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root/jsr166/jsr166/src/main/java/util/ArrayDeque.java

Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.5 by dl, Tue Mar 22 01:29:00 2005 UTC vs.
Revision 1.74 by jsr166, Wed Aug 24 21:46:18 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
11		/**
12		* Resizable-array implementation of the {@link Deque} interface.  Array
#	Line 15 | Line 17 | import java.io.*;
17		* {@link Stack} when used as a stack, and faster than {@link LinkedList}
18		* when used as a queue.
19		*
20	<	* <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time.
21	<	* Exceptions include {@link #remove(Object) remove}, {@link
22	<	* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
23	<	* removeLastOccurrence}, {@link #contains contains }, {@link #iterator
24	<	* iterator.remove()}, and the bulk operations, all of which run in linear
25	<	* time.
20	>	* <p>Most {@code ArrayDeque} operations run in amortized constant time.
21	>	* Exceptions include
22	>	* {@link #remove(Object) remove},
23	>	* {@link #removeFirstOccurrence removeFirstOccurrence},
24	>	* {@link #removeLastOccurrence removeLastOccurrence},
25	>	* {@link #contains contains},
26	>	* {@link #iterator iterator.remove()},
27	>	* and the bulk operations, all of which run in linear time.
28		*
29	<	* <p>The iterators returned by this class's <tt>iterator</tt> method are
30	<	* <i>fail-fast</i>: If the deque is modified at any time after the iterator
31	<	* is created, in any way except through the iterator's own remove method, the
32	<	* iterator will generally throw a {@link ConcurrentModificationException}.
33	<	* Thus, in the face of concurrent modification, the iterator fails quickly
34	<	* and cleanly, rather than risking arbitrary, non-deterministic behavior at
35	<	* an undetermined time in the future.
29	>	* <p>The iterators returned by this class's {@link #iterator() iterator}
30	>	* method are <em>fail-fast</em>: If the deque is modified at any time after
31	>	* the iterator is created, in any way except through the iterator's own
32	>	* {@code remove} method, the iterator will generally throw a {@link
33	>	* ConcurrentModificationException}.  Thus, in the face of concurrent
34	>	* modification, the iterator fails quickly and cleanly, rather than risking
35	>	* arbitrary, non-deterministic behavior at an undetermined time in the
36	>	* future.
37		*
38		* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
39		* as it is, generally speaking, impossible to make any hard guarantees in the
40		* presence of unsynchronized concurrent modification.  Fail-fast iterators
41	<	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
41	>	* throw {@code ConcurrentModificationException} on a best-effort basis.
42		* Therefore, it would be wrong to write a program that depended on this
43		* exception for its correctness: <i>the fail-fast behavior of iterators
44		* should be used only to detect bugs.</i>
45		*
46		* <p>This class and its iterator implement all of the
47	<	* optional methods of the {@link Collection} and {@link
48	<	* Iterator} interfaces.  This class is a member of the <a
49	<	* href="{@docRoot}/../guide/collections/index.html"> Java Collections
50	<	* Framework</a>.
47	>	* <em>optional</em> methods of the {@link Collection} and {@link
48	>	* Iterator} interfaces.
49	>	*
50	>	* <p>This class is a member of the
51	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
52	>	* Java Collections Framework</a>.
53		*
54		* @author  Josh Bloch and Doug Lea
55	+	* @param <E> the type of elements held in this deque
56		* @since   1.6
49	–	* @param <E> the type of elements held in this collection
57		*/
58		public class ArrayDeque<E> extends AbstractCollection<E>
59		implements Deque<E>, Cloneable, Serializable
#	Line 61 | Line 68 | public class ArrayDeque<E> extends Abstr
68		* other.  We also guarantee that all array cells not holding
69		* deque elements are always null.
70		*/
71	<	private transient E[] elements;
71	>	transient Object[] elements; // non-private to simplify nested class access
72
73		/**
74		* The index of the element at the head of the deque (which is the
75		* element that would be removed by remove() or pop()); or an
76		* arbitrary number equal to tail if the deque is empty.
77		*/
78	<	private transient int head;
78	>	transient int head;
79
80		/**
81		* The index at which the next element would be added to the tail
82		* of the deque (via addLast(E), add(E), or push(E)).
83		*/
84	<	private transient int tail;
84	>	transient int tail;
85
86		/**
87		* The minimum capacity that we'll use for a newly created deque.
#	Line 85 | Line 92 | public class ArrayDeque<E> extends Abstr
92		// ******  Array allocation and resizing utilities ******
93
94		/**
95	<	* Allocate empty array to hold the given number of elements.
95	>	* Allocates empty array to hold the given number of elements.
96		*
97	<	* @param numElements  the number of elements to hold.
97	>	* @param numElements  the number of elements to hold
98		*/
99		private void allocateElements(int numElements) {
100		int initialCapacity = MIN_INITIAL_CAPACITY;
#	Line 102 | Line 109 | public class ArrayDeque<E> extends Abstr
109		initialCapacity |= (initialCapacity >>> 16);
110		initialCapacity++;
111
112	<	if (initialCapacity < 0)   // Too many elements, must back off
113	<	initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
112	>	if (initialCapacity < 0)    // Too many elements, must back off
113	>	initialCapacity >>>= 1; // Good luck allocating 2^30 elements
114		}
115	<	elements = (E[]) new Object[initialCapacity];
115	>	elements = new Object[initialCapacity];
116		}
117
118		/**
119	<	* Double the capacity of this deque.  Call only when full, i.e.,
119	>	* Doubles the capacity of this deque.  Call only when full, i.e.,
120		* when head and tail have wrapped around to become equal.
