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Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.12 by jsr166, Tue May 17 16:14:34 2005 UTC vs.
Revision 1.79 by jsr166, Tue Oct 18 20:32:55 2016 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Josh Bloch of Google Inc. and released to the public domain,
3	<	* as explained at http://creativecommons.org/licenses/publicdomain.
3	>	* as explained at http://creativecommons.org/publicdomain/zero/1.0/.
4		*/
5
6		package java.util;
7	<	import java.io.*;
7	>
8	>	import java.io.Serializable;
9	>	import java.util.function.Consumer;
10	>	import java.util.function.Predicate;
11	>	import java.util.function.UnaryOperator;
12
13		/**
14		* Resizable-array implementation of the {@link Deque} interface.  Array
#	Line 15 | Line 19 | import java.io.*;
19		* {@link Stack} when used as a stack, and faster than {@link LinkedList}
20		* when used as a queue.
21		*
22	<	* <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time.
23	<	* Exceptions include {@link #remove(Object) remove}, {@link
24	<	* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
25	<	* removeLastOccurrence}, {@link #contains contains}, {@link #iterator
26	<	* iterator.remove()}, and the bulk operations, all of which run in linear
27	<	* time.
22	>	* <p>Most {@code ArrayDeque} operations run in amortized constant time.
23	>	* Exceptions include
24	>	* {@link #remove(Object) remove},
25	>	* {@link #removeFirstOccurrence removeFirstOccurrence},
26	>	* {@link #removeLastOccurrence removeLastOccurrence},
27	>	* {@link #contains contains},
28	>	* {@link #iterator iterator.remove()},
29	>	* and the bulk operations, all of which run in linear time.
30		*
31	<	* <p>The iterators returned by this class's <tt>iterator</tt> method are
32	<	* <i>fail-fast</i>: If the deque is modified at any time after the iterator
33	<	* is created, in any way except through the iterator's own <tt>remove</tt>
34	<	* method, the iterator will generally throw a {@link
31	>	* <p>The iterators returned by this class's {@link #iterator() iterator}
32	>	* method are <em>fail-fast</em>: If the deque is modified at any time after
33	>	* the iterator is created, in any way except through the iterator's own
34	>	* {@code remove} method, the iterator will generally throw a {@link
35		* ConcurrentModificationException}.  Thus, in the face of concurrent
36		* modification, the iterator fails quickly and cleanly, rather than risking
37		* arbitrary, non-deterministic behavior at an undetermined time in the
#	Line 34 | Line 40 | import java.io.*;
40		* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
41		* as it is, generally speaking, impossible to make any hard guarantees in the
42		* presence of unsynchronized concurrent modification.  Fail-fast iterators
43	<	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
43	>	* throw {@code ConcurrentModificationException} on a best-effort basis.
44		* Therefore, it would be wrong to write a program that depended on this
45		* exception for its correctness: <i>the fail-fast behavior of iterators
46		* should be used only to detect bugs.</i>
#	Line 44 | Line 50 | import java.io.*;
50		* Iterator} interfaces.
51		*
52		* <p>This class is a member of the
53	<	* <a href="{@docRoot}/../guide/collections/index.html">
53	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
54		* Java Collections Framework</a>.
55		*
56		* @author  Josh Bloch and Doug Lea
57	+	* @param <E> the type of elements held in this deque
58		* @since   1.6
52	–	* @param <E> the type of elements held in this collection
59		*/
60		public class ArrayDeque<E> extends AbstractCollection<E>
61		implements Deque<E>, Cloneable, Serializable
62		{
63		/**
64		* The array in which the elements of the deque are stored.
65	<	* The capacity of the deque is the length of this array, which is
66	<	* always a power of two. The array is never allowed to become
61	<	* full, except transiently within an addX method where it is
62	<	* resized (see doubleCapacity) immediately upon becoming full,
63	<	* thus avoiding head and tail wrapping around to equal each
64	<	* other.  We also guarantee that all array cells not holding
65	<	* deque elements are always null.
65	>	* We guarantee that all array cells not holding deque elements
66	>	* are always null.
67		*/
68	<	private transient E[] elements;
68	>	transient Object[] elements;
69
70		/**
71		* The index of the element at the head of the deque (which is the
72		* element that would be removed by remove() or pop()); or an
73	<	* arbitrary number equal to tail if the deque is empty.
73	<	*/
74	<	private transient int head;
75	<
76	<	/**
77	<	* The index at which the next element would be added to the tail
78	<	* of the deque (via addLast(E), add(E), or push(E)).
79	<	*/
80	<	private transient int tail;
81	<
82	<	/**
83	<	* The minimum capacity that we'll use for a newly created deque.
84	<	* Must be a power of 2.
73	>	* arbitrary number 0 <= head < elements.length if the deque is empty.
74		*/
75	<	private static final int MIN_INITIAL_CAPACITY = 8;
75	>	transient int head;
76
77	<	// ******  Array allocation and resizing utilities ******
77	>	/** Number of elements in this collection. */
78	>	transient int size;
79
80		/**
81	<	* Allocate empty array to hold the given number of elements.
82	<	*
83	<	* @param numElements  the number of elements to hold
84	<	*/
85	<	private void allocateElements(int numElements) {
86	<	int initialCapacity = MIN_INITIAL_CAPACITY;
87	<	// Find the best power of two to hold elements.
88	<	// Tests "<=" because arrays aren't kept full.
89	<	if (numElements >= initialCapacity) {
90	<	initialCapacity = numElements;
91	<	initialCapacity |= (initialCapacity >>>  1);
92	<	initialCapacity |= (initialCapacity >>>  2);
93	<	initialCapacity |= (initialCapacity >>>  4);
94	<	initialCapacity |= (initialCapacity >>>  8);
95	<	initialCapacity |= (initialCapacity >>> 16);
96	<	initialCapacity++;
81	>	* The maximum size of array to allocate.
82	>	* Some VMs reserve some header words in an array.
83	>	* Attempts to allocate larger arrays may result in
84	>	* OutOfMemoryError: Requested array size exceeds VM limit
85	>	*/
86	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
87	>
88	>	/**
89	>	* Increases the capacity of this deque by at least the given amount.
