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

Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.4 by dl, Tue Mar 8 19:07:39 2005 UTC vs.
Revision 1.51 by jsr166, Wed Feb 20 12:39:06 2013 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	>	import java.io.Serializable;
8	>	import java.util.function.Consumer;
9	>	import java.util.stream.Stream;
10	>	import java.util.stream.Streams;
11
12		/**
13		* Resizable-array implementation of the {@link Deque} interface.  Array
#	Line 15 | Line 18 | import java.io.*;
18		* {@link Stack} when used as a stack, and faster than {@link LinkedList}
19		* when used as a queue.
20		*
21	<	* <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time.
22	<	* Exceptions include {@link #remove(Object) remove}, {@link
23	<	* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
24	<	* removeLastOccurrence}, {@link #contains contains }, {@link #iterator
25	<	* iterator.remove()}, and the bulk operations, all of which run in linear
26	<	* time.
21	>	* <p>Most {@code ArrayDeque} operations run in amortized constant time.
22	>	* Exceptions include
23	>	* {@link #remove(Object) remove},
24	>	* {@link #removeFirstOccurrence removeFirstOccurrence},
25	>	* {@link #removeLastOccurrence removeLastOccurrence},
26	>	* {@link #contains contains},
27	>	* {@link #iterator iterator.remove()},
28	>	* and the bulk operations, all of which run in linear time.
29		*
30	<	* <p>The iterators returned by this class's <tt>iterator</tt> method are
31	<	* <i>fail-fast</i>: If the deque is modified at any time after the iterator
32	<	* is created, in any way except through the iterator's own remove method, the
33	<	* iterator will generally throw a {@link ConcurrentModificationException}.
34	<	* Thus, in the face of concurrent modification, the iterator fails quickly
35	<	* and cleanly, rather than risking arbitrary, non-deterministic behavior at
36	<	* an undetermined time in the future.
30	>	* <p>The iterators returned by this class's {@link #iterator() iterator}
31	>	* method are <em>fail-fast</em>: If the deque is modified at any time after
32	>	* the iterator is created, in any way except through the iterator's own
33	>	* {@code remove} method, the iterator will generally throw a {@link
34	>	* ConcurrentModificationException}.  Thus, in the face of concurrent
35	>	* modification, the iterator fails quickly and cleanly, rather than risking
36	>	* arbitrary, non-deterministic behavior at an undetermined time in the
37	>	* future.
38		*
39		* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
40		* as it is, generally speaking, impossible to make any hard guarantees in the
41		* presence of unsynchronized concurrent modification.  Fail-fast iterators
42	<	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
42	>	* throw {@code ConcurrentModificationException} on a best-effort basis.
43		* Therefore, it would be wrong to write a program that depended on this
44		* exception for its correctness: <i>the fail-fast behavior of iterators
45		* should be used only to detect bugs.</i>
46		*
47		* <p>This class and its iterator implement all of the
48	<	* optional methods of the {@link Collection} and {@link
49	<	* Iterator} interfaces.  This class is a member of the <a
50	<	* href="{@docRoot}/../guide/collections/index.html"> Java Collections
51	<	* Framework</a>.
48	>	* <em>optional</em> methods of the {@link Collection} and {@link
49	>	* Iterator} interfaces.
50	>	*
51	>	* <p>This class is a member of the
52	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
53	>	* Java Collections Framework</a>.
54		*
55		* @author  Josh Bloch and Doug Lea
56		* @since   1.6
#	Line 61 | Line 69 | public class ArrayDeque<E> extends Abstr
69		* other.  We also guarantee that all array cells not holding
70		* deque elements are always null.
71		*/
72	<	private transient E[] elements;
72	>	transient Object[] elements; // non-private to simplify nested class access
73
74		/**
75		* The index of the element at the head of the deque (which is the
76		* element that would be removed by remove() or pop()); or an
77		* arbitrary number equal to tail if the deque is empty.
78		*/
79	<	private transient int head;
79	>	transient int head;
80
81		/**
82		* The index at which the next element would be added to the tail
83		* of the deque (via addLast(E), add(E), or push(E)).
84		*/
85	<	private transient int tail;
85	>	transient int tail;
86
87		/**
88		* The minimum capacity that we'll use for a newly created deque.
#	Line 85 | Line 93 | public class ArrayDeque<E> extends Abstr
93		// ******  Array allocation and resizing utilities ******
94
95		/**
96	<	* Allocate empty array to hold the given number of elements.
96	>	* Allocates empty array to hold the given number of elements.
97		*
98	<	* @param numElements  the number of elements to hold.
98	>	* @param numElements  the number of elements to hold
99		*/
100	<	private void allocateElements(int numElements) {
100	>	private void allocateElements(int numElements) {
101		int initialCapacity = MIN_INITIAL_CAPACITY;
102		// Find the best power of two to hold elements.
103		// Tests "<=" because arrays aren't kept full.
