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Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.30 by jsr166, Sun May 18 23:47:55 2008 UTC vs.
Revision 1.76 by jsr166, Mon Oct 17 23:49:00 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 48 | Line 54 | import java.io.*;
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	>	* arbitrary number 0 <= head < elements.length if the deque is empty.
74		*/
75	<	private transient int head;
75	>	transient int head;
76
77	<	/**
78	<	* The index at which the next element would be added to the tail
78	<	* of the deque (via addLast(E), add(E), or push(E)).
79	<	*/
80	<	private transient int tail;
77	>	/** Number of elements in this collection. */
78	>	transient int size;
79
80		/**
81	<	* The minimum capacity that we'll use for a newly created deque.
82	<	* Must be a power of 2.
83	<	*/
84	<	private static final int MIN_INITIAL_CAPACITY = 8;
85	<
86	<	// ******  Array allocation and resizing utilities ******
87	<
88	<	/**
89	<	* Allocate empty array to hold the given number of elements.
90	<	*
91	<	* @param numElements  the number of elements to hold
92	<	*/
93	<	private void allocateElements(int numElements) {
94	<	int initialCapacity = MIN_INITIAL_CAPACITY;
95	<	// Find the best power of two to hold elements.
96	<	// Tests "<=" because arrays aren't kept full.
97	<	if (numElements >= initialCapacity) {
98	<	initialCapacity = numElements;
99	<	initialCapacity |= (initialCapacity >>>  1);
100	<	initialCapacity |= (initialCapacity >>>  2);
101	<	initialCapacity |= (initialCapacity >>>  4);
102	<	initialCapacity |= (initialCapacity >>>  8);
103	<	initialCapacity |= (initialCapacity >>> 16);
104	<	initialCapacity++;
81	>	* The maximum size of array to allocate.
82	>	* Some VMs reserve some header words in an array.
83	>	* Attempts to allocate larger arrays may result in
84	>	* OutOfMemoryError: Requested array size exceeds VM limit
85	>	*/
86	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
87	>
88	>	/**
89	>	* Increases the capacity of this deque by at least the given amount.
90	>	*
91	>	* @param needed the required minimum extra capacity; must be positive
92	>	*/
93	>	private void grow(int needed) {
94	>	// overflow-conscious code
95	>	// checkInvariants();
96	>	int oldCapacity = elements.length;
97	>	int newCapacity;
98	>	// Double size if small; else grow by 50%
99	>	int jump = (oldCapacity < 64) ? (oldCapacity + 2) : (oldCapacity >> 1);
100	>	if (jump < needed
101	>	|| (newCapacity = (oldCapacity + jump)) - MAX_ARRAY_SIZE > 0)
102	>	newCapacity = newCapacity(needed, jump);
103	>	elements = Arrays.copyOf(elements, newCapacity);
104	>	if (oldCapacity - head < size) {
105	>	// wrap around; slide first leg forward to end of array
106	>	int newSpace = newCapacity - oldCapacity;
107	>	System.arraycopy(elements, head,
108	>	elements, head + newSpace,
109	>	oldCapacity - head);
110	>	Arrays.fill(elements, head, head + newSpace, null);
111	>	head += newSpace;
112	>	}
113	>	// checkInvariants();
114	>	}
115
116	<	if (initialCapacity < 0)   // Too many elements, must back off
117	<	initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
116	>	/** Capacity calculation for edge conditions, especially overflow. */
117	>	private int newCapacity(int needed, int jump) {
118	>	int oldCapacity = elements.length;
119	>	int minCapacity;
120	>	if ((minCapacity = oldCapacity + needed) - MAX_ARRAY_SIZE > 0) {
121	>	if (minCapacity < 0)
122	>	throw new IllegalStateException("Sorry, deque too big");
123	>	return Integer.MAX_VALUE;
124		}
125	<	elements = (E[]) new Object[initialCapacity];
125	>	if (needed > jump)
126	>	return minCapacity;
127	>	return (oldCapacity + jump - MAX_ARRAY_SIZE < 0)
128	>	? oldCapacity + jump
129	>	: MAX_ARRAY_SIZE;
130		}
131
132		/**
133	<	* Double the capacity of this deque.  Call only when full, i.e.,
134	<	* when head and tail have wrapped around to become equal.
133	>	* Increases the internal storage of this collection, if necessary,
134	>	* to ensure that it can hold at least the given number of elements.
135	>	*
136	>	* @param minCapacity the desired minimum capacity
137	>	* @since 9
138		*/
139	<	private void doubleCapacity() {
140	<	assert head == tail;
141	<	int p = head;
142	<	int n = elements.length;
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;
139	>	public void ensureCapacity(int minCapacity) {
140	>	if (minCapacity > elements.length)
141	>	grow(minCapacity - elements.length);
142	>	// checkInvariants();
143		}
144
145		/**
146	<	* Copies the elements from our element array into the specified array,
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.
146	>	* Minimizes the internal storage of this collection.
147		*
148	<	* @return its argument
148	>	* @since 9
149		*/
150	<	private <T> T[] copyElements(T[] a) {
151	<	if (head < tail) {
152	<	System.arraycopy(elements, head, a, 0, size());
153	<	} else if (head > tail) {
145	<	int headPortionLen = elements.length - head;
146	<	System.arraycopy(elements, head, a, 0, headPortionLen);
147	<	System.arraycopy(elements, 0, a, headPortionLen, tail);
150	>	public void trimToSize() {
151	>	if (size < elements.length) {
152	>	elements = toArray();
153	>	head = 0;
154		}
155	<	return a;
155	>	// checkInvariants();
156		}
157
158		/**
#	Line 154 | Line 160 | public class ArrayDeque<E> extends Abstr
160		* sufficient to hold 16 elements.