121		*/
122		private void doubleCapacity() {
#	Line 123 | Line 130 | public class ArrayDeque<E> extends Abstr
130		Object[] a = new Object[newCapacity];
131		System.arraycopy(elements, p, a, 0, r);
132		System.arraycopy(elements, 0, a, r, p);
133	<	elements = (E[])a;
133	>	elements = a;
134		head = 0;
135		tail = n;
136		}
137
138		/**
132	–	* Copy the elements from our element array into the specified array,
133	–	* in order (from first to last element in the deque).  It is assumed
134	–	* that the array is large enough to hold all elements in the deque.
135	–	*
136	–	* @return its argument
137	–	*/
138	–	private <T> T[] copyElements(T[] a) {
139	–	if (head < tail) {
140	–	System.arraycopy(elements, head, a, 0, size());
141	–	} else if (head > tail) {
142	–	int headPortionLen = elements.length - head;
143	–	System.arraycopy(elements, head, a, 0, headPortionLen);
144	–	System.arraycopy(elements, 0, a, headPortionLen, tail);
145	–	}
146	–	return a;
147	–	}
148	–
149	–	/**
139		* Constructs an empty array deque with an initial capacity
140		* sufficient to hold 16 elements.
141		*/
142		public ArrayDeque() {
143	<	elements = (E[]) new Object[16];
143	>	elements = new Object[16];
144		}
145
146		/**
#	Line 186 | Line 175 | public class ArrayDeque<E> extends Abstr
175		/**
176		* Inserts the specified element at the front of this deque.
177		*
178	<	* @param e the element to insert
179	<	* @throws NullPointerException if <tt>e</tt> is null
178	>	* @param e the element to add
179	>	* @throws NullPointerException if the specified element is null
180		*/
181		public void addFirst(E e) {
182		if (e == null)
#	Line 198 | Line 187 | public class ArrayDeque<E> extends Abstr
187		}
188
189		/**
190	<	* Inserts the specified element to the end of this deque.
191	<	* This method is equivalent to {@link Collection#add} and
192	<	* {@link #push}.
190	>	* Inserts the specified element at the end of this deque.
191	>	*
192	>	* <p>This method is equivalent to {@link #add}.
193		*
194	<	* @param e the element to insert
195	<	* @throws NullPointerException if <tt>e</tt> is null
194	>	* @param e the element to add
195	>	* @throws NullPointerException if the specified element is null
196		*/
197		public void addLast(E e) {
198		if (e == null)
#	Line 214 | Line 203 | public class ArrayDeque<E> extends Abstr
203		}
204
205		/**
217	–	* Retrieves and removes the first element of this deque, or
218	–	* <tt>null</tt> if this deque is empty.
219	–	*
220	–	* @return the first element of this deque, or <tt>null</tt> if
221	–	*     this deque is empty
222	–	*/
223	–	public E pollFirst() {
224	–	int h = head;
225	–	E result = elements[h]; // Element is null if deque empty
226	–	if (result == null)
227	–	return null;
228	–	elements[h] = null;     // Must null out slot
229	–	head = (h + 1) & (elements.length - 1);
230	–	return result;
231	–	}
232	–
233	–	/**
234	–	* Retrieves and removes the last element of this deque, or
235	–	* <tt>null</tt> if this deque is empty.
236	–	*
237	–	* @return the last element of this deque, or <tt>null</tt> if
238	–	*     this deque is empty
239	–	*/
240	–	public E pollLast() {
241	–	int t = (tail - 1) & (elements.length - 1);
242	–	E result = elements[t];
243	–	if (result == null)
244	–	return null;
245	–	elements[t] = null;
246	–	tail = t;
247	–	return result;
248	–	}
249	–
250	–	/**
206		* Inserts the specified element at the front of this deque.
207		*
208	<	* @param e the element to insert
209	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst})
210	<	* @throws NullPointerException if <tt>e</tt> is null
208	>	* @param e the element to add
209	>	* @return {@code true} (as specified by {@link Deque#offerFirst})
210	>	* @throws NullPointerException if the specified element is null
211		*/
212		public boolean offerFirst(E e) {
213		addFirst(e);
#	Line 260 | Line 215 | public class ArrayDeque<E> extends Abstr
215		}
216
217		/**
218	<	* Inserts the specified element to the end of this deque.
218	>	* Inserts the specified element at the end of this deque.
219		*
220	<	* @param e the element to insert
221	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
222	<	* @throws NullPointerException if <tt>e</tt> is null
220	>	* @param e the element to add
221	>	* @return {@code true} (as specified by {@link Deque#offerLast})
222	>	* @throws NullPointerException if the specified element is null
223		*/
224		public boolean offerLast(E e) {
225		addLast(e);
#	Line 272 | Line 227 | public class ArrayDeque<E> extends Abstr
227		}
228
229		/**
230	<	* Retrieves and removes the first element of this deque.  This method
276	<	* differs from the <tt>pollFirst</tt> method in that it throws an
277	<	* exception if this deque is empty.
278	<	*
279	<	* @return the first element of this deque
280	<	* @throws NoSuchElementException if this deque is empty
230	>	* @throws NoSuchElementException {@inheritDoc}
231		*/
232		public E removeFirst() {
233		E x = pollFirst();
#	Line 287 | Line 237 | public class ArrayDeque<E> extends Abstr
237		}
238
239		/**
240	<	* Retrieves and removes the last element of this deque.  This method
291	<	* differs from the <tt>pollLast</tt> method in that it throws an
292	<	* exception if this deque is empty.
