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Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.8 by jsr166, Mon May 2 04:19:58 2005 UTC vs.
Revision 1.17 by dl, Thu Sep 15 16:55:24 2005 UTC

#	Line 4 | Line 4
4		*/
5
6		package java.util;
7	+	import java.util.*; // for javadoc (till 6280605 is fixed)
8		import java.io.*;
9
10		/**
#	Line 18 | Line 19 | import java.io.*;
19		* <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time.
20		* Exceptions include {@link #remove(Object) remove}, {@link
21		* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
22	<	* removeLastOccurrence}, {@link #contains contains }, {@link #iterator
22	>	* removeLastOccurrence}, {@link #contains contains}, {@link #iterator
23		* iterator.remove()}, and the bulk operations, all of which run in linear
24		* time.
25		*
#	Line 40 | Line 41 | import java.io.*;
41		* should be used only to detect bugs.</i>
42		*
43		* <p>This class and its iterator implement all of the
44	<	* optional methods of the {@link Collection} and {@link
45	<	* Iterator} interfaces.  This class is a member of the <a
46	<	* href="{@docRoot}/../guide/collections/index.html"> Java Collections
47	<	* Framework</a>.
44	>	* <em>optional</em> methods of the {@link Collection} and {@link
45	>	* Iterator} interfaces.
46	>	*
47	>	* <p>This class is a member of the
48	>	* <a href="{@docRoot}/../guide/collections/index.html">
49	>	* Java Collections Framework</a>.
50		*
51		* @author  Josh Bloch and Doug Lea
52		* @since   1.6
#	Line 88 | Line 91 | public class ArrayDeque<E> extends Abstr
91		/**
92		* Allocate empty array to hold the given number of elements.
93		*
94	<	* @param numElements  the number of elements to hold.
94	>	* @param numElements  the number of elements to hold
95		*/
96		private void allocateElements(int numElements) {
97		int initialCapacity = MIN_INITIAL_CAPACITY;
#	Line 187 | Line 190 | public class ArrayDeque<E> extends Abstr
190		/**
191		* Inserts the specified element at the front of this deque.
192		*
193	<	* @param e the element to insert
194	<	* @throws NullPointerException if <tt>e</tt> is null
193	>	* @param e the element to add
194	>	* @throws NullPointerException if the specified element is null
195		*/
196		public void addFirst(E e) {
197		if (e == null)
#	Line 200 | Line 203 | public class ArrayDeque<E> extends Abstr
203
204		/**
205		* Inserts the specified element at the end of this deque.
203	–	* This method is equivalent to {@link Collection#add} and
204	–	* {@link #push}.
206		*
207	<	* @param e the element to insert
208	<	* @throws NullPointerException if <tt>e</tt> is null
207	>	* <p>This method is equivalent to {@link #add}.
208	>	*
209	>	* @param e the element to add
210	>	* @throws NullPointerException if the specified element is null
211		*/
212		public void addLast(E e) {
213		if (e == null)
#	Line 215 | Line 218 | public class ArrayDeque<E> extends Abstr
218		}
219
220		/**
218	–	* Retrieves and removes the first element of this deque, or
219	–	* <tt>null</tt> if this deque is empty.
220	–	*
221	–	* @return the first element of this deque, or <tt>null</tt> if
222	–	*     this deque is empty
223	–	*/
224	–	public E pollFirst() {
225	–	int h = head;
226	–	E result = elements[h]; // Element is null if deque empty
227	–	if (result == null)
228	–	return null;
229	–	elements[h] = null;     // Must null out slot
230	–	head = (h + 1) & (elements.length - 1);
231	–	return result;
232	–	}
233	–
234	–	/**
235	–	* Retrieves and removes the last element of this deque, or
236	–	* <tt>null</tt> if this deque is empty.
237	–	*
238	–	* @return the last element of this deque, or <tt>null</tt> if
239	–	*     this deque is empty
240	–	*/
241	–	public E pollLast() {
242	–	int t = (tail - 1) & (elements.length - 1);
243	–	E result = elements[t];
244	–	if (result == null)
245	–	return null;
246	–	elements[t] = null;
247	–	tail = t;
248	–	return result;
249	–	}
250	–
251	–	/**
221		* Inserts the specified element at the front of this deque.
