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Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.9 by jsr166, Mon May 16 06:16:12 2005 UTC vs.
Revision 1.50 by jsr166, Wed Feb 20 12:32:01 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	>	import java.util.stream.Streams;
11
12		/**
13		* Resizable-array implementation of the {@link Deque} interface.  Array
#	Line 15 | Line 18 | import java.io.*;
18		* {@link Stack} when used as a stack, and faster than {@link LinkedList}
19		* when used as a queue.
20		*
21	<	* <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time.
21	>	* <p>Most {@code ArrayDeque} operations run in amortized constant time.
22		* Exceptions include {@link #remove(Object) remove}, {@link
23		* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
24		* removeLastOccurrence}, {@link #contains contains}, {@link #iterator
25		* iterator.remove()}, and the bulk operations, all of which run in linear
26		* time.
27		*
28	<	* <p>The iterators returned by this class's <tt>iterator</tt> method are
28	>	* <p>The iterators returned by this class's {@code iterator} method are
29		* <i>fail-fast</i>: If the deque is modified at any time after the iterator
30	<	* is created, in any way except through the iterator's own <tt>remove</tt>
30	>	* is created, in any way except through the iterator's own {@code remove}
31		* method, the iterator will generally throw a {@link
32		* ConcurrentModificationException}.  Thus, in the face of concurrent
33		* modification, the iterator fails quickly and cleanly, rather than risking
#	Line 34 | Line 37 | import java.io.*;
37		* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
38		* as it is, generally speaking, impossible to make any hard guarantees in the
39		* presence of unsynchronized concurrent modification.  Fail-fast iterators
40	<	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
40	>	* throw {@code ConcurrentModificationException} on a best-effort basis.
41		* Therefore, it would be wrong to write a program that depended on this
42		* exception for its correctness: <i>the fail-fast behavior of iterators
43		* should be used only to detect bugs.</i>
#	Line 44 | Line 47 | import java.io.*;
47		* Iterator} interfaces.
48		*
49		* <p>This class is a member of the
50	<	* <a href="{@docRoot}/../guide/collections/index.html">
50	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
51		* Java Collections Framework</a>.
52		*
53		* @author  Josh Bloch and Doug Lea
#	Line 64 | Line 67 | public class ArrayDeque<E> extends Abstr
67		* other.  We also guarantee that all array cells not holding
68		* deque elements are always null.
69		*/
70	<	private transient E[] elements;
70	>	transient Object[] elements; // non-private to simplify nested class access
71
72		/**
73		* The index of the element at the head of the deque (which is the
74		* element that would be removed by remove() or pop()); or an
75		* arbitrary number equal to tail if the deque is empty.
76		*/
77	<	private transient int head;
77	>	transient int head;
78
79		/**
80		* The index at which the next element would be added to the tail
81		* of the deque (via addLast(E), add(E), or push(E)).
82		*/
83	<	private transient int tail;
83	>	transient int tail;
84
85		/**
86		* The minimum capacity that we'll use for a newly created deque.
#	Line 88 | Line 91 | public class ArrayDeque<E> extends Abstr
91		// ******  Array allocation and resizing utilities ******
92
93		/**
94	<	* Allocate empty array to hold the given number of elements.
94	>	* Allocates empty array to hold the given number of elements.
95		*
96		* @param numElements  the number of elements to hold
97		*/
#	Line 108 | Line 111 | public class ArrayDeque<E> extends Abstr
111		if (initialCapacity < 0)   // Too many elements, must back off
112		initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
113		}
114	<	elements = (E[]) new Object[initialCapacity];
114	>	elements = new Object[initialCapacity];
115		}
116
117		/**
118	<	* Double the capacity of this deque.  Call only when full, i.e.,
118	>	* Doubles the capacity of this deque.  Call only when full, i.e.,
119		* when head and tail have wrapped around to become equal.
120		*/
121		private void doubleCapacity() {
#	Line 126 | Line 129 | public class ArrayDeque<E> extends Abstr
129		Object[] a = new Object[newCapacity];
130		System.arraycopy(elements, p, a, 0, r);
131		System.arraycopy(elements, 0, a, r, p);
132	<	elements = (E[])a;
132	>	elements = a;
133		head = 0;
134		tail = n;
135		}
136
137		/**
135	–	* Copies the elements from our element array into the specified array,
136	–	* in order (from first to last element in the deque).  It is assumed
137	–	* that the array is large enough to hold all elements in the deque.
