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Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.19 by dl, Fri Sep 16 11:15:41 2005 UTC vs.
Revision 1.108 by jsr166, Sat Nov 5 14:41:14 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.util.*; // for javadoc (till 6280605 is fixed)
8	<	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 16 | 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 35 | 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 45 | Line 50 | import java.io.*;
50		* Iterator} interfaces.
51		*
52		* <p>This class is a member of the
53	<	* <a href="{@docRoot}/../guide/collections/index.html">
53	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
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
53	–	* @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.
72	+	*/
73	+
74		/**
75		* The array in which the elements of the deque are stored.
76	<	* The capacity of the deque is the length of this array, which is
77	<	* always a power of two. The array is never allowed to become
62	<	* full, except transiently within an addX method where it is
63	<	* resized (see doubleCapacity) immediately upon becoming full,
64	<	* thus avoiding head and tail wrapping around to equal each
65	<	* other.  We also guarantee that all array cells not holding
66	<	* deque elements are always null.
76	>	* We guarantee that all array cells not holding deque elements
77	>	* are always null.
78		*/
79	<	private transient E[] elements;
79	>	transient Object[] elements;
80
81		/**
82		* The index of the element at the head of the deque (which is the
83		* element that would be removed by remove() or pop()); or an
84	<	* arbitrary number equal to tail if the deque is empty.
84	>	* arbitrary number 0 <= head < elements.length equal to tail if
85	>	* the deque is empty.
86		*/
87	<	private transient int head;
87	>	transient int head;
88
89		/**
90		* The index at which the next element would be added to the tail
91		* of the deque (via addLast(E), add(E), or push(E)).
92		*/
93	<	private transient int tail;
82	<
83	<	/**
84	<	* The minimum capacity that we'll use for a newly created deque.
85	<	* Must be a power of 2.
86	<	*/
87	<	private static final int MIN_INITIAL_CAPACITY = 8;
88	<
89	<	// ******  Array allocation and resizing utilities ******
93	>	transient int tail;
94
95		/**
96	<	* Allocate empty array to hold the given number of elements.
97	<	*
98	<	* @param numElements  the number of elements to hold
99	<	*/
100	<	private void allocateElements(int numElements) {
101	<	int initialCapacity = MIN_INITIAL_CAPACITY;
102	<	// Find the best power of two to hold elements.
103	<	// Tests "<=" because arrays aren't kept full.
104	<	if (numElements >= initialCapacity) {
105	<	initialCapacity = numElements;
106	<	initialCapacity |= (initialCapacity >>>  1);
107	<	initialCapacity |= (initialCapacity >>>  2);
108	<	initialCapacity |= (initialCapacity >>>  4);
109	<	initialCapacity |= (initialCapacity >>>  8);
110	<	initialCapacity |= (initialCapacity >>> 16);
111	<	initialCapacity++;
96	>	* The maximum size of array to allocate.
97	>	* Some VMs reserve some header words in an array.
98	>	* Attempts to allocate larger arrays may result in
99	>	* OutOfMemoryError: Requested array size exceeds VM limit
100	>	*/
101	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
102	>
103	>	/**
104	>	* Increases the capacity of this deque by at least the given amount.
105	>	*
106	>	* @param needed the required minimum extra capacity; must be positive
107	>	*/
108	>	private void grow(int needed) {
109	>	// overflow-conscious code
110	>	final int oldCapacity = elements.length;
111	>	int newCapacity;
112	>	// Double capacity if small; else grow by 50%
113	>	int jump = (oldCapacity < 64) ? (oldCapacity + 2) : (oldCapacity >> 1);
114	>	if (jump < needed
115	>	|| (newCapacity = (oldCapacity + jump)) - MAX_ARRAY_SIZE > 0)
116	>	newCapacity = newCapacity(needed, jump);
117	>	elements = Arrays.copyOf(elements, newCapacity);
118	>	// Exceptionally, here tail == head needs to be disambiguated
119	>	if (tail < head || (tail == head && elements[head] != null)) {
120	>	// wrap around; slide first leg forward to end of array
121	>	int newSpace = newCapacity - oldCapacity;
122	>	System.arraycopy(elements, head,
123	>	elements, head + newSpace,
124	>	oldCapacity - head);
125	>	Arrays.fill(elements, head, head + newSpace, null);
126	>	head += newSpace;
127	>	}
128	>	// checkInvariants();
129	>	}
130
131	<	if (initialCapacity < 0)   // Too many elements, must back off
132	<	initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
131	>	/** Capacity calculation for edge conditions, especially overflow. */
132	>	private int newCapacity(int needed, int jump) {
133	>	final int oldCapacity = elements.length, minCapacity;
134	>	if ((minCapacity = oldCapacity + needed) - MAX_ARRAY_SIZE > 0) {
135	>	if (minCapacity < 0)
136	>	throw new IllegalStateException("Sorry, deque too big");
137	>	return Integer.MAX_VALUE;
138		}
139	<	elements = (E[]) new Object[initialCapacity];
139	>	if (needed > jump)
140	>	return minCapacity;
141	>	return (oldCapacity + jump - MAX_ARRAY_SIZE < 0)
142	>	? oldCapacity + jump
143	>	: MAX_ARRAY_SIZE;
144		}
145
146		/**
147	<	* Double the capacity of this deque.  Call only when full, i.e.,
148	<	* when head and tail have wrapped around to become equal.
