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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 1.33 by jsr166, Fri Jun 10 00:20:44 2011 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		/**
9		* Resizable-array implementation of the {@link Deque} interface.  Array
#	Line 44 | Line 43 | import java.io.*;
43		* Iterator} interfaces.
44		*
45		* <p>This class is a member of the
46	<	* <a href="{@docRoot}/../guide/collections/index.html">
46	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
47		* Java Collections Framework</a>.
48		*
49		* @author  Josh Bloch and Doug Lea
#	Line 52 | Line 51 | import java.io.*;
51		* @param <E> the type of elements held in this collection
52		*/
53		public class ArrayDeque<E> extends AbstractCollection<E>
54	<	implements Deque<E>, Cloneable, Serializable
54	>	implements Deque<E>, Cloneable, java.io.Serializable
55		{
56		/**
57		* The array in which the elements of the deque are stored.
#	Line 202 | Line 201 | public class ArrayDeque<E> extends Abstr
201
202		/**
203		* Inserts the specified element at the end of this deque.
204	<	* This method is equivalent to {@link #add} and {@link #push}.
204	>	*
205	>	* <p>This method is equivalent to {@link #add}.
206		*
207		* @param e the element to add
208		* @throws NullPointerException if the specified element is null
#	Line 219 | Line 219 | public class ArrayDeque<E> extends Abstr
219		* Inserts the specified element at the front of this deque.
220		*
221		* @param e the element to add
222	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst})
222	>	* @return <tt>true</tt> (as specified by {@link Deque#offerFirst})
223		* @throws NullPointerException if the specified element is null
224		*/
225		public boolean offerFirst(E e) {
#	Line 231 | Line 231 | public class ArrayDeque<E> extends Abstr
231		* Inserts the specified element at the end of this deque.
232		*
233		* @param e the element to add
234	<	* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast})
234	>	* @return <tt>true</tt> (as specified by {@link Deque#offerLast})
235		* @throws NullPointerException if the specified element is null
236		*/
237		public boolean offerLast(E e) {
#	Line 371 | Line 371 | public class ArrayDeque<E> extends Abstr
371		* <p>This method is equivalent to {@link #addLast}.
372		*
373		* @param e the element to add
374	<	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
374	>	* @return <tt>true</tt> (as specified by {@link Collection#add})
375		* @throws NullPointerException if the specified element is null
376		*/
377		public boolean add(E e) {
#	Line 385 | Line 385 | public class ArrayDeque<E> extends Abstr
385		* <p>This method is equivalent to {@link #offerLast}.
386		*
387		* @param e the element to add
388	<	* @return <tt>true</tt> (as per the spec for {@link Queue#offer})
388	>	* @return <tt>true</tt> (as specified by {@link Queue#offer})
389		* @throws NullPointerException if the specified element is null
390		*/
391		public boolean offer(E e) {
#	Line 394 | Line 394 | public class ArrayDeque<E> extends Abstr
394
395		/**
396		* Retrieves and removes the head of the queue represented by this deque.
397	<	* This method differs from {@link #poll} only in that it throws an
397	>	*
398	>	* This method differs from {@link #poll poll} only in that it throws an
399		* exception if this deque is empty.
400		*
401		* <p>This method is equivalent to {@link #removeFirst}.
#	Line 422 | Line 423 | public class ArrayDeque<E> extends Abstr
423
424		/**
425		* Retrieves, but does not remove, the head of the queue represented by
426	<	* this deque.  This method differs from {@link #peek} only in that it
427	<	* throws an exception if this deque is empty.
426	>	* this deque.  This method differs from {@link #peek peek} only in
427	>	* that it throws an exception if this deque is empty.
428		*
429		* <p>This method is equivalent to {@link #getFirst}.
