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Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.30 by jsr166, Sun May 18 23:47:55 2008 UTC vs.
Revision 1.124 by jsr166, Mon Nov 28 02:52:36 2016 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	>	import java.io.Serializable;
9	>	import java.util.function.Consumer;
10	>	import java.util.function.Predicate;
11	>	import java.util.function.UnaryOperator;
12
13		/**
14		* Resizable-array implementation of the {@link Deque} interface.  Array
#	Line 15 | Line 19 | import java.io.*;
19		* {@link Stack} when used as a stack, and faster than {@link LinkedList}
20		* when used as a queue.
21		*
22	<	* <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time.
23	<	* Exceptions include {@link #remove(Object) remove}, {@link
24	<	* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
25	<	* removeLastOccurrence}, {@link #contains contains}, {@link #iterator
26	<	* iterator.remove()}, and the bulk operations, all of which run in linear
27	<	* time.
22	>	* <p>Most {@code ArrayDeque} operations run in amortized constant time.
23	>	* Exceptions include
24	>	* {@link #remove(Object) remove},
25	>	* {@link #removeFirstOccurrence removeFirstOccurrence},
26	>	* {@link #removeLastOccurrence removeLastOccurrence},
27	>	* {@link #contains contains},
28	>	* {@link #iterator iterator.remove()},
29	>	* and the bulk operations, all of which run in linear time.
30		*
31	<	* <p>The iterators returned by this class's <tt>iterator</tt> method are
32	<	* <i>fail-fast</i>: If the deque is modified at any time after the iterator
33	<	* is created, in any way except through the iterator's own <tt>remove</tt>
34	<	* method, the iterator will generally throw a {@link
31	>	* <p>The iterators returned by this class's {@link #iterator() iterator}
32	>	* method are <em>fail-fast</em>: If the deque is modified at any time after
33	>	* the iterator is created, in any way except through the iterator's own
34	>	* {@code remove} method, the iterator will generally throw a {@link
35		* ConcurrentModificationException}.  Thus, in the face of concurrent
36		* modification, the iterator fails quickly and cleanly, rather than risking
37		* arbitrary, non-deterministic behavior at an undetermined time in the
#	Line 34 | Line 40 | import java.io.*;
40		* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
41		* as it is, generally speaking, impossible to make any hard guarantees in the
42		* presence of unsynchronized concurrent modification.  Fail-fast iterators
43	<	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
43	>	* throw {@code ConcurrentModificationException} on a best-effort basis.
44		* Therefore, it would be wrong to write a program that depended on this
45		* exception for its correctness: <i>the fail-fast behavior of iterators
46		* should be used only to detect bugs.</i>
#	Line 48 | Line 54 | import java.io.*;
54		* Java Collections Framework</a>.
55		*
56		* @author  Josh Bloch and Doug Lea
57	+	* @param <E> the type of elements held in this deque
58		* @since   1.6
52	–	* @param <E> the type of elements held in this collection
59		*/
60		public class ArrayDeque<E> extends AbstractCollection<E>
61		implements Deque<E>, Cloneable, Serializable
62		{
63	+	/*
64	+	* VMs excel at optimizing simple array loops where indices are
65	+	* incrementing or decrementing over a valid slice, e.g.
66	+	*
67	+	* for (int i = start; i < end; i++) ... elements[i]
68	+	*
69	+	* Because in a circular array, elements are in general stored in
70	+	* two disjoint such slices, we help the VM by writing unusual
71	+	* nested loops for all traversals over the elements.  Having only
72	+	* one hot inner loop body instead of two or three eases human
73	+	* maintenance and encourages VM loop inlining into the caller.
74	+	*/
75	+
76		/**
77		* The array in which the elements of the deque are stored.
78	<	* The capacity of the deque is the length of this array, which is
79	<	* always a power of two. The array is never allowed to become
61	<	* full, except transiently within an addX method where it is
62	<	* resized (see doubleCapacity) immediately upon becoming full,
63	<	* thus avoiding head and tail wrapping around to equal each
64	<	* other.  We also guarantee that all array cells not holding
65	<	* deque elements are always null.
78	>	* All array cells not holding deque elements are always null.
79	>	* The array always has at least one null slot (at tail).
80		*/
81	<	private transient E[] elements;
81	>	transient Object[] elements;
82
83		/**
84		* The index of the element at the head of the deque (which is the
85		* element that would be removed by remove() or pop()); or an
86	<	* arbitrary number equal to tail if the deque is empty.
86	>	* arbitrary number 0 <= head < elements.length equal to tail if
87	>	* the deque is empty.
88		*/
89	<	private transient int head;
89	>	transient int head;
90
91		/**
92		* The index at which the next element would be added to the tail
93	<	* of the deque (via addLast(E), add(E), or push(E)).
93	>	* of the deque (via addLast(E), add(E), or push(E));
94	>	* elements[tail] is always null.
95		*/
96	<	private transient int tail;
96	>	transient int tail;
97
98		/**
99	<	* The minimum capacity that we'll use for a newly created deque.
100	<	* Must be a power of 2.
101	<	*/
102	<	private static final int MIN_INITIAL_CAPACITY = 8;
103	<
104	<	// ******  Array allocation and resizing utilities ******
105	<
106	<	/**
107	<	* Allocate empty array to hold the given number of elements.
108	<	*
109	<	* @param numElements  the number of elements to hold
110	<	*/
111	<	private void allocateElements(int numElements) {
112	<	int initialCapacity = MIN_INITIAL_CAPACITY;
113	<	// Find the best power of two to hold elements.
114	<	// Tests "<=" because arrays aren't kept full.
115	<	if (numElements >= initialCapacity) {
116	<	initialCapacity = numElements;
117	<	initialCapacity |= (initialCapacity >>>  1);
118	<	initialCapacity |= (initialCapacity >>>  2);
119	<	initialCapacity |= (initialCapacity >>>  4);
120	<	initialCapacity |= (initialCapacity >>>  8);
121	<	initialCapacity |= (initialCapacity >>> 16);
122	<	initialCapacity++;
99	>	* The maximum size of array to allocate.
100	>	* Some VMs reserve some header words in an array.
101	>	* Attempts to allocate larger arrays may result in
102	>	* OutOfMemoryError: Requested array size exceeds VM limit
103	>	*/
104	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
105	>
106	>	/**
107	>	* Increases the capacity of this deque by at least the given amount.