138	–	*
139	–	* @return its argument
140	–	*/
141	–	private <T> T[] copyElements(T[] a) {
142	–	if (head < tail) {
143	–	System.arraycopy(elements, head, a, 0, size());
144	–	} else if (head > tail) {
145	–	int headPortionLen = elements.length - head;
146	–	System.arraycopy(elements, head, a, 0, headPortionLen);
147	–	System.arraycopy(elements, 0, a, headPortionLen, tail);
148	–	}
149	–	return a;
150	–	}
151	–
152	–	/**
138		* Constructs an empty array deque with an initial capacity
139		* sufficient to hold 16 elements.
140		*/
141		public ArrayDeque() {
142	<	elements = (E[]) new Object[16];
142	>	elements = new Object[16];
143		}
144
145		/**
#	Line 202 | Line 187 | public class ArrayDeque<E> extends Abstr
187
188		/**
189		* Inserts the specified element at the end of this deque.
190	<	* This method is equivalent to {@link #add} and {@link #push}.
190	>	*
191	>	* <p>This method is equivalent to {@link #add}.
192		*
193		* @param e the element to add
194		* @throws NullPointerException if the specified element is null
#	Line 219 | Line 205 | public class ArrayDeque<E> extends Abstr
205		* Inserts the specified element at the front of this deque.
206		*
207		* @param e the element to add
208	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst})
208	>	* @return {@code true} (as specified by {@link Deque#offerFirst})
209		* @throws NullPointerException if the specified element is null
210		*/
211		public boolean offerFirst(E e) {
#	Line 231 | Line 217 | public class ArrayDeque<E> extends Abstr
217		* Inserts the specified element at the end of this deque.
218		*
219		* @param e the element to add
220	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
220	>	* @return {@code true} (as specified by {@link Deque#offerLast})
221		* @throws NullPointerException if the specified element is null
222		*/
223		public boolean offerLast(E e) {
#	Line 261 | Line 247 | public class ArrayDeque<E> extends Abstr
247
248		public E pollFirst() {
249		int h = head;
250	<	E result = elements[h]; // Element is null if deque empty
250	>	@SuppressWarnings("unchecked")
251	>	E result = (E) elements[h];
252	>	// Element is null if deque empty
253		if (result == null)
254		return null;
255		elements[h] = null;     // Must null out slot
#	Line 271 | Line 259 | public class ArrayDeque<E> extends Abstr
259
260		public E pollLast() {
261		int t = (tail - 1) & (elements.length - 1);
262	<	E result = elements[t];
262	>	@SuppressWarnings("unchecked")
263	>	E result = (E) elements[t];
264		if (result == null)
265		return null;
266		elements[t] = null;
#	Line 283 | Line 272 | public class ArrayDeque<E> extends Abstr
272		* @throws NoSuchElementException {@inheritDoc}
273		*/
274		public E getFirst() {
275	<	E x = elements[head];
276	<	if (x == null)
275	>	@SuppressWarnings("unchecked")
276	>	E result = (E) elements[head];
277	>	if (result == null)
278		throw new NoSuchElementException();
279	<	return x;
279	>	return result;
280		}
281
282		/**
283		* @throws NoSuchElementException {@inheritDoc}
284		*/
285		public E getLast() {
286	<	E x = elements[(tail - 1) & (elements.length - 1)];
287	<	if (x == null)
286	>	@SuppressWarnings("unchecked")
287	>	E result = (E) elements[(tail - 1) & (elements.length - 1)];
288	>	if (result == null)
289		throw new NoSuchElementException();
290	<	return x;
290	>	return result;
291		}
292
293	+	@SuppressWarnings("unchecked")
294		public E peekFirst() {
295	<	return elements[head]; // elements[head] is null if deque empty
295	>	// elements[head] is null if deque empty
296	>	return (E) elements[head];
297		}
298
299	+	@SuppressWarnings("unchecked")
300		public E peekLast() {
301	<	return elements[(tail - 1) & (elements.length - 1)];
301	>	return (E) elements[(tail - 1) & (elements.length - 1)];
302		}
303
304		/**
305		* Removes the first occurrence of the specified element in this
306		* deque (when traversing the deque from head to tail).
307		* If the deque does not contain the element, it is unchanged.
308	<	* More formally, removes the first element <tt>e</tt> such that
309	<	* <tt>o.equals(e)</tt> (if such an element exists).
