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

Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.1 by dl, Tue Dec 28 12:14:07 2004 UTC vs.
Revision 1.39 by jsr166, Tue Feb 21 01:54:03 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 12 | Line 11 | import java.io.*;
11		* usage.  They are not thread-safe; in the absence of external
12		* synchronization, they do not support concurrent access by multiple threads.
13		* Null elements are prohibited.  This class is likely to be faster than
14	<	* {@link Stack} when used as as a stack, and faster than {@link LinkedList}
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
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 85 | Line 87 | public class ArrayDeque<E> extends Abstr
87		// ******  Array allocation and resizing utilities ******
88
89		/**
90	<	* Allocate empty array to hold the given number of elements.
90	>	* Allocates 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		/**
114	<	* Double the capacity of this deque.  Call only when full, i.e.,
114	>	* Doubles the capacity of this deque.  Call only when full, i.e.,
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")
265	>	E result = (E) elements[h];
266	>	// Element is null if deque empty
267	>	if (result == null)
268	>	return null;
269	>	elements[h] = null;     // Must null out slot
270	>	head = (h + 1) & (elements.length - 1);
271	>	return result;
272		}
273
274	<	/**
275	<	* Retrieves, but does not remove, the last element of this deque,
276	<	* returning <tt>null</tt> if this deque is empty.
277	<	*
278	<	* @return the last element of this deque, or <tt>null</tt> if this deque
279	<	*     is empty
280	<	*/
281	<	public E peekLast() {
282	<	return elements[(tail - 1) & (elements.length - 1)];
274	>	public E pollLast() {
275	>	int t = (tail - 1) & (elements.length - 1);
276	>	@SuppressWarnings("unchecked")
277	>	E result = (E) elements[t];
278	>	if (result == null)
279	>	return null;
280	>	elements[t] = null;
281	>	tail = t;
282	>	return result;
283		}
284
285		/**
286	<	* 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
286	>	* @throws NoSuchElementException {@inheritDoc}
287		*/
288		public E getFirst() {
289	<	E x = elements[head];
290	<	if (x == null)
289	>	@SuppressWarnings("unchecked")
290	>	E result = (E) elements[head];
291	>	if (result == null)
292		throw new NoSuchElementException();
293	<	return x;
293	>	return result;
294		}
295
296		/**
297	<	* 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
297	>	* @throws NoSuchElementException {@inheritDoc}
298		*/
299		public E getLast() {
300	<	E x = elements[(tail - 1) & (elements.length - 1)];
301	<	if (x == null)
300	>	@SuppressWarnings("unchecked")
301	>	E result = (E) elements[(tail - 1) & (elements.length - 1)];
302	>	if (result == null)
303		throw new NoSuchElementException();
304	<	return x;
304	>	return result;
305	>	}
306	>
307	>	@SuppressWarnings("unchecked")
308	>	public E peekFirst() {
309	>	// elements[head] is null if deque empty
310	>	return (E) elements[head];
311	>	}
312	>
313	>	@SuppressWarnings("unchecked")
314	>	public E peekLast() {
315	>	return (E) elements[(tail - 1) & (elements.length - 1)];
316		}
317
318		/**
319		* Removes the first occurrence of the specified element in this
320	<	* deque (when traversing the deque from head to tail).  If the deque
321	<	* does not contain the element, it is unchanged.
320	>	* deque (when traversing the deque from head to tail).
321	>	* If the deque does not contain the element, it is unchanged.
322	>	* More formally, removes the first element <tt>e</tt> such that
323	>	* <tt>o.equals(e)</tt> (if such an element exists).
324	>	* Returns <tt>true</tt> if this deque contained the specified element
325	>	* (or equivalently, if this deque changed as a result of the call).
