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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 1.55 by jsr166, Thu May 2 06:02:17 2013 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	>	import java.io.Serializable;
8	>	import java.util.function.Consumer;
9	>	import java.util.stream.Stream;
10
11		/**
12		* Resizable-array implementation of the {@link Deque} interface.  Array
#	Line 12 | Line 14 | import java.io.*;
14		* usage.  They are not thread-safe; in the absence of external
15		* synchronization, they do not support concurrent access by multiple threads.
16		* Null elements are prohibited.  This class is likely to be faster than
17	<	* {@link Stack} when used as as a stack, and faster than {@link LinkedList}
17	>	* {@link Stack} when used as a stack, and faster than {@link LinkedList}
18		* when used as a queue.
19		*
20	<	* <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time.
21	<	* Exceptions include {@link #remove(Object) remove}, {@link
22	<	* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
23	<	* removeLastOccurrence}, {@link #contains contains }, {@link #iterator
24	<	* iterator.remove()}, and the bulk operations, all of which run in linear
25	<	* time.
20	>	* <p>Most {@code ArrayDeque} operations run in amortized constant time.
21	>	* Exceptions include
22	>	* {@link #remove(Object) remove},
23	>	* {@link #removeFirstOccurrence removeFirstOccurrence},
24	>	* {@link #removeLastOccurrence removeLastOccurrence},
25	>	* {@link #contains contains},
26	>	* {@link #iterator iterator.remove()},
27	>	* and the bulk operations, all of which run in linear time.
28		*
29	<	* <p>The iterators returned by this class's <tt>iterator</tt> method are
30	<	* <i>fail-fast</i>: If the deque is modified at any time after the iterator
31	<	* is created, in any way except through the iterator's own remove method, the
32	<	* iterator will generally throw a {@link ConcurrentModificationException}.
33	<	* Thus, in the face of concurrent modification, the iterator fails quickly
34	<	* and cleanly, rather than risking arbitrary, non-deterministic behavior at
35	<	* an undetermined time in the future.
29	>	* <p>The iterators returned by this class's {@link #iterator() iterator}
30	>	* method are <em>fail-fast</em>: If the deque is modified at any time after
31	>	* the iterator is created, in any way except through the iterator's own
32	>	* {@code remove} method, the iterator will generally throw a {@link
33	>	* ConcurrentModificationException}.  Thus, in the face of concurrent
34	>	* modification, the iterator fails quickly and cleanly, rather than risking
35	>	* arbitrary, non-deterministic behavior at an undetermined time in the
36	>	* future.
37		*
38		* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
39		* as it is, generally speaking, impossible to make any hard guarantees in the
40		* presence of unsynchronized concurrent modification.  Fail-fast iterators
41	<	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
41	>	* throw {@code ConcurrentModificationException} on a best-effort basis.
42		* Therefore, it would be wrong to write a program that depended on this
43		* exception for its correctness: <i>the fail-fast behavior of iterators
44		* should be used only to detect bugs.</i>
45		*
46		* <p>This class and its iterator implement all of the
47	<	* optional methods of the {@link Collection} and {@link
48	<	* Iterator} interfaces.  This class is a member of the <a
49	<	* href="{@docRoot}/../guide/collections/index.html"> Java Collections
50	<	* Framework</a>.
47	>	* <em>optional</em> methods of the {@link Collection} and {@link
48	>	* Iterator} interfaces.
49	>	*
50	>	* <p>This class is a member of the
51	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
52	>	* Java Collections Framework</a>.
53		*
54		* @author  Josh Bloch and Doug Lea
55		* @since   1.6
#	Line 52 | Line 59 | public class ArrayDeque<E> extends Abstr
59		implements Deque<E>, Cloneable, Serializable
60		{
61		/**
62	<	* The array in which the elements of in the deque are stored.
62	>	* The array in which the elements of the deque are stored.
63		* The capacity of the deque is the length of this array, which is
64		* always a power of two. The array is never allowed to become
65		* full, except transiently within an addX method where it is
#	Line 61 | Line 68 | public class ArrayDeque<E> extends Abstr
68		* other.  We also guarantee that all array cells not holding
69		* deque elements are always null.
70		*/
71	<	private transient E[] elements;
71	>	transient Object[] elements; // non-private to simplify nested class access
72
73		/**
74		* The index of the element at the head of the deque (which is the
75		* element that would be removed by remove() or pop()); or an
76		* arbitrary number equal to tail if the deque is empty.
77		*/
78	<	private transient int head;
78	>	transient int head;
79
80		/**
81		* The index at which the next element would be added to the tail
82		* of the deque (via addLast(E), add(E), or push(E)).
83		*/
84	<	private transient int tail;
84	>	transient int tail;
85
86		/**
87		* The minimum capacity that we'll use for a newly created deque.
#	Line 85 | Line 92 | public class ArrayDeque<E> extends Abstr
92		// ******  Array allocation and resizing utilities ******
93
94		/**
95	<	* Allocate empty array to hold the given number of elements.
95	>	* Allocates empty array to hold the given number of elements.
96		*
97	<	* @param numElements  the number of elements to hold.