108	>	*
109	>	* @param needed the required minimum extra capacity; must be positive
110	>	*/
111	>	private void grow(int needed) {
112	>	// overflow-conscious code
113	>	final int oldCapacity = elements.length;
114	>	int newCapacity;
115	>	// Double capacity if small; else grow by 50%
116	>	int jump = (oldCapacity < 64) ? (oldCapacity + 2) : (oldCapacity >> 1);
117	>	if (jump < needed
118	>	|| (newCapacity = (oldCapacity + jump)) - MAX_ARRAY_SIZE > 0)
119	>	newCapacity = newCapacity(needed, jump);
120	>	elements = Arrays.copyOf(elements, newCapacity);
121	>	// Exceptionally, here tail == head needs to be disambiguated
122	>	if (tail < head || (tail == head && elements[head] != null)) {
123	>	// wrap around; slide first leg forward to end of array
124	>	int newSpace = newCapacity - oldCapacity;
125	>	System.arraycopy(elements, head,
126	>	elements, head + newSpace,
127	>	oldCapacity - head);
128	>	Arrays.fill(elements, head, head + newSpace, null);
129	>	head += newSpace;
130	>	}
131	>	// checkInvariants();
132	>	}
133
134	<	if (initialCapacity < 0)   // Too many elements, must back off
135	<	initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
134	>	/** Capacity calculation for edge conditions, especially overflow. */
135	>	private int newCapacity(int needed, int jump) {
136	>	final int oldCapacity = elements.length, minCapacity;
137	>	if ((minCapacity = oldCapacity + needed) - MAX_ARRAY_SIZE > 0) {
138	>	if (minCapacity < 0)
139	>	throw new IllegalStateException("Sorry, deque too big");
140	>	return Integer.MAX_VALUE;
141		}
142	<	elements = (E[]) new Object[initialCapacity];
142	>	if (needed > jump)
143	>	return minCapacity;
144	>	return (oldCapacity + jump - MAX_ARRAY_SIZE < 0)
145	>	? oldCapacity + jump
146	>	: MAX_ARRAY_SIZE;
147		}
148
149		/**
150	<	* Double the capacity of this deque.  Call only when full, i.e.,
151	<	* when head and tail have wrapped around to become equal.
150	>	* Increases the internal storage of this collection, if necessary,
151	>	* to ensure that it can hold at least the given number of elements.
152	>	*
153	>	* @param minCapacity the desired minimum capacity
154	>	* @since TBD
155		*/
156	<	private void doubleCapacity() {
157	<	assert head == tail;
158	<	int p = head;
159	<	int n = elements.length;
160	<	int r = n - p; // number of elements to the right of p
123	<	int newCapacity = n << 1;
124	<	if (newCapacity < 0)
125	<	throw new IllegalStateException("Sorry, deque too big");
126	<	Object[] a = new Object[newCapacity];
127	<	System.arraycopy(elements, p, a, 0, r);
128	<	System.arraycopy(elements, 0, a, r, p);
129	<	elements = (E[])a;
130	<	head = 0;
131	<	tail = n;
156	>	/* public */ void ensureCapacity(int minCapacity) {
157	>	int needed;
158	>	if ((needed = (minCapacity + 1 - elements.length)) > 0)
159	>	grow(needed);
160	>	// checkInvariants();
161		}
162
163		/**
164	<	* 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.
164	>	* Minimizes the internal storage of this collection.
165		*
166	<	* @return its argument
166	>	* @since TBD
167		*/
168	<	private <T> T[] copyElements(T[] a) {
169	<	if (head < tail) {
170	<	System.arraycopy(elements, head, a, 0, size());
171	<	} else if (head > tail) {
172	<	int headPortionLen = elements.length - head;
173	<	System.arraycopy(elements, head, a, 0, headPortionLen);
147	<	System.arraycopy(elements, 0, a, headPortionLen, tail);
168	>	/* public */ void trimToSize() {
169	>	int size;
170	>	if ((size = size()) + 1 < elements.length) {
171	>	elements = toArray(new Object[size + 1]);
172	>	head = 0;
173	>	tail = size;
174		}
175	<	return a;
175	>	// checkInvariants();
176		}
177
178		/**
#	Line 154 | Line 180 | public class ArrayDeque<E> extends Abstr
180		* sufficient to hold 16 elements.
181		*/
182		public ArrayDeque() {
183	<	elements = (E[]) new Object[16];
183	>	elements = new Object[16];
184		}
185
186		/**
187		* Constructs an empty array deque with an initial capacity
188		* sufficient to hold the specified number of elements.
189		*
190	<	* @param numElements  lower bound on initial capacity of the deque
190	>	* @param numElements lower bound on initial capacity of the deque
191		*/
192		public ArrayDeque(int numElements) {
193	<	allocateElements(numElements);
193	>	elements =
194	>	new Object[(numElements < 1) ? 1 :
195	>	(numElements == Integer.MAX_VALUE) ? Integer.MAX_VALUE :
196	>	numElements + 1];
197		}
198
199		/**
#	Line 178 | Line 207 | public class ArrayDeque<E> extends Abstr
207		* @throws NullPointerException if the specified collection is null
208		*/
209		public ArrayDeque(Collection<? extends E> c) {
210	<	allocateElements(c.size());
210	>	this(c.size());
211		addAll(c);
212		}
213
214	+	/**
215	+	* Increments i, mod modulus.
216	+	* Precondition and postcondition: 0 <= i < modulus.
217	+	*/
218	+	static final int inc(int i, int modulus) {
219	+	if (++i >= modulus) i = 0;
220	+	return i;
221	+	}
222	+
223	+	/**
224	+	* Decrements i, mod modulus.
225	+	* Precondition and postcondition: 0 <= i < modulus.
226	+	*/
227	+	static final int dec(int i, int modulus) {
228	+	if (--i < 0) i = modulus - 1;
229	+	return i;
230	+	}
231	+
232	+	/**
233	+	* Circularly adds the given distance to index i, mod modulus.
234	+	* Precondition: 0 <= i < modulus, 0 <= distance <= modulus.
235	+	* @return index 0 <= i < modulus
236	+	*/
237	+	static final int add(int i, int distance, int modulus) {
238	+	if ((i += distance) - modulus >= 0) i -= modulus;
239	+	return i;
240	+	}
241	+
242	+	/**
243	+	* Subtracts j from i, mod modulus.
244	+	* Index i must be logically ahead of index j.
245	+	* Precondition: 0 <= i < modulus, 0 <= j < modulus.
246	+	* @return the "circular distance" from j to i; corner case i == j
247	+	* is diambiguated to "empty", returning 0.
248	+	*/
249	+	static final int sub(int i, int j, int modulus) {
250	+	if ((i -= j) < 0) i += modulus;
251	+	return i;
252	+	}
253	+
254	+	/**
255	+	* Returns element at array index i.
256	+	* This is a slight abuse of generics, accepted by javac.
257	+	*/
258	+	@SuppressWarnings("unchecked")
259	+	static final <E> E elementAt(Object[] es, int i) {
260	+	return (E) es[i];
261	+	}
262	+
263	+	/**
264	+	* A version of elementAt that checks for null elements.