222		*
223	<	* @param e the element to insert
224	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst})
225	<	* @throws NullPointerException if <tt>e</tt> is null
223	>	* @param e the element to add
224	>	* @return <tt>true</tt> (as specified by {@link Deque#offerFirst})
225	>	* @throws NullPointerException if the specified element is null
226		*/
227		public boolean offerFirst(E e) {
228		addFirst(e);
#	Line 263 | Line 232 | public class ArrayDeque<E> extends Abstr
232		/**
233		* Inserts the specified element at the end of this deque.
234		*
235	<	* @param e the element to insert
236	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
237	<	* @throws NullPointerException if <tt>e</tt> is null
235	>	* @param e the element to add
236	>	* @return <tt>true</tt> (as specified by {@link Deque#offerLast})
237	>	* @throws NullPointerException if the specified element is null
238		*/
239		public boolean offerLast(E e) {
240		addLast(e);
#	Line 273 | Line 242 | public class ArrayDeque<E> extends Abstr
242		}
243
244		/**
245	<	* Retrieves and removes the first element of this deque.  This method
277	<	* differs from the {@link #pollFirst} method only in that it throws an
278	<	* exception if this deque is empty.
279	<	*
280	<	* @return the first element of this deque
281	<	* @throws NoSuchElementException if this deque is empty
245	>	* @throws NoSuchElementException {@inheritDoc}
246		*/
247		public E removeFirst() {
248		E x = pollFirst();
#	Line 288 | Line 252 | public class ArrayDeque<E> extends Abstr
252		}
253
254		/**
255	<	* Retrieves and removes the last element of this deque.  This method
292	<	* differs from the {@link #pollLast} method only in that it throws an
293	<	* exception if this deque is empty.
294	<	*
295	<	* @return the last element of this deque
296	<	* @throws NoSuchElementException if this deque is empty
255	>	* @throws NoSuchElementException {@inheritDoc}
256		*/
257		public E removeLast() {
258		E x = pollLast();
#	Line 302 | Line 261 | public class ArrayDeque<E> extends Abstr
261		return x;
262		}
263
264	<	/**
265	<	* Retrieves, but does not remove, the first element of this deque,
266	<	* returning <tt>null</tt> if this deque is empty.
267	<	*
268	<	* @return the first element of this deque, or <tt>null</tt> if
269	<	*     this deque is empty
270	<	*/
271	<	public E peekFirst() {
313	<	return elements[head]; // elements[head] is null if deque empty
264	>	public E pollFirst() {
265	>	int h = head;
266	>	E result = elements[h]; // Element is null if deque empty
267	>	if (result == null)
268	>	return null;
269	>	elements[h] = null;     // Must null out slot
270	>	head = (h + 1) & (elements.length - 1);
271	>	return result;
272		}
273
274	<	/**
275	<	* Retrieves, but does not remove, the last element of this deque,
276	<	* returning <tt>null</tt> if this deque is empty.
277	<	*
278	<	* @return the last element of this deque, or <tt>null</tt> if this deque
279	<	*     is empty
280	<	*/
281	<	public E peekLast() {
324	<	return elements[(tail - 1) & (elements.length - 1)];
274	>	public E pollLast() {
275	>	int t = (tail - 1) & (elements.length - 1);
276	>	E result = elements[t];
277	>	if (result == null)
278	>	return null;
279	>	elements[t] = null;
280	>	tail = t;
281	>	return result;
282		}
283
284		/**
285	<	* Retrieves, but does not remove, the first element of this
329	<	* deque.  This method differs from the {@link #peekFirst} method only
330	<	* in that it throws an exception if this deque is empty.
331	<	*
332	<	* @return the first element of this deque
333	<	* @throws NoSuchElementException if this deque is empty
285	>	* @throws NoSuchElementException {@inheritDoc}
286		*/
287		public E getFirst() {
288		E x = elements[head];
#	Line 340 | Line 292 | public class ArrayDeque<E> extends Abstr
292		}
293
294		/**
295	<	* Retrieves, but does not remove, the last element of this
344	<	* deque.  This method differs from the {@link #peekLast} method only
345	<	* in that it throws an exception if this deque is empty.
