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/* |
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* Written by Josh Bloch of Google Inc. and released to the public domain, |
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* as explained at http://creativecommons.org/licenses/publicdomain. |
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* as explained at http://creativecommons.org/publicdomain/zero/1.0/. |
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*/ |
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package java.util; |
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import java.util.*; // for javadoc (till 6280605 is fixed) |
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import java.io.*; |
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/** |
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* Resizable-array implementation of the {@link Deque} interface. Array |
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* Iterator} interfaces. |
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* |
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* <p>This class is a member of the |
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* <a href="{@docRoot}/../guide/collections/index.html"> |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @author Josh Bloch and Doug Lea |
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* @param <E> the type of elements held in this collection |
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*/ |
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public class ArrayDeque<E> extends AbstractCollection<E> |
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implements Deque<E>, Cloneable, Serializable |
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implements Deque<E>, Cloneable, java.io.Serializable |
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{ |
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/** |
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* The array in which the elements of the deque are stored. |
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* other. We also guarantee that all array cells not holding |
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* deque elements are always null. |
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*/ |
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private transient E[] elements; |
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private transient Object[] elements; |
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|
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/** |
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* The index of the element at the head of the deque (which is the |
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// ****** Array allocation and resizing utilities ****** |
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|
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/** |
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* Allocate empty array to hold the given number of elements. |
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* Allocates empty array to hold the given number of elements. |
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* |
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* @param numElements the number of elements to hold |
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*/ |
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if (initialCapacity < 0) // Too many elements, must back off |
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initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements |
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} |
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elements = (E[]) new Object[initialCapacity]; |
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elements = new Object[initialCapacity]; |
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} |
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|
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/** |
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* Double the capacity of this deque. Call only when full, i.e., |
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* Doubles the capacity of this deque. Call only when full, i.e., |
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* when head and tail have wrapped around to become equal. |
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*/ |
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private void doubleCapacity() { |
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Object[] a = new Object[newCapacity]; |
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System.arraycopy(elements, p, a, 0, r); |
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System.arraycopy(elements, 0, a, r, p); |
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elements = (E[])a; |
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elements = a; |
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head = 0; |
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tail = n; |
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} |
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* sufficient to hold 16 elements. |
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*/ |
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public ArrayDeque() { |
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elements = (E[]) new Object[16]; |
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elements = new Object[16]; |
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} |
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|
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/** |
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|
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public E pollFirst() { |
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int h = head; |
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E result = elements[h]; // Element is null if deque empty |
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@SuppressWarnings("unchecked") |
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E result = (E) elements[h]; |
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// Element is null if deque empty |
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if (result == null) |
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return null; |
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elements[h] = null; // Must null out slot |
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|
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public E pollLast() { |
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int t = (tail - 1) & (elements.length - 1); |
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E result = elements[t]; |
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@SuppressWarnings("unchecked") |
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E result = (E) elements[t]; |
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if (result == null) |
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return null; |
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elements[t] = null; |
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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E getFirst() { |
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E x = elements[head]; |
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if (x == null) |
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@SuppressWarnings("unchecked") |
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E result = (E) elements[head]; |
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if (result == null) |
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throw new NoSuchElementException(); |
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return x; |
