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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 1.40 by jsr166, Sun Feb 26 22:43:03 2012 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 15 | Line 14 | import java.io.*;
14		* {@link Stack} when used as a stack, and faster than {@link LinkedList}
15		* when used as a queue.
16		*
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
21	<	* iterator.remove()}, and the bulk operations, all of which run in linear
22	<	* time.
17	>	* <p>Most {@code ArrayDeque} operations run in amortized constant time.
18	>	* Exceptions include
19	>	* {@link #remove(Object) remove},
20	>	* {@link #removeFirstOccurrence removeFirstOccurrence},
21	>	* {@link #removeLastOccurrence removeLastOccurrence},
22	>	* {@link #contains contains},
23	>	* {@link #iterator iterator.remove()},
24	>	* and the bulk operations, all of which run in linear 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.
26	>	* <p>The iterators returned by this class's {@link #iterator() iterator}
27	>	* method are <em>fail-fast</em>: If the deque is modified at any time after
28	>	* the iterator is created, in any way except through the iterator's own
29	>	* {@code remove} 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 {@code ConcurrentModificationException} 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}/../technotes/guides/collections/index.html">
49	>	* Java Collections Framework</a>.
50		*
51		* @author  Josh Bloch and Doug Lea
52		* @since   1.6
53		* @param <E> the type of elements held in this collection
54		*/
55		public class ArrayDeque<E> extends AbstractCollection<E>
56	<	implements Deque<E>, Cloneable, Serializable
56	>	implements Deque<E>, Cloneable, java.io.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 61 | Line 65 | public class ArrayDeque<E> extends Abstr
65		* other.  We also guarantee that all array cells not holding
66		* deque elements are always null.
67		*/
68	<	private transient E[] elements;
68	>	private transient Object[] elements;
69
70		/**
71		* The index of the element at the head of the deque (which is the
#	Line 85 | Line 89 | public class ArrayDeque<E> extends Abstr
89		// ******  Array allocation and resizing utilities ******
90
91		/**
92	<	* Allocate empty array to hold the given number of elements.
92	>	* Allocates 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 105 | Line 109 | public class ArrayDeque<E> extends Abstr
109		if (initialCapacity < 0)   // Too many elements, must back off
110		initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
111		}
112	<	elements = (E[]) new Object[initialCapacity];
112	>	elements = new Object[initialCapacity];
113		}
114
115		/**
116	<	* Double the capacity of this deque.  Call only when full, i.e.,
116	>	* Doubles the capacity of this deque.  Call only when full, i.e.,
117		* when head and tail have wrapped around to become equal.
118		*/
119		private void doubleCapacity() {
120	<	assert head == tail;
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 123 | Line 127 | public class ArrayDeque<E> extends Abstr
127		Object[] a = new Object[newCapacity];
128		System.arraycopy(elements, p, a, 0, r);
129		System.arraycopy(elements, 0, a, r, p);
130	<	elements = (E[])a;
130	>	elements = a;
131		head = 0;
132		tail = n;
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() {
158	<	elements = (E[]) new Object[16];
158	>	elements = new Object[16];
159		}
160
161		/**
#	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.
221	>	* Inserts the specified element at the front of this deque.
222		*
223	<	* @return the last element of this deque, or <tt>null</tt> if
224	<	*     this deque is empty
225	<	*/
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
223	>	* @param e the element to add
224	>	* @return {@code true} (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 {@code true} (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() {
272	<	return elements[head]; // elements[head] is null if deque empty
264	>	public E pollFirst() {
265	>	int h = head;
266	>	@SuppressWarnings("unchecked")
267	>	E result = (E) elements[h];
268	>	// Element is null if deque empty
269	>	if (result == null)
270	>	return null;
271	>	elements[h] = null;     // Must null out slot
272	>	head = (h + 1) & (elements.length - 1);
273	>	return result;
274		}
275
276	<	/**
277	<	* Retrieves, but does not remove, the last element of this deque,
278	<	* returning <tt>null</tt> if this deque is empty.
