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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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* 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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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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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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* Inserts the specified element at the end of this deque. |
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* This method is equivalent to {@link #add} and {@link #push}. |
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* |
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* <p>This method is equivalent to {@link #add}. |
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* |
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* @param e the element to add |
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* @throws NullPointerException if the specified element is null |
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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 per the spec for {@link Deque#offerFirst}) |
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* @return <tt>true</tt> (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 per the spec for {@link Deque#offerLast}) |
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* @return <tt>true</tt> (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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|
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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") 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") 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") 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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|
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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 |
307 |
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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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/** |
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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 true if this deque contained the specified element (or |
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* equivalently, if this deque changed as a result of the call). |
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* Returns <tt>true</tt> 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 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) { |
334 |
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if (o.equals(x)) { |
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delete(i); |
346 |
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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). |
349 |
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* Returns true if this deque contained the specified element (or |
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* equivalently, if this deque changed as a result of the call). |
349 |
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* Returns <tt>true</tt> if this deque contained the specified element |
350 |
> |
* (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 false; |
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int mask = elements.length - 1; |
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int i = (tail - 1) & mask; |
360 |
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E x; |
360 |
> |
Object x; |
361 |
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while ( (x = elements[i]) != null) { |
362 |
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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}. |
377 |
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* |
378 |
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* @param e the element to add |
379 |
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* @return <tt>true</tt> (as per the spec for {@link Collection#add}) |
379 |
> |
* @return <tt>true</tt> (as specified by {@link Collection#add}) |
380 |
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* @throws NullPointerException if the specified element is null |
381 |
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*/ |
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public boolean add(E e) { |
390 |
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* <p>This method is equivalent to {@link #offerLast}. |