147	>	* Increases the internal storage of this collection, if necessary,
148	>	* to ensure that it can hold at least the given number of elements.
149	>	*
150	>	* @param minCapacity the desired minimum capacity
151	>	* @since TBD
152		*/
153	<	private void doubleCapacity() {
154	<	assert head == tail;
155	<	int p = head;
156	<	int n = elements.length;
157	<	int r = n - p; // number of elements to the right of p
124	<	int newCapacity = n << 1;
125	<	if (newCapacity < 0)
126	<	throw new IllegalStateException("Sorry, deque too big");
127	<	Object[] a = new Object[newCapacity];
128	<	System.arraycopy(elements, p, a, 0, r);
129	<	System.arraycopy(elements, 0, a, r, p);
130	<	elements = (E[])a;
131	<	head = 0;
132	<	tail = n;
153	>	/* public */ void ensureCapacity(int minCapacity) {
154	>	int needed;
155	>	if ((needed = (minCapacity + 1 - elements.length)) > 0)
156	>	grow(needed);
157	>	// checkInvariants();
158		}
159
160		/**
161	<	* Copies the elements from our element array into the specified array,
137	<	* in order (from first to last element in the deque).  It is assumed
138	<	* that the array is large enough to hold all elements in the deque.
161	>	* Minimizes the internal storage of this collection.
162		*
163	<	* @return its argument
163	>	* @since TBD
164		*/
165	<	private <T> T[] copyElements(T[] a) {
166	<	if (head < tail) {
167	<	System.arraycopy(elements, head, a, 0, size());
168	<	} else if (head > tail) {
169	<	int headPortionLen = elements.length - head;
170	<	System.arraycopy(elements, head, a, 0, headPortionLen);
148	<	System.arraycopy(elements, 0, a, headPortionLen, tail);
165	>	/* public */ void trimToSize() {
166	>	int size;
167	>	if ((size = size()) + 1 < elements.length) {
168	>	elements = toArray(new Object[size + 1]);
169	>	head = 0;
170	>	tail = size;
171		}
172	<	return a;
172	>	// checkInvariants();
173		}
174
175		/**
#	Line 155 | Line 177 | public class ArrayDeque<E> extends Abstr
177		* sufficient to hold 16 elements.
178		*/
179		public ArrayDeque() {
180	<	elements = (E[]) new Object[16];
180	>	elements = new Object[16];
181		}
182
183		/**
184		* Constructs an empty array deque with an initial capacity
185		* sufficient to hold the specified number of elements.
186		*
187	<	* @param numElements  lower bound on initial capacity of the deque
187	>	* @param numElements lower bound on initial capacity of the deque
188		*/
189		public ArrayDeque(int numElements) {
190	<	allocateElements(numElements);
190	>	elements = new Object[Math.max(1, numElements + 1)];
191		}
192
193		/**
#	Line 179 | Line 201 | public class ArrayDeque<E> extends Abstr
201		* @throws NullPointerException if the specified collection is null
202		*/
203		public ArrayDeque(Collection<? extends E> c) {
204	<	allocateElements(c.size());
204	>	elements = new Object[c.size() + 1];
205		addAll(c);
206		}
207
208	+	/**
209	+	* Increments i, mod modulus.
210	+	* Precondition and postcondition: 0 <= i < modulus.
211	+	*/
212	+	static final int inc(int i, int modulus) {
213	+	if (++i >= modulus) i = 0;
214	+	return i;
215	+	}
216	+
217	+	/**
218	+	* Decrements i, mod modulus.
219	+	* Precondition and postcondition: 0 <= i < modulus.
220	+	*/
221	+	static final int dec(int i, int modulus) {
222	+	if (--i < 0) i = modulus - 1;
223	+	return i;
224	+	}
225	+
226	+	/**
227	+	* Adds i and j, mod modulus.