#	Line 105 | Line 113 | public class ArrayDeque<E> extends Abstr
113		if (initialCapacity < 0)   // Too many elements, must back off
114		initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
115		}
116	<	elements = (E[]) new Object[initialCapacity];
116	>	elements = new Object[initialCapacity];
117		}
118
119		/**
120	<	* Double the capacity of this deque.  Call only when full, i.e.,
120	>	* Doubles the capacity of this deque.  Call only when full, i.e.,
121		* when head and tail have wrapped around to become equal.
122		*/
123		private void doubleCapacity() {
124	<	assert head == tail;
124	>	assert head == tail;
125		int p = head;
126		int n = elements.length;
127		int r = n - p; // number of elements to the right of p
#	Line 123 | Line 131 | public class ArrayDeque<E> extends Abstr
131		Object[] a = new Object[newCapacity];
132		System.arraycopy(elements, p, a, 0, r);
133		System.arraycopy(elements, 0, a, r, p);
134	<	elements = (E[])a;
134	>	elements = a;
135		head = 0;
136		tail = n;
137		}
138
139		/**
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	–	/**
140		* Constructs an empty array deque with an initial capacity
141		* sufficient to hold 16 elements.
142		*/
143		public ArrayDeque() {
144	<	elements = (E[]) new Object[16];
144	>	elements = new Object[16];
145		}
146
147		/**
#	Line 184 | Line 174 | public class ArrayDeque<E> extends Abstr
174		// terms of these.
175
176		/**
177	<	* Inserts the specified element to the front this deque.
177	>	* Inserts the specified element at the front of this deque.
178		*
179	<	* @param e the element to insert
180	<	* @throws NullPointerException if <tt>e</tt> is null
179	>	* @param e the element to add
180	>	* @throws NullPointerException if the specified element is null
181		*/
182		public void addFirst(E e) {
183		if (e == null)
184		throw new NullPointerException();
185		elements[head = (head - 1) & (elements.length - 1)] = e;
186	<	if (head == tail)
186	>	if (head == tail)
187		doubleCapacity();
188		}
189
190		/**
191	<	* Inserts the specified element to the end this deque.
202	<	* This method is equivalent to {@link Collection#add} and
203	<	* {@link #push}.
191	>	* Inserts the specified element at the end of this deque.
192		*
193	<	* @param e the element to insert
194	<	* @throws NullPointerException if <tt>e</tt> is null
193	>	* <p>This method is equivalent to {@link #add}.
194	>	*
195	>	* @param e the element to add
196	>	* @throws NullPointerException if the specified element is null
197		*/
198		public void addLast(E e) {
199		if (e == null)
#	Line 214 | Line 204 | public class ArrayDeque<E> extends Abstr
204		}
205
206		/**
207	<	* 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	<	/**
251	<	* Inserts the specified element to the front this deque.
207	>	* Inserts the specified element at the front of this deque.
208		*
209	<	* @param e the element to insert
210	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst})
211	<	* @throws NullPointerException if <tt>e</tt> is null
209	>	* @param e the element to add
210	>	* @return {@code true} (as specified by {@link Deque#offerFirst})
211	>	* @throws NullPointerException if the specified element is null
212		*/
213		public boolean offerFirst(E e) {
214		addFirst(e);
#	Line 260 | Line 216 | public class ArrayDeque<E> extends Abstr
216		}
217
218		/**
219	<	* Inserts the specified element to the end this deque.
219	>	* Inserts the specified element at the end of this deque.
220		*
221	<	* @param e the element to insert
222	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
223	<	* @throws NullPointerException if <tt>e</tt> is null
221	>	* @param e the element to add
222	>	* @return {@code true} (as specified by {@link Deque#offerLast})
223	>	* @throws NullPointerException if the specified element is null
224		*/
225		public boolean offerLast(E e) {
226		addLast(e);
#	Line 272 | Line 228 | public class ArrayDeque<E> extends Abstr
228		}
229
230		/**
231	<	* 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
231	>	* @throws NoSuchElementException {@inheritDoc}
232		*/
233		public E removeFirst() {
234		E x = pollFirst();
#	Line 287 | Line 238 | public class ArrayDeque<E> extends Abstr
238		}
239
240		/**
241	<	* 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
241	>	* @throws NoSuchElementException {@inheritDoc}
242		*/
243		public E removeLast() {
244		E x = pollLast();
#	Line 301 | Line 247 | public class ArrayDeque<E> extends Abstr
247		return x;
248		}
249
250	<	/**
251	<	* Retrieves, but does not remove, the first element of this deque,
252	<	* returning <tt>null</tt> if this deque is empty.
