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Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.7 by jsr166, Tue Apr 26 19:54:03 2005 UTC vs.
Revision 1.75 by jsr166, Mon Oct 17 21:56:25 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>
47		*
48		* <p>This class and its iterator implement all of the
49	<	* optional methods of the {@link Collection} and {@link
50	<	* Iterator} interfaces.  This class is a member of the <a
51	<	* href="{@docRoot}/../guide/collections/index.html"> Java Collections
52	<	* Framework</a>.
49	>	* <em>optional</em> methods of the {@link Collection} and {@link
50	>	* Iterator} interfaces.
51	>	*
52	>	* <p>This class is a member of the
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
50	–	* @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		* The array in which the elements of the deque are stored.
65	<	* The capacity of the deque is the length of this array, which is
66	<	* always a power of two. The array is never allowed to become
59	<	* full, except transiently within an addX method where it is
60	<	* resized (see doubleCapacity) immediately upon becoming full,
61	<	* thus avoiding head and tail wrapping around to equal each
62	<	* other.  We also guarantee that all array cells not holding
63	<	* deque elements are always null.
65	>	* We guarantee that all array cells not holding deque elements
66	>	* are always null.
67		*/
68	<	private transient E[] elements;
68	>	transient Object[] elements;
69
70		/**
71		* The index of the element at the head of the deque (which is the
72		* element that would be removed by remove() or pop()); or an
73	<	* arbitrary number equal to tail if the deque is empty.
73	>	* arbitrary number 0 <= head < elements.length if the deque is empty.
74		*/
75	<	private transient int head;
75	>	transient int head;
76
77	<	/**
78	<	* The index at which the next element would be added to the tail
76	<	* of the deque (via addLast(E), add(E), or push(E)).
77	<	*/
78	<	private transient int tail;
77	>	/** Number of elements in this collection. */
78	>	transient int size;
79
80		/**
81	<	* The minimum capacity that we'll use for a newly created deque.
82	<	* Must be a power of 2.
83	<	*/
84	<	private static final int MIN_INITIAL_CAPACITY = 8;
85	<
86	<	// ******  Array allocation and resizing utilities ******
87	<
88	<	/**
89	<	* Allocate empty array to hold the given number of elements.
90	<	*
91	<	* @param numElements  the number of elements to hold.
92	<	*/
93	<	private void allocateElements(int numElements) {
94	<	int initialCapacity = MIN_INITIAL_CAPACITY;
95	<	// Find the best power of two to hold elements.
96	<	// Tests "<=" because arrays aren't kept full.
97	<	if (numElements >= initialCapacity) {
98	<	initialCapacity = numElements;
99	<	initialCapacity |= (initialCapacity >>>  1);
100	<	initialCapacity |= (initialCapacity >>>  2);
101	<	initialCapacity |= (initialCapacity >>>  4);
102	<	initialCapacity |= (initialCapacity >>>  8);
103	<	initialCapacity |= (initialCapacity >>> 16);
104	<	initialCapacity++;
81	>	* The maximum size of array to allocate.
82	>	* Some VMs reserve some header words in an array.
83	>	* Attempts to allocate larger arrays may result in
84	>	* OutOfMemoryError: Requested array size exceeds VM limit
85	>	*/
86	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
87	>
88	>	/**
89	>	* Increases the capacity of this deque by at least the given amount.
90	>	*
91	>	* @param needed the required minimum extra capacity; must be positive
92	>	*/
93	>	private void grow(int needed) {
94	>	// overflow-conscious code
95	>	// checkInvariants();
96	>	int oldCapacity = elements.length;
97	>	int newCapacity;
98	>	// Double size if small; else grow by 50%
99	>	int jump = (oldCapacity < 64) ? (oldCapacity + 2) : (oldCapacity >> 1);
100	>	if (jump < needed
101	>	|| (newCapacity = (oldCapacity + jump)) - MAX_ARRAY_SIZE > 0)
102	>	newCapacity = newCapacity(needed, jump);
103	>	elements = Arrays.copyOf(elements, newCapacity);
104	>	if (oldCapacity - head < size) {
105	>	// wrap around; slide first leg forward to end of array
106	>	int newSpace = newCapacity - oldCapacity;
107	>	System.arraycopy(elements, head,
108	>	elements, head + newSpace,
109	>	oldCapacity - head);
110	>	Arrays.fill(elements, head, head + newSpace, null);
111	>	head += newSpace;
112	>	}
113	>	// checkInvariants();
114	>	}
115
116	<	if (initialCapacity < 0)   // Too many elements, must back off
117	<	initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
116	>	/** Capacity calculation for edge conditions, especially overflow. */
117	>	private int newCapacity(int needed, int jump) {
118	>	int oldCapacity = elements.length;
119	>	int minCapacity;
120	>	if ((minCapacity = oldCapacity + needed) - MAX_ARRAY_SIZE > 0) {
121	>	if (minCapacity < 0)
122	>	throw new IllegalStateException("Sorry, deque too big");
123	>	return Integer.MAX_VALUE;
124		}
125	<	elements = (E[]) new Object[initialCapacity];
125	>	if (needed > jump)
126	>	return minCapacity;
127	>	return (oldCapacity + jump - MAX_ARRAY_SIZE < 0)
128	>	? oldCapacity + jump
129	>	: MAX_ARRAY_SIZE;
130		}
131
132		/**
133	<	* Double the capacity of this deque.  Call only when full, i.e.,
134	<	* when head and tail have wrapped around to become equal.
133	>	* Increases the internal storage of this collection, if necessary,
134	>	* to ensure that it can hold at least the given number of elements.
135	>	*
136	>	* @param minCapacity the desired minimum capacity
137	>	* @since 9
138		*/
139	<	private void doubleCapacity() {
140	<	assert head == tail;
141	<	int p = head;
142	<	int n = elements.length;
120	<	int r = n - p; // number of elements to the right of p
121	<	int newCapacity = n << 1;
122	<	if (newCapacity < 0)
123	<	throw new IllegalStateException("Sorry, deque too big");
124	<	Object[] a = new Object[newCapacity];
125	<	System.arraycopy(elements, p, a, 0, r);
126	<	System.arraycopy(elements, 0, a, r, p);
127	<	elements = (E[])a;
128	<	head = 0;
129	<	tail = n;
139	>	public void ensureCapacity(int minCapacity) {
140	>	if (minCapacity > elements.length)
141	>	grow(minCapacity - elements.length);
142	>	// checkInvariants();
143		}
144
145		/**
146	<	* Copies the elements from our element array into the specified array,
134	<	* in order (from first to last element in the deque).  It is assumed
135	<	* that the array is large enough to hold all elements in the deque.
