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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 1.138 by jsr166, Fri Aug 30 18:05:38 2019 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	>	// OPENJDK import jdk.internal.access.SharedSecrets;
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 remove method, the
34	<	* iterator will generally throw a {@link ConcurrentModificationException}.
35	<	* Thus, in the face of concurrent modification, the iterator fails quickly
36	<	* and cleanly, rather than risking arbitrary, non-deterministic behavior at
37	<	* an undetermined time in the future.
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
38	>	* future.
39		*
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}/java.base/java/util/package-summary.html#CollectionsFramework">
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
49	–	* @param <E> the type of elements held in this collection
59		*/
60		public class ArrayDeque<E> extends AbstractCollection<E>
61		implements Deque<E>, Cloneable, Serializable
62		{
63	+	/*
64	+	* VMs excel at optimizing simple array loops where indices are
65	+	* incrementing or decrementing over a valid slice, e.g.
66	+	*
67	+	* for (int i = start; i < end; i++) ... elements[i]
68	+	*
69	+	* Because in a circular array, elements are in general stored in
70	+	* two disjoint such slices, we help the VM by writing unusual
71	+	* nested loops for all traversals over the elements.  Having only
72	+	* one hot inner loop body instead of two or three eases human
73	+	* maintenance and encourages VM loop inlining into the caller.
74	+	*/
75	+
76		/**
77		* The array in which the elements of the deque are stored.
78	<	* The capacity of the deque is the length of this array, which is
79	<	* always a power of two. The array is never allowed to become
58	<	* full, except transiently within an addX method where it is
59	<	* resized (see doubleCapacity) immediately upon becoming full,
60	<	* thus avoiding head and tail wrapping around to equal each
61	<	* other.  We also guarantee that all array cells not holding
62	<	* deque elements are always null.
78	>	* All array cells not holding deque elements are always null.
79	>	* The array always has at least one null slot (at tail).
80		*/
81	<	private transient E[] elements;
81	>	transient Object[] elements;
82
83		/**
84		* The index of the element at the head of the deque (which is the
85		* element that would be removed by remove() or pop()); or an
86	<	* arbitrary number equal to tail if the deque is empty.
86	>	* arbitrary number 0 <= head < elements.length equal to tail if
87	>	* the deque is empty.
88		*/
89	<	private transient int head;
89	>	transient int head;
90
91		/**
92		* The index at which the next element would be added to the tail
93	<	* of the deque (via addLast(E), add(E), or push(E)).
93	>	* of the deque (via addLast(E), add(E), or push(E));
94	>	* elements[tail] is always null.
95		*/
96	<	private transient int tail;
78	<
79	<	/**
80	<	* The minimum capacity that we'll use for a newly created deque.
81	<	* Must be a power of 2.
82	<	*/
83	<	private static final int MIN_INITIAL_CAPACITY = 8;
84	<
85	<	// ******  Array allocation and resizing utilities ******
96	>	transient int tail;
97
98		/**
99	<	* Allocate empty array to hold the given number of elements.
100	<	*
101	<	* @param numElements  the number of elements to hold.
102	<	*/
103	<	private void allocateElements(int numElements) {
104	<	int initialCapacity = MIN_INITIAL_CAPACITY;
105	<	// Find the best power of two to hold elements.
106	<	// Tests "<=" because arrays aren't kept full.
107	<	if (numElements >= initialCapacity) {
108	<	initialCapacity = numElements;
109	<	initialCapacity |= (initialCapacity >>>  1);
110	<	initialCapacity |= (initialCapacity >>>  2);
111	<	initialCapacity |= (initialCapacity >>>  4);
112	<	initialCapacity |= (initialCapacity >>>  8);
113	<	initialCapacity |= (initialCapacity >>> 16);
114	<	initialCapacity++;
99	>	* The maximum size of array to allocate.
100	>	* Some VMs reserve some header words in an array.
101	>	* Attempts to allocate larger arrays may result in
102	>	* OutOfMemoryError: Requested array size exceeds VM limit
103	>	*/
104	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
105	>
106	>	/**
107	>	* Increases the capacity of this deque by at least the given amount.
108	>	*
109	>	* @param needed the required minimum extra capacity; must be positive
110	>	*/
111	>	private void grow(int needed) {
112	>	// overflow-conscious code
113	>	final int oldCapacity = elements.length;
114	>	int newCapacity;
115	>	// Double capacity if small; else grow by 50%
116	>	int jump = (oldCapacity < 64) ? (oldCapacity + 2) : (oldCapacity >> 1);
117	>	if (jump < needed
118	>	|| (newCapacity = (oldCapacity + jump)) - MAX_ARRAY_SIZE > 0)
119	>	newCapacity = newCapacity(needed, jump);
120	>	final Object[] es = elements = Arrays.copyOf(elements, newCapacity);
121	>	// Exceptionally, here tail == head needs to be disambiguated
122	>	if (tail < head || (tail == head && es[head] != null)) {
123	>	// wrap around; slide first leg forward to end of array
124	>	int newSpace = newCapacity - oldCapacity;
125	>	System.arraycopy(es, head,
126	>	es, head + newSpace,
127	>	oldCapacity - head);
128	>	for (int i = head, to = (head += newSpace); i < to; i++)
129	>	es[i] = null;
130	>	}
131	>	// checkInvariants();
132	>	}
133
134	<	if (initialCapacity < 0)   // Too many elements, must back off
135	<	initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
134	>	/** Capacity calculation for edge conditions, especially overflow. */
135	>	private int newCapacity(int needed, int jump) {
136	>	final int oldCapacity = elements.length, minCapacity;
137	>	if ((minCapacity = oldCapacity + needed) - MAX_ARRAY_SIZE > 0) {
138	>	if (minCapacity < 0)
139	>	throw new IllegalStateException("Sorry, deque too big");
140	>	return Integer.MAX_VALUE;
141		}
142	<	elements = (E[]) new Object[initialCapacity];
142	>	if (needed > jump)
143	>	return minCapacity;
144	>	return (oldCapacity + jump - MAX_ARRAY_SIZE < 0)
145	>	? oldCapacity + jump
146	>	: MAX_ARRAY_SIZE;
147		}
148
149		/**
150	<	* Double the capacity of this deque.  Call only when full, i.e.,
151	<	* when head and tail have wrapped around to become equal.
150	>	* Increases the internal storage of this collection, if necessary,
151	>	* to ensure that it can hold at least the given number of elements.
152	>	*
153	>	* @param minCapacity the desired minimum capacity
154	>	* @since TBD
155		*/
156	<	private void doubleCapacity() {
157	<	assert head == tail;
158	<	int p = head;
159	<	int n = elements.length;
160	<	int r = n - p; // number of elements to the right of p
120	<	int newCapacity = n << 1;
121	<	if (newCapacity < 0)
122	<	throw new IllegalStateException("Sorry, deque too big");
123	<	Object[] a = new Object[newCapacity];
124	<	System.arraycopy(elements, p, a, 0, r);
125	<	System.arraycopy(elements, 0, a, r, p);
126	<	elements = (E[])a;
127	<	head = 0;
128	<	tail = n;
156	>	/* public */ void ensureCapacity(int minCapacity) {
157	>	int needed;
158	>	if ((needed = (minCapacity + 1 - elements.length)) > 0)
159	>	grow(needed);
160	>	// checkInvariants();
161		}
162
163		/**
164	<	* 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.