326		*
327	<	* @param e element to be removed from this deque, if present
327	>	* @param o element to be removed from this deque, if present
328		* @return <tt>true</tt> if the deque contained the specified element
329		*/
330	<	public boolean removeFirstOccurrence(Object e) {
331	<	if (e == null)
330	>	public boolean removeFirstOccurrence(Object o) {
331	>	if (o == null)
332		return false;
333		int mask = elements.length - 1;
334		int i = head;
335	<	E x;
335	>	Object x;
336		while ( (x = elements[i]) != null) {
337	<	if (e.equals(x)) {
337	>	if (o.equals(x)) {
338		delete(i);
339		return true;
340		}
#	Line 379 | Line 345 | public class ArrayDeque<E> extends Abstr
345
346		/**
347		* Removes the last occurrence of the specified element in this
348	<	* deque (when traversing the deque from head to tail).  If the deque
349	<	* does not contain the element, it is unchanged.
348	>	* deque (when traversing the deque from head to tail).
349	>	* If the deque does not contain the element, it is unchanged.
350	>	* More formally, removes the last element <tt>e</tt> such that
351	>	* <tt>o.equals(e)</tt> (if such an element exists).
352	>	* Returns <tt>true</tt> if this deque contained the specified element
353	>	* (or equivalently, if this deque changed as a result of the call).
354		*
355	<	* @param e element to be removed from this deque, if present
355	>	* @param o element to be removed from this deque, if present
356		* @return <tt>true</tt> if the deque contained the specified element
357		*/
358	<	public boolean removeLastOccurrence(Object e) {
359	<	if (e == null)
358	>	public boolean removeLastOccurrence(Object o) {
359	>	if (o == null)
360		return false;
361		int mask = elements.length - 1;
362		int i = (tail - 1) & mask;
363	<	E x;
363	>	Object x;
364		while ( (x = elements[i]) != null) {
365	<	if (e.equals(x)) {
365	>	if (o.equals(x)) {
366		delete(i);
367		return true;
368		}
#	Line 404 | Line 374 | public class ArrayDeque<E> extends Abstr
374		// *** Queue methods ***
375
376		/**
377	<	* 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.
377	>	* Inserts the specified element at the end of this deque.
378		*
379		* <p>This method is equivalent to {@link #addLast}.
380		*
381	<	* @param e the element to insert
382	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
383	<	* @throws NullPointerException if <tt>e</tt> is null
381	>	* @param e the element to add
382	>	* @return <tt>true</tt> (as specified by {@link Collection#add})
383	>	* @throws NullPointerException if the specified element is null
384		*/
385		public boolean add(E e) {
386		addLast(e);
#	Line 431 | Line 388 | public class ArrayDeque<E> extends Abstr
388		}
389
390		/**
391	<	* 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.
391	>	* Inserts the specified element at the end of this deque.
392		*
393	<	* <p>This method is equivalent to {@link #pollFirst}.
393	>	* <p>This method is equivalent to {@link #offerLast}.
394		*
395	<	* @return the first element of this deque, or <tt>null</tt> if
396	<	*     this deque is empty
395	>	* @param e the element to add
396	>	* @return <tt>true</tt> (as specified by {@link Queue#offer})
397	>	* @throws NullPointerException if the specified element is null
398		*/
399	<	public E poll() {
400	<	return pollFirst();
399	>	public boolean offer(E e) {
400	>	return offerLast(e);
401		}
402
403		/**
404		* Retrieves and removes the head of the queue represented by this deque.
405	<	* This method differs from the <tt>poll</tt> method in that it throws an
405	>	*
406	>	* This method differs from {@link #poll poll} only in that it throws an
407		* exception if this deque is empty.
408		*
409		* <p>This method is equivalent to {@link #removeFirst}.
410		*
411		* @return the head of the queue represented by this deque
412	<	* @throws NoSuchElementException if this deque is empty
412	>	* @throws NoSuchElementException {@inheritDoc}
413		*/
414		public E remove() {
415		return removeFirst();
416		}
417
418		/**
419	<	* Retrieves, but does not remove, the head of the queue represented by
420	<	* this deque, returning <tt>null</tt> if this deque is empty.
419	>	* Retrieves and removes the head of the queue represented by this deque
420	>	* (in other words, the first element of this deque), or returns
421	>	* <tt>null</tt> if this deque is empty.