90	>	*
91	>	* @param needed the required minimum extra capacity; must be positive
92	>	*/
93	>	private void grow(int needed) {
94	>	// overflow-conscious code
95	>	// checkInvariants();
96	>	int oldCapacity = elements.length;
97	>	int newCapacity;
98	>	// Double size if small; else grow by 50%
99	>	int jump = (oldCapacity < 64) ? (oldCapacity + 2) : (oldCapacity >> 1);
100	>	if (jump < needed
101	>	|| (newCapacity = (oldCapacity + jump)) - MAX_ARRAY_SIZE > 0)
102	>	newCapacity = newCapacity(needed, jump);
103	>	elements = Arrays.copyOf(elements, newCapacity);
104	>	if (oldCapacity - head < size) {
105	>	// wrap around; slide first leg forward to end of array
106	>	int newSpace = newCapacity - oldCapacity;
107	>	System.arraycopy(elements, head,
108	>	elements, head + newSpace,
109	>	oldCapacity - head);
110	>	Arrays.fill(elements, head, head + newSpace, null);
111	>	head += newSpace;
112	>	}
113	>	// checkInvariants();
114	>	}
115
116	<	if (initialCapacity < 0)   // Too many elements, must back off
117	<	initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
116	>	/** Capacity calculation for edge conditions, especially overflow. */
117	>	private int newCapacity(int needed, int jump) {
118	>	int oldCapacity = elements.length;
119	>	int minCapacity;
120	>	if ((minCapacity = oldCapacity + needed) - MAX_ARRAY_SIZE > 0) {
121	>	if (minCapacity < 0)
122	>	throw new IllegalStateException("Sorry, deque too big");
123	>	return Integer.MAX_VALUE;
124		}
125	<	elements = (E[]) new Object[initialCapacity];
125	>	if (needed > jump)
126	>	return minCapacity;
127	>	return (oldCapacity + jump - MAX_ARRAY_SIZE < 0)
128	>	? oldCapacity + jump
129	>	: MAX_ARRAY_SIZE;
130		}
131
132		/**
133	<	* Double the capacity of this deque.  Call only when full, i.e.,
134	<	* when head and tail have wrapped around to become equal.
133	>	* Increases the internal storage of this collection, if necessary,
134	>	* to ensure that it can hold at least the given number of elements.
135	>	*
136	>	* @param minCapacity the desired minimum capacity
137		*/
138	<	private void doubleCapacity() {
139	<	assert head == tail;
140	<	int p = head;
141	<	int n = elements.length;
122	<	int r = n - p; // number of elements to the right of p
123	<	int newCapacity = n << 1;
124	<	if (newCapacity < 0)
125	<	throw new IllegalStateException("Sorry, deque too big");
126	<	Object[] a = new Object[newCapacity];
127	<	System.arraycopy(elements, p, a, 0, r);
128	<	System.arraycopy(elements, 0, a, r, p);
129	<	elements = (E[])a;
130	<	head = 0;
131	<	tail = n;
138	>	/* TODO: public */ private void ensureCapacity(int minCapacity) {
139	>	if (minCapacity > elements.length)
140	>	grow(minCapacity - elements.length);
141	>	// checkInvariants();
142		}
143
144		/**
145	<	* Copies the elements from our element array into the specified array,
136	<	* in order (from first to last element in the deque).  It is assumed
137	<	* that the array is large enough to hold all elements in the deque.
138	<	*
139	<	* @return its argument
145	>	* Minimizes the internal storage of this collection.
146		*/
147	<	private <T> T[] copyElements(T[] a) {
148	<	if (head < tail) {
149	<	System.arraycopy(elements, head, a, 0, size());
150	<	} else if (head > tail) {
145	<	int headPortionLen = elements.length - head;
146	<	System.arraycopy(elements, head, a, 0, headPortionLen);
147	<	System.arraycopy(elements, 0, a, headPortionLen, tail);
147	>	/* TODO: public */ private void trimToSize() {
148	>	if (size < elements.length) {
149	>	elements = toArray();
150	>	head = 0;
151		}
152	<	return a;
152	>	// checkInvariants();
153		}
154
155		/**
#	Line 154 | Line 157 | public class ArrayDeque<E> extends Abstr
157		* sufficient to hold 16 elements.
158		*/
159		public ArrayDeque() {
160	<	elements = (E[]) new Object[16];
160	>	elements = new Object[16];
161		}
162
163		/**
164		* Constructs an empty array deque with an initial capacity
165		* sufficient to hold the specified number of elements.
166		*
167	<	* @param numElements  lower bound on initial capacity of the deque
167	>	* @param numElements lower bound on initial capacity of the deque
168		*/
169		public ArrayDeque(int numElements) {
170	<	allocateElements(numElements);
170	>	elements = new Object[numElements];
171		}
172
173		/**
#	Line 178 | Line 181 | public class ArrayDeque<E> extends Abstr
181		* @throws NullPointerException if the specified collection is null
182		*/
183		public ArrayDeque(Collection<? extends E> c) {
184	<	allocateElements(c.size());
185	<	addAll(c);
184	>	Object[] elements = c.toArray();
185	>	// defend against c.toArray (incorrectly) not returning Object[]
186	>	// (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)
187	>	if (elements.getClass() != Object[].class)
188	>	elements = Arrays.copyOf(elements, size, Object[].class);
189	>	for (Object obj : elements)
190	>	Objects.requireNonNull(obj);
191	>	size = elements.length;
192	>	this.elements = elements;
193	>	}
194	>
195	>	/**
196	>	* Increments i, mod modulus.
197	>	* Precondition and postcondition: 0 <= i < modulus.
198	>	*/
199	>	static final int inc(int i, int modulus) {
200	>	if (++i == modulus) i = 0;
201	>	return i;
202	>	}
203	>
204	>	/**
205	>	* Decrements i, mod modulus.
206	>	* Precondition and postcondition: 0 <= i < modulus.
207	>	*/
208	>	static final int dec(int i, int modulus) {
209	>	if (--i < 0) i += modulus;
210	>	return i;
211	>	}
212	>
213	>	/**
214	>	* Adds i and j, mod modulus.
215	>	* Precondition and postcondition: 0 <= i < modulus, 0 <= j <= modulus.