164	>	* Minimizes the internal storage of this collection.
165		*
166	<	* @return its argument
166	>	* @since TBD
167		*/
168	<	private <T> T[] copyElements(T[] a) {
169	<	if (head < tail) {
170	<	System.arraycopy(elements, head, a, 0, size());
171	<	} else if (head > tail) {
172	<	int headPortionLen = elements.length - head;
173	<	System.arraycopy(elements, head, a, 0, headPortionLen);
144	<	System.arraycopy(elements, 0, a, headPortionLen, tail);
168	>	/* public */ void trimToSize() {
169	>	int size;
170	>	if ((size = size()) + 1 < elements.length) {
171	>	elements = toArray(new Object[size + 1]);
172	>	head = 0;
173	>	tail = size;
174		}
175	<	return a;
175	>	// checkInvariants();
176		}
177
178		/**
#	Line 151 | Line 180 | public class ArrayDeque<E> extends Abstr
180		* sufficient to hold 16 elements.
181		*/
182		public ArrayDeque() {
183	<	elements = (E[]) new Object[16];
183	>	elements = new Object[16 + 1];
184		}
185
186		/**
187		* Constructs an empty array deque with an initial capacity
188		* sufficient to hold the specified number of elements.
189		*
190	<	* @param numElements  lower bound on initial capacity of the deque
190	>	* @param numElements lower bound on initial capacity of the deque
191		*/
192		public ArrayDeque(int numElements) {
193	<	allocateElements(numElements);
193	>	elements =
194	>	new Object[(numElements < 1) ? 1 :
195	>	(numElements == Integer.MAX_VALUE) ? Integer.MAX_VALUE :
196	>	numElements + 1];
197		}
198
199		/**
#	Line 175 | Line 207 | public class ArrayDeque<E> extends Abstr
207		* @throws NullPointerException if the specified collection is null
208		*/
209		public ArrayDeque(Collection<? extends E> c) {
210	<	allocateElements(c.size());
211	<	addAll(c);
210	>	this(c.size());
211	>	copyElements(c);
212	>	}
213	>
214	>	/**
215	>	* Circularly increments i, mod modulus.
216	>	* Precondition and postcondition: 0 <= i < modulus.
217	>	*/
218	>	static final int inc(int i, int modulus) {
219	>	if (++i >= modulus) i = 0;
220	>	return i;
221	>	}
222	>
223	>	/**
224	>	* Circularly decrements i, mod modulus.
225	>	* Precondition and postcondition: 0 <= i < modulus.
226	>	*/
227	>	static final int dec(int i, int modulus) {
228	>	if (--i < 0) i = modulus - 1;
229	>	return i;
230	>	}
231	>
232	>	/**
233	>	* Circularly adds the given distance to index i, mod modulus.
234	>	* Precondition: 0 <= i < modulus, 0 <= distance <= modulus.
235	>	* @return index 0 <= i < modulus
236	>	*/
237	>	static final int inc(int i, int distance, int modulus) {
238	>	if ((i += distance) - modulus >= 0) i -= modulus;
239	>	return i;
240	>	}
241	>
242	>	/**
243	>	* Subtracts j from i, mod modulus.
244	>	* Index i must be logically ahead of index j.
245	>	* Precondition: 0 <= i < modulus, 0 <= j < modulus.
246	>	* @return the "circular distance" from j to i; corner case i == j
247	>	* is disambiguated to "empty", returning 0.
248	>	*/
249	>	static final int sub(int i, int j, int modulus) {
250	>	if ((i -= j) < 0) i += modulus;
251	>	return i;
252	>	}
253	>
254	>	/**
255	>	* Returns element at array index i.
256	>	* This is a slight abuse of generics, accepted by javac.
257	>	*/
258	>	@SuppressWarnings("unchecked")
259	>	static final <E> E elementAt(Object[] es, int i) {
260	>	return (E) es[i];
261	>	}
262	>
263	>	/**
264	>	* A version of elementAt that checks for null elements.
265	>	* This check doesn't catch all possible comodifications,
266	>	* but does catch ones that corrupt traversal.
267	>	*/
268	>	static final <E> E nonNullElementAt(Object[] es, int i) {
269	>	@SuppressWarnings("unchecked") E e = (E) es[i];
270	>	if (e == null)
271	>	throw new ConcurrentModificationException();
272	>	return e;
273		}
274
275		// The main insertion and extraction methods are addFirst,
#	Line 186 | Line 279 | public class ArrayDeque<E> extends Abstr
279		/**
280		* Inserts the specified element at the front of this deque.
281		*
282	<	* @param e the element to insert
283	<	* @throws NullPointerException if <tt>e</tt> is null
282	>	* @param e the element to add
283	>	* @throws NullPointerException if the specified element is null
284		*/
285		public void addFirst(E e) {
286		if (e == null)
287		throw new NullPointerException();
288	<	elements[head = (head - 1) & (elements.length - 1)] = e;
288	>	final Object[] es = elements;
289	>	es[head = dec(head, es.length)] = e;
290		if (head == tail)
291	<	doubleCapacity();
291	>	grow(1);
292	>	// checkInvariants();
293		}
294
295		/**
296	<	* Inserts the specified element to the end of this deque.
297	<	* This method is equivalent to {@link Collection#add} and
298	<	* {@link #push}.
296	>	* Inserts the specified element at the end of this deque.
297	>	*
298	>	* <p>This method is equivalent to {@link #add}.
299		*
300	<	* @param e the element to insert
301	<	* @throws NullPointerException if <tt>e</tt> is null
300	>	* @param e the element to add
301	>	* @throws NullPointerException if the specified element is null
302		*/
303		public void addLast(E e) {
304		if (e == null)
305		throw new NullPointerException();
306	<	elements[tail] = e;
307	<	if ( (tail = (tail + 1) & (elements.length - 1)) == head)
308	<	doubleCapacity();
306	>	final Object[] es = elements;
307	>	es[tail] = e;
308	>	if (head == (tail = inc(tail, es.length)))
309	>	grow(1);
310	>	// checkInvariants();
311		}
312
313		/**
314	<	* Retrieves and removes the first element of this deque, or
315	<	* <tt>null</tt> if this deque is empty.
316	<	*
317	<	* @return the first element of this deque, or <tt>null</tt> if
318	<	*     this deque is empty
319	<	*/
320	<	public E pollFirst() {
321	<	int h = head;
322	<	E result = elements[h]; // Element is null if deque empty
323	<	if (result == null)
324	<	return null;
325	<	elements[h] = null;     // Must null out slot
326	<	head = (h + 1) & (elements.length - 1);
327	<	return result;
314	>	* Adds all of the elements in the specified collection at the end
315	>	* of this deque, as if by calling {@link #addLast} on each one,
316	>	* in the order that they are returned by the collection's iterator.