161		*/
162		public ArrayDeque() {
163	<	elements = (E[]) new Object[16];
163	>	elements = new Object[16];
164		}
165
166		/**
167		* Constructs an empty array deque with an initial capacity
168		* sufficient to hold the specified number of elements.
169		*
170	<	* @param numElements  lower bound on initial capacity of the deque
170	>	* @param numElements lower bound on initial capacity of the deque
171		*/
172		public ArrayDeque(int numElements) {
173	<	allocateElements(numElements);
173	>	elements = new Object[numElements];
174		}
175
176		/**
#	Line 178 | Line 184 | public class ArrayDeque<E> extends Abstr
184		* @throws NullPointerException if the specified collection is null
185		*/
186		public ArrayDeque(Collection<? extends E> c) {
187	<	allocateElements(c.size());
188	<	addAll(c);
187	>	Object[] elements = c.toArray();
188	>	// defend against c.toArray (incorrectly) not returning Object[]
189	>	// (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)
190	>	if (elements.getClass() != Object[].class)
191	>	elements = Arrays.copyOf(elements, size, Object[].class);
192	>	for (Object obj : elements)
193	>	Objects.requireNonNull(obj);
194	>	size = elements.length;
195	>	this.elements = elements;
196	>	}
197	>
198	>	/**
199	>	* Returns the array index of the last element.
200	>	* May return invalid index -1 if there are no elements.
201	>	*/
202	>	final int tail() {
203	>	return add(head, size - 1, elements.length);
204	>	}
205	>
206	>	/**
207	>	* Adds i and j, mod modulus.
208	>	* Precondition and postcondition: 0 <= i < modulus, 0 <= j <= modulus.
209	>	*/
210	>	static final int add(int i, int j, int modulus) {
211	>	if ((i += j) - modulus >= 0) i -= modulus;
212	>	return i;
213	>	}
214	>
215	>	/**
216	>	* Increments i, mod modulus.
217	>	* Precondition and postcondition: 0 <= i < modulus.
218	>	*/
219	>	static final int inc(int i, int modulus) {
220	>	if (++i == modulus) i = 0;
221	>	return i;
222	>	}
223	>
224	>	/**
225	>	* Decrements i, mod modulus.
226	>	* Precondition and postcondition: 0 <= i < modulus.
227	>	*/
228	>	static final int dec(int i, int modulus) {
229	>	if (--i < 0) i += modulus;
230	>	return i;
231	>	}
232	>
233	>	/**
234	>	* Returns element at array index i.
235	>	*/
236	>	@SuppressWarnings("unchecked")
237	>	final E elementAt(int i) {
238	>	return (E) elements[i];
239	>	}
240	>
241	>	/**
242	>	* A version of elementAt that checks for null elements.
243	>	* This check doesn't catch all possible comodifications,
244	>	* but does catch ones that corrupt traversal.
245	>	*/
246	>	E checkedElementAt(Object[] elements, int i) {
247	>	@SuppressWarnings("unchecked") E e = (E) elements[i];
248	>	if (e == null)
249	>	throw new ConcurrentModificationException();
250	>	return e;
251		}
252
253		// The main insertion and extraction methods are addFirst,
#	Line 193 | Line 261 | public class ArrayDeque<E> extends Abstr
261		* @throws NullPointerException if the specified element is null
262		*/
263		public void addFirst(E e) {
264	<	if (e == null)
265	<	throw new NullPointerException();
266	<	elements[head = (head - 1) & (elements.length - 1)] = e;
267	<	if (head == tail)
268	<	doubleCapacity();
264	>	// checkInvariants();
265	>	Objects.requireNonNull(e);
266	>	Object[] elements;
267	>	int capacity, s = size;
268	>	while (s == (capacity = (elements = this.elements).length))
269	>	grow(1);
270	>	elements[head = dec(head, capacity)] = e;
271	>	size = s + 1;
272		}
273
274		/**
#	Line 209 | Line 280 | public class ArrayDeque<E> extends Abstr
280		* @throws NullPointerException if the specified element is null
281		*/
282		public void addLast(E e) {
283	<	if (e == null)
284	<	throw new NullPointerException();
285	<	elements[tail] = e;
286	<	if ( (tail = (tail + 1) & (elements.length - 1)) == head)
287	<	doubleCapacity();
283	>	// checkInvariants();
284	>	Objects.requireNonNull(e);
285	>	Object[] elements;
286	>	int capacity, s = size;
287	>	while (s == (capacity = (elements = this.elements).length))
288	>	grow(1);
289	>	elements[add(head, s, capacity)] = e;
290	>	size = s + 1;
291	>	}
292	>
293	>	/**
294	>	* Adds all of the elements in the specified collection at the end
295	>	* of this deque, as if by calling {@link #addLast} on each one,
296	>	* in the order that they are returned by the collection's
297	>	* iterator.
298	>	*
299	>	* @param c the elements to be inserted into this deque
300	>	* @return {@code true} if this deque changed as a result of the call
301	>	* @throws NullPointerException if the specified collection or any
302	>	*         of its elements are null
303	>	*/
304	>	@Override
305	>	public boolean addAll(Collection<? extends E> c) {
306	>	// checkInvariants();
307	>	Object[] a, elements;
308	>	int len, capacity, s = size;
309	>	if ((len = (a = c.toArray()).length) == 0)
310	>	return false;
311	>	while ((capacity = (elements = this.elements).length) - s < len)
312	>	grow(len - (capacity - s));
313	>	int i = add(head, s, capacity);
314	>	for (Object x : a) {
315	>	Objects.requireNonNull(x);
316	>	elements[i] = x;
317	>	i = inc(i, capacity);
318	>	size++;
319	>	}
320	>	return true;
321		}
322
323		/**
324		* Inserts the specified element at the front of this deque.