253	<	*
254	<	* @return the first element of this deque, or <tt>null</tt> if
255	<	*     this deque is empty
256	<	*/
257	<	public E peekFirst() {
258	<	return elements[head]; // elements[head] is null if deque empty
250	>	public E pollFirst() {
251	>	int h = head;
252	>	@SuppressWarnings("unchecked")
253	>	E result = (E) elements[h];
254	>	// Element is null if deque empty
255	>	if (result == null)
256	>	return null;
257	>	elements[h] = null;     // Must null out slot
258	>	head = (h + 1) & (elements.length - 1);
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	>	int t = (tail - 1) & (elements.length - 1);
264	>	@SuppressWarnings("unchecked")
265	>	E result = (E) elements[t];
266	>	if (result == null)
267	>	return null;
268	>	elements[t] = null;
269	>	tail = t;
270	>	return result;
271		}
272
273		/**
274	<	* Retrieves, but does not remove, the first element of this
328	<	* deque.  This method differs from the <tt>peek</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
274	>	* @throws NoSuchElementException {@inheritDoc}
275		*/
276		public E getFirst() {
277	<	E x = elements[head];
278	<	if (x == null)
277	>	@SuppressWarnings("unchecked")
278	>	E result = (E) elements[head];
279	>	if (result == null)
280		throw new NoSuchElementException();
281	<	return x;
281	>	return result;
282		}
283
284		/**
285	<	* Retrieves, but does not remove, the last element of this
343	<	* deque.  This method differs from the <tt>peek</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
285	>	* @throws NoSuchElementException {@inheritDoc}
286		*/
287		public E getLast() {
288	<	E x = elements[(tail - 1) & (elements.length - 1)];
289	<	if (x == null)
288	>	@SuppressWarnings("unchecked")
289	>	E result = (E) elements[(tail - 1) & (elements.length - 1)];
290	>	if (result == null)
291		throw new NoSuchElementException();
292	<	return x;
292	>	return result;
293	>	}
294	>
295	>	@SuppressWarnings("unchecked")
296	>	public E peekFirst() {
297	>	// elements[head] is null if deque empty
298	>	return (E) elements[head];
299	>	}
300	>
301	>	@SuppressWarnings("unchecked")
302	>	public E peekLast() {
303	>	return (E) elements[(tail - 1) & (elements.length - 1)];
304		}
305
306		/**
307		* Removes the first occurrence of the specified element in this
308	<	* deque (when traversing the deque from head to tail).  If the deque
309	<	* does not contain the element, it is unchanged.
308	>	* deque (when traversing the deque from head to tail).
309	>	* If the deque does not contain the element, it is unchanged.
310	>	* More formally, removes the first element {@code e} such that
311	>	* {@code o.equals(e)} (if such an element exists).
312	>	* Returns {@code true} if this deque contained the specified element
313	>	* (or equivalently, if this deque changed as a result of the call).
314		*
315	<	* @param e element to be removed from this deque, if present
316	<	* @return <tt>true</tt> if the deque contained the specified element
315	>	* @param o element to be removed from this deque, if present
316	>	* @return {@code true} if the deque contained the specified element
317		*/
318	<	public boolean removeFirstOccurrence(Object e) {
319	<	if (e == null)
318	>	public boolean removeFirstOccurrence(Object o) {
319	>	if (o == null)
320		return false;
321		int mask = elements.length - 1;
322		int i = head;
323	<	E x;
323	>	Object x;
324		while ( (x = elements[i]) != null) {
325	<	if (e.equals(x)) {
325	>	if (o.equals(x)) {
326		delete(i);
327		return true;
328		}
#	Line 379 | Line 333 | public class ArrayDeque<E> extends Abstr
333
334		/**
335		* Removes the last occurrence of the specified element in this
336	<	* deque (when traversing the deque from head to tail).  If the deque
337	<	* does not contain the element, it is unchanged.
336	>	* deque (when traversing the deque from head to tail).
337	>	* If the deque does not contain the element, it is unchanged.
338	>	* More formally, removes the last element {@code e} such that
339	>	* {@code o.equals(e)} (if such an element exists).
340	>	* Returns {@code true} if this deque contained the specified element
341	>	* (or equivalently, if this deque changed as a result of the call).
342		*
343	<	* @param e element to be removed from this deque, if present
344	<	* @return <tt>true</tt> if the deque contained the specified element
343	>	* @param o element to be removed from this deque, if present
344	>	* @return {@code true} if the deque contained the specified element
345		*/
346	<	public boolean removeLastOccurrence(Object e) {
347	<	if (e == null)
346	>	public boolean removeLastOccurrence(Object o) {
347	>	if (o == null)
348		return false;
349		int mask = elements.length - 1;
350		int i = (tail - 1) & mask;
351	<	E x;
351	>	Object x;
352		while ( (x = elements[i]) != null) {
353	<	if (e.equals(x)) {
353	>	if (o.equals(x)) {
354		delete(i);
355		return true;
356		}
#	Line 404 | Line 362 | public class ArrayDeque<E> extends Abstr
362		// *** Queue methods ***
363
364		/**
365	<	* Inserts the specified element to the end of this deque.
408	<	*
409	<	* <p>This method is equivalent to {@link #offerLast}.
