	if (o.equals(x)) {
335		delete(i);
336		return true;
337		}
#	Line 379 | Line 342 | public class ArrayDeque<E> extends Abstr
342
343		/**
344		* Removes the last occurrence of the specified element in this
345	<	* deque (when traversing the deque from head to tail).  If the deque
346	<	* does not contain the element, it is unchanged.
345	>	* deque (when traversing the deque from head to tail).
346	>	* If the deque does not contain the element, it is unchanged.
347	>	* More formally, removes the last element <tt>e</tt> such that
348	>	* <tt>o.equals(e)</tt> (if such an element exists).
349	>	* Returns <tt>true</tt> if this deque contained the specified element
350	>	* (or equivalently, if this deque changed as a result of the call).
351		*
352	<	* @param e element to be removed from this deque, if present
352	>	* @param o element to be removed from this deque, if present
353		* @return <tt>true</tt> if the deque contained the specified element
354		*/
355	<	public boolean removeLastOccurrence(Object e) {
356	<	if (e == null)
355	>	public boolean removeLastOccurrence(Object o) {
356	>	if (o == null)
357		return false;
358		int mask = elements.length - 1;
359		int i = (tail - 1) & mask;
360	<	E x;
360	>	Object x;
361		while ( (x = elements[i]) != null) {
362	<	if (e.equals(x)) {
362	>	if (o.equals(x)) {
363		delete(i);
364		return true;
365		}
#	Line 404 | Line 371 | public class ArrayDeque<E> extends Abstr
371		// *** Queue methods ***
372
373		/**
374	<	* 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.
374	>	* Inserts the specified element at the end of this deque.
375		*
376		* <p>This method is equivalent to {@link #addLast}.
377		*
378	<	* @param e the element to insert
379	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
380	<	* @throws NullPointerException if <tt>e</tt> is null
378	>	* @param e the element to add
379	>	* @return <tt>true</tt> (as specified by {@link Collection#add})
380	>	* @throws NullPointerException if the specified element is null
381		*/
382		public boolean add(E e) {
383		addLast(e);
#	Line 431 | Line 385 | public class ArrayDeque<E> extends Abstr
385		}
386
387		/**
388	<	* 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.
388	>	* Inserts the specified element at the end of this deque.
389		*
390	<	* <p>This method is equivalent to {@link #pollFirst}.
390	>	* <p>This method is equivalent to {@link #offerLast}.
391		*
392	<	* @return the first element of this deque, or <tt>null</tt> if
393	<	*     this deque is empty
392	>	* @param e the element to add
393	>	* @return <tt>true</tt> (as specified by {@link Queue#offer})
394	>	* @throws NullPointerException if the specified element is null
395		*/
396	<	public E poll() {
397	<	return pollFirst();
396	>	public boolean offer(E e) {
397	>	return offerLast(e);
398		}
399
400		/**
401		* Retrieves and removes the head of the queue represented by this deque.
402	<	* This method differs from the <tt>poll</tt> method in that it throws an
402	>	*
403	>	* This method differs from {@link #poll poll} only in that it throws an
404		* exception if this deque is empty.
405		*
406		* <p>This method is equivalent to {@link #removeFirst}.
407		*
408		* @return the head of the queue represented by this deque
409	<	* @throws NoSuchElementException if this deque is empty
409	>	* @throws NoSuchElementException {@inheritDoc}
410		*/
411		public E remove() {
412		return removeFirst();
413		}
414
415		/**
416	<	* Retrieves, but does not remove, the head of the queue represented by
417	<	* this deque, returning <tt>null</tt> if this deque is empty.
416	>	* Retrieves and removes the head of the queue represented by this deque
417	>	* (in other words, the first element of this deque), or returns
418	>	* <tt>null</tt> if this deque is empty.
419		*
420	<	* <p>This method is equivalent to {@link #peekFirst}
420	>	* <p>This method is equivalent to {@link #pollFirst}.