146	>	* Minimizes the internal storage of this collection.
147		*
148	<	* @return its argument
148	>	* @since 9
149		*/
150	<	private <T> T[] copyElements(T[] a) {
151	<	if (head < tail) {
152	<	System.arraycopy(elements, head, a, 0, size());
153	<	} else if (head > tail) {
143	<	int headPortionLen = elements.length - head;
144	<	System.arraycopy(elements, head, a, 0, headPortionLen);
145	<	System.arraycopy(elements, 0, a, headPortionLen, tail);
150	>	public void trimToSize() {
151	>	if (size < elements.length) {
152	>	elements = toArray();
153	>	head = 0;
154		}
155	<	return a;
155	>	// checkInvariants();
156		}
157
158		/**
#	Line 152 | Line 160 | public class ArrayDeque<E> extends Abstr
160		* sufficient to hold 16 elements.
161		*/
162		public ArrayDeque() {
163	<	elements = (E[]) new Object[16];
163	>	elements = new Object[16];
164		}
165
166		/**
167		* Constructs an empty array deque with an initial capacity
168		* sufficient to hold the specified number of elements.
169		*
170	<	* @param numElements  lower bound on initial capacity of the deque
170	>	* @param numElements lower bound on initial capacity of the deque
171		*/
172		public ArrayDeque(int numElements) {
173	<	allocateElements(numElements);
173	>	elements = new Object[numElements];
174		}
175
176		/**
#	Line 176 | Line 184 | public class ArrayDeque<E> extends Abstr
184		* @throws NullPointerException if the specified collection is null
185		*/
186		public ArrayDeque(Collection<? extends E> c) {
187	<	allocateElements(c.size());
188	<	addAll(c);
187	>	Object[] elements = c.toArray();
188	>	// defend against c.toArray (incorrectly) not returning Object[]
189	>	// (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)
190	>	if (elements.getClass() != Object[].class)
191	>	elements = Arrays.copyOf(elements, size, Object[].class);
192	>	for (Object obj : elements)
193	>	Objects.requireNonNull(obj);
194	>	size = elements.length;
195	>	this.elements = elements;
196	>	}
197	>
198	>	/**
199	>	* Returns the array index of the last element.
200	>	* May return invalid index -1 if there are no elements.
201	>	*/
202	>	final int tail() {
203	>	return add(head, size - 1, elements.length);
204	>	}
205	>
206	>	/**
207	>	* Adds i and j, mod modulus.
208	>	* Precondition and postcondition: 0 <= i < modulus, 0 <= j <= modulus.
209	>	*/
210	>	static final int add(int i, int j, int modulus) {
211	>	if ((i += j) - modulus >= 0) i -= modulus;
212	>	return i;
213	>	}
214	>
215	>	/**
216	>	* Increments i, mod modulus.
217	>	* Precondition and postcondition: 0 <= i < modulus.
218	>	*/
219	>	static final int inc(int i, int modulus) {
220	>	if (++i == modulus) i = 0;
221	>	return i;
222	>	}
223	>
224	>	/**
225	>	* Decrements i, mod modulus.
226	>	* Precondition and postcondition: 0 <= i < modulus.
227	>	*/
228	>	static final int dec(int i, int modulus) {
229	>	if (--i < 0) i += modulus;
230	>	return i;
231	>	}
232	>
233	>	/**
234	>	* Returns element at array index i.
235	>	*/
236	>	@SuppressWarnings("unchecked")
237	>	final E elementAt(int i) {
238	>	return (E) elements[i];
239	>	}
240	>
241	>	/**
242	>	* A version of elementAt that checks for null elements.
243	>	* This check doesn't catch all possible comodifications,
244	>	* but does catch ones that corrupt traversal.
245	>	*/
246	>	E checkedElementAt(Object[] elements, int i) {
247	>	@SuppressWarnings("unchecked") E e = (E) elements[i];
248	>	if (e == null)
249	>	throw new ConcurrentModificationException();
250	>	return e;
251		}
252
253		// The main insertion and extraction methods are addFirst,
#	Line 187 | Line 257 | public class ArrayDeque<E> extends Abstr
257		/**
258		* Inserts the specified element at the front of this deque.
259		*
260	<	* @param e the element to insert
261	<	* @throws NullPointerException if <tt>e</tt> is null
260	>	* @param e the element to add
261	>	* @throws NullPointerException if the specified element is null
262		*/
263		public void addFirst(E e) {
264	<	if (e == null)
265	<	throw new NullPointerException();
266	<	elements[head = (head - 1) & (elements.length - 1)] = e;
267	<	if (head == tail)
268	<	doubleCapacity();
264	>	// checkInvariants();
265	>	Objects.requireNonNull(e);
266	>	Object[] elements;
267	>	int capacity, s = size;
268	>	while (s == (capacity = (elements = this.elements).length))
269	>	grow(1);
270	>	elements[head = dec(head, capacity)] = e;
271	>	size = s + 1;
272		}
273
274		/**
275		* Inserts the specified element at the end of this deque.
203	–	* This method is equivalent to {@link Collection#add} and
204	–	* {@link #push}.
276		*
277	<	* @param e the element to insert
207	<	* @throws NullPointerException if <tt>e</tt> is null
208	<	*/
209	<	public void addLast(E e) {
210	<	if (e == null)
211	<	throw new NullPointerException();
212	<	elements[tail] = e;
213	<	if ( (tail = (tail + 1) & (elements.length - 1)) == head)
214	<	doubleCapacity();
215	<	}
216	<
217	<	/**
218	<	* Retrieves and removes the first element of this deque, or
219	<	* <tt>null</tt> if this deque is empty.
277	>	* <p>This method is equivalent to {@link #add}.
278		*
279	<	* @return the first element of this deque, or <tt>null</tt> if
280	<	*     this deque is empty
279	>	* @param e the element to add
280	>	* @throws NullPointerException if the specified element is null
281		*/
282	<	public E pollFirst() {
283	<	int h = head;
284	<	E result = elements[h]; // Element is null if deque empty
285	<	if (result == null)
286	<	return null;
287	<	elements[h] = null;     // Must null out slot
288	<	head = (h + 1) & (elements.length - 1);
289	<	return result;
282	>	public void addLast(E e) {
283	>	// checkInvariants();
284	>	Objects.requireNonNull(e);
285	>	Object[] elements;
286	>	int capacity, s = size;
287	>	while (s == (capacity = (elements = this.elements).length))
288	>	grow(1);
289	>	elements[add(head, s, capacity)] = e;
290	>	size = s + 1;
291		}
292
293		/**
294	<	* Retrieves and removes the last element of this deque, or
295	<	* <tt>null</tt> if this deque is empty.