216	>	*/
217	>	static final int add(int i, int j, int modulus) {
218	>	if ((i += j) - modulus >= 0) i -= modulus;
219	>	return i;
220	>	}
221	>
222	>	/**
223	>	* Returns the array index of the last element.
224	>	* May return invalid index -1 if there are no elements.
225	>	*/
226	>	final int tail() {
227	>	return add(head, size - 1, elements.length);
228	>	}
229	>
230	>	/**
231	>	* Returns element at array index i.
232	>	*/
233	>	@SuppressWarnings("unchecked")
234	>	final E elementAt(int i) {
235	>	return (E) elements[i];
236	>	}
237	>
238	>	/**
239	>	* A version of elementAt that checks for null elements.
240	>	* This check doesn't catch all possible comodifications,
241	>	* but does catch ones that corrupt traversal.
242	>	*/
243	>	E checkedElementAt(Object[] elements, int i) {
244	>	@SuppressWarnings("unchecked") E e = (E) elements[i];
245	>	if (e == null)
246	>	throw new ConcurrentModificationException();
247	>	return e;
248		}
249
250		// The main insertion and extraction methods are addFirst,
#	Line 193 | Line 258 | public class ArrayDeque<E> extends Abstr
258		* @throws NullPointerException if the specified element is null
259		*/
260		public void addFirst(E e) {
261	<	if (e == null)
262	<	throw new NullPointerException();
263	<	elements[head = (head - 1) & (elements.length - 1)] = e;
264	<	if (head == tail)
265	<	doubleCapacity();
261	>	// checkInvariants();
262	>	Objects.requireNonNull(e);
263	>	Object[] elements;
264	>	int capacity, s = size;
265	>	while (s == (capacity = (elements = this.elements).length))
266	>	grow(1);
267	>	elements[head = dec(head, capacity)] = e;
268	>	size = s + 1;
269		}
270
271		/**
272		* Inserts the specified element at the end of this deque.
273	<	* This method is equivalent to {@link #add} and {@link #push}.
273	>	*
274	>	* <p>This method is equivalent to {@link #add}.
275		*
276		* @param e the element to add
277		* @throws NullPointerException if the specified element is null
278		*/
279		public void addLast(E e) {
280	<	if (e == null)
281	<	throw new NullPointerException();
282	<	elements[tail] = e;
283	<	if ( (tail = (tail + 1) & (elements.length - 1)) == head)
284	<	doubleCapacity();
280	>	// checkInvariants();
281	>	Objects.requireNonNull(e);
282	>	Object[] elements;
283	>	int capacity, s = size;
284	>	while (s == (capacity = (elements = this.elements).length))
285	>	grow(1);
286	>	elements[add(head, s, capacity)] = e;
287	>	size = s + 1;
288	>	}
289	>
290	>	/**
291	>	* Adds all of the elements in the specified collection at the end
292	>	* of this deque, as if by calling {@link #addLast} on each one,
293	>	* in the order that they are returned by the collection's
294	>	* iterator.
295	>	*
296	>	* @param c the elements to be inserted into this deque
297	>	* @return {@code true} if this deque changed as a result of the call
298	>	* @throws NullPointerException if the specified collection or any
299	>	*         of its elements are null
300	>	*/
301	>	@Override
302	>	public boolean addAll(Collection<? extends E> c) {
303	>	// checkInvariants();
304	>	Object[] a, elements;
305	>	int newcomers, capacity, s = size;
306	>	if ((newcomers = (a = c.toArray()).length) == 0)
307	>	return false;
308	>	while ((capacity = (elements = this.elements).length) - s < newcomers)
309	>	grow(newcomers - (capacity - s));
310	>	int i = add(head, s, capacity);
311	>	for (Object x : a) {
312	>	Objects.requireNonNull(x);
313	>	elements[i] = x;
314	>	i = inc(i, capacity);
315	>	size++;
316	>	}
317	>	return true;
318		}
319
320		/**
321		* Inserts the specified element at the front of this deque.
322		*
323		* @param e the element to add
324	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst})
324	>	* @return {@code true} (as specified by {@link Deque#offerFirst})
325		* @throws NullPointerException if the specified element is null
326		*/
327		public boolean offerFirst(E e) {
#	Line 231 | Line 333 | public class ArrayDeque<E> extends Abstr
333		* Inserts the specified element at the end of this deque.
334		*
335		* @param e the element to add
336	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
336	>	* @return {@code true} (as specified by {@link Deque#offerLast})
337		* @throws NullPointerException if the specified element is null
338		*/
339		public boolean offerLast(E e) {
#	Line 243 | Line 345 | public class ArrayDeque<E> extends Abstr
345		* @throws NoSuchElementException {@inheritDoc}
346		*/
347		public E removeFirst() {
348	+	// checkInvariants();
349		E x = pollFirst();
350		if (x == null)
351		throw new NoSuchElementException();
#	Line 253 | Line 356 | public class ArrayDeque<E> extends Abstr
356		* @throws NoSuchElementException {@inheritDoc}
357		*/
358		public E removeLast() {
359	+	// checkInvariants();
360		E x = pollLast();
361		if (x == null)
362		throw new NoSuchElementException();
#	Line 260 | Line 364 | public class ArrayDeque<E> extends Abstr
364		}
365
366		public E pollFirst() {
367	<	int h = head;
368	<	E result = elements[h]; // Element is null if deque empty
369	<	if (result == null)
367	>	// checkInvariants();
368	>	final int s, h;
369	>	if ((s = size) == 0)
370		return null;
371	<	elements[h] = null;     // Must null out slot
372	<	head = (h + 1) & (elements.length - 1);
373	<	return result;
371	>	final Object[] elements = this.elements;
372	>	@SuppressWarnings("unchecked") E e = (E) elements[h = head];
373	>	elements[h] = null;
374	>	head = inc(h, elements.length);
375	>	size = s - 1;
376	>	return e;
377		}
378
379		public E pollLast() {
380	<	int t = (tail - 1) & (elements.length - 1);
381	<	E result = elements[t];
382	<	if (result == null)
380	>	// checkInvariants();
381	>	final int s, tail;
382	>	if ((s = size) == 0)
383		return null;
384	<	elements[t] = null;
385	<	tail = t;
386	<	return result;
384	>	final Object[] elements = this.elements;
385	>	@SuppressWarnings("unchecked")
386	>	E e = (E) elements[tail = add(head, s - 1, elements.length)];
387	>	elements[tail] = null;
388	>	size = s - 1;
389	>	return e;
390		}
391
392		/**
393		* @throws NoSuchElementException {@inheritDoc}
394		*/
395		public E getFirst() {
396	<	E x = elements[head];
397	<	if (x == null)
398	<	throw new NoSuchElementException();
289	<	return x;
396	>	// checkInvariants();
397	>	if (size == 0) throw new NoSuchElementException();
398	>	return elementAt(head);
399		}
400
401		/**
402		* @throws NoSuchElementException {@inheritDoc}
403		*/
404		public E getLast() {
405	<	E x = elements[(tail - 1) & (elements.length - 1)];
406	<	if (x == null)
407	<	throw new NoSuchElementException();
299	<	return x;
405	>	// checkInvariants();
406	>	if (size == 0) throw new NoSuchElementException();
407	>	return elementAt(tail());
408		}
409
410		public E peekFirst() {
411	<	return elements[head]; // elements[head] is null if deque empty
411	>	// checkInvariants();
412	>	return (size == 0) ? null : elementAt(head);
413		}
414
415		public E peekLast() {
416	<	return elements[(tail - 1) & (elements.length - 1)];
416	>	// checkInvariants();
417	>	return (size == 0) ? null : elementAt(tail());
418		}
419
420		/**
421		* Removes the first occurrence of the specified element in this
422		* deque (when traversing the deque from head to tail).
