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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/publicdomain/zero/1.0/. |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* 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.Spliterator; |
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import java.util.stream.Stream; |
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import java.util.stream.Streams; |
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import java.util.function.Consumer; |
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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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* <p>Most {@code ArrayDeque} 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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* |
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* <p>The iterators returned by this class's <tt>iterator</tt> method are |
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* <p>The iterators returned by this class's {@code iterator} 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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* is created, in any way except through the iterator's own {@code remove} |
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* 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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* <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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* 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 Object[] elements; |
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transient Object[] elements; // non-private to simplify nested class access |
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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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* element that would be removed by remove() or pop()); or an |
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* arbitrary number equal to tail if the deque is empty. |
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*/ |
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private transient int head; |
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transient int head; |
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|
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/** |
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* The index at which the next element would be added to the tail |
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* of the deque (via addLast(E), add(E), or push(E)). |
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*/ |
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private transient int tail; |
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transient int tail; |
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|
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/** |
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* The minimum capacity that we'll use for a newly created deque. |
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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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* 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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* 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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* <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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* Retrieves, but does not remove, the head of the queue represented by |
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* 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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/** |
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* Returns <tt>true</tt> if this deque contains no elements. |
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* Returns {@code true} if this deque contains no elements. |
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* |
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* @return <tt>true</tt> if this deque contains no elements |
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* @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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} |
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/** |
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* Returns <tt>true</tt> if this deque contains the specified element. |
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* More formally, returns <tt>true</tt> if and only if this deque contains |
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* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>. |
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* Returns {@code true} if this deque contains the specified element. |
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* More formally, returns {@code true} if and only if this deque contains |
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* at least one element {@code e} such that {@code o.equals(e)}. |
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* |
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* @param o object to be checked for containment in this deque |
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* @return <tt>true</tt> if this deque contains the specified element |
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* @return {@code true} if this deque contains the specified element |
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*/ |
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public boolean contains(Object o) { |
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if (o == null) |
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/** |
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* Removes a single instance of the specified element from this deque. |
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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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* <p>This method is equivalent to {@link #removeFirstOccurrence}. |
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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 this deque contained the specified element |
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* @return {@code true} if this deque contained the specified element |
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*/ |
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public boolean remove(Object o) { |
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return removeFirstOccurrence(o); |
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* <p>If this deque fits in the specified array with room to spare |
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* (i.e., the array has more elements than this deque), the element in |
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* the array immediately following the end of the deque is set to |
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* <tt>null</tt>. |
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* {@code null}. |
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* |
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* <p>Like the {@link #toArray()} method, this method acts as bridge between |
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* array-based and collection-based APIs. Further, this method allows |
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* precise control over the runtime type of the output array, and may, |
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* under certain circumstances, be used to save allocation costs. |
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* |
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* <p>Suppose <tt>x</tt> is a deque known to contain only strings. |
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* <p>Suppose {@code x} is a deque known to contain only strings. |
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* The following code can be used to dump the deque into a newly |
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* allocated array of <tt>String</tt>: |
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* allocated array of {@code String}: |
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* |
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* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
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* |
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* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
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* <tt>toArray()</tt>. |
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* Note that {@code toArray(new Object[0])} is identical in function to |
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* {@code toArray()}. |
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* |
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* @param a the array into which the elements of the deque are to |
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* be stored, if it is big enough; otherwise, a new array of the |
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/** |
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* Saves this deque to a stream (that is, serializes it). |
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* |
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* @serialData The current size (<tt>int</tt>) of the deque, |
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* @serialData The current size ({@code int}) of the deque, |
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* followed by all of its elements (each an object reference) in |
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* first-to-last order. |
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*/ |
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for (int i = 0; i < size; i++) |
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elements[i] = s.readObject(); |
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} |
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|
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public Stream<E> stream() { |
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int flags = Streams.STREAM_IS_ORDERED | Streams.STREAM_IS_SIZED; |
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return Streams.stream |
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(() -> new DeqSpliterator<E>(this, head, tail), flags); |
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} |
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public Stream<E> parallelStream() { |
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int flags = Streams.STREAM_IS_ORDERED | Streams.STREAM_IS_SIZED; |
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return Streams.parallelStream |
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(() -> new DeqSpliterator<E>(this, head, tail), flags); |
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} |
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|
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static final class DeqSpliterator<E> implements Spliterator<E> { |
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private final ArrayDeque<E> deq; |
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private final int fence; // initially tail |
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private int index; // current index, modified on traverse/split |
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|
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/** Create new spliterator covering the given array and range */ |
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DeqSpliterator(ArrayDeque<E> deq, int origin, int fence) { |
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this.deq = deq; this.index = origin; this.fence = fence; |
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} |
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|
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public DeqSpliterator<E> trySplit() { |
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int n = deq.elements.length; |
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int h = index, t = fence; |
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if (h != t && ((h + 1) & (n - 1)) != t) { |
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if (h > t) |
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t += n; |
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int m = ((h + t) >>> 1) & (n - 1); |
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return new DeqSpliterator<E>(deq, h, index = m); |
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} |
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return null; |
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} |
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|
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public void forEach(Consumer<? super E> block) { |
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if (block == null) |
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throw new NullPointerException(); |
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Object[] a = deq.elements; |
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int m = a.length - 1, f = fence, i = index; |
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index = f; |
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while (i != f) { |
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@SuppressWarnings("unchecked") E e = (E)a[i]; |
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i = (i + 1) & m; |
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if (e == null) |
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throw new ConcurrentModificationException(); |
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block.accept(e); |
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} |
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} |
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|
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public boolean tryAdvance(Consumer<? super E> block) { |
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if (block == null) |
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throw new NullPointerException(); |
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Object[] a = deq.elements; |
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int m = a.length - 1, i = index; |
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if (i != fence) { |
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@SuppressWarnings("unchecked") E e = (E)a[i]; |
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index = (i + 1) & m; |
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if (e == null) |
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throw new ConcurrentModificationException(); |
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block.accept(e); |
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return true; |
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} |
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return false; |
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} |
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|
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// Other spliterator methods |
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public long estimateSize() { |
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int n = fence - index; |
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if (n < 0) |
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n += deq.elements.length; |
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return (long)n; |
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} |
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public boolean hasExactSize() { return true; } |
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public boolean hasExactSplits() { return true; } |
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} |
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|
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} |