265	+	* This check doesn't catch all possible comodifications,
266	+	* but does catch ones that corrupt traversal.
267	+	*/
268	+	static final <E> E nonNullElementAt(Object[] es, int i) {
269	+	@SuppressWarnings("unchecked") E e = (E) es[i];
270	+	if (e == null)
271	+	throw new ConcurrentModificationException();
272	+	return e;
273	+	}
274	+
275		// The main insertion and extraction methods are addFirst,
276		// addLast, pollFirst, pollLast. The other methods are defined in
277		// terms of these.
#	Line 195 | Line 285 | public class ArrayDeque<E> extends Abstr
285		public void addFirst(E e) {
286		if (e == null)
287		throw new NullPointerException();
288	<	elements[head = (head - 1) & (elements.length - 1)] = e;
288	>	final Object[] es = elements;
289	>	es[head = dec(head, es.length)] = e;
290		if (head == tail)
291	<	doubleCapacity();
291	>	grow(1);
292	>	// checkInvariants();
293		}
294
295		/**
#	Line 211 | Line 303 | public class ArrayDeque<E> extends Abstr
303		public void addLast(E e) {
304		if (e == null)
305		throw new NullPointerException();
306	<	elements[tail] = e;
307	<	if ( (tail = (tail + 1) & (elements.length - 1)) == head)
308	<	doubleCapacity();
306	>	final Object[] es = elements;
307	>	es[tail] = e;
308	>	if (head == (tail = inc(tail, es.length)))
309	>	grow(1);
310	>	// checkInvariants();
311	>	}
312	>
313	>	/**
314	>	* Adds all of the elements in the specified collection at the end
315	>	* of this deque, as if by calling {@link #addLast} on each one,
316	>	* in the order that they are returned by the collection's
317	>	* iterator.
318	>	*
319	>	* @param c the elements to be inserted into this deque
320	>	* @return {@code true} if this deque changed as a result of the call
321	>	* @throws NullPointerException if the specified collection or any
322	>	*         of its elements are null
323	>	*/
324	>	public boolean addAll(Collection<? extends E> c) {
325	>	final int s, needed;
326	>	if ((needed = (s = size()) + c.size() + 1 - elements.length) > 0)
327	>	grow(needed);
328	>	c.forEach(this::addLast);
329	>	// checkInvariants();
330	>	return size() > s;
331		}
332
333		/**
334		* Inserts the specified element at the front of this deque.
335		*
336		* @param e the element to add
337	<	* @return <tt>true</tt> (as specified by {@link Deque#offerFirst})
337	>	* @return {@code true} (as specified by {@link Deque#offerFirst})
338		* @throws NullPointerException if the specified element is null
339		*/
340		public boolean offerFirst(E e) {
#	Line 232 | Line 346 | public class ArrayDeque<E> extends Abstr
346		* Inserts the specified element at the end of this deque.
347		*
348		* @param e the element to add
349	<	* @return <tt>true</tt> (as specified by {@link Deque#offerLast})
349	>	* @return {@code true} (as specified by {@link Deque#offerLast})
350		* @throws NullPointerException if the specified element is null
351		*/
352		public boolean offerLast(E e) {
#	Line 244 | Line 358 | public class ArrayDeque<E> extends Abstr
358		* @throws NoSuchElementException {@inheritDoc}
359		*/
360		public E removeFirst() {
361	<	E x = pollFirst();
362	<	if (x == null)
361	>	E e = pollFirst();
362	>	if (e == null)
363		throw new NoSuchElementException();
364	<	return x;
364	>	// checkInvariants();
365	>	return e;
366		}
367
368		/**
369		* @throws NoSuchElementException {@inheritDoc}
370		*/
371		public E removeLast() {
372	<	E x = pollLast();
373	<	if (x == null)
372	>	E e = pollLast();
373	>	if (e == null)
374		throw new NoSuchElementException();
375	<	return x;
375	>	// checkInvariants();
376	>	return e;
377		}
378
379		public E pollFirst() {
380	<	int h = head;
381	<	E result = elements[h]; // Element is null if deque empty
382	<	if (result == null)
383	<	return null;
384	<	elements[h] = null;     // Must null out slot
385	<	head = (h + 1) & (elements.length - 1);
386	<	return result;
380	>	final Object[] es;
381	>	final int h;
382	>	E e = elementAt(es = elements, h = head);
383	>	if (e != null) {
384	>	es[h] = null;
385	>	head = inc(h, es.length);
386	>	}
387	>	// checkInvariants();
388	>	return e;
389		}
390
391		public E pollLast() {
392	<	int t = (tail - 1) & (elements.length - 1);
393	<	E result = elements[t];
394	<	if (result == null)
395	<	return null;
396	<	elements[t] = null;
397	<	tail = t;
398	<	return result;
392	>	final Object[] es;
393	>	final int t;
394	>	E e = elementAt(es = elements, t = dec(tail, es.length));
395	>	if (e != null)
396	>	es[tail = t] = null;
397	>	// checkInvariants();
398	>	return e;
399		}
400
401		/**
402		* @throws NoSuchElementException {@inheritDoc}
403		*/
404		public E getFirst() {
405	<	E x = elements[head];
406	<	if (x == null)
405	>	E e = elementAt(elements, head);
406	>	if (e == null)
407		throw new NoSuchElementException();
408	<	return x;
408	>	// checkInvariants();
409	>	return e;
410		}
411
412		/**
413		* @throws NoSuchElementException {@inheritDoc}
414		*/
415		public E getLast() {
416	<	E x = elements[(tail - 1) & (elements.length - 1)];
417	<	if (x == null)
416	>	final Object[] es = elements;
417	>	E e = elementAt(es, dec(tail, es.length));
418	>	if (e == null)
419		throw new NoSuchElementException();
420	<	return x;
420	>	// checkInvariants();
421	>	return e;
422		}
423
424		public E peekFirst() {
425	<	return elements[head]; // elements[head] is null if deque empty
425	>	// checkInvariants();
426	>	return elementAt(elements, head);
427		}
428
429		public E peekLast() {
430	<	return elements[(tail - 1) & (elements.length - 1)];
430	>	// checkInvariants();
431	>	final Object[] es;
432	>	return elementAt(es = elements, dec(tail, es.length));
433		}
434
435		/**
436		* Removes the first occurrence of the specified element in this
437		* deque (when traversing the deque from head to tail).
438		* If the deque does not contain the element, it is unchanged.
439	<	* More formally, removes the first element <tt>e</tt> such that
440	<	* <tt>o.equals(e)</tt> (if such an element exists).
441	<	* Returns <tt>true</tt> if this deque contained the specified element
439	>	* More formally, removes the first element {@code e} such that
440	>	* {@code o.equals(e)} (if such an element exists).
441	>	* Returns {@code true} if this deque contained the specified element
442		* (or equivalently, if this deque changed as a result of the call).