421		*
422		* @return the head of the queue represented by this deque, or
423	<	*     <tt>null</tt> if this deque is empty
423	>	*         <tt>null</tt> if this deque is empty
424		*/
425	<	public E peek() {
426	<	return peekFirst();
425	>	public E poll() {
426	>	return pollFirst();
427		}
428
429		/**
430		* Retrieves, but does not remove, the head of the queue represented by
431	<	* this deque.  This method differs from the <tt>peek</tt> method only in
431	>	* this deque.  This method differs from {@link #peek peek} only in
432		* that it throws an exception if this deque is empty.
433		*
434	<	* <p>This method is equivalent to {@link #getFirst}
434	>	* <p>This method is equivalent to {@link #getFirst}.
435		*
436		* @return the head of the queue represented by this deque
437	<	* @throws NoSuchElementException if this deque is empty
437	>	* @throws NoSuchElementException {@inheritDoc}
438		*/
439		public E element() {
440		return getFirst();
441		}
442
443	+	/**
444	+	* Retrieves, but does not remove, the head of the queue represented by
445	+	* this deque, or returns <tt>null</tt> if this deque is empty.
446	+	*
447	+	* <p>This method is equivalent to {@link #peekFirst}.
448	+	*
449	+	* @return the head of the queue represented by this deque, or
450	+	*         <tt>null</tt> if this deque is empty
451	+	*/
452	+	public E peek() {
453	+	return peekFirst();
454	+	}
455	+
456		// *** Stack methods ***
457
458		/**
459		* Pushes an element onto the stack represented by this deque.  In other
460	<	* words, inserts the element to the front this deque.
460	>	* words, inserts the element at the front of this deque.
461		*
462		* <p>This method is equivalent to {@link #addFirst}.
463		*
464		* @param e the element to push
465	<	* @throws NullPointerException if <tt>e</tt> is null
465	>	* @throws NullPointerException if the specified element is null
466		*/
467		public void push(E e) {
468		addFirst(e);
#	Line 508 | Line 475 | public class ArrayDeque<E> extends Abstr
475		* <p>This method is equivalent to {@link #removeFirst()}.
476		*
477		* @return the element at the front of this deque (which is the top
478	<	*     of the stack represented by this deque)
479	<	* @throws NoSuchElementException if this deque is empty
478	>	*         of the stack represented by this deque)
479	>	* @throws NoSuchElementException {@inheritDoc}
480		*/
481		public E pop() {
482		return removeFirst();
483		}
484
485	+	private void checkInvariants() {
486	+	assert elements[tail] == null;
487	+	assert head == tail ? elements[head] == null :
488	+	(elements[head] != null &&
489	+	elements[(tail - 1) & (elements.length - 1)] != null);
490	+	assert elements[(head - 1) & (elements.length - 1)] == null;
491	+	}
492	+
493		/**
494	<	* Remove the element at the specified position in the elements array,
495	<	* adjusting head, tail, and size as necessary.  This can result in
496	<	* motion of elements backwards or forwards in the array.
497	<	*
498	<	* <p>This method is called delete rather than remove to emphasize the
499	<	* that its semantics differ from those of List.remove(int).
500	<	*
494	>	* Removes the element at the specified position in the elements array,
495	>	* adjusting head and tail as necessary.  This can result in motion of
496	>	* elements backwards or forwards in the array.
497	>	*
498	>	* <p>This method is called delete rather than remove to emphasize
499	>	* that its semantics differ from those of {@link List#remove(int)}.