228	+	* Precondition and postcondition: 0 <= i < modulus, 0 <= j <= modulus.
229	+	*/
230	+	static final int add(int i, int j, int modulus) {
231	+	if ((i += j) - modulus >= 0) i -= modulus;
232	+	return i;
233	+	}
234	+
235	+	/**
236	+	* Subtracts j from i, mod modulus.
237	+	* Index i must be logically ahead of j.
238	+	* Returns the "circular distance" from j to i.
239	+	* Precondition and postcondition: 0 <= i < modulus, 0 <= j < modulus.
240	+	*/
241	+	static final int sub(int i, int j, int modulus) {
242	+	if ((i -= j) < 0) i += modulus;
243	+	return i;
244	+	}
245	+
246	+	/**
247	+	* Returns the array index of the last element.
248	+	* May return invalid index -1 if there are no elements.
249	+	*/
250	+	final int last() {
251	+	return dec(tail, elements.length);
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 196 | 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 212 | 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 = size(), needed;
326	>	if ((needed = s + c.size() - elements.length + 1) > 0)
327	>	grow(needed);
328	>	c.forEach((e) -> addLast(e));
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 233 | 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 245 | 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		}
335	–	i = (i + 1) & mask;
459		}
460		return false;
461		}
#	Line 341 | 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	>	while (--i >= to)
481	>	if (o.equals(es[i])) {
482	>	delete(i);
483	>	return true;
484	>	}
485	>	if (to == end) break;
486		}
363	–	i = (i - 1) & mask;
487		}
488		return false;
489		}
#	Line 373 | 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 387 | 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 412 | 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 439 | 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 480 | Line 603 | public class ArrayDeque<E> extends Abstr
603		}
604
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	<	int mask = elements.length - 1;
617	<
618	<	// Invariant: head <= i < tail mod circularity
619	<	if (((i - head) & mask) >= ((tail - head) & mask))
620	<	throw new ConcurrentModificationException();
621	<
622	<	// Case 1: Deque doesn't wrap
623	<	// Case 2: Deque does wrap and removed element is in the head portion
624	<	if (i >= head) {
625	<	System.arraycopy(elements, head, elements, head + 1, i - head);
626	<	elements[head] = null;
627	<	head = (head + 1) & mask;
615	>	boolean delete(int i) {
616	>	// checkInvariants();
617	>	final Object[] es = elements;
618	>	final int capacity = es.length;
619	>	final int h = head;
620	>	// number of elements before to-be-deleted elt
621	>	final int front = sub(i, h, capacity);
622	>	final int back = size() - front - 1; // number of elements after
623	>	if (front < back) {
624	>	// move front elements forwards
625	>	if (h <= i) {
626	>	System.arraycopy(es, h, es, h + 1, front);
627	>	} else { // Wrap around
628	>	System.arraycopy(es, 0, es, 1, i);
629	>	es[0] = es[capacity - 1];
630	>	System.arraycopy(es, h, es, h + 1, front - (i + 1));
631	>	}
632	>	es[h] = null;
633	>	head = inc(h, capacity);
634	>	// checkInvariants();
635		return false;
636	+	} else {
637	+	// move back elements backwards
638	+	tail = dec(tail, capacity);
639	+	if (i <= tail) {
640	+	System.arraycopy(es, i + 1, es, i, back);
641	+	} else { // Wrap around
642	+	int firstLeg = capacity - (i + 1);
643	+	System.arraycopy(es, i + 1, es, i, firstLeg);
644	+	es[capacity - 1] = es[0];
645	+	System.arraycopy(es, 1, es, 0, back - firstLeg - 1);
646	+	}
647	+	es[tail] = null;
648	+	// checkInvariants();
649	+	return true;
650		}
507	–
508	–	// Case 3: Deque wraps and removed element is in the tail portion
509	–	tail--;
510	–	System.arraycopy(elements, i + 1, elements, i, tail - i);
511	–	elements[tail] = null;
512	–	return true;
651		}
652
653		// *** Collection Methods ***
#	Line 520 | 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 549 | 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.
554	<	*/
555	<	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
559	<	* iterator and also to check for comodification.