430		*
#	Line 476 | Line 477 | public class ArrayDeque<E> extends Abstr
477		return removeFirst();
478		}
479
480	+	private void checkInvariants() {
481	+	assert elements[tail] == null;
482	+	assert head == tail ? elements[head] == null :
483	+	(elements[head] != null &&
484	+	elements[(tail - 1) & (elements.length - 1)] != null);
485	+	assert elements[(head - 1) & (elements.length - 1)] == null;
486	+	}
487	+
488		/**
489		* Removes the element at the specified position in the elements array,
490		* adjusting head and tail as necessary.  This can result in motion of
#	Line 487 | Line 496 | public class ArrayDeque<E> extends Abstr
496		* @return true if elements moved backwards
497		*/
498		private boolean delete(int i) {
499	<	int mask = elements.length - 1;
500	<
501	<	// Invariant: head <= i < tail mod circularity
502	<	if (((i - head) & mask) >= ((tail - head) & mask))
503	<	throw new ConcurrentModificationException();
504	<
505	<	// Case 1: Deque doesn't wrap
506	<	// Case 2: Deque does wrap and removed element is in the head portion
507	<	if (i >= head) {
508	<	System.arraycopy(elements, head, elements, head + 1, i - head);
509	<	elements[head] = null;
510	<	head = (head + 1) & mask;
499	>	checkInvariants();
500	>	final E[] elements = this.elements;
501	>	final int mask = elements.length - 1;
502	>	final int h = head;
503	>	final int t = tail;
504	>	final int front = (i - h) & mask;
505	>	final int back  = (t - i) & mask;
506	>
507	>	// Invariant: head <= i < tail mod circularity
508	>	if (front >= ((t - h) & mask))
509	>	throw new ConcurrentModificationException();
510	>
511	>	// Optimize for least element motion
512	>	if (front < back) {
513	>	if (h <= i) {
514	>	System.arraycopy(elements, h, elements, h + 1, front);
515	>	} else { // Wrap around
516	>	System.arraycopy(elements, 0, elements, 1, i);
517	>	elements[0] = elements[mask];
518	>	System.arraycopy(elements, h, elements, h + 1, mask - h);
519	>	}
520	>	elements[h] = null;
521	>	head = (h + 1) & mask;
522		return false;
523	+	} else {
524	+	if (i < t) { // Copy the null tail as well
525	+	System.arraycopy(elements, i + 1, elements, i, back);
526	+	tail = t - 1;
527	+	} else { // Wrap around
528	+	System.arraycopy(elements, i + 1, elements, i, mask - i);
529	+	elements[mask] = elements[0];
530	+	System.arraycopy(elements, 1, elements, 0, t);
531	+	tail = (t - 1) & mask;
532	+	}
533	+	return true;
534		}
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;
535		}
536
537		// *** Collection Methods ***
#	Line 535 | Line 560 | public class ArrayDeque<E> extends Abstr
560		* order that elements would be dequeued (via successive calls to
561		* {@link #remove} or popped (via successive calls to {@link #pop}).
562		*
563	<	* @return an <tt>Iterator</tt> over the elements in this deque
563	>	* @return an iterator over the elements in this deque
564		*/
565		public Iterator<E> iterator() {
566		return new DeqIterator();
567		}
568
569	+	public Iterator<E> descendingIterator() {
570	+	return new DescendingIterator();
571	+	}
572	+
573		private class DeqIterator implements Iterator<E> {
574		/**
575		* Index of element to be returned by subsequent call to next.
#	Line 564 | Line 593 | public class ArrayDeque<E> extends Abstr
593		}
594
595		public E next() {
567	–	E result;
596		if (cursor == fence)
597		throw new NoSuchElementException();
598	+	E result = elements[cursor];
599		// This check doesn't catch all possible comodifications,
600		// but does catch the ones that corrupt traversal
601	<	if (tail != fence || (result = elements[cursor]) == null)
601	>	if (tail != fence || result == null)
602		throw new ConcurrentModificationException();
603		lastRet = cursor;
604		cursor = (cursor + 1) & (elements.length - 1);
#	Line 579 | Line 608 | public class ArrayDeque<E> extends Abstr
608		public void remove() {
609		if (lastRet < 0)
610		throw new IllegalStateException();
611	<	if (delete(lastRet))
612	<	cursor--;
611	>	if (delete(lastRet)) { // if left-shifted, undo increment in next()
612	>	cursor = (cursor - 1) & (elements.length - 1);
613	>	fence = tail;
614	>	}
615	>	lastRet = -1;
616	>	}
617	>	}
618	>
619	>	private class DescendingIterator implements Iterator<E> {
620	>	/*
621	>	* This class is nearly a mirror-image of DeqIterator, using
622	>	* tail instead of head for initial cursor, and head instead of
623	>	* tail for fence.
