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 *** |
617 |
|
} |
618 |
|
} |
619 |
|
|
596 |
– |
|
620 |
|
private class DescendingIterator implements Iterator<E> { |
621 |
|
/* |
622 |
|
* This class is nearly a mirror-image of DeqIterator, using |
813 |
|
s.defaultWriteObject(); |
814 |
|
|
815 |
|
// Write out size |
816 |
< |
int size = size(); |
794 |
< |
s.writeInt(size); |
816 |
> |
s.writeInt(size()); |
817 |
|
|
818 |
|
// Write out elements in order. |
797 |
– |
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]); |
801 |
– |
i = (i + 1) & mask; |
802 |
– |
} |
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(); |
821 |
– |
|
840 |
|
} |
841 |
|
} |