346	<	*
347	<	* @return the last element of this deque
348	<	* @throws NoSuchElementException if this deque is empty
295	>	* @throws NoSuchElementException {@inheritDoc}
296		*/
297		public E getLast() {
298		E x = elements[(tail - 1) & (elements.length - 1)];
#	Line 354 | Line 301 | public class ArrayDeque<E> extends Abstr
301		return x;
302		}
303
304	+	public E peekFirst() {
305	+	return elements[head]; // elements[head] is null if deque empty
306	+	}
307	+
308	+	public E peekLast() {
309	+	return elements[(tail - 1) & (elements.length - 1)];
310	+	}
311	+
312		/**
313		* Removes the first occurrence of the specified element in this
314	<	* deque (when traversing the deque from head to tail).  More
315	<	* formally, removes the first element e such that (o==null ?
316	<	* e==null : o.equals(e)). If the deque does not contain the
317	<	* element, it is unchanged.
314	>	* deque (when traversing the deque from head to tail).
315	>	* If the deque does not contain the element, it is unchanged.
316	>	* More formally, removes the first element <tt>e</tt> such that
317	>	* <tt>o.equals(e)</tt> (if such an element exists).
318	>	* Returns <tt>true</tt> if this deque contained the specified element
319	>	* (or equivalently, if this deque changed as a result of the call).
320		*
321		* @param o element to be removed from this deque, if present
322		* @return <tt>true</tt> if the deque contained the specified element
#	Line 382 | Line 339 | public class ArrayDeque<E> extends Abstr
339
340		/**
341		* Removes the last occurrence of the specified element in this
342	<	* deque (when traversing the deque from head to tail). More
343	<	* formally, removes the last element e such that (o==null ?
344	<	* e==null : o.equals(e)). If the deque
345	<	* does not contain the element, it is unchanged.
342	>	* deque (when traversing the deque from head to tail).
343	>	* If the deque does not contain the element, it is unchanged.
344	>	* More formally, removes the last element <tt>e</tt> such that
345	>	* <tt>o.equals(e)</tt> (if such an element exists).
346	>	* Returns <tt>true</tt> if this deque contained the specified element
347	>	* (or equivalently, if this deque changed as a result of the call).
348		*
349		* @param o element to be removed from this deque, if present
350		* @return <tt>true</tt> if the deque contained the specified element
#	Line 411 | Line 370 | public class ArrayDeque<E> extends Abstr
370		/**
371		* Inserts the specified element at the end of this deque.
372		*
414	–	* <p>This method is equivalent to {@link #offerLast}.
415	–	*
416	–	* @param e the element to insert
417	–	* @return <tt>true</tt> (as per the spec for {@link Queue#offer})
418	–	* @throws NullPointerException if <tt>e</tt> is null
419	–	*/
420	–	public boolean offer(E e) {
421	–	return offerLast(e);
422	–	}
423	–
424	–	/**
425	–	* Inserts the specified element at the end of this deque.
426	–	*
373		* <p>This method is equivalent to {@link #addLast}.
374		*
375	<	* @param e the element to insert
376	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
377	<	* @throws NullPointerException if <tt>e</tt> is null
375	>	* @param e the element to add
376	>	* @return <tt>true</tt> (as specified by {@link Collection#add})
377	>	* @throws NullPointerException if the specified element is null
378		*/
379		public boolean add(E e) {
380		addLast(e);
#	Line 436 | Line 382 | public class ArrayDeque<E> extends Abstr
382		}
383
384		/**
385	<	* Retrieves and removes the head of the queue represented by
440	<	* this deque, or <tt>null</tt> if this deque is empty.  In other words,
441	<	* retrieves and removes the first element of this deque, or <tt>null</tt>
442	<	* if this deque is empty.
385	>	* Inserts the specified element at the end of this deque.
386		*
387	<	* <p>This method is equivalent to {@link #pollFirst}.
387	>	* <p>This method is equivalent to {@link #offerLast}.
388		*
389	<	* @return the first element of this deque, or <tt>null</tt> if
390	<	*     this deque is empty
389	>	* @param e the element to add
390	>	* @return <tt>true</tt> (as specified by {@link Queue#offer})
391	>	* @throws NullPointerException if the specified element is null
392		*/
393	<	public E poll() {
394	<	return pollFirst();
393	>	public boolean offer(E e) {
394	>	return offerLast(e);
395		}
396
397		/**
398		* Retrieves and removes the head of the queue represented by this deque.