423		* If the deque does not contain the element, it is unchanged.
424	<	* More formally, removes the first element <tt>e</tt> such that
425	<	* <tt>o.equals(e)</tt> (if such an element exists).
426	<	* Returns <tt>true</tt> if this deque contained the specified element
424	>	* More formally, removes the first element {@code e} such that
425	>	* {@code o.equals(e)} (if such an element exists).
426	>	* Returns {@code true} if this deque contained the specified element
427		* (or equivalently, if this deque changed as a result of the call).
428		*
429		* @param o element to be removed from this deque, if present
430	<	* @return <tt>true</tt> if the deque contained the specified element
430	>	* @return {@code true} if the deque contained the specified element
431		*/
432		public boolean removeFirstOccurrence(Object o) {
433	<	if (o == null)
434	<	return false;
435	<	int mask = elements.length - 1;
436	<	int i = head;
437	<	E x;
438	<	while ( (x = elements[i]) != null) {
439	<	if (o.equals(x)) {
440	<	delete(i);
441	<	return true;
433	>	// checkInvariants();
434	>	if (o != null) {
435	>	final Object[] elements = this.elements;
436	>	final int capacity = elements.length;
437	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity)) {
438	>	if (o.equals(elements[i])) {
439	>	delete(i);
440	>	return true;
441	>	}
442		}
333	–	i = (i + 1) & mask;
443		}
444		return false;
445		}
#	Line 339 | Line 448 | public class ArrayDeque<E> extends Abstr
448		* Removes the last occurrence of the specified element in this
449		* deque (when traversing the deque from head to tail).
450		* If the deque does not contain the element, it is unchanged.
451	<	* More formally, removes the last element <tt>e</tt> such that
452	<	* <tt>o.equals(e)</tt> (if such an element exists).
453	<	* Returns <tt>true</tt> if this deque contained the specified element
451	>	* More formally, removes the last element {@code e} such that
452	>	* {@code o.equals(e)} (if such an element exists).
453	>	* Returns {@code true} if this deque contained the specified element
454		* (or equivalently, if this deque changed as a result of the call).
455		*
456		* @param o element to be removed from this deque, if present
457	<	* @return <tt>true</tt> if the deque contained the specified element
457	>	* @return {@code true} if the deque contained the specified element
458		*/
459		public boolean removeLastOccurrence(Object o) {
460	<	if (o == null)
461	<	return false;
462	<	int mask = elements.length - 1;
463	<	int i = (tail - 1) & mask;
464	<	E x;
465	<	while ( (x = elements[i]) != null) {
466	<	if (o.equals(x)) {
467	<	delete(i);
468	<	return true;
460	>	if (o != null) {
461	>	final Object[] elements = this.elements;
462	>	final int capacity = elements.length;
463	>	for (int k = size, i = add(head, k - 1, capacity);
464	>	--k >= 0; i = dec(i, capacity)) {
465	>	if (o.equals(elements[i])) {
466	>	delete(i);
467	>	return true;
468	>	}
469		}
361	–	i = (i - 1) & mask;
470		}
471		return false;
472		}
#	Line 371 | Line 479 | public class ArrayDeque<E> extends Abstr
479		* <p>This method is equivalent to {@link #addLast}.
480		*
481		* @param e the element to add
482	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
482	>	* @return {@code true} (as specified by {@link Collection#add})
483		* @throws NullPointerException if the specified element is null
484		*/
485		public boolean add(E e) {
#	Line 385 | Line 493 | public class ArrayDeque<E> extends Abstr
493		* <p>This method is equivalent to {@link #offerLast}.
494		*
495		* @param e the element to add
496	<	* @return <tt>true</tt> (as per the spec for {@link Queue#offer})
496	>	* @return {@code true} (as specified by {@link Queue#offer})
497		* @throws NullPointerException if the specified element is null
498		*/
499		public boolean offer(E e) {
#	Line 394 | Line 502 | public class ArrayDeque<E> extends Abstr
502
503		/**
504		* Retrieves and removes the head of the queue represented by this deque.
505	<	* This method differs from {@link #poll} only in that it throws an
505	>	*
506	>	* This method differs from {@link #poll poll} only in that it throws an
507		* exception if this deque is empty.
508		*
509		* <p>This method is equivalent to {@link #removeFirst}.
#	Line 409 | Line 518 | public class ArrayDeque<E> extends Abstr
518		/**
519		* Retrieves and removes the head of the queue represented by this deque
520		* (in other words, the first element of this deque), or returns
521	<	* <tt>null</tt> if this deque is empty.
521	>	* {@code null} if this deque is empty.
522		*
523		* <p>This method is equivalent to {@link #pollFirst}.