391 |
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* |
392 |
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* @param e the element to add |
393 |
< |
* @return <tt>true</tt> (as per the spec for {@link Queue#offer}) |
393 |
> |
* @return <tt>true</tt> (as specified by {@link Queue#offer}) |
394 |
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* @throws NullPointerException if the specified element is null |
395 |
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*/ |
396 |
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public boolean offer(E e) { |
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|
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/** |
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* Retrieves and removes the head of the queue represented by this deque. |
402 |
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* This method differs from {@link #poll} only in that it throws an |
402 |
> |
* |
403 |
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* This method differs from {@link #poll poll} only in that it throws an |
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* exception if this deque is empty. |
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* |
406 |
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* <p>This method is equivalent to {@link #removeFirst}. |
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|
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/** |
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* Retrieves, but does not remove, the head of the queue represented by |
431 |
< |
* this deque. This method differs from {@link #peek} only in that it |
432 |
< |
* throws an exception if this deque is empty. |
431 |
> |
* this deque. This method differs from {@link #peek peek} only in |
432 |
> |
* that it throws an exception if this deque is empty. |
433 |
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* |
434 |
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* <p>This method is equivalent to {@link #getFirst}. |
435 |
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* |
482 |
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return removeFirst(); |
483 |
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} |
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|
485 |
+ |
private void checkInvariants() { |
486 |
+ |
assert elements[tail] == null; |
487 |
+ |
assert head == tail ? elements[head] == null : |
488 |
+ |
(elements[head] != null && |
489 |
+ |
elements[(tail - 1) & (elements.length - 1)] != null); |
490 |
+ |
assert elements[(head - 1) & (elements.length - 1)] == null; |
491 |
+ |
} |
492 |
+ |
|
493 |
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/** |
494 |
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* Removes the element at the specified position in the elements array, |
495 |
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* adjusting head and tail as necessary. This can result in motion of |
501 |
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* @return true if elements moved backwards |
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*/ |
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private boolean delete(int i) { |
504 |
< |
int mask = elements.length - 1; |
505 |
< |
|
506 |
< |
// Invariant: head <= i < tail mod circularity |
507 |
< |
if (((i - head) & mask) >= ((tail - head) & mask)) |
508 |
< |
throw new ConcurrentModificationException(); |
509 |
< |
|
510 |
< |
// Case 1: Deque doesn't wrap |
511 |
< |
// Case 2: Deque does wrap and removed element is in the head portion |
512 |
< |
if (i >= head) { |
513 |
< |
System.arraycopy(elements, head, elements, head + 1, i - head); |
514 |
< |
elements[head] = null; |
515 |
< |
head = (head + 1) & mask; |
504 |
> |
checkInvariants(); |
505 |
> |
final Object[] elements = this.elements; |
506 |
> |
final int mask = elements.length - 1; |
507 |
> |
final int h = head; |
508 |
> |
final int t = tail; |
509 |
> |
final int front = (i - h) & mask; |
510 |
> |
final int back = (t - i) & mask; |
511 |
> |
|
512 |
> |
// Invariant: head <= i < tail mod circularity |
513 |
> |
if (front >= ((t - h) & mask)) |
514 |
> |
throw new ConcurrentModificationException(); |
515 |
> |
|
516 |
> |
// Optimize for least element motion |
517 |
> |
if (front < back) { |
518 |
> |
if (h <= i) { |
519 |
> |
System.arraycopy(elements, h, elements, h + 1, front); |
520 |
> |
} else { // Wrap around |
521 |
> |