410	<	*
411	<	* @param e the element to insert
412	<	* @return <tt>true</tt> (as per the spec for {@link Queue#offer})
413	<	* @throws NullPointerException if <tt>e</tt> is null
414	<	*/
415	<	public boolean offer(E e) {
416	<	return offerLast(e);
417	<	}
418	<
419	<	/**
420	<	* Inserts the specified element to the end of this deque.
365	>	* Inserts the specified element at the end of this deque.
366		*
367		* <p>This method is equivalent to {@link #addLast}.
368		*
369	<	* @param e the element to insert
370	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
371	<	* @throws NullPointerException if <tt>e</tt> is null
369	>	* @param e the element to add
370	>	* @return {@code true} (as specified by {@link Collection#add})
371	>	* @throws NullPointerException if the specified element is null
372		*/
373		public boolean add(E e) {
374		addLast(e);
#	Line 431 | Line 376 | public class ArrayDeque<E> extends Abstr
376		}
377
378		/**
379	<	* Retrieves and removes the head of the queue represented by
435	<	* this deque, or <tt>null</tt> if this deque is empty.  In other words,
436	<	* retrieves and removes the first element of this deque, or <tt>null</tt>
437	<	* if this deque is empty.
379	>	* Inserts the specified element at the end of this deque.
380		*
381	<	* <p>This method is equivalent to {@link #pollFirst}.
381	>	* <p>This method is equivalent to {@link #offerLast}.
382		*
383	<	* @return the first element of this deque, or <tt>null</tt> if
384	<	*     this deque is empty
383	>	* @param e the element to add
384	>	* @return {@code true} (as specified by {@link Queue#offer})
385	>	* @throws NullPointerException if the specified element is null
386		*/
387	<	public E poll() {
388	<	return pollFirst();
387	>	public boolean offer(E e) {
388	>	return offerLast(e);
389		}
390
391		/**
392		* Retrieves and removes the head of the queue represented by this deque.
393	<	* This method differs from the <tt>poll</tt> method in that it throws an
393	>	*
394	>	* This method differs from {@link #poll poll} only in that it throws an
395		* exception if this deque is empty.
396		*
397		* <p>This method is equivalent to {@link #removeFirst}.
398		*
399		* @return the head of the queue represented by this deque
400	<	* @throws NoSuchElementException if this deque is empty
400	>	* @throws NoSuchElementException {@inheritDoc}
401		*/
402		public E remove() {
403		return removeFirst();
404		}
405
406		/**
407	<	* Retrieves, but does not remove, the head of the queue represented by
408	<	* this deque, returning <tt>null</tt> if this deque is empty.
407	>	* Retrieves and removes the head of the queue represented by this deque
408	>	* (in other words, the first element of this deque), or returns
409	>	* {@code null} if this deque is empty.
410		*
411	<	* <p>This method is equivalent to {@link #peekFirst}
411	>	* <p>This method is equivalent to {@link #pollFirst}.
412		*
413		* @return the head of the queue represented by this deque, or
414	<	*     <tt>null</tt> if this deque is empty
414	>	*         {@code null} if this deque is empty
415		*/
416	<	public E peek() {
417	<	return peekFirst();
416	>	public E poll() {
417	>	return pollFirst();
418		}
419
420		/**
421		* Retrieves, but does not remove, the head of the queue represented by
422	<	* this deque.  This method differs from the <tt>peek</tt> method only in
422	>	* this deque.  This method differs from {@link #peek peek} only in
423		* that it throws an exception if this deque is empty.
424		*
425	<	* <p>This method is equivalent to {@link #getFirst}
425	>	* <p>This method is equivalent to {@link #getFirst}.
426		*
427		* @return the head of the queue represented by this deque
428	<	* @throws NoSuchElementException if this deque is empty
428	>	* @throws NoSuchElementException {@inheritDoc}
429		*/
430		public E element() {
431		return getFirst();
432		}
433
434	+	/**
435	+	* Retrieves, but does not remove, the head of the queue represented by
436	+	* this deque, or returns {@code null} if this deque is empty.
437	+	*
438	+	* <p>This method is equivalent to {@link #peekFirst}.
439	+	*
440	+	* @return the head of the queue represented by this deque, or
441	+	*         {@code null} if this deque is empty
442	+	*/
443	+	public E peek() {
444	+	return peekFirst();
445	+	}
446	+
447		// *** Stack methods ***
448
449		/**
450		* Pushes an element onto the stack represented by this deque.  In other
451	<	* words, inserts the element to the front this deque.
451	>	* words, inserts the element at the front of this deque.
452		*
453		* <p>This method is equivalent to {@link #addFirst}.
454		*
455		* @param e the element to push
456	<	* @throws NullPointerException if <tt>e</tt> is null
456	>	* @throws NullPointerException if the specified element is null
457		*/
458		public void push(E e) {
459		addFirst(e);
#	Line 508 | Line 466 | public class ArrayDeque<E> extends Abstr
466		* <p>This method is equivalent to {@link #removeFirst()}.