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return result; |
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} |
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|
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/** |
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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E getLast() { |
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E x = elements[(tail - 1) & (elements.length - 1)]; |
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if (x == null) |
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@SuppressWarnings("unchecked") |
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E result = (E) elements[(tail - 1) & (elements.length - 1)]; |
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if (result == null) |
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throw new NoSuchElementException(); |
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return x; |
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return result; |
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} |
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|
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@SuppressWarnings("unchecked") |
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public E peekFirst() { |
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return elements[head]; // elements[head] is null if deque empty |
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// elements[head] is null if deque empty |
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return (E) elements[head]; |
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} |
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|
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@SuppressWarnings("unchecked") |
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public E peekLast() { |
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return elements[(tail - 1) & (elements.length - 1)]; |
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return (E) elements[(tail - 1) & (elements.length - 1)]; |
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} |
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/** |
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return false; |
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int mask = elements.length - 1; |
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int i = head; |
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E x; |
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Object x; |
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while ( (x = elements[i]) != null) { |
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if (o.equals(x)) { |
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delete(i); |
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return false; |
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int mask = elements.length - 1; |
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int i = (tail - 1) & mask; |
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E x; |
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Object x; |
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while ( (x = elements[i]) != null) { |
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if (o.equals(x)) { |
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delete(i); |
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return removeFirst(); |
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} |
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|
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private void checkInvariants() { |
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assert elements[tail] == null; |
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assert head == tail ? elements[head] == null : |
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(elements[head] != null && |
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elements[(tail - 1) & (elements.length - 1)] != null); |
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assert elements[(head - 1) & (elements.length - 1)] == null; |
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} |
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|
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/** |
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* Removes the element at the specified position in the elements array, |
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* adjusting head and tail as necessary. This can result in motion of |
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* @return true if elements moved backwards |
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*/ |
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private boolean delete(int i) { |
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int mask = elements.length - 1; |
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|
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// Invariant: head <= i < tail mod circularity |
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if (((i - head) & mask) >= ((tail - head) & mask)) |
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throw new ConcurrentModificationException(); |
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|
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// Case 1: Deque doesn't wrap |
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// Case 2: Deque does wrap and removed element is in the head portion |
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if (i >= head) { |
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System.arraycopy(elements, head, elements, head + 1, i - head); |
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elements[head] = null; |
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head = (head + 1) & mask; |
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checkInvariants(); |
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final Object[] elements = this.elements; |
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final int mask = elements.length - 1; |
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final int h = head; |
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final int t = tail; |
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final int front = (i - h) & mask; |
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final int back = (t - i) & mask; |
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|
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// Invariant: head <= i < tail mod circularity |
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if (front >= ((t - h) & mask)) |
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throw new ConcurrentModificationException(); |
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|
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// Optimize for least element motion |
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if (front < back) { |
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if (h <= i) { |
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System.arraycopy(elements, h, elements, h + 1, front); |
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} else { // Wrap around |
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System.arraycopy(elements, 0, elements, 1, i); |
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elements[0] = elements[mask]; |
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System.arraycopy(elements, h, elements, h + 1, mask - h); |
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} |
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elements[h] = null; |
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head = (h + 1) & mask; |
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return false; |
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} else { |