560	<	*/
561	<	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	<	E result;
575	<	if (cursor == fence)
709	>	if (remaining <= 0)
710		throw new NoSuchElementException();
711	<	// This check doesn't catch all possible comodifications,
712	<	// but does catch the ones that corrupt traversal
579	<	if (tail != fence || (result = elements[cursor]) == null)
580	<	throw new ConcurrentModificationException();
711	>	final Object[] es = elements;
712	>	E e = nonNullElementAt(es, cursor);
713		lastRet = cursor;
714	<	cursor = (cursor + 1) & (elements.length - 1);
715	<	return result;
714	>	cursor = inc(cursor, es.length);
715	>	remaining--;
716	>	return e;
717	>	}
718	>
719	>	void postDelete(boolean leftShifted) {
720	>	if (leftShifted)
721	>	cursor = dec(cursor, elements.length);
722		}
723
724	<	public void remove() {
724	>	public final void remove() {
725		if (lastRet < 0)
726		throw new IllegalStateException();
727	<	if (delete(lastRet)) // if left-shifted, undo increment in next()
590	<	cursor = (cursor - 1) & (elements.length - 1);
727	>	postDelete(delete(lastRet));
728		lastRet = -1;
729	<	fence = tail;
729	>	}
730	>
731	>	public void forEachRemaining(Consumer<? super E> action) {
732	>	Objects.requireNonNull(action);
733	>	int r;
734	>	if ((r = remaining) <= 0)
735	>	return;
736	>	remaining = 0;
737	>	final Object[] es = elements;
738	>	if (es[cursor] == null || sub(tail, cursor, es.length) != r)
739	>	throw new ConcurrentModificationException();
740	>	for (int i = cursor, end = tail, to = (i <= end) ? end : es.length;
741	>	; i = 0, to = end) {
742	>	for (; i < to; i++)
743	>	action.accept(elementAt(es, i));
744	>	if (to == end) {
745	>	if (end != tail)
746	>	throw new ConcurrentModificationException();
747	>	lastRet = dec(end, es.length);
748	>	break;
749	>	}
750	>	}
751		}
752		}
753
754	+	private class DescendingIterator extends DeqIterator {
755	+	DescendingIterator() { cursor = last(); }
756
757	<	private class DescendingIterator implements Iterator<E> {
758	<	/*
759	<	* This class is nearly a mirror-image of DeqIterator, using
760	<	* (tail-1) instead of head for initial cursor, (head-1)
761	<	* instead of tail for fence, and elements.length instead of -1
762	<	* for sentinel. It shares the same structure, but not many
763	<	* actual lines of code.
764	<	*/
765	<	private int cursor = (tail - 1) & (elements.length - 1);
766	<	private int fence =  (head - 1) & (elements.length - 1);
607	<	private int lastRet = elements.length;
757	>	public final E next() {
758	>	if (remaining <= 0)
759	>	throw new NoSuchElementException();
760	>	final Object[] es = elements;
761	>	E e = nonNullElementAt(es, cursor);
762	>	lastRet = cursor;
763	>	cursor = dec(cursor, es.length);
764	>	remaining--;
765	>	return e;
766	>	}
767
768	<	public boolean hasNext() {
769	<	return cursor != fence;
768	>	void postDelete(boolean leftShifted) {
769	>	if (!leftShifted)
770	>	cursor = inc(cursor, elements.length);
771		}
772
773	<	public E next() {
774	<	E result;
775	<	if (cursor == fence)
776	<	throw new NoSuchElementException();
777	<	if (((head - 1) & (elements.length - 1)) != fence ||
778	<	(result = elements[cursor]) == null)
773	>	public final void forEachRemaining(Consumer<? super E> action) {
774	>	Objects.requireNonNull(action);
775	>	int r;
776	>	if ((r = remaining) <= 0)
777	>	return;
778	>	remaining = 0;
779	>	final Object[] es = elements;
780	>	if (es[cursor] == null || sub(cursor, head, es.length) + 1 != r)
781		throw new ConcurrentModificationException();
782	<	lastRet = cursor;
783	<	cursor = (cursor - 1) & (elements.length - 1);
784	<	return result;
782	>	for (int i = cursor, end = head, to = (i >= end) ? end : 0;
783	>	; i = es.length - 1, to = end) {
784	>	for (; i >= to; i--)
785	>	action.accept(elementAt(es, i));
786	>	if (to == end) {
787	>	if (end != head)
788	>	throw new ConcurrentModificationException();
789	>	lastRet = head;
790	>	break;
791	>	}
792	>	}
793		}
794	+	}
795
796	<	public void remove() {
797	<	if (lastRet >= elements.length)
798	<	throw new IllegalStateException();
799	<	if (!delete(lastRet))
800	<	cursor = (cursor + 1) & (elements.length - 1);
801	<	lastRet = elements.length;
802	<	fence = (head - 1) & (elements.length - 1);
796	>	/**
797	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
798	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
799	>	* deque.