443		*
444		* @param o element to be removed from this deque, if present
445	<	* @return <tt>true</tt> if the deque contained the specified element
445	>	* @return {@code true} if the deque contained the specified element
446		*/
447		public boolean removeFirstOccurrence(Object o) {
448	<	if (o == null)
449	<	return false;
450	<	int mask = elements.length - 1;
451	<	int i = head;
452	<	E x;
453	<	while ( (x = elements[i]) != null) {
454	<	if (o.equals(x)) {
455	<	delete(i);
456	<	return true;
448	>	if (o != null) {
449	>	final Object[] es = elements;
450	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
451	>	; i = 0, to = end) {
452	>	for (; i < to; i++)
453	>	if (o.equals(es[i])) {
454	>	delete(i);
455	>	return true;
456	>	}
457	>	if (to == end) break;
458		}
334	–	i = (i + 1) & mask;
459		}
460		return false;
461		}
#	Line 340 | Line 464 | public class ArrayDeque<E> extends Abstr
464		* Removes the last occurrence of the specified element in this
465		* deque (when traversing the deque from head to tail).
466		* If the deque does not contain the element, it is unchanged.
467	<	* More formally, removes the last element <tt>e</tt> such that
468	<	* <tt>o.equals(e)</tt> (if such an element exists).
469	<	* Returns <tt>true</tt> if this deque contained the specified element
467	>	* More formally, removes the last element {@code e} such that
468	>	* {@code o.equals(e)} (if such an element exists).
469	>	* Returns {@code true} if this deque contained the specified element
470		* (or equivalently, if this deque changed as a result of the call).
471		*
472		* @param o element to be removed from this deque, if present
473	<	* @return <tt>true</tt> if the deque contained the specified element
473	>	* @return {@code true} if the deque contained the specified element
474		*/
475		public boolean removeLastOccurrence(Object o) {
476	<	if (o == null)
477	<	return false;
478	<	int mask = elements.length - 1;
479	<	int i = (tail - 1) & mask;
480	<	E x;
481	<	while ( (x = elements[i]) != null) {
482	<	if (o.equals(x)) {
483	<	delete(i);
484	<	return true;
476	>	if (o != null) {
477	>	final Object[] es = elements;
478	>	for (int i = tail, end = head, to = (i >= end) ? end : 0;
479	>	; i = es.length, to = end) {
480	>	for (i--; i > to - 1; i--)
481	>	if (o.equals(es[i])) {
482	>	delete(i);
483	>	return true;
484	>	}
485	>	if (to == end) break;
486		}
362	–	i = (i - 1) & mask;
487		}
488		return false;
489		}
#	Line 372 | Line 496 | public class ArrayDeque<E> extends Abstr
496		* <p>This method is equivalent to {@link #addLast}.
497		*
498		* @param e the element to add
499	<	* @return <tt>true</tt> (as specified by {@link Collection#add})
499	>	* @return {@code true} (as specified by {@link Collection#add})
500		* @throws NullPointerException if the specified element is null
501		*/
502		public boolean add(E e) {
#	Line 386 | Line 510 | public class ArrayDeque<E> extends Abstr
510		* <p>This method is equivalent to {@link #offerLast}.
511		*
512		* @param e the element to add
513	<	* @return <tt>true</tt> (as specified by {@link Queue#offer})
513	>	* @return {@code true} (as specified by {@link Queue#offer})
514		* @throws NullPointerException if the specified element is null
515		*/
516		public boolean offer(E e) {
#	Line 411 | Line 535 | public class ArrayDeque<E> extends Abstr
535		/**
536		* Retrieves and removes the head of the queue represented by this deque
537		* (in other words, the first element of this deque), or returns
538	<	* <tt>null</tt> if this deque is empty.
538	>	* {@code null} if this deque is empty.
539		*
540		* <p>This method is equivalent to {@link #pollFirst}.
541		*
542		* @return the head of the queue represented by this deque, or
543	<	*         <tt>null</tt> if this deque is empty
543	>	*         {@code null} if this deque is empty
544		*/
545		public E poll() {
546		return pollFirst();
#	Line 438 | Line 562 | public class ArrayDeque<E> extends Abstr
562
563		/**
564		* Retrieves, but does not remove, the head of the queue represented by
565	<	* this deque, or returns <tt>null</tt> if this deque is empty.
565	>	* this deque, or returns {@code null} if this deque is empty.
566		*
567		* <p>This method is equivalent to {@link #peekFirst}.
568		*
569		* @return the head of the queue represented by this deque, or
570	<	*         <tt>null</tt> if this deque is empty
570	>	*         {@code null} if this deque is empty
571		*/
572		public E peek() {
573		return peekFirst();
#	Line 478 | Line 602 | public class ArrayDeque<E> extends Abstr
602		return removeFirst();
603		}
604
481	–	private void checkInvariants() {
482	–	assert elements[tail] == null;
483	–	assert head == tail ? elements[head] == null :
484	–	(elements[head] != null &&
485	–	elements[(tail - 1) & (elements.length - 1)] != null);
486	–	assert elements[(head - 1) & (elements.length - 1)] == null;
487	–	}
488	–
605		/**
606	<	* Removes the element at the specified position in the elements array,
607	<	* adjusting head and tail as necessary.  This can result in motion of
608	<	* elements backwards or forwards in the array.
606	>	* Removes the element at the specified position in the elements array.
607	>	* This can result in forward or backwards motion of array elements.
608	>	* We optimize for least element motion.
609		*
610		* <p>This method is called delete rather than remove to emphasize
611		* that its semantics differ from those of {@link List#remove(int)}.