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if (i < t) { // Copy the null tail as well |
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System.arraycopy(elements, i + 1, elements, i, back); |
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tail = t - 1; |
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} else { // Wrap around |
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System.arraycopy(elements, i + 1, elements, i, mask - i); |
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elements[mask] = elements[0]; |
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System.arraycopy(elements, 1, elements, 0, t); |
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tail = (t - 1) & mask; |
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} |
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return true; |
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} |
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|
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// Case 3: Deque wraps and removed element is in the tail portion |
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tail--; |
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System.arraycopy(elements, i + 1, elements, i, tail - i); |
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elements[tail] = null; |
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return true; |
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} |
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|
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// *** Collection Methods *** |
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* order that elements would be dequeued (via successive calls to |
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* {@link #remove} or popped (via successive calls to {@link #pop}). |
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* |
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* @return an <tt>Iterator</tt> over the elements in this deque |
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* @return an iterator over the elements in this deque |
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*/ |
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public Iterator<E> iterator() { |
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return new DeqIterator(); |
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} |
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|
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/** |
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* Returns an iterator over the elements in this deque in reverse |
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* sequential order. The elements will be returned in order from |
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* last (tail) to first (head). |
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* |
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* @return an iterator over the elements in this deque in reverse |
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* sequence |
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*/ |
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public Iterator<E> descendingIterator() { |
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return new DescendingIterator(); |
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} |
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} |
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|
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public E next() { |
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E result; |
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if (cursor == fence) |
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throw new NoSuchElementException(); |
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@SuppressWarnings("unchecked") |
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E result = (E) elements[cursor]; |
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// This check doesn't catch all possible comodifications, |
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// but does catch the ones that corrupt traversal |
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if (tail != fence || (result = elements[cursor]) == null) |
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if (tail != fence || result == null) |
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throw new ConcurrentModificationException(); |
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lastRet = cursor; |
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cursor = (cursor + 1) & (elements.length - 1); |
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public void remove() { |
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if (lastRet < 0) |
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throw new IllegalStateException(); |
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if (delete(lastRet)) // if left-shifted, undo increment in next() |
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if (delete(lastRet)) { // if left-shifted, undo increment in next() |
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cursor = (cursor - 1) & (elements.length - 1); |
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fence = tail; |
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} |
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lastRet = -1; |
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fence = tail; |
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} |
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} |
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|
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|
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private class DescendingIterator implements Iterator<E> { |
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/* |
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/* |
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* This class is nearly a mirror-image of DeqIterator, using |
631 |
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* (tail-1) instead of head for initial cursor, (head-1) |
632 |
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* instead of tail for fence, and elements.length instead of -1 |
610 |
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* for sentinel. It shares the same structure, but not many |
611 |
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* actual lines of code. |
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* tail instead of head for initial cursor, and head instead of |
632 |
> |
* tail for fence. |
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*/ |
634 |
< |
private int cursor = (tail - 1) & (elements.length - 1); |
635 |
< |
private int fence = (head - 1) & (elements.length - 1); |
636 |
< |
private int lastRet = elements.length; |
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> |
private int cursor = tail; |
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> |
private int fence = head; |
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> |
private int lastRet = -1; |
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|
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public boolean hasNext() { |
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return cursor != fence; |
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} |
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|
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public E next() { |
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E result; |
643 |
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if (cursor == fence) |
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throw new NoSuchElementException(); |
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< |
if (((head - 1) & (elements.length - 1)) != fence || |