310	<	* Returns true if this deque contained the specified element (or
311	<	* equivalently, if this deque changed as a result of the call).
308	>	* More formally, removes the first element {@code e} such that
309	>	* {@code o.equals(e)} (if such an element exists).
310	>	* Returns {@code true} if this deque contained the specified element
311	>	* (or equivalently, if this deque changed as a result of the call).
312		*
313		* @param o element to be removed from this deque, if present
314	<	* @return <tt>true</tt> if the deque contained the specified element
314	>	* @return {@code true} if the deque contained the specified element
315		*/
316		public boolean removeFirstOccurrence(Object o) {
317		if (o == null)
318		return false;
319		int mask = elements.length - 1;
320		int i = head;
321	<	E x;
321	>	Object x;
322		while ( (x = elements[i]) != null) {
323		if (o.equals(x)) {
324		delete(i);
#	Line 339 | Line 333 | public class ArrayDeque<E> extends Abstr
333		* Removes the last occurrence of the specified element in this
334		* deque (when traversing the deque from head to tail).
335		* If the deque does not contain the element, it is unchanged.
336	<	* More formally, removes the last element <tt>e</tt> such that
337	<	* <tt>o.equals(e)</tt> (if such an element exists).
338	<	* Returns true if this deque contained the specified element (or
339	<	* equivalently, if this deque changed as a result of the call).
336	>	* More formally, removes the last element {@code e} such that
337	>	* {@code o.equals(e)} (if such an element exists).
338	>	* Returns {@code true} if this deque contained the specified element
339	>	* (or equivalently, if this deque changed as a result of the call).
340		*
341		* @param o element to be removed from this deque, if present
342	<	* @return <tt>true</tt> if the deque contained the specified element
342	>	* @return {@code true} if the deque contained the specified element
343		*/
344		public boolean removeLastOccurrence(Object o) {
345		if (o == null)
346		return false;
347		int mask = elements.length - 1;
348		int i = (tail - 1) & mask;
349	<	E x;
349	>	Object x;
350		while ( (x = elements[i]) != null) {
351		if (o.equals(x)) {
352		delete(i);
#	Line 371 | Line 365 | public class ArrayDeque<E> extends Abstr
365		* <p>This method is equivalent to {@link #addLast}.
366		*
367		* @param e the element to add
368	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
368	>	* @return {@code true} (as specified by {@link Collection#add})
369		* @throws NullPointerException if the specified element is null
370		*/
371		public boolean add(E e) {
#	Line 385 | Line 379 | public class ArrayDeque<E> extends Abstr
379		* <p>This method is equivalent to {@link #offerLast}.
380		*
381		* @param e the element to add
382	<	* @return <tt>true</tt> (as per the spec for {@link Queue#offer})
382	>	* @return {@code true} (as specified by {@link Queue#offer})
383		* @throws NullPointerException if the specified element is null
384		*/
385		public boolean offer(E e) {
#	Line 394 | Line 388 | public class ArrayDeque<E> extends Abstr
388
389		/**
390		* Retrieves and removes the head of the queue represented by this deque.
391	<	* This method differs from {@link #poll} only in that it throws an
391	>	*
392	>	* This method differs from {@link #poll poll} only in that it throws an
393		* exception if this deque is empty.
394		*
395		* <p>This method is equivalent to {@link #removeFirst}.
#	Line 409 | Line 404 | public class ArrayDeque<E> extends Abstr
404		/**
405		* Retrieves and removes the head of the queue represented by this deque
406		* (in other words, the first element of this deque), or returns
407	<	* <tt>null</tt> if this deque is empty.
407	>	* {@code null} if this deque is empty.
408		*
409		* <p>This method is equivalent to {@link #pollFirst}.
410		*
411		* @return the head of the queue represented by this deque, or
412	<	*         <tt>null</tt> if this deque is empty
412	>	*         {@code null} if this deque is empty
413		*/
414		public E poll() {
415		return pollFirst();
#	Line 422 | Line 417 | public class ArrayDeque<E> extends Abstr
417
418		/**
419		* Retrieves, but does not remove, the head of the queue represented by
420	<	* this deque.  This method differs from {@link #peek} only in that it
421	<	* throws an exception if this deque is empty.
420	>	* this deque.  This method differs from {@link #peek peek} only in
421	>	* that it throws an exception if this deque is empty.
422		*
423		* <p>This method is equivalent to {@link #getFirst}.