500	>	*
501		* @return true if elements moved backwards
502		*/
503		private boolean delete(int i) {
504	<	// Case 1: Deque doesn't wrap
505	<	// Case 2: Deque does wrap and removed element is in the head portion
506	<	if ((head < tail || tail == 0) || i >= head) {
507	<	System.arraycopy(elements, head, elements, head + 1, i - head);
508	<	elements[head] = null;
509	<	head = (head + 1) & (elements.length - 1);
504	>	checkInvariants();
505	>	final Object[] elements = this.elements;
506	>	final int mask = elements.length - 1;
507	>	final int h = head;
508	>	final int t = tail;
509	>	final int front = (i - h) & mask;
510	>	final int back  = (t - i) & mask;
511	>
512	>	// Invariant: head <= i < tail mod circularity
513	>	if (front >= ((t - h) & mask))
514	>	throw new ConcurrentModificationException();
515	>
516	>	// Optimize for least element motion
517	>	if (front < back) {
518	>	if (h <= i) {
519	>	System.arraycopy(elements, h, elements, h + 1, front);
520	>	} else { // Wrap around
521	>	System.arraycopy(elements, 0, elements, 1, i);
522	>	elements[0] = elements[mask];
523	>	System.arraycopy(elements, h, elements, h + 1, mask - h);
524	>	}
525	>	elements[h] = null;
526	>	head = (h + 1) & mask;
527		return false;
528	+	} else {
529	+	if (i < t) { // Copy the null tail as well
530	+	System.arraycopy(elements, i + 1, elements, i, back);
531	+	tail = t - 1;
532	+	} else { // Wrap around
533	+	System.arraycopy(elements, i + 1, elements, i, mask - i);
534	+	elements[mask] = elements[0];
535	+	System.arraycopy(elements, 1, elements, 0, t);
536	+	tail = (t - 1) & mask;
537	+	}
538	+	return true;
539		}
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;
540		}
541
542		// *** Collection Methods ***
#	Line 554 | Line 551 | public class ArrayDeque<E> extends Abstr
551		}
552
553		/**
554	<	* Returns <tt>true</tt> if this collection contains no elements.<p>
554	>	* Returns <tt>true</tt> if this deque contains no elements.
555		*
556	<	* @return <tt>true</tt> if this collection contains no elements.
556	>	* @return <tt>true</tt> if this deque contains no elements
557		*/
558		public boolean isEmpty() {
559		return head == tail;
#	Line 567 | Line 564 | public class ArrayDeque<E> extends Abstr
564		* will be ordered from first (head) to last (tail).  This is the same
565		* order that elements would be dequeued (via successive calls to
566		* {@link #remove} or popped (via successive calls to {@link #pop}).
567	<	*
568	<	* @return an <tt>Iterator</tt> over the elements in this deque
567	>	*
568	>	* @return an iterator over the elements in this deque
569		*/
570		public Iterator<E> iterator() {
571		return new DeqIterator();
572		}
573
574	+	public Iterator<E> descendingIterator() {
575	+	return new DescendingIterator();
576	+	}
577	+
578		private class DeqIterator implements Iterator<E> {
579		/**
580		* Index of element to be returned by subsequent call to next.
#	Line 597 | Line 598 | public class ArrayDeque<E> extends Abstr
598		}
599
600		public E next() {
600	–	E result;
601		if (cursor == fence)
602		throw new NoSuchElementException();
603	+	@SuppressWarnings("unchecked") E result = (E) elements[cursor];
604		// This check doesn't catch all possible comodifications,
605		// but does catch the ones that corrupt traversal
606	<	if (tail != fence || (result = elements[cursor]) == null)
606	>	if (tail != fence || result == null)
607		throw new ConcurrentModificationException();
608		lastRet = cursor;
609		cursor = (cursor + 1) & (elements.length - 1);
#	Line 612 | Line 613 | public class ArrayDeque<E> extends Abstr
613		public void remove() {
614		if (lastRet < 0)
615		throw new IllegalStateException();
616	<	if (delete(lastRet))
617	<	cursor--;
616	>	if (delete(lastRet)) { // if left-shifted, undo increment in next()
617	>	cursor = (cursor - 1) & (elements.length - 1);
618	>	fence = tail;
619	>	}
620	>	lastRet = -1;
621	>	}
622	>	}
623	>
624	>	private class DescendingIterator implements Iterator<E> {
625	>	/*
626	>	* This class is nearly a mirror-image of DeqIterator, using
627	>	* tail instead of head for initial cursor, and head instead of
628	>	* tail for fence.