97	>	* @param numElements  the number of elements to hold
98		*/
99	<	private void allocateElements(int numElements) {
99	>	private void allocateElements(int numElements) {
100		int initialCapacity = MIN_INITIAL_CAPACITY;
101		// Find the best power of two to hold elements.
102		// Tests "<=" because arrays aren't kept full.
#	Line 105 | Line 112 | public class ArrayDeque<E> extends Abstr
112		if (initialCapacity < 0)   // Too many elements, must back off
113		initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
114		}
115	<	elements = (E[]) new Object[initialCapacity];
115	>	elements = new Object[initialCapacity];
116		}
117
118		/**
119	<	* Double the capacity of this deque.  Call only when full, i.e.,
119	>	* Doubles the capacity of this deque.  Call only when full, i.e.,
120		* when head and tail have wrapped around to become equal.
121		*/
122		private void doubleCapacity() {
123	<	assert head == tail;
123	>	assert head == tail;
124		int p = head;
125		int n = elements.length;
126		int r = n - p; // number of elements to the right of p
#	Line 123 | Line 130 | public class ArrayDeque<E> extends Abstr
130		Object[] a = new Object[newCapacity];
131		System.arraycopy(elements, p, a, 0, r);
132		System.arraycopy(elements, 0, a, r, p);
133	<	elements = (E[])a;
133	>	elements = a;
134		head = 0;
135		tail = n;
136		}
137
138		/**
139	<	* Copy the elements from our element array into the specified array,
133	<	* in order (from first to last element in the deque).  It is assumed
134	<	* that the array is large enough to hold all elements in the deque.
135	<	*
136	<	* @return its argument
137	<	*/
138	<	private <T> T[] copyElements(T[] a) {
139	<	if (head < tail) {
140	<	System.arraycopy(elements, head, a, 0, size());
141	<	} else if (head > tail) {
142	<	int headPortionLen = elements.length - head;
143	<	System.arraycopy(elements, head, a, 0, headPortionLen);
144	<	System.arraycopy(elements, 0, a, headPortionLen, tail);
145	<	}
146	<	return a;
147	<	}
148	<
149	<	/**
150	<	* Constructs an empty array deque with the an initial capacity
139	>	* Constructs an empty array deque with an initial capacity
140		* sufficient to hold 16 elements.
141		*/
142		public ArrayDeque() {
143	<	elements = (E[]) new Object[16];
143	>	elements = new Object[16];
144		}
145
146		/**
#	Line 184 | Line 173 | public class ArrayDeque<E> extends Abstr
173		// terms of these.
174
175		/**
176	<	* Inserts the specified element to the front this deque.
176	>	* Inserts the specified element at the front of this deque.
177		*
178	<	* @param e the element to insert
179	<	* @throws NullPointerException if <tt>e</tt> is null
178	>	* @param e the element to add
179	>	* @throws NullPointerException if the specified element is null
180		*/
181		public void addFirst(E e) {
182		if (e == null)
183		throw new NullPointerException();
184		elements[head = (head - 1) & (elements.length - 1)] = e;
185	<	if (head == tail)
185	>	if (head == tail)
186		doubleCapacity();
187		}
188
189		/**
190	<	* Inserts the specified element to the end this deque.
191	<	* This method is equivalent to {@link Collection#add} and
192	<	* {@link #push}.
190	>	* Inserts the specified element at the end of this deque.
191	>	*
192	>	* <p>This method is equivalent to {@link #add}.
193		*
194	<	* @param e the element to insert
195	<	* @throws NullPointerException if <tt>e</tt> is null
194	>	* @param e the element to add
195	>	* @throws NullPointerException if the specified element is null
196		*/
197		public void addLast(E e) {
198		if (e == null)
#	Line 214 | Line 203 | public class ArrayDeque<E> extends Abstr
203		}
204
205		/**
206	<	* Retrieves and removes the first element of this deque, or
218	<	* <tt>null</tt> if this deque is empty.
206	>	* Inserts the specified element at the front of this deque.
207		*
208	<	* @return the first element of this deque, or <tt>null</tt> if
209	<	*     this deque is empty
210	<	*/
223	<	public E pollFirst() {
224	<	int h = head;
225	<	E result = elements[h]; // Element is null if deque empty
226	<	if (result == null)
227	<	return null;
228	<	elements[h] = null;     // Must null out slot
229	<	head = (h + 1) & (elements.length - 1);
230	<	return result;
231	<	}
232	<
233	<	/**
234	<	* Retrieves and removes the last element of this deque, or
235	<	* <tt>null</tt> if this deque is empty.
236	<	*
237	<	* @return the last element of this deque, or <tt>null</tt> if
238	<	*     this deque is empty
239	<	*/
240	<	public E pollLast() {
241	<	int t = (tail - 1) & (elements.length - 1);
242	<	E result = elements[t];
243	<	if (result == null)
244	<	return null;
245	<	elements[t] = null;
246	<	tail = t;
247	<	return result;
248	<	}
249	<
250	<	/**
251	<	* Inserts the specified element to the front this deque.