467		*
468		* @return the element at the front of this deque (which is the top
469	<	*     of the stack represented by this deque)
470	<	* @throws NoSuchElementException if this deque is empty
469	>	*         of the stack represented by this deque)
470	>	* @throws NoSuchElementException {@inheritDoc}
471		*/
472		public E pop() {
473		return removeFirst();
474		}
475
476	+	private void checkInvariants() {
477	+	assert elements[tail] == null;
478	+	assert head == tail ? elements[head] == null :
479	+	(elements[head] != null &&
480	+	elements[(tail - 1) & (elements.length - 1)] != null);
481	+	assert elements[(head - 1) & (elements.length - 1)] == null;
482	+	}
483	+
484		/**
485	<	* Remove the element at the specified position in the elements array,
486	<	* adjusting head, tail, and size as necessary.  This can result in
487	<	* motion of elements backwards or forwards in the array.
488	<	*
489	<	* <p>This method is called delete rather than remove to emphasize
490	<	* that its semantics differ from those of List.remove(int).
491	<	*
485	>	* Removes the element at the specified position in the elements array,
486	>	* adjusting head and tail as necessary.  This can result in motion of
487	>	* elements backwards or forwards in the array.
488	>	*
489	>	* <p>This method is called delete rather than remove to emphasize
490	>	* that its semantics differ from those of {@link List#remove(int)}.
491	>	*
492		* @return true if elements moved backwards
493		*/
494		private boolean delete(int i) {
495	<	// Case 1: Deque doesn't wrap
496	<	// Case 2: Deque does wrap and removed element is in the head portion
497	<	if ((head < tail || tail == 0) || i >= head) {
498	<	System.arraycopy(elements, head, elements, head + 1, i - head);
499	<	elements[head] = null;
500	<	head = (head + 1) & (elements.length - 1);
495	>	checkInvariants();
496	>	final Object[] elements = this.elements;
497	>	final int mask = elements.length - 1;
498	>	final int h = head;
499	>	final int t = tail;
500	>	final int front = (i - h) & mask;
501	>	final int back  = (t - i) & mask;
502	>
503	>	// Invariant: head <= i < tail mod circularity
504	>	if (front >= ((t - h) & mask))
505	>	throw new ConcurrentModificationException();
506	>
507	>	// Optimize for least element motion
508	>	if (front < back) {
509	>	if (h <= i) {
510	>	System.arraycopy(elements, h, elements, h + 1, front);
511	>	} else { // Wrap around
512	>	System.arraycopy(elements, 0, elements, 1, i);
513	>	elements[0] = elements[mask];
514	>	System.arraycopy(elements, h, elements, h + 1, mask - h);
515	>	}
516	>	elements[h] = null;
517	>	head = (h + 1) & mask;
518		return false;
519	+	} else {
520	+	if (i < t) { // Copy the null tail as well
521	+	System.arraycopy(elements, i + 1, elements, i, back);
522	+	tail = t - 1;
523	+	} else { // Wrap around
524	+	System.arraycopy(elements, i + 1, elements, i, mask - i);
525	+	elements[mask] = elements[0];
526	+	System.arraycopy(elements, 1, elements, 0, t);
527	+	tail = (t - 1) & mask;
528	+	}
529	+	return true;
530		}
537	–
538	–	// Case 3: Deque wraps and removed element is in the tail portion
539	–	tail--;
540	–	System.arraycopy(elements, i + 1, elements, i, tail - i);
541	–	elements[tail] = null;
542	–	return true;
531		}
532
533		// *** Collection Methods ***
#	Line 554 | Line 542 | public class ArrayDeque<E> extends Abstr
542		}
543
544		/**
545	<	* Returns <tt>true</tt> if this collection contains no elements.<p>
545	>	* Returns {@code true} if this deque contains no elements.
546		*
547	<	* @return <tt>true</tt> if this collection contains no elements.
547	>	* @return {@code true} if this deque contains no elements
548		*/
549		public boolean isEmpty() {
550		return head == tail;
#	Line 567 | Line 555 | public class ArrayDeque<E> extends Abstr
555		* will be ordered from first (head) to last (tail).  This is the same
556		* order that elements would be dequeued (via successive calls to
557		* {@link #remove} or popped (via successive calls to {@link #pop}).
558	<	*
559	<	* @return an <tt>Iterator</tt> over the elements in this deque
558	>	*
559	>	* @return an iterator over the elements in this deque
560		*/
561		public Iterator<E> iterator() {
562		return new DeqIterator();
563		}
564
565	+	public Iterator<E> descendingIterator() {
566	+	return new DescendingIterator();
567	+	}
568	+
569		private class DeqIterator implements Iterator<E> {
570		/**
571		* Index of element to be returned by subsequent call to next.