325		*
326		* @param e the element to add
327	<	* @return <tt>true</tt> (as specified by {@link Deque#offerFirst})
327	>	* @return {@code true} (as specified by {@link Deque#offerFirst})
328		* @throws NullPointerException if the specified element is null
329		*/
330		public boolean offerFirst(E e) {
#	Line 232 | Line 336 | public class ArrayDeque<E> extends Abstr
336		* Inserts the specified element at the end of this deque.
337		*
338		* @param e the element to add
339	<	* @return <tt>true</tt> (as specified by {@link Deque#offerLast})
339	>	* @return {@code true} (as specified by {@link Deque#offerLast})
340		* @throws NullPointerException if the specified element is null
341		*/
342		public boolean offerLast(E e) {
#	Line 244 | Line 348 | public class ArrayDeque<E> extends Abstr
348		* @throws NoSuchElementException {@inheritDoc}
349		*/
350		public E removeFirst() {
351	+	// checkInvariants();
352		E x = pollFirst();
353		if (x == null)
354		throw new NoSuchElementException();
#	Line 254 | Line 359 | public class ArrayDeque<E> extends Abstr
359		* @throws NoSuchElementException {@inheritDoc}
360		*/
361		public E removeLast() {
362	+	// checkInvariants();
363		E x = pollLast();
364		if (x == null)
365		throw new NoSuchElementException();
#	Line 261 | Line 367 | public class ArrayDeque<E> extends Abstr
367		}
368
369		public E pollFirst() {
370	<	int h = head;
371	<	E result = elements[h]; // Element is null if deque empty
372	<	if (result == null)
370	>	// checkInvariants();
371	>	final int s, h;
372	>	if ((s = size) == 0)
373		return null;
374	<	elements[h] = null;     // Must null out slot
375	<	head = (h + 1) & (elements.length - 1);
376	<	return result;
374	>	final Object[] elements = this.elements;
375	>	@SuppressWarnings("unchecked") E e = (E) elements[h = head];
376	>	elements[h] = null;
377	>	head = inc(h, elements.length);
378	>	size = s - 1;
379	>	return e;
380		}
381
382		public E pollLast() {
383	<	int t = (tail - 1) & (elements.length - 1);
384	<	E result = elements[t];
385	<	if (result == null)
383	>	// checkInvariants();
384	>	final int s, tail;
385	>	if ((s = size) == 0)
386		return null;
387	<	elements[t] = null;
388	<	tail = t;
389	<	return result;
387	>	final Object[] elements = this.elements;
388	>	@SuppressWarnings("unchecked")
389	>	E e = (E) elements[tail = add(head, s - 1, elements.length)];
390	>	elements[tail] = null;
391	>	size = s - 1;
392	>	return e;
393		}
394
395		/**
396		* @throws NoSuchElementException {@inheritDoc}
397		*/
398		public E getFirst() {
399	<	E x = elements[head];
400	<	if (x == null)
401	<	throw new NoSuchElementException();
290	<	return x;
399	>	// checkInvariants();
400	>	if (size == 0) throw new NoSuchElementException();
401	>	return elementAt(head);
402		}
403
404		/**
405		* @throws NoSuchElementException {@inheritDoc}
406		*/
407		public E getLast() {
408	<	E x = elements[(tail - 1) & (elements.length - 1)];
409	<	if (x == null)
410	<	throw new NoSuchElementException();
300	<	return x;
408	>	// checkInvariants();
409	>	if (size == 0) throw new NoSuchElementException();
410	>	return elementAt(tail());
411		}
412
413		public E peekFirst() {
414	<	return elements[head]; // elements[head] is null if deque empty
414	>	// checkInvariants();
415	>	return (size == 0) ? null : elementAt(head);
416		}
417
418		public E peekLast() {
419	<	return elements[(tail - 1) & (elements.length - 1)];
419	>	// checkInvariants();
420	>	return (size == 0) ? null : elementAt(tail());
421		}
422
423		/**
424		* Removes the first occurrence of the specified element in this
425		* deque (when traversing the deque from head to tail).
426		* If the deque does not contain the element, it is unchanged.
427	<	* More formally, removes the first element <tt>e</tt> such that
428	<	* <tt>o.equals(e)</tt> (if such an element exists).
429	<	* Returns <tt>true</tt> if this deque contained the specified element
427	>	* More formally, removes the first element {@code e} such that
428	>	* {@code o.equals(e)} (if such an element exists).
429	>	* Returns {@code true} if this deque contained the specified element
430		* (or equivalently, if this deque changed as a result of the call).
431		*
432		* @param o element to be removed from this deque, if present
433	<	* @return <tt>true</tt> if the deque contained the specified element
433	>	* @return {@code true} if the deque contained the specified element
434		*/
435		public boolean removeFirstOccurrence(Object o) {
436	<	if (o == null)
437	<	return false;
438	<	int mask = elements.length - 1;
439	<	int i = head;
440	<	E x;
441	<	while ( (x = elements[i]) != null) {
442	<	if (o.equals(x)) {
443	<	delete(i);
444	<	return true;
436	>	// checkInvariants();
437	>	if (o != null) {
438	>	final Object[] elements = this.elements;
439	>	final int capacity = elements.length;
440	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity)) {
441	>	if (o.equals(elements[i])) {
442	>	delete(i);
443	>	return true;
444	>	}
445		}
334	–	i = (i + 1) & mask;
446		}
447		return false;
448		}
#	Line 340 | Line 451 | public class ArrayDeque<E> extends Abstr
451		* Removes the last occurrence of the specified element in this
452		* deque (when traversing the deque from head to tail).