296	<	*
297	<	* @return the last element of this deque, or <tt>null</tt> if
298	<	*     this deque is empty
299	<	*/
300	<	public E pollLast() {
301	<	int t = (tail - 1) & (elements.length - 1);
302	<	E result = elements[t];
303	<	if (result == null)
304	<	return null;
305	<	elements[t] = null;
306	<	tail = t;
307	<	return result;
294	>	* Adds all of the elements in the specified collection at the end
295	>	* of this deque, as if by calling {@link #addLast} on each one,
296	>	* in the order that they are returned by the collection's
297	>	* iterator.
298	>	*
299	>	* @param c the elements to be inserted into this deque
300	>	* @return {@code true} if this deque changed as a result of the call
301	>	* @throws NullPointerException if the specified collection or any
302	>	*         of its elements are null
303	>	*/
304	>	@Override
305	>	public boolean addAll(Collection<? extends E> c) {
306	>	// checkInvariants();
307	>	Object[] a, elements;
308	>	int len, capacity, s = size;
309	>	if ((len = (a = c.toArray()).length) == 0)
310	>	return false;
311	>	while ((capacity = (elements = this.elements).length) - s < len)
312	>	grow(len - (capacity - s));
313	>	int i = add(head, s, capacity);
314	>	for (Object x : a) {
315	>	Objects.requireNonNull(x);
316	>	elements[i] = x;
317	>	i = inc(i, capacity);
318	>	size++;
319	>	}
320	>	return true;
321		}
322
323		/**
324		* Inserts the specified element at the front of this deque.
325		*
326	<	* @param e the element to insert
327	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst})
328	<	* @throws NullPointerException if <tt>e</tt> is null
326	>	* @param e the element to add
327	>	* @return {@code true} (as specified by {@link Deque#offerFirst})
328	>	* @throws NullPointerException if the specified element is null
329		*/
330		public boolean offerFirst(E e) {
331		addFirst(e);
#	Line 263 | Line 335 | public class ArrayDeque<E> extends Abstr
335		/**
336		* Inserts the specified element at the end of this deque.
337		*
338	<	* @param e the element to insert
339	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
340	<	* @throws NullPointerException if <tt>e</tt> is null
338	>	* @param e the element to add
339	>	* @return {@code true} (as specified by {@link Deque#offerLast})
340	>	* @throws NullPointerException if the specified element is null
341		*/
342		public boolean offerLast(E e) {
343		addLast(e);
#	Line 273 | Line 345 | public class ArrayDeque<E> extends Abstr
345		}
346
347		/**
348	<	* Retrieves and removes the first element of this deque.  This method
277	<	* differs from the <tt>pollFirst</tt> method in that it throws an
278	<	* exception if this deque is empty.
279	<	*
280	<	* @return the first element of this deque
281	<	* @throws NoSuchElementException if this deque is empty
348	>	* @throws NoSuchElementException {@inheritDoc}
349		*/
350		public E removeFirst() {
351	+	// checkInvariants();
352		E x = pollFirst();
353		if (x == null)
354		throw new NoSuchElementException();
#	Line 288 | Line 356 | public class ArrayDeque<E> extends Abstr
356		}
357
358		/**
359	<	* Retrieves and removes the last element of this deque.  This method
292	<	* differs from the <tt>pollLast</tt> method in that it throws an
293	<	* exception if this deque is empty.
294	<	*
295	<	* @return the last element of this deque
296	<	* @throws NoSuchElementException if this deque is empty
359	>	* @throws NoSuchElementException {@inheritDoc}
360		*/
361		public E removeLast() {
362	+	// checkInvariants();
363		E x = pollLast();
364		if (x == null)
365		throw new NoSuchElementException();
366		return x;
367		}
368
369	<	/**
370	<	* Retrieves, but does not remove, the first element of this deque,
371	<	* returning <tt>null</tt> if this deque is empty.
372	<	*
373	<	* @return the first element of this deque, or <tt>null</tt> if
374	<	*     this deque is empty
375	<	*/
376	<	public E peekFirst() {
377	<	return elements[head]; // elements[head] is null if deque empty
369	>	public E pollFirst() {
370	>	// checkInvariants();
371	>	final int s, h;
372	>	if ((s = size) == 0)
373	>	return null;
374	>	final Object[] elements = this.elements;
375	>	@SuppressWarnings("unchecked") E e = (E) elements[h = head];
376	>	elements[h] = null;
377	>	head = inc(h, elements.length);
378	>	size = s - 1;
379	>	return e;
380		}
381
382	<	/**
383	<	* Retrieves, but does not remove, the last element of this deque,
384	<	* returning <tt>null</tt> if this deque is empty.
385	<	*
386	<	* @return the last element of this deque, or <tt>null</tt> if this deque
387	<	*     is empty
388	<	*/
389	<	public E peekLast() {
390	<	return elements[(tail - 1) & (elements.length - 1)];
382	>	public E pollLast() {
383	>	// checkInvariants();
384	>	final int s, tail;
385	>	if ((s = size) == 0)
386	>	return null;
387	>	final Object[] elements = this.elements;
388	>	@SuppressWarnings("unchecked")
389	>	E e = (E) elements[tail = add(head, s - 1, elements.length)];
390	>	elements[tail] = null;
391	>	size = s - 1;
392	>	return e;
393		}
394
395		/**
396	<	* Retrieves, but does not remove, the first element of this
329	<	* deque.  This method differs from the <tt>peekFirst</tt> method only
330	<	* in that it throws an exception if this deque is empty.
331	<	*
332	<	* @return the first element of this deque
333	<	* @throws NoSuchElementException if this deque is empty
396	>	* @throws NoSuchElementException {@inheritDoc}
397		*/
398		public E getFirst() {
399	<	E x = elements[head];
400	<	if (x == null)
401	<	throw new NoSuchElementException();
339	<	return x;
399	>	// checkInvariants();
400	>	if (size == 0) throw new NoSuchElementException();
401	>	return elementAt(head);
402		}
403
404		/**
405	<	* Retrieves, but does not remove, the last element of this
344	<	* deque.  This method differs from the <tt>peekLast</tt> method only
345	<	* in that it throws an exception if this deque is empty.