293	<	*
294	<	* @return the last element of this deque
295	<	* @throws NoSuchElementException if this deque is empty
240	>	* @throws NoSuchElementException {@inheritDoc}
241		*/
242		public E removeLast() {
243		E x = pollLast();
#	Line 301 | Line 246 | public class ArrayDeque<E> extends Abstr
246		return x;
247		}
248
249	<	/**
250	<	* Retrieves, but does not remove, the first element of this deque,
251	<	* returning <tt>null</tt> if this deque is empty.
252	<	*
253	<	* @return the first element of this deque, or <tt>null</tt> if
254	<	*     this deque is empty
255	<	*/
256	<	public E peekFirst() {
257	<	return elements[head]; // elements[head] is null if deque empty
249	>	public E pollFirst() {
250	>	final Object[] elements = this.elements;
251	>	final int h = head;
252	>	@SuppressWarnings("unchecked")
253	>	E result = (E) elements[h];
254	>	// Element is null if deque empty
255	>	if (result != null) {
256	>	elements[h] = null; // Must null out slot
257	>	head = (h + 1) & (elements.length - 1);
258	>	}
259	>	return result;
260		}
261
262	<	/**
263	<	* Retrieves, but does not remove, the last element of this deque,
264	<	* returning <tt>null</tt> if this deque is empty.
265	<	*
266	<	* @return the last element of this deque, or <tt>null</tt> if this deque
267	<	*     is empty
268	<	*/
269	<	public E peekLast() {
270	<	return elements[(tail - 1) & (elements.length - 1)];
262	>	public E pollLast() {
263	>	final Object[] elements = this.elements;
264	>	final int t = (tail - 1) & (elements.length - 1);
265	>	@SuppressWarnings("unchecked")
266	>	E result = (E) elements[t];
267	>	if (result != null) {
268	>	elements[t] = null;
269	>	tail = t;
270	>	}
271	>	return result;
272		}
273
274		/**
275	<	* Retrieves, but does not remove, the first element of this
328	<	* deque.  This method differs from the <tt>peekFirst</tt> method only
329	<	* in that it throws an exception if this deque is empty.
330	<	*
331	<	* @return the first element of this deque
332	<	* @throws NoSuchElementException if this deque is empty
275	>	* @throws NoSuchElementException {@inheritDoc}
276		*/
277		public E getFirst() {
278	<	E x = elements[head];
279	<	if (x == null)
278	>	@SuppressWarnings("unchecked")
279	>	E result = (E) elements[head];
280	>	if (result == null)
281		throw new NoSuchElementException();
282	<	return x;
282	>	return result;
283		}
284
285		/**
286	<	* Retrieves, but does not remove, the last element of this
343	<	* deque.  This method differs from the <tt>peekLast</tt> method only
344	<	* in that it throws an exception if this deque is empty.
345	<	*
346	<	* @return the last element of this deque
347	<	* @throws NoSuchElementException if this deque is empty
286	>	* @throws NoSuchElementException {@inheritDoc}
287		*/
288		public E getLast() {
289	<	E x = elements[(tail - 1) & (elements.length - 1)];
290	<	if (x == null)
289	>	@SuppressWarnings("unchecked")
290	>	E result = (E) elements[(tail - 1) & (elements.length - 1)];
291	>	if (result == null)
292		throw new NoSuchElementException();
293	<	return x;
293	>	return result;
294	>	}
295	>
296	>	@SuppressWarnings("unchecked")
297	>	public E peekFirst() {
298	>	// elements[head] is null if deque empty
299	>	return (E) elements[head];
300	>	}
301	>
302	>	@SuppressWarnings("unchecked")
303	>	public E peekLast() {
304	>	return (E) elements[(tail - 1) & (elements.length - 1)];
305		}
306
307		/**
308		* Removes the first occurrence of the specified element in this
309	<	* deque (when traversing the deque from head to tail).  More
310	<	* formally, removes the first element e such that (o==null ?
311	<	* e==null : o.equals(e)). If the deque does not contain the
312	<	* element, it is unchanged.
309	>	* deque (when traversing the deque from head to tail).
310	>	* If the deque does not contain the element, it is unchanged.
311	>	* More formally, removes the first element {@code e} such that
312	>	* {@code o.equals(e)} (if such an element exists).
313	>	* Returns {@code true} if this deque contained the specified element
314	>	* (or equivalently, if this deque changed as a result of the call).
315		*
316		* @param o element to be removed from this deque, if present
317	<	* @return <tt>true</tt> if the deque contained the specified element
317	>	* @return {@code true} if the deque contained the specified element
318		*/
319		public boolean removeFirstOccurrence(Object o) {
320	<	if (o == null)
321	<	return false;
322	<	int mask = elements.length - 1;
323	<	int i = head;
324	<	E x;
325	<	while ( (x = elements[i]) != null) {
326	<	if (o.equals(x)) {
327	<	delete(i);
375	<	return true;
320	>	if (o != null) {
321	>	int mask = elements.length - 1;
322	>	int i = head;
323	>	for (Object x; (x = elements[i]) != null; i = (i + 1) & mask) {
324	>	if (o.equals(x)) {
325	>	delete(i);
326	>	return true;
327	>	}
328		}
377	–	i = (i + 1) & mask;
329		}
330		return false;
331		}
332
333		/**
334		* Removes the last occurrence of the specified element in this
335	<	* deque (when traversing the deque from head to tail). More
336	<	* formally, removes the last element e such that (o==null ?