#	Line 597 | Line 589 | public class ArrayDeque<E> extends Abstr
589		}
590
591		public E next() {
600	–	E result;
592		if (cursor == fence)
593		throw new NoSuchElementException();
594	+	@SuppressWarnings("unchecked")
595	+	E result = (E) elements[cursor];
596		// This check doesn't catch all possible comodifications,
597		// but does catch the ones that corrupt traversal
598	<	if (tail != fence || (result = elements[cursor]) == null)
598	>	if (tail != fence || result == null)
599		throw new ConcurrentModificationException();
600		lastRet = cursor;
601		cursor = (cursor + 1) & (elements.length - 1);
#	Line 612 | Line 605 | public class ArrayDeque<E> extends Abstr
605		public void remove() {
606		if (lastRet < 0)
607		throw new IllegalStateException();
608	<	if (delete(lastRet))
609	<	cursor--;
608	>	if (delete(lastRet)) { // if left-shifted, undo increment in next()
609	>	cursor = (cursor - 1) & (elements.length - 1);
610	>	fence = tail;
611	>	}
612	>	lastRet = -1;
613	>	}
614	>	}
615	>
616	>	private class DescendingIterator implements Iterator<E> {
617	>	/*
618	>	* This class is nearly a mirror-image of DeqIterator, using
619	>	* tail instead of head for initial cursor, and head instead of
620	>	* tail for fence.
621	>	*/
622	>	private int cursor = tail;
623	>	private int fence = head;
624	>	private int lastRet = -1;
625	>
626	>	public boolean hasNext() {
627	>	return cursor != fence;
628	>	}
629	>
630	>	public E next() {
631	>	if (cursor == fence)
632	>	throw new NoSuchElementException();
633	>	cursor = (cursor - 1) & (elements.length - 1);
634	>	@SuppressWarnings("unchecked")
635	>	E result = (E) elements[cursor];
636	>	if (head != fence || result == null)
637	>	throw new ConcurrentModificationException();
638	>	lastRet = cursor;
639	>	return result;
640	>	}
641	>
642	>	public void remove() {
643	>	if (lastRet < 0)
644	>	throw new IllegalStateException();
645	>	if (!delete(lastRet)) {
646	>	cursor = (cursor + 1) & (elements.length - 1);
647	>	fence = head;
648	>	}
649		lastRet = -1;
618	–	fence = tail;
650		}
651		}
652
653		/**
654	<	* Returns <tt>true</tt> if this deque contains the specified
655	<	* element.  More formally, returns <tt>true</tt> if and only if this
656	<	* deque contains at least one element <tt>e</tt> such that
626	<	* <tt>e.equals(o)</tt>.
654	>	* Returns {@code true} if this deque contains the specified element.
655	>	* More formally, returns {@code true} if and only if this deque contains
656	>	* at least one element {@code e} such that {@code o.equals(e)}.
657		*
658		* @param o object to be checked for containment in this deque
659	<	* @return <tt>true</tt> if this deque contains the specified element
659	>	* @return {@code true} if this deque contains the specified element
660		*/
661		public boolean contains(Object o) {
662		if (o == null)
663		return false;
664		int mask = elements.length - 1;
665		int i = head;
666	<	E x;
666	>	Object x;
667		while ( (x = elements[i]) != null) {
668		if (o.equals(x))
669		return true;
#	Line 644 | Line 674 | public class ArrayDeque<E> extends Abstr
674
675		/**
676		* Removes a single instance of the specified element from this deque.
677	<	* This method is equivalent to {@link #removeFirstOccurrence}.
677	>	* If the deque does not contain the element, it is unchanged.
678	>	* More formally, removes the first element {@code e} such that
679	>	* {@code o.equals(e)} (if such an element exists).
680	>	* Returns {@code true} if this deque contained the specified element
681	>	* (or equivalently, if this deque changed as a result of the call).
682	>	*
683	>	* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
684		*
685	<	* @param e element to be removed from this deque, if present
686	<	* @return <tt>true</tt> if this deque contained the specified element
685	>	* @param o element to be removed from this deque, if present
686	>	* @return {@code true} if this deque contained the specified element
687		*/
688	<	public boolean remove(Object e) {
689	<	return removeFirstOccurrence(e);
688	>	public boolean remove(Object o) {
689	>	return removeFirstOccurrence(o);
690		}
691
692		/**
693		* Removes all of the elements from this deque.
694	+	* The deque will be empty after this call returns.
695		*/
696		public void clear() {
697		int h = head;
#	Line 666 | Line 703 | public class ArrayDeque<E> extends Abstr
703		do {
704		elements[i] = null;
705		i = (i + 1) & mask;
706	<	} while(i != t);
706	>	} while (i != t);
707		}
708		}
709
710		/**
711	<	* Returns an array containing all of the elements in this list
712	<	* in the correct order.
711	>	* Returns an array containing all of the elements in this deque
712	>	* in proper sequence (from first to last element).
713	>	*
714	>	* <p>The returned array will be "safe" in that no references to it are
715	>	* maintained by this deque.  (In other words, this method must allocate
716	>	* a new array).  The caller is thus free to modify the returned array.