399	<	* This method differs from the {@link #poll} method only in that it
400	<	* throws an exception if this deque is empty.
399	>	*
400	>	* This method differs from {@link #poll poll} only in that it throws an
401	>	* exception if this deque is empty.
402		*
403		* <p>This method is equivalent to {@link #removeFirst}.
404		*
405		* @return the head of the queue represented by this deque
406	<	* @throws NoSuchElementException if this deque is empty
406	>	* @throws NoSuchElementException {@inheritDoc}
407		*/
408		public E remove() {
409		return removeFirst();
410		}
411
412		/**
413	<	* Retrieves, but does not remove, the head of the queue represented by
414	<	* this deque, returning <tt>null</tt> if this deque is empty.
413	>	* Retrieves and removes the head of the queue represented by this deque
414	>	* (in other words, the first element of this deque), or returns
415	>	* <tt>null</tt> if this deque is empty.
416		*
417	<	* <p>This method is equivalent to {@link #peekFirst}.
417	>	* <p>This method is equivalent to {@link #pollFirst}.
418		*
419		* @return the head of the queue represented by this deque, or
420	<	*     <tt>null</tt> if this deque is empty
420	>	*         <tt>null</tt> if this deque is empty
421		*/
422	<	public E peek() {
423	<	return peekFirst();
422	>	public E poll() {
423	>	return pollFirst();
424		}
425
426		/**
427		* Retrieves, but does not remove, the head of the queue represented by
428	<	* this deque.  This method differs from the {@link #peek} method only in
428	>	* this deque.  This method differs from {@link #peek peek} only in
429		* that it throws an exception if this deque is empty.
430		*
431		* <p>This method is equivalent to {@link #getFirst}.
432		*
433		* @return the head of the queue represented by this deque
434	<	* @throws NoSuchElementException if this deque is empty
434	>	* @throws NoSuchElementException {@inheritDoc}
435		*/
436		public E element() {
437		return getFirst();
438		}
439
440	+	/**
441	+	* Retrieves, but does not remove, the head of the queue represented by
442	+	* this deque, or returns <tt>null</tt> if this deque is empty.
443	+	*
444	+	* <p>This method is equivalent to {@link #peekFirst}.
445	+	*
446	+	* @return the head of the queue represented by this deque, or
447	+	*         <tt>null</tt> if this deque is empty
448	+	*/
449	+	public E peek() {
450	+	return peekFirst();
451	+	}
452	+
453		// *** Stack methods ***
454
455		/**
#	Line 500 | Line 459 | public class ArrayDeque<E> extends Abstr
459		* <p>This method is equivalent to {@link #addFirst}.
460		*
461		* @param e the element to push
462	<	* @throws NullPointerException if <tt>e</tt> is null
462	>	* @throws NullPointerException if the specified element is null
463		*/
464		public void push(E e) {
465		addFirst(e);
#	Line 513 | Line 472 | public class ArrayDeque<E> extends Abstr
472		* <p>This method is equivalent to {@link #removeFirst()}.
473		*
474		* @return the element at the front of this deque (which is the top
475	<	*     of the stack represented by this deque)
476	<	* @throws NoSuchElementException if this deque is empty
475	>	*         of the stack represented by this deque)
476	>	* @throws NoSuchElementException {@inheritDoc}
477		*/
478		public E pop() {
479		return removeFirst();
#	Line 522 | Line 481 | public class ArrayDeque<E> extends Abstr
481
482		/**
483		* Removes the element at the specified position in the elements array,
484	<	* adjusting head, tail, and size as necessary.  This can result in
485	<	* motion of elements backwards or forwards in the array.
484	>	* adjusting head and tail as necessary.  This can result in motion of
485	>	* elements backwards or forwards in the array.
486		*
487		* <p>This method is called delete rather than remove to emphasize
488	<	* that its semantics differ from those of List.remove(int).
488	>	* that its semantics differ from those of {@link List#remove(int)}.