337	<	* e==null : o.equals(e)). If the deque
338	<	* does not contain the element, it is unchanged.
335	>	* deque (when traversing the deque from head to tail).
336	>	* If the deque does not contain the element, it is unchanged.
337	>	* More formally, removes the last element {@code e} such that
338	>	* {@code o.equals(e)} (if such an element exists).
339	>	* Returns {@code true} if this deque contained the specified element
340	>	* (or equivalently, if this deque changed as a result of the call).
341		*
342		* @param o element to be removed from this deque, if present
343	<	* @return <tt>true</tt> if the deque contained the specified element
343	>	* @return {@code true} if the deque contained the specified element
344		*/
345		public boolean removeLastOccurrence(Object o) {
346	<	if (o == null)
347	<	return false;
348	<	int mask = elements.length - 1;
349	<	int i = (tail - 1) & mask;
350	<	E x;
351	<	while ( (x = elements[i]) != null) {
352	<	if (o.equals(x)) {
353	<	delete(i);
401	<	return true;
346	>	if (o != null) {
347	>	int mask = elements.length - 1;
348	>	int i = (tail - 1) & mask;
349	>	for (Object x; (x = elements[i]) != null; i = (i - 1) & mask) {
350	>	if (o.equals(x)) {
351	>	delete(i);
352	>	return true;
353	>	}
354		}
403	–	i = (i - 1) & mask;
355		}
356		return false;
357		}
#	Line 408 | Line 359 | public class ArrayDeque<E> extends Abstr
359		// *** Queue methods ***
360
361		/**
362	<	* Inserts the specified element to the end of this deque.
412	<	*
413	<	* <p>This method is equivalent to {@link #offerLast}.
414	<	*
415	<	* @param e the element to insert
416	<	* @return <tt>true</tt> (as per the spec for {@link Queue#offer})
417	<	* @throws NullPointerException if <tt>e</tt> is null
418	<	*/
419	<	public boolean offer(E e) {
420	<	return offerLast(e);
421	<	}
422	<
423	<	/**
424	<	* Inserts the specified element to the end of this deque.
362	>	* Inserts the specified element at the end of this deque.
363		*
364		* <p>This method is equivalent to {@link #addLast}.
365		*
366	<	* @param e the element to insert
367	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
368	<	* @throws NullPointerException if <tt>e</tt> is null
366	>	* @param e the element to add
367	>	* @return {@code true} (as specified by {@link Collection#add})
368	>	* @throws NullPointerException if the specified element is null
369		*/
370		public boolean add(E e) {
371		addLast(e);
#	Line 435 | Line 373 | public class ArrayDeque<E> extends Abstr
373		}
374
375		/**
376	<	* Retrieves and removes the head of the queue represented by
439	<	* this deque, or <tt>null</tt> if this deque is empty.  In other words,
440	<	* retrieves and removes the first element of this deque, or <tt>null</tt>
441	<	* if this deque is empty.
376	>	* Inserts the specified element at the end of this deque.
377		*
378	<	* <p>This method is equivalent to {@link #pollFirst}.
378	>	* <p>This method is equivalent to {@link #offerLast}.
379		*
380	<	* @return the first element of this deque, or <tt>null</tt> if
381	<	*     this deque is empty
380	>	* @param e the element to add
381	>	* @return {@code true} (as specified by {@link Queue#offer})
382	>	* @throws NullPointerException if the specified element is null
383		*/
384	<	public E poll() {
385	<	return pollFirst();
384	>	public boolean offer(E e) {
385	>	return offerLast(e);
386		}
387
388		/**
389		* Retrieves and removes the head of the queue represented by this deque.
390	<	* This method differs from the <tt>poll</tt> method in that it throws an
390	>	*
391	>	* This method differs from {@link #poll poll} only in that it throws an
392		* exception if this deque is empty.
393		*
394		* <p>This method is equivalent to {@link #removeFirst}.
395		*
396		* @return the head of the queue represented by this deque
397	<	* @throws NoSuchElementException if this deque is empty
397	>	* @throws NoSuchElementException {@inheritDoc}
398		*/
399		public E remove() {
400		return removeFirst();
401		}
402
403		/**
404	<	* Retrieves, but does not remove, the head of the queue represented by
405	<	* this deque, returning <tt>null</tt> if this deque is empty.
404	>	* Retrieves and removes the head of the queue represented by this deque
405	>	* (in other words, the first element of this deque), or returns
406	>	* {@code null} if this deque is empty.
407		*
408	<	* <p>This method is equivalent to {@link #peekFirst}
408	>	* <p>This method is equivalent to {@link #pollFirst}.
409		*
410		* @return the head of the queue represented by this deque, or
411	<	*     <tt>null</tt> if this deque is empty
411	>	*         {@code null} if this deque is empty
412		*/
413	<	public E peek() {
414	<	return peekFirst();
413	>	public E poll() {
414	>	return pollFirst();
415		}
416
417		/**
418		* Retrieves, but does not remove, the head of the queue represented by
419	<	* this deque.  This method differs from the <tt>peek</tt> method only in
419	>	* this deque.  This method differs from {@link #peek peek} only in
420		* that it throws an exception if this deque is empty.
421		*
422	<	* <p>This method is equivalent to {@link #getFirst}
422	>	* <p>This method is equivalent to {@link #getFirst}.