317	>	*
318	>	* @param c the elements to be inserted into this deque
319	>	* @return {@code true} if this deque changed as a result of the call
320	>	* @throws NullPointerException if the specified collection or any
321	>	*         of its elements are null
322	>	*/
323	>	public boolean addAll(Collection<? extends E> c) {
324	>	final int s, needed;
325	>	if ((needed = (s = size()) + c.size() + 1 - elements.length) > 0)
326	>	grow(needed);
327	>	copyElements(c);
328	>	// checkInvariants();
329	>	return size() > s;
330		}
331
332	<	/**
333	<	* 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;
332	>	private void copyElements(Collection<? extends E> c) {
333	>	c.forEach(this::addLast);
334		}
335
336		/**
337		* Inserts the specified element at the front of this deque.
338		*
339	<	* @param e the element to insert
340	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst})
341	<	* @throws NullPointerException if <tt>e</tt> is null
339	>	* @param e the element to add
340	>	* @return {@code true} (as specified by {@link Deque#offerFirst})
341	>	* @throws NullPointerException if the specified element is null
342		*/
343		public boolean offerFirst(E e) {
344		addFirst(e);
#	Line 260 | Line 346 | public class ArrayDeque<E> extends Abstr
346		}
347
348		/**
349	<	* Inserts the specified element to the end of this deque.
349	>	* Inserts the specified element at the end of this deque.
350		*
351	<	* @param e the element to insert
352	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
353	<	* @throws NullPointerException if <tt>e</tt> is null
351	>	* @param e the element to add
352	>	* @return {@code true} (as specified by {@link Deque#offerLast})
353	>	* @throws NullPointerException if the specified element is null
354		*/
355		public boolean offerLast(E e) {
356		addLast(e);
#	Line 272 | Line 358 | public class ArrayDeque<E> extends Abstr
358		}
359
360		/**
361	<	* 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
361	>	* @throws NoSuchElementException {@inheritDoc}
362		*/
363		public E removeFirst() {
364	<	E x = pollFirst();
365	<	if (x == null)
364	>	E e = pollFirst();
365	>	if (e == null)
366		throw new NoSuchElementException();
367	<	return x;
367	>	// checkInvariants();
368	>	return e;
369		}
370
371		/**
372	<	* 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
372	>	* @throws NoSuchElementException {@inheritDoc}
373		*/
374		public E removeLast() {
375	<	E x = pollLast();
376	<	if (x == null)
375	>	E e = pollLast();
376	>	if (e == null)
377		throw new NoSuchElementException();
378	<	return x;
378	>	// checkInvariants();
379	>	return e;
380		}
381
382	<	/**
383	<	* Retrieves, but does not remove, the first element of this deque,
384	<	* returning <tt>null</tt> if this deque is empty.
385	<	*
386	<	* @return the first element of this deque, or <tt>null</tt> if
387	<	*     this deque is empty
388	<	*/
389	<	public E peekFirst() {
390	<	return elements[head]; // elements[head] is null if deque empty
382	>	public E pollFirst() {
383	>	final Object[] es;
384	>	final int h;
385	>	E e = elementAt(es = elements, h = head);
386	>	if (e != null) {
387	>	es[h] = null;
388	>	head = inc(h, es.length);
389	>	}
390	>	// checkInvariants();
391	>	return e;
392		}
393
394	<	/**
395	<	* Retrieves, but does not remove, the last element of this deque,
396	<	* returning <tt>null</tt> if this deque is empty.
397	<	*
398	<	* @return the last element of this deque, or <tt>null</tt> if this deque
399	<	*     is empty
400	<	*/
401	<	public E peekLast() {
323	<	return elements[(tail - 1) & (elements.length - 1)];
394	>	public E pollLast() {
395	>	final Object[] es;
396	>	final int t;
397	>	E e = elementAt(es = elements, t = dec(tail, es.length));
398	>	if (e != null)
399	>	es[tail = t] = null;
400	>	// checkInvariants();
401	>	return e;
402		}
403
404		/**
405	<	* 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
405	>	* @throws NoSuchElementException {@inheritDoc}
406		*/
407		public E getFirst() {
408	<	E x = elements[head];
409	<	if (x == null)
408	>	E e = elementAt(elements, head);
409	>	if (e == null)
410		throw new NoSuchElementException();
411	<	return x;
411	>	// checkInvariants();
412	>	return e;
413		}
414
415		/**
416	<	* 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
416	>	* @throws NoSuchElementException {@inheritDoc}
417		*/
418		public E getLast() {
419	<	E x = elements[(tail - 1) & (elements.length - 1)];
420	<	if (x == null)
419	>	final Object[] es = elements;
420	>	E e = elementAt(es, dec(tail, es.length));
421	>	if (e == null)
422		throw new NoSuchElementException();
423	<	return x;
423	>	// checkInvariants();
424	>	return e;
425	>	}
426	>
427	>	public E peekFirst() {
428	>	// checkInvariants();
429	>	return elementAt(elements, head);
430	>	}
431	>
432	>	public E peekLast() {
433	>	// checkInvariants();
434	>	final Object[] es;
435	>	return elementAt(es = elements, dec(tail, es.length));
436		}
437
438		/**
439		* Removes the first occurrence of the specified element in this
440	<	* deque (when traversing the deque from head to tail).  More
441	<	* formally, removes the first element e such that (o==null ?
442	<	* e==null : o.equals(e)). If the deque does not contain the
443	<	* element, it is unchanged.
440	>	* deque (when traversing the deque from head to tail).
441	>	* If the deque does not contain the element, it is unchanged.
442	>	* More formally, removes the first element {@code e} such that
443	>	* {@code o.equals(e)} (if such an element exists).
444	>	* Returns {@code true} if this deque contained the specified element
445	>	* (or equivalently, if this deque changed as a result of the call).
446		*
447		* @param o element to be removed from this deque, if present
448	<	* @return <tt>true</tt> if the deque contained the specified element
448	>	* @return {@code true} if the deque contained the specified element
449		*/
450		public boolean removeFirstOccurrence(Object o) {
451	<	if (o == null)
452	<	return false;
453	<	int mask = elements.length - 1;
454	<	int i = head;
455	<	E x;
456	<	while ( (x = elements[i]) != null) {
457	<	if (o.equals(x)) {
458	<	delete(i);
459	<	return true;
451	>	if (o != null) {
452	>	final Object[] es = elements;
453	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
454	>	; i = 0, to = end) {
455	>	for (; i < to; i++)
456	>	if (o.equals(es[i])) {
457	>	delete(i);
458	>	return true;
459	>	}
460	>	if (to == end) break;
461		}
377	–	i = (i + 1) & mask;
462		}
463		return false;
464		}
465
466		/**
467		* Removes the last occurrence of the specified element in this
468	<	* deque (when traversing the deque from head to tail). More
469	<	* formally, removes the last element e such that (o==null ?
470	<	* e==null : o.equals(e)). If the deque
471	<	* does not contain the element, it is unchanged.
468	>	* deque (when traversing the deque from head to tail).
469	>	* If the deque does not contain the element, it is unchanged.