717		*
718	<	* @return an array containing all of the elements in this list
719	<	*         in the correct order
718	>	* <p>This method acts as bridge between array-based and collection-based
719	>	* APIs.
720	>	*
721	>	* @return an array containing all of the elements in this deque
722		*/
723		public Object[] toArray() {
724	<	return copyElements(new Object[size()]);
724	>	final int head = this.head;
725	>	final int tail = this.tail;
726	>	boolean wrap = (tail < head);
727	>	int end = wrap ? tail + elements.length : tail;
728	>	Object[] a = Arrays.copyOfRange(elements, head, end);
729	>	if (wrap)
730	>	System.arraycopy(elements, 0, a, elements.length - head, tail);
731	>	return a;
732		}
733
734		/**
735	<	* Returns an array containing all of the elements in this deque in the
736	<	* correct order; the runtime type of the returned array is that of the
737	<	* specified array.  If the deque fits in the specified array, it is
738	<	* returned therein.  Otherwise, a new array is allocated with the runtime
739	<	* type of the specified array and the size of this deque.
735	>	* Returns an array containing all of the elements in this deque in
736	>	* proper sequence (from first to last element); the runtime type of the
737	>	* returned array is that of the specified array.  If the deque fits in
738	>	* the specified array, it is returned therein.  Otherwise, a new array
739	>	* is allocated with the runtime type of the specified array and the
740	>	* size of this deque.
741	>	*
742	>	* <p>If this deque fits in the specified array with room to spare
743	>	* (i.e., the array has more elements than this deque), the element in
744	>	* the array immediately following the end of the deque is set to
745	>	* {@code null}.
746	>	*
747	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
748	>	* array-based and collection-based APIs.  Further, this method allows
749	>	* precise control over the runtime type of the output array, and may,
750	>	* under certain circumstances, be used to save allocation costs.
751	>	*
752	>	* <p>Suppose {@code x} is a deque known to contain only strings.
753	>	* The following code can be used to dump the deque into a newly
754	>	* allocated array of {@code String}:
755	>	*
756	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
757		*
758	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
759	<	* the array has more elements than the deque), the element in the array
693	<	* immediately following the end of the collection is set to <tt>null</tt>.
758	>	* Note that {@code toArray(new Object[0])} is identical in function to
759	>	* {@code toArray()}.
760		*
761		* @param a the array into which the elements of the deque are to
762	<	*          be stored, if it is big enough; otherwise, a new array of the
763	<	*          same runtime type is allocated for this purpose
764	<	* @return an array containing the elements of the deque
765	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
766	<	*         of the runtime type of every element in this deque
762	>	*          be stored, if it is big enough; otherwise, a new array of the
763	>	*          same runtime type is allocated for this purpose
764	>	* @return an array containing all of the elements in this deque
765	>	* @throws ArrayStoreException if the runtime type of the specified array
766	>	*         is not a supertype of the runtime type of every element in
767	>	*         this deque
768	>	* @throws NullPointerException if the specified array is null
769		*/
770	+	@SuppressWarnings("unchecked")
771		public <T> T[] toArray(T[] a) {
772	<	int size = size();
773	<	if (a.length < size)
774	<	a = (T[])java.lang.reflect.Array.newInstance(
775	<	a.getClass().getComponentType(), size);
776	<	copyElements(a);
777	<	if (a.length > size)
778	<	a[size] = null;
772	>	final int head = this.head;
773	>	final int tail = this.tail;
774	>	boolean wrap = (tail < head);
775	>	int size = (tail - head) + (wrap ? elements.length : 0);
776	>	int firstLeg = size - (wrap ? tail : 0);
777	>	int len = a.length;
778	>	if (size > len) {
779	>	a = (T[]) Arrays.copyOfRange(elements, head, head + size,
780	>	a.getClass());
781	>	} else {
782	>	System.arraycopy(elements, head, a, 0, firstLeg);
783	>	if (size < len)
784	>	a[size] = null;
785	>	}
786	>	if (wrap)
787	>	System.arraycopy(elements, 0, a, firstLeg, tail);
788		return a;
789		}
790
#	Line 718 | Line 796 | public class ArrayDeque<E> extends Abstr
796		* @return a copy of this deque
797		*/
798		public ArrayDeque<E> clone() {
799	<	try {
799	>	try {
800	>	@SuppressWarnings("unchecked")
801		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
802	<	// These two lines are currently faster than cloning the array:
724	<	result.elements = (E[]) new Object[elements.length];
725	<	System.arraycopy(elements, 0, result.elements, 0, elements.length);
802	>	result.elements = Arrays.copyOf(elements, elements.length);
803		return result;
804	<
728	<	} catch (CloneNotSupportedException e) {
804	>	} catch (CloneNotSupportedException e) {
805		throw new AssertionError();
806		}
807		}
808
733	–	/**
734	–	* Appease the serialization gods.
