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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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import java.io.Serializable; |
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import java.util.function.Consumer; |
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import java.util.stream.Stream; |
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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 remove method, the |
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* iterator will generally throw a {@link ConcurrentModificationException}. |
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* Thus, in the face of concurrent modification, the iterator fails quickly |
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* and cleanly, rather than risking arbitrary, non-deterministic behavior at |
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* an undetermined time in the future. |
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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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* future. |
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* |
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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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* |
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* <p>This class and its iterator implement all of the |
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* optional methods of the {@link Collection} and {@link |
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* Iterator} interfaces. This class is a member of the <a |
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* href="{@docRoot}/../guide/collections/index.html"> Java Collections |
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* Framework</a>. |
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* <em>optional</em> methods of the {@link Collection} and {@link |
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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}/../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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* @since 1.6 |
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* @param <E> the type of elements held in this collection |
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* @param <E> the type of elements held in this deque |
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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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{ |
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/** |
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* The array in which the elements of in the deque are stored. |
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* The array in which the elements of the deque are stored. |
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* The capacity of the deque is the length of this array, which is |
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* always a power of two. The array is never allowed to become |
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* full, except transiently within an addX method where it is |
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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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transient Object[] elements; // non-private to simplify nested class access |
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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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// ****** Array allocation and resizing utilities ****** |
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|
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/** |
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* Allocate empty array to hold the given number of elements. |
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* Allocates empty array to hold the given number of elements. |
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* |
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* @param numElements the number of elements to hold. |
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* @param numElements the number of elements to hold |
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*/ |
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private void allocateElements(int numElements) { |
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private void allocateElements(int numElements) { |
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int initialCapacity = MIN_INITIAL_CAPACITY; |
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// Find the best power of two to hold elements. |
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// Tests "<=" because arrays aren't kept full. |
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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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assert head == tail; |
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assert head == tail; |
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int p = head; |
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int n = elements.length; |
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int r = n - p; // number of elements to the right of p |
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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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|
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/** |
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* Copy the elements from our element array into the specified array, |
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* in order (from first to last element in the deque). It is assumed |
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* that the array is large enough to hold all elements in the deque. |
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* |
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* @return its argument |
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*/ |
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private <T> T[] copyElements(T[] a) { |