524		*
525		* @return the head of the queue represented by this deque, or
526	<	*         <tt>null</tt> if this deque is empty
526	>	*         {@code null} if this deque is empty
527		*/
528		public E poll() {
529		return pollFirst();
#	Line 422 | Line 531 | public class ArrayDeque<E> extends Abstr
531
532		/**
533		* Retrieves, but does not remove, the head of the queue represented by
534	<	* this deque.  This method differs from {@link #peek} only in that it
535	<	* throws an exception if this deque is empty.
534	>	* this deque.  This method differs from {@link #peek peek} only in
535	>	* that it throws an exception if this deque is empty.
536		*
537		* <p>This method is equivalent to {@link #getFirst}.
538		*
#	Line 436 | Line 545 | public class ArrayDeque<E> extends Abstr
545
546		/**
547		* Retrieves, but does not remove, the head of the queue represented by
548	<	* this deque, or returns <tt>null</tt> if this deque is empty.
548	>	* this deque, or returns {@code null} if this deque is empty.
549		*
550		* <p>This method is equivalent to {@link #peekFirst}.
551		*
552		* @return the head of the queue represented by this deque, or
553	<	*         <tt>null</tt> if this deque is empty
553	>	*         {@code null} if this deque is empty
554		*/
555		public E peek() {
556		return peekFirst();
#	Line 477 | Line 586 | public class ArrayDeque<E> extends Abstr
586		}
587
588		/**
589	<	* Removes the element at the specified position in the elements array,
590	<	* adjusting head and tail as necessary.  This can result in motion of
591	<	* elements backwards or forwards in the array.
589	>	* Removes the element at the specified position in the elements array.
590	>	* This can result in forward or backwards motion of array elements.
591	>	* We optimize for least element motion.
592		*
593		* <p>This method is called delete rather than remove to emphasize
594		* that its semantics differ from those of {@link List#remove(int)}.
595		*
596		* @return true if elements moved backwards
597		*/
598	<	private boolean delete(int i) {
599	<	int mask = elements.length - 1;
600	<
601	<	// Invariant: head <= i < tail mod circularity
602	<	if (((i - head) & mask) >= ((tail - head) & mask))
603	<	throw new ConcurrentModificationException();
604	<
605	<	// Case 1: Deque doesn't wrap
606	<	// Case 2: Deque does wrap and removed element is in the head portion
607	<	if (i >= head) {
608	<	System.arraycopy(elements, head, elements, head + 1, i - head);
609	<	elements[head] = null;
610	<	head = (head + 1) & mask;
598	>	boolean delete(int i) {
599	>	// checkInvariants();
600	>	final Object[] elements = this.elements;
601	>	final int capacity = elements.length;
602	>	final int h = head;
603	>	int front;              // number of elements before to-be-deleted elt
604	>	if ((front = i - h) < 0) front += capacity;
605	>	final int back = size - front - 1; // number of elements after
606	>	if (front < back) {
607	>	// move front elements forwards
608	>	if (h <= i) {
609	>	System.arraycopy(elements, h, elements, h + 1, front);
610	>	} else { // Wrap around
611	>	System.arraycopy(elements, 0, elements, 1, i);
612	>	elements[0] = elements[capacity - 1];
613	>	System.arraycopy(elements, h, elements, h + 1, front - (i + 1));
614	>	}
615	>	elements[h] = null;
616	>	head = inc(h, capacity);
617	>	size--;
618	>	// checkInvariants();
619		return false;
620	+	} else {
621	+	// move back elements backwards
622	+	int tail = tail();
623	+	if (i <= tail) {
624	+	System.arraycopy(elements, i + 1, elements, i, back);
625	+	} else { // Wrap around
626	+	int firstLeg = capacity - (i + 1);
627	+	System.arraycopy(elements, i + 1, elements, i, firstLeg);
628	+	elements[capacity - 1] = elements[0];
629	+	System.arraycopy(elements, 1, elements, 0, back - firstLeg - 1);
630	+	}
631	+	elements[tail] = null;
632	+	size--;
633	+	// checkInvariants();
634	+	return true;
635		}
504	–
505	–	// Case 3: Deque wraps and removed element is in the tail portion
506	–	tail--;
507	–	System.arraycopy(elements, i + 1, elements, i, tail - i);
508	–	elements[tail] = null;
509	–	return true;
636		}
637
638		// *** Collection Methods ***
#	Line 517 | Line 643 | public class ArrayDeque<E> extends Abstr
643		* @return the number of elements in this deque
644		*/
645		public int size() {
646	<	return (tail - head) & (elements.length - 1);
646	>	return size;
647		}
648
649		/**
650	<	* Returns <tt>true</tt> if this deque contains no elements.
650	>	* Returns {@code true} if this deque contains no elements.
651		*
652	<	* @return <tt>true</tt> if this deque contains no elements
652	>	* @return {@code true} if this deque contains no elements
653		*/
654		public boolean isEmpty() {
655	<	return head == tail;
655	>	return size == 0;
656		}
657
658		/**
#	Line 535 | Line 661 | public class ArrayDeque<E> extends Abstr
661		* order that elements would be dequeued (via successive calls to
662		* {@link #remove} or popped (via successive calls to {@link #pop}).
663		*
664	<	* @return an <tt>Iterator</tt> over the elements in this deque
664	>	* @return an iterator over the elements in this deque
665		*/
666		public Iterator<E> iterator() {
667		return new DeqIterator();
668		}
669
670	+	public Iterator<E> descendingIterator() {
671	+	return new DescendingIterator();
672	+	}
673	+
674		private class DeqIterator implements Iterator<E> {
675	<	/**
676	<	* Index of element to be returned by subsequent call to next.
547	<	*/
548	<	private int cursor = head;
675	>	/** Index of element to be returned by subsequent call to next. */
676	>	int cursor;
677
678	<	/**
679	<	* Tail recorded at construction (also in remove), to stop
552	<	* iterator and also to check for comodification.
553	<	*/
554	<	private int fence = tail;
678	>	/** Number of elements yet to be returned. */
679	>	int remaining = size;
680
681		/**
682		* Index of element returned by most recent call to next.
683		* Reset to -1 if element is deleted by a call to remove.