346	<	*
347	<	* @return the last element of this deque
348	<	* @throws NoSuchElementException if this deque is empty
405	>	* @throws NoSuchElementException {@inheritDoc}
406		*/
407		public E getLast() {
408	<	E x = elements[(tail - 1) & (elements.length - 1)];
409	<	if (x == null)
410	<	throw new NoSuchElementException();
411	<	return x;
408	>	// checkInvariants();
409	>	if (size == 0) throw new NoSuchElementException();
410	>	return elementAt(tail());
411	>	}
412	>
413	>	public E peekFirst() {
414	>	// checkInvariants();
415	>	return (size == 0) ? null : elementAt(head);
416	>	}
417	>
418	>	public E peekLast() {
419	>	// checkInvariants();
420	>	return (size == 0) ? null : elementAt(tail());
421		}
422
423		/**
424		* Removes the first occurrence of the specified element in this
425	<	* deque (when traversing the deque from head to tail).  More
426	<	* formally, removes the first element e such that (o==null ?
427	<	* e==null : o.equals(e)). If the deque does not contain the
428	<	* element, it is unchanged.
425	>	* deque (when traversing the deque from head to tail).
426	>	* If the deque does not contain the element, it is unchanged.
427	>	* More formally, removes the first element {@code e} such that
428	>	* {@code o.equals(e)} (if such an element exists).
429	>	* Returns {@code true} if this deque contained the specified element
430	>	* (or equivalently, if this deque changed as a result of the call).
431		*
432		* @param o element to be removed from this deque, if present
433	<	* @return <tt>true</tt> if the deque contained the specified element
433	>	* @return {@code true} if the deque contained the specified element
434		*/
435		public boolean removeFirstOccurrence(Object o) {
436	<	if (o == null)
437	<	return false;
438	<	int mask = elements.length - 1;
439	<	int i = head;
440	<	E x;
441	<	while ( (x = elements[i]) != null) {
442	<	if (o.equals(x)) {
443	<	delete(i);
444	<	return true;
436	>	// checkInvariants();
437	>	if (o != null) {
438	>	final Object[] elements = this.elements;
439	>	final int capacity = elements.length;
440	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity)) {
441	>	if (o.equals(elements[i])) {
442	>	delete(i);
443	>	return true;
444	>	}
445		}
378	–	i = (i + 1) & mask;
446		}
447		return false;
448		}
449
450		/**
451		* Removes the last occurrence of the specified element in this
452	<	* deque (when traversing the deque from head to tail). More
453	<	* formally, removes the last element e such that (o==null ?
454	<	* e==null : o.equals(e)). If the deque
455	<	* does not contain the element, it is unchanged.
452	>	* deque (when traversing the deque from head to tail).
453	>	* If the deque does not contain the element, it is unchanged.
454	>	* More formally, removes the last element {@code e} such that
455	>	* {@code o.equals(e)} (if such an element exists).
456	>	* Returns {@code true} if this deque contained the specified element
457	>	* (or equivalently, if this deque changed as a result of the call).
458		*
459		* @param o element to be removed from this deque, if present
460	<	* @return <tt>true</tt> if the deque contained the specified element
460	>	* @return {@code true} if the deque contained the specified element
461		*/
462		public boolean removeLastOccurrence(Object o) {
463	<	if (o == null)
464	<	return false;
465	<	int mask = elements.length - 1;
466	<	int i = (tail - 1) & mask;
467	<	E x;
468	<	while ( (x = elements[i]) != null) {
469	<	if (o.equals(x)) {
470	<	delete(i);
471	<	return true;
463	>	if (o != null) {
464	>	final Object[] elements = this.elements;
465	>	final int capacity = elements.length;
466	>	for (int k = size, i = add(head, k - 1, capacity);
467	>	--k >= 0; i = dec(i, capacity)) {
468	>	if (o.equals(elements[i])) {
469	>	delete(i);
470	>	return true;
471	>	}
472		}
404	–	i = (i - 1) & mask;
473		}
474		return false;
475		}
#	Line 411 | Line 479 | public class ArrayDeque<E> extends Abstr
479		/**
480		* Inserts the specified element at the end of this deque.
481		*
414	–	* <p>This method is equivalent to {@link #offerLast}.
415	–	*
416	–	* @param e the element to insert
417	–	* @return <tt>true</tt> (as per the spec for {@link Queue#offer})
418	–	* @throws NullPointerException if <tt>e</tt> is null
419	–	*/
420	–	public boolean offer(E e) {
421	–	return offerLast(e);
422	–	}
423	–
424	–	/**
425	–	* Inserts the specified element at the end of this deque.
426	–	*
482		* <p>This method is equivalent to {@link #addLast}.
483		*
484	<	* @param e the element to insert
485	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
486	<	* @throws NullPointerException if <tt>e</tt> is null
484	>	* @param e the element to add
485	>	* @return {@code true} (as specified by {@link Collection#add})
486	>	* @throws NullPointerException if the specified element is null
487		*/
488		public boolean add(E e) {
489		addLast(e);
#	Line 436 | Line 491 | public class ArrayDeque<E> extends Abstr
491		}
492
493		/**
494	<	* Retrieves and removes the head of the queue represented by
440	<	* this deque, or <tt>null</tt> if this deque is empty.  In other words,
441	<	* retrieves and removes the first element of this deque, or <tt>null</tt>
442	<	* if this deque is empty.
494	>	* Inserts the specified element at the end of this deque.
495		*
496	<	* <p>This method is equivalent to {@link #pollFirst}.
496	>	* <p>This method is equivalent to {@link #offerLast}.
497		*
498	<	* @return the first element of this deque, or <tt>null</tt> if
499	<	*     this deque is empty
498	>	* @param e the element to add
499	>	* @return {@code true} (as specified by {@link Queue#offer})
500	>	* @throws NullPointerException if the specified element is null
501		*/
502	<	public E poll() {
503	<	return pollFirst();
502	>	public boolean offer(E e) {
503	>	return offerLast(e);
504		}
505
506		/**
507		* Retrieves and removes the head of the queue represented by this deque.
508	<	* This method differs from the <tt>poll</tt> method in that it throws an
508	>	*
509	>	* This method differs from {@link #poll poll} only in that it throws an
510		* exception if this deque is empty.
511		*
512		* <p>This method is equivalent to {@link #removeFirst}.
513		*
514		* @return the head of the queue represented by this deque
515	<	* @throws NoSuchElementException if this deque is empty
515	>	* @throws NoSuchElementException {@inheritDoc}
516		*/
517		public E remove() {
518		return removeFirst();
519		}
520
521		/**
522	<	* Retrieves, but does not remove, the head of the queue represented by
523	<	* this deque, returning <tt>null</tt> if this deque is empty.
522	>	* Retrieves and removes the head of the queue represented by this deque
523	>	* (in other words, the first element of this deque), or returns
524	>	* {@code null} if this deque is empty.