279	<	*
280	<	* @return the last element of this deque, or <tt>null</tt> if this deque
281	<	*     is empty
282	<	*/
283	<	public E peekLast() {
284	<	return elements[(tail - 1) & (elements.length - 1)];
276	>	public E pollLast() {
277	>	int t = (tail - 1) & (elements.length - 1);
278	>	@SuppressWarnings("unchecked")
279	>	E result = (E) elements[t];
280	>	if (result == null)
281	>	return null;
282	>	elements[t] = null;
283	>	tail = t;
284	>	return result;
285		}
286
287		/**
288	<	* 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
288	>	* @throws NoSuchElementException {@inheritDoc}
289		*/
290		public E getFirst() {
291	<	E x = elements[head];
292	<	if (x == null)
291	>	@SuppressWarnings("unchecked")
292	>	E result = (E) elements[head];
293	>	if (result == null)
294		throw new NoSuchElementException();
295	<	return x;
295	>	return result;
296		}
297
298		/**
299	<	* 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
299	>	* @throws NoSuchElementException {@inheritDoc}
300		*/
301		public E getLast() {
302	<	E x = elements[(tail - 1) & (elements.length - 1)];
303	<	if (x == null)
302	>	@SuppressWarnings("unchecked")
303	>	E result = (E) elements[(tail - 1) & (elements.length - 1)];
304	>	if (result == null)
305		throw new NoSuchElementException();
306	<	return x;
306	>	return result;
307	>	}
308	>
309	>	@SuppressWarnings("unchecked")
310	>	public E peekFirst() {
311	>	// elements[head] is null if deque empty
312	>	return (E) elements[head];
313	>	}
314	>
315	>	@SuppressWarnings("unchecked")
316	>	public E peekLast() {
317	>	return (E) elements[(tail - 1) & (elements.length - 1)];
318		}
319
320		/**
321		* Removes the first occurrence of the specified element in this
322	<	* deque (when traversing the deque from head to tail).  If the deque
323	<	* does not contain the element, it is unchanged.
322	>	* deque (when traversing the deque from head to tail).
323	>	* If the deque does not contain the element, it is unchanged.
324	>	* More formally, removes the first element {@code e} such that
325	>	* {@code o.equals(e)} (if such an element exists).
326	>	* Returns {@code true} if this deque contained the specified element
327	>	* (or equivalently, if this deque changed as a result of the call).
328		*
329	<	* @param e element to be removed from this deque, if present
330	<	* @return <tt>true</tt> if the deque contained the specified element
329	>	* @param o element to be removed from this deque, if present
330	>	* @return {@code true} if the deque contained the specified element
331		*/
332	<	public boolean removeFirstOccurrence(Object e) {
333	<	if (e == null)
332	>	public boolean removeFirstOccurrence(Object o) {
333	>	if (o == null)
334		return false;
335		int mask = elements.length - 1;
336		int i = head;
337	<	E x;
337	>	Object x;
338		while ( (x = elements[i]) != null) {
339	<	if (e.equals(x)) {
339	>	if (o.equals(x)) {
340		delete(i);
341		return true;
342		}
#	Line 379 | Line 347 | public class ArrayDeque<E> extends Abstr
347
348		/**
349		* Removes the last occurrence of the specified element in this
350	<	* deque (when traversing the deque from head to tail).  If the deque
351	<	* does not contain the element, it is unchanged.
350	>	* deque (when traversing the deque from head to tail).
351	>	* If the deque does not contain the element, it is unchanged.
352	>	* More formally, removes the last element {@code e} such that
353	>	* {@code o.equals(e)} (if such an element exists).
354	>	* Returns {@code true} if this deque contained the specified element
355	>	* (or equivalently, if this deque changed as a result of the call).