684		*/
685	<	private int lastRet = -1;
685	>	int lastRet = -1;
686	>
687	>	DeqIterator() { cursor = head; }
688
689	<	public boolean hasNext() {
690	<	return cursor != fence;
689	>	int advance(int i, int modulus) {
690	>	return inc(i, modulus);
691		}
692
693	<	public E next() {
694	<	E result;
695	<	if (cursor == fence)
693	>	void doRemove() {
694	>	if (delete(lastRet))
695	>	// if left-shifted, undo advance in next()
696	>	cursor = dec(cursor, elements.length);
697	>	}
698	>
699	>	public final boolean hasNext() {
700	>	return remaining > 0;
701	>	}
702	>
703	>	public final E next() {
704	>	if (remaining == 0)
705		throw new NoSuchElementException();
706	<	// This check doesn't catch all possible comodifications,
571	<	// but does catch the ones that corrupt traversal
572	<	if (tail != fence || (result = elements[cursor]) == null)
573	<	throw new ConcurrentModificationException();
706	>	E e = checkedElementAt(elements, cursor);
707		lastRet = cursor;
708	<	cursor = (cursor + 1) & (elements.length - 1);
709	<	return result;
708	>	cursor = advance(cursor, elements.length);
709	>	remaining--;
710	>	return e;
711		}
712
713	<	public void remove() {
713	>	public final void remove() {
714		if (lastRet < 0)
715		throw new IllegalStateException();
716	<	if (delete(lastRet))
583	<	cursor--;
716	>	doRemove();
717		lastRet = -1;
585	–	fence = tail;
718		}
719	+
720	+	public final void forEachRemaining(Consumer<? super E> action) {
721	+	Objects.requireNonNull(action);
722	+	final Object[] elements = ArrayDeque.this.elements;
723	+	final int capacity = elements.length;
724	+	int k = remaining;
725	+	remaining = 0;
726	+	for (int i = cursor; --k >= 0; i = advance(i, capacity))
727	+	action.accept(checkedElementAt(elements, i));
728	+	}
729	+	}
730	+
731	+	private class DescendingIterator extends DeqIterator {
732	+	DescendingIterator() { cursor = tail(); }
733	+
734	+	@Override int advance(int i, int modulus) {
735	+	return dec(i, modulus);
736	+	}
737	+
738	+	@Override void doRemove() {
739	+	if (!delete(lastRet))
740	+	// if right-shifted, undo advance in next
741	+	cursor = inc(cursor, elements.length);
742	+	}
743	+	}
744	+
745	+	/**
746	+	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
747	+	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
748	+	* deque.
749	+	*
750	+	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
751	+	* {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and
752	+	* {@link Spliterator#NONNULL}.  Overriding implementations should document
753	+	* the reporting of additional characteristic values.
754	+	*
755	+	* @return a {@code Spliterator} over the elements in this deque
756	+	* @since 1.8
757	+	*/
758	+	public Spliterator<E> spliterator() {
759	+	return new ArrayDequeSpliterator();
760	+	}
761	+
762	+	final class ArrayDequeSpliterator implements Spliterator<E> {
763	+	private int cursor;
764	+	private int remaining; // -1 until late-binding first use
765	+
766	+	/** Constructs late-binding spliterator over all elements. */
767	+	ArrayDequeSpliterator() {
768	+	this.remaining = -1;
769	+	}
770	+
771	+	/** Constructs spliterator over the given slice. */
772	+	ArrayDequeSpliterator(int cursor, int count) {
773	+	this.cursor = cursor;
774	+	this.remaining = count;
775	+	}
776	+
777	+	/** Ensures late-binding initialization; then returns remaining. */
778	+	private int remaining() {
779	+	if (remaining < 0) {
780	+	cursor = head;
781	+	remaining = size;
782	+	}
783	+	return remaining;
784	+	}
785	+
786	+	public ArrayDequeSpliterator trySplit() {
787	+	final int mid;
788	+	if ((mid = remaining() >> 1) > 0) {
789	+	int oldCursor = cursor;
790	+	cursor = add(cursor, mid, elements.length);
791	+	remaining -= mid;
792	+	return new ArrayDequeSpliterator(oldCursor, mid);
793	+	}
794	+	return null;
795	+	}
796	+
797	+	public void forEachRemaining(Consumer<? super E> action) {
798	+	Objects.requireNonNull(action);
799	+	final Object[] elements = ArrayDeque.this.elements;
800	+	final int capacity = elements.length;
801	+	int k = remaining();
802	+	remaining = 0;
803	+	for (int i = cursor; --k >= 0; i = inc(i, capacity))
804	+	action.accept(checkedElementAt(elements, i));
805	+	}
806	+
807	+	public boolean tryAdvance(Consumer<? super E> action) {
808	+	Objects.requireNonNull(action);
809	+	if (remaining() == 0)
810	+	return false;
811	+	action.accept(checkedElementAt(elements, cursor));
812	+	cursor = inc(cursor, elements.length);
813	+	remaining--;
814	+	return true;
815	+	}
816	+
817	+	public long estimateSize() {
818	+	return remaining();
819	+	}
820	+
821	+	public int characteristics() {
822	+	return Spliterator.NONNULL
823	+	| Spliterator.ORDERED
824	+	| Spliterator.SIZED
825	+	| Spliterator.SUBSIZED;
826	+	}
827	+	}
828	+
829	+	@Override
830	+	public void forEach(Consumer<? super E> action) {
831	+	// checkInvariants();
832	+	Objects.requireNonNull(action);
833	+	final Object[] elements = this.elements;
834	+	final int capacity = elements.length;
835	+	for (int k = size, i = head; --k >= 0; i = inc(i, capacity))
836	+	action.accept(elementAt(i));
837	+	// checkInvariants();
838		}
839
840		/**
841	<	* Returns <tt>true</tt> if this deque contains the specified element.
842	<	* More formally, returns <tt>true</tt> if and only if this deque contains
843	<	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
841	>	* Replaces each element of this deque with the result of applying the
842	>	* operator to that element, as specified by {@link List#replaceAll}.