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
208	>	* @param e the element to add
209	>	* @return {@code true} (as specified by {@link Deque#offerFirst})
210	>	* @throws NullPointerException if the specified element is null
211		*/
212		public boolean offerFirst(E e) {
213		addFirst(e);
#	Line 260 | Line 215 | public class ArrayDeque<E> extends Abstr
215		}
216
217		/**
218	<	* Inserts the specified element to the end this deque.
218	>	* Inserts the specified element at the end of this deque.
219		*
220	<	* @param e the element to insert
221	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
222	<	* @throws NullPointerException if <tt>e</tt> is null
220	>	* @param e the element to add
221	>	* @return {@code true} (as specified by {@link Deque#offerLast})
222	>	* @throws NullPointerException if the specified element is null
223		*/
224		public boolean offerLast(E e) {
225		addLast(e);
#	Line 272 | Line 227 | public class ArrayDeque<E> extends Abstr
227		}
228
229		/**
230	<	* 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
230	>	* @throws NoSuchElementException {@inheritDoc}
231		*/
232		public E removeFirst() {
233		E x = pollFirst();
#	Line 287 | Line 237 | public class ArrayDeque<E> extends Abstr
237		}
238
239		/**
240	<	* 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
240	>	* @throws NoSuchElementException {@inheritDoc}
241		*/
242		public E removeLast() {
243		E x = pollLast();
#	Line 301 | Line 246 | public class ArrayDeque<E> extends Abstr
246		return x;
247		}
248
249	<	/**
250	<	* Retrieves, but does not remove, the first element of this deque,
251	<	* returning <tt>null</tt> if this deque is empty.
252	<	*
253	<	* @return the first element of this deque, or <tt>null</tt> if
254	<	*     this deque is empty
255	<	*/
256	<	public E peekFirst() {
257	<	return elements[head]; // elements[head] is null if deque empty
249	>	public E pollFirst() {
250	>	int h = head;
251	>	@SuppressWarnings("unchecked")
252	>	E result = (E) elements[h];
253	>	// Element is null if deque empty
254	>	if (result == null)
255	>	return null;
256	>	elements[h] = null;     // Must null out slot
257	>	head = (h + 1) & (elements.length - 1);
258	>	return result;
259		}
260
261	<	/**
262	<	* Retrieves, but does not remove, the last element of this deque,
263	<	* returning <tt>null</tt> if this deque is empty.
264	<	*
265	<	* @return the last element of this deque, or <tt>null</tt> if this deque
266	<	*     is empty
267	<	*/
268	<	public E peekLast() {
269	<	return elements[(tail - 1) & (elements.length - 1)];
261	>	public E pollLast() {
262	>	int t = (tail - 1) & (elements.length - 1);
263	>	@SuppressWarnings("unchecked")
264	>	E result = (E) elements[t];
265	>	if (result == null)
266	>	return null;
267	>	elements[t] = null;
268	>	tail = t;
269	>	return result;
270		}
271
272		/**
273	<	* 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
273	>	* @throws NoSuchElementException {@inheritDoc}
274		*/
275		public E getFirst() {
276	<	E x = elements[head];
277	<	if (x == null)
276	>	@SuppressWarnings("unchecked")
277	>	E result = (E) elements[head];
278	>	if (result == null)
279		throw new NoSuchElementException();
280	<	return x;
280	>	return result;
281		}
282
283		/**
284	<	* 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
284	>	* @throws NoSuchElementException {@inheritDoc}
285		*/
286		public E getLast() {
287	<	E x = elements[(tail - 1) & (elements.length - 1)];
288	<	if (x == null)
287	>	@SuppressWarnings("unchecked")
288	>	E result = (E) elements[(tail - 1) & (elements.length - 1)];
289	>	if (result == null)
290		throw new NoSuchElementException();
291	<	return x;
291	>	return result;
292	>	}
293	>
294	>	@SuppressWarnings("unchecked")
295	>	public E peekFirst() {
296	>	// elements[head] is null if deque empty
297	>	return (E) elements[head];
298	>	}
299	>
300	>	@SuppressWarnings("unchecked")
301	>	public E peekLast() {
302	>	return (E) elements[(tail - 1) & (elements.length - 1)];
303		}
304
305		/**
306		* Removes the first occurrence of the specified element in this
307	<	* deque (when traversing the deque from head to tail).  If the deque
308	<	* does not contain the element, it is unchanged.
307	>	* deque (when traversing the deque from head to tail).
308	>	* If the deque does not contain the element, it is unchanged.
309	>	* More formally, removes the first element {@code e} such that
310	>	* {@code o.equals(e)} (if such an element exists).
311	>	* Returns {@code true} if this deque contained the specified element
312	>	* (or equivalently, if this deque changed as a result of the call).