423		*
424		* @return the head of the queue represented by this deque
425	<	* @throws NoSuchElementException if this deque is empty
425	>	* @throws NoSuchElementException {@inheritDoc}
426		*/
427		public E element() {
428		return getFirst();
429		}
430
431	+	/**
432	+	* Retrieves, but does not remove, the head of the queue represented by
433	+	* this deque, or returns {@code null} if this deque is empty.
434	+	*
435	+	* <p>This method is equivalent to {@link #peekFirst}.
436	+	*
437	+	* @return the head of the queue represented by this deque, or
438	+	*         {@code null} if this deque is empty
439	+	*/
440	+	public E peek() {
441	+	return peekFirst();
442	+	}
443	+
444		// *** Stack methods ***
445
446		/**
#	Line 499 | Line 450 | public class ArrayDeque<E> extends Abstr
450		* <p>This method is equivalent to {@link #addFirst}.
451		*
452		* @param e the element to push
453	<	* @throws NullPointerException if <tt>e</tt> is null
453	>	* @throws NullPointerException if the specified element is null
454		*/
455		public void push(E e) {
456		addFirst(e);
#	Line 512 | Line 463 | public class ArrayDeque<E> extends Abstr
463		* <p>This method is equivalent to {@link #removeFirst()}.
464		*
465		* @return the element at the front of this deque (which is the top
466	<	*     of the stack represented by this deque)
467	<	* @throws NoSuchElementException if this deque is empty
466	>	*         of the stack represented by this deque)
467	>	* @throws NoSuchElementException {@inheritDoc}
468		*/
469		public E pop() {
470		return removeFirst();
471		}
472
473	+	private void checkInvariants() {
474	+	assert elements[tail] == null;
475	+	assert head == tail ? elements[head] == null :
476	+	(elements[head] != null &&
477	+	elements[(tail - 1) & (elements.length - 1)] != null);
478	+	assert elements[(head - 1) & (elements.length - 1)] == null;
479	+	}
480	+
481		/**
482	<	* Remove the element at the specified position in the elements array,
483	<	* adjusting head, tail, and size as necessary.  This can result in
484	<	* motion of elements backwards or forwards in the array.
482	>	* Removes the element at the specified position in the elements array,
483	>	* adjusting head and tail as necessary.  This can result in motion of
484	>	* elements backwards or forwards in the array.
485		*
486		* <p>This method is called delete rather than remove to emphasize
487	<	* that its semantics differ from those of List.remove(int).
487	>	* that its semantics differ from those of {@link List#remove(int)}.
488		*
489		* @return true if elements moved backwards
490		*/
491	<	private boolean delete(int i) {
492	<	// Case 1: Deque doesn't wrap
493	<	// Case 2: Deque does wrap and removed element is in the head portion
494	<	if ((head < tail || tail == 0) || i >= head) {
495	<	System.arraycopy(elements, head, elements, head + 1, i - head);
496	<	elements[head] = null;
497	<	head = (head + 1) & (elements.length - 1);
491	>	boolean delete(int i) {
492	>	checkInvariants();
493	>	final Object[] elements = this.elements;
494	>	final int mask = elements.length - 1;
495	>	final int h = head;
496	>	final int t = tail;
497	>	final int front = (i - h) & mask;
498	>	final int back  = (t - i) & mask;
499	>
500	>	// Invariant: head <= i < tail mod circularity
501	>	if (front >= ((t - h) & mask))
502	>	throw new ConcurrentModificationException();
503	>
504	>	// Optimize for least element motion
505	>	if (front < back) {
506	>	if (h <= i) {
507	>	System.arraycopy(elements, h, elements, h + 1, front);
508	>	} else { // Wrap around
509	>	System.arraycopy(elements, 0, elements, 1, i);
510	>	elements[0] = elements[mask];
511	>	System.arraycopy(elements, h, elements, h + 1, mask - h);
512	>	}
513	>	elements[h] = null;
514	>	head = (h + 1) & mask;
515		return false;
516	+	} else {
517	+	if (i < t) { // Copy the null tail as well
518	+	System.arraycopy(elements, i + 1, elements, i, back);
519	+	tail = t - 1;
520	+	} else { // Wrap around
521	+	System.arraycopy(elements, i + 1, elements, i, mask - i);
522	+	elements[mask] = elements[0];
523	+	System.arraycopy(elements, 1, elements, 0, t);
524	+	tail = (t - 1) & mask;
525	+	}
526	+	return true;
527		}
541	–
542	–	// Case 3: Deque wraps and removed element is in the tail portion
543	–	tail--;
544	–	System.arraycopy(elements, i + 1, elements, i, tail - i);
545	–	elements[tail] = null;
546	–	return true;
528		}
529
530		// *** Collection Methods ***
#	Line 558 | Line 539 | public class ArrayDeque<E> extends Abstr
539		}
540
541		/**
542	<	* Returns <tt>true</tt> if this collection contains no elements.<p>
542	>	* Returns {@code true} if this deque contains no elements.
543		*
544	<	* @return <tt>true</tt> if this collection contains no elements.
544	>	* @return {@code true} if this deque contains no elements
545		*/
546		public boolean isEmpty() {
547		return head == tail;
#	Line 572 | Line 553 | public class ArrayDeque<E> extends Abstr
553		* order that elements would be dequeued (via successive calls to
554		* {@link #remove} or popped (via successive calls to {@link #pop}).