470	>	* More formally, removes the last element {@code e} such that
471	>	* {@code o.equals(e)} (if such an element exists).
472	>	* Returns {@code true} if this deque contained the specified element
473	>	* (or equivalently, if this deque changed as a result of the call).
474		*
475		* @param o element to be removed from this deque, if present
476	<	* @return <tt>true</tt> if the deque contained the specified element
476	>	* @return {@code true} if the deque contained the specified element
477		*/
478		public boolean removeLastOccurrence(Object o) {
479	<	if (o == null)
480	<	return false;
481	<	int mask = elements.length - 1;
482	<	int i = (tail - 1) & mask;
483	<	E x;
484	<	while ( (x = elements[i]) != null) {
485	<	if (o.equals(x)) {
486	<	delete(i);
487	<	return true;
479	>	if (o != null) {
480	>	final Object[] es = elements;
481	>	for (int i = tail, end = head, to = (i >= end) ? end : 0;
482	>	; i = es.length, to = end) {
483	>	for (i--; i > to - 1; i--)
484	>	if (o.equals(es[i])) {
485	>	delete(i);
486	>	return true;
487	>	}
488	>	if (to == end) break;
489		}
403	–	i = (i - 1) & mask;
490		}
491		return false;
492		}
#	Line 408 | Line 494 | public class ArrayDeque<E> extends Abstr
494		// *** Queue methods ***
495
496		/**
497	<	* 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.
497	>	* Inserts the specified element at the end of this deque.
498		*
499		* <p>This method is equivalent to {@link #addLast}.
500		*
501	<	* @param e the element to insert
502	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
503	<	* @throws NullPointerException if <tt>e</tt> is null
501	>	* @param e the element to add
502	>	* @return {@code true} (as specified by {@link Collection#add})
503	>	* @throws NullPointerException if the specified element is null
504		*/
505		public boolean add(E e) {
506		addLast(e);
#	Line 435 | Line 508 | public class ArrayDeque<E> extends Abstr
508		}
509
510		/**
511	<	* 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.
511	>	* Inserts the specified element at the end of this deque.
512		*
513	<	* <p>This method is equivalent to {@link #pollFirst}.
513	>	* <p>This method is equivalent to {@link #offerLast}.
514		*
515	<	* @return the first element of this deque, or <tt>null</tt> if
516	<	*     this deque is empty
515	>	* @param e the element to add
516	>	* @return {@code true} (as specified by {@link Queue#offer})
517	>	* @throws NullPointerException if the specified element is null
518		*/
519	<	public E poll() {
520	<	return pollFirst();
519	>	public boolean offer(E e) {
520	>	return offerLast(e);
521		}
522
523		/**
524		* Retrieves and removes the head of the queue represented by this deque.
525	<	* This method differs from the <tt>poll</tt> method in that it throws an
526	<	* exception if this deque is empty.
525	>	*
526	>	* This method differs from {@link #poll() poll()} only in that it
527	>	* throws an exception if this deque is empty.
528		*
529		* <p>This method is equivalent to {@link #removeFirst}.
530		*
531		* @return the head of the queue represented by this deque
532	<	* @throws NoSuchElementException if this deque is empty
532	>	* @throws NoSuchElementException {@inheritDoc}
533		*/
534		public E remove() {
535		return removeFirst();
536		}
537
538		/**
539	<	* Retrieves, but does not remove, the head of the queue represented by
540	<	* this deque, returning <tt>null</tt> if this deque is empty.
539	>	* Retrieves and removes the head of the queue represented by this deque
540	>	* (in other words, the first element of this deque), or returns
541	>	* {@code null} if this deque is empty.
542		*
543	<	* <p>This method is equivalent to {@link #peekFirst}
543	>	* <p>This method is equivalent to {@link #pollFirst}.
544		*
545		* @return the head of the queue represented by this deque, or
546	<	*     <tt>null</tt> if this deque is empty
546	>	*         {@code null} if this deque is empty
547		*/
548	<	public E peek() {
549	<	return peekFirst();
548	>	public E poll() {
549	>	return pollFirst();
550		}
551
552		/**
553		* Retrieves, but does not remove, the head of the queue represented by
554	<	* this deque.  This method differs from the <tt>peek</tt> method only in
554	>	* this deque.  This method differs from {@link #peek peek} only in
555		* that it throws an exception if this deque is empty.
556		*
557	<	* <p>This method is equivalent to {@link #getFirst}
557	>	* <p>This method is equivalent to {@link #getFirst}.
558		*
559		* @return the head of the queue represented by this deque
560	<	* @throws NoSuchElementException if this deque is empty
560	>	* @throws NoSuchElementException {@inheritDoc}
561		*/
562		public E element() {
563		return getFirst();
564		}
565
566	+	/**
567	+	* Retrieves, but does not remove, the head of the queue represented by
568	+	* this deque, or returns {@code null} if this deque is empty.
569	+	*
570	+	* <p>This method is equivalent to {@link #peekFirst}.
571	+	*
572	+	* @return the head of the queue represented by this deque, or
573	+	*         {@code null} if this deque is empty
574	+	*/
575	+	public E peek() {
576	+	return peekFirst();
577	+	}
578	+
579		// *** Stack methods ***
580
581		/**
#	Line 499 | Line 585 | public class ArrayDeque<E> extends Abstr
585		* <p>This method is equivalent to {@link #addFirst}.
586		*
587		* @param e the element to push
588	<	* @throws NullPointerException if <tt>e</tt> is null
588	>	* @throws NullPointerException if the specified element is null
589		*/
590		public void push(E e) {
591		addFirst(e);
#	Line 512 | Line 598 | public class ArrayDeque<E> extends Abstr
598		* <p>This method is equivalent to {@link #removeFirst()}.
599		*
600		* @return the element at the front of this deque (which is the top
601	<	*     of the stack represented by this deque)
602	<	* @throws NoSuchElementException if this deque is empty
601	>	*         of the stack represented by this deque)
602	>	* @throws NoSuchElementException {@inheritDoc}
603		*/
604		public E pop() {
605		return removeFirst();
606		}
607
608		/**
609	<	* Remove the element at the specified position in the elements array,
610	<	* adjusting head, tail, and size as necessary.  This can result in
611	<	* motion of elements backwards or forwards in the array.
609	>	* Removes the element at the specified position in the elements array.
610	>	* This can result in forward or backwards motion of array elements.
611	>	* We optimize for least element motion.
612		*
613		* <p>This method is called delete rather than remove to emphasize
614	<	* that its semantics differ from those of List.remove(int).
614	>	* that its semantics differ from those of {@link List#remove(int)}.