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if (head < tail) { |
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System.arraycopy(elements, head, a, 0, size()); |
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} else if (head > tail) { |
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int headPortionLen = elements.length - head; |
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System.arraycopy(elements, head, a, 0, headPortionLen); |
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System.arraycopy(elements, 0, a, headPortionLen, tail); |
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} |
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return a; |
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} |
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|
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/** |
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* Constructs an empty array deque with the an initial capacity |
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* Constructs an empty array deque with an initial capacity |
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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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// terms of these. |
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|
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/** |
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* Inserts the specified element to the front this 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 insert |
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* @throws NullPointerException if <tt>e</tt> is null |
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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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*/ |
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public void addFirst(E e) { |
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if (e == null) |
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throw new NullPointerException(); |
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elements[head = (head - 1) & (elements.length - 1)] = e; |
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if (head == tail) |
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if (head == tail) |
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doubleCapacity(); |
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} |
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|
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/** |
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* Inserts the specified element to the end this deque. |
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* This method is equivalent to {@link Collection#add} and |
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* {@link #push}. |
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* Inserts the specified element at the end of this deque. |
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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 insert |
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* @throws NullPointerException if <tt>e</tt> is null |
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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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*/ |
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public void addLast(E e) { |
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if (e == null) |
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} |
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|
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/** |
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* Retrieves and removes the first element of this deque, or |
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* <tt>null</tt> if this deque is empty. |
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* |
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* @return the first element of this deque, or <tt>null</tt> if |
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* this deque is empty |
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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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if (result == null) |
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return null; |
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elements[h] = null; // Must null out slot |
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head = (h + 1) & (elements.length - 1); |
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return result; |
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} |
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|
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/** |
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* Retrieves and removes the last element of this deque, or |
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* <tt>null</tt> if this deque is empty. |
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* |
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* @return the last element of this deque, or <tt>null</tt> if |
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* this deque is empty |
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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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if (result == null) |
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return null; |
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elements[t] = null; |
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tail = t; |
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return result; |
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} |
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|
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/** |
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* Inserts the specified element to the front this 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 insert |
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* @return <tt>true</tt> (as per the spec for {@link Deque#offerFirst}) |