453		* If the deque does not contain the element, it is unchanged.
454	<	* More formally, removes the last element <tt>e</tt> such that
455	<	* <tt>o.equals(e)</tt> (if such an element exists).
456	<	* Returns <tt>true</tt> if this deque contained the specified element
454	>	* More formally, removes the last element {@code e} such that
455	>	* {@code o.equals(e)} (if such an element exists).
456	>	* Returns {@code true} if this deque contained the specified element
457		* (or equivalently, if this deque changed as a result of the call).
458		*
459		* @param o element to be removed from this deque, if present
460	<	* @return <tt>true</tt> if the deque contained the specified element
460	>	* @return {@code true} if the deque contained the specified element
461		*/
462		public boolean removeLastOccurrence(Object o) {
463	<	if (o == null)
464	<	return false;
465	<	int mask = elements.length - 1;
466	<	int i = (tail - 1) & mask;
467	<	E x;
468	<	while ( (x = elements[i]) != null) {
469	<	if (o.equals(x)) {
470	<	delete(i);
471	<	return true;
463	>	if (o != null) {
464	>	final Object[] elements = this.elements;
465	>	final int capacity = elements.length;
466	>	for (int k = size, i = add(head, k - 1, capacity);
467	>	--k >= 0; i = dec(i, capacity)) {
468	>	if (o.equals(elements[i])) {
469	>	delete(i);
470	>	return true;
471	>	}
472		}
362	–	i = (i - 1) & mask;
473		}
474		return false;
475		}
#	Line 372 | Line 482 | public class ArrayDeque<E> extends Abstr
482		* <p>This method is equivalent to {@link #addLast}.
483		*
484		* @param e the element to add
485	<	* @return <tt>true</tt> (as specified by {@link Collection#add})
485	>	* @return {@code true} (as specified by {@link Collection#add})
486		* @throws NullPointerException if the specified element is null
487		*/
488		public boolean add(E e) {
#	Line 386 | Line 496 | public class ArrayDeque<E> extends Abstr
496		* <p>This method is equivalent to {@link #offerLast}.
497		*
498		* @param e the element to add
499	<	* @return <tt>true</tt> (as specified by {@link Queue#offer})
499	>	* @return {@code true} (as specified by {@link Queue#offer})
500		* @throws NullPointerException if the specified element is null
501		*/
502		public boolean offer(E e) {
#	Line 411 | Line 521 | public class ArrayDeque<E> extends Abstr
521		/**
522		* Retrieves and removes the head of the queue represented by this deque
523		* (in other words, the first element of this deque), or returns
524	<	* <tt>null</tt> if this deque is empty.
524	>	* {@code null} if this deque is empty.
525		*
526		* <p>This method is equivalent to {@link #pollFirst}.
527		*
528		* @return the head of the queue represented by this deque, or
529	<	*         <tt>null</tt> if this deque is empty
529	>	*         {@code null} if this deque is empty
530		*/
531		public E poll() {
532		return pollFirst();
#	Line 438 | Line 548 | public class ArrayDeque<E> extends Abstr
548
549		/**
550		* Retrieves, but does not remove, the head of the queue represented by
551	<	* this deque, or returns <tt>null</tt> if this deque is empty.
551	>	* this deque, or returns {@code null} if this deque is empty.
552		*
553		* <p>This method is equivalent to {@link #peekFirst}.
554		*
555		* @return the head of the queue represented by this deque, or
556	<	*         <tt>null</tt> if this deque is empty
556	>	*         {@code null} if this deque is empty
557		*/
558		public E peek() {
559		return peekFirst();
#	Line 478 | Line 588 | public class ArrayDeque<E> extends Abstr
588		return removeFirst();
589		}
590
481	–	private void checkInvariants() {
482	–	assert elements[tail] == null;
483	–	assert head == tail ? elements[head] == null :
484	–	(elements[head] != null &&
485	–	elements[(tail - 1) & (elements.length - 1)] != null);
486	–	assert elements[(head - 1) & (elements.length - 1)] == null;
487	–	}
488	–
591		/**
592	<	* Removes the element at the specified position in the elements array,
593	<	* adjusting head and tail as necessary.  This can result in motion of
594	<	* elements backwards or forwards in the array.
592	>	* Removes the element at the specified position in the elements array.
593	>	* This can result in forward or backwards motion of array elements.
594	>	* We optimize for least element motion.
595		*
596		* <p>This method is called delete rather than remove to emphasize
597		* that its semantics differ from those of {@link List#remove(int)}.