800	>	*
801	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
802	>	* {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and
803	>	* {@link Spliterator#NONNULL}.  Overriding implementations should document
804	>	* the reporting of additional characteristic values.
805	>	*
806	>	* @return a {@code Spliterator} over the elements in this deque
807	>	* @since 1.8
808	>	*/
809	>	public Spliterator<E> spliterator() {
810	>	return new DeqSpliterator();
811	>	}
812	>
813	>	final class DeqSpliterator implements Spliterator<E> {
814	>	private int fence;      // -1 until first use
815	>	private int cursor;     // current index, modified on traverse/split
816	>
817	>	/** Constructs late-binding spliterator over all elements. */
818	>	DeqSpliterator() {
819	>	this.fence = -1;
820	>	}
821	>
822	>	/** Constructs spliterator over the given range. */
823	>	DeqSpliterator(int origin, int fence) {
824	>	this.cursor = origin;
825	>	this.fence = fence;
826	>	}
827	>
828	>	/** Ensures late-binding initialization; then returns fence. */
829	>	private int getFence() { // force initialization
830	>	int t;
831	>	if ((t = fence) < 0) {
832	>	t = fence = tail;
833	>	cursor = head;
834	>	}
835	>	return t;
836	>	}
837	>
838	>	public DeqSpliterator trySplit() {
839	>	final Object[] es = elements;
840	>	final int i, n;
841	>	return ((n = sub(getFence(), i = cursor, es.length) >> 1) <= 0)
842	>	? null
843	>	: new DeqSpliterator(i, cursor = add(i, n, es.length));
844	>	}
845	>
846	>	public void forEachRemaining(Consumer<? super E> action) {
847	>	if (action == null)
848	>	throw new NullPointerException();
849	>	final int end = getFence(), cursor = this.cursor;
850	>	final Object[] es = elements;
851	>	if (cursor != end) {
852	>	this.cursor = end;
853	>	// null check at both ends of range is sufficient
854	>	if (es[cursor] == null || es[dec(end, es.length)] == null)
855	>	throw new ConcurrentModificationException();
856	>	for (int i = cursor, to = (i <= end) ? end : es.length;
857	>	; i = 0, to = end) {
858	>	for (; i < to; i++)
859	>	action.accept(elementAt(es, i));
860	>	if (to == end) break;
861	>	}
862	>	}
863	>	}
864	>
865	>	public boolean tryAdvance(Consumer<? super E> action) {
866	>	if (action == null)
867	>	throw new NullPointerException();
868	>	int t, i;
869	>	if ((t = fence) < 0) t = getFence();
870	>	if (t == (i = cursor))
871	>	return false;
872	>	final Object[] es;
873	>	action.accept(nonNullElementAt(es = elements, i));
874	>	cursor = inc(i, es.length);
875	>	return true;
876	>	}
877	>
878	>	public long estimateSize() {
879	>	return sub(getFence(), cursor, elements.length);
880	>	}
881	>
882	>	public int characteristics() {
883	>	return Spliterator.NONNULL
884	>	| Spliterator.ORDERED
885	>	| Spliterator.SIZED
886	>	| Spliterator.SUBSIZED;
887	>	}
888	>	}
889	>
890	>	public void forEach(Consumer<? super E> action) {
891	>	Objects.requireNonNull(action);
892	>	final Object[] es = elements;
893	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
894	>	; i = 0, to = end) {
895	>	for (; i < to; i++)
896	>	action.accept(elementAt(es, i));
897	>	if (to == end) {
898	>	if (end != tail) throw new ConcurrentModificationException();
899	>	break;
900	>	}
901	>	}
902	>	// checkInvariants();
903	>	}
904	>
905	>	/**
906	>	* Replaces each element of this deque with the result of applying the
907	>	* operator to that element, as specified by {@link List#replaceAll}.