843	>	*
844	>	* @param operator the operator to apply to each element
845	>	*/
846	>	/* TODO: public */ private void replaceAll(UnaryOperator<E> operator) {
847	>	Objects.requireNonNull(operator);
848	>	final Object[] elements = this.elements;
849	>	final int capacity = elements.length;
850	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity))
851	>	elements[i] = operator.apply(elementAt(i));
852	>	// checkInvariants();
853	>	}
854	>
855	>	/**
856	>	* @throws NullPointerException {@inheritDoc}
857	>	*/
858	>	@Override
859	>	public boolean removeIf(Predicate<? super E> filter) {
860	>	Objects.requireNonNull(filter);
861	>	return bulkRemove(filter);
862	>	}
863	>
864	>	/**
865	>	* @throws NullPointerException {@inheritDoc}
866	>	*/
867	>	@Override
868	>	public boolean removeAll(Collection<?> c) {
869	>	Objects.requireNonNull(c);
870	>	return bulkRemove(e -> c.contains(e));
871	>	}
872	>
873	>	/**
874	>	* @throws NullPointerException {@inheritDoc}
875	>	*/
876	>	@Override
877	>	public boolean retainAll(Collection<?> c) {
878	>	Objects.requireNonNull(c);
879	>	return bulkRemove(e -> !c.contains(e));
880	>	}
881	>
882	>	/** Implementation of bulk remove methods. */
883	>	private boolean bulkRemove(Predicate<? super E> filter) {
884	>	// checkInvariants();
885	>	final Object[] elements = this.elements;
886	>	final int capacity = elements.length;
887	>	int i = head, j = i, remaining = size, deleted = 0;
888	>	try {
889	>	for (; remaining > 0; remaining--, i = inc(i, capacity)) {
890	>	@SuppressWarnings("unchecked") E e = (E) elements[i];
891	>	if (filter.test(e))
892	>	deleted++;
893	>	else {
894	>	if (j != i)
895	>	elements[j] = e;
896	>	j = inc(j, capacity);
897	>	}
898	>	}
899	>	return deleted > 0;
900	>	} catch (Throwable ex) {
901	>	if (deleted > 0)
902	>	for (; remaining > 0;
903	>	remaining--, i = inc(i, capacity), j = inc(j, capacity))
904	>	elements[j] = elements[i];
905	>	throw ex;
906	>	} finally {
907	>	size -= deleted;
908	>	for (; --deleted >= 0; j = inc(j, capacity))
909	>	elements[j] = null;
910	>	// checkInvariants();
911	>	}
912	>	}
913	>
914	>	/**
915	>	* Returns {@code true} if this deque contains the specified element.
916	>	* More formally, returns {@code true} if and only if this deque contains
917	>	* at least one element {@code e} such that {@code o.equals(e)}.
918		*
919		* @param o object to be checked for containment in this deque
920	<	* @return <tt>true</tt> if this deque contains the specified element
920	>	* @return {@code true} if this deque contains the specified element
921		*/
922		public boolean contains(Object o) {
923	<	if (o == null)
924	<	return false;
925	<	int mask = elements.length - 1;
926	<	int i = head;
927	<	E x;
928	<	while ( (x = elements[i]) != null) {
604	<	if (o.equals(x))
605	<	return true;
606	<	i = (i + 1) & mask;
923	>	if (o != null) {
924	>	final Object[] elements = this.elements;
925	>	final int capacity = elements.length;
926	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity))
927	>	if (o.equals(elements[i]))
928	>	return true;
929		}
930		return false;
931		}
#	Line 611 | Line 933 | public class ArrayDeque<E> extends Abstr
933		/**
934		* Removes a single instance of the specified element from this deque.
935		* If the deque does not contain the element, it is unchanged.
936	<	* More formally, removes the first element <tt>e</tt> such that
937	<	* <tt>o.equals(e)</tt> (if such an element exists).
938	<	* Returns <tt>true</tt> if this deque contained the specified element
936	>	* More formally, removes the first element {@code e} such that
937	>	* {@code o.equals(e)} (if such an element exists).
938	>	* Returns {@code true} if this deque contained the specified element
939		* (or equivalently, if this deque changed as a result of the call).
940		*
941	<	* <p>This method is equivalent to {@link #removeFirstOccurrence}.
941	>	* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
942		*
943		* @param o element to be removed from this deque, if present
944	<	* @return <tt>true</tt> if this deque contained the specified element
944	>	* @return {@code true} if this deque contained the specified element
945		*/
946		public boolean remove(Object o) {
947		return removeFirstOccurrence(o);
#	Line 630 | Line 952 | public class ArrayDeque<E> extends Abstr
952		* The deque will be empty after this call returns.
953		*/
954		public void clear() {
955	<	int h = head;
956	<	int t = tail;
957	<	if (h != t) { // clear all cells
958	<	head = tail = 0;
959	<	int i = h;
960	<	int mask = elements.length - 1;
961	<	do {
962	<	elements[i] = null;
963	<	i = (i + 1) & mask;
642	<	} while (i != t);
955	>	final Object[] elements = this.elements;
956	>	final int capacity = elements.length;
957	>	final int h = this.head;
958	>	final int s = size;
959	>	if (capacity - h >= s)
960	>	Arrays.fill(elements, h, h + s, null);
961	>	else {
962	>	Arrays.fill(elements, h, capacity, null);
963	>	Arrays.fill(elements, 0, s - capacity + h, null);
964		}
965	+	size = head = 0;
966	+	// checkInvariants();
967		}
968
969		/**
#	Line 650 | Line 973 | public class ArrayDeque<E> extends Abstr
973		* <p>The returned array will be "safe" in that no references to it are
974		* maintained by this deque.  (In other words, this method must allocate
975		* a new array).  The caller is thus free to modify the returned array.
976	<	*
976	>	*
977		* <p>This method acts as bridge between array-based and collection-based
978		* APIs.
979		*
980		* @return an array containing all of the elements in this deque
981		*/
982		public Object[] toArray() {
983	<	return copyElements(new Object[size()]);
983	>	final int head = this.head;
984	>	final int firstLeg;
985	>	Object[] a = Arrays.copyOfRange(elements, head, head + size);
986	>	if ((firstLeg = elements.length - head) < size)
987	>	System.arraycopy(elements, 0, a, firstLeg, size - firstLeg);
988	>	return a;
989		}
990
991		/**
#	Line 671 | Line 999 | public class ArrayDeque<E> extends Abstr
999		* <p>If this deque fits in the specified array with room to spare
1000		* (i.e., the array has more elements than this deque), the element in
1001		* the array immediately following the end of the deque is set to
1002	<	* <tt>null</tt>.