356		*
357	<	* @param e element to be removed from this deque, if present
358	<	* @return <tt>true</tt> if the deque contained the specified element
357	>	* @param o element to be removed from this deque, if present
358	>	* @return {@code true} if the deque contained the specified element
359		*/
360	<	public boolean removeLastOccurrence(Object e) {
361	<	if (e == null)
360	>	public boolean removeLastOccurrence(Object o) {
361	>	if (o == null)
362		return false;
363		int mask = elements.length - 1;
364		int i = (tail - 1) & mask;
365	<	E x;
365	>	Object x;
366		while ( (x = elements[i]) != null) {
367	<	if (e.equals(x)) {
367	>	if (o.equals(x)) {
368		delete(i);
369		return true;
370		}
#	Line 404 | Line 376 | public class ArrayDeque<E> extends Abstr
376		// *** Queue methods ***
377
378		/**
379	<	* 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.
379	>	* Inserts the specified element at the end of this deque.
380		*
381		* <p>This method is equivalent to {@link #addLast}.
382		*
383	<	* @param e the element to insert
384	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
385	<	* @throws NullPointerException if <tt>e</tt> is null
383	>	* @param e the element to add
384	>	* @return {@code true} (as specified by {@link Collection#add})
385	>	* @throws NullPointerException if the specified element is null
386		*/
387		public boolean add(E e) {
388		addLast(e);
#	Line 431 | Line 390 | public class ArrayDeque<E> extends Abstr
390		}
391
392		/**
393	<	* 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.
393	>	* Inserts the specified element at the end of this deque.
394		*
395	<	* <p>This method is equivalent to {@link #pollFirst}.
395	>	* <p>This method is equivalent to {@link #offerLast}.
396		*
397	<	* @return the first element of this deque, or <tt>null</tt> if
398	<	*     this deque is empty
397	>	* @param e the element to add
398	>	* @return {@code true} (as specified by {@link Queue#offer})
399	>	* @throws NullPointerException if the specified element is null
400		*/
401	<	public E poll() {
402	<	return pollFirst();
401	>	public boolean offer(E e) {
402	>	return offerLast(e);
403		}
404
405		/**
406		* Retrieves and removes the head of the queue represented by this deque.
407	<	* This method differs from the <tt>poll</tt> method in that it throws an
407	>	*
408	>	* This method differs from {@link #poll poll} only in that it throws an
409		* exception if this deque is empty.
410		*
411		* <p>This method is equivalent to {@link #removeFirst}.
412		*
413		* @return the head of the queue represented by this deque
414	<	* @throws NoSuchElementException if this deque is empty
414	>	* @throws NoSuchElementException {@inheritDoc}
415		*/
416		public E remove() {
417		return removeFirst();
418		}
419
420		/**
421	<	* Retrieves, but does not remove, the head of the queue represented by
422	<	* this deque, returning <tt>null</tt> if this deque is empty.
421	>	* Retrieves and removes the head of the queue represented by this deque
422	>	* (in other words, the first element of this deque), or returns
423	>	* {@code null} if this deque is empty.
424		*
425	<	* <p>This method is equivalent to {@link #peekFirst}
425	>	* <p>This method is equivalent to {@link #pollFirst}.
426		*
427		* @return the head of the queue represented by this deque, or
428	<	*     <tt>null</tt> if this deque is empty
428	>	*         {@code null} if this deque is empty
429		*/
430	<	public E peek() {
431	<	return peekFirst();
430	>	public E poll() {
431	>	return pollFirst();
432		}
433
434		/**
435		* Retrieves, but does not remove, the head of the queue represented by
436	<	* this deque.  This method differs from the <tt>peek</tt> method only in
436	>	* this deque.  This method differs from {@link #peek peek} only in
437		* that it throws an exception if this deque is empty.
438		*
439	<	* <p>This method is equivalent to {@link #getFirst}
439	>	* <p>This method is equivalent to {@link #getFirst}.
440		*
441		* @return the head of the queue represented by this deque
442	<	* @throws NoSuchElementException if this deque is empty
442	>	* @throws NoSuchElementException {@inheritDoc}
443		*/
444		public E element() {
445		return getFirst();
446		}
447
448	+	/**
449	+	* Retrieves, but does not remove, the head of the queue represented by
450	+	* this deque, or returns {@code null} if this deque is empty.
451	+	*
452	+	* <p>This method is equivalent to {@link #peekFirst}.