624	>	*/
625	>	private int cursor = tail;
626	>	private int fence = head;
627	>	private int lastRet = -1;
628	>
629	>	public boolean hasNext() {
630	>	return cursor != fence;
631	>	}
632	>
633	>	public E next() {
634	>	if (cursor == fence)
635	>	throw new NoSuchElementException();
636	>	cursor = (cursor - 1) & (elements.length - 1);
637	>	E result = elements[cursor];
638	>	if (head != fence || result == null)
639	>	throw new ConcurrentModificationException();
640	>	lastRet = cursor;
641	>	return result;
642	>	}
643	>
644	>	public void remove() {
645	>	if (lastRet < 0)
646	>	throw new IllegalStateException();
647	>	if (!delete(lastRet)) {
648	>	cursor = (cursor + 1) & (elements.length - 1);
649	>	fence = head;
650	>	}
651		lastRet = -1;
585	–	fence = tail;
652		}
653		}
654
#	Line 650 | Line 716 | public class ArrayDeque<E> extends Abstr
716		* <p>The returned array will be "safe" in that no references to it are
717		* maintained by this deque.  (In other words, this method must allocate
718		* a new array).  The caller is thus free to modify the returned array.
719	<	*
719	>	*
720		* <p>This method acts as bridge between array-based and collection-based
721		* APIs.
722		*
723		* @return an array containing all of the elements in this deque
724		*/
725		public Object[] toArray() {
726	<	return copyElements(new Object[size()]);
726	>	return copyElements(new Object[size()]);
727		}
728
729		/**
#	Line 682 | Line 748 | public class ArrayDeque<E> extends Abstr
748		* The following code can be used to dump the deque into a newly
749		* allocated array of <tt>String</tt>:
750		*
751	<	* <pre>
686	<	*     String[] y = x.toArray(new String[0]);</pre>
751	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
752		*
753		* Note that <tt>toArray(new Object[0])</tt> is identical in function to
754		* <tt>toArray()</tt>.
#	Line 702 | Line 767 | public class ArrayDeque<E> extends Abstr
767		if (a.length < size)
768		a = (T[])java.lang.reflect.Array.newInstance(
769		a.getClass().getComponentType(), size);
770	<	copyElements(a);
770	>	copyElements(a);
771		if (a.length > size)
772		a[size] = null;
773		return a;
#	Line 718 | Line 783 | public class ArrayDeque<E> extends Abstr
783		public ArrayDeque<E> clone() {
784		try {
785		ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
786	<	// 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);
786	>	result.elements = Arrays.copyOf(elements, elements.length);
787		return result;
788
789		} catch (CloneNotSupportedException e) {
#	Line 740 | Line 803 | public class ArrayDeque<E> extends Abstr
803		* followed by all of its elements (each an object reference) in
804		* first-to-last order.
805		*/
806	<	private void writeObject(ObjectOutputStream s) throws IOException {
806	>	private void writeObject(java.io.ObjectOutputStream s)
807	>	throws java.io.IOException {
808		s.defaultWriteObject();
809
810		// Write out size
811	<	int size = size();
748	<	s.writeInt(size);
811	>	s.writeInt(size());
812
813		// Write out elements in order.
751	–	int i = head;
814		int mask = elements.length - 1;
815	<	for (int j = 0; j < size; j++) {
815	>	for (int i = head; i != tail; i = (i + 1) & mask)
816		s.writeObject(elements[i]);
755	–	i = (i + 1) & mask;
756	–	}
817		}
818
819		/**
820		* Deserialize this deque.
821		*/
822	<	private void readObject(ObjectInputStream s)
823	<	throws IOException, ClassNotFoundException {
822	>	private void readObject(java.io.ObjectInputStream s)
823	>	throws java.io.IOException, ClassNotFoundException {
824		s.defaultReadObject();
825
826		// Read in size and allocate array
#	Line 772 | Line 832 | public class ArrayDeque<E> extends Abstr
832		// Read in all elements in the proper order.
833		for (int i = 0; i < size; i++)
834		elements[i] = (E)s.readObject();
775	–
835		}
836		}

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