424		*
#	Line 436 | Line 431 | public class ArrayDeque<E> extends Abstr
431
432		/**
433		* Retrieves, but does not remove, the head of the queue represented by
434	<	* this deque, or returns <tt>null</tt> if this deque is empty.
434	>	* this deque, or returns {@code null} if this deque is empty.
435		*
436		* <p>This method is equivalent to {@link #peekFirst}.
437		*
438		* @return the head of the queue represented by this deque, or
439	<	*         <tt>null</tt> if this deque is empty
439	>	*         {@code null} if this deque is empty
440		*/
441		public E peek() {
442		return peekFirst();
#	Line 476 | Line 471 | public class ArrayDeque<E> extends Abstr
471		return removeFirst();
472		}
473
474	+	private void checkInvariants() {
475	+	assert elements[tail] == null;
476	+	assert head == tail ? elements[head] == null :
477	+	(elements[head] != null &&
478	+	elements[(tail - 1) & (elements.length - 1)] != null);
479	+	assert elements[(head - 1) & (elements.length - 1)] == null;
480	+	}
481	+
482		/**
483		* Removes the element at the specified position in the elements array,
484		* adjusting head and tail as necessary.  This can result in motion of
#	Line 487 | Line 490 | public class ArrayDeque<E> extends Abstr
490		* @return true if elements moved backwards
491		*/
492		private boolean delete(int i) {
493	<	int mask = elements.length - 1;
494	<
495	<	// Invariant: head <= i < tail mod circularity
496	<	if (((i - head) & mask) >= ((tail - head) & mask))
497	<	throw new ConcurrentModificationException();
498	<
499	<	// Case 1: Deque doesn't wrap
500	<	// Case 2: Deque does wrap and removed element is in the head portion
501	<	if (i >= head) {
502	<	System.arraycopy(elements, head, elements, head + 1, i - head);
503	<	elements[head] = null;
504	<	head = (head + 1) & mask;
493	>	checkInvariants();
494	>	final Object[] elements = this.elements;
495	>	final int mask = elements.length - 1;
496	>	final int h = head;
497	>	final int t = tail;
498	>	final int front = (i - h) & mask;
499	>	final int back  = (t - i) & mask;
500	>
501	>	// Invariant: head <= i < tail mod circularity
502	>	if (front >= ((t - h) & mask))
503	>	throw new ConcurrentModificationException();
504	>
505	>	// Optimize for least element motion
506	>	if (front < back) {
507	>	if (h <= i) {
508	>	System.arraycopy(elements, h, elements, h + 1, front);
509	>	} else { // Wrap around
510	>	System.arraycopy(elements, 0, elements, 1, i);
511	>	elements[0] = elements[mask];
512	>	System.arraycopy(elements, h, elements, h + 1, mask - h);
513	>	}
514	>	elements[h] = null;
515	>	head = (h + 1) & mask;
516		return false;
517	+	} else {
518	+	if (i < t) { // Copy the null tail as well
519	+	System.arraycopy(elements, i + 1, elements, i, back);
520	+	tail = t - 1;
521	+	} else { // Wrap around
522	+	System.arraycopy(elements, i + 1, elements, i, mask - i);
523	+	elements[mask] = elements[0];
524	+	System.arraycopy(elements, 1, elements, 0, t);
525	+	tail = (t - 1) & mask;
526	+	}
527	+	return true;
528		}
504	–
505	–	// Case 3: Deque wraps and removed element is in the tail portion
506	–	tail--;
507	–	System.arraycopy(elements, i + 1, elements, i, tail - i);
508	–	elements[tail] = null;
509	–	return true;
529		}
530
531		// *** Collection Methods ***
#	Line 521 | Line 540 | public class ArrayDeque<E> extends Abstr
540		}
541
542		/**
543	<	* Returns <tt>true</tt> if this deque contains no elements.
543	>	* Returns {@code true} if this deque contains no elements.
544		*
545	<	* @return <tt>true</tt> if this deque contains no elements
545	>	* @return {@code true} if this deque contains no elements
546		*/
547		public boolean isEmpty() {
548		return head == tail;
#	Line 535 | Line 554 | public class ArrayDeque<E> extends Abstr
554		* order that elements would be dequeued (via successive calls to
555		* {@link #remove} or popped (via successive calls to {@link #pop}).