629	>	*/
630	>	private int cursor = tail;
631	>	private int fence = head;
632	>	private int lastRet = -1;
633	>
634	>	public boolean hasNext() {
635	>	return cursor != fence;
636	>	}
637	>
638	>	public E next() {
639	>	if (cursor == fence)
640	>	throw new NoSuchElementException();
641	>	cursor = (cursor - 1) & (elements.length - 1);
642	>	@SuppressWarnings("unchecked") E result = (E) elements[cursor];
643	>	if (head != fence || result == null)
644	>	throw new ConcurrentModificationException();
645	>	lastRet = cursor;
646	>	return result;
647	>	}
648	>
649	>	public void remove() {
650	>	if (lastRet < 0)
651	>	throw new IllegalStateException();
652	>	if (!delete(lastRet)) {
653	>	cursor = (cursor + 1) & (elements.length - 1);
654	>	fence = head;
655	>	}
656		lastRet = -1;
618	–	fence = tail;
657		}
658		}
659
660		/**
661	<	* Returns <tt>true</tt> if this deque contains the specified
662	<	* element.  More formally, returns <tt>true</tt> if and only if this
663	<	* deque contains at least one element <tt>e</tt> such that
626	<	* <tt>e.equals(o)</tt>.
661	>	* Returns <tt>true</tt> if this deque contains the specified element.
662	>	* More formally, returns <tt>true</tt> if and only if this deque contains
663	>	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
664		*
665		* @param o object to be checked for containment in this deque
666		* @return <tt>true</tt> if this deque contains the specified element
#	Line 633 | Line 670 | public class ArrayDeque<E> extends Abstr
670		return false;
671		int mask = elements.length - 1;
672		int i = head;
673	<	E x;
673	>	Object x;
674		while ( (x = elements[i]) != null) {
675		if (o.equals(x))
676		return true;
#	Line 644 | Line 681 | public class ArrayDeque<E> extends Abstr
681
682		/**
683		* Removes a single instance of the specified element from this deque.
684	<	* This method is equivalent to {@link #removeFirstOccurrence}.
684	>	* If the deque does not contain the element, it is unchanged.
685	>	* More formally, removes the first element <tt>e</tt> such that
686	>	* <tt>o.equals(e)</tt> (if such an element exists).
687	>	* Returns <tt>true</tt> if this deque contained the specified element
688	>	* (or equivalently, if this deque changed as a result of the call).
689	>	*
690	>	* <p>This method is equivalent to {@link #removeFirstOccurrence}.
691		*
692	<	* @param e element to be removed from this deque, if present
692	>	* @param o element to be removed from this deque, if present
693		* @return <tt>true</tt> if this deque contained the specified element
694		*/
695	<	public boolean remove(Object e) {
696	<	return removeFirstOccurrence(e);
695	>	public boolean remove(Object o) {
696	>	return removeFirstOccurrence(o);
697		}
698
699		/**
700		* Removes all of the elements from this deque.
701	+	* The deque will be empty after this call returns.
702		*/
703		public void clear() {
704		int h = head;
#	Line 666 | Line 710 | public class ArrayDeque<E> extends Abstr
710		do {
711		elements[i] = null;
712		i = (i + 1) & mask;
713	<	} while(i != t);
713	>	} while (i != t);
714		}
715		}
716
717		/**
718	<	* Returns an array containing all of the elements in this list
719	<	* in the correct order.
718	>	* Returns an array containing all of the elements in this deque
719	>	* in proper sequence (from first to last element).
720	>	*
721	>	* <p>The returned array will be "safe" in that no references to it are
722	>	* maintained by this deque.  (In other words, this method must allocate
723	>	* a new array).  The caller is thus free to modify the returned array.
724	>	*
725	>	* <p>This method acts as bridge between array-based and collection-based
726	>	* APIs.
727		*
728	<	* @return an array containing all of the elements in this list
678	<	*         in the correct order
728	>	* @return an array containing all of the elements in this deque
729		*/
730		public Object[] toArray() {
731	<	return copyElements(new Object[size()]);
731	>	return copyElements(new Object[size()]);
732		}
733
734		/**
735	<	* Returns an array containing all of the elements in this deque in the
736	<	* correct order; the runtime type of the returned array is that of the
737	<	* specified array.  If the deque fits in the specified array, it is
738	<	* returned therein.  Otherwise, a new array is allocated with the runtime
739	<	* type of the specified array and the size of this deque.
735	>	* Returns an array containing all of the elements in this deque in
736	>	* proper sequence (from first to last element); the runtime type of the
737	>	* returned array is that of the specified array.  If the deque fits in
738	>	* the specified array, it is returned therein.  Otherwise, a new array
739	>	* is allocated with the runtime type of the specified array and the
740	>	* size of this deque.
