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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.io.*; |
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/** |
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* Resizable-array implementation of the {@link Deque} interface. Array |
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* {@link Stack} when used as a stack, and faster than {@link LinkedList} |
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* when used as a queue. |
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* |
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* <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time. |
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* Exceptions include {@link #remove(Object) remove}, {@link |
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* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence |
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* removeLastOccurrence}, {@link #contains contains}, {@link #iterator |
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* iterator.remove()}, and the bulk operations, all of which run in linear |
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* time. |
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* <p>Most {@code ArrayDeque} operations run in amortized constant time. |
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* Exceptions include |
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* {@link #remove(Object) remove}, |
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* {@link #removeFirstOccurrence removeFirstOccurrence}, |
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* {@link #removeLastOccurrence removeLastOccurrence}, |
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* {@link #contains contains}, |
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* {@link #iterator iterator.remove()}, |
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* and the bulk operations, all of which run in linear time. |
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* |
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* <p>The iterators returned by this class's <tt>iterator</tt> method are |
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* <i>fail-fast</i>: If the deque is modified at any time after the iterator |
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* is created, in any way except through the iterator's own <tt>remove</tt> |
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* method, the iterator will generally throw a {@link |
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* <p>The iterators returned by this class's {@link #iterator() iterator} |
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* method are <em>fail-fast</em>: If the deque is modified at any time after |
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* the iterator is created, in any way except through the iterator's own |
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* {@code remove} method, the iterator will generally throw a {@link |
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* ConcurrentModificationException}. Thus, in the face of concurrent |
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* modification, the iterator fails quickly and cleanly, rather than risking |
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* arbitrary, non-deterministic behavior at an undetermined time in the |
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* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed |
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* as it is, generally speaking, impossible to make any hard guarantees in the |
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* presence of unsynchronized concurrent modification. Fail-fast iterators |
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* throw <tt>ConcurrentModificationException</tt> on a best-effort basis. |
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* throw {@code ConcurrentModificationException} on a best-effort basis. |
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* Therefore, it would be wrong to write a program that depended on this |
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* exception for its correctness: <i>the fail-fast behavior of iterators |
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* should be used only to detect bugs.</i> |
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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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* 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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* 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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* 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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* Inserts the specified element at the front of this deque. |
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* |
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* @param e the element to add |
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* @return <tt>true</tt> (as specified by {@link Deque#offerFirst}) |
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* @return {@code true} (as specified by {@link Deque#offerFirst}) |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public boolean offerFirst(E e) { |
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* Inserts the specified element at the end of this deque. |
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* |
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* @param e the element to add |
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* @return <tt>true</tt> (as specified by {@link Deque#offerLast}) |
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* @return {@code true} (as specified by {@link Deque#offerLast}) |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public boolean offerLast(E e) { |
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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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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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* @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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+ |
@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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+ |
@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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/** |
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* Removes the first occurrence of the specified element in this |
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* deque (when traversing the deque from head to tail). |
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* If the deque does not contain the element, it is unchanged. |
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< |
* More formally, removes the first element <tt>e</tt> such that |
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* <tt>o.equals(e)</tt> (if such an element exists). |
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* Returns <tt>true</tt> if this deque contained the specified element |
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* More formally, removes the first element {@code e} such that |
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* {@code o.equals(e)} (if such an element exists). |
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> |
* Returns {@code true} if this deque contained the specified element |
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* (or equivalently, if this deque changed as a result of the call). |
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* |
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* @param o element to be removed from this deque, if present |