System.arraycopy(elements, 0, elements, 1, i); |
522 |
> |
elements[0] = elements[mask]; |
523 |
> |
System.arraycopy(elements, h, elements, h + 1, mask - h); |
524 |
> |
} |
525 |
> |
elements[h] = null; |
526 |
> |
head = (h + 1) & mask; |
527 |
|
return false; |
528 |
+ |
} else { |
529 |
+ |
if (i < t) { // Copy the null tail as well |
530 |
+ |
System.arraycopy(elements, i + 1, elements, i, back); |
531 |
+ |
tail = t - 1; |
532 |
+ |
} else { // Wrap around |
533 |
+ |
System.arraycopy(elements, i + 1, elements, i, mask - i); |
534 |
+ |
elements[mask] = elements[0]; |
535 |
+ |
System.arraycopy(elements, 1, elements, 0, t); |
536 |
+ |
tail = (t - 1) & mask; |
537 |
+ |
} |
538 |
+ |
return true; |
539 |
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} |
504 |
– |
|
505 |
– |
// Case 3: Deque wraps and removed element is in the tail portion |
506 |
– |
tail--; |
507 |
– |
System.arraycopy(elements, i + 1, elements, i, tail - i); |
508 |
– |
elements[tail] = null; |
509 |
– |
return true; |
540 |
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} |
541 |
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|
542 |
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// *** Collection Methods *** |
565 |
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* order that elements would be dequeued (via successive calls to |
566 |
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* {@link #remove} or popped (via successive calls to {@link #pop}). |
567 |
|
* |
568 |
< |
* @return an <tt>Iterator</tt> over the elements in this deque |
568 |
> |
* @return an iterator over the elements in this deque |
569 |
|
*/ |
570 |
|
public Iterator<E> iterator() { |
571 |
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return new DeqIterator(); |
572 |
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} |
573 |
|
|
574 |
+ |
public Iterator<E> descendingIterator() { |
575 |
+ |
return new DescendingIterator(); |
576 |
+ |
} |
577 |
+ |
|
578 |
|
private class DeqIterator implements Iterator<E> { |
579 |
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/** |
580 |
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* Index of element to be returned by subsequent call to next. |
598 |
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} |
599 |
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|
600 |
|
public E next() { |
567 |
– |
E result; |
601 |
|
if (cursor == fence) |
602 |
|
throw new NoSuchElementException(); |
603 |
+ |
@SuppressWarnings("unchecked") E result = (E) elements[cursor]; |
604 |
|
// This check doesn't catch all possible comodifications, |
605 |
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// but does catch the ones that corrupt traversal |
606 |
< |
if (tail != fence || (result = elements[cursor]) == null) |
606 |
> |
if (tail != fence || result == null) |
607 |
|
throw new ConcurrentModificationException(); |
608 |
|
lastRet = cursor; |
609 |
|
cursor = (cursor + 1) & (elements.length - 1); |
613 |
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public void remove() { |
614 |
|
if (lastRet < 0) |
615 |
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throw new IllegalStateException(); |
616 |
< |
if (delete(lastRet)) |
617 |
< |
cursor--; |
616 |
> |
if (delete(lastRet)) { // if left-shifted, undo increment in next() |
617 |
> |
cursor = (cursor - 1) & (elements.length - 1); |
618 |
> |
fence = tail; |
619 |
> |
} |
620 |
> |
lastRet = -1; |
621 |
> |
} |
622 |
> |
} |
623 |
> |
|
624 |
> |
private class DescendingIterator implements Iterator<E> { |
625 |
> |
/* |
626 |
> |
* This class is nearly a mirror-image of DeqIterator, using |
627 |
> |
* tail instead of head for initial cursor, and head instead of |
628 |
> |
* tail for fence. |
629 |
> |
*/ |
630 |
> |
private int cursor = tail; |
631 |
> |
private int fence = head; |
632 |
> |
private int lastRet = -1; |
633 |
> |
|
634 |
> |
public boolean hasNext() { |
635 |
> |
return cursor != fence; |
636 |
> |
} |
637 |
> |
|
638 |
> |
public E next() { |
639 |
> |
if (cursor == fence) |
640 |
> |
throw new NoSuchElementException(); |
641 |
> |
cursor = (cursor - 1) & (elements.length - 1); |
642 |
> |
@SuppressWarnings("unchecked") E result = (E) elements[cursor]; |
643 |
> |
if (head != fence || result == null) |
644 |
> |
throw new ConcurrentModificationException(); |
645 |
> |
lastRet = cursor; |
646 |
> |
return result; |
647 |
> |
} |
648 |
> |
|
649 |
> |
public void remove() { |
650 |
> |
if (lastRet < 0) |
651 |
> |
throw new IllegalStateException(); |
652 |
> |
