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

Comparing jsr166/src/main/java/util/ArrayDeque.java (file contents):
Revision 1.12 by jsr166, Tue May 17 16:14:34 2005 UTC vs.
Revision 1.27 by jsr166, Tue Feb 7 20:54:24 2006 UTC

#	Line 202 | Line 202 | public class ArrayDeque<E> extends Abstr
202
203		/**
204		* Inserts the specified element at the end of this deque.
205	<	* This method is equivalent to {@link #add} and {@link #push}.
205	>	*
206	>	* <p>This method is equivalent to {@link #add}.
207		*
208		* @param e the element to add
209		* @throws NullPointerException if the specified element is null
#	Line 219 | Line 220 | public class ArrayDeque<E> extends Abstr
220		* Inserts the specified element at the front of this deque.
221		*
222		* @param e the element to add
223	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst})
223	>	* @return <tt>true</tt> (as specified by {@link Deque#offerFirst})
224		* @throws NullPointerException if the specified element is null
225		*/
226		public boolean offerFirst(E e) {
#	Line 231 | Line 232 | public class ArrayDeque<E> extends Abstr
232		* Inserts the specified element at the end of this deque.
233		*
234		* @param e the element to add
235	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
235	>	* @return <tt>true</tt> (as specified by {@link Deque#offerLast})
236		* @throws NullPointerException if the specified element is null
237		*/
238		public boolean offerLast(E e) {
#	Line 371 | Line 372 | public class ArrayDeque<E> extends Abstr
372		* <p>This method is equivalent to {@link #addLast}.
373		*
374		* @param e the element to add
375	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
375	>	* @return <tt>true</tt> (as specified by {@link Collection#add})
376		* @throws NullPointerException if the specified element is null
377		*/
378		public boolean add(E e) {
#	Line 385 | Line 386 | public class ArrayDeque<E> extends Abstr
386		* <p>This method is equivalent to {@link #offerLast}.
387		*
388		* @param e the element to add
389	<	* @return <tt>true</tt> (as per the spec for {@link Queue#offer})
389	>	* @return <tt>true</tt> (as specified by {@link Queue#offer})
390		* @throws NullPointerException if the specified element is null
391		*/
392		public boolean offer(E e) {
#	Line 394 | Line 395 | public class ArrayDeque<E> extends Abstr
395
396		/**
397		* Retrieves and removes the head of the queue represented by this deque.
398	<	* This method differs from {@link #poll} only in that it throws an
398	>	*
399	>	* This method differs from {@link #poll poll} only in that it throws an
400		* exception if this deque is empty.
401		*
402		* <p>This method is equivalent to {@link #removeFirst}.
#	Line 422 | Line 424 | public class ArrayDeque<E> extends Abstr
424
425		/**
426		* Retrieves, but does not remove, the head of the queue represented by
427	<	* this deque.  This method differs from {@link #peek} only in that it
428	<	* throws an exception if this deque is empty.
427	>	* this deque.  This method differs from {@link #peek peek} only in
428	>	* that it throws an exception if this deque is empty.
429		*
430		* <p>This method is equivalent to {@link #getFirst}.
431		*
#	Line 476 | Line 478 | public class ArrayDeque<E> extends Abstr
478		return removeFirst();
479		}
480
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	+
489		/**
490		* Removes the element at the specified position in the elements array,
491		* adjusting head and tail as necessary.  This can result in motion of
#	Line 487 | Line 497 | public class ArrayDeque<E> extends Abstr
497		* @return true if elements moved backwards
498		*/
499		private boolean delete(int i) {
500	<	int mask = elements.length - 1;
500	>	checkInvariants();
501	>	final E[] elements = this.elements;
502	>	final int mask = elements.length - 1;
503	>	final int h = head;
504	>	final int t = tail;
505	>	final int front = (i - h) & mask;
506	>	final int back  = (t - i) & mask;
507
508		// Invariant: head <= i < tail mod circularity
509	<	if (((i - head) & mask) >= ((tail - head) & mask))
509	>	if (front >= ((t - h) & mask))
510		throw new ConcurrentModificationException();
511
512	<	// Case 1: Deque doesn't wrap
513	<	// Case 2: Deque does wrap and removed element is in the head portion
514	<	if (i >= head) {
515	<	System.arraycopy(elements, head, elements, head + 1, i - head);
516	<	elements[head] = null;