612		*
613	<	* @return true if elements moved backwards
613	>	* @return true if elements near tail moved backwards
614		*/
615	<	private boolean delete(int i) {
616	<	checkInvariants();
617	<	final E[] elements = this.elements;
618	<	final int mask = elements.length - 1;
619	<	final int h = head;
620	<	final int t = tail;
621	<	final int front = (i - h) & mask;
622	<	final int back  = (t - i) & mask;
623	<
508	<	// Invariant: head <= i < tail mod circularity
509	<	if (front >= ((t - h) & mask))
510	<	throw new ConcurrentModificationException();
511	<
512	<	// Optimize for least element motion
615	>	boolean delete(int i) {
616	>	// checkInvariants();
617	>	final Object[] es = elements;
618	>	final int capacity = es.length;
619	>	final int h, t;
620	>	// number of elements before to-be-deleted elt
621	>	final int front = sub(i, h = head, capacity);
622	>	// number of elements after to-be-deleted elt
623	>	final int back = sub(t = tail, i, capacity) - 1;
624		if (front < back) {
625	+	// move front elements forwards
626		if (h <= i) {
627	<	System.arraycopy(elements, h, elements, h + 1, front);
627	>	System.arraycopy(es, h, es, h + 1, front);
628		} else { // Wrap around
629	<	System.arraycopy(elements, 0, elements, 1, i);
630	<	elements[0] = elements[mask];
631	<	System.arraycopy(elements, h, elements, h + 1, mask - h);
629	>	System.arraycopy(es, 0, es, 1, i);
630	>	es[0] = es[capacity - 1];
631	>	System.arraycopy(es, h, es, h + 1, front - (i + 1));
632		}
633	<	elements[h] = null;
634	<	head = (h + 1) & mask;
633	>	es[h] = null;
634	>	head = inc(h, capacity);
635	>	// checkInvariants();
636		return false;
637		} else {
638	<	if (i < t) { // Copy the null tail as well
639	<	System.arraycopy(elements, i + 1, elements, i, back);
640	<	tail = t - 1;
638	>	// move back elements backwards
639	>	tail = dec(t, capacity);
640	>	if (i <= tail) {
641	>	System.arraycopy(es, i + 1, es, i, back);
642		} else { // Wrap around
643	<	System.arraycopy(elements, i + 1, elements, i, mask - i);
644	<	elements[mask] = elements[0];
645	<	System.arraycopy(elements, 1, elements, 0, t);
532	<	tail = (t - 1) & mask;
643	>	System.arraycopy(es, i + 1, es, i, capacity - (i + 1));
644	>	es[capacity - 1] = es[0];
645	>	System.arraycopy(es, 1, es, 0, t - 1);
646		}
647	+	es[tail] = null;
648	+	// checkInvariants();
649		return true;
650		}
651		}
#	Line 543 | Line 658 | public class ArrayDeque<E> extends Abstr
658		* @return the number of elements in this deque
659		*/
660		public int size() {
661	<	return (tail - head) & (elements.length - 1);
661	>	return sub(tail, head, elements.length);
662		}
663
664		/**
665	<	* Returns <tt>true</tt> if this deque contains no elements.
665	>	* Returns {@code true} if this deque contains no elements.
666		*
667	<	* @return <tt>true</tt> if this deque contains no elements
667	>	* @return {@code true} if this deque contains no elements
668		*/
669		public boolean isEmpty() {
670		return head == tail;
#	Line 572 | Line 687 | public class ArrayDeque<E> extends Abstr
687		}
688
689		private class DeqIterator implements Iterator<E> {
690	<	/**
691	<	* Index of element to be returned by subsequent call to next.
577	<	*/
578	<	private int cursor = head;
690	>	/** Index of element to be returned by subsequent call to next. */
691	>	int cursor;
692
693	<	/**
694	<	* Tail recorded at construction (also in remove), to stop
582	<	* iterator and also to check for comodification.
583	<	*/
584	<	private int fence = tail;
693	>	/** Number of elements yet to be returned. */
694	>	int remaining = size();
695
696		/**
697		* Index of element returned by most recent call to next.
698		* Reset to -1 if element is deleted by a call to remove.
699		*/
700	<	private int lastRet = -1;
700	>	int lastRet = -1;
701	>
702	>	DeqIterator() { cursor = head; }
703
704	<	public boolean hasNext() {
705	<	return cursor != fence;
704	>	public final boolean hasNext() {
705	>	return remaining > 0;
706		}
707
708		public E next() {
709	<	if (cursor == fence)
709	>	if (remaining <= 0)
710		throw new NoSuchElementException();
711	<	E result = elements[cursor];
712	<	// This check doesn't catch all possible comodifications,
713	<	// but does catch the ones that corrupt traversal
714	<	if (tail != fence || result == null)
715	<	throw new ConcurrentModificationException();
604	<	lastRet = cursor;
605	<	cursor = (cursor + 1) & (elements.length - 1);
606	<	return result;
711	>	final Object[] es = elements;
712	>	E e = nonNullElementAt(es, cursor);
713	>	cursor = inc(lastRet = cursor, es.length);
714	>	remaining--;
715	>	return e;
716		}
717
718	<	public void remove() {
718	>	void postDelete(boolean leftShifted) {
719	>	if (leftShifted)
720	>	cursor = dec(cursor, elements.length);
721	>	}
722	>
723	>	public final void remove() {
724		if (lastRet < 0)
725		throw new IllegalStateException();
726	<	if (delete(lastRet)) { // if left-shifted, undo increment in next()
613	<	cursor = (cursor - 1) & (elements.length - 1);
614	<	fence = tail;
615	<	}
726	>	postDelete(delete(lastRet));
727		lastRet = -1;
728		}
729	+
730	+	public void forEachRemaining(Consumer<? super E> action) {
731	+	Objects.requireNonNull(action);
732	+	int r;
733	+	if ((r = remaining) <= 0)
734	+	return;
735	+	remaining = 0;
736	+	final Object[] es = elements;
737	+	if (es[cursor] == null || sub(tail, cursor, es.length) != r)
738	+	throw new ConcurrentModificationException();
739	+	for (int i = cursor, end = tail, to = (i <= end) ? end : es.length;
740	+	; i = 0, to = end) {
741	+	for (; i < to; i++)
742	+	action.accept(elementAt(es, i));
743	+	if (to == end) {
744	+	if (end != tail)
745	+	throw new ConcurrentModificationException();
746	+	lastRet = dec(end, es.length);
747	+	break;
748	+	}
749	+	}
750	+	}
751		}
752
753	<	private class DescendingIterator implements Iterator<E> {
754	<	/*
622	<	* This class is nearly a mirror-image of DeqIterator, using
623	<	* tail instead of head for initial cursor, and head instead of
624	<	* tail for fence.
625	<	*/
626	<	private int cursor = tail;
627	<	private int fence = head;
628	<	private int lastRet = -1;
753	>	private class DescendingIterator extends DeqIterator {
754	>	DescendingIterator() { cursor = dec(tail, elements.length); }
755
756	<	public boolean hasNext() {
757	<	return cursor != fence;
756	>	public final E next() {
757	>	if (remaining <= 0)
758	>	throw new NoSuchElementException();
759	>	final Object[] es = elements;
760	>	E e = nonNullElementAt(es, cursor);
761	>	cursor = dec(lastRet = cursor, es.length);
762	>	remaining--;
763	>	return e;
764		}
765
766	<	public E next() {
767	<	if (cursor == fence)
768	<	throw new NoSuchElementException();
769	<	cursor = (cursor - 1) & (elements.length - 1);
770	<	E result = elements[cursor];
771	<	if (head != fence || result == null)
766	>	void postDelete(boolean leftShifted) {
767	>	if (!leftShifted)
768	>	cursor = inc(cursor, elements.length);
769	>	}
770	>
771	>	public final void forEachRemaining(Consumer<? super E> action) {
772	>	Objects.requireNonNull(action);
773	>	int r;
774	>	if ((r = remaining) <= 0)
775	>	return;
776	>	remaining = 0;
777	>	final Object[] es = elements;
778	>	if (es[cursor] == null || sub(cursor, head, es.length) + 1 != r)
779		throw new ConcurrentModificationException();
780	<	lastRet = cursor;
781	<	return result;
780	>	for (int i = cursor, end = head, to = (i >= end) ? end : 0;
781	>	; i = es.length - 1, to = end) {
782	>	// hotspot generates faster code than for: i >= to !