615		*
616	<	* @return true if elements moved backwards
616	>	* @return true if elements near tail moved backwards
617		*/
618	<	private boolean delete(int i) {
619	<	// Case 1: Deque doesn't wrap
620	<	// Case 2: Deque does wrap and removed element is in the head portion
621	<	if ((head < tail || tail == 0) || i >= head) {
622	<	System.arraycopy(elements, head, elements, head + 1, i - head);
623	<	elements[head] = null;
624	<	head = (head + 1) & (elements.length - 1);
618	>	boolean delete(int i) {
619	>	// checkInvariants();
620	>	final Object[] es = elements;
621	>	final int capacity = es.length;
622	>	final int h, t;
623	>	// number of elements before to-be-deleted elt
624	>	final int front = sub(i, h = head, capacity);
625	>	// number of elements after to-be-deleted elt
626	>	final int back = sub(t = tail, i, capacity) - 1;
627	>	if (front < back) {
628	>	// move front elements forwards
629	>	if (h <= i) {
630	>	System.arraycopy(es, h, es, h + 1, front);
631	>	} else { // Wrap around
632	>	System.arraycopy(es, 0, es, 1, i);
633	>	es[0] = es[capacity - 1];
634	>	System.arraycopy(es, h, es, h + 1, front - (i + 1));
635	>	}
636	>	es[h] = null;
637	>	head = inc(h, capacity);
638	>	// checkInvariants();
639		return false;
640	+	} else {
641	+	// move back elements backwards
642	+	tail = dec(t, capacity);
643	+	if (i <= tail) {
644	+	System.arraycopy(es, i + 1, es, i, back);
645	+	} else { // Wrap around
646	+	System.arraycopy(es, i + 1, es, i, capacity - (i + 1));
647	+	es[capacity - 1] = es[0];
648	+	System.arraycopy(es, 1, es, 0, t - 1);
649	+	}
650	+	es[tail] = null;
651	+	// checkInvariants();
652	+	return true;
653		}
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;
654		}
655
656		// *** Collection Methods ***
#	Line 554 | Line 661 | public class ArrayDeque<E> extends Abstr
661		* @return the number of elements in this deque
662		*/
663		public int size() {
664	<	return (tail - head) & (elements.length - 1);
664	>	return sub(tail, head, elements.length);
665		}
666
667		/**
668	<	* Returns <tt>true</tt> if this collection contains no elements.<p>
668	>	* Returns {@code true} if this deque contains no elements.
669		*
670	<	* @return <tt>true</tt> if this collection contains no elements.
670	>	* @return {@code true} if this deque contains no elements
671		*/
672		public boolean isEmpty() {
673		return head == tail;
#	Line 572 | Line 679 | public class ArrayDeque<E> extends Abstr
679		* order that elements would be dequeued (via successive calls to
680		* {@link #remove} or popped (via successive calls to {@link #pop}).
681		*
682	<	* @return an <tt>Iterator</tt> over the elements in this deque
682	>	* @return an iterator over the elements in this deque
683		*/
684		public Iterator<E> iterator() {
685		return new DeqIterator();
686		}
687
688	+	public Iterator<E> descendingIterator() {
689	+	return new DescendingIterator();
690	+	}
691	+
692		private class DeqIterator implements Iterator<E> {
693	<	/**
694	<	* Index of element to be returned by subsequent call to next.
584	<	*/
585	<	private int cursor = head;
693	>	/** Index of element to be returned by subsequent call to next. */
694	>	int cursor;
695
696	<	/**
697	<	* Tail recorded at construction (also in remove), to stop
589	<	* iterator and also to check for comodification.
590	<	*/
591	<	private int fence = tail;
696	>	/** Number of elements yet to be returned. */
697	>	int remaining = size();
698
699		/**
700		* Index of element returned by most recent call to next.
701		* Reset to -1 if element is deleted by a call to remove.
702		*/
703	<	private int lastRet = -1;
703	>	int lastRet = -1;
704
705	<	public boolean hasNext() {
706	<	return cursor != fence;
705	>	DeqIterator() { cursor = head; }
706	>
707	>	public final boolean hasNext() {
708	>	return remaining > 0;
709		}
710
711		public E next() {
712	<	E result;
605	<	if (cursor == fence)
712	>	if (remaining <= 0)
713		throw new NoSuchElementException();
714	<	// This check doesn't catch all possible comodifications,
715	<	// but does catch the ones that corrupt traversal
716	<	if (tail != fence || (result = elements[cursor]) == null)
717	<	throw new ConcurrentModificationException();
718	<	lastRet = cursor;
719	<	cursor = (cursor + 1) & (elements.length - 1);
720	<	return result;
714	>	final Object[] es = elements;
715	>	E e = nonNullElementAt(es, cursor);
716	>	cursor = inc(lastRet = cursor, es.length);
717	>	remaining--;
718	>	return e;
719	>	}
720	>
721	>	void postDelete(boolean leftShifted) {
722	>	if (leftShifted)
723	>	cursor = dec(cursor, elements.length);
724		}
725
726	<	public void remove() {
726	>	public final void remove() {
727		if (lastRet < 0)
728		throw new IllegalStateException();
729	<	if (delete(lastRet))
620	<	cursor--;
729	>	postDelete(delete(lastRet));
730		lastRet = -1;
731	<	fence = tail;
731	>	}
732	>
733	>	public void forEachRemaining(Consumer<? super E> action) {
734	>	Objects.requireNonNull(action);
735	>	int r;
736	>	if ((r = remaining) <= 0)
737	>	return;
738	>	remaining = 0;
739	>	final Object[] es = elements;
740	>	if (es[cursor] == null || sub(tail, cursor, es.length) != r)
741	>	throw new ConcurrentModificationException();
742	>	for (int i = cursor, end = tail, to = (i <= end) ? end : es.length;
743	>	; i = 0, to = end) {
744	>	for (; i < to; i++)
745	>	action.accept(elementAt(es, i));
746	>	if (to == end) {
747	>	if (end != tail)
748	>	throw new ConcurrentModificationException();
749	>	lastRet = dec(end, es.length);
750	>	break;
751	>	}
752	>	}
753	>	}
754	>	}
755	>
756	>	private class DescendingIterator extends DeqIterator {
757	>	DescendingIterator() { cursor = dec(tail, elements.length); }
758	>
759	>	public final E next() {
760	>	if (remaining <= 0)
761	>	throw new NoSuchElementException();
762	>	final Object[] es = elements;
763	>	E e = nonNullElementAt(es, cursor);
764	>	cursor = dec(lastRet = cursor, es.length);
765	>	remaining--;
766	>	return e;
767	>	}
768	>
769	>	void postDelete(boolean leftShifted) {
770	>	if (!leftShifted)
771	>	cursor = inc(cursor, elements.length);
772	>	}
773	>
774	>	public final void forEachRemaining(Consumer<? super E> action) {
775	>	Objects.requireNonNull(action);
776	>	int r;
777	>	if ((r = remaining) <= 0)
778	>	return;
779	>	remaining = 0;
780	>	final Object[] es = elements;
781	>	if (es[cursor] == null || sub(cursor, head, es.length) + 1 != r)
782	>	throw new ConcurrentModificationException();
783	>	for (int i = cursor, end = head, to = (i >= end) ? end : 0;
784	>	; i = es.length - 1, to = end) {
785	>	// hotspot generates faster code than for: i >= to !
