| 479 |
|
return removeFirst(); |
| 480 |
|
} |
| 481 |
|
|
| 482 |
+ |
private void checkInvariants() { |
| 483 |
+ |
assert elements[tail] == null; |
| 484 |
+ |
assert head == tail ? elements[head] == null : |
| 485 |
+ |
(elements[head] != null && |
| 486 |
+ |
elements[(tail - 1) & (elements.length - 1)] != null); |
| 487 |
+ |
assert elements[(head - 1) & (elements.length - 1)] == null; |
| 488 |
+ |
} |
| 489 |
+ |
|
| 490 |
|
/** |
| 491 |
|
* Removes the element at the specified position in the elements array, |
| 492 |
|
* adjusting head and tail as necessary. This can result in motion of |
| 498 |
|
* @return true if elements moved backwards |
| 499 |
|
*/ |
| 500 |
|
private boolean delete(int i) { |
| 501 |
< |
int mask = elements.length - 1; |
| 501 |
> |
checkInvariants(); |
| 502 |
> |
final E[] elements = this.elements; |
| 503 |
> |
final int mask = elements.length - 1; |
| 504 |
> |
final int h = head; |
| 505 |
> |
final int t = tail; |
| 506 |
> |
final int front = (i - h) & mask; |
| 507 |
> |
final int back = (t - i) & mask; |
| 508 |
|
|
| 509 |
|
// Invariant: head <= i < tail mod circularity |
| 510 |
< |
if (((i - head) & mask) >= ((tail - head) & mask)) |
| 510 |
> |
if (front >= ((t - h) & mask)) |
| 511 |
|
throw new ConcurrentModificationException(); |
| 512 |
|
|
| 513 |
< |
// Case 1: Deque doesn't wrap |
| 514 |
< |
// Case 2: Deque does wrap and removed element is in the head portion |
| 515 |
< |
if (i >= head) { |
| 516 |
< |
System.arraycopy(elements, head, elements, head + 1, i - head); |
| 517 |
< |
elements[head] = null; |
| 518 |
< |
head = (head + 1) & mask; |
| 519 |
< |
return false; |
| 520 |
< |
} |
| 521 |
< |
|
| 522 |
< |
// Case 3: Deque wraps and removed element is in the tail portion |
| 523 |
< |
tail--; |
| 524 |
< |
System.arraycopy(elements, i + 1, elements, i, tail - i); |
| 525 |
< |
elements[tail] = null; |
| 526 |
< |
return true; |
| 513 |
> |
// Optimize for least element motion |
| 514 |
> |
if (front < back) { |
| 515 |
> |
if (h <= i) { |
| 516 |
> |
System.arraycopy(elements, h, elements, h + 1, front); |
| 517 |
> |
} else { // Wrap around |
| 518 |
> |
System.arraycopy(elements, 0, elements, 1, i); |
| 519 |
> |
elements[0] = elements[mask]; |
| 520 |
> |
System.arraycopy(elements, h, elements, h + 1, mask - h); |
| 521 |
> |
} |
| 522 |
> |
elements[h] = null; |
| 523 |
> |
head = (h + 1) & mask; |
| 524 |
> |
return false; |
| 525 |
> |
} else { |
| 526 |
> |
if (i < t) { // Copy the null tail as well |
| 527 |
> |
System.arraycopy(elements, i + 1, elements, i, back); |
| 528 |
> |
tail = t - 1; |
| 529 |
> |
} else { // Wrap around |
| 530 |
> |
System.arraycopy(elements, i + 1, elements, i, mask - i); |
| 531 |
> |
elements[mask] = elements[0]; |
| 532 |
> |
System.arraycopy(elements, 1, elements, 0, t); |
| 533 |
> |
tail = (t - 1) & mask; |
| 534 |
> |
} |
| 535 |
> |
return true; |
| 536 |
> |
} |
| 537 |
|
} |
| 538 |
|
|
| 539 |
|
// *** Collection Methods *** |
| 562 |
|
* order that elements would be dequeued (via successive calls to |
| 563 |
|
* {@link #remove} or popped (via successive calls to {@link #pop}). |
| 564 |
|
* |
| 565 |
< |
* @return an <tt>Iterator</tt> over the elements in this deque |
| 565 |
> |
* @return an iterator over the elements in this deque |
| 566 |
|
*/ |
| 567 |
|
public Iterator<E> iterator() { |
| 568 |
|
return new DeqIterator(); |
| 569 |
|
} |
| 570 |
|
|
| 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 |
– |
*/ |
| 571 |
|
public Iterator<E> descendingIterator() { |
| 572 |
|
return new DescendingIterator(); |
| 573 |
|
} |
| 617 |
|
} |
| 618 |
|
} |
| 619 |
|
|
| 604 |
– |
|
| 620 |
|
private class DescendingIterator implements Iterator<E> { |
| 621 |
< |
/* |
| 621 |
> |
/* |
| 622 |
|
* This class is nearly a mirror-image of DeqIterator, using |
| 623 |
|
* (tail-1) instead of head for initial cursor, (head-1) |
| 624 |
|
* instead of tail for fence, and elements.length instead of -1 |
| 637 |
|
E result; |
| 638 |
|
if (cursor == fence) |
| 639 |
|
throw new NoSuchElementException(); |
| 640 |
< |
if (((head - 1) & (elements.length - 1)) != fence || |
| 640 |
> |
if (((head - 1) & (elements.length - 1)) != fence || |
| 641 |
|
(result = elements[cursor]) == null) |
| 642 |
|
throw new ConcurrentModificationException(); |
| 643 |
|
lastRet = cursor; |
| 648 |
|
public void remove() { |
| 649 |
|
if (lastRet >= elements.length) |
| 650 |
|
throw new IllegalStateException(); |
| 651 |
< |
if (!delete(lastRet)) |
| 651 |
> |
if (!delete(lastRet)) |
| 652 |
|
cursor = (cursor + 1) & (elements.length - 1); |
| 653 |
|
lastRet = elements.length; |
| 654 |
|
fence = (head - 1) & (elements.length - 1); |
| 813 |
|
s.defaultWriteObject(); |
| 814 |
|
|
| 815 |
|
// Write out size |
| 816 |
< |
int size = size(); |
| 802 |
< |
s.writeInt(size); |
| 816 |
> |
s.writeInt(size()); |
| 817 |
|
|
| 818 |
|
// Write out elements in order. |
| 805 |
– |
int i = head; |
| 819 |
|
int mask = elements.length - 1; |
| 820 |
< |
for (int j = 0; j < size; j++) { |
| 820 |
> |
for (int i = head; i != tail; i = (i + 1) & mask) |
| 821 |
|
s.writeObject(elements[i]); |
| 809 |
– |
i = (i + 1) & mask; |
| 810 |
– |
} |
| 822 |
|
} |
| 823 |
|
|
| 824 |
|
/** |
| 837 |
|
// Read in all elements in the proper order. |
| 838 |
|
for (int i = 0; i < size; i++) |
| 839 |
|
elements[i] = (E)s.readObject(); |
| 829 |
– |
|
| 840 |
|
} |
| 841 |
|
} |