783	>	for (; i > to - 1; i--)
784	>	action.accept(elementAt(es, i));
785	>	if (to == end) {
786	>	if (end != head)
787	>	throw new ConcurrentModificationException();
788	>	lastRet = end;
789	>	break;
790	>	}
791	>	}
792		}
793	+	}
794
795	<	public void remove() {
796	<	if (lastRet < 0)
797	<	throw new IllegalStateException();
798	<	if (!delete(lastRet)) {
799	<	cursor = (cursor + 1) & (elements.length - 1);
800	<	fence = head;
795	>	/**
796	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
797	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
798	>	* deque.
799	>	*
800	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
801	>	* {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and
802	>	* {@link Spliterator#NONNULL}.  Overriding implementations should document
803	>	* the reporting of additional characteristic values.
804	>	*
805	>	* @return a {@code Spliterator} over the elements in this deque
806	>	* @since 1.8
807	>	*/
808	>	public Spliterator<E> spliterator() {
809	>	return new DeqSpliterator();
810	>	}
811	>
812	>	final class DeqSpliterator implements Spliterator<E> {
813	>	private int fence;      // -1 until first use
814	>	private int cursor;     // current index, modified on traverse/split
815	>
816	>	/** Constructs late-binding spliterator over all elements. */
817	>	DeqSpliterator() {
818	>	this.fence = -1;
819	>	}
820	>
821	>	/** Constructs spliterator over the given range. */
822	>	DeqSpliterator(int origin, int fence) {
823	>	// assert 0 <= origin && origin < elements.length;
824	>	// assert 0 <= fence && fence < elements.length;
825	>	this.cursor = origin;
826	>	this.fence = fence;
827	>	}
828	>
829	>	/** Ensures late-binding initialization; then returns fence. */
830	>	private int getFence() { // force initialization
831	>	int t;
832	>	if ((t = fence) < 0) {
833	>	t = fence = tail;
834	>	cursor = head;
835		}
836	<	lastRet = -1;
836	>	return t;
837	>	}
838	>
839	>	public DeqSpliterator trySplit() {
840	>	final Object[] es = elements;
841	>	final int i, n;
842	>	return ((n = sub(getFence(), i = cursor, es.length) >> 1) <= 0)
843	>	? null
844	>	: new DeqSpliterator(i, cursor = add(i, n, es.length));
845	>	}
846	>
847	>	public void forEachRemaining(Consumer<? super E> action) {
848	>	if (action == null)
849	>	throw new NullPointerException();
850	>	final int end = getFence(), cursor = this.cursor;
851	>	final Object[] es = elements;
852	>	if (cursor != end) {
853	>	this.cursor = end;
854	>	// null check at both ends of range is sufficient
855	>	if (es[cursor] == null || es[dec(end, es.length)] == null)
856	>	throw new ConcurrentModificationException();
857	>	for (int i = cursor, to = (i <= end) ? end : es.length;
858	>	; i = 0, to = end) {
859	>	for (; i < to; i++)
860	>	action.accept(elementAt(es, i));
861	>	if (to == end) break;
862	>	}
863	>	}
864	>	}
865	>
866	>	public boolean tryAdvance(Consumer<? super E> action) {
867	>	Objects.requireNonNull(action);
868	>	final Object[] es = elements;
869	>	if (fence < 0) { fence = tail; cursor = head; } // late-binding
870	>	final int i;
871	>	if ((i = cursor) == fence)
872	>	return false;
873	>	E e = nonNullElementAt(es, i);
874	>	cursor = inc(i, es.length);
875	>	action.accept(e);
876	>	return true;
877	>	}
878	>
879	>	public long estimateSize() {
880	>	return sub(getFence(), cursor, elements.length);
881	>	}
882	>
883	>	public int characteristics() {
884	>	return Spliterator.NONNULL
885	>	| Spliterator.ORDERED
886	>	| Spliterator.SIZED
887	>	| Spliterator.SUBSIZED;
888		}
889		}
890
891	+	public void forEach(Consumer<? super E> action) {
892	+	Objects.requireNonNull(action);
893	+	final Object[] es = elements;
894	+	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
895	+	; i = 0, to = end) {
896	+	for (; i < to; i++)
897	+	action.accept(elementAt(es, i));
898	+	if (to == end) {
899	+	if (end != tail) throw new ConcurrentModificationException();
900	+	break;
901	+	}
902	+	}
903	+	// checkInvariants();
904	+	}
905	+
906		/**
907	<	* Returns <tt>true</tt> if this deque contains the specified element.
908	<	* More formally, returns <tt>true</tt> if and only if this deque contains
909	<	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
907	>	* Replaces each element of this deque with the result of applying the
908	>	* operator to that element, as specified by {@link List#replaceAll}.
909	>	*
910	>	* @param operator the operator to apply to each element
911	>	* @since TBD
912	>	*/
913	>	/* public */ void replaceAll(UnaryOperator<E> operator) {
914	>	Objects.requireNonNull(operator);
915	>	final Object[] es = elements;
916	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
917	>	; i = 0, to = end) {
918	>	for (; i < to; i++)
919	>	es[i] = operator.apply(elementAt(es, i));
920	>	if (to == end) {
921	>	if (end != tail) throw new ConcurrentModificationException();
922	>	break;
923	>	}
924	>	}
925	>	// checkInvariants();
926	>	}
927	>
928	>	/**
929	>	* @throws NullPointerException {@inheritDoc}
930	>	*/
931	>	public boolean removeIf(Predicate<? super E> filter) {
932	>	Objects.requireNonNull(filter);
933	>	return bulkRemove(filter);
934	>	}
935	>
936	>	/**
937	>	* @throws NullPointerException {@inheritDoc}
938	>	*/
939	>	public boolean removeAll(Collection<?> c) {
940	>	Objects.requireNonNull(c);
941	>	return bulkRemove(e -> c.contains(e));
942	>	}
943	>
944	>	/**
945	>	* @throws NullPointerException {@inheritDoc}
946	>	*/
947	>	public boolean retainAll(Collection<?> c) {
948	>	Objects.requireNonNull(c);
949	>	return bulkRemove(e -> !c.contains(e));
950	>	}
951	>
952	>	/** Implementation of bulk remove methods. */
953	>	private boolean bulkRemove(Predicate<? super E> filter) {
954	>	// checkInvariants();
955	>	final Object[] es = elements;
956	>	// Optimize for initial run of survivors
957	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
958	>	; i = 0, to = end) {
959	>	for (; i < to; i++)
960	>	if (filter.test(elementAt(es, i)))
961	>	return bulkRemoveModified(filter, i);
962	>	if (to == end) {
963	>	if (end != tail) throw new ConcurrentModificationException();
964	>	break;
965	>	}
966	>	}
967	>	return false;
968	>	}
969	>
970	>	// A tiny bit set implementation
971	>
972	>	private static long[] nBits(int n) {
973	>	return new long[((n - 1) >> 6) + 1];
974	>	}
975	>	private static void setBit(long[] bits, int i) {
976	>	bits[i >> 6] |= 1L << i;
977	>	}
978	>	private static boolean isClear(long[] bits, int i) {
979	>	return (bits[i >> 6] & (1L << i)) == 0;
980	>	}
981	>
982	>	/**
983	>	* Helper for bulkRemove, in case of at least one deletion.