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* @return <tt>true</tt> if the deque contained the specified element |
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* @return {@code true} if the deque contained the specified element |
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*/ |
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public boolean removeFirstOccurrence(Object o) { |
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if (o == null) |
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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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* Removes the last occurrence of the specified element in this |
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* deque (when traversing the deque from head to tail). |
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* If the deque does not contain the element, it is unchanged. |
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< |
* More formally, removes the last element <tt>e</tt> such that |
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* <tt>o.equals(e)</tt> (if such an element exists). |
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< |
* Returns <tt>true</tt> if this deque contained the specified element |
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> |
* More formally, removes the last element {@code e} such that |
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* {@code o.equals(e)} (if such an element exists). |
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> |
* Returns {@code true} if this deque contained the specified element |
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* (or equivalently, if this deque changed as a result of the call). |
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* |
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* @param o element to be removed from this deque, if present |
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< |
* @return <tt>true</tt> if the deque contained the specified element |
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> |
* @return {@code true} if the deque contained the specified element |
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*/ |
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public boolean removeLastOccurrence(Object o) { |
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if (o == null) |
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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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* <p>This method is equivalent to {@link #addLast}. |
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* |
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* @param e the element to add |
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< |
* @return <tt>true</tt> (as specified by {@link Collection#add}) |
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> |
* @return {@code true} (as specified by {@link Collection#add}) |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public boolean add(E e) { |
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* <p>This method is equivalent to {@link #offerLast}. |
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* |
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* @param e the element to add |
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< |
* @return <tt>true</tt> (as specified by {@link Queue#offer}) |
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> |
* @return {@code true} (as specified by {@link Queue#offer}) |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public boolean offer(E e) { |
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/** |
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* Retrieves and removes the head of the queue represented by this deque |
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* (in other words, the first element of this deque), or returns |
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< |
* <tt>null</tt> if this deque is empty. |
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> |
* {@code null} if this deque is empty. |
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* |
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* <p>This method is equivalent to {@link #pollFirst}. |
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* |
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* @return the head of the queue represented by this deque, or |
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< |
* <tt>null</tt> if this deque is empty |
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> |
* {@code null} if this deque is empty |
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*/ |
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public E poll() { |
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return pollFirst(); |
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|
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/** |
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* Retrieves, but does not remove, the head of the queue represented by |
| 450 |
< |
* this deque, or returns <tt>null</tt> if this deque is empty. |
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> |
* this deque, or returns {@code null} if this deque is empty. |
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* |
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* <p>This method is equivalent to {@link #peekFirst}. |
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* |
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* @return the head of the queue represented by this deque, or |
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< |
* <tt>null</tt> if this deque is empty |
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> |
* {@code null} if this deque is empty |
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*/ |
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public E peek() { |
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return peekFirst(); |
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*/ |
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private boolean delete(int i) { |
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checkInvariants(); |
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< |
final E[] elements = this.elements; |
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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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} |
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|
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/** |
| 559 |
< |
* Returns <tt>true</tt> if this deque contains no elements. |
| 559 |
> |
* Returns {@code true} if this deque contains no elements. |
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* |
| 561 |
< |
* @return <tt>true</tt> if this deque contains no elements |
| 561 |
> |
* @return {@code true} if this deque contains no elements |
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*/ |
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public boolean isEmpty() { |
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return head == tail; |
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public E next() { |
| 606 |
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if (cursor == fence) |
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throw new NoSuchElementException(); |
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< |
E result = elements[cursor]; |
| 608 |
> |
@SuppressWarnings("unchecked") |
| 609 |
> |
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 == null) |
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if (cursor == fence) |
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throw new NoSuchElementException(); |
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cursor = (cursor - 1) & (elements.length - 1); |
| 648 |
< |
E result = elements[cursor]; |
| 648 |