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* @throws NullPointerException if <tt>e</tt> is null |
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* @param e the element to add |
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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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addFirst(e); |
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} |
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|
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/** |
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* Inserts the specified element to the end this deque. |
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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 insert |
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* @return <tt>true</tt> (as per the spec for {@link Deque#offerLast}) |
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* @throws NullPointerException if <tt>e</tt> is null |
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* @param e the element to add |
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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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addLast(e); |
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} |
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|
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/** |
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* Retrieves and removes the first element of this deque. This method |
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* differs from the <tt>pollFirst</tt> method in that it throws an |
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* exception if this deque is empty. |
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* |
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* @return the first element of this deque |
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* @throws NoSuchElementException if this deque is empty |
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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E removeFirst() { |
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E x = pollFirst(); |
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} |
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|
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/** |
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* Retrieves and removes the last element of this deque. This method |
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* differs from the <tt>pollLast</tt> method in that it throws an |
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* exception if this deque is empty. |
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* |
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* @return the last element of this deque |
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* @throws NoSuchElementException if this deque is empty |
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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E removeLast() { |
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E x = pollLast(); |
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return x; |
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} |
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|
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/** |
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* Retrieves, but does not remove, the first element of this deque, |
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* returning <tt>null</tt> if this deque is empty. |
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* |
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* @return the first element of this deque, or <tt>null</tt> if |
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* this deque is empty |
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*/ |
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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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public E pollFirst() { |
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int h = head; |
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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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head = (h + 1) & (elements.length - 1); |
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return result; |
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} |
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|
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/** |
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* Retrieves, but does not remove, the last element of this deque, |
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* returning <tt>null</tt> if this deque is empty. |
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* |
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* @return the last element of this deque, or <tt>null</tt> if this deque |
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* is empty |
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*/ |
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public E peekLast() { |
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return elements[(tail - 1) & (elements.length - 1)]; |
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public E pollLast() { |
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int t = (tail - 1) & (elements.length - 1); |
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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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tail = t; |
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return result; |
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} |
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|
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/** |
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* Retrieves, but does not remove, the first element of this |
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* deque. This method differs from the <tt>peek</tt> method only |
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* in that it throws an exception if this deque is empty. |