984	>	* Tolerate predicates that reentrantly access the collection for
985	>	* read (but writers still get CME), so traverse once to find
986	>	* elements to delete, a second pass to physically expunge.
987	>	*
988	>	* @param beg valid index of first element to be deleted
989	>	*/
990	>	private boolean bulkRemoveModified(
991	>	Predicate<? super E> filter, final int beg) {
992	>	final Object[] es = elements;
993	>	final int capacity = es.length;
994	>	final int end = tail;
995	>	final long[] deathRow = nBits(sub(end, beg, capacity));
996	>	deathRow[0] = 1L;   // set bit 0
997	>	for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg;
998	>	; i = 0, to = end, k -= capacity) {
999	>	for (; i < to; i++)
1000	>	if (filter.test(elementAt(es, i)))
1001	>	setBit(deathRow, i - k);
1002	>	if (to == end) break;
1003	>	}
1004	>	// a two-finger traversal, with hare i reading, tortoise w writing
1005	>	int w = beg;
1006	>	for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg;
1007	>	; w = 0) { // w rejoins i on second leg
1008	>	// In this loop, i and w are on the same leg, with i > w
1009	>	for (; i < to; i++)
1010	>	if (isClear(deathRow, i - k))
1011	>	es[w++] = es[i];
1012	>	if (to == end) break;
1013	>	// In this loop, w is on the first leg, i on the second
1014	>	for (i = 0, to = end, k -= capacity; i < to && w < capacity; i++)
1015	>	if (isClear(deathRow, i - k))
1016	>	es[w++] = es[i];
1017	>	if (i >= to) {
1018	>	if (w == capacity) w = 0; // "corner" case
1019	>	break;
1020	>	}
1021	>	}
1022	>	if (end != tail) throw new ConcurrentModificationException();
1023	>	circularClear(es, tail = w, end);
1024	>	// checkInvariants();
1025	>	return true;
1026	>	}
1027	>
1028	>	/**
1029	>	* Returns {@code true} if this deque contains the specified element.
1030	>	* More formally, returns {@code true} if and only if this deque contains
1031	>	* at least one element {@code e} such that {@code o.equals(e)}.
1032		*
1033		* @param o object to be checked for containment in this deque
1034	<	* @return <tt>true</tt> if this deque contains the specified element
1034	>	* @return {@code true} if this deque contains the specified element
1035		*/
1036		public boolean contains(Object o) {
1037	<	if (o == null)
1038	<	return false;
1039	<	int mask = elements.length - 1;
1040	<	int i = head;
1041	<	E x;
1042	<	while ( (x = elements[i]) != null) {
1043	<	if (o.equals(x))
1044	<	return true;
1045	<	i = (i + 1) & mask;
1037	>	if (o != null) {
1038	>	final Object[] es = elements;
1039	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
1040	>	; i = 0, to = end) {
1041	>	for (; i < to; i++)
1042	>	if (o.equals(es[i]))
1043	>	return true;
1044	>	if (to == end) break;
1045	>	}
1046		}
1047		return false;
1048		}
#	Line 678 | Line 1050 | public class ArrayDeque<E> extends Abstr
1050		/**
1051		* Removes a single instance of the specified element from this deque.
1052		* If the deque does not contain the element, it is unchanged.
1053	<	* More formally, removes the first element <tt>e</tt> such that
1054	<	* <tt>o.equals(e)</tt> (if such an element exists).
1055	<	* Returns <tt>true</tt> if this deque contained the specified element
1053	>	* More formally, removes the first element {@code e} such that
1054	>	* {@code o.equals(e)} (if such an element exists).
1055	>	* Returns {@code true} if this deque contained the specified element
1056		* (or equivalently, if this deque changed as a result of the call).
1057		*
1058	<	* <p>This method is equivalent to {@link #removeFirstOccurrence}.
1058	>	* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
1059		*
1060		* @param o element to be removed from this deque, if present
1061	<	* @return <tt>true</tt> if this deque contained the specified element
1061	>	* @return {@code true} if this deque contained the specified element
1062		*/
1063		public boolean remove(Object o) {
1064		return removeFirstOccurrence(o);
#	Line 697 | Line 1069 | public class ArrayDeque<E> extends Abstr
1069		* The deque will be empty after this call returns.
1070		*/
1071		public void clear() {
1072	<	int h = head;
1073	<	int t = tail;
1074	<	if (h != t) { // clear all cells
1075	<	head = tail = 0;
1076	<	int i = h;
1077	<	int mask = elements.length - 1;
1078	<	do {
1079	<	elements[i] = null;
1080	<	i = (i + 1) & mask;
1081	<	} while (i != t);
1072	>	circularClear(elements, head, tail);
1073	>	head = tail = 0;
1074	>	// checkInvariants();
1075	>	}
1076	>
1077	>	/**
1078	>	* Nulls out slots starting at array index i, upto index end.
1079	>	*/
1080	>	private static void circularClear(Object[] es, int i, int end) {
1081	>	for (int to = (i <= end) ? end : es.length;
1082	>	; i = 0, to = end) {
1083	>	Arrays.fill(es, i, to, null);
1084	>	if (to == end) break;
1085		}
1086		}
1087
#	Line 724 | Line 1099 | public class ArrayDeque<E> extends Abstr
1099		* @return an array containing all of the elements in this deque
1100		*/
1101		public Object[] toArray() {
1102	<	return copyElements(new Object[size()]);
1102	>	return toArray(Object[].class);
1103	>	}
1104	>
1105	>	private <T> T[] toArray(Class<T[]> klazz) {
1106	>	final Object[] es = elements;
1107	>	final T[] a;
1108	>	final int head = this.head, tail = this.tail, end;
1109	>	if ((end = tail + ((head <= tail) ? 0 : es.length)) >= 0) {
1110	>	// Uses null extension feature of copyOfRange
1111	>	a = Arrays.copyOfRange(es, head, end, klazz);
1112	>	} else {
1113	>	// integer overflow!