422		*
423	<	* <p>This method is equivalent to {@link #peekFirst}
423	>	* <p>This method is equivalent to {@link #pollFirst}.
424		*
425		* @return the head of the queue represented by this deque, or
426	<	*     <tt>null</tt> if this deque is empty
426	>	*         <tt>null</tt> if this deque is empty
427		*/
428	<	public E peek() {
429	<	return peekFirst();
428	>	public E poll() {
429	>	return pollFirst();
430		}
431
432		/**
433		* Retrieves, but does not remove, the head of the queue represented by
434	<	* this deque.  This method differs from the <tt>peek</tt> method only in
434	>	* this deque.  This method differs from {@link #peek peek} only in
435		* that it throws an exception if this deque is empty.
436		*
437	<	* <p>This method is equivalent to {@link #getFirst}
437	>	* <p>This method is equivalent to {@link #getFirst}.
438		*
439		* @return the head of the queue represented by this deque
440	<	* @throws NoSuchElementException if this deque is empty
440	>	* @throws NoSuchElementException {@inheritDoc}
441		*/
442		public E element() {
443		return getFirst();
444		}
445
446	+	/**
447	+	* Retrieves, but does not remove, the head of the queue represented by
448	+	* this deque, or returns <tt>null</tt> if this deque is empty.
449	+	*
450	+	* <p>This method is equivalent to {@link #peekFirst}.
451	+	*
452	+	* @return the head of the queue represented by this deque, or
453	+	*         <tt>null</tt> if this deque is empty
454	+	*/
455	+	public E peek() {
456	+	return peekFirst();
457	+	}
458	+
459		// *** Stack methods ***
460
461		/**
462		* Pushes an element onto the stack represented by this deque.  In other
463	<	* words, inserts the element to the front this deque.
463	>	* words, inserts the element at the front of this deque.
464		*
465		* <p>This method is equivalent to {@link #addFirst}.
466		*
467		* @param e the element to push
468	<	* @throws NullPointerException if <tt>e</tt> is null
468	>	* @throws NullPointerException if the specified element is null
469		*/
470		public void push(E e) {
471		addFirst(e);
#	Line 503 | Line 473 | public class ArrayDeque<E> extends Abstr
473
474		/**
475		* Pops an element from the stack represented by this deque.  In other
476	<	* words, removes and returns the the first element of this deque.
476	>	* words, removes and returns the first element of this deque.
477		*
478		* <p>This method is equivalent to {@link #removeFirst()}.
479		*
480		* @return the element at the front of this deque (which is the top
481	<	*     of the stack represented by this deque)
482	<	* @throws NoSuchElementException if this deque is empty
481	>	*         of the stack represented by this deque)
482	>	* @throws NoSuchElementException {@inheritDoc}
483		*/
484		public E pop() {
485		return removeFirst();
486		}
487
488	+	private void checkInvariants() {
489	+	assert elements[tail] == null;
490	+	assert head == tail ? elements[head] == null :
491	+	(elements[head] != null &&
492	+	elements[(tail - 1) & (elements.length - 1)] != null);
493	+	assert elements[(head - 1) & (elements.length - 1)] == null;
494	+	}
495	+
496		/**
497	<	* Remove the element at the specified position in the elements array,
498	<	* adjusting head, tail, and size as necessary.  This can result in
499	<	* motion of elements backwards or forwards in the array.
500	<	*
501	<	* <p>This method is called delete rather than remove to emphasize the
502	<	* that that its semantics differ from those of List.remove(int).
503	<	*
497	>	* Removes the element at the specified position in the elements array,
498	>	* adjusting head and tail as necessary.  This can result in motion of
499	>	* elements backwards or forwards in the array.
500	>	*
501	>	* <p>This method is called delete rather than remove to emphasize
502	>	* that its semantics differ from those of {@link List#remove(int)}.