735	–	*/
809		private static final long serialVersionUID = 2340985798034038923L;
810
811		/**
812	<	* Serialize this deque.
812	>	* Saves this deque to a stream (that is, serializes it).
813		*
814	<	* @serialData The current size (<tt>int</tt>) of the deque,
814	>	* @serialData The current size ({@code int}) of the deque,
815		* followed by all of its elements (each an object reference) in
816		* first-to-last order.
817		*/
818	<	private void writeObject(ObjectOutputStream s) throws IOException {
818	>	private void writeObject(java.io.ObjectOutputStream s)
819	>	throws java.io.IOException {
820		s.defaultWriteObject();
821
822		// Write out size
823	<	int size = size();
750	<	s.writeInt(size);
823	>	s.writeInt(size());
824
825		// Write out elements in order.
753	–	int i = head;
826		int mask = elements.length - 1;
827	<	for (int j = 0; j < size; j++) {
827	>	for (int i = head; i != tail; i = (i + 1) & mask)
828		s.writeObject(elements[i]);
757	–	i = (i + 1) & mask;
758	–	}
829		}
830
831		/**
832	<	* Deserialize this deque.
832	>	* Reconstitutes this deque from a stream (that is, deserializes it).
833		*/
834	<	private void readObject(ObjectInputStream s)
835	<	throws IOException, ClassNotFoundException {
834	>	private void readObject(java.io.ObjectInputStream s)
835	>	throws java.io.IOException, ClassNotFoundException {
836		s.defaultReadObject();
837
838		// Read in size and allocate array
#	Line 773 | Line 843 | public class ArrayDeque<E> extends Abstr
843
844		// Read in all elements in the proper order.
845		for (int i = 0; i < size; i++)
846	<	elements[i] = (E)s.readObject();
846	>	elements[i] = s.readObject();
847	>	}
848
849	+	Spliterator<E> spliterator() {
850	+	return new DeqSpliterator<E>(this, -1, -1);
851		}
852	+
853	+	public Stream<E> stream() {
854	+	return Streams.stream(spliterator());
855	+	}
856	+
857	+	public Stream<E> parallelStream() {
858	+	return Streams.parallelStream(spliterator());
859	+	}
860	+
861	+	static final class DeqSpliterator<E> implements Spliterator<E> {
862	+	private final ArrayDeque<E> deq;
863	+	private int fence;  // -1 until first use
864	+	private int index;  // current index, modified on traverse/split
865	+
866	+	/** Creates new spliterator covering the given array and range */
867	+	DeqSpliterator(ArrayDeque<E> deq, int origin, int fence) {
868	+	this.deq = deq;
869	+	this.index = origin;
870	+	this.fence = fence;
871	+	}
872	+
873	+	private int getFence() { // force initialization
874	+	int t;
875	+	if ((t = fence) < 0) {
876	+	t = fence = deq.tail;
877	+	index = deq.head;
878	+	}
879	+	return t;
880	+	}
881	+
882	+	public DeqSpliterator<E> trySplit() {
883	+	int t = getFence(), h = index, n = deq.elements.length;
884	+	if (h != t && ((h + 1) & (n - 1)) != t) {
885	+	if (h > t)
886	+	t += n;
887	+	int m = ((h + t) >>> 1) & (n - 1);
888	+	return new DeqSpliterator<>(deq, h, index = m);
889	+	}
890	+	return null;
891	+	}
892	+
893	+	public void forEach(Consumer<? super E> consumer) {
894	+	if (consumer == null)
895	+	throw new NullPointerException();
896	+	Object[] a = deq.elements;
897	+	int m = a.length - 1, f = getFence(), i = index;
898	+	index = f;
899	+	while (i != f) {
900	+	@SuppressWarnings("unchecked") E e = (E)a[i];
901	+	i = (i + 1) & m;
902	+	if (e == null)
903	+	throw new ConcurrentModificationException();
904	+	consumer.accept(e);
905	+	}
906	+	}
907	+
908	+	public boolean tryAdvance(Consumer<? super E> consumer) {
909	+	if (consumer == null)
910	+	throw new NullPointerException();
911	+	Object[] a = deq.elements;
912	+	int m = a.length - 1, f = getFence(), i = index;
913	+	if (i != fence) {
914	+	@SuppressWarnings("unchecked") E e = (E)a[i];
915	+	index = (i + 1) & m;
916	+	if (e == null)
917	+	throw new ConcurrentModificationException();
918	+	consumer.accept(e);
919	+	return true;
920	+	}
921	+	return false;
922	+	}
923	+
924	+	public long estimateSize() {
925	+	int n = getFence() - index;
926	+	if (n < 0)
927	+	n += deq.elements.length;
928	+	return (long) n;
929	+	}
930	+
931	+	@Override
932	+	public int characteristics() {
933	+	return Spliterator.ORDERED | Spliterator.SIZED |
934	+	Spliterator.NONNULL | Spliterator.SUBSIZED;
935	+	}
936	+	}
937	+
938		}

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