525		*
526	<	* <p>This method is equivalent to {@link #peekFirst}
526	>	* <p>This method is equivalent to {@link #pollFirst}.
527		*
528		* @return the head of the queue represented by this deque, or
529	<	*     <tt>null</tt> if this deque is empty
529	>	*         {@code null} if this deque is empty
530		*/
531	<	public E peek() {
532	<	return peekFirst();
531	>	public E poll() {
532	>	return pollFirst();
533		}
534
535		/**
536		* Retrieves, but does not remove, the head of the queue represented by
537	<	* this deque.  This method differs from the <tt>peek</tt> method only in
537	>	* this deque.  This method differs from {@link #peek peek} only in
538		* that it throws an exception if this deque is empty.
539		*
540	<	* <p>This method is equivalent to {@link #getFirst}
540	>	* <p>This method is equivalent to {@link #getFirst}.
541		*
542		* @return the head of the queue represented by this deque
543	<	* @throws NoSuchElementException if this deque is empty
543	>	* @throws NoSuchElementException {@inheritDoc}
544		*/
545		public E element() {
546		return getFirst();
547		}
548
549	+	/**
550	+	* Retrieves, but does not remove, the head of the queue represented by
551	+	* this deque, or returns {@code null} if this deque is empty.
552	+	*
553	+	* <p>This method is equivalent to {@link #peekFirst}.
554	+	*
555	+	* @return the head of the queue represented by this deque, or
556	+	*         {@code null} if this deque is empty
557	+	*/
558	+	public E peek() {
559	+	return peekFirst();
560	+	}
561	+
562		// *** Stack methods ***
563
564		/**
#	Line 500 | Line 568 | public class ArrayDeque<E> extends Abstr
568		* <p>This method is equivalent to {@link #addFirst}.
569		*
570		* @param e the element to push
571	<	* @throws NullPointerException if <tt>e</tt> is null
571	>	* @throws NullPointerException if the specified element is null
572		*/
573		public void push(E e) {
574		addFirst(e);
#	Line 513 | Line 581 | public class ArrayDeque<E> extends Abstr
581		* <p>This method is equivalent to {@link #removeFirst()}.
582		*
583		* @return the element at the front of this deque (which is the top
584	<	*     of the stack represented by this deque)
585	<	* @throws NoSuchElementException if this deque is empty
584	>	*         of the stack represented by this deque)
585	>	* @throws NoSuchElementException {@inheritDoc}
586		*/
587		public E pop() {
588		return removeFirst();
589		}
590
591		/**
592	<	* Removes the element at the specified position in the elements array,
593	<	* adjusting head, tail, and size as necessary.  This can result in
594	<	* motion of elements backwards or forwards in the array.
592	>	* Removes the element at the specified position in the elements array.
593	>	* This can result in forward or backwards motion of array elements.
594	>	* We optimize for least element motion.
595		*
596		* <p>This method is called delete rather than remove to emphasize
597	<	* that its semantics differ from those of List.remove(int).
597	>	* that its semantics differ from those of {@link List#remove(int)}.
598		*
599		* @return true if elements moved backwards
600		*/
601	<	private boolean delete(int i) {
602	<	// Case 1: Deque doesn't wrap
603	<	// Case 2: Deque does wrap and removed element is in the head portion
604	<	if ((head < tail || tail == 0) || i >= head) {
605	<	System.arraycopy(elements, head, elements, head + 1, i - head);
606	<	elements[head] = null;
607	<	head = (head + 1) & (elements.length - 1);
601	>	boolean delete(int i) {
602	>	// checkInvariants();
603	>	final Object[] elements = this.elements;
604	>	final int capacity = elements.length;
605	>	final int h = head;
606	>	int front;              // number of elements before to-be-deleted elt
607	>	if ((front = i - h) < 0) front += capacity;
608	>	final int back = size - front - 1; // number of elements after
609	>	if (front < back) {
610	>	// move front elements forwards
611	>	if (h <= i) {
612	>	System.arraycopy(elements, h, elements, h + 1, front);
613	>	} else { // Wrap around
614	>	System.arraycopy(elements, 0, elements, 1, i);
615	>	elements[0] = elements[capacity - 1];
616	>	System.arraycopy(elements, h, elements, h + 1, front - (i + 1));
617	>	}
618	>	elements[h] = null;
619	>	head = inc(h, capacity);
620	>	size--;
621	>	// checkInvariants();
622		return false;
623	+	} else {
624	+	// move back elements backwards
625	+	int tail = tail();
626	+	if (i <= tail) {
627	+	System.arraycopy(elements, i + 1, elements, i, back);
628	+	} else { // Wrap around
629	+	int firstLeg = capacity - (i + 1);
630	+	System.arraycopy(elements, i + 1, elements, i, firstLeg);
631	+	elements[capacity - 1] = elements[0];
632	+	System.arraycopy(elements, 1, elements, 0, back - firstLeg - 1);
633	+	}
634	+	elements[tail] = null;
635	+	size--;
636	+	// checkInvariants();
637	+	return true;
638		}
542	–
543	–	// Case 3: Deque wraps and removed element is in the tail portion
544	–	tail--;
545	–	System.arraycopy(elements, i + 1, elements, i, tail - i);
546	–	elements[tail] = null;
547	–	return true;
639		}
640
641		// *** Collection Methods ***
#	Line 555 | Line 646 | public class ArrayDeque<E> extends Abstr
646		* @return the number of elements in this deque
647		*/
648		public int size() {
649	<	return (tail - head) & (elements.length - 1);
649	>	return size;
650		}
651
652		/**
653	<	* Returns <tt>true</tt> if this deque contains no elements.<p>
653	>	* Returns {@code true} if this deque contains no elements.
654		*
655	<	* @return <tt>true</tt> if this deque contains no elements.
655	>	* @return {@code true} if this deque contains no elements
656		*/
657		public boolean isEmpty() {
658	<	return head == tail;
658	>	return size == 0;
659		}
660
661		/**
#	Line 573 | Line 664 | public class ArrayDeque<E> extends Abstr
664		* order that elements would be dequeued (via successive calls to
665		* {@link #remove} or popped (via successive calls to {@link #pop}).
666		*
667	<	* @return an <tt>Iterator</tt> over the elements in this deque
667	>	* @return an iterator over the elements in this deque
668		*/
669		public Iterator<E> iterator() {
670		return new DeqIterator();
671		}
672
673	+	public Iterator<E> descendingIterator() {
674	+	return new DescendingIterator();
675	+	}
676	+
677		private class DeqIterator implements Iterator<E> {
678	<	/**
679	<	* Index of element to be returned by subsequent call to next.