786	>	for (; i > to - 1; i--)
787	>	action.accept(elementAt(es, i));
788	>	if (to == end) {
789	>	if (end != head)
790	>	throw new ConcurrentModificationException();
791	>	lastRet = end;
792	>	break;
793	>	}
794	>	}
795		}
796		}
797
798		/**
799	<	* Returns <tt>true</tt> if this deque contains the specified
800	<	* element.  More formally, returns <tt>true</tt> if and only if this
801	<	* deque contains at least one element <tt>e</tt> such that
802	<	* <tt>e.equals(o)</tt>.
799	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
800	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
801	>	* deque.
802	>	*
803	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
804	>	* {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and
805	>	* {@link Spliterator#NONNULL}.  Overriding implementations should document
806	>	* the reporting of additional characteristic values.
807	>	*
808	>	* @return a {@code Spliterator} over the elements in this deque
809	>	* @since 1.8
810	>	*/
811	>	public Spliterator<E> spliterator() {
812	>	return new DeqSpliterator();
813	>	}
814	>
815	>	final class DeqSpliterator implements Spliterator<E> {
816	>	private int fence;      // -1 until first use
817	>	private int cursor;     // current index, modified on traverse/split
818	>
819	>	/** Constructs late-binding spliterator over all elements. */
820	>	DeqSpliterator() {
821	>	this.fence = -1;
822	>	}
823	>
824	>	/** Constructs spliterator over the given range. */
825	>	DeqSpliterator(int origin, int fence) {
826	>	// assert 0 <= origin && origin < elements.length;
827	>	// assert 0 <= fence && fence < elements.length;
828	>	this.cursor = origin;
829	>	this.fence = fence;
830	>	}
831	>
832	>	/** Ensures late-binding initialization; then returns fence. */
833	>	private int getFence() { // force initialization
834	>	int t;
835	>	if ((t = fence) < 0) {
836	>	t = fence = tail;
837	>	cursor = head;
838	>	}
839	>	return t;
840	>	}
841	>
842	>	public DeqSpliterator trySplit() {
843	>	final Object[] es = elements;
844	>	final int i, n;
845	>	return ((n = sub(getFence(), i = cursor, es.length) >> 1) <= 0)
846	>	? null
847	>	: new DeqSpliterator(i, cursor = inc(i, n, es.length));
848	>	}
849	>
850	>	public void forEachRemaining(Consumer<? super E> action) {
851	>	if (action == null)
852	>	throw new NullPointerException();
853	>	final int end = getFence(), cursor = this.cursor;
854	>	final Object[] es = elements;
855	>	if (cursor != end) {
856	>	this.cursor = end;
857	>	// null check at both ends of range is sufficient
858	>	if (es[cursor] == null || es[dec(end, es.length)] == null)
859	>	throw new ConcurrentModificationException();
860	>	for (int i = cursor, to = (i <= end) ? end : es.length;
861	>	; i = 0, to = end) {
862	>	for (; i < to; i++)
863	>	action.accept(elementAt(es, i));
864	>	if (to == end) break;
865	>	}
866	>	}
867	>	}
868	>
869	>	public boolean tryAdvance(Consumer<? super E> action) {
870	>	Objects.requireNonNull(action);
871	>	final Object[] es = elements;
872	>	if (fence < 0) { fence = tail; cursor = head; } // late-binding
873	>	final int i;
874	>	if ((i = cursor) == fence)
875	>	return false;
876	>	E e = nonNullElementAt(es, i);
877	>	cursor = inc(i, es.length);
878	>	action.accept(e);
879	>	return true;
880	>	}
881	>
882	>	public long estimateSize() {
883	>	return sub(getFence(), cursor, elements.length);
884	>	}
885	>
886	>	public int characteristics() {
887	>	return Spliterator.NONNULL
888	>	| Spliterator.ORDERED
889	>	| Spliterator.SIZED
890	>	| Spliterator.SUBSIZED;
891	>	}
892	>	}
893	>
894	>	/**
895	>	* @throws NullPointerException {@inheritDoc}
896	>	*/
897	>	public void forEach(Consumer<? super E> action) {
898	>	Objects.requireNonNull(action);
899	>	final Object[] es = elements;
900	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
901	>	; i = 0, to = end) {
902	>	for (; i < to; i++)
903	>	action.accept(elementAt(es, i));
904	>	if (to == end) {
905	>	if (end != tail) throw new ConcurrentModificationException();
906	>	break;
907	>	}
908	>	}
909	>	// checkInvariants();
910	>	}
911	>
912	>	/**
913	>	* Replaces each element of this deque with the result of applying the
914	>	* operator to that element, as specified by {@link List#replaceAll}.
915	>	*
916	>	* @param operator the operator to apply to each element
917	>	* @since TBD
918	>	*/
919	>	/* public */ void replaceAll(java.util.function.UnaryOperator<E> operator) {
920	>	Objects.requireNonNull(operator);
921	>	final Object[] es = elements;
922	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
923	>	; i = 0, to = end) {
924	>	for (; i < to; i++)
925	>	es[i] = operator.apply(elementAt(es, i));
926	>	if (to == end) {
927	>	if (end != tail) throw new ConcurrentModificationException();
928	>	break;
929	>	}
930	>	}
931	>	// checkInvariants();
932	>	}
933	>
934	>	/**
935	>	* @throws NullPointerException {@inheritDoc}
936	>	*/
937	>	public boolean removeIf(Predicate<? super E> filter) {
938	>	Objects.requireNonNull(filter);
939	>	return bulkRemove(filter);
940	>	}
941	>
942	>	/**
943	>	* @throws NullPointerException {@inheritDoc}
944	>	*/
945	>	public boolean removeAll(Collection<?> c) {
946	>	Objects.requireNonNull(c);
947	>	return bulkRemove(e -> c.contains(e));
948	>	}
949	>
950	>	/**
951	>	* @throws NullPointerException {@inheritDoc}
952	>	*/
953	>	public boolean retainAll(Collection<?> c) {
954	>	Objects.requireNonNull(c);
955	>	return bulkRemove(e -> !c.contains(e));
956	>	}
957	>
958	>	/** Implementation of bulk remove methods. */
959	>	private boolean bulkRemove(Predicate<? super E> filter) {
960	>	// checkInvariants();
961	>	final Object[] es = elements;
962	>	// Optimize for initial run of survivors
963	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
964	>	; i = 0, to = end) {
965	>	for (; i < to; i++)
966	>	if (filter.test(elementAt(es, i)))
967	>	return bulkRemoveModified(filter, i);
968	>	if (to == end) {
969	>	if (end != tail) throw new ConcurrentModificationException();
970	>	break;
971	>	}
972	>	}
973	>	return false;
974	>	}
975	>
976	>	// A tiny bit set implementation
977	>
978	>	private static long[] nBits(int n) {
979	>	return new long[((n - 1) >> 6) + 1];
980	>	}
981	>	private static void setBit(long[] bits, int i) {
982	>	bits[i >> 6] |= 1L << i;
983	>	}
984	>	private static boolean isClear(long[] bits, int i) {
985	>	return (bits[i >> 6] & (1L << i)) == 0;
986	>	}
987	>
988	>	/**
989	>	* Helper for bulkRemove, in case of at least one deletion.
990	>	* Tolerate predicates that reentrantly access the collection for
991	>	* read (but writers still get CME), so traverse once to find
992	>	* elements to delete, a second pass to physically expunge.