453	+	*
454	+	* @return the head of the queue represented by this deque, or
455	+	*         {@code null} if this deque is empty
456	+	*/
457	+	public E peek() {
458	+	return peekFirst();
459	+	}
460	+
461		// *** Stack methods ***
462
463		/**
464		* Pushes an element onto the stack represented by this deque.  In other
465	<	* words, inserts the element to the front this deque.
465	>	* words, inserts the element at the front of this deque.
466		*
467		* <p>This method is equivalent to {@link #addFirst}.
468		*
469		* @param e the element to push
470	<	* @throws NullPointerException if <tt>e</tt> is null
470	>	* @throws NullPointerException if the specified element is null
471		*/
472		public void push(E e) {
473		addFirst(e);
#	Line 508 | Line 480 | public class ArrayDeque<E> extends Abstr
480		* <p>This method is equivalent to {@link #removeFirst()}.
481		*
482		* @return the element at the front of this deque (which is the top
483	<	*     of the stack represented by this deque)
484	<	* @throws NoSuchElementException if this deque is empty
483	>	*         of the stack represented by this deque)
484	>	* @throws NoSuchElementException {@inheritDoc}
485		*/
486		public E pop() {
487		return removeFirst();
488		}
489
490	+	private void checkInvariants() {
491	+	assert elements[tail] == null;
492	+	assert head == tail ? elements[head] == null :
493	+	(elements[head] != null &&
494	+	elements[(tail - 1) & (elements.length - 1)] != null);
495	+	assert elements[(head - 1) & (elements.length - 1)] == null;
496	+	}
497	+
498		/**
499	<	* Remove the element at the specified position in the elements array,
500	<	* adjusting head, tail, and size as necessary.  This can result in
501	<	* motion of elements backwards or forwards in the array.
502	<	*
503	<	* <p>This method is called delete rather than remove to emphasize
504	<	* that its semantics differ from those of List.remove(int).
505	<	*
499	>	* Removes the element at the specified position in the elements array,
500	>	* adjusting head and tail as necessary.  This can result in motion of
501	>	* elements backwards or forwards in the array.
502	>	*
503	>	* <p>This method is called delete rather than remove to emphasize
504	>	* that its semantics differ from those of {@link List#remove(int)}.
505	>	*
506		* @return true if elements moved backwards
507		*/
508		private boolean delete(int i) {
509	<	// Case 1: Deque doesn't wrap
510	<	// Case 2: Deque does wrap and removed element is in the head portion
511	<	if ((head < tail || tail == 0) || i >= head) {
512	<	System.arraycopy(elements, head, elements, head + 1, i - head);
513	<	elements[head] = null;
514	<	head = (head + 1) & (elements.length - 1);
509	>	checkInvariants();
510	>	final Object[] elements = this.elements;
511	>	final int mask = elements.length - 1;
512	>	final int h = head;
513	>	final int t = tail;
514	>	final int front = (i - h) & mask;
515	>	final int back  = (t - i) & mask;
516	>
517	>	// Invariant: head <= i < tail mod circularity
518	>	if (front >= ((t - h) & mask))
519	>	throw new ConcurrentModificationException();
520	>
521	>	// Optimize for least element motion
522	>	if (front < back) {
523	>	if (h <= i) {
524	>	System.arraycopy(elements, h, elements, h + 1, front);
525	>	} else { // Wrap around
526	>	System.arraycopy(elements, 0, elements, 1, i);
527	>	elements[0] = elements[mask];
528	>	System.arraycopy(elements, h, elements, h + 1, mask - h);
529	>	}
530	>	elements[h] = null;
531	>	head = (h + 1) & mask;
532		return false;
533	+	} else {
534	+	if (i < t) { // Copy the null tail as well
535	+	System.arraycopy(elements, i + 1, elements, i, back);
536	+	tail = t - 1;
537	+	} else { // Wrap around
538	+	System.arraycopy(elements, i + 1, elements, i, mask - i);
539	+	elements[mask] = elements[0];
540	+	System.arraycopy(elements, 1, elements, 0, t);
541	+	tail = (t - 1) & mask;
542	+	}
543	+	return true;
544		}
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;
545		}
546
547		// *** Collection Methods ***
#	Line 554 | Line 556 | public class ArrayDeque<E> extends Abstr
556		}
557
558		/**
559	<	* Returns <tt>true</tt> if this collection contains no elements.<p>
559	>	* Returns {@code true} if this deque contains no elements.