> |
@SuppressWarnings("unchecked") |
| 649 |
> |
E result = (E) elements[cursor]; |
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if (head != fence || result == null) |
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throw new ConcurrentModificationException(); |
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lastRet = cursor; |
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} |
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|
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/** |
| 668 |
< |
* Returns <tt>true</tt> if this deque contains the specified element. |
| 669 |
< |
* More formally, returns <tt>true</tt> if and only if this deque contains |
| 670 |
< |
* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>. |
| 668 |
> |
* Returns {@code true} if this deque contains the specified element. |
| 669 |
> |
* More formally, returns {@code true} if and only if this deque contains |
| 670 |
> |
* at least one element {@code e} such that {@code o.equals(e)}. |
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* |
| 672 |
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* @param o object to be checked for containment in this deque |
| 673 |
< |
* @return <tt>true</tt> if this deque contains the specified element |
| 673 |
> |
* @return {@code true} if this deque contains the specified element |
| 674 |
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*/ |
| 675 |
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public boolean contains(Object o) { |
| 676 |
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if (o == null) |
| 677 |
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return false; |
| 678 |
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int mask = elements.length - 1; |
| 679 |
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int i = head; |
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< |
E x; |
| 680 |
> |
Object x; |
| 681 |
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while ( (x = elements[i]) != null) { |
| 682 |
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if (o.equals(x)) |
| 683 |
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return true; |
| 689 |
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/** |
| 690 |
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* Removes a single instance of the specified element from this deque. |
| 691 |
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* If the deque does not contain the element, it is unchanged. |
| 692 |
< |
* More formally, removes the first element <tt>e</tt> such that |
| 693 |
< |
* <tt>o.equals(e)</tt> (if such an element exists). |
| 694 |
< |
* Returns <tt>true</tt> if this deque contained the specified element |
| 692 |
> |
* More formally, removes the first element {@code e} such that |
| 693 |
> |
* {@code o.equals(e)} (if such an element exists). |
| 694 |
> |
* Returns {@code true} if this deque contained the specified element |
| 695 |
|
* (or equivalently, if this deque changed as a result of the call). |
| 696 |
|
* |
| 697 |
|
* <p>This method is equivalent to {@link #removeFirstOccurrence}. |
| 698 |
|
* |
| 699 |
|
* @param o element to be removed from this deque, if present |
| 700 |
< |
* @return <tt>true</tt> if this deque contained the specified element |
| 700 |
> |
* @return {@code true} if this deque contained the specified element |
| 701 |
|
*/ |
| 702 |
|
public boolean remove(Object o) { |
| 703 |
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return removeFirstOccurrence(o); |
| 749 |
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* <p>If this deque fits in the specified array with room to spare |
| 750 |
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* (i.e., the array has more elements than this deque), the element in |
| 751 |
|
* the array immediately following the end of the deque is set to |
| 752 |
< |
* <tt>null</tt>. |
| 752 |
> |
* {@code null}. |
| 753 |
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* |
| 754 |
|
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
| 755 |
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* array-based and collection-based APIs. Further, this method allows |
| 756 |
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* precise control over the runtime type of the output array, and may, |
| 757 |
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* under certain circumstances, be used to save allocation costs. |
| 758 |
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* |
| 759 |
< |
* <p>Suppose <tt>x</tt> is a deque known to contain only strings. |
| 759 |
> |
* <p>Suppose {@code x} is a deque known to contain only strings. |
| 760 |
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* The following code can be used to dump the deque into a newly |
| 761 |
< |
* allocated array of <tt>String</tt>: |
| 761 |
> |
* allocated array of {@code String}: |
| 762 |
|
* |
| 763 |
< |
* <pre> |
| 753 |
< |
* String[] y = x.toArray(new String[0]);</pre> |
| 763 |
> |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
| 764 |
|
* |
| 765 |
< |
* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
| 766 |
< |
* <tt>toArray()</tt>. |
| 765 |
> |
* Note that {@code toArray(new Object[0])} is identical in function to |
| 766 |
> |
* {@code toArray()}. |
| 767 |
|
* |
| 768 |
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* @param a the array into which the elements of the deque are to |
| 769 |
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* be stored, if it is big enough; otherwise, a new array of the |
| 774 |
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* this deque |
| 775 |
|
* @throws NullPointerException if the specified array is null |
| 776 |
|
*/ |
| 777 |
+ |
@SuppressWarnings("unchecked") |
| 778 |
|
public <T> T[] toArray(T[] a) { |
| 779 |
|
int size = size(); |
| 780 |
|
if (a.length < size) |
| 795 |
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*/ |
| 796 |
|
public ArrayDeque<E> clone() { |
| 797 |
|
try { |
| 798 |
+ |
@SuppressWarnings("unchecked") |
| 799 |
|
ArrayDeque<E> result = (ArrayDeque<E>) super.clone(); |
| 800 |
|
result.elements = Arrays.copyOf(elements, elements.length); |
| 801 |
|
return result; |
| 790 |
– |
|
| 802 |
|
} catch (CloneNotSupportedException e) { |
| 803 |
|
throw new AssertionError(); |
| 804 |
|
} |
| 805 |
|
} |
| 806 |
|
|
| 796 |
– |
/** |
| 797 |
– |
* Appease the serialization gods. |
| 798 |
– |
*/ |
| 807 |
|
private static final long serialVersionUID = 2340985798034038923L; |
| 808 |
|
|
| 809 |
|
/** |
| 810 |
< |
* Serialize this deque. |
| 810 |
> |
* Saves this deque to a stream (that is, serializes it). |
| 811 |
|
* |
| 812 |
< |
* @serialData The current size (<tt>int</tt>) of the deque, |
| 812 |
> |
* @serialData The current size ({@code int}) of the deque, |
| 813 |
|
* followed by all of its elements (each an object reference) in |
| 814 |
|
* first-to-last order. |
| 815 |
|
*/ |
| 816 |
< |
private void writeObject(ObjectOutputStream s) throws IOException { |
| 816 |
> |
private void writeObject(java.io.ObjectOutputStream s) |
| 817 |
> |
throws java.io.IOException { |
| 818 |
|
s.defaultWriteObject(); |
| 819 |
|
|
| 820 |
|
// Write out size |
| 827 |
|
} |
| 828 |
|
|
| 829 |
|
/** |
| 830 |
< |
* Deserialize this deque. |
| 830 |
> |
* Reconstitutes this deque from a stream (that is, deserializes it). |
| 831 |
|
*/ |
| 832 |
< |
private void readObject(ObjectInputStream s) |
| 833 |
< |
throws IOException, ClassNotFoundException { |
| 832 |
> |
private void readObject(java.io.ObjectInputStream s) |
| 833 |
> |
throws java.io.IOException, ClassNotFoundException { |
| 834 |
|
s.defaultReadObject(); |
| 835 |
|
|
| 836 |
|
// Read in size and allocate array |
| 841 |
|
|
| 842 |
|
// Read in all elements in the proper order. |
| 843 |
|
for (int i = 0; i < size; i++) |
| 844 |
< |
elements[i] = (E)s.readObject(); |
| 844 |
> |
elements[i] = s.readObject(); |
| 845 |
|
} |
| 846 |
|
} |