1002	>	* {@code null}.
1003		*
1004		* <p>Like the {@link #toArray()} method, this method acts as bridge between
1005		* array-based and collection-based APIs.  Further, this method allows
1006		* precise control over the runtime type of the output array, and may,
1007		* under certain circumstances, be used to save allocation costs.
1008		*
1009	<	* <p>Suppose <tt>x</tt> is a deque known to contain only strings.
1009	>	* <p>Suppose {@code x} is a deque known to contain only strings.
1010		* The following code can be used to dump the deque into a newly
1011	<	* allocated array of <tt>String</tt>:
1011	>	* allocated array of {@code String}:
1012		*
1013	<	* <pre>
686	<	*     String[] y = x.toArray(new String[0]);</pre>
1013	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
1014		*
1015	<	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
1016	<	* <tt>toArray()</tt>.
1015	>	* Note that {@code toArray(new Object[0])} is identical in function to
1016	>	* {@code toArray()}.
1017		*
1018		* @param a the array into which the elements of the deque are to
1019		*          be stored, if it is big enough; otherwise, a new array of the
#	Line 697 | Line 1024 | public class ArrayDeque<E> extends Abstr
1024		*         this deque
1025		* @throws NullPointerException if the specified array is null
1026		*/
1027	+	@SuppressWarnings("unchecked")
1028		public <T> T[] toArray(T[] a) {
1029	<	int size = size();
1030	<	if (a.length < size)
1031	<	a = (T[])java.lang.reflect.Array.newInstance(
1032	<	a.getClass().getComponentType(), size);
1033	<	copyElements(a);
1034	<	if (a.length > size)
1035	<	a[size] = null;
1029	>	final Object[] elements = this.elements;
1030	>	final int head = this.head;
1031	>	final int firstLeg;
1032	>	boolean wrap = (firstLeg = elements.length - head) < size;
1033	>	if (size > a.length) {
1034	>	a = (T[]) Arrays.copyOfRange(elements, head, head + size,
1035	>	a.getClass());
1036	>	} else {
1037	>	System.arraycopy(elements, head, a, 0, wrap ? firstLeg : size);
1038	>	if (size < a.length)
1039	>	a[size] = null;
1040	>	}
1041	>	if (wrap)
1042	>	System.arraycopy(elements, 0, a, firstLeg, size - firstLeg);
1043		return a;
1044		}
1045
#	Line 717 | Line 1052 | public class ArrayDeque<E> extends Abstr
1052		*/
1053		public ArrayDeque<E> clone() {
1054		try {
1055	+	@SuppressWarnings("unchecked")
1056		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
1057	<	// These two lines are currently faster than cloning the array:
722	<	result.elements = (E[]) new Object[elements.length];
723	<	System.arraycopy(elements, 0, result.elements, 0, elements.length);
1057	>	result.elements = Arrays.copyOf(elements, elements.length);
1058		return result;
725	–
1059		} catch (CloneNotSupportedException e) {
1060		throw new AssertionError();
1061		}
1062		}
1063
731	–	/**
732	–	* Appease the serialization gods.
733	–	*/
1064		private static final long serialVersionUID = 2340985798034038923L;
1065
1066		/**
1067	<	* Serialize this deque.
1067	>	* Saves this deque to a stream (that is, serializes it).
1068		*
1069	<	* @serialData The current size (<tt>int</tt>) of the deque,
1069	>	* @param s the stream
1070	>	* @throws java.io.IOException if an I/O error occurs
1071	>	* @serialData The current size ({@code int}) of the deque,
1072		* followed by all of its elements (each an object reference) in
1073		* first-to-last order.
1074		*/
1075	<	private void writeObject(ObjectOutputStream s) throws IOException {
1075	>	private void writeObject(java.io.ObjectOutputStream s)
1076	>	throws java.io.IOException {
1077		s.defaultWriteObject();
1078
1079		// Write out size
747	–	int size = size();
1080		s.writeInt(size);
1081
1082		// Write out elements in order.
1083	<	int i = head;
1084	<	int mask = elements.length - 1;
1085	<	for (int j = 0; j < size; j++) {
1083	>	final Object[] elements = this.elements;
1084	>	final int capacity = elements.length;
1085	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity))
1086		s.writeObject(elements[i]);
755	–	i = (i + 1) & mask;
756	–	}
1087		}
1088
1089		/**
1090	<	* Deserialize this deque.
1090	>	* Reconstitutes this deque from a stream (that is, deserializes it).
1091	>	* @param s the stream
1092	>	* @throws ClassNotFoundException if the class of a serialized object
1093	>	*         could not be found
1094	>	* @throws java.io.IOException if an I/O error occurs
1095		*/
1096	<	private void readObject(ObjectInputStream s)
1097	<	throws IOException, ClassNotFoundException {
1096	>	private void readObject(java.io.ObjectInputStream s)
1097	>	throws java.io.IOException, ClassNotFoundException {
1098		s.defaultReadObject();
1099
1100		// Read in size and allocate array
1101	<	int size = s.readInt();
768	<	allocateElements(size);
769	<	head = 0;
770	<	tail = size;
1101	>	elements = new Object[size = s.readInt()];
1102
1103		// Read in all elements in the proper order.
1104		for (int i = 0; i < size; i++)
1105	<	elements[i] = (E)s.readObject();
1105	>	elements[i] = s.readObject();
1106	>	}
1107
1108	+	/** debugging */
1109	+	private void checkInvariants() {
1110	+	try {
1111	+	int capacity = elements.length;
1112	+	assert size >= 0 && size <= capacity;
1113	+	assert head >= 0 && ((capacity == 0 && head == 0 && size == 0)
1114	+	|| head < capacity);
1115	+	assert size == 0
1116	+	|| (elements[head] != null && elements[tail()] != null);
1117	+	assert size == capacity
1118	+	|| (elements[dec(head, capacity)] == null
1119	+	&& elements[inc(tail(), capacity)] == null);
1120	+	} catch (Throwable t) {
1121	+	System.err.printf("head=%d size=%d capacity=%d%n",
1122	+	head, size, elements.length);
1123	+	System.err.printf("elements=%s%n",
1124	+	Arrays.toString(elements));
1125	+	throw t;
1126	+	}
1127		}
1128	+
1129		}

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