503	>	*
504		* @return true if elements moved backwards
505		*/
506		private boolean delete(int i) {
507	<	// Case 1: Deque doesn't wrap
508	<	// Case 2: Deque does wrap and removed element is in the head portion
509	<	if ((head < tail || tail == 0) || i >= head) {
510	<	System.arraycopy(elements, head, elements, head + 1, i - head);
511	<	elements[head] = null;
512	<	head = (head + 1) & (elements.length - 1);
507	>	checkInvariants();
508	>	final Object[] elements = this.elements;
509	>	final int mask = elements.length - 1;
510	>	final int h = head;
511	>	final int t = tail;
512	>	final int front = (i - h) & mask;
513	>	final int back  = (t - i) & mask;
514	>
515	>	// Invariant: head <= i < tail mod circularity
516	>	if (front >= ((t - h) & mask))
517	>	throw new ConcurrentModificationException();
518	>
519	>	// Optimize for least element motion
520	>	if (front < back) {
521	>	if (h <= i) {
522	>	System.arraycopy(elements, h, elements, h + 1, front);
523	>	} else { // Wrap around
524	>	System.arraycopy(elements, 0, elements, 1, i);
525	>	elements[0] = elements[mask];
526	>	System.arraycopy(elements, h, elements, h + 1, mask - h);
527	>	}
528	>	elements[h] = null;
529	>	head = (h + 1) & mask;
530		return false;
531	+	} else {
532	+	if (i < t) { // Copy the null tail as well
533	+	System.arraycopy(elements, i + 1, elements, i, back);
534	+	tail = t - 1;
535	+	} else { // Wrap around
536	+	System.arraycopy(elements, i + 1, elements, i, mask - i);
537	+	elements[mask] = elements[0];
538	+	System.arraycopy(elements, 1, elements, 0, t);
539	+	tail = (t - 1) & mask;
540	+	}
541	+	return true;
542		}
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;
543		}
544
545		// *** Collection Methods ***
#	Line 554 | Line 554 | public class ArrayDeque<E> extends Abstr
554		}
555
556		/**
557	<	* Returns <tt>true</tt> if this collection contains no elements.<p>
557	>	* Returns <tt>true</tt> if this deque contains no elements.
558		*
559	<	* @return <tt>true</tt> if this collection contains no elements.
559	>	* @return <tt>true</tt> if this deque contains no elements
560		*/
561		public boolean isEmpty() {
562		return head == tail;
#	Line 567 | Line 567 | public class ArrayDeque<E> extends Abstr
567		* will be ordered from first (head) to last (tail).  This is the same
568		* order that elements would be dequeued (via successive calls to
569		* {@link #remove} or popped (via successive calls to {@link #pop}).
570	<	*
571	<	* @return an <tt>Iterator</tt> over the elements in this deque
570	>	*
571	>	* @return an iterator over the elements in this deque
572		*/
573		public Iterator<E> iterator() {
574		return new DeqIterator();
575		}
576
577	+	public Iterator<E> descendingIterator() {
578	+	return new DescendingIterator();
579	+	}
580	+
581		private class DeqIterator implements Iterator<E> {
582		/**
583		* Index of element to be returned by subsequent call to next.
#	Line 597 | Line 601 | public class ArrayDeque<E> extends Abstr
601		}
602
603		public E next() {
600	–	E result;
604		if (cursor == fence)
605		throw new NoSuchElementException();
606	+	@SuppressWarnings("unchecked")
607	+	E result = (E) elements[cursor];
608		// This check doesn't catch all possible comodifications,
609		// but does catch the ones that corrupt traversal
610	<	if (tail != fence || (result = elements[cursor]) == null)
610	>	if (tail != fence || result == null)
611		throw new ConcurrentModificationException();
612		lastRet = cursor;
613		cursor = (cursor + 1) & (elements.length - 1);
#	Line 612 | Line 617 | public class ArrayDeque<E> extends Abstr
617		public void remove() {
618		if (lastRet < 0)
619		throw new IllegalStateException();
620	<	if (delete(lastRet))
621	<	cursor--;
620	>	if (delete(lastRet)) { // if left-shifted, undo increment in next()
621	>	cursor = (cursor - 1) & (elements.length - 1);
622	>	fence = tail;
623	>	}
624	>	lastRet = -1;
625	>	}
626	>	}
627	>
628	>	private class DescendingIterator implements Iterator<E> {
629	>	/*
630	>	* This class is nearly a mirror-image of DeqIterator, using
631	>	* tail instead of head for initial cursor, and head instead of
632	>	* tail for fence.