555		*
556	<	* @return an <tt>Iterator</tt> over the elements in this deque
556	>	* @return an iterator over the elements in this deque
557		*/
558		public Iterator<E> iterator() {
559		return new DeqIterator();
560		}
561
562	+	public Iterator<E> descendingIterator() {
563	+	return new DescendingIterator();
564	+	}
565	+
566		private class DeqIterator implements Iterator<E> {
567		/**
568		* Index of element to be returned by subsequent call to next.
#	Line 601 | Line 586 | public class ArrayDeque<E> extends Abstr
586		}
587
588		public E next() {
604	–	E result;
589		if (cursor == fence)
590		throw new NoSuchElementException();
591	+	@SuppressWarnings("unchecked")
592	+	E result = (E) elements[cursor];
593		// This check doesn't catch all possible comodifications,
594		// but does catch the ones that corrupt traversal
595	<	if (tail != fence || (result = elements[cursor]) == null)
595	>	if (tail != fence || result == null)
596		throw new ConcurrentModificationException();
597		lastRet = cursor;
598		cursor = (cursor + 1) & (elements.length - 1);
#	Line 616 | Line 602 | public class ArrayDeque<E> extends Abstr
602		public void remove() {
603		if (lastRet < 0)
604		throw new IllegalStateException();
605	<	if (delete(lastRet))
606	<	cursor--;
605	>	if (delete(lastRet)) { // if left-shifted, undo increment in next()
606	>	cursor = (cursor - 1) & (elements.length - 1);
607	>	fence = tail;
608	>	}
609	>	lastRet = -1;
610	>	}
611	>
612	>	public void forEachRemaining(Consumer<? super E> action) {
613	>	Objects.requireNonNull(action);
614	>	Object[] a = elements;
615	>	int m = a.length - 1, f = fence, i = cursor;
616	>	cursor = f;
617	>	while (i != f) {
618	>	@SuppressWarnings("unchecked") E e = (E)a[i];
619	>	i = (i + 1) & m;
620	>	if (e == null)
621	>	throw new ConcurrentModificationException();
622	>	action.accept(e);
623	>	}
624	>	}
625	>	}
626	>
627	>	/**
628	>	* This class is nearly a mirror-image of DeqIterator, using tail
629	>	* instead of head for initial cursor, and head instead of tail
630	>	* for fence.
631	>	*/
632	>	private class DescendingIterator implements Iterator<E> {
633	>	private int cursor = tail;
634	>	private int fence = head;
635	>	private int lastRet = -1;
636	>
637	>	public boolean hasNext() {
638	>	return cursor != fence;
639	>	}
640	>
641	>	public E next() {
642	>	if (cursor == fence)
643	>	throw new NoSuchElementException();
644	>	cursor = (cursor - 1) & (elements.length - 1);
645	>	@SuppressWarnings("unchecked")
646	>	E result = (E) elements[cursor];
647	>	if (head != fence || result == null)
648	>	throw new ConcurrentModificationException();
649	>	lastRet = cursor;
650	>	return result;
651	>	}
652	>
653	>	public void remove() {
654	>	if (lastRet < 0)
655	>	throw new IllegalStateException();
656	>	if (!delete(lastRet)) {
657	>	cursor = (cursor + 1) & (elements.length - 1);
658	>	fence = head;
659	>	}
660		lastRet = -1;
622	–	fence = tail;
661		}
662		}
663
664		/**
665	<	* Returns <tt>true</tt> if this deque contains the specified
666	<	* element.  More formally, returns <tt>true</tt> if and only if this
667	<	* deque contains at least one element <tt>e</tt> such that
630	<	* <tt>e.equals(o)</tt>.
665	>	* Returns {@code true} if this deque contains the specified element.
666	>	* More formally, returns {@code true} if and only if this deque contains
667	>	* at least one element {@code e} such that {@code o.equals(e)}.
668		*
669		* @param o object to be checked for containment in this deque
670	<	* @return <tt>true</tt> if this deque contains the specified element
670	>	* @return {@code true} if this deque contains the specified element
671		*/
672		public boolean contains(Object o) {
673	<	if (o == null)
674	<	return false;
675	<	int mask = elements.length - 1;
676	<	int i = head;
677	<	E x;
678	<	while ( (x = elements[i]) != null) {
679	<	if (o.equals(x))
643	<	return true;
644	<	i = (i + 1) & mask;
673	>	if (o != null) {
674	>	int mask = elements.length - 1;
675	>	int i = head;
676	>	for (Object x; (x = elements[i]) != null; i = (i + 1) & mask) {
677	>	if (o.equals(x))
678	>	return true;
679	>	}
680		}
681		return false;
682		}
683
684		/**
685		* Removes a single instance of the specified element from this deque.
686	<	* This method is equivalent to {@link #removeFirstOccurrence}.
686	>	* If the deque does not contain the element, it is unchanged.
687	>	* More formally, removes the first element {@code e} such that
688	>	* {@code o.equals(e)} (if such an element exists).
689	>	* Returns {@code true} if this deque contained the specified element
690	>	* (or equivalently, if this deque changed as a result of the call).
691	>	*
692	>	* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
693		*
694	<	* @param e element to be removed from this deque, if present
695	<	* @return <tt>true</tt> if this deque contained the specified element
694	>	* @param o element to be removed from this deque, if present
695	>	* @return {@code true} if this deque contained the specified element
696		*/
697	<	public boolean remove(Object e) {
698	<	return removeFirstOccurrence(e);
697	>	public boolean remove(Object o) {
698	>	return removeFirstOccurrence(o);
699		}
700
701		/**
702		* Removes all of the elements from this deque.