313		*
314	<	* @param e element to be removed from this deque, if present
315	<	* @return <tt>true</tt> if the deque contained the specified element
314	>	* @param o element to be removed from this deque, if present
315	>	* @return {@code true} if the deque contained the specified element
316		*/
317	<	public boolean removeFirstOccurrence(Object e) {
318	<	if (e == null)
317	>	public boolean removeFirstOccurrence(Object o) {
318	>	if (o == null)
319		return false;
320		int mask = elements.length - 1;
321		int i = head;
322	<	E x;
322	>	Object x;
323		while ( (x = elements[i]) != null) {
324	<	if (e.equals(x)) {
324	>	if (o.equals(x)) {
325		delete(i);
326		return true;
327		}
#	Line 379 | Line 332 | public class ArrayDeque<E> extends Abstr
332
333		/**
334		* Removes the last occurrence of the specified element in this
335	<	* deque (when traversing the deque from head to tail).  If the deque
336	<	* does not contain the element, it is unchanged.
335	>	* deque (when traversing the deque from head to tail).
336	>	* If the deque does not contain the element, it is unchanged.
337	>	* More formally, removes the last element {@code e} such that
338	>	* {@code o.equals(e)} (if such an element exists).
339	>	* Returns {@code true} if this deque contained the specified element
340	>	* (or equivalently, if this deque changed as a result of the call).
341		*
342	<	* @param e element to be removed from this deque, if present
343	<	* @return <tt>true</tt> if the deque contained the specified element
342	>	* @param o element to be removed from this deque, if present
343	>	* @return {@code true} if the deque contained the specified element
344		*/
345	<	public boolean removeLastOccurrence(Object e) {
346	<	if (e == null)
345	>	public boolean removeLastOccurrence(Object o) {
346	>	if (o == null)
347		return false;
348		int mask = elements.length - 1;
349		int i = (tail - 1) & mask;
350	<	E x;
350	>	Object x;
351		while ( (x = elements[i]) != null) {
352	<	if (e.equals(x)) {
352	>	if (o.equals(x)) {
353		delete(i);
354		return true;
355		}
#	Line 404 | Line 361 | public class ArrayDeque<E> extends Abstr
361		// *** Queue methods ***
362
363		/**
364	<	* 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.
364	>	* Inserts the specified element at the end of this deque.
365		*
366		* <p>This method is equivalent to {@link #addLast}.
367		*
368	<	* @param e the element to insert
369	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
370	<	* @throws NullPointerException if <tt>e</tt> is null
368	>	* @param e the element to add
369	>	* @return {@code true} (as specified by {@link Collection#add})
370	>	* @throws NullPointerException if the specified element is null
371		*/
372		public boolean add(E e) {
373		addLast(e);
#	Line 431 | Line 375 | public class ArrayDeque<E> extends Abstr
375		}
376
377		/**
378	<	* 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.
378	>	* Inserts the specified element at the end of this deque.
379		*
380	<	* <p>This method is equivalent to {@link #pollFirst}.
380	>	* <p>This method is equivalent to {@link #offerLast}.
381		*
382	<	* @return the first element of this deque, or <tt>null</tt> if
383	<	*     this deque is empty
382	>	* @param e the element to add
383	>	* @return {@code true} (as specified by {@link Queue#offer})
384	>	* @throws NullPointerException if the specified element is null
385		*/
386	<	public E poll() {
387	<	return pollFirst();
386	>	public boolean offer(E e) {
387	>	return offerLast(e);
388		}
389
390		/**
391		* Retrieves and removes the head of the queue represented by this deque.
392	<	* This method differs from the <tt>poll</tt> method in that it throws an
392	>	*
393	>	* This method differs from {@link #poll poll} only in that it throws an
394		* exception if this deque is empty.
395		*
396		* <p>This method is equivalent to {@link #removeFirst}.
397		*
398		* @return the head of the queue represented by this deque
399	<	* @throws NoSuchElementException if this deque is empty
399	>	* @throws NoSuchElementException {@inheritDoc}
400		*/
401		public E remove() {
402		return removeFirst();
403		}
404
405		/**
406	<	* Retrieves, but does not remove, the head of the queue represented by
407	<	* this deque, returning <tt>null</tt> if this deque is empty.
406	>	* Retrieves and removes the head of the queue represented by this deque
407	>	* (in other words, the first element of this deque), or returns
408	>	* {@code null} if this deque is empty.
409		*
410	<	* <p>This method is equivalent to {@link #peekFirst}
410	>	* <p>This method is equivalent to {@link #pollFirst}.
411		*
412		* @return the head of the queue represented by this deque, or
413	<	*     <tt>null</tt> if this deque is empty
413	>	*         {@code null} if this deque is empty
414		*/
415	<	public E peek() {
416	<	return peekFirst();
415	>	public E poll() {
416	>	return pollFirst();
417		}
418
419		/**
420		* Retrieves, but does not remove, the head of the queue represented by
421	<	* this deque.  This method differs from the <tt>peek</tt> method only in
421	>	* this deque.  This method differs from {@link #peek peek} only in
422		* that it throws an exception if this deque is empty.
423		*
424	<	* <p>This method is equivalent to {@link #getFirst}
424	>	* <p>This method is equivalent to {@link #getFirst}.
425		*
426		* @return the head of the queue represented by this deque
427	<	* @throws NoSuchElementException if this deque is empty
427	>	* @throws NoSuchElementException {@inheritDoc}
428		*/
429		public E element() {
430		return getFirst();
431		}
432
433	+	/**
434	+	* Retrieves, but does not remove, the head of the queue represented by
435	+	* this deque, or returns {@code null} if this deque is empty.