585	<	*/
586	<	private int cursor = head;
678	>	/** Index of element to be returned by subsequent call to next. */
679	>	int cursor;
680
681	<	/**
682	<	* Tail recorded at construction (also in remove), to stop
590	<	* iterator and also to check for comodification.
591	<	*/
592	<	private int fence = tail;
681	>	/** Number of elements yet to be returned. */
682	>	int remaining = size;
683
684		/**
685		* Index of element returned by most recent call to next.
686		* Reset to -1 if element is deleted by a call to remove.
687		*/
688	<	private int lastRet = -1;
688	>	int lastRet = -1;
689
690	<	public boolean hasNext() {
691	<	return cursor != fence;
690	>	DeqIterator() { cursor = head; }
691	>
692	>	void doAdvance() {
693	>	cursor = inc(cursor, elements.length);
694		}
695
696	<	public E next() {
697	<	E result;
698	<	if (cursor == fence)
696	>	void doRemove() {
697	>	if (delete(lastRet))
698	>	// if left-shifted, undo advance in next()
699	>	cursor = dec(cursor, elements.length);
700	>	}
701	>
702	>	public final boolean hasNext() {
703	>	return remaining > 0;
704	>	}
705	>
706	>	public final E next() {
707	>	if (remaining == 0)
708		throw new NoSuchElementException();
709	<	// This check doesn't catch all possible comodifications,
609	<	// but does catch the ones that corrupt traversal
610	<	if (tail != fence || (result = elements[cursor]) == null)
611	<	throw new ConcurrentModificationException();
709	>	E e = checkedElementAt(elements, cursor);
710		lastRet = cursor;
711	<	cursor = (cursor + 1) & (elements.length - 1);
712	<	return result;
711	>	doAdvance();
712	>	remaining--;
713	>	return e;
714		}
715
716	<	public void remove() {
716	>	public final void remove() {
717		if (lastRet < 0)
718		throw new IllegalStateException();
719	<	if (delete(lastRet))
621	<	cursor--;
719	>	doRemove();
720		lastRet = -1;
721	<	fence = tail;
721	>	}
722	>
723	>	public final void forEachRemaining(Consumer<? super E> action) {
724	>	Objects.requireNonNull(action);
725	>	final Object[] elements = ArrayDeque.this.elements;
726	>	final int capacity = elements.length;
727	>	for (; remaining > 0; remaining--) {
728	>	action.accept(checkedElementAt(elements, cursor));
729	>	doAdvance();
730	>	}
731	>	}
732	>	}
733	>
734	>	private class DescendingIterator extends DeqIterator {
735	>	DescendingIterator() { cursor = tail(); }
736	>
737	>	@Override void doAdvance() {
738	>	cursor = dec(cursor, elements.length);
739	>	}
740	>
741	>	@Override void doRemove() {
742	>	if (!delete(lastRet))
743	>	// if right-shifted, undo advance in next
744	>	cursor = inc(cursor, elements.length);
745	>	}
746	>	}
747	>
748	>	/**
749	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
750	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
751	>	* deque.
752	>	*
753	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
754	>	* {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and
755	>	* {@link Spliterator#NONNULL}.  Overriding implementations should document
756	>	* the reporting of additional characteristic values.
757	>	*
758	>	* @return a {@code Spliterator} over the elements in this deque
759	>	* @since 1.8
760	>	*/
761	>	public Spliterator<E> spliterator() {
762	>	return new ArrayDequeSpliterator(head, size);
763	>	}
764	>
765	>	final class ArrayDequeSpliterator implements Spliterator<E> {
766	>	private int cursor;
767	>	private int remaining;
768	>
769	>	/** Creates new spliterator covering the given array slice. */
770	>	ArrayDequeSpliterator(int cursor, int count) {
771	>	this.cursor = cursor;
772	>	this.remaining = count;
773	>	}
774	>
775	>	public ArrayDequeSpliterator trySplit() {
776	>	if (remaining > 1) {
777	>	int mid = remaining >> 1;
778	>	int oldCursor = cursor;
779	>	cursor += mid;
780	>	if (cursor >= elements.length) cursor -= elements.length;
781	>	remaining -= mid;
782	>	return new ArrayDequeSpliterator(oldCursor, mid);
783	>	}
784	>	return null;
785	>	}
786	>
787	>	public void forEachRemaining(Consumer<? super E> action) {
788	>	Objects.requireNonNull(action);
789	>	final Object[] elements = ArrayDeque.this.elements;
790	>	final int capacity = elements.length;
791	>	for (; remaining > 0; cursor = inc(cursor, capacity), remaining--)
792	>	action.accept(checkedElementAt(elements, cursor));
793	>	}
794	>
795	>	public boolean tryAdvance(Consumer<? super E> action) {
796	>	Objects.requireNonNull(action);
797	>	if (remaining <= 0)
798	>	return false;
799	>	action.accept(checkedElementAt(elements, cursor));
800	>	cursor = inc(cursor, elements.length);
801	>	remaining--;
802	>	return true;
803	>	}
804	>
805	>	public long estimateSize() {
806	>	return remaining;
807	>	}
808	>
809	>	public int characteristics() {
810	>	return Spliterator.NONNULL
811	>	| Spliterator.ORDERED
812	>	| Spliterator.SIZED
813	>	| Spliterator.SUBSIZED;
814	>	}
815	>	}
816	>
817	>	@Override
818	>	public void forEach(Consumer<? super E> action) {
819	>	// checkInvariants();
820	>	Objects.requireNonNull(action);
821	>	final Object[] elements = this.elements;
822	>	final int capacity = elements.length;
823	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity))
824	>	action.accept(elementAt(i));
825	>	// checkInvariants();
826	>	}
827	>
828	>	/**
829	>	* Replaces each element of this deque with the result of applying the
830	>	* operator to that element, as specified by {@link List#replaceAll}.
