| 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 |
| 837 |
|
// Read in all elements in the proper order. |
| 838 |
|
for (int i = 0; i < size; i++) |
| 839 |
|
elements[i] = (E)s.readObject(); |
| 817 |
– |
|
| 840 |
|
} |
| 841 |
|
} |