436	+	*
437	+	* <p>This method is equivalent to {@link #peekFirst}.
438	+	*
439	+	* @return the head of the queue represented by this deque, or
440	+	*         {@code null} if this deque is empty
441	+	*/
442	+	public E peek() {
443	+	return peekFirst();
444	+	}
445	+
446		// *** Stack methods ***
447
448		/**
449		* Pushes an element onto the stack represented by this deque.  In other
450	<	* words, inserts the element to the front this deque.
450	>	* words, inserts the element at the front of this deque.
451		*
452		* <p>This method is equivalent to {@link #addFirst}.
453		*
454		* @param e the element to push
455	<	* @throws NullPointerException if <tt>e</tt> is null
455	>	* @throws NullPointerException if the specified element is null
456		*/
457		public void push(E e) {
458		addFirst(e);
#	Line 503 | Line 460 | public class ArrayDeque<E> extends Abstr
460
461		/**
462		* Pops an element from the stack represented by this deque.  In other
463	<	* words, removes and returns the the first element of this deque.
463	>	* words, removes and returns the first element of this deque.
464		*
465		* <p>This method is equivalent to {@link #removeFirst()}.
466		*
467		* @return the element at the front of this deque (which is the top
468	<	*     of the stack represented by this deque)
469	<	* @throws NoSuchElementException if this deque is empty
468	>	*         of the stack represented by this deque)
469	>	* @throws NoSuchElementException {@inheritDoc}
470		*/
471		public E pop() {
472		return removeFirst();
473		}
474
475	+	private void checkInvariants() {
476	+	assert elements[tail] == null;
477	+	assert head == tail ? elements[head] == null :
478	+	(elements[head] != null &&
479	+	elements[(tail - 1) & (elements.length - 1)] != null);
480	+	assert elements[(head - 1) & (elements.length - 1)] == null;
481	+	}
482	+
483		/**
484	<	* Remove the element at the specified position in the elements array,
485	<	* adjusting head, tail, and size as necessary.  This can result in
486	<	* motion of elements backwards or forwards in the array.
487	<	*
488	<	* <p>This method is called delete rather than remove to emphasize the
489	<	* that that its semantics differ from those of List.remove(int).
490	<	*
484	>	* Removes the element at the specified position in the elements array,
485	>	* adjusting head and tail as necessary.  This can result in motion of
486	>	* elements backwards or forwards in the array.
487	>	*
488	>	* <p>This method is called delete rather than remove to emphasize
489	>	* that its semantics differ from those of {@link List#remove(int)}.
490	>	*
491		* @return true if elements moved backwards
492		*/
493		private boolean delete(int i) {
494	<	// Case 1: Deque doesn't wrap
495	<	// Case 2: Deque does wrap and removed element is in the head portion
496	<	if ((head < tail || tail == 0) || i >= head) {
497	<	System.arraycopy(elements, head, elements, head + 1, i - head);
498	<	elements[head] = null;
499	<	head = (head + 1) & (elements.length - 1);
494	>	checkInvariants();
495	>	final Object[] elements = this.elements;
496	>	final int mask = elements.length - 1;
497	>	final int h = head;
498	>	final int t = tail;
499	>	final int front = (i - h) & mask;
500	>	final int back  = (t - i) & mask;
501	>
502	>	// Invariant: head <= i < tail mod circularity
503	>	if (front >= ((t - h) & mask))
504	>	throw new ConcurrentModificationException();
505	>
506	>	// Optimize for least element motion
507	>	if (front < back) {
508	>	if (h <= i) {
509	>	System.arraycopy(elements, h, elements, h + 1, front);
510	>	} else { // Wrap around
511	>	System.arraycopy(elements, 0, elements, 1, i);
512	>	elements[0] = elements[mask];
513	>	System.arraycopy(elements, h, elements, h + 1, mask - h);
514	>	}
515	>	elements[h] = null;
516	>	head = (h + 1) & mask;
517		return false;
518	+	} else {
519	+	if (i < t) { // Copy the null tail as well
520	+	System.arraycopy(elements, i + 1, elements, i, back);
521	+	tail = t - 1;
522	+	} else { // Wrap around
523	+	System.arraycopy(elements, i + 1, elements, i, mask - i);
524	+	elements[mask] = elements[0];
525	+	System.arraycopy(elements, 1, elements, 0, t);
526	+	tail = (t - 1) & mask;
527	+	}
528	+	return true;
529		}
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;
530		}
531
532		// *** Collection Methods ***
#	Line 554 | Line 541 | public class ArrayDeque<E> extends Abstr
541		}
542
543		/**
544	<	* Returns <tt>true</tt> if this collection contains no elements.<p>
544	>	* Returns {@code true} if this deque contains no elements.
545		*
546	<	* @return <tt>true</tt> if this collection contains no elements.