741		*
742	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
743	<	* the array has more elements than the deque), the element in the array
744	<	* immediately following the end of the collection is set to <tt>null</tt>.
742	>	* <p>If this deque fits in the specified array with room to spare
743	>	* (i.e., the array has more elements than this deque), the element in
744	>	* the array immediately following the end of the deque is set to
745	>	* <tt>null</tt>.
746	>	*
747	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
748	>	* array-based and collection-based APIs.  Further, this method allows
749	>	* precise control over the runtime type of the output array, and may,
750	>	* under certain circumstances, be used to save allocation costs.
751	>	*
752	>	* <p>Suppose <tt>x</tt> is a deque known to contain only strings.
753	>	* The following code can be used to dump the deque into a newly
754	>	* allocated array of <tt>String</tt>:
755	>	*
756	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
757	>	*
758	>	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
759	>	* <tt>toArray()</tt>.
760		*
761		* @param a the array into which the elements of the deque are to
762	<	*          be stored, if it is big enough; otherwise, a new array of the
763	<	*          same runtime type is allocated for this purpose
764	<	* @return an array containing the elements of the deque
765	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
766	<	*         of the runtime type of every element in this deque
762	>	*          be stored, if it is big enough; otherwise, a new array of the
763	>	*          same runtime type is allocated for this purpose
764	>	* @return an array containing all of the elements in this deque
765	>	* @throws ArrayStoreException if the runtime type of the specified array
766	>	*         is not a supertype of the runtime type of every element in
767	>	*         this deque
768	>	* @throws NullPointerException if the specified array is null
769		*/
770	+	@SuppressWarnings("unchecked")
771		public <T> T[] toArray(T[] a) {
772		int size = size();
773		if (a.length < size)
774		a = (T[])java.lang.reflect.Array.newInstance(
775		a.getClass().getComponentType(), size);
776	<	copyElements(a);
776	>	copyElements(a);
777		if (a.length > size)
778		a[size] = null;
779		return a;
#	Line 718 | Line 787 | public class ArrayDeque<E> extends Abstr
787		* @return a copy of this deque
788		*/
789		public ArrayDeque<E> clone() {
790	<	try {
790	>	try {
791	>	@SuppressWarnings("unchecked")
792		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
793	<	// 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);
793	>	result.elements = Arrays.copyOf(elements, elements.length);
794		return result;
795
796	<	} catch (CloneNotSupportedException e) {
796	>	} catch (CloneNotSupportedException e) {
797		throw new AssertionError();
798		}
799		}
#	Line 742 | Line 810 | public class ArrayDeque<E> extends Abstr
810		* followed by all of its elements (each an object reference) in
811		* first-to-last order.
812		*/
813	<	private void writeObject(ObjectOutputStream s) throws IOException {
813	>	private void writeObject(java.io.ObjectOutputStream s)
814	>	throws java.io.IOException {
815		s.defaultWriteObject();
816
817		// Write out size
818	<	int size = size();
750	<	s.writeInt(size);
818	>	s.writeInt(size());
819
820		// Write out elements in order.
753	–	int i = head;
821		int mask = elements.length - 1;
822	<	for (int j = 0; j < size; j++) {
822	>	for (int i = head; i != tail; i = (i + 1) & mask)
823		s.writeObject(elements[i]);
757	–	i = (i + 1) & mask;
758	–	}
824		}
825
826		/**
827		* Deserialize this deque.
828		*/
829	<	private void readObject(ObjectInputStream s)
830	<	throws IOException, ClassNotFoundException {
829	>	private void readObject(java.io.ObjectInputStream s)
830	>	throws java.io.IOException, ClassNotFoundException {
831		s.defaultReadObject();
832
833		// Read in size and allocate array
#	Line 773 | Line 838 | public class ArrayDeque<E> extends Abstr
838
839		// Read in all elements in the proper order.
840		for (int i = 0; i < size; i++)
841	<	elements[i] = (E)s.readObject();
777	<
841	>	elements[i] = s.readObject();
842		}
843		}

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