598		*
599		* @return true if elements moved backwards
600		*/
601	<	private boolean delete(int i) {
602	<	checkInvariants();
603	<	final E[] elements = this.elements;
604	<	final int mask = elements.length - 1;
601	>	boolean delete(int i) {
602	>	// checkInvariants();
603	>	final Object[] elements = this.elements;
604	>	final int capacity = elements.length;
605		final int h = head;
606	<	final int t = tail;
607	<	final int front = (i - h) & mask;
608	<	final int back  = (t - i) & mask;
507	<
508	<	// Invariant: head <= i < tail mod circularity
509	<	if (front >= ((t - h) & mask))
510	<	throw new ConcurrentModificationException();
511	<
512	<	// Optimize for least element motion
606	>	int front;              // number of elements before to-be-deleted elt
607	>	if ((front = i - h) < 0) front += capacity;
608	>	final int back = size - front - 1; // number of elements after
609		if (front < back) {
610	+	// move front elements forwards
611		if (h <= i) {
612		System.arraycopy(elements, h, elements, h + 1, front);
613		} else { // Wrap around
614		System.arraycopy(elements, 0, elements, 1, i);
615	<	elements[0] = elements[mask];
616	<	System.arraycopy(elements, h, elements, h + 1, mask - h);
615	>	elements[0] = elements[capacity - 1];
616	>	System.arraycopy(elements, h, elements, h + 1, front - (i + 1));
617		}
618		elements[h] = null;
619	<	head = (h + 1) & mask;
619	>	head = inc(h, capacity);
620	>	size--;
621	>	// checkInvariants();
622		return false;
623		} else {
624	<	if (i < t) { // Copy the null tail as well
624	>	// move back elements backwards
625	>	int tail = tail();
626	>	if (i <= tail) {
627		System.arraycopy(elements, i + 1, elements, i, back);
527	–	tail = t - 1;
628		} else { // Wrap around
629	<	System.arraycopy(elements, i + 1, elements, i, mask - i);
630	<	elements[mask] = elements[0];
631	<	System.arraycopy(elements, 1, elements, 0, t);
632	<	tail = (t - 1) & mask;
629	>	int firstLeg = capacity - (i + 1);
630	>	System.arraycopy(elements, i + 1, elements, i, firstLeg);
631	>	elements[capacity - 1] = elements[0];
632	>	System.arraycopy(elements, 1, elements, 0, back - firstLeg - 1);
633		}
634	+	elements[tail] = null;
635	+	size--;
636	+	// checkInvariants();
637		return true;
638		}
639		}
#	Line 543 | Line 646 | public class ArrayDeque<E> extends Abstr
646		* @return the number of elements in this deque
647		*/
648		public int size() {
649	<	return (tail - head) & (elements.length - 1);
649	>	return size;
650		}
651
652		/**
653	<	* Returns <tt>true</tt> if this deque contains no elements.
653	>	* Returns {@code true} if this deque contains no elements.
654		*
655	<	* @return <tt>true</tt> if this deque contains no elements
655	>	* @return {@code true} if this deque contains no elements
656		*/
657		public boolean isEmpty() {
658	<	return head == tail;
658	>	return size == 0;
659		}
660
661		/**
#	Line 572 | Line 675 | public class ArrayDeque<E> extends Abstr
675		}
676
677		private class DeqIterator implements Iterator<E> {
678	<	/**
679	<	* Index of element to be returned by subsequent call to next.
577	<	*/
578	<	private int cursor = head;
678	>	/** Index of element to be returned by subsequent call to next. */
679	>	int cursor;
680
681	<	/**
682	<	* Tail recorded at construction (also in remove), to stop
582	<	* iterator and also to check for comodification.
583	<	*/
584	<	private int fence = tail;
681	>	/** Number of elements yet to be returned. */
682	>	int remaining = size;
683
684		/**
685		* Index of element returned by most recent call to next.
686		* Reset to -1 if element is deleted by a call to remove.
687		*/
688	<	private int lastRet = -1;
688	>	int lastRet = -1;
689	>
690	>	DeqIterator() { cursor = head; }
691	>
692	>	void doAdvance() {
693	>	cursor = inc(cursor, elements.length);
694	>	}
695
696	<	public boolean hasNext() {
697	<	return cursor != fence;
696	>	void doRemove() {
697	>	if (delete(lastRet))
698	>	// if left-shifted, undo advance in next()
699	>	cursor = dec(cursor, elements.length);
700		}
701
702	<	public E next() {
703	<	if (cursor == fence)
702	>	public final boolean hasNext() {
703	>	return remaining > 0;
704	>	}
705	>
706	>	public final E next() {
707	>	if (remaining == 0)
708		throw new NoSuchElementException();
709	<	E result = elements[cursor];
600	<	// This check doesn't catch all possible comodifications,
601	<	// but does catch the ones that corrupt traversal
602	<	if (tail != fence || result == null)
603	<	throw new ConcurrentModificationException();
709	>	E e = checkedElementAt(elements, cursor);
710		lastRet = cursor;
711	<	cursor = (cursor + 1) & (elements.length - 1);
712	<	return result;
711	>	doAdvance();
712	>	remaining--;
713	>	return e;
714		}
715
716	<	public void remove() {
716	>	public final void remove() {
717		if (lastRet < 0)
718		throw new IllegalStateException();
719	<	if (delete(lastRet)) { // if left-shifted, undo increment in next()
613	<	cursor = (cursor - 1) & (elements.length - 1);
614	<	fence = tail;
615	<	}
719	>	doRemove();
720		lastRet = -1;
721		}
722	+
723	+	public final void forEachRemaining(Consumer<? super E> action) {
724	+	Objects.requireNonNull(action);
725	+	final Object[] elements = ArrayDeque.this.elements;
726	+	final int capacity = elements.length;
727	+	for (; remaining > 0; remaining--) {
728	+	action.accept(checkedElementAt(elements, cursor));
729	+	doAdvance();
730	+	}
731	+	}
732		}
733
734	<	private class DescendingIterator implements Iterator<E> {
735	<	/*
622	<	* This class is nearly a mirror-image of DeqIterator, using
623	<	* tail instead of head for initial cursor, and head instead of
624	<	* tail for fence.