546	>	* @return {@code true} if this deque contains no elements
547		*/
548		public boolean isEmpty() {
549		return head == tail;
#	Line 567 | Line 554 | public class ArrayDeque<E> extends Abstr
554		* will be ordered from first (head) to last (tail).  This is the same
555		* order that elements would be dequeued (via successive calls to
556		* {@link #remove} or popped (via successive calls to {@link #pop}).
557	<	*
558	<	* @return an <tt>Iterator</tt> over the elements in this deque
557	>	*
558	>	* @return an iterator over the elements in this deque
559		*/
560		public Iterator<E> iterator() {
561		return new DeqIterator();
562		}
563
564	+	public Iterator<E> descendingIterator() {
565	+	return new DescendingIterator();
566	+	}
567	+
568		private class DeqIterator implements Iterator<E> {
569		/**
570		* Index of element to be returned by subsequent call to next.
#	Line 597 | Line 588 | public class ArrayDeque<E> extends Abstr
588		}
589
590		public E next() {
600	–	E result;
591		if (cursor == fence)
592		throw new NoSuchElementException();
593	+	@SuppressWarnings("unchecked")
594	+	E result = (E) elements[cursor];
595		// This check doesn't catch all possible comodifications,
596		// but does catch the ones that corrupt traversal
597	<	if (tail != fence || (result = elements[cursor]) == null)
597	>	if (tail != fence || result == null)
598		throw new ConcurrentModificationException();
599		lastRet = cursor;
600		cursor = (cursor + 1) & (elements.length - 1);
#	Line 612 | Line 604 | public class ArrayDeque<E> extends Abstr
604		public void remove() {
605		if (lastRet < 0)
606		throw new IllegalStateException();
607	<	if (delete(lastRet))
608	<	cursor--;
607	>	if (delete(lastRet)) { // if left-shifted, undo increment in next()
608	>	cursor = (cursor - 1) & (elements.length - 1);
609	>	fence = tail;
610	>	}
611	>	lastRet = -1;
612	>	}
613	>	}
614	>
615	>	/**
616	>	* This class is nearly a mirror-image of DeqIterator, using tail
617	>	* instead of head for initial cursor, and head instead of tail
618	>	* for fence.
619	>	*/
620	>	private class DescendingIterator implements Iterator<E> {
621	>	private int cursor = tail;
622	>	private int fence = head;
623	>	private int lastRet = -1;
624	>
625	>	public boolean hasNext() {
626	>	return cursor != fence;
627	>	}
628	>
629	>	public E next() {
630	>	if (cursor == fence)
631	>	throw new NoSuchElementException();
632	>	cursor = (cursor - 1) & (elements.length - 1);
633	>	@SuppressWarnings("unchecked")
634	>	E result = (E) elements[cursor];
635	>	if (head != fence || result == null)
636	>	throw new ConcurrentModificationException();
637	>	lastRet = cursor;
638	>	return result;
639	>	}
640	>
641	>	public void remove() {
642	>	if (lastRet < 0)
643	>	throw new IllegalStateException();
644	>	if (!delete(lastRet)) {
645	>	cursor = (cursor + 1) & (elements.length - 1);
646	>	fence = head;
647	>	}
648		lastRet = -1;
618	–	fence = tail;
649		}
650		}
651
652		/**
653	<	* Returns <tt>true</tt> if this deque contains the specified
654	<	* element.  More formally, returns <tt>true</tt> if and only if this
655	<	* deque contains at least one element <tt>e</tt> such that
626	<	* <tt>e.equals(o)</tt>.
653	>	* Returns {@code true} if this deque contains the specified element.
654	>	* More formally, returns {@code true} if and only if this deque contains
655	>	* at least one element {@code e} such that {@code o.equals(e)}.
656		*
657		* @param o object to be checked for containment in this deque
658	<	* @return <tt>true</tt> if this deque contains the specified element
658	>	* @return {@code true} if this deque contains the specified element
659		*/
660		public boolean contains(Object o) {
661		if (o == null)
662		return false;
663		int mask = elements.length - 1;
664		int i = head;
665	<	E x;
665	>	Object x;
666		while ( (x = elements[i]) != null) {
667		if (o.equals(x))
668		return true;
#	Line 644 | Line 673 | public class ArrayDeque<E> extends Abstr
673
674		/**
675		* Removes a single instance of the specified element from this deque.
676	<	* This method is equivalent to {@link #removeFirstOccurrence}.
676	>	* If the deque does not contain the element, it is unchanged.
677	>	* More formally, removes the first element {@code e} such that
678	>	* {@code o.equals(e)} (if such an element exists).
679	>	* Returns {@code true} if this deque contained the specified element
680	>	* (or equivalently, if this deque changed as a result of the call).
681	>	*
682	>	* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
683		*
684	<	* @param e element to be removed from this deque, if present
685	<	* @return <tt>true</tt> if this deque contained the specified element
684	>	* @param o element to be removed from this deque, if present
685	>	* @return {@code true} if this deque contained the specified element
686		*/
687	<	public boolean remove(Object e) {
688	<	return removeFirstOccurrence(e);
687	>	public boolean remove(Object o) {
688	>	return removeFirstOccurrence(o);
689		}
690
691		/**
692		* Removes all of the elements from this deque.