1114	>	a = Arrays.copyOfRange(es, 0, end - head, klazz);
1115	>	System.arraycopy(es, head, a, 0, es.length - head);
1116	>	}
1117	>	if (end != tail)
1118	>	System.arraycopy(es, 0, a, es.length - head, tail);
1119	>	return a;
1120		}
1121
1122		/**
#	Line 738 | Line 1130 | public class ArrayDeque<E> extends Abstr
1130		* <p>If this deque fits in the specified array with room to spare
1131		* (i.e., the array has more elements than this deque), the element in
1132		* the array immediately following the end of the deque is set to
1133	<	* <tt>null</tt>.
1133	>	* {@code null}.
1134		*
1135		* <p>Like the {@link #toArray()} method, this method acts as bridge between
1136		* array-based and collection-based APIs.  Further, this method allows
1137		* precise control over the runtime type of the output array, and may,
1138		* under certain circumstances, be used to save allocation costs.
1139		*
1140	<	* <p>Suppose <tt>x</tt> is a deque known to contain only strings.
1140	>	* <p>Suppose {@code x} is a deque known to contain only strings.
1141		* The following code can be used to dump the deque into a newly
1142	<	* allocated array of <tt>String</tt>:
1142	>	* allocated array of {@code String}:
1143		*
1144	<	* <pre>
753	<	*     String[] y = x.toArray(new String[0]);</pre>
1144	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
1145		*
1146	<	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
1147	<	* <tt>toArray()</tt>.
1146	>	* Note that {@code toArray(new Object[0])} is identical in function to
1147	>	* {@code toArray()}.
1148		*
1149		* @param a the array into which the elements of the deque are to
1150		*          be stored, if it is big enough; otherwise, a new array of the
#	Line 764 | Line 1155 | public class ArrayDeque<E> extends Abstr
1155		*         this deque
1156		* @throws NullPointerException if the specified array is null
1157		*/
1158	+	@SuppressWarnings("unchecked")
1159		public <T> T[] toArray(T[] a) {
1160	<	int size = size();
1161	<	if (a.length < size)
1162	<	a = (T[])java.lang.reflect.Array.newInstance(
1163	<	a.getClass().getComponentType(), size);
1164	<	copyElements(a);
1165	<	if (a.length > size)
1160	>	final int size;
1161	>	if ((size = size()) > a.length)
1162	>	return toArray((Class<T[]>) a.getClass());
1163	>	final Object[] es = elements;
1164	>	for (int i = head, j = 0, len = Math.min(size, es.length - i);
1165	>	; i = 0, len = tail) {
1166	>	System.arraycopy(es, i, a, j, len);
1167	>	if ((j += len) == size) break;
1168	>	}
1169	>	if (size < a.length)
1170		a[size] = null;
1171		return a;
1172		}
#	Line 784 | Line 1180 | public class ArrayDeque<E> extends Abstr
1180		*/
1181		public ArrayDeque<E> clone() {
1182		try {
1183	+	@SuppressWarnings("unchecked")
1184		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
1185		result.elements = Arrays.copyOf(elements, elements.length);
1186		return result;
790	–
1187		} catch (CloneNotSupportedException e) {
1188		throw new AssertionError();
1189		}
1190		}
1191
796	–	/**
797	–	* Appease the serialization gods.
798	–	*/
1192		private static final long serialVersionUID = 2340985798034038923L;
1193
1194		/**
1195	<	* Serialize this deque.
1195	>	* Saves this deque to a stream (that is, serializes it).
1196		*
1197	<	* @serialData The current size (<tt>int</tt>) of the deque,
1197	>	* @param s the stream
1198	>	* @throws java.io.IOException if an I/O error occurs
1199	>	* @serialData The current size ({@code int}) of the deque,
1200		* followed by all of its elements (each an object reference) in
1201		* first-to-last order.
1202		*/
1203	<	private void writeObject(ObjectOutputStream s) throws IOException {
1203	>	private void writeObject(java.io.ObjectOutputStream s)
1204	>	throws java.io.IOException {
1205		s.defaultWriteObject();
1206
1207		// Write out size
1208		s.writeInt(size());
1209
1210		// Write out elements in order.
1211	<	int mask = elements.length - 1;
1212	<	for (int i = head; i != tail; i = (i + 1) & mask)
1213	<	s.writeObject(elements[i]);
1211	>	final Object[] es = elements;
1212	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
1213	>	; i = 0, to = end) {
1214	>	for (; i < to; i++)
1215	>	s.writeObject(es[i]);
1216	>	if (to == end) break;
1217	>	}
1218		}
1219
1220		/**
1221	<	* Deserialize this deque.
1221	>	* Reconstitutes this deque from a stream (that is, deserializes it).
1222	>	* @param s the stream
1223	>	* @throws ClassNotFoundException if the class of a serialized object
1224	>	*         could not be found
1225	>	* @throws java.io.IOException if an I/O error occurs
1226		*/
1227	<	private void readObject(ObjectInputStream s)
1228	<	throws IOException, ClassNotFoundException {
1227	>	private void readObject(java.io.ObjectInputStream s)
1228	>	throws java.io.IOException, ClassNotFoundException {
1229		s.defaultReadObject();
1230
1231		// Read in size and allocate array
1232		int size = s.readInt();
1233	<	allocateElements(size);
1234	<	head = 0;
831	<	tail = size;
1233	>	elements = new Object[size + 1];
1234	>	this.tail = size;
1235
1236		// Read in all elements in the proper order.
1237		for (int i = 0; i < size; i++)
1238	<	elements[i] = (E)s.readObject();
1238	>	elements[i] = s.readObject();
1239		}
1240	+
1241	+	/** debugging */
1242	+	void checkInvariants() {
1243	+	// Use head and tail fields with empty slot at tail strategy.
1244	+	// head == tail disambiguates to "empty".
1245	+	try {
1246	+	int capacity = elements.length;
1247	+	// assert 0 <= head && head < capacity;
1248	+	// assert 0 <= tail && tail < capacity;
1249	+	// assert capacity > 0;
1250	+	// assert size() < capacity;
1251	+	// assert head == tail || elements[head] != null;
1252	+	// assert elements[tail] == null;
1253	+	// assert head == tail || elements[dec(tail, capacity)] != null;
1254	+	} catch (Throwable t) {
1255	+	System.err.printf("head=%d tail=%d capacity=%d%n",
1256	+	head, tail, elements.length);
1257	+	System.err.printf("elements=%s%n",
1258	+	Arrays.toString(elements));
1259	+	throw t;
1260	+	}
1261	+	}
1262	+
1263		}

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