625	<	*/
626	<	private int cursor = tail;
627	<	private int fence = head;
628	<	private int lastRet = -1;
734	>	private class DescendingIterator extends DeqIterator {
735	>	DescendingIterator() { cursor = tail(); }
736
737	<	public boolean hasNext() {
738	<	return cursor != fence;
737	>	@Override void doAdvance() {
738	>	cursor = dec(cursor, elements.length);
739		}
740
741	<	public E next() {
742	<	if (cursor == fence)
743	<	throw new NoSuchElementException();
744	<	cursor = (cursor - 1) & (elements.length - 1);
638	<	E result = elements[cursor];
639	<	if (head != fence || result == null)
640	<	throw new ConcurrentModificationException();
641	<	lastRet = cursor;
642	<	return result;
741	>	@Override void doRemove() {
742	>	if (!delete(lastRet))
743	>	// if right-shifted, undo advance in next
744	>	cursor = inc(cursor, elements.length);
745		}
746	+	}
747
748	<	public void remove() {
749	<	if (lastRet < 0)
750	<	throw new IllegalStateException();
751	<	if (!delete(lastRet)) {
752	<	cursor = (cursor + 1) & (elements.length - 1);
753	<	fence = head;
748	>	/**
749	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
750	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
751	>	* deque.
752	>	*
753	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
754	>	* {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and
755	>	* {@link Spliterator#NONNULL}.  Overriding implementations should document
756	>	* the reporting of additional characteristic values.
757	>	*
758	>	* @return a {@code Spliterator} over the elements in this deque
759	>	* @since 1.8
760	>	*/
761	>	public Spliterator<E> spliterator() {
762	>	return new ArrayDequeSpliterator();
763	>	}
764	>
765	>	final class ArrayDequeSpliterator implements Spliterator<E> {
766	>	private int cursor;
767	>	private int remaining; // -1 until late-binding first use
768	>
769	>	/** Constructs late-binding spliterator over all elements. */
770	>	ArrayDequeSpliterator() {
771	>	this.remaining = -1;
772	>	}
773	>
774	>	/** Constructs spliterator over the given slice. */
775	>	ArrayDequeSpliterator(int cursor, int count) {
776	>	this.cursor = cursor;
777	>	this.remaining = count;
778	>	}
779	>
780	>	/** Ensures late-binding initialization; then returns remaining. */
781	>	private int remaining() {
782	>	if (remaining < 0) {
783	>	cursor = head;
784	>	remaining = size;
785		}
786	<	lastRet = -1;
786	>	return remaining;
787	>	}
788	>
789	>	public ArrayDequeSpliterator trySplit() {
790	>	if (remaining() > 1) {
791	>	int mid = remaining >> 1;
792	>	int oldCursor = cursor;
793	>	cursor = add(cursor, mid, elements.length);
794	>	remaining -= mid;
795	>	return new ArrayDequeSpliterator(oldCursor, mid);
796	>	}
797	>	return null;
798	>	}
799	>
800	>	public void forEachRemaining(Consumer<? super E> action) {
801	>	Objects.requireNonNull(action);
802	>	final Object[] elements = ArrayDeque.this.elements;
803	>	final int capacity = elements.length;
804	>	remaining();        // for the initialization side-effect
805	>	for (; remaining > 0; cursor = inc(cursor, capacity), remaining--)
806	>	action.accept(checkedElementAt(elements, cursor));
807	>	}
808	>
809	>	public boolean tryAdvance(Consumer<? super E> action) {
810	>	Objects.requireNonNull(action);
811	>	if (remaining() == 0)
812	>	return false;
813	>	action.accept(checkedElementAt(elements, cursor));
814	>	cursor = inc(cursor, elements.length);
815	>	remaining--;
816	>	return true;
817	>	}
818	>
819	>	public long estimateSize() {
820	>	return remaining();
821	>	}
822	>
823	>	public int characteristics() {
824	>	return Spliterator.NONNULL
825	>	| Spliterator.ORDERED
826	>	| Spliterator.SIZED
827	>	| Spliterator.SUBSIZED;
828	>	}
829	>	}
830	>
831	>	@Override
832	>	public void forEach(Consumer<? super E> action) {
833	>	// checkInvariants();
834	>	Objects.requireNonNull(action);
835	>	final Object[] elements = this.elements;
836	>	final int capacity = elements.length;
837	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity))
838	>	action.accept(elementAt(i));
839	>	// checkInvariants();
840	>	}
841	>
842	>	/**
843	>	* Replaces each element of this deque with the result of applying the
844	>	* operator to that element, as specified by {@link List#replaceAll}.
845	>	*
846	>	* @param operator the operator to apply to each element
847	>	* @since 9
848	>	*/
849	>	public void replaceAll(UnaryOperator<E> operator) {
850	>	Objects.requireNonNull(operator);
851	>	final Object[] elements = this.elements;
852	>	final int capacity = elements.length;
853	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity))
854	>	elements[i] = operator.apply(elementAt(i));
855	>	// checkInvariants();
856	>	}
857	>
858	>	/**
859	>	* @throws NullPointerException {@inheritDoc}
860	>	*/
861	>	@Override
862	>	public boolean removeIf(Predicate<? super E> filter) {
863	>	Objects.requireNonNull(filter);
864	>	return bulkRemove(filter);
865	>	}
866	>
867	>	/**
868	>	* @throws NullPointerException {@inheritDoc}
869	>	*/
870	>	@Override
871	>	public boolean removeAll(Collection<?> c) {
872	>	Objects.requireNonNull(c);
873	>	return bulkRemove(e -> c.contains(e));
874	>	}
875	>
876	>	/**
877	>	* @throws NullPointerException {@inheritDoc}
878	>	*/
879	>	@Override
880	>	public boolean retainAll(Collection<?> c) {
881	>	Objects.requireNonNull(c);
882	>	return bulkRemove(e -> !c.contains(e));
883	>	}
884	>
885	>	/** Implementation of bulk remove methods. */
886	>	private boolean bulkRemove(Predicate<? super E> filter) {
887	>	// checkInvariants();
888	>	final Object[] elements = this.elements;
889	>	final int capacity = elements.length;
890	>	int i = head, j = i, remaining = size, deleted = 0;
891	>	try {
892	>	for (; remaining > 0; remaining--, i = inc(i, capacity)) {
893	>	@SuppressWarnings("unchecked") E e = (E) elements[i];
894	>	if (filter.test(e))
895	>	deleted++;
896	>	else {
897	>	if (j != i)
898	>	elements[j] = e;
899	>	j = inc(j, capacity);
900	>	}
901	>	}
902	>	return deleted > 0;
903	>	} catch (Throwable ex) {
904	>	for (; remaining > 0;
905	>	remaining--, i = inc(i, capacity), j = inc(j, capacity))
906	>	elements[j] = elements[i];
907	>	throw ex;
908	>	} finally {
909	>	size -= deleted;
910	>	for (; --deleted >= 0; j = inc(j, capacity))
911	>	elements[j] = null;
912	>	// checkInvariants();
913		}
914		}
915
916		/**
917	<	* Returns <tt>true</tt> if this deque contains the specified element.