693	+	* The deque will be empty after this call returns.
694		*/
695		public void clear() {
696		int h = head;
#	Line 666 | Line 702 | public class ArrayDeque<E> extends Abstr
702		do {
703		elements[i] = null;
704		i = (i + 1) & mask;
705	<	} while(i != t);
705	>	} while (i != t);
706		}
707		}
708
709		/**
710	<	* Returns an array containing all of the elements in this list
711	<	* in the correct order.
710	>	* Returns an array containing all of the elements in this deque
711	>	* in proper sequence (from first to last element).
712		*
713	<	* @return an array containing all of the elements in this list
714	<	*         in the correct order
713	>	* <p>The returned array will be "safe" in that no references to it are
714	>	* maintained by this deque.  (In other words, this method must allocate
715	>	* a new array).  The caller is thus free to modify the returned array.
716	>	*
717	>	* <p>This method acts as bridge between array-based and collection-based
718	>	* APIs.
719	>	*
720	>	* @return an array containing all of the elements in this deque
721		*/
722		public Object[] toArray() {
723	<	return copyElements(new Object[size()]);
723	>	final int head = this.head;
724	>	final int tail = this.tail;
725	>	boolean wrap = (tail < head);
726	>	int end = wrap ? tail + elements.length : tail;
727	>	Object[] a = Arrays.copyOfRange(elements, head, end);
728	>	if (wrap)
729	>	System.arraycopy(elements, 0, a, elements.length - head, tail);
730	>	return a;
731		}
732
733		/**
734	<	* Returns an array containing all of the elements in this deque in the
735	<	* correct order; the runtime type of the returned array is that of the
736	<	* specified array.  If the deque fits in the specified array, it is
737	<	* returned therein.  Otherwise, a new array is allocated with the runtime
738	<	* type of the specified array and the size of this deque.
734	>	* Returns an array containing all of the elements in this deque in
735	>	* proper sequence (from first to last element); the runtime type of the
736	>	* returned array is that of the specified array.  If the deque fits in
737	>	* the specified array, it is returned therein.  Otherwise, a new array
738	>	* is allocated with the runtime type of the specified array and the
739	>	* size of this deque.
740	>	*
741	>	* <p>If this deque fits in the specified array with room to spare
742	>	* (i.e., the array has more elements than this deque), the element in
743	>	* the array immediately following the end of the deque is set to
744	>	* {@code null}.
745	>	*
746	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
747	>	* array-based and collection-based APIs.  Further, this method allows
748	>	* precise control over the runtime type of the output array, and may,
749	>	* under certain circumstances, be used to save allocation costs.
750	>	*
751	>	* <p>Suppose {@code x} is a deque known to contain only strings.
752	>	* The following code can be used to dump the deque into a newly
753	>	* allocated array of {@code String}:
754		*
755	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
756	<	* the array has more elements than the deque), the element in the array
757	<	* immediately following the end of the collection is set to <tt>null</tt>.
755	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
756	>	*
757	>	* Note that {@code toArray(new Object[0])} is identical in function to
758	>	* {@code toArray()}.
759		*
760		* @param a the array into which the elements of the deque are to
761	<	*          be stored, if it is big enough; otherwise, a new array of the
762	<	*          same runtime type is allocated for this purpose
763	<	* @return an array containing the elements of the deque
764	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
765	<	*         of the runtime type of every element in this deque
761	>	*          be stored, if it is big enough; otherwise, a new array of the
762	>	*          same runtime type is allocated for this purpose
763	>	* @return an array containing all of the elements in this deque
764	>	* @throws ArrayStoreException if the runtime type of the specified array
765	>	*         is not a supertype of the runtime type of every element in
766	>	*         this deque
767	>	* @throws NullPointerException if the specified array is null
768		*/
769	+	@SuppressWarnings("unchecked")
770		public <T> T[] toArray(T[] a) {
771	<	int size = size();
772	<	if (a.length < size)
773	<	a = (T[])java.lang.reflect.Array.newInstance(
774	<	a.getClass().getComponentType(), size);
775	<	copyElements(a);
776	<	if (a.length > size)
777	<	a[size] = null;
771	>	final int head = this.head;
772	>	final int tail = this.tail;
773	>	boolean wrap = (tail < head);
774	>	int size = (tail - head) + (wrap ? elements.length : 0);
775	>	int firstLeg = size - (wrap ? tail : 0);
776	>	int len = a.length;
777	>	if (size > len) {
778	>	a = (T[]) Arrays.copyOfRange(elements, head, head + size,
779	>	a.getClass());
780	>	} else {
781	>	System.arraycopy(elements, head, a, 0, firstLeg);
782	>	if (size < len)
783	>	a[size] = null;
784	>	}
785	>	if (wrap)
786	>	System.arraycopy(elements, 0, a, firstLeg, tail);
787		return a;
788		}
789
#	Line 718 | Line 795 | public class ArrayDeque<E> extends Abstr
795		* @return a copy of this deque
796		*/
797		public ArrayDeque<E> clone() {
798	<	try {
798	>	try {
799	>	@SuppressWarnings("unchecked")
800		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
801	<	// 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);
801	>	result.elements = Arrays.copyOf(elements, elements.length);
802		return result;
803	<
728	<	} catch (CloneNotSupportedException e) {
803	>	} catch (CloneNotSupportedException e) {
804		throw new AssertionError();
805		}
806		}
807
733	–	/**
734	–	* Appease the serialization gods.