556		*
557	<	* @return an <tt>Iterator</tt> over the elements in this deque
557	>	* @return an iterator over the elements in this deque
558		*/
559		public Iterator<E> iterator() {
560		return new DeqIterator();
561		}
562
563	+	public Iterator<E> descendingIterator() {
564	+	return new DescendingIterator();
565	+	}
566	+
567		private class DeqIterator implements Iterator<E> {
568		/**
569		* Index of element to be returned by subsequent call to next.
#	Line 564 | Line 587 | public class ArrayDeque<E> extends Abstr
587		}
588
589		public E next() {
567	–	E result;
590		if (cursor == fence)
591		throw new NoSuchElementException();
592	+	@SuppressWarnings("unchecked")
593	+	E result = (E) elements[cursor];
594		// This check doesn't catch all possible comodifications,
595		// but does catch the ones that corrupt traversal
596	<	if (tail != fence || (result = elements[cursor]) == null)
596	>	if (tail != fence || result == null)
597		throw new ConcurrentModificationException();
598		lastRet = cursor;
599		cursor = (cursor + 1) & (elements.length - 1);
#	Line 579 | Line 603 | public class ArrayDeque<E> extends Abstr
603		public void remove() {
604		if (lastRet < 0)
605		throw new IllegalStateException();
606	<	if (delete(lastRet))
607	<	cursor--;
606	>	if (delete(lastRet)) { // if left-shifted, undo increment in next()
607	>	cursor = (cursor - 1) & (elements.length - 1);
608	>	fence = tail;
609	>	}
610	>	lastRet = -1;
611	>	}
612	>	}
613	>
614	>	private class DescendingIterator implements Iterator<E> {
615	>	/*
616	>	* This class is nearly a mirror-image of DeqIterator, using
617	>	* tail instead of head for initial cursor, and head instead of
618	>	* tail for fence.
619	>	*/
620	>	private int cursor = tail;
621	>	private int fence = head;
622	>	private int lastRet = -1;
623	>
624	>	public boolean hasNext() {
625	>	return cursor != fence;
626	>	}
627	>
628	>	public E next() {
629	>	if (cursor == fence)
630	>	throw new NoSuchElementException();
631	>	cursor = (cursor - 1) & (elements.length - 1);
632	>	@SuppressWarnings("unchecked")
633	>	E result = (E) elements[cursor];
634	>	if (head != fence || result == null)
635	>	throw new ConcurrentModificationException();
636	>	lastRet = cursor;
637	>	return result;
638	>	}
639	>
640	>	public void remove() {
641	>	if (lastRet < 0)
642	>	throw new IllegalStateException();
643	>	if (!delete(lastRet)) {
644	>	cursor = (cursor + 1) & (elements.length - 1);
645	>	fence = head;
646	>	}
647		lastRet = -1;
585	–	fence = tail;
648		}
649		}
650
651		/**
652	<	* Returns <tt>true</tt> if this deque contains the specified element.
653	<	* More formally, returns <tt>true</tt> if and only if this deque contains
654	<	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
652	>	* Returns {@code true} if this deque contains the specified element.
653	>	* More formally, returns {@code true} if and only if this deque contains
654	>	* at least one element {@code e} such that {@code o.equals(e)}.
655		*
656		* @param o object to be checked for containment in this deque
657	<	* @return <tt>true</tt> if this deque contains the specified element
657	>	* @return {@code true} if this deque contains the specified element
658		*/
659		public boolean contains(Object o) {
660		if (o == null)
661		return false;
662		int mask = elements.length - 1;
663		int i = head;
664	<	E x;
664	>	Object x;
665		while ( (x = elements[i]) != null) {
666		if (o.equals(x))
667		return true;
#	Line 611 | Line 673 | public class ArrayDeque<E> extends Abstr
673		/**
674		* Removes a single instance of the specified element from this deque.
675		* If the deque does not contain the element, it is unchanged.
676	<	* More formally, removes the first element <tt>e</tt> such that
677	<	* <tt>o.equals(e)</tt> (if such an element exists).
678	<	* Returns true if this deque contained the specified element (or
679	<	* equivalently, if this deque changed as a result of the call).
676	>	* More formally, removes the first element {@code e} such that
677	>	* {@code o.equals(e)} (if such an element exists).
678	>	* Returns {@code true} if this deque contained the specified element
679	>	* (or equivalently, if this deque changed as a result of the call).
680		*
681	<	* <p>This method is equivalent to {@link #removeFirstOccurrence}.