560		*
561	<	* @return <tt>true</tt> if this collection contains no elements.
561	>	* @return {@code true} if this deque contains no elements
562		*/
563		public boolean isEmpty() {
564		return head == tail;
#	Line 567 | Line 569 | public class ArrayDeque<E> extends Abstr
569		* will be ordered from first (head) to last (tail).  This is the same
570		* order that elements would be dequeued (via successive calls to
571		* {@link #remove} or popped (via successive calls to {@link #pop}).
572	<	*
573	<	* @return an <tt>Iterator</tt> over the elements in this deque
572	>	*
573	>	* @return an iterator over the elements in this deque
574		*/
575		public Iterator<E> iterator() {
576		return new DeqIterator();
577		}
578
579	+	public Iterator<E> descendingIterator() {
580	+	return new DescendingIterator();
581	+	}
582	+
583		private class DeqIterator implements Iterator<E> {
584		/**
585		* Index of element to be returned by subsequent call to next.
#	Line 597 | Line 603 | public class ArrayDeque<E> extends Abstr
603		}
604
605		public E next() {
600	–	E result;
606		if (cursor == fence)
607		throw new NoSuchElementException();
608	+	@SuppressWarnings("unchecked")
609	+	E result = (E) elements[cursor];
610		// This check doesn't catch all possible comodifications,
611		// but does catch the ones that corrupt traversal
612	<	if (tail != fence || (result = elements[cursor]) == null)
612	>	if (tail != fence || result == null)
613		throw new ConcurrentModificationException();
614		lastRet = cursor;
615		cursor = (cursor + 1) & (elements.length - 1);
#	Line 612 | Line 619 | public class ArrayDeque<E> extends Abstr
619		public void remove() {
620		if (lastRet < 0)
621		throw new IllegalStateException();
622	<	if (delete(lastRet))
623	<	cursor--;
622	>	if (delete(lastRet)) { // if left-shifted, undo increment in next()
623	>	cursor = (cursor - 1) & (elements.length - 1);
624	>	fence = tail;
625	>	}
626	>	lastRet = -1;
627	>	}
628	>	}
629	>
630	>	private class DescendingIterator implements Iterator<E> {
631	>	/*
632	>	* This class is nearly a mirror-image of DeqIterator, using
633	>	* tail instead of head for initial cursor, and head instead of
634	>	* tail for fence.
635	>	*/
636	>	private int cursor = tail;
637	>	private int fence = head;
638	>	private int lastRet = -1;
639	>
640	>	public boolean hasNext() {
641	>	return cursor != fence;
642	>	}
643	>
644	>	public E next() {
645	>	if (cursor == fence)
646	>	throw new NoSuchElementException();
647	>	cursor = (cursor - 1) & (elements.length - 1);
648	>	@SuppressWarnings("unchecked")
649	>	E result = (E) elements[cursor];
650	>	if (head != fence || result == null)
651	>	throw new ConcurrentModificationException();
652	>	lastRet = cursor;
653	>	return result;
654	>	}
655	>
656	>	public void remove() {
657	>	if (lastRet < 0)
658	>	throw new IllegalStateException();
659	>	if (!delete(lastRet)) {
660	>	cursor = (cursor + 1) & (elements.length - 1);
661	>	fence = head;
662	>	}
663		lastRet = -1;
618	–	fence = tail;
664		}
665		}
666
667		/**
668	<	* Returns <tt>true</tt> if this deque contains the specified
669	<	* element.  More formally, returns <tt>true</tt> if and only if this
670	<	* deque contains at least one element <tt>e</tt> such that
626	<	* <tt>e.equals(o)</tt>.