918	<	* More formally, returns <tt>true</tt> if and only if this deque contains
919	<	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
917	>	* Returns {@code true} if this deque contains the specified element.
918	>	* More formally, returns {@code true} if and only if this deque contains
919	>	* at least one element {@code e} such that {@code o.equals(e)}.
920		*
921		* @param o object to be checked for containment in this deque
922	<	* @return <tt>true</tt> if this deque contains the specified element
922	>	* @return {@code true} if this deque contains the specified element
923		*/
924		public boolean contains(Object o) {
925	<	if (o == null)
926	<	return false;
927	<	int mask = elements.length - 1;
928	<	int i = head;
929	<	E x;
930	<	while ( (x = elements[i]) != null) {
671	<	if (o.equals(x))
672	<	return true;
673	<	i = (i + 1) & mask;
925	>	if (o != null) {
926	>	final Object[] elements = this.elements;
927	>	final int capacity = elements.length;
928	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity))
929	>	if (o.equals(elements[i]))
930	>	return true;
931		}
932		return false;
933		}
#	Line 678 | Line 935 | public class ArrayDeque<E> extends Abstr
935		/**
936		* Removes a single instance of the specified element from this deque.
937		* If the deque does not contain the element, it is unchanged.
938	<	* More formally, removes the first element <tt>e</tt> such that
939	<	* <tt>o.equals(e)</tt> (if such an element exists).
940	<	* Returns <tt>true</tt> if this deque contained the specified element
938	>	* More formally, removes the first element {@code e} such that
939	>	* {@code o.equals(e)} (if such an element exists).
940	>	* Returns {@code true} if this deque contained the specified element
941		* (or equivalently, if this deque changed as a result of the call).
942		*
943	<	* <p>This method is equivalent to {@link #removeFirstOccurrence}.
943	>	* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
944		*
945		* @param o element to be removed from this deque, if present
946	<	* @return <tt>true</tt> if this deque contained the specified element
946	>	* @return {@code true} if this deque contained the specified element
947		*/
948		public boolean remove(Object o) {
949		return removeFirstOccurrence(o);
#	Line 697 | Line 954 | public class ArrayDeque<E> extends Abstr
954		* The deque will be empty after this call returns.
955		*/
956		public void clear() {
957	<	int h = head;
958	<	int t = tail;
959	<	if (h != t) { // clear all cells
960	<	head = tail = 0;
961	<	int i = h;
962	<	int mask = elements.length - 1;
963	<	do {
964	<	elements[i] = null;
965	<	i = (i + 1) & mask;
709	<	} while (i != t);
957	>	final Object[] elements = this.elements;
958	>	final int capacity = elements.length;
959	>	final int h = this.head;
960	>	final int s = size;
961	>	if (capacity - h >= s)
962	>	Arrays.fill(elements, h, h + s, null);
963	>	else {
964	>	Arrays.fill(elements, h, capacity, null);
965	>	Arrays.fill(elements, 0, s - capacity + h, null);
966		}
967	+	size = head = 0;
968	+	// checkInvariants();
969		}
970
971		/**
#	Line 724 | Line 982 | public class ArrayDeque<E> extends Abstr
982		* @return an array containing all of the elements in this deque
983		*/
984		public Object[] toArray() {
985	<	return copyElements(new Object[size()]);
985	>	final int head = this.head;
986	>	final int firstLeg;
987	>	Object[] a = Arrays.copyOfRange(elements, head, head + size);
988	>	if ((firstLeg = elements.length - head) < size)
989	>	System.arraycopy(elements, 0, a, firstLeg, size - firstLeg);
990	>	return a;
991		}
992
993		/**
#	Line 738 | Line 1001 | public class ArrayDeque<E> extends Abstr
1001		* <p>If this deque fits in the specified array with room to spare
1002		* (i.e., the array has more elements than this deque), the element in
1003		* the array immediately following the end of the deque is set to
1004	<	* <tt>null</tt>.
1004	>	* {@code null}.
1005		*
1006		* <p>Like the {@link #toArray()} method, this method acts as bridge between
1007		* array-based and collection-based APIs.  Further, this method allows
1008		* precise control over the runtime type of the output array, and may,
1009		* under certain circumstances, be used to save allocation costs.
1010		*
1011	<	* <p>Suppose <tt>x</tt> is a deque known to contain only strings.
1011	>	* <p>Suppose {@code x} is a deque known to contain only strings.