703	+	* The deque will be empty after this call returns.
704		*/
705		public void clear() {
706		int h = head;
#	Line 670 | Line 712 | public class ArrayDeque<E> extends Abstr
712		do {
713		elements[i] = null;
714		i = (i + 1) & mask;
715	<	} while(i != t);
715	>	} while (i != t);
716		}
717		}
718
719		/**
720		* Returns an array containing all of the elements in this deque
721	<	* in the correct order.
721	>	* in proper sequence (from first to last element).
722	>	*
723	>	* <p>The returned array will be "safe" in that no references to it are
724	>	* maintained by this deque.  (In other words, this method must allocate
725	>	* a new array).  The caller is thus free to modify the returned array.
726	>	*
727	>	* <p>This method acts as bridge between array-based and collection-based
728	>	* APIs.
729		*
730		* @return an array containing all of the elements in this deque
682	–	*         in the correct order
731		*/
732		public Object[] toArray() {
733	<	return copyElements(new Object[size()]);
733	>	final int head = this.head;
734	>	final int tail = this.tail;
735	>	boolean wrap = (tail < head);
736	>	int end = wrap ? tail + elements.length : tail;
737	>	Object[] a = Arrays.copyOfRange(elements, head, end);
738	>	if (wrap)
739	>	System.arraycopy(elements, 0, a, elements.length - head, tail);
740	>	return a;
741		}
742
743		/**
744	<	* Returns an array containing all of the elements in this deque in the
745	<	* correct order; the runtime type of the returned array is that of the
746	<	* specified array.  If the deque fits in the specified array, it is
747	<	* returned therein.  Otherwise, a new array is allocated with the runtime
748	<	* type of the specified array and the size of this deque.
744	>	* Returns an array containing all of the elements in this deque in
745	>	* proper sequence (from first to last element); the runtime type of the
746	>	* returned array is that of the specified array.  If the deque fits in
747	>	* the specified array, it is returned therein.  Otherwise, a new array
748	>	* is allocated with the runtime type of the specified array and the
749	>	* size of this deque.
750	>	*
751	>	* <p>If this deque fits in the specified array with room to spare
752	>	* (i.e., the array has more elements than this deque), the element in
753	>	* the array immediately following the end of the deque is set to
754	>	* {@code null}.
755	>	*
756	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
757	>	* array-based and collection-based APIs.  Further, this method allows
758	>	* precise control over the runtime type of the output array, and may,
759	>	* under certain circumstances, be used to save allocation costs.
760	>	*
761	>	* <p>Suppose {@code x} is a deque known to contain only strings.
762	>	* The following code can be used to dump the deque into a newly
763	>	* allocated array of {@code String}:
764		*
765	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
766	<	* the array has more elements than the deque), the element in the array
767	<	* immediately following the end of the collection is set to <tt>null</tt>.
765	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
766	>	*
767	>	* Note that {@code toArray(new Object[0])} is identical in function to
768	>	* {@code toArray()}.
769		*
770		* @param a the array into which the elements of the deque are to
771	<	*          be stored, if it is big enough; otherwise, a new array of the
772	<	*          same runtime type is allocated for this purpose
773	<	* @return an array containing the elements of the deque
774	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
775	<	*         of the runtime type of every element in this deque
771	>	*          be stored, if it is big enough; otherwise, a new array of the
772	>	*          same runtime type is allocated for this purpose
773	>	* @return an array containing all of the elements in this deque
774	>	* @throws ArrayStoreException if the runtime type of the specified array
775	>	*         is not a supertype of the runtime type of every element in
776	>	*         this deque
777	>	* @throws NullPointerException if the specified array is null
778		*/
779	+	@SuppressWarnings("unchecked")
780		public <T> T[] toArray(T[] a) {
781	<	int size = size();
782	<	if (a.length < size)
783	<	a = (T[])java.lang.reflect.Array.newInstance(
784	<	a.getClass().getComponentType(), size);
785	<	copyElements(a);
786	<	if (a.length > size)
787	<	a[size] = null;
781	>	final int head = this.head;
782	>	final int tail = this.tail;
783	>	boolean wrap = (tail < head);
784	>	int size = (tail - head) + (wrap ? elements.length : 0);
785	>	int firstLeg = size - (wrap ? tail : 0);
786	>	int len = a.length;
787	>	if (size > len) {
788	>	a = (T[]) Arrays.copyOfRange(elements, head, head + size,
789	>	a.getClass());
790	>	} else {
791	>	System.arraycopy(elements, head, a, 0, firstLeg);
792	>	if (size < len)
793	>	a[size] = null;
794	>	}
795	>	if (wrap)
796	>	System.arraycopy(elements, 0, a, firstLeg, tail);
797		return a;
798		}
799
#	Line 723 | Line 806 | public class ArrayDeque<E> extends Abstr
806		*/
807		public ArrayDeque<E> clone() {
808		try {
809	+	@SuppressWarnings("unchecked")
810		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
811	<	// These two lines are currently faster than cloning the array:
728	<	result.elements = (E[]) new Object[elements.length];
729	<	System.arraycopy(elements, 0, result.elements, 0, elements.length);
811	>	result.elements = Arrays.copyOf(elements, elements.length);
812		return result;
731	–
813		} catch (CloneNotSupportedException e) {
814		throw new AssertionError();
815		}
816		}
817
737	–	/**
738	–	* Appease the serialization gods.