668	>	* Returns {@code true} if this deque contains the specified element.
669	>	* More formally, returns {@code true} if and only if this deque contains
670	>	* at least one element {@code e} such that {@code o.equals(e)}.
671		*
672		* @param o object to be checked for containment in this deque
673	<	* @return <tt>true</tt> if this deque contains the specified element
673	>	* @return {@code true} if this deque contains the specified element
674		*/
675		public boolean contains(Object o) {
676		if (o == null)
677		return false;
678		int mask = elements.length - 1;
679		int i = head;
680	<	E x;
680	>	Object x;
681		while ( (x = elements[i]) != null) {
682		if (o.equals(x))
683		return true;
#	Line 644 | Line 688 | public class ArrayDeque<E> extends Abstr
688
689		/**
690		* Removes a single instance of the specified element from this deque.
691	<	* This method is equivalent to {@link #removeFirstOccurrence}.
691	>	* If the deque does not contain the element, it is unchanged.
692	>	* More formally, removes the first element {@code e} such that
693	>	* {@code o.equals(e)} (if such an element exists).
694	>	* Returns {@code true} if this deque contained the specified element
695	>	* (or equivalently, if this deque changed as a result of the call).
696	>	*
697	>	* <p>This method is equivalent to {@link #removeFirstOccurrence}.
698		*
699	<	* @param e element to be removed from this deque, if present
700	<	* @return <tt>true</tt> if this deque contained the specified element
699	>	* @param o element to be removed from this deque, if present
700	>	* @return {@code true} if this deque contained the specified element
701		*/
702	<	public boolean remove(Object e) {
703	<	return removeFirstOccurrence(e);
702	>	public boolean remove(Object o) {
703	>	return removeFirstOccurrence(o);
704		}
705
706		/**
707		* Removes all of the elements from this deque.
708	+	* The deque will be empty after this call returns.
709		*/
710		public void clear() {
711		int h = head;
#	Line 666 | Line 717 | public class ArrayDeque<E> extends Abstr
717		do {
718		elements[i] = null;
719		i = (i + 1) & mask;
720	<	} while(i != t);
720	>	} while (i != t);
721		}
722		}
723
724		/**
725	<	* Returns an array containing all of the elements in this list
726	<	* in the correct order.
725	>	* Returns an array containing all of the elements in this deque
726	>	* in proper sequence (from first to last element).
727		*
728	<	* @return an array containing all of the elements in this list
729	<	*         in the correct order
728	>	* <p>The returned array will be "safe" in that no references to it are
729	>	* maintained by this deque.  (In other words, this method must allocate
730	>	* a new array).  The caller is thus free to modify the returned array.
731	>	*
732	>	* <p>This method acts as bridge between array-based and collection-based
733	>	* APIs.
734	>	*
735	>	* @return an array containing all of the elements in this deque
736		*/
737		public Object[] toArray() {
738	<	return copyElements(new Object[size()]);
738	>	return copyElements(new Object[size()]);
739		}
740
741		/**
742	<	* Returns an array containing all of the elements in this deque in the
743	<	* correct order; the runtime type of the returned array is that of the
744	<	* specified array.  If the deque fits in the specified array, it is
745	<	* returned therein.  Otherwise, a new array is allocated with the runtime
746	<	* type of the specified array and the size of this deque.
742	>	* Returns an array containing all of the elements in this deque in
743	>	* proper sequence (from first to last element); the runtime type of the
744	>	* returned array is that of the specified array.  If the deque fits in
745	>	* the specified array, it is returned therein.  Otherwise, a new array
746	>	* is allocated with the runtime type of the specified array and the
747	>	* size of this deque.
748	>	*
749	>	* <p>If this deque fits in the specified array with room to spare
750	>	* (i.e., the array has more elements than this deque), the element in
751	>	* the array immediately following the end of the deque is set to
752	>	* {@code null}.
753	>	*
754	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
755	>	* array-based and collection-based APIs.  Further, this method allows
756	>	* precise control over the runtime type of the output array, and may,
757	>	* under certain circumstances, be used to save allocation costs.