489		*
490		* @return true if elements moved backwards
491		*/
492		private boolean delete(int i) {
493	+	int mask = elements.length - 1;
494	+
495	+	// Invariant: head <= i < tail mod circularity
496	+	if (((i - head) & mask) >= ((tail - head) & mask))
497	+	throw new ConcurrentModificationException();
498	+
499		// Case 1: Deque doesn't wrap
500		// Case 2: Deque does wrap and removed element is in the head portion
501	<	if ((head < tail || tail == 0) || i >= head) {
501	>	if (i >= head) {
502		System.arraycopy(elements, head, elements, head + 1, i - head);
503		elements[head] = null;
504	<	head = (head + 1) & (elements.length - 1);
504	>	head = (head + 1) & mask;
505		return false;
506		}
507
#	Line 559 | Line 524 | public class ArrayDeque<E> extends Abstr
524		}
525
526		/**
527	<	* Returns <tt>true</tt> if this deque contains no elements.<p>
527	>	* Returns <tt>true</tt> if this deque contains no elements.
528		*
529	<	* @return <tt>true</tt> if this deque contains no elements.
529	>	* @return <tt>true</tt> if this deque contains no elements
530		*/
531		public boolean isEmpty() {
532		return head == tail;
#	Line 579 | Line 544 | public class ArrayDeque<E> extends Abstr
544		return new DeqIterator();
545		}
546
547	+	/**
548	+	* Returns an iterator over the elements in this deque in reverse
549	+	* sequential order.  The elements will be returned in order from
550	+	* last (tail) to first (head).
551	+	*
552	+	* @return an iterator over the elements in this deque in reverse
553	+	* sequence
554	+	*/
555	+	public Iterator<E> descendingIterator() {
556	+	return new DescendingIterator();
557	+	}
558	+
559		private class DeqIterator implements Iterator<E> {
560		/**
561		* Index of element to be returned by subsequent call to next.
#	Line 617 | Line 594 | public class ArrayDeque<E> extends Abstr
594		public void remove() {
595		if (lastRet < 0)
596		throw new IllegalStateException();
597	<	if (delete(lastRet))
598	<	cursor--;
597	>	if (delete(lastRet)) // if left-shifted, undo increment in next()
598	>	cursor = (cursor - 1) & (elements.length - 1);
599		lastRet = -1;
600		fence = tail;
601		}
602		}
603
604	+
605	+	private class DescendingIterator implements Iterator<E> {
606	+	/*
607	+	* This class is nearly a mirror-image of DeqIterator, using
608	+	* (tail-1) instead of head for initial cursor, (head-1)
609	+	* instead of tail for fence, and elements.length instead of -1
610	+	* for sentinel. It shares the same structure, but not many
611	+	* actual lines of code.
612	+	*/
613	+	private int cursor = (tail - 1) & (elements.length - 1);
614	+	private int fence =  (head - 1) & (elements.length - 1);
615	+	private int lastRet = elements.length;
616	+
617	+	public boolean hasNext() {
618	+	return cursor != fence;
619	+	}
620	+
621	+	public E next() {
622	+	E result;
623	+	if (cursor == fence)
624	+	throw new NoSuchElementException();
625	+	if (((head - 1) & (elements.length - 1)) != fence ||
626	+	(result = elements[cursor]) == null)
627	+	throw new ConcurrentModificationException();
628	+	lastRet = cursor;
629	+	cursor = (cursor - 1) & (elements.length - 1);
630	+	return result;
631	+	}
632	+
633	+	public void remove() {
634	+	if (lastRet >= elements.length)
635	+	throw new IllegalStateException();
636	+	if (!delete(lastRet))
637	+	cursor = (cursor + 1) & (elements.length - 1);
638	+	lastRet = elements.length;
639	+	fence = (head - 1) & (elements.length - 1);
640	+	}
641	+	}
642	+
643		/**
644	<	* Returns <tt>true</tt> if this deque contains the specified
645	<	* element.  More formally, returns <tt>true</tt> if and only if this
646	<	* deque contains at least one element <tt>e</tt> such that
631	<	* <tt>e.equals(o)</tt>.
644	>	* Returns <tt>true</tt> if this deque contains the specified element.
645	>	* More formally, returns <tt>true</tt> if and only if this deque contains
646	>	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
647		*
648		* @param o object to be checked for containment in this deque
649		* @return <tt>true</tt> if this deque contains the specified element
#	Line 649 | Line 664 | public class ArrayDeque<E> extends Abstr
664
665		/**
666		* Removes a single instance of the specified element from this deque.
667	<	* This method is equivalent to {@link #removeFirstOccurrence}.