633	>	*/
634	>	private int cursor = tail;
635	>	private int fence = head;
636	>	private int lastRet = -1;
637	>
638	>	public boolean hasNext() {
639	>	return cursor != fence;
640	>	}
641	>
642	>	public E next() {
643	>	if (cursor == fence)
644	>	throw new NoSuchElementException();
645	>	cursor = (cursor - 1) & (elements.length - 1);
646	>	@SuppressWarnings("unchecked")
647	>	E result = (E) elements[cursor];
648	>	if (head != fence || result == null)
649	>	throw new ConcurrentModificationException();
650	>	lastRet = cursor;
651	>	return result;
652	>	}
653	>
654	>	public void remove() {
655	>	if (lastRet < 0)
656	>	throw new IllegalStateException();
657	>	if (!delete(lastRet)) {
658	>	cursor = (cursor + 1) & (elements.length - 1);
659	>	fence = head;
660	>	}
661		lastRet = -1;
618	–	fence = tail;
662		}
663		}
664
665		/**
666	<	* Returns <tt>true</tt> if this deque contains the specified
667	<	* element.  More formally, returns <tt>true</tt> if and only if this
668	<	* deque contains at least one element <tt>e</tt> such that
626	<	* <tt>e.equals(o)</tt>.
666	>	* Returns <tt>true</tt> if this deque contains the specified element.
667	>	* More formally, returns <tt>true</tt> if and only if this deque contains
668	>	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
669		*
670		* @param o object to be checked for containment in this deque
671		* @return <tt>true</tt> if this deque contains the specified element
#	Line 633 | Line 675 | public class ArrayDeque<E> extends Abstr
675		return false;
676		int mask = elements.length - 1;
677		int i = head;
678	<	E x;
678	>	Object x;
679		while ( (x = elements[i]) != null) {
680		if (o.equals(x))
681		return true;
#	Line 644 | Line 686 | public class ArrayDeque<E> extends Abstr
686
687		/**
688		* Removes a single instance of the specified element from this deque.
689	<	* This method is equivalent to {@link #removeFirstOccurrence}.
689	>	* If the deque does not contain the element, it is unchanged.
690	>	* More formally, removes the first element <tt>e</tt> such that
691	>	* <tt>o.equals(e)</tt> (if such an element exists).
692	>	* Returns <tt>true</tt> if this deque contained the specified element
693	>	* (or equivalently, if this deque changed as a result of the call).
694	>	*
695	>	* <p>This method is equivalent to {@link #removeFirstOccurrence}.
696		*
697	<	* @param e element to be removed from this deque, if present
697	>	* @param o element to be removed from this deque, if present
698		* @return <tt>true</tt> if this deque contained the specified element
699		*/
700	<	public boolean remove(Object e) {
701	<	return removeFirstOccurrence(e);
700	>	public boolean remove(Object o) {
701	>	return removeFirstOccurrence(o);
702		}
703
704		/**
705		* Removes all of the elements from this deque.
706	+	* The deque will be empty after this call returns.
707		*/
708		public void clear() {
709		int h = head;
#	Line 666 | Line 715 | public class ArrayDeque<E> extends Abstr
715		do {
716		elements[i] = null;
717		i = (i + 1) & mask;
718	<	} while(i != t);
718	>	} while (i != t);
719		}
720		}
721
722		/**
723	<	* Returns an array containing all of the elements in this list
724	<	* in the correct order.
723	>	* Returns an array containing all of the elements in this deque
724	>	* in proper sequence (from first to last element).
725		*
726	<	* @return an array containing all of the elements in this list
727	<	*         in the correct order
726	>	* <p>The returned array will be "safe" in that no references to it are
727	>	* maintained by this deque.  (In other words, this method must allocate
728	>	* a new array).  The caller is thus free to modify the returned array.