517	<	head = (head + 1) & mask;
518	<	return false;
519	<	}
520	<
521	<	// Case 3: Deque wraps and removed element is in the tail portion
522	<	tail--;
523	<	System.arraycopy(elements, i + 1, elements, i, tail - i);
524	<	elements[tail] = null;
525	<	return true;
512	>	// Optimize for least element motion
513	>	if (front < back) {
514	>	if (h <= i) {
515	>	System.arraycopy(elements, h, elements, h + 1, front);
516	>	} else { // Wrap around
517	>	System.arraycopy(elements, 0, elements, 1, i);
518	>	elements[0] = elements[mask];
519	>	System.arraycopy(elements, h, elements, h + 1, mask - h);
520	>	}
521	>	elements[h] = null;
522	>	head = (h + 1) & mask;
523	>	return false;
524	>	} else {
525	>	if (i < t) { // Copy the null tail as well
526	>	System.arraycopy(elements, i + 1, elements, i, back);
527	>	tail = t - 1;
528	>	} else { // Wrap around
529	>	System.arraycopy(elements, i + 1, elements, i, mask - i);
530	>	elements[mask] = elements[0];
531	>	System.arraycopy(elements, 1, elements, 0, t);
532	>	tail = (t - 1) & mask;
533	>	}
534	>	return true;
535	>	}
536		}
537
538		// *** Collection Methods ***
#	Line 535 | Line 561 | public class ArrayDeque<E> extends Abstr
561		* order that elements would be dequeued (via successive calls to
562		* {@link #remove} or popped (via successive calls to {@link #pop}).
563		*
564	<	* @return an <tt>Iterator</tt> over the elements in this deque
564	>	* @return an iterator over the elements in this deque
565		*/
566		public Iterator<E> iterator() {
567		return new DeqIterator();
568		}
569
570	+	public Iterator<E> descendingIterator() {
571	+	return new DescendingIterator();
572	+	}
573	+
574		private class DeqIterator implements Iterator<E> {
575		/**
576		* Index of element to be returned by subsequent call to next.
#	Line 564 | Line 594 | public class ArrayDeque<E> extends Abstr
594		}
595
596		public E next() {
567	–	E result;
597		if (cursor == fence)
598		throw new NoSuchElementException();
599	+	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 = elements[cursor]) == null)
602	>	if (tail != fence || result == null)
603		throw new ConcurrentModificationException();
604		lastRet = cursor;
605		cursor = (cursor + 1) & (elements.length - 1);
#	Line 579 | Line 609 | public class ArrayDeque<E> extends Abstr
609		public void remove() {
610		if (lastRet < 0)
611		throw new IllegalStateException();
612	<	if (delete(lastRet))
613	<	cursor--;
612	>	if (delete(lastRet)) { // if left-shifted, undo increment in next()
613	>	cursor = (cursor - 1) & (elements.length - 1);
614	>	fence = tail;
615	>	}
616	>	lastRet = -1;
617	>	}
618	>	}
619	>
620	>	private class DescendingIterator implements Iterator<E> {
621	>	/*
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;
629	>
630	>	public boolean hasNext() {
631	>	return cursor != fence;
632	>	}
633	>
634	>	public E next() {
635	>	if (cursor == fence)
636	>	throw new NoSuchElementException();
637	>	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;
643	>	}
644	>
645	>	public void remove() {
646	>	if (lastRet < 0)
647	>	throw new IllegalStateException();
648	>	if (!delete(lastRet)) {
649	>	cursor = (cursor + 1) & (elements.length - 1);
650	>	fence = head;
651	>	}
652		lastRet = -1;
585	–	fence = tail;
653		}
654		}
655
#	Line 650 | Line 717 | public class ArrayDeque<E> extends Abstr
717		* <p>The returned array will be "safe" in that no references to it are
718		* maintained by this deque.  (In other words, this method must allocate
719		* a new array).  The caller is thus free to modify the returned array.
720	<	*
720	>	*
721		* <p>This method acts as bridge between array-based and collection-based
722		* APIs.
723		*
#	Line 744 | Line 811 | public class ArrayDeque<E> extends Abstr
811		s.defaultWriteObject();
812
813		// Write out size
814	<	int size = size();
748	<	s.writeInt(size);
814	>	s.writeInt(size());
815
816		// Write out elements in order.
751	–	int i = head;
817		int mask = elements.length - 1;
818	<	for (int j = 0; j < size; j++) {
818	>	for (int i = head; i != tail; i = (i + 1) & mask)
819		s.writeObject(elements[i]);
755	–	i = (i + 1) & mask;
756	–	}
820		}
821
822		/**
#	Line 772 | Line 835 | public class ArrayDeque<E> extends Abstr
835		// Read in all elements in the proper order.
836		for (int i = 0; i < size; i++)
837		elements[i] = (E)s.readObject();
775	–
838		}
839		}

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