667	>	* If the deque does not contain the element, it is unchanged.
668	>	* More formally, removes the first element <tt>e</tt> such that
669	>	* <tt>o.equals(e)</tt> (if such an element exists).
670	>	* Returns <tt>true</tt> if this deque contained the specified element
671	>	* (or equivalently, if this deque changed as a result of the call).
672	>	*
673	>	* <p>This method is equivalent to {@link #removeFirstOccurrence}.
674		*
675	<	* @param e element to be removed from this deque, if present
675	>	* @param o element to be removed from this deque, if present
676		* @return <tt>true</tt> if this deque contained the specified element
677		*/
678	<	public boolean remove(Object e) {
679	<	return removeFirstOccurrence(e);
678	>	public boolean remove(Object o) {
679	>	return removeFirstOccurrence(o);
680		}
681
682		/**
#	Line 672 | Line 693 | public class ArrayDeque<E> extends Abstr
693		do {
694		elements[i] = null;
695		i = (i + 1) & mask;
696	<	} while(i != t);
696	>	} while (i != t);
697		}
698		}
699
700		/**
701		* Returns an array containing all of the elements in this deque
702	<	* in the correct order.
702	>	* in proper sequence (from first to last element).
703	>	*
704	>	* <p>The returned array will be "safe" in that no references to it are
705	>	* maintained by this deque.  (In other words, this method must allocate
706	>	* a new array).  The caller is thus free to modify the returned array.
707	>	*
708	>	* <p>This method acts as bridge between array-based and collection-based
709	>	* APIs.
710		*
711		* @return an array containing all of the elements in this deque
684	–	*         in the correct order
712		*/
713		public Object[] toArray() {
714		return copyElements(new Object[size()]);
715		}
716
717		/**
718	<	* Returns an array containing all of the elements in this deque in the
719	<	* correct order; the runtime type of the returned array is that of the
720	<	* specified array.  If the deque fits in the specified array, it is
721	<	* returned therein.  Otherwise, a new array is allocated with the runtime
722	<	* type of the specified array and the size of this deque.
723	<	*
724	<	* <p>If the deque fits in the specified array with room to spare (i.e.,
725	<	* the array has more elements than the deque), the element in the array
726	<	* immediately following the end of the collection is set to <tt>null</tt>.
718	>	* Returns an array containing all of the elements in this deque in
719	>	* proper sequence (from first to last element); the runtime type of the
720	>	* returned array is that of the specified array.  If the deque fits in
721	>	* the specified array, it is returned therein.  Otherwise, a new array
722	>	* is allocated with the runtime type of the specified array and the
723	>	* size of this deque.
724	>	*
725	>	* <p>If this deque fits in the specified array with room to spare
726	>	* (i.e., the array has more elements than this deque), the element in
727	>	* the array immediately following the end of the deque is set to
728	>	* <tt>null</tt>.
729	>	*
730	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
731	>	* array-based and collection-based APIs.  Further, this method allows
732	>	* precise control over the runtime type of the output array, and may,
733	>	* under certain circumstances, be used to save allocation costs.
734	>	*
735	>	* <p>Suppose <tt>x</tt> is a deque known to contain only strings.
736	>	* The following code can be used to dump the deque into a newly
737	>	* allocated array of <tt>String</tt>:
738	>	*
739	>	* <pre>
740	>	*     String[] y = x.toArray(new String[0]);</pre>
741	>	*
742	>	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
743	>	* <tt>toArray()</tt>.
744		*
745		* @param a the array into which the elements of the deque are to
746	<	*          be stored, if it is big enough; otherwise, a new array of the
747	<	*          same runtime type is allocated for this purpose
748	<	* @return an array containing the elements of the deque
749	<	* @throws ArrayStoreException if the runtime type of a is not a supertype
750	<	*         of the runtime type of every element in this deque
746	>	*          be stored, if it is big enough; otherwise, a new array of the
747	>	*          same runtime type is allocated for this purpose
748	>	* @return an array containing all of the elements in this deque
749	>	* @throws ArrayStoreException if the runtime type of the specified array
750	>	*         is not a supertype of the runtime type of every element in
751	>	*         this deque
752	>	* @throws NullPointerException if the specified array is null
753		*/
754		public <T> T[] toArray(T[] a) {
755		int size = size();

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