729	>	*
730	>	* <p>This method acts as bridge between array-based and collection-based
731	>	* APIs.
732	>	*
733	>	* @return an array containing all of the elements in this deque
734		*/
735		public Object[] toArray() {
736	<	return copyElements(new Object[size()]);
736	>	return copyElements(new Object[size()]);
737		}
738
739		/**
740	<	* Returns an array containing all of the elements in this deque in the
741	<	* correct order; the runtime type of the returned array is that of the
742	<	* specified array.  If the deque fits in the specified array, it is
743	<	* returned therein.  Otherwise, a new array is allocated with the runtime
744	<	* type of the specified array and the size of this deque.
740	>	* Returns an array containing all of the elements in this deque in
741	>	* proper sequence (from first to last element); the runtime type of the
742	>	* returned array is that of the specified array.  If the deque fits in
743	>	* the specified array, it is returned therein.  Otherwise, a new array
744	>	* is allocated with the runtime type of the specified array and the
745	>	* size of this deque.
746	>	*
747	>	* <p>If this deque fits in the specified array with room to spare
748	>	* (i.e., the array has more elements than this deque), the element in
749	>	* the array immediately following the end of the deque is set to
750	>	* <tt>null</tt>.
751	>	*
752	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
753	>	* array-based and collection-based APIs.  Further, this method allows
754	>	* precise control over the runtime type of the output array, and may,
755	>	* under certain circumstances, be used to save allocation costs.
756	>	*
757	>	* <p>Suppose <tt>x</tt> is a deque known to contain only strings.
758	>	* The following code can be used to dump the deque into a newly
759	>	* allocated array of <tt>String</tt>:
760		*
761	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
762	<	* the array has more elements than the deque), the element in the array
763	<	* immediately following the end of the collection is set to <tt>null</tt>.
761	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
762	>	*
763	>	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
764	>	* <tt>toArray()</tt>.
765		*
766		* @param a the array into which the elements of the deque are to
767	<	*          be stored, if it is big enough; otherwise, a new array of the
768	<	*          same runtime type is allocated for this purpose
769	<	* @return an array containing the elements of the deque
770	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
771	<	*         of the runtime type of every element in this deque
767	>	*          be stored, if it is big enough; otherwise, a new array of the
768	>	*          same runtime type is allocated for this purpose
769	>	* @return an array containing all of the elements in this deque
770	>	* @throws ArrayStoreException if the runtime type of the specified array
771	>	*         is not a supertype of the runtime type of every element in
772	>	*         this deque
773	>	* @throws NullPointerException if the specified array is null
774		*/
775	+	@SuppressWarnings("unchecked")
776		public <T> T[] toArray(T[] a) {
777		int size = size();
778		if (a.length < size)
779		a = (T[])java.lang.reflect.Array.newInstance(
780		a.getClass().getComponentType(), size);
781	<	copyElements(a);
781	>	copyElements(a);
782		if (a.length > size)
783		a[size] = null;
784		return a;
#	Line 718 | Line 792 | public class ArrayDeque<E> extends Abstr
792		* @return a copy of this deque
793		*/
794		public ArrayDeque<E> clone() {
795	<	try {
795	>	try {
796	>	@SuppressWarnings("unchecked")
797		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
798	<	// 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);
798	>	result.elements = Arrays.copyOf(elements, elements.length);
799		return result;
800	<
728	<	} catch (CloneNotSupportedException e) {
800	>	} catch (CloneNotSupportedException e) {
801		throw new AssertionError();
802		}
803		}
804
733	–	/**
734	–	* Appease the serialization gods.
735	–	*/
805		private static final long serialVersionUID = 2340985798034038923L;
806
807		/**
808	<	* Serialize this deque.
808	>	* Saves this deque to a stream (that is, serializes it).
809		*
810		* @serialData The current size (<tt>int</tt>) of the deque,
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.
828	>	* Reconstitutes this deque from a stream (that is, deserializes it).
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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