908	>	*
909	>	* @param operator the operator to apply to each element
910	>	* @since TBD
911	>	*/
912	>	/* public */ void replaceAll(UnaryOperator<E> operator) {
913	>	Objects.requireNonNull(operator);
914	>	final Object[] es = elements;
915	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
916	>	; i = 0, to = end) {
917	>	for (; i < to; i++)
918	>	es[i] = operator.apply(elementAt(es, i));
919	>	if (to == end) {
920	>	if (end != tail) throw new ConcurrentModificationException();
921	>	break;
922	>	}
923	>	}
924	>	// checkInvariants();
925	>	}
926	>
927	>	/**
928	>	* @throws NullPointerException {@inheritDoc}
929	>	*/
930	>	public boolean removeIf(Predicate<? super E> filter) {
931	>	Objects.requireNonNull(filter);
932	>	return bulkRemove(filter);
933	>	}
934	>
935	>	/**
936	>	* @throws NullPointerException {@inheritDoc}
937	>	*/
938	>	public boolean removeAll(Collection<?> c) {
939	>	Objects.requireNonNull(c);
940	>	return bulkRemove(e -> c.contains(e));
941	>	}
942	>
943	>	/**
944	>	* @throws NullPointerException {@inheritDoc}
945	>	*/
946	>	public boolean retainAll(Collection<?> c) {
947	>	Objects.requireNonNull(c);
948	>	return bulkRemove(e -> !c.contains(e));
949	>	}
950	>
951	>	/** Implementation of bulk remove methods. */
952	>	private boolean bulkRemove(Predicate<? super E> filter) {
953	>	// checkInvariants();
954	>	final Object[] es = elements;
955	>	// Optimize for initial run of survivors
956	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
957	>	; i = 0, to = end) {
958	>	for (; i < to; i++)
959	>	if (filter.test(elementAt(es, i)))
960	>	return bulkRemoveModified(filter, i, to);
961	>	if (to == end) {
962	>	if (end != tail) throw new ConcurrentModificationException();
963	>	break;
964	>	}
965	>	}
966	>	return false;
967	>	}
968	>
969	>	/**
970	>	* Helper for bulkRemove, in case of at least one deletion.
971	>	* @param i valid index of first element to be deleted
972	>	*/
973	>	private boolean bulkRemoveModified(
974	>	Predicate<? super E> filter, int i, int to) {
975	>	final Object[] es = elements;
976	>	final int capacity = es.length;
977	>	// a two-finger algorithm, with hare i reading, tortoise j writing
978	>	int j = i++;
979	>	final int end = tail;
980	>	try {
981	>	for (;; j = 0) {    // j rejoins i on second leg
982	>	E e;
983	>	// In this loop, i and j are on the same leg, with i > j
984	>	for (; i < to; i++)
985	>	if (!filter.test(e = elementAt(es, i)))
986	>	es[j++] = e;
987	>	if (to == end) break;
988	>	// In this loop, j is on the first leg, i on the second
989	>	for (i = 0, to = end; i < to && j < capacity; i++)
990	>	if (!filter.test(e = elementAt(es, i)))
991	>	es[j++] = e;
992	>	if (i >= to) {
993	>	if (j == capacity) j = 0; // "corner" case
994	>	break;
995	>	}
996	>	}
997	>	return true;
998	>	} catch (Throwable ex) {
999	>	// copy remaining elements
1000	>	for (; i != end; i = inc(i, capacity), j = inc(j, capacity))
1001	>	es[j] = es[i];
1002	>	throw ex;
1003	>	} finally {
1004	>	if (end != tail) throw new ConcurrentModificationException();
1005	>	circularClear(es, tail = j, end);
1006	>	// checkInvariants();
1007		}
1008		}
1009
1010		/**
1011	<	* Returns <tt>true</tt> if this deque contains the specified element.
1012	<	* More formally, returns <tt>true</tt> if and only if this deque contains
1013	<	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
1011	>	* Returns {@code true} if this deque contains the specified element.
1012	>	* More formally, returns {@code true} if and only if this deque contains
1013	>	* at least one element {@code e} such that {@code o.equals(e)}.
1014		*
1015		* @param o object to be checked for containment in this deque
1016	<	* @return <tt>true</tt> if this deque contains the specified element
1016	>	* @return {@code true} if this deque contains the specified element
1017		*/
1018		public boolean contains(Object o) {
1019	<	if (o == null)
1020	<	return false;
1021	<	int mask = elements.length - 1;
1022	<	int i = head;
1023	<	E x;
1024	<	while ( (x = elements[i]) != null) {
1025	<	if (o.equals(x))
1026	<	return true;
1027	<	i = (i + 1) & mask;
1019	>	if (o != null) {
1020	>	final Object[] es = elements;
1021	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
1022	>	; i = 0, to = end) {
1023	>	for (; i < to; i++)
1024	>	if (o.equals(es[i]))
1025	>	return true;
1026	>	if (to == end) break;
1027	>	}
1028		}
1029		return false;
1030		}
#	Line 657 | Line 1032 | public class ArrayDeque<E> extends Abstr
1032		/**
1033		* Removes a single instance of the specified element from this deque.
1034		* If the deque does not contain the element, it is unchanged.
1035	<	* More formally, removes the first element <tt>e</tt> such that
1036	<	* <tt>o.equals(e)</tt> (if such an element exists).