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* |
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* @return the first element of this deque |
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* @throws NoSuchElementException if this deque is empty |
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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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/** |
285 |
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* Retrieves, but does not remove, the last element of this |
343 |
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* deque. This method differs from the <tt>peek</tt> method only |
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* in that it throws an exception if this deque is empty. |
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* |
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* @return the last element of this deque |
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* @throws NoSuchElementException if this deque is empty |
285 |
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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") |
289 |
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E result = (E) elements[(tail - 1) & (elements.length - 1)]; |
290 |
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if (result == null) |
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throw new NoSuchElementException(); |
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return x; |
292 |
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return result; |
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} |
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|
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@SuppressWarnings("unchecked") |
296 |
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public E peekFirst() { |
297 |
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// elements[head] is null if deque empty |
298 |
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return (E) elements[head]; |
299 |
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} |
300 |
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|
301 |
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@SuppressWarnings("unchecked") |
302 |
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public E peekLast() { |
303 |
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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 |
308 |
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* deque (when traversing the deque from head to tail). If the deque |
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* does not contain the element, it is unchanged. |
308 |
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* deque (when traversing the deque from head to tail). |
309 |
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* If the deque does not contain the element, it is unchanged. |
310 |
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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 e 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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* @param o element to be removed from this deque, if present |
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* @return {@code true} if the deque contained the specified element |
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*/ |
318 |
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public boolean removeFirstOccurrence(Object e) { |
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if (e == null) |
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return false; |
321 |
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int mask = elements.length - 1; |
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int i = head; |
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E x; |
324 |
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while ( (x = elements[i]) != null) { |
325 |
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if (e.equals(x)) { |
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delete(i); |
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return true; |
318 |
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public boolean removeFirstOccurrence(Object o) { |
319 |
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if (o != null) { |
320 |
> |
int mask = elements.length - 1; |
321 |
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int i = head; |
322 |
> |
for (Object x; (x = elements[i]) != null; i = (i + 1) & mask) { |
323 |
> |
if (o.equals(x)) { |
324 |
> |
delete(i); |
325 |
> |
return true; |
326 |
> |
} |
327 |
|
} |
375 |
– |
i = (i + 1) & mask; |
328 |
|
} |
329 |
|
return false; |
330 |
|
} |
331 |
|
|
332 |
|
/** |
333 |
|
* Removes the last occurrence of the specified element in this |
334 |
< |
* deque (when traversing the deque from head to tail). If the deque |
335 |
< |
* does not contain the element, it is unchanged. |
334 |
> |
* deque (when traversing the deque from head to tail). |
335 |
> |
* If the deque does not contain the element, it is unchanged. |
336 |
> |
* More formally, removes the last element {@code e} such that |
337 |
> |
* {@code o.equals(e)} (if such an element exists). |
338 |
> |
* Returns {@code true} if this deque contained the specified element |
339 |
> |
* (or equivalently, if this deque changed as a result of the call). |
340 |
|
* |
341 |
< |
* @param e element to be removed from this deque, if present |
342 |
< |
* @return <tt>true</tt> if the deque contained the specified element |
341 |
> |
* @param o element to be removed from this deque, if present |
342 |
> |
* @return {@code true} if the deque contained the specified element |
343 |
|
*/ |
344 |
< |
public boolean removeLastOccurrence(Object e) { |
345 |
< |
if (e == null) |
346 |
< |
return false; |
347 |
< |
int mask = elements.length - 1; |
348 |
< |
int i = (tail - 1) & mask; |
349 |
< |
E x; |
350 |
< |
while ( (x = elements[i]) != null) { |
351 |
< |
if (e.equals(x)) { |
352 |
< |
delete(i); |
397 |
< |
return true; |
344 |
> |
public boolean removeLastOccurrence(Object o) { |
345 |
> |
if (o != null) { |
346 |
> |
int mask = elements.length - 1; |
347 |
> |
int i = (tail - 1) & mask; |
348 |
> |
for (Object x; (x = elements[i]) != null; i = (i - 1) & mask) { |
349 |
> |
if (o.equals(x)) { |
350 |
> |
delete(i); |
351 |
> |
return true; |
352 |
> |
} |
353 |
|
} |
399 |
– |
i = (i - 1) & mask; |
354 |
|
} |
355 |
|
return false; |
356 |
|
} |
358 |
|
// *** Queue methods *** |
359 |
|
|
360 |
|
/** |
361 |
< |
* Inserts the specified element to the end of this deque. |
408 |
< |
* |
409 |
< |
* <p>This method is equivalent to {@link #offerLast}. |
410 |
< |
* |
411 |
< |
* @param e the element to insert |
412 |
< |
* @return <tt>true</tt> (as per the spec for {@link Queue#offer}) |
413 |
< |
* @throws NullPointerException if <tt>e</tt> is null |
414 |
< |
*/ |
415 |
< |
public boolean offer(E e) { |
416 |
< |
return offerLast(e); |
417 |
< |
} |
418 |
< |
|
419 |
< |
/** |
420 |
< |
* Inserts the specified element to the end of this deque. |
361 |
> |
* Inserts the specified element at the end of this deque. |
362 |
|
* |
363 |
|
* <p>This method is equivalent to {@link #addLast}. |
364 |
|
* |
365 |
< |
* @param e the element to insert |
366 |
< |
* @return <tt>true</tt> (as per the spec for {@link Collection#add}) |
367 |
< |
* @throws NullPointerException if <tt>e</tt> is null |
365 |
> |
* @param e the element to add |
366 |
> |
* @return {@code true} (as specified by {@link Collection#add}) |
367 |
> |
* @throws NullPointerException if the specified element is null |
368 |
|
*/ |
369 |
|
public boolean add(E e) { |
370 |
|
addLast(e); |
372 |
|
} |
373 |
|
|
374 |
|
/** |
375 |
< |
* Retrieves and removes the head of the queue represented by |
435 |
< |
* this deque, or <tt>null</tt> if this deque is empty. In other words, |
436 |
< |
* retrieves and removes the first element of this deque, or <tt>null</tt> |
437 |
< |
* if this deque is empty. |
375 |
> |
* Inserts the specified element at the end of this deque. |
376 |
|
* |
377 |
< |
* <p>This method is equivalent to {@link #pollFirst}. |
377 |
> |
* <p>This method is equivalent to {@link #offerLast}. |
378 |
|
* |
379 |
< |
* @return the first element of this deque, or <tt>null</tt> if |
380 |
< |
* this deque is empty |
379 |
> |
* @param e the element to add |
380 |
> |
* @return {@code true} (as specified by {@link Queue#offer}) |
381 |
> |
* @throws NullPointerException if the specified element is null |
382 |
|
*/ |
383 |
< |
public E poll() { |
384 |
< |
return pollFirst(); |
383 |
> |
public boolean offer(E e) { |
384 |
> |
return offerLast(e); |
385 |
|
} |
386 |
|
|
387 |
|
/** |
388 |
|
* Retrieves and removes the head of the queue represented by this deque. |
389 |
< |
* This method differs from the <tt>poll</tt> method in that it throws an |
389 |
> |
* |
390 |
> |
* This method differs from {@link #poll poll} only in that it throws an |
391 |
|
* exception if this deque is empty. |
392 |
|
* |
393 |
|
* <p>This method is equivalent to {@link #removeFirst}. |
394 |
|
* |
395 |
|
* @return the head of the queue represented by this deque |
396 |
< |
* @throws NoSuchElementException if this deque is empty |
396 |
> |
* @throws NoSuchElementException {@inheritDoc} |
397 |
|
*/ |
398 |
|
public E remove() { |
399 |
|
return removeFirst(); |
400 |
|
} |
401 |
|
|
402 |
|
/** |
403 |
< |
* Retrieves, but does not remove, the head of the queue represented by |
404 |
< |
* this deque, returning <tt>null</tt> if this deque is empty. |
403 |
> |
* Retrieves and removes the head of the queue represented by this deque |
404 |
> |
* (in other words, the first element of this deque), or returns |
405 |
> |
* {@code null} if this deque is empty. |
406 |
|
* |
407 |
< |
* <p>This method is equivalent to {@link #peekFirst} |
407 |
> |
* <p>This method is equivalent to {@link #pollFirst}. |
408 |
|
* |
409 |
|
* @return the head of the queue represented by this deque, or |
410 |
< |
* <tt>null</tt> if this deque is empty |
410 |
> |
* {@code null} if this deque is empty |
411 |
|
*/ |
412 |
< |
public E peek() { |
413 |
< |
return peekFirst(); |
412 |
> |
public E poll() { |
413 |
> |
return pollFirst(); |
414 |
|
} |
415 |
|
|
416 |
|
/** |
417 |
|
* Retrieves, but does not remove, the head of the queue represented by |
418 |
< |
* this deque. This method differs from the <tt>peek</tt> method only in |
418 |
> |
* this deque. This method differs from {@link #peek peek} only in |
419 |
|
* that it throws an exception if this deque is empty. |
420 |
|
* |
421 |
< |
* <p>This method is equivalent to {@link #getFirst} |
421 |
> |
* <p>This method is equivalent to {@link #getFirst}. |
422 |
|
* |
423 |
|
* @return the head of the queue represented by this deque |
424 |
< |
* @throws NoSuchElementException if this deque is empty |
424 |
> |
* @throws NoSuchElementException {@inheritDoc} |
425 |
|
*/ |
426 |
|
public E element() { |
427 |
|
return getFirst(); |
428 |
|
} |
429 |
|
|
430 |
+ |
/** |
431 |
+ |
* Retrieves, but does not remove, the head of the queue represented by |
432 |
+ |
* this deque, or returns {@code null} if this deque is empty. |
433 |
+ |
* |
434 |
+ |
* <p>This method is equivalent to {@link #peekFirst}. |
435 |
+ |
* |
436 |
+ |
* @return the head of the queue represented by this deque, or |
437 |
+ |
* {@code null} if this deque is empty |
438 |
+ |
*/ |
439 |
+ |
public E peek() { |
440 |
+ |
return peekFirst(); |
441 |
+ |
} |
442 |
+ |
|
443 |
|
// *** Stack methods *** |
444 |
|
|
445 |
|
/** |
446 |
|
* Pushes an element onto the stack represented by this deque. In other |
447 |
< |
* words, inserts the element to the front this deque. |
447 |
> |
* words, inserts the element at the front of this deque. |
448 |
|
* |
449 |
|
* <p>This method is equivalent to {@link #addFirst}. |
450 |
|
* |
451 |
|
* @param e the element to push |
452 |
< |
* @throws NullPointerException if <tt>e</tt> is null |
452 |
> |
* @throws NullPointerException if the specified element is null |
453 |
|
*/ |
454 |
|
public void push(E e) { |
455 |
|
addFirst(e); |
462 |
|
* <p>This method is equivalent to {@link #removeFirst()}. |
463 |
|
* |
464 |
|
* @return the element at the front of this deque (which is the top |
465 |
< |
* of the stack represented by this deque) |
466 |
< |
* @throws NoSuchElementException if this deque is empty |
465 |
> |
* of the stack represented by this deque) |
466 |
> |
* @throws NoSuchElementException {@inheritDoc} |
467 |
|
*/ |
468 |
|
public E pop() { |
469 |
|
return removeFirst(); |
470 |
|
} |
471 |
|
|
472 |
+ |
private void checkInvariants() { |
473 |
+ |
assert elements[tail] == null; |
474 |
+ |
assert head == tail ? elements[head] == null : |
475 |
+ |
(elements[head] != null && |
476 |
+ |
elements[(tail - 1) & (elements.length - 1)] != null); |
477 |
+ |
assert elements[(head - 1) & (elements.length - 1)] == null; |
478 |
+ |
} |
479 |
+ |
|
480 |
|
/** |
481 |
< |
* Remove the element at the specified position in the elements array, |
482 |
< |
* adjusting head, tail, and size as necessary. This can result in |
483 |
< |
* motion of elements backwards or forwards in the array. |
484 |
< |
* |
485 |
< |
* <p>This method is called delete rather than remove to emphasize the |
486 |
< |
* that its semantics differ from those of List.remove(int). |
487 |
< |
* |
481 |
> |
* Removes the element at the specified position in the elements array, |
482 |
> |
* adjusting head and tail as necessary. This can result in motion of |
483 |
> |
* elements backwards or forwards in the array. |
484 |
> |
* |
485 |
> |
* <p>This method is called delete rather than remove to emphasize |
486 |
> |
* that its semantics differ from those of {@link List#remove(int)}. |
487 |
> |
* |
488 |
|
* @return true if elements moved backwards |
489 |
|
*/ |
490 |
|
private boolean delete(int i) { |
491 |
< |
// Case 1: Deque doesn't wrap |
492 |
< |
// Case 2: Deque does wrap and removed element is in the head portion |
493 |
< |
if ((head < tail || tail == 0) || i >= head) { |
494 |
< |
System.arraycopy(elements, head, elements, head + 1, i - head); |
495 |
< |
elements[head] = null; |
496 |
< |
head = (head + 1) & (elements.length - 1); |
491 |
> |
checkInvariants(); |
492 |
> |
final Object[] elements = this.elements; |
493 |
> |
final int mask = elements.length - 1; |
494 |
> |
final int h = head; |
495 |
> |
final int t = tail; |
496 |
> |
final int front = (i - h) & mask; |
497 |
> |
final int back = (t - i) & mask; |
498 |
> |
|
499 |
> |
// Invariant: head <= i < tail mod circularity |
500 |
> |
if (front >= ((t - h) & mask)) |
501 |
> |
throw new ConcurrentModificationException(); |
502 |
> |
|
503 |
> |
// Optimize for least element motion |
504 |
> |
if (front < back) { |
505 |
> |
if (h <= i) { |
506 |
> |
System.arraycopy(elements, h, elements, h + 1, front); |
507 |
> |
} else { // Wrap around |
508 |
> |
System.arraycopy(elements, 0, elements, 1, i); |
509 |
> |
elements[0] = elements[mask]; |
510 |
> |
System.arraycopy(elements, h, elements, h + 1, mask - h); |
511 |
> |
} |
512 |
> |
elements[h] = null; |
513 |
> |
head = (h + 1) & mask; |
514 |
|
return false; |
515 |
+ |
} else { |
516 |
+ |
if (i < t) { // Copy the null tail as well |
517 |
+ |
System.arraycopy(elements, i + 1, elements, i, back); |
518 |
+ |
tail = t - 1; |
519 |
+ |
} else { // Wrap around |
520 |
+ |
System.arraycopy(elements, i + 1, elements, i, mask - i); |
521 |
+ |
elements[mask] = elements[0]; |
522 |
+ |
System.arraycopy(elements, 1, elements, 0, t); |
523 |
+ |
tail = (t - 1) & mask; |
524 |
+ |
} |
525 |
+ |
return true; |
526 |
|
} |
537 |
– |
|
538 |
– |
// Case 3: Deque wraps and removed element is in the tail portion |
539 |
– |
tail--; |
540 |
– |
System.arraycopy(elements, i + 1, elements, i, tail - i); |
541 |
– |
elements[tail] = null; |
542 |
– |
return true; |
527 |
|
} |
528 |
|
|
529 |
|
// *** Collection Methods *** |
538 |
|
} |
539 |
|
|
540 |
|
/** |
541 |
< |
* Returns <tt>true</tt> if this collection contains no elements.<p> |
541 |
> |
* Returns {@code true} if this deque contains no elements. |
542 |
|
* |
543 |
< |
* @return <tt>true</tt> if this collection contains no elements. |
543 |
> |
* @return {@code true} if this deque contains no elements |
544 |
|
*/ |
545 |
|
public boolean isEmpty() { |
546 |
|
return head == tail; |
551 |
|
* will be ordered from first (head) to last (tail). This is the same |
552 |
|
* order that elements would be dequeued (via successive calls to |
553 |
|
* {@link #remove} or popped (via successive calls to {@link #pop}). |
554 |
< |
* |
555 |
< |
* @return an <tt>Iterator</tt> over the elements in this deque |
554 |
> |
* |
555 |
> |
* @return an iterator over the elements in this deque |
556 |
|
*/ |
557 |
|
public Iterator<E> iterator() { |
558 |
|
return new DeqIterator(); |
559 |
|
} |
560 |
|
|
561 |
+ |
public Iterator<E> descendingIterator() { |
562 |
+ |
return new DescendingIterator(); |
563 |
+ |
} |
564 |
+ |
|
565 |
|
private class DeqIterator implements Iterator<E> { |
566 |
|
/** |
567 |
|
* Index of element to be returned by subsequent call to next. |
585 |
|
} |
586 |
|
|
587 |
|
public E next() { |
600 |
– |
E result; |
588 |
|
if (cursor == fence) |
589 |
|
throw new NoSuchElementException(); |
590 |
+ |
@SuppressWarnings("unchecked") |
591 |
+ |
E result = (E) elements[cursor]; |
592 |
|
// This check doesn't catch all possible comodifications, |
593 |
|
// but does catch the ones that corrupt traversal |
594 |
< |
if (tail != fence || (result = elements[cursor]) == null) |
594 |
> |
if (tail != fence || result == null) |
595 |
|
throw new ConcurrentModificationException(); |
596 |
|
lastRet = cursor; |
597 |
|
cursor = (cursor + 1) & (elements.length - 1); |
601 |
|
public void remove() { |
602 |
|
if (lastRet < 0) |
603 |
|
throw new IllegalStateException(); |
604 |
< |
if (delete(lastRet)) |
605 |
< |
cursor--; |
604 |
> |
if (delete(lastRet)) { // if left-shifted, undo increment in next() |
605 |
> |
cursor = (cursor - 1) & (elements.length - 1); |
606 |
> |
fence = tail; |
607 |
> |
} |
608 |
|
lastRet = -1; |
618 |
– |
fence = tail; |
609 |
|
} |
610 |
|
} |
611 |
|
|
612 |
|
/** |
613 |
< |
* Returns <tt>true</tt> if this deque contains the specified |
614 |
< |
* element. More formally, returns <tt>true</tt> if and only if this |
615 |
< |
* deque contains at least one element <tt>e</tt> such that |
616 |
< |
* <tt>e.equals(o)</tt>. |
613 |
> |
* This class is nearly a mirror-image of DeqIterator, using tail |
614 |
> |
* instead of head for initial cursor, and head instead of