758	>	*
759	>	* <p>Suppose {@code x} is a deque known to contain only strings.
760	>	* The following code can be used to dump the deque into a newly
761	>	* allocated array of {@code String}:
762		*
763	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
764	<	* the array has more elements than the deque), the element in the array
765	<	* immediately following the end of the collection is set to <tt>null</tt>.
763	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
764	>	*
765	>	* Note that {@code toArray(new Object[0])} is identical in function to
766	>	* {@code toArray()}.
767		*
768		* @param a the array into which the elements of the deque are to
769	<	*          be stored, if it is big enough; otherwise, a new array of the
770	<	*          same runtime type is allocated for this purpose
771	<	* @return an array containing the elements of the deque
772	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
773	<	*         of the runtime type of every element in this deque
769	>	*          be stored, if it is big enough; otherwise, a new array of the
770	>	*          same runtime type is allocated for this purpose
771	>	* @return an array containing all of the elements in this deque
772	>	* @throws ArrayStoreException if the runtime type of the specified array
773	>	*         is not a supertype of the runtime type of every element in
774	>	*         this deque
775	>	* @throws NullPointerException if the specified array is null
776		*/
777	+	@SuppressWarnings("unchecked")
778		public <T> T[] toArray(T[] a) {
779		int size = size();
780		if (a.length < size)
781		a = (T[])java.lang.reflect.Array.newInstance(
782		a.getClass().getComponentType(), size);
783	<	copyElements(a);
783	>	copyElements(a);
784		if (a.length > size)
785		a[size] = null;
786		return a;
#	Line 718 | Line 794 | public class ArrayDeque<E> extends Abstr
794		* @return a copy of this deque
795		*/
796		public ArrayDeque<E> clone() {
797	<	try {
797	>	try {
798	>	@SuppressWarnings("unchecked")
799		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
800	<	// 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);
800	>	result.elements = Arrays.copyOf(elements, elements.length);
801		return result;
802	<
728	<	} catch (CloneNotSupportedException e) {
802	>	} catch (CloneNotSupportedException e) {
803		throw new AssertionError();
804		}
805		}
806
733	–	/**
734	–	* Appease the serialization gods.
735	–	*/
807		private static final long serialVersionUID = 2340985798034038923L;
808
809		/**
810	<	* Serialize this deque.
810	>	* Saves this deque to a stream (that is, serializes it).
811		*
812	<	* @serialData The current size (<tt>int</tt>) of the deque,
812	>	* @serialData The current size ({@code int}) of the deque,
813		* followed by all of its elements (each an object reference) in
814		* first-to-last order.
815		*/
816	<	private void writeObject(ObjectOutputStream s) throws IOException {
816	>	private void writeObject(java.io.ObjectOutputStream s)
817	>	throws java.io.IOException {
818		s.defaultWriteObject();
819
820		// Write out size
821	<	int size = size();
750	<	s.writeInt(size);
821	>	s.writeInt(size());
822
823		// Write out elements in order.
753	–	int i = head;
824		int mask = elements.length - 1;
825	<	for (int j = 0; j < size; j++) {
825	>	for (int i = head; i != tail; i = (i + 1) & mask)
826		s.writeObject(elements[i]);
757	–	i = (i + 1) & mask;
758	–	}
827		}
828
829		/**
830	<	* Deserialize this deque.
830	>	* Reconstitutes this deque from a stream (that is, deserializes it).
831		*/
832	<	private void readObject(ObjectInputStream s)
833	<	throws IOException, ClassNotFoundException {
832	>	private void readObject(java.io.ObjectInputStream s)
833	>	throws java.io.IOException, ClassNotFoundException {
834		s.defaultReadObject();
835
836		// Read in size and allocate array
#	Line 773 | Line 841 | public class ArrayDeque<E> extends Abstr
841
842		// Read in all elements in the proper order.
843		for (int i = 0; i < size; i++)
844	<	elements[i] = (E)s.readObject();
777	<
844	>	elements[i] = s.readObject();
845		}
846		}

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