if (!delete(lastRet)) { |
653 |
> |
cursor = (cursor + 1) & (elements.length - 1); |
654 |
> |
fence = head; |
655 |
> |
} |
656 |
|
lastRet = -1; |
585 |
– |
fence = tail; |
657 |
|
} |
658 |
|
} |
659 |
|
|
670 |
|
return false; |
671 |
|
int mask = elements.length - 1; |
672 |
|
int i = head; |
673 |
< |
E x; |
673 |
> |
Object x; |
674 |
|
while ( (x = elements[i]) != null) { |
675 |
|
if (o.equals(x)) |
676 |
|
return true; |
684 |
|
* If the deque does not contain the element, it is unchanged. |
685 |
|
* More formally, removes the first element <tt>e</tt> such that |
686 |
|
* <tt>o.equals(e)</tt> (if such an element exists). |
687 |
< |
* Returns true if this deque contained the specified element (or |
688 |
< |
* equivalently, if this deque changed as a result of the call). |
687 |
> |
* Returns <tt>true</tt> if this deque contained the specified element |
688 |
> |
* (or equivalently, if this deque changed as a result of the call). |
689 |
|
* |
690 |
|
* <p>This method is equivalent to {@link #removeFirstOccurrence}. |
691 |
|
* |
721 |
|
* <p>The returned array will be "safe" in that no references to it are |
722 |
|
* maintained by this deque. (In other words, this method must allocate |
723 |
|
* a new array). The caller is thus free to modify the returned array. |
724 |
< |
* |
724 |
> |
* |
725 |
|
* <p>This method acts as bridge between array-based and collection-based |
726 |
|
* APIs. |
727 |
|
* |
728 |
|
* @return an array containing all of the elements in this deque |
729 |
|
*/ |
730 |
|
public Object[] toArray() { |
731 |
< |
return copyElements(new Object[size()]); |
731 |
> |
return copyElements(new Object[size()]); |
732 |
|
} |
733 |
|
|
734 |
|
/** |
753 |
|
* The following code can be used to dump the deque into a newly |
754 |
|
* allocated array of <tt>String</tt>: |
755 |
|
* |
756 |
< |
* <pre> |
686 |
< |
* String[] y = x.toArray(new String[0]);</pre> |
756 |
> |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
757 |
|
* |
758 |
|
* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
759 |
|
* <tt>toArray()</tt>. |
767 |
|
* this deque |
768 |
|
* @throws NullPointerException if the specified array is null |
769 |
|
*/ |
770 |
+ |
@SuppressWarnings("unchecked") |
771 |
|
public <T> T[] toArray(T[] a) { |
772 |
|
int size = size(); |
773 |
|
if (a.length < size) |
774 |
|
a = (T[])java.lang.reflect.Array.newInstance( |
775 |
|
a.getClass().getComponentType(), size); |
776 |
< |
copyElements(a); |
776 |
> |
copyElements(a); |
777 |
|
if (a.length > size) |
778 |
|
a[size] = null; |
779 |
|
return a; |
788 |
|
*/ |
789 |
|
public ArrayDeque<E> clone() { |
790 |
|
try { |
791 |
+ |
@SuppressWarnings("unchecked") |
792 |
|
ArrayDeque<E> result = (ArrayDeque<E>) super.clone(); |
793 |
< |
// These two lines are currently faster than cloning the array: |
722 |
< |
result.elements = (E[]) new Object[elements.length]; |
723 |
< |
System.arraycopy(elements, 0, result.elements, 0, elements.length); |
793 |
> |
result.elements = Arrays.copyOf(elements, elements.length); |
794 |
|
return result; |
795 |
|
|
796 |
|
} catch (CloneNotSupportedException e) { |
810 |
|
* followed by all of its elements (each an object reference) in |
811 |
|
* first-to-last order. |
812 |
|
*/ |
813 |
< |
private void writeObject(ObjectOutputStream s) throws IOException { |
813 |
> |
private void writeObject(java.io.ObjectOutputStream s) |
814 |
> |
throws java.io.IOException { |
815 |
|
s.defaultWriteObject(); |
816 |
|
|
817 |
|
// Write out size |
818 |
< |
int size = size(); |
748 |
< |
s.writeInt(size); |
818 |
> |
s.writeInt(size()); |
819 |
|
|
820 |
|
// Write out elements in order. |
751 |
– |
int i = head; |
821 |
|
int mask = elements.length - 1; |
822 |
< |
for (int j = 0; j < size; j++) { |
822 |
> |
for (int i = head; i != tail; i = (i + 1) & mask) |
823 |
|
s.writeObject(elements[i]); |
755 |
– |
i = (i + 1) & mask; |
756 |
– |
} |
824 |
|
} |
825 |
|
|
826 |
|
/** |
827 |
|
* Deserialize this deque. |
828 |
|
*/ |
829 |
< |
private void readObject(ObjectInputStream s) |
830 |
< |
throws IOException, ClassNotFoundException { |
829 |
> |
private void readObject(java.io.ObjectInputStream s) |
830 |
> |
throws java.io.IOException, ClassNotFoundException { |
831 |
|
s.defaultReadObject(); |
832 |
|
|
833 |
|
// Read in size and allocate array |
838 |
|
|
839 |
|
// Read in all elements in the proper order. |
840 |
|
for (int i = 0; i < size; i++) |
841 |
< |
elements[i] = (E)s.readObject(); |
775 |
< |
|
841 |
> |
elements[i] = s.readObject(); |
842 |
|
} |
843 |
|
} |