831	>	*
832	>	* @param operator the operator to apply to each element
833	>	* @since 9
834	>	*/
835	>	public void replaceAll(UnaryOperator<E> operator) {
836	>	Objects.requireNonNull(operator);
837	>	final Object[] elements = this.elements;
838	>	final int capacity = elements.length;
839	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity))
840	>	elements[i] = operator.apply(elementAt(i));
841	>	// checkInvariants();
842	>	}
843	>
844	>	/**
845	>	* @throws NullPointerException {@inheritDoc}
846	>	*/
847	>	@Override
848	>	public boolean removeIf(Predicate<? super E> filter) {
849	>	Objects.requireNonNull(filter);
850	>	return bulkRemove(filter);
851	>	}
852	>
853	>	/**
854	>	* @throws NullPointerException {@inheritDoc}
855	>	*/
856	>	@Override
857	>	public boolean removeAll(Collection<?> c) {
858	>	Objects.requireNonNull(c);
859	>	return bulkRemove(e -> c.contains(e));
860	>	}
861	>
862	>	/**
863	>	* @throws NullPointerException {@inheritDoc}
864	>	*/
865	>	@Override
866	>	public boolean retainAll(Collection<?> c) {
867	>	Objects.requireNonNull(c);
868	>	return bulkRemove(e -> !c.contains(e));
869	>	}
870	>
871	>	/** Implementation of bulk remove methods. */
872	>	private boolean bulkRemove(Predicate<? super E> filter) {
873	>	// checkInvariants();
874	>	final Object[] elements = this.elements;
875	>	final int capacity = elements.length;
876	>	int i = head, j = i, remaining = size, deleted = 0;
877	>	try {
878	>	for (; remaining > 0; remaining--, i = inc(i, capacity)) {
879	>	@SuppressWarnings("unchecked") E e = (E) elements[i];
880	>	if (filter.test(e))
881	>	deleted++;
882	>	else {
883	>	if (j != i)
884	>	elements[j] = e;
885	>	j = inc(j, capacity);
886	>	}
887	>	}
888	>	return deleted > 0;
889	>	} catch (Throwable ex) {
890	>	for (; remaining > 0;
891	>	remaining--, i = inc(i, capacity), j = inc(j, capacity))
892	>	elements[j] = elements[i];
893	>	throw ex;
894	>	} finally {
895	>	size -= deleted;
896	>	for (; --deleted >= 0; j = inc(j, capacity))
897	>	elements[j] = null;
898	>	// checkInvariants();
899		}
900		}
901
902		/**
903	<	* Returns <tt>true</tt> if this deque contains the specified
904	<	* element.  More formally, returns <tt>true</tt> if and only if this
905	<	* deque contains at least one element <tt>e</tt> such that
631	<	* <tt>e.equals(o)</tt>.
903	>	* Returns {@code true} if this deque contains the specified element.
904	>	* More formally, returns {@code true} if and only if this deque contains
905	>	* at least one element {@code e} such that {@code o.equals(e)}.
906		*
907		* @param o object to be checked for containment in this deque
908	<	* @return <tt>true</tt> if this deque contains the specified element
908	>	* @return {@code true} if this deque contains the specified element
909		*/
910		public boolean contains(Object o) {
911	<	if (o == null)
912	<	return false;
913	<	int mask = elements.length - 1;
914	<	int i = head;
915	<	E x;
916	<	while ( (x = elements[i]) != null) {
643	<	if (o.equals(x))
644	<	return true;
645	<	i = (i + 1) & mask;
911	>	if (o != null) {
912	>	final Object[] elements = this.elements;
913	>	final int capacity = elements.length;
914	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity))
915	>	if (o.equals(elements[i]))
916	>	return true;
917		}
918		return false;
919		}
920
921		/**
922		* Removes a single instance of the specified element from this deque.
923	<	* This method is equivalent to {@link #removeFirstOccurrence}.
923	>	* If the deque does not contain the element, it is unchanged.
924	>	* More formally, removes the first element {@code e} such that
925	>	* {@code o.equals(e)} (if such an element exists).
926	>	* Returns {@code true} if this deque contained the specified element
927	>	* (or equivalently, if this deque changed as a result of the call).
928		*
929	<	* @param e element to be removed from this deque, if present
930	<	* @return <tt>true</tt> if this deque contained the specified element
929	>	* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
930	>	*
931	>	* @param o element to be removed from this deque, if present
932	>	* @return {@code true} if this deque contained the specified element
933		*/
934	<	public boolean remove(Object e) {
935	<	return removeFirstOccurrence(e);
934	>	public boolean remove(Object o) {
935	>	return removeFirstOccurrence(o);
936		}
937
938		/**
#	Line 663 | Line 940 | public class ArrayDeque<E> extends Abstr
940		* The deque will be empty after this call returns.
941		*/
942		public void clear() {
943	<	int h = head;
944	<	int t = tail;
945	<	if (h != t) { // clear all cells
946	<	head = tail = 0;
947	<	int i = h;
948	<	int mask = elements.length - 1;
949	<	do {
950	<	elements[i] = null;
951	<	i = (i + 1) & mask;
675	<	} while(i != t);
943	>	final Object[] elements = this.elements;
944	>	final int capacity = elements.length;
945	>	final int h = this.head;
946	>	final int s = size;
947	>	if (capacity - h >= s)
948	>	Arrays.fill(elements, h, h + s, null);
949	>	else {
950	>	Arrays.fill(elements, h, capacity, null);
951	>	Arrays.fill(elements, 0, s - capacity + h, null);
952		}
953	+	size = head = 0;
954	+	// checkInvariants();
955		}
956
957		/**
958		* Returns an array containing all of the elements in this deque
959	<	* in the correct order.
959	>	* in proper sequence (from first to last element).
960	>	*
961	>	* <p>The returned array will be "safe" in that no references to it are
962	>	* maintained by this deque.  (In other words, this method must allocate
963	>	* a new array).  The caller is thus free to modify the returned array.
964	>	*
965	>	* <p>This method acts as bridge between array-based and collection-based
966	>	* APIs.
967		*
968		* @return an array containing all of the elements in this deque
684	–	*         in the correct order
969		*/
970		public Object[] toArray() {
971	<	return copyElements(new Object[size()]);
971	>	final int head = this.head;
972	>	final int firstLeg;
973	>	Object[] a = Arrays.copyOfRange(elements, head, head + size);
974	>	if ((firstLeg = elements.length - head) < size)
975	>	System.arraycopy(elements, 0, a, firstLeg, size - firstLeg);
976	>	return a;
977		}
978
979		/**
980	<	* Returns an array containing all of the elements in this deque in the
981	<	* correct order; the runtime type of the returned array is that of the
982	<	* specified array.  If the deque fits in the specified array, it is
983	<	* returned therein.  Otherwise, a new array is allocated with the runtime
984	<	* type of the specified array and the size of this deque.
980	>	* Returns an array containing all of the elements in this deque in
981	>	* proper sequence (from first to last element); the runtime type of the
982	>	* returned array is that of the specified array.  If the deque fits in
983	>	* the specified array, it is returned therein.  Otherwise, a new array
984	>	* is allocated with the runtime type of the specified array and the
985	>	* size of this deque.