1037	<	* Returns <tt>true</tt> if this deque contained the specified element
1035	>	* More formally, removes the first element {@code e} such that
1036	>	* {@code o.equals(e)} (if such an element exists).
1037	>	* Returns {@code true} if this deque contained the specified element
1038		* (or equivalently, if this deque changed as a result of the call).
1039		*
1040	<	* <p>This method is equivalent to {@link #removeFirstOccurrence}.
1040	>	* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
1041		*
1042		* @param o element to be removed from this deque, if present
1043	<	* @return <tt>true</tt> if this deque contained the specified element
1043	>	* @return {@code true} if this deque contained the specified element
1044		*/
1045		public boolean remove(Object o) {
1046		return removeFirstOccurrence(o);
#	Line 676 | Line 1051 | public class ArrayDeque<E> extends Abstr
1051		* The deque will be empty after this call returns.
1052		*/
1053		public void clear() {
1054	<	int h = head;
1055	<	int t = tail;
1056	<	if (h != t) { // clear all cells
1057	<	head = tail = 0;
1058	<	int i = h;
1059	<	int mask = elements.length - 1;
1060	<	do {
1061	<	elements[i] = null;
1062	<	i = (i + 1) & mask;
1063	<	} while (i != t);
1054	>	circularClear(elements, head, tail);
1055	>	head = tail = 0;
1056	>	// checkInvariants();
1057	>	}
1058	>
1059	>	/**
1060	>	* Nulls out slots starting at array index i, upto index end.
1061	>	*/
1062	>	private static void circularClear(Object[] es, int i, int end) {
1063	>	for (int to = (i <= end) ? end : es.length;
1064	>	; i = 0, to = end) {
1065	>	Arrays.fill(es, i, to, null);
1066	>	if (to == end) break;
1067		}
1068		}
1069
#	Line 703 | Line 1081 | public class ArrayDeque<E> extends Abstr
1081		* @return an array containing all of the elements in this deque
1082		*/
1083		public Object[] toArray() {
1084	<	return copyElements(new Object[size()]);
1084	>	return toArray(Object[].class);
1085	>	}
1086	>
1087	>	private <T> T[] toArray(Class<T[]> klazz) {
1088	>	final Object[] es = elements;
1089	>	final T[] a;
1090	>	final int size = size(), head = this.head, end;
1091	>	final int len = Math.min(size, es.length - head);
1092	>	if ((end = head + size) >= 0) {
1093	>	a = Arrays.copyOfRange(es, head, end, klazz);
1094	>	} else {
1095	>	// integer overflow!
1096	>	a = Arrays.copyOfRange(es, 0, size, klazz);
1097	>	System.arraycopy(es, head, a, 0, len);
1098	>	}
1099	>	if (tail < head)
1100	>	System.arraycopy(es, 0, a, len, tail);
1101	>	return a;
1102		}
1103
1104		/**
#	Line 717 | Line 1112 | public class ArrayDeque<E> extends Abstr
1112		* <p>If this deque fits in the specified array with room to spare
1113		* (i.e., the array has more elements than this deque), the element in
1114		* the array immediately following the end of the deque is set to
1115	<	* <tt>null</tt>.
1115	>	* {@code null}.
1116		*
1117		* <p>Like the {@link #toArray()} method, this method acts as bridge between
1118		* array-based and collection-based APIs.  Further, this method allows
1119		* precise control over the runtime type of the output array, and may,
1120		* under certain circumstances, be used to save allocation costs.
1121		*
1122	<	* <p>Suppose <tt>x</tt> is a deque known to contain only strings.
1122	>	* <p>Suppose {@code x} is a deque known to contain only strings.
1123		* The following code can be used to dump the deque into a newly
1124	<	* allocated array of <tt>String</tt>:
1124	>	* allocated array of {@code String}:
1125		*
1126	<	* <pre>
732	<	*     String[] y = x.toArray(new String[0]);</pre>
1126	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
1127		*
1128	<	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
1129	<	* <tt>toArray()</tt>.
1128	>	* Note that {@code toArray(new Object[0])} is identical in function to
1129	>	* {@code toArray()}.