681	>	* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
682		*
683		* @param o element to be removed from this deque, if present
684	<	* @return <tt>true</tt> if this deque contained the specified element
684	>	* @return {@code true} if this deque contained the specified element
685		*/
686		public boolean remove(Object o) {
687		return removeFirstOccurrence(o);
#	Line 645 | Line 707 | public class ArrayDeque<E> extends Abstr
707
708		/**
709		* Returns an array containing all of the elements in this deque
710	<	* in the correct order.
710	>	* in proper sequence (from first to last element).
711	>	*
712	>	* <p>The returned array will be "safe" in that no references to it are
713	>	* maintained by this deque.  (In other words, this method must allocate
714	>	* a new array).  The caller is thus free to modify the returned array.
715	>	*
716	>	* <p>This method acts as bridge between array-based and collection-based
717	>	* APIs.
718		*
719		* @return an array containing all of the elements in this deque
651	–	*         in the correct order
720		*/
721		public Object[] toArray() {
722	<	return copyElements(new Object[size()]);
722	>	final int head = this.head;
723	>	final int tail = this.tail;
724	>	boolean wrap = (tail < head);
725	>	int end = wrap ? tail + elements.length : tail;
726	>	Object[] a = Arrays.copyOfRange(elements, head, end);
727	>	if (wrap)
728	>	System.arraycopy(elements, 0, a, elements.length - head, tail);
729	>	return a;
730		}
731
732		/**
733	<	* Returns an array containing all of the elements in this deque in the
734	<	* correct order; the runtime type of the returned array is that of the
735	<	* specified array.  If the deque fits in the specified array, it is
736	<	* returned therein.  Otherwise, a new array is allocated with the runtime
737	<	* type of the specified array and the size of this deque.
733	>	* Returns an array containing all of the elements in this deque in
734	>	* proper sequence (from first to last element); the runtime type of the
735	>	* returned array is that of the specified array.  If the deque fits in
736	>	* the specified array, it is returned therein.  Otherwise, a new array
737	>	* is allocated with the runtime type of the specified array and the
738	>	* size of this deque.
739	>	*
740	>	* <p>If this deque fits in the specified array with room to spare
741	>	* (i.e., the array has more elements than this deque), the element in
742	>	* the array immediately following the end of the deque is set to
743	>	* {@code null}.
744	>	*
745	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
746	>	* array-based and collection-based APIs.  Further, this method allows
747	>	* precise control over the runtime type of the output array, and may,
748	>	* under certain circumstances, be used to save allocation costs.
749	>	*
750	>	* <p>Suppose {@code x} is a deque known to contain only strings.
751	>	* The following code can be used to dump the deque into a newly
752	>	* allocated array of {@code String}:
753		*
754	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
755	<	* the array has more elements than the deque), the element in the array
756	<	* immediately following the end of the collection is set to <tt>null</tt>.
754	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
755	>	*
756	>	* Note that {@code toArray(new Object[0])} is identical in function to
757	>	* {@code toArray()}.
758		*
759		* @param a the array into which the elements of the deque are to
760		*          be stored, if it is big enough; otherwise, a new array of the
761		*          same runtime type is allocated for this purpose
762	<	* @return an array containing the elements of the deque
763	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
764	<	*         of the runtime type of every element in this deque
762	>	* @return an array containing all of the elements in this deque
763	>	* @throws ArrayStoreException if the runtime type of the specified array
764	>	*         is not a supertype of the runtime type of every element in
765	>	*         this deque
766	>	* @throws NullPointerException if the specified array is null
767		*/
768	+	@SuppressWarnings("unchecked")
769		public <T> T[] toArray(T[] a) {
770	<	int size = size();
771	<	if (a.length < size)
772	<	a = (T[])java.lang.reflect.Array.newInstance(
773	<	a.getClass().getComponentType(), size);
774	<	copyElements(a);
775	<	if (a.length > size)
776	<	a[size] = null;
770	>	final int head = this.head;
771	>	final int tail = this.tail;
772	>	boolean wrap = (tail < head);
773	>	int size = (tail - head) + (wrap ? elements.length : 0);
774	>	int firstLeg = size - (wrap ? tail : 0);
775	>	int len = a.length;
776	>	if (size > len) {
777	>	a = (T[]) Arrays.copyOfRange(elements, head, head + size,
778	>	a.getClass());
779	>	} else {
780	>	System.arraycopy(elements, head, a, 0, firstLeg);
781	>	if (size < len)
782	>	a[size] = null;
783	>	}
784	>	if (wrap)
785	>	System.arraycopy(elements, 0, a, firstLeg, tail);
786		return a;
787		}
788
#	Line 692 | Line 795 | public class ArrayDeque<E> extends Abstr
795		*/
796		public ArrayDeque<E> clone() {
797		try {
798	+	@SuppressWarnings("unchecked")
799		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
800	<	// These two lines are currently faster than cloning the array:
697	<	result.elements = (E[]) new Object[elements.length];
698	<	System.arraycopy(elements, 0, result.elements, 0, elements.length);
800	>	result.elements = Arrays.copyOf(elements, elements.length);
801		return result;
700	–
802		} catch (CloneNotSupportedException e) {
803		throw new AssertionError();
804		}
805		}
806
706	–	/**
707	–	* Appease the serialization gods.