993	>	*
994	>	* @param beg valid index of first element to be deleted
995	>	*/
996	>	private boolean bulkRemoveModified(
997	>	Predicate<? super E> filter, final int beg) {
998	>	final Object[] es = elements;
999	>	final int capacity = es.length;
1000	>	final int end = tail;
1001	>	final long[] deathRow = nBits(sub(end, beg, capacity));
1002	>	deathRow[0] = 1L;   // set bit 0
1003	>	for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg;
1004	>	; i = 0, to = end, k -= capacity) {
1005	>	for (; i < to; i++)
1006	>	if (filter.test(elementAt(es, i)))
1007	>	setBit(deathRow, i - k);
1008	>	if (to == end) break;
1009	>	}
1010	>	// a two-finger traversal, with hare i reading, tortoise w writing
1011	>	int w = beg;
1012	>	for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg;
1013	>	; w = 0) { // w rejoins i on second leg
1014	>	// In this loop, i and w are on the same leg, with i > w
1015	>	for (; i < to; i++)
1016	>	if (isClear(deathRow, i - k))
1017	>	es[w++] = es[i];
1018	>	if (to == end) break;
1019	>	// In this loop, w is on the first leg, i on the second
1020	>	for (i = 0, to = end, k -= capacity; i < to && w < capacity; i++)
1021	>	if (isClear(deathRow, i - k))
1022	>	es[w++] = es[i];
1023	>	if (i >= to) {
1024	>	if (w == capacity) w = 0; // "corner" case
1025	>	break;
1026	>	}
1027	>	}
1028	>	if (end != tail) throw new ConcurrentModificationException();
1029	>	circularClear(es, tail = w, end);
1030	>	// checkInvariants();
1031	>	return true;
1032	>	}
1033	>
1034	>	/**
1035	>	* Returns {@code true} if this deque contains the specified element.
1036	>	* More formally, returns {@code true} if and only if this deque contains
1037	>	* at least one element {@code e} such that {@code o.equals(e)}.
1038		*
1039		* @param o object to be checked for containment in this deque
1040	<	* @return <tt>true</tt> if this deque contains the specified element
1040	>	* @return {@code true} if this deque contains the specified element
1041		*/
1042		public boolean contains(Object o) {
1043	<	if (o == null)
1044	<	return false;
1045	<	int mask = elements.length - 1;
1046	<	int i = head;
1047	<	E x;
1048	<	while ( (x = elements[i]) != null) {
1049	<	if (o.equals(x))
1050	<	return true;
1051	<	i = (i + 1) & mask;
1043	>	if (o != null) {
1044	>	final Object[] es = elements;
1045	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
1046	>	; i = 0, to = end) {
1047	>	for (; i < to; i++)
1048	>	if (o.equals(es[i]))
1049	>	return true;
1050	>	if (to == end) break;
1051	>	}
1052		}
1053		return false;
1054		}
1055
1056		/**
1057		* Removes a single instance of the specified element from this deque.
1058	<	* This method is equivalent to {@link #removeFirstOccurrence}.
1058	>	* If the deque does not contain the element, it is unchanged.
1059	>	* More formally, removes the first element {@code e} such that
1060	>	* {@code o.equals(e)} (if such an element exists).
1061	>	* Returns {@code true} if this deque contained the specified element
1062	>	* (or equivalently, if this deque changed as a result of the call).
1063	>	*
1064	>	* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
1065		*
1066	<	* @param e element to be removed from this deque, if present
1067	<	* @return <tt>true</tt> if this deque contained the specified element
1066	>	* @param o element to be removed from this deque, if present
1067	>	* @return {@code true} if this deque contained the specified element
1068		*/
1069	<	public boolean remove(Object e) {
1070	<	return removeFirstOccurrence(e);
1069	>	public boolean remove(Object o) {
1070	>	return removeFirstOccurrence(o);
1071		}
1072
1073		/**
1074		* Removes all of the elements from this deque.
1075	+	* The deque will be empty after this call returns.
1076		*/
1077		public void clear() {
1078	<	int h = head;
1079	<	int t = tail;
1080	<	if (h != t) { // clear all cells
1081	<	head = tail = 0;
1082	<	int i = h;
1083	<	int mask = elements.length - 1;
1084	<	do {
1085	<	elements[i] = null;
1086	<	i = (i + 1) & mask;
1087	<	} while(i != t);
1078	>	circularClear(elements, head, tail);
1079	>	head = tail = 0;
1080	>	// checkInvariants();
1081	>	}
1082	>
1083	>	/**
1084	>	* Nulls out slots starting at array index i, upto index end.
1085	>	* Condition i == end means "empty" - nothing to do.
1086	>	*/
1087	>	private static void circularClear(Object[] es, int i, int end) {
1088	>	// assert 0 <= i && i < es.length;
1089	>	// assert 0 <= end && end < es.length;
1090	>	for (int to = (i <= end) ? end : es.length;
1091	>	; i = 0, to = end) {
1092	>	for (; i < to; i++) es[i] = null;
1093	>	if (to == end) break;
1094		}
1095		}
1096
1097		/**
1098		* Returns an array containing all of the elements in this deque
1099	<	* in the correct order.
1099	>	* in proper sequence (from first to last element).
1100	>	*
1101	>	* <p>The returned array will be "safe" in that no references to it are
1102	>	* maintained by this deque.  (In other words, this method must allocate
1103	>	* a new array).  The caller is thus free to modify the returned array.
1104	>	*
1105	>	* <p>This method acts as bridge between array-based and collection-based
1106	>	* APIs.
1107		*
1108		* @return an array containing all of the elements in this deque
682	–	*         in the correct order
1109		*/
1110		public Object[] toArray() {
1111	<	return copyElements(new Object[size()]);
1111	>	return toArray(Object[].class);
1112	>	}
1113	>
1114	>	private <T> T[] toArray(Class<T[]> klazz) {
1115	>	final Object[] es = elements;
1116	>	final T[] a;
1117	>	final int head = this.head, tail = this.tail, end;
1118	>	if ((end = tail + ((head <= tail) ? 0 : es.length)) >= 0) {
1119	>	// Uses null extension feature of copyOfRange
1120	>	a = Arrays.copyOfRange(es, head, end, klazz);
1121	>	} else {
1122	>	// integer overflow!
1123	>	a = Arrays.copyOfRange(es, 0, end - head, klazz);
1124	>	System.arraycopy(es, head, a, 0, es.length - head);
1125	>	}
1126	>	if (end != tail)
1127	>	System.arraycopy(es, 0, a, es.length - head, tail);
1128	>	return a;
1129		}
1130
1131		/**
1132	<	* Returns an array containing all of the elements in this deque in the
1133	<	* correct order; the runtime type of the returned array is that of the
1134	<	* specified array.  If the deque fits in the specified array, it is
1135	<	* returned therein.  Otherwise, a new array is allocated with the runtime
1136	<	* type of the specified array and the size of this deque.