986	>	*
987	>	* <p>If this deque fits in the specified array with room to spare
988	>	* (i.e., the array has more elements than this deque), the element in
989	>	* the array immediately following the end of the deque is set to
990	>	* {@code null}.
991	>	*
992	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
993	>	* array-based and collection-based APIs.  Further, this method allows
994	>	* precise control over the runtime type of the output array, and may,
995	>	* under certain circumstances, be used to save allocation costs.
996	>	*
997	>	* <p>Suppose {@code x} is a deque known to contain only strings.
998	>	* The following code can be used to dump the deque into a newly
999	>	* allocated array of {@code String}:
1000		*
1001	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
1002	<	* the array has more elements than the deque), the element in the array
1003	<	* immediately following the end of the collection is set to <tt>null</tt>.
1001	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
1002	>	*
1003	>	* Note that {@code toArray(new Object[0])} is identical in function to
1004	>	* {@code toArray()}.
1005		*
1006		* @param a the array into which the elements of the deque are to
1007	<	*          be stored, if it is big enough; otherwise, a new array of the
1008	<	*          same runtime type is allocated for this purpose
1009	<	* @return an array containing the elements of the deque
1010	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
1011	<	*         of the runtime type of every element in this deque
1007	>	*          be stored, if it is big enough; otherwise, a new array of the
1008	>	*          same runtime type is allocated for this purpose
1009	>	* @return an array containing all of the elements in this deque
1010	>	* @throws ArrayStoreException if the runtime type of the specified array
1011	>	*         is not a supertype of the runtime type of every element in
1012	>	*         this deque
1013	>	* @throws NullPointerException if the specified array is null
1014		*/
1015	+	@SuppressWarnings("unchecked")
1016		public <T> T[] toArray(T[] a) {
1017	<	int size = size();
1018	<	if (a.length < size)
1019	<	a = (T[])java.lang.reflect.Array.newInstance(
1020	<	a.getClass().getComponentType(), size);
1021	<	copyElements(a);
1022	<	if (a.length > size)
1023	<	a[size] = null;
1017	>	final Object[] elements = this.elements;
1018	>	final int head = this.head;
1019	>	final int firstLeg;
1020	>	boolean wrap = (firstLeg = elements.length - head) < size;
1021	>	if (size > a.length) {
1022	>	a = (T[]) Arrays.copyOfRange(elements, head, head + size,
1023	>	a.getClass());
1024	>	} else {
1025	>	System.arraycopy(elements, head, a, 0, wrap ? firstLeg : size);
1026	>	if (size < a.length)
1027	>	a[size] = null;
1028	>	}
1029	>	if (wrap)
1030	>	System.arraycopy(elements, 0, a, firstLeg, size - firstLeg);
1031		return a;
1032		}
1033
#	Line 725 | Line 1040 | public class ArrayDeque<E> extends Abstr
1040		*/
1041		public ArrayDeque<E> clone() {
1042		try {
1043	+	@SuppressWarnings("unchecked")
1044		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
1045	<	// These two lines are currently faster than cloning the array:
730	<	result.elements = (E[]) new Object[elements.length];
731	<	System.arraycopy(elements, 0, result.elements, 0, elements.length);
1045	>	result.elements = Arrays.copyOf(elements, elements.length);
1046		return result;
733	–
1047		} catch (CloneNotSupportedException e) {
1048		throw new AssertionError();
1049		}
1050		}
1051
739	–	/**
740	–	* Appease the serialization gods.
741	–	*/
1052		private static final long serialVersionUID = 2340985798034038923L;
1053
1054		/**
1055	<	* Serialize this deque.
1055	>	* Saves this deque to a stream (that is, serializes it).
1056		*
1057	<	* @serialData The current size (<tt>int</tt>) of the deque,
1057	>	* @param s the stream
1058	>	* @throws java.io.IOException if an I/O error occurs
1059	>	* @serialData The current size ({@code int}) of the deque,
1060		* followed by all of its elements (each an object reference) in
1061		* first-to-last order.
1062		*/
1063	<	private void writeObject(ObjectOutputStream s) throws IOException {
1063	>	private void writeObject(java.io.ObjectOutputStream s)
1064	>	throws java.io.IOException {
1065		s.defaultWriteObject();
1066
1067		// Write out size
755	–	int size = size();
1068		s.writeInt(size);
1069
1070		// Write out elements in order.
1071	<	int i = head;
1072	<	int mask = elements.length - 1;
1073	<	for (int j = 0; j < size; j++) {
1071	>	final Object[] elements = this.elements;
1072	>	final int capacity = elements.length;
1073	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity))
1074		s.writeObject(elements[i]);
763	–	i = (i + 1) & mask;
764	–	}
1075		}
1076
1077		/**
1078	<	* Deserialize this deque.
1078	>	* Reconstitutes this deque from a stream (that is, deserializes it).
1079	>	* @param s the stream
1080	>	* @throws ClassNotFoundException if the class of a serialized object
1081	>	*         could not be found
1082	>	* @throws java.io.IOException if an I/O error occurs
1083		*/
1084	<	private void readObject(ObjectInputStream s)
1085	<	throws IOException, ClassNotFoundException {
1084	>	private void readObject(java.io.ObjectInputStream s)
1085	>	throws java.io.IOException, ClassNotFoundException {
1086		s.defaultReadObject();
1087
1088		// Read in size and allocate array
1089	<	int size = s.readInt();
776	<	allocateElements(size);
777	<	head = 0;
778	<	tail = size;
1089	>	elements = new Object[size = s.readInt()];
1090
1091		// Read in all elements in the proper order.
1092		for (int i = 0; i < size; i++)
1093	<	elements[i] = (E)s.readObject();
1093	>	elements[i] = s.readObject();
1094	>	}
1095
1096	+	/** debugging */
1097	+	private void checkInvariants() {
1098	+	try {
1099	+	int capacity = elements.length;
1100	+	assert size >= 0 && size <= capacity;
1101	+	assert head >= 0 && ((capacity == 0 && head == 0 && size == 0)
1102	+	|| head < capacity);
1103	+	assert size == 0
1104	+	|| (elements[head] != null && elements[tail()] != null);
1105	+	assert size == capacity
1106	+	|| (elements[dec(head, capacity)] == null
1107	+	&& elements[inc(tail(), capacity)] == null);
1108	+	} catch (Throwable t) {
1109	+	System.err.printf("head=%d size=%d capacity=%d%n",
1110	+	head, size, elements.length);
1111	+	System.err.printf("elements=%s%n",
1112	+	Arrays.toString(elements));
1113	+	throw t;
1114	+	}
1115		}
1116	+
1117		}

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