708	–	*/
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();
723	<	s.writeInt(size);
821	>	s.writeInt(size());
822
823		// Write out elements in order.
726	–	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]);
730	–	i = (i + 1) & mask;
731	–	}
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 746 | 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();
844	>	elements[i] = s.readObject();
845	>	}
846	>
847	>	Spliterator<E> spliterator() {
848	>	return new DeqSpliterator<E>(this, -1, -1);
849	>	}
850	>
851	>	public Stream<E> stream() {
852	>	return Streams.stream(spliterator());
853	>	}
854	>
855	>	public Stream<E> parallelStream() {
856	>	return Streams.parallelStream(spliterator());
857	>	}
858
859	+	static final class DeqSpliterator<E> implements Spliterator<E> {
860	+	private final ArrayDeque<E> deq;
861	+	private int fence;  // -1 until first use
862	+	private int index;  // current index, modified on traverse/split
863	+
864	+	/** Creates new spliterator covering the given array and range */
865	+	DeqSpliterator(ArrayDeque<E> deq, int origin, int fence) {
866	+	this.deq = deq;
867	+	this.index = origin;
868	+	this.fence = fence;
869	+	}
870	+
871	+	private int getFence() { // force initialization
872	+	int t;
873	+	if ((t = fence) < 0) {
874	+	t = fence = deq.tail;
875	+	index = deq.head;
876	+	}
877	+	return t;
878	+	}
879	+
880	+	public DeqSpliterator<E> trySplit() {
881	+	int t = getFence(), h = index, n = deq.elements.length;
882	+	if (h != t && ((h + 1) & (n - 1)) != t) {
883	+	if (h > t)
884	+	t += n;
885	+	int m = ((h + t) >>> 1) & (n - 1);
886	+	return new DeqSpliterator<>(deq, h, index = m);
887	+	}
888	+	return null;
889	+	}
890	+
891	+	public void forEach(Consumer<? super E> consumer) {
892	+	if (consumer == null)
893	+	throw new NullPointerException();
894	+	Object[] a = deq.elements;
895	+	int m = a.length - 1, f = getFence(), i = index;
896	+	index = f;
897	+	while (i != f) {
898	+	@SuppressWarnings("unchecked") E e = (E)a[i];
899	+	i = (i + 1) & m;
900	+	if (e == null)
901	+	throw new ConcurrentModificationException();
902	+	consumer.accept(e);
903	+	}
904	+	}
905	+
906	+	public boolean tryAdvance(Consumer<? super E> consumer) {
907	+	if (consumer == null)
908	+	throw new NullPointerException();
909	+	Object[] a = deq.elements;
910	+	int m = a.length - 1, f = getFence(), i = index;
911	+	if (i != fence) {
912	+	@SuppressWarnings("unchecked") E e = (E)a[i];
913	+	index = (i + 1) & m;
914	+	if (e == null)
915	+	throw new ConcurrentModificationException();
916	+	consumer.accept(e);
917	+	return true;
918	+	}
919	+	return false;
920	+	}
921	+
922	+	public long estimateSize() {
923	+	int n = getFence() - index;
924	+	if (n < 0)
925	+	n += deq.elements.length;
926	+	return (long) n;
927	+	}
928	+
929	+	@Override
930	+	public int characteristics() {
931	+	return Spliterator.ORDERED | Spliterator.SIZED |
932	+	Spliterator.NONNULL | Spliterator.SUBSIZED;
933	+	}
934		}
935	+
936		}

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