646 |
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(result = elements[cursor]) == null) |
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> |
cursor = (cursor - 1) & (elements.length - 1); |
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> |
@SuppressWarnings("unchecked") |
647 |
> |
E result = (E) elements[cursor]; |
648 |
> |
if (head != fence || result == null) |
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throw new ConcurrentModificationException(); |
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lastRet = cursor; |
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cursor = (cursor - 1) & (elements.length - 1); |
651 |
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return result; |
652 |
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} |
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|
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public void remove() { |
655 |
< |
if (lastRet >= elements.length) |
655 |
> |
if (lastRet < 0) |
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throw new IllegalStateException(); |
657 |
< |
if (!delete(lastRet)) |
657 |
> |
if (!delete(lastRet)) { |
658 |
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cursor = (cursor + 1) & (elements.length - 1); |
659 |
< |
lastRet = elements.length; |
660 |
< |
fence = (head - 1) & (elements.length - 1); |
659 |
> |
fence = head; |
660 |
> |
} |
661 |
> |
lastRet = -1; |
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} |
663 |
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} |
664 |
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|
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return false; |
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int mask = elements.length - 1; |
677 |
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int i = head; |
678 |
< |
E x; |
678 |
> |
Object x; |
679 |
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while ( (x = elements[i]) != null) { |
680 |
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if (o.equals(x)) |
681 |
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return true; |
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* @return an array containing all of the elements in this deque |
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*/ |
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public Object[] toArray() { |
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return copyElements(new Object[size()]); |
736 |
> |
return copyElements(new Object[size()]); |
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} |
738 |
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|
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/** |
758 |
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* The following code can be used to dump the deque into a newly |
759 |
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* allocated array of <tt>String</tt>: |
760 |
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* |
761 |
< |
* <pre> |
740 |
< |
* String[] y = x.toArray(new String[0]);</pre> |
761 |
> |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
762 |
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* |
763 |
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* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
764 |
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* <tt>toArray()</tt>. |
772 |
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* this deque |
773 |
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* @throws NullPointerException if the specified array is null |
774 |
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*/ |
775 |
+ |
@SuppressWarnings("unchecked") |
776 |
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public <T> T[] toArray(T[] a) { |
777 |
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int size = size(); |
778 |
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if (a.length < size) |
779 |
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a = (T[])java.lang.reflect.Array.newInstance( |
780 |
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a.getClass().getComponentType(), size); |
781 |
< |
copyElements(a); |
781 |
> |
copyElements(a); |
782 |
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if (a.length > size) |
783 |
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a[size] = null; |
784 |
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return a; |
793 |
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*/ |
794 |
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public ArrayDeque<E> clone() { |
795 |
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try { |
796 |
+ |
@SuppressWarnings("unchecked") |
797 |
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ArrayDeque<E> result = (ArrayDeque<E>) super.clone(); |
798 |
< |
// These two lines are currently faster than cloning the array: |
776 |
< |
result.elements = (E[]) new Object[elements.length]; |
777 |
< |
System.arraycopy(elements, 0, result.elements, 0, elements.length); |
798 |
> |
result.elements = Arrays.copyOf(elements, elements.length); |
799 |
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return result; |
779 |
– |
|
800 |
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} catch (CloneNotSupportedException e) { |
801 |
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throw new AssertionError(); |
802 |
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} |
803 |
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} |
804 |
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|
785 |
– |
/** |
786 |
– |
* Appease the serialization gods. |
787 |
– |
*/ |
805 |
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private static final long serialVersionUID = 2340985798034038923L; |
806 |
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|
807 |
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/** |
808 |
< |
* Serialize this deque. |
808 |
> |
* Saves this deque to a stream (that is, serializes it). |
809 |
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* |
810 |
|
* @serialData The current size (<tt>int</tt>) of the deque, |
811 |
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* followed by all of its elements (each an object reference) in |
812 |
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* first-to-last order. |
813 |
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*/ |
814 |
< |
private void writeObject(ObjectOutputStream s) throws IOException { |
814 |
> |
private void writeObject(java.io.ObjectOutputStream s) |
815 |
> |
throws java.io.IOException { |
816 |
|
s.defaultWriteObject(); |
817 |
|
|
818 |
|
// Write out size |
819 |
< |
int size = size(); |
802 |
< |
s.writeInt(size); |
819 |
> |
s.writeInt(size()); |
820 |
|
|
821 |
|
// Write out elements in order. |
805 |
– |
int i = head; |
822 |
|
int mask = elements.length - 1; |
823 |
< |
for (int j = 0; j < size; j++) { |
823 |
> |
for (int i = head; i != tail; i = (i + 1) & mask) |
824 |
|
s.writeObject(elements[i]); |
809 |
– |
i = (i + 1) & mask; |
810 |
– |
} |
825 |
|
} |
826 |
|
|
827 |
|
/** |
828 |
< |
* Deserialize this deque. |
828 |
> |
* Reconstitutes this deque from a stream (that is, deserializes it). |
829 |
|
*/ |
830 |
< |
private void readObject(ObjectInputStream s) |
831 |
< |
throws IOException, ClassNotFoundException { |
830 |
> |
private void readObject(java.io.ObjectInputStream s) |
831 |
> |
throws java.io.IOException, ClassNotFoundException { |
832 |
|
s.defaultReadObject(); |
833 |
|
|
834 |
|
// Read in size and allocate array |
839 |
|
|
840 |
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// Read in all elements in the proper order. |
841 |
|
for (int i = 0; i < size; i++) |
842 |
< |
elements[i] = (E)s.readObject(); |
829 |
< |
|
842 |
> |
elements[i] = s.readObject(); |
843 |
|
} |
844 |
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} |