1012		* The following code can be used to dump the deque into a newly
1013	<	* allocated array of <tt>String</tt>:
1013	>	* allocated array of {@code String}:
1014		*
1015	<	* <pre>
753	<	*     String[] y = x.toArray(new String[0]);</pre>
1015	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
1016		*
1017	<	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
1018	<	* <tt>toArray()</tt>.
1017	>	* Note that {@code toArray(new Object[0])} is identical in function to
1018	>	* {@code toArray()}.
1019		*
1020		* @param a the array into which the elements of the deque are to
1021		*          be stored, if it is big enough; otherwise, a new array of the
#	Line 764 | Line 1026 | public class ArrayDeque<E> extends Abstr
1026		*         this deque
1027		* @throws NullPointerException if the specified array is null
1028		*/
1029	+	@SuppressWarnings("unchecked")
1030		public <T> T[] toArray(T[] a) {
1031	<	int size = size();
1032	<	if (a.length < size)
1033	<	a = (T[])java.lang.reflect.Array.newInstance(
1034	<	a.getClass().getComponentType(), size);
1035	<	copyElements(a);
1036	<	if (a.length > size)
1037	<	a[size] = null;
1031	>	final Object[] elements = this.elements;
1032	>	final int head = this.head;
1033	>	final int firstLeg;
1034	>	boolean wrap = (firstLeg = elements.length - head) < size;
1035	>	if (size > a.length) {
1036	>	a = (T[]) Arrays.copyOfRange(elements, head, head + size,
1037	>	a.getClass());
1038	>	} else {
1039	>	System.arraycopy(elements, head, a, 0, wrap ? firstLeg : size);
1040	>	if (size < a.length)
1041	>	a[size] = null;
1042	>	}
1043	>	if (wrap)
1044	>	System.arraycopy(elements, 0, a, firstLeg, size - firstLeg);
1045		return a;
1046		}
1047
#	Line 784 | Line 1054 | public class ArrayDeque<E> extends Abstr
1054		*/
1055		public ArrayDeque<E> clone() {
1056		try {
1057	+	@SuppressWarnings("unchecked")
1058		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
1059		result.elements = Arrays.copyOf(elements, elements.length);
1060		return result;
790	–
1061		} catch (CloneNotSupportedException e) {
1062		throw new AssertionError();
1063		}
1064		}
1065
796	–	/**
797	–	* Appease the serialization gods.
798	–	*/
1066		private static final long serialVersionUID = 2340985798034038923L;
1067
1068		/**
1069	<	* Serialize this deque.
1069	>	* Saves this deque to a stream (that is, serializes it).
1070		*
1071	<	* @serialData The current size (<tt>int</tt>) of the deque,
1071	>	* @param s the stream
1072	>	* @throws java.io.IOException if an I/O error occurs
1073	>	* @serialData The current size ({@code int}) of the deque,
1074		* followed by all of its elements (each an object reference) in
1075		* first-to-last order.
1076		*/
1077	<	private void writeObject(ObjectOutputStream s) throws IOException {
1077	>	private void writeObject(java.io.ObjectOutputStream s)
1078	>	throws java.io.IOException {
1079		s.defaultWriteObject();
1080
1081		// Write out size
1082	<	s.writeInt(size());
1082	>	s.writeInt(size);
1083
1084		// Write out elements in order.
1085	<	int mask = elements.length - 1;
1086	<	for (int i = head; i != tail; i = (i + 1) & mask)
1085	>	final Object[] elements = this.elements;
1086	>	final int capacity = elements.length;
1087	>	for (int k = size, i = head; --k >= 0; i = inc(i, capacity))
1088		s.writeObject(elements[i]);
1089		}
1090
1091		/**
1092	<	* Deserialize this deque.
1092	>	* Reconstitutes this deque from a stream (that is, deserializes it).
1093	>	* @param s the stream
1094	>	* @throws ClassNotFoundException if the class of a serialized object
1095	>	*         could not be found
1096	>	* @throws java.io.IOException if an I/O error occurs
1097		*/
1098	<	private void readObject(ObjectInputStream s)
1099	<	throws IOException, ClassNotFoundException {
1098	>	private void readObject(java.io.ObjectInputStream s)
1099	>	throws java.io.IOException, ClassNotFoundException {
1100		s.defaultReadObject();
1101
1102		// Read in size and allocate array
1103	<	int size = s.readInt();
829	<	allocateElements(size);
830	<	head = 0;
831	<	tail = size;
1103	>	elements = new Object[size = s.readInt()];
1104
1105		// Read in all elements in the proper order.
1106		for (int i = 0; i < size; i++)
1107	<	elements[i] = (E)s.readObject();
1107	>	elements[i] = s.readObject();
1108		}
1109	+
1110	+	/** debugging */
1111	+	private void checkInvariants() {
1112	+	try {
1113	+	int capacity = elements.length;
1114	+	assert size >= 0 && size <= capacity;
1115	+	assert head >= 0 && ((capacity == 0 && head == 0 && size == 0)
1116	+	|| head < capacity);
1117	+	assert size == 0
1118	+	|| (elements[head] != null && elements[tail()] != null);
1119	+	assert size == capacity
1120	+	|| (elements[dec(head, capacity)] == null
1121	+	&& elements[inc(tail(), capacity)] == null);
1122	+	} catch (Throwable t) {
1123	+	System.err.printf("head=%d size=%d capacity=%d%n",
1124	+	head, size, elements.length);
1125	+	System.err.printf("elements=%s%n",
1126	+	Arrays.toString(elements));
1127	+	throw t;
1128	+	}
1129	+	}
1130	+
1131		}

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