1130		*
1131		* @param a the array into which the elements of the deque are to
1132		*          be stored, if it is big enough; otherwise, a new array of the
#	Line 743 | Line 1137 | public class ArrayDeque<E> extends Abstr
1137		*         this deque
1138		* @throws NullPointerException if the specified array is null
1139		*/
1140	+	@SuppressWarnings("unchecked")
1141		public <T> T[] toArray(T[] a) {
1142	<	int size = size();
1143	<	if (a.length < size)
1144	<	a = (T[])java.lang.reflect.Array.newInstance(
1145	<	a.getClass().getComponentType(), size);
1146	<	copyElements(a);
1147	<	if (a.length > size)
1142	>	final int size;
1143	>	if ((size = size()) > a.length)
1144	>	return toArray((Class<T[]>) a.getClass());
1145	>	final Object[] es = elements;
1146	>	for (int i = head, j = 0, len = Math.min(size, es.length - i);
1147	>	; i = 0, len = tail) {
1148	>	System.arraycopy(es, i, a, j, len);
1149	>	if ((j += len) == size) break;
1150	>	}
1151	>	if (size < a.length)
1152		a[size] = null;
1153		return a;
1154		}
#	Line 763 | Line 1162 | public class ArrayDeque<E> extends Abstr
1162		*/
1163		public ArrayDeque<E> clone() {
1164		try {
1165	+	@SuppressWarnings("unchecked")
1166		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
1167	<	// These two lines are currently faster than cloning the array:
768	<	result.elements = (E[]) new Object[elements.length];
769	<	System.arraycopy(elements, 0, result.elements, 0, elements.length);
1167	>	result.elements = Arrays.copyOf(elements, elements.length);
1168		return result;
771	–
1169		} catch (CloneNotSupportedException e) {
1170		throw new AssertionError();
1171		}
1172		}
1173
777	–	/**
778	–	* Appease the serialization gods.
779	–	*/
1174		private static final long serialVersionUID = 2340985798034038923L;
1175
1176		/**
1177	<	* Serialize this deque.
1177	>	* Saves this deque to a stream (that is, serializes it).
1178		*
1179	<	* @serialData The current size (<tt>int</tt>) of the deque,
1179	>	* @param s the stream
1180	>	* @throws java.io.IOException if an I/O error occurs
1181	>	* @serialData The current size ({@code int}) of the deque,
1182		* followed by all of its elements (each an object reference) in
1183		* first-to-last order.
1184		*/
1185	<	private void writeObject(ObjectOutputStream s) throws IOException {
1185	>	private void writeObject(java.io.ObjectOutputStream s)
1186	>	throws java.io.IOException {
1187		s.defaultWriteObject();
1188
1189		// Write out size
1190		s.writeInt(size());
1191
1192		// Write out elements in order.
1193	<	int mask = elements.length - 1;
1194	<	for (int i = head; i != tail; i = (i + 1) & mask)
1195	<	s.writeObject(elements[i]);
1193	>	final Object[] es = elements;
1194	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
1195	>	; i = 0, to = end) {
1196	>	for (; i < to; i++)
1197	>	s.writeObject(es[i]);
1198	>	if (to == end) break;
1199	>	}
1200		}
1201
1202		/**
1203	<	* Deserialize this deque.
1203	>	* Reconstitutes this deque from a stream (that is, deserializes it).
1204	>	* @param s the stream
1205	>	* @throws ClassNotFoundException if the class of a serialized object
1206	>	*         could not be found
1207	>	* @throws java.io.IOException if an I/O error occurs
1208		*/
1209	<	private void readObject(ObjectInputStream s)
1210	<	throws IOException, ClassNotFoundException {
1209	>	private void readObject(java.io.ObjectInputStream s)
1210	>	throws java.io.IOException, ClassNotFoundException {
1211		s.defaultReadObject();
1212
1213		// Read in size and allocate array
1214		int size = s.readInt();
1215	<	allocateElements(size);
1216	<	head = 0;
812	<	tail = size;
1215	>	elements = new Object[size + 1];
1216	>	this.tail = size;
1217
1218		// Read in all elements in the proper order.
1219		for (int i = 0; i < size; i++)
1220	<	elements[i] = (E)s.readObject();
1220	>	elements[i] = s.readObject();
1221	>	}
1222
1223	+	/** debugging */
1224	+	void checkInvariants() {
1225	+	try {
1226	+	int capacity = elements.length;
1227	+	// assert head >= 0 && head < capacity;
1228	+	// assert tail >= 0 && tail < capacity;
1229	+	// assert capacity > 0;
1230	+	// assert size() < capacity;
1231	+	// assert head == tail || elements[head] != null;
1232	+	// assert elements[tail] == null;
1233	+	// assert head == tail || elements[dec(tail, capacity)] != null;
1234	+	} catch (Throwable t) {
1235	+	System.err.printf("head=%d tail=%d capacity=%d%n",
1236	+	head, tail, elements.length);
1237	+	System.err.printf("elements=%s%n",
1238	+	Arrays.toString(elements));
1239	+	throw t;
1240	+	}
1241		}
1242	+
1243		}

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