1132	>	* Returns an array containing all of the elements in this deque in
1133	>	* proper sequence (from first to last element); the runtime type of the
1134	>	* returned array is that of the specified array.  If the deque fits in
1135	>	* the specified array, it is returned therein.  Otherwise, a new array
1136	>	* is allocated with the runtime type of the specified array and the
1137	>	* size of this deque.
1138	>	*
1139	>	* <p>If this deque fits in the specified array with room to spare
1140	>	* (i.e., the array has more elements than this deque), the element in
1141	>	* the array immediately following the end of the deque is set to
1142	>	* {@code null}.
1143	>	*
1144	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
1145	>	* array-based and collection-based APIs.  Further, this method allows
1146	>	* precise control over the runtime type of the output array, and may,
1147	>	* under certain circumstances, be used to save allocation costs.
1148	>	*
1149	>	* <p>Suppose {@code x} is a deque known to contain only strings.
1150	>	* The following code can be used to dump the deque into a newly
1151	>	* allocated array of {@code String}:
1152	>	*
1153	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
1154		*
1155	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
1156	<	* the array has more elements than the deque), the element in the array
697	<	* immediately following the end of the collection is set to <tt>null</tt>.
1155	>	* Note that {@code toArray(new Object[0])} is identical in function to
1156	>	* {@code toArray()}.
1157		*
1158		* @param a the array into which the elements of the deque are to
1159	<	*          be stored, if it is big enough; otherwise, a new array of the
1160	<	*          same runtime type is allocated for this purpose
1161	<	* @return an array containing the elements of the deque
1162	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
1163	<	*         of the runtime type of every element in this deque
1159	>	*          be stored, if it is big enough; otherwise, a new array of the
1160	>	*          same runtime type is allocated for this purpose
1161	>	* @return an array containing all of the elements in this deque
1162	>	* @throws ArrayStoreException if the runtime type of the specified array
1163	>	*         is not a supertype of the runtime type of every element in
1164	>	*         this deque
1165	>	* @throws NullPointerException if the specified array is null
1166		*/
1167	+	@SuppressWarnings("unchecked")
1168		public <T> T[] toArray(T[] a) {
1169	<	int size = size();
1170	<	if (a.length < size)
1171	<	a = (T[])java.lang.reflect.Array.newInstance(
1172	<	a.getClass().getComponentType(), size);
1173	<	copyElements(a);
1174	<	if (a.length > size)
1169	>	final int size;
1170	>	if ((size = size()) > a.length)
1171	>	return toArray((Class<T[]>) a.getClass());
1172	>	final Object[] es = elements;
1173	>	for (int i = head, j = 0, len = Math.min(size, es.length - i);
1174	>	; i = 0, len = tail) {
1175	>	System.arraycopy(es, i, a, j, len);
1176	>	if ((j += len) == size) break;
1177	>	}
1178	>	if (size < a.length)
1179		a[size] = null;
1180		return a;
1181		}
#	Line 723 | Line 1189 | public class ArrayDeque<E> extends Abstr
1189		*/
1190		public ArrayDeque<E> clone() {
1191		try {
1192	+	@SuppressWarnings("unchecked")
1193		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
1194	<	// 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);
1194	>	result.elements = Arrays.copyOf(elements, elements.length);
1195		return result;
731	–
1196		} catch (CloneNotSupportedException e) {
1197		throw new AssertionError();
1198		}
1199		}
1200
1201	<	/**
738	<	* Appease the serialization gods.
739	<	*/
1201	>	// OPENJDK @java.io.Serial
1202		private static final long serialVersionUID = 2340985798034038923L;
1203
1204		/**
1205	<	* Serialize this deque.
1205	>	* Saves this deque to a stream (that is, serializes it).
1206		*
1207	<	* @serialData The current size (<tt>int</tt>) of the deque,
1207	>	* @param s the stream
1208	>	* @throws java.io.IOException if an I/O error occurs
1209	>	* @serialData The current size ({@code int}) of the deque,
1210		* followed by all of its elements (each an object reference) in
1211		* first-to-last order.
1212		*/
1213	<	private void writeObject(ObjectOutputStream s) throws IOException {
1213	>	// OPENJDK @java.io.Serial
1214	>	private void writeObject(java.io.ObjectOutputStream s)
1215	>	throws java.io.IOException {
1216		s.defaultWriteObject();
1217
1218		// Write out size
1219	<	int size = size();
754	<	s.writeInt(size);
1219	>	s.writeInt(size());
1220
1221		// Write out elements in order.
1222	<	int i = head;
1223	<	int mask = elements.length - 1;
1224	<	for (int j = 0; j < size; j++) {
1225	<	s.writeObject(elements[i]);
1226	<	i = (i + 1) & mask;
1222	>	final Object[] es = elements;
1223	>	for (int i = head, end = tail, to = (i <= end) ? end : es.length;
1224	>	; i = 0, to = end) {
1225	>	for (; i < to; i++)
1226	>	s.writeObject(es[i]);
1227	>	if (to == end) break;
1228		}
1229		}
1230
1231		/**
1232	<	* Deserialize this deque.
1233	<	*/
1234	<	private void readObject(ObjectInputStream s)
1235	<	throws IOException, ClassNotFoundException {
1232	>	* Reconstitutes this deque from a stream (that is, deserializes it).
1233	>	* @param s the stream
1234	>	* @throws ClassNotFoundException if the class of a serialized object
1235	>	*         could not be found
1236	>	* @throws java.io.IOException if an I/O error occurs
1237	>	*/
1238	>	// OPENJDK @java.io.Serial
1239	>	private void readObject(java.io.ObjectInputStream s)
1240	>	throws java.io.IOException, ClassNotFoundException {
1241		s.defaultReadObject();
1242
1243		// Read in size and allocate array
1244		int size = s.readInt();
1245	<	allocateElements(size);
1246	<	head = 0;
1247	<	tail = size;
1245	>	jsr166.Platform.checkArray(s, Object[].class, size + 1);
1246	>	elements = new Object[size + 1];
1247	>	this.tail = size;
1248
1249		// Read in all elements in the proper order.
1250		for (int i = 0; i < size; i++)
1251	<	elements[i] = (E)s.readObject();
1251	>	elements[i] = s.readObject();
1252	>	}
1253
1254	+	/** debugging */
1255	+	void checkInvariants() {
1256	+	// Use head and tail fields with empty slot at tail strategy.
1257	+	// head == tail disambiguates to "empty".
1258	+	try {
1259	+	int capacity = elements.length;
1260	+	// assert 0 <= head && head < capacity;
1261	+	// assert 0 <= tail && tail < capacity;
1262	+	// assert capacity > 0;
1263	+	// assert size() < capacity;
1264	+	// assert head == tail || elements[head] != null;
1265	+	// assert elements[tail] == null;
1266	+	// assert head == tail || elements[dec(tail, capacity)] != null;
1267	+	} catch (Throwable t) {
1268	+	System.err.printf("head=%d tail=%d capacity=%d%n",
1269	+	head, tail, elements.length);
1270	+	System.err.printf("elements=%s%n",
1271	+	Arrays.toString(elements));
1272	+	throw t;
1273	+	}
1274		}
1275	+
1276		}

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