735	–	*/
808		private static final long serialVersionUID = 2340985798034038923L;
809
810		/**
811	<	* Serialize this deque.
811	>	* Saves this deque to a stream (that is, serializes it).
812		*
813	<	* @serialData The current size (<tt>int</tt>) of the deque,
813	>	* @serialData The current size ({@code int}) of the deque,
814		* followed by all of its elements (each an object reference) in
815		* first-to-last order.
816		*/
817	<	private void writeObject(ObjectOutputStream s) throws IOException {
817	>	private void writeObject(java.io.ObjectOutputStream s)
818	>	throws java.io.IOException {
819		s.defaultWriteObject();
820
821		// Write out size
822	<	int size = size();
750	<	s.writeInt(size);
822	>	s.writeInt(size());
823
824		// Write out elements in order.
753	–	int i = head;
825		int mask = elements.length - 1;
826	<	for (int j = 0; j < size; j++) {
826	>	for (int i = head; i != tail; i = (i + 1) & mask)
827		s.writeObject(elements[i]);
757	–	i = (i + 1) & mask;
758	–	}
828		}
829
830		/**
831	<	* Deserialize this deque.
831	>	* Reconstitutes this deque from a stream (that is, deserializes it).
832		*/
833	<	private void readObject(ObjectInputStream s)
834	<	throws IOException, ClassNotFoundException {
833	>	private void readObject(java.io.ObjectInputStream s)
834	>	throws java.io.IOException, ClassNotFoundException {
835		s.defaultReadObject();
836
837		// Read in size and allocate array
#	Line 773 | Line 842 | public class ArrayDeque<E> extends Abstr
842
843		// Read in all elements in the proper order.
844		for (int i = 0; i < size; i++)
845	<	elements[i] = (E)s.readObject();
845	>	elements[i] = s.readObject();
846	>	}
847
848	+	public Spliterator<E> spliterator() {
849	+	return new DeqSpliterator<E>(this, -1, -1);
850		}
851	+
852	+	static final class DeqSpliterator<E> implements Spliterator<E> {
853	+	private final ArrayDeque<E> deq;
854	+	private int fence;  // -1 until first use
855	+	private int index;  // current index, modified on traverse/split
856	+
857	+	/** Creates new spliterator covering the given array and range */
858	+	DeqSpliterator(ArrayDeque<E> deq, int origin, int fence) {
859	+	this.deq = deq;
860	+	this.index = origin;
861	+	this.fence = fence;
862	+	}
863	+
864	+	private int getFence() { // force initialization
865	+	int t;
866	+	if ((t = fence) < 0) {
867	+	t = fence = deq.tail;
868	+	index = deq.head;
869	+	}
870	+	return t;
871	+	}
872	+
873	+	public Spliterator<E> trySplit() {
874	+	int t = getFence(), h = index, n = deq.elements.length;
875	+	if (h != t && ((h + 1) & (n - 1)) != t) {
876	+	if (h > t)
877	+	t += n;
878	+	int m = ((h + t) >>> 1) & (n - 1);
879	+	return new DeqSpliterator<>(deq, h, index = m);
880	+	}
881	+	return null;
882	+	}
883	+
884	+	public void forEachRemaining(Consumer<? super E> consumer) {
885	+	if (consumer == null)
886	+	throw new NullPointerException();
887	+	Object[] a = deq.elements;
888	+	int m = a.length - 1, f = getFence(), i = index;
889	+	index = f;
890	+	while (i != f) {
891	+	@SuppressWarnings("unchecked") E e = (E)a[i];
892	+	i = (i + 1) & m;
893	+	if (e == null)
894	+	throw new ConcurrentModificationException();
895	+	consumer.accept(e);
896	+	}
897	+	}
898	+
899	+	public boolean tryAdvance(Consumer<? super E> consumer) {
900	+	if (consumer == null)
901	+	throw new NullPointerException();
902	+	Object[] a = deq.elements;
903	+	int m = a.length - 1, f = getFence(), i = index;
904	+	if (i != fence) {
905	+	@SuppressWarnings("unchecked") E e = (E)a[i];
906	+	index = (i + 1) & m;
907	+	if (e == null)
908	+	throw new ConcurrentModificationException();
909	+	consumer.accept(e);
910	+	return true;
911	+	}
912	+	return false;
913	+	}
914	+
915	+	public long estimateSize() {
916	+	int n = getFence() - index;
917	+	if (n < 0)
918	+	n += deq.elements.length;
919	+	return (long) n;
920	+	}
921	+
922	+	@Override
923	+	public int characteristics() {
924	+	return Spliterator.ORDERED | Spliterator.SIZED |
925	+	Spliterator.NONNULL | Spliterator.SUBSIZED;
926	+	}
927	+	}
928	+
929		}

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