739	–	*/
818		private static final long serialVersionUID = 2340985798034038923L;
819
820		/**
821	<	* Serialize this deque.
821	>	* Saves this deque to a stream (that is, serializes it).
822		*
823	<	* @serialData The current size (<tt>int</tt>) of the deque,
823	>	* @param s the stream
824	>	* @throws java.io.IOException if an I/O error occurs
825	>	* @serialData The current size ({@code int}) of the deque,
826		* followed by all of its elements (each an object reference) in
827		* first-to-last order.
828		*/
829	<	private void writeObject(ObjectOutputStream s) throws IOException {
829	>	private void writeObject(java.io.ObjectOutputStream s)
830	>	throws java.io.IOException {
831		s.defaultWriteObject();
832
833		// Write out size
834	<	int size = size();
754	<	s.writeInt(size);
834	>	s.writeInt(size());
835
836		// Write out elements in order.
757	–	int i = head;
837		int mask = elements.length - 1;
838	<	for (int j = 0; j < size; j++) {
838	>	for (int i = head; i != tail; i = (i + 1) & mask)
839		s.writeObject(elements[i]);
761	–	i = (i + 1) & mask;
762	–	}
840		}
841
842		/**
843	<	* Deserialize this deque.
843	>	* Reconstitutes this deque from a stream (that is, deserializes it).
844	>	* @param s the stream
845	>	* @throws ClassNotFoundException if the class of a serialized object
846	>	*         could not be found
847	>	* @throws java.io.IOException if an I/O error occurs
848		*/
849	<	private void readObject(ObjectInputStream s)
850	<	throws IOException, ClassNotFoundException {
849	>	private void readObject(java.io.ObjectInputStream s)
850	>	throws java.io.IOException, ClassNotFoundException {
851		s.defaultReadObject();
852
853		// Read in size and allocate array
#	Line 777 | Line 858 | public class ArrayDeque<E> extends Abstr
858
859		// Read in all elements in the proper order.
860		for (int i = 0; i < size; i++)
861	<	elements[i] = (E)s.readObject();
861	>	elements[i] = s.readObject();
862	>	}
863
864	+	/**
865	+	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
866	+	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
867	+	* deque.
868	+	*
869	+	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
870	+	* {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and
871	+	* {@link Spliterator#NONNULL}.  Overriding implementations should document
872	+	* the reporting of additional characteristic values.
873	+	*
874	+	* @return a {@code Spliterator} over the elements in this deque
875	+	* @since 1.8
876	+	*/
877	+	public Spliterator<E> spliterator() {
878	+	return new DeqSpliterator<>(this, -1, -1);
879		}
880	+
881	+	static final class DeqSpliterator<E> implements Spliterator<E> {
882	+	private final ArrayDeque<E> deq;
883	+	private int fence;  // -1 until first use
884	+	private int index;  // current index, modified on traverse/split
885	+
886	+	/** Creates new spliterator covering the given array and range. */
887	+	DeqSpliterator(ArrayDeque<E> deq, int origin, int fence) {
888	+	this.deq = deq;
889	+	this.index = origin;
890	+	this.fence = fence;
891	+	}
892	+
893	+	private int getFence() { // force initialization
894	+	int t;
895	+	if ((t = fence) < 0) {
896	+	t = fence = deq.tail;
897	+	index = deq.head;
898	+	}
899	+	return t;
900	+	}
901	+
902	+	public DeqSpliterator<E> trySplit() {
903	+	int t = getFence(), h = index, n = deq.elements.length;
904	+	if (h != t && ((h + 1) & (n - 1)) != t) {
905	+	if (h > t)
906	+	t += n;
907	+	int m = ((h + t) >>> 1) & (n - 1);
908	+	return new DeqSpliterator<E>(deq, h, index = m);
909	+	}
910	+	return null;
911	+	}
912	+
913	+	public void forEachRemaining(Consumer<? super E> consumer) {
914	+	if (consumer == null)
915	+	throw new NullPointerException();
916	+	Object[] a = deq.elements;
917	+	int m = a.length - 1, f = getFence(), i = index;
918	+	index = f;
919	+	while (i != f) {
920	+	@SuppressWarnings("unchecked") E e = (E)a[i];
921	+	i = (i + 1) & m;
922	+	if (e == null)
923	+	throw new ConcurrentModificationException();
924	+	consumer.accept(e);
925	+	}
926	+	}
927	+
928	+	public boolean tryAdvance(Consumer<? super E> consumer) {
929	+	if (consumer == null)
930	+	throw new NullPointerException();
931	+	Object[] a = deq.elements;
932	+	int m = a.length - 1, f = getFence(), i = index;
933	+	if (i != f) {
934	+	@SuppressWarnings("unchecked") E e = (E)a[i];
935	+	index = (i + 1) & m;
936	+	if (e == null)
937	+	throw new ConcurrentModificationException();
938	+	consumer.accept(e);
939	+	return true;
940	+	}
941	+	return false;
942	+	}
943	+
944	+	public long estimateSize() {
945	+	int n = getFence() - index;
946	+	if (n < 0)
947	+	n += deq.elements.length;
948	+	return (long) n;
949	+	}
950	+
951	+	@Override
952	+	public int characteristics() {
953	+	return Spliterator.ORDERED | Spliterator.SIZED |
954	+	Spliterator.NONNULL | Spliterator.SUBSIZED;
955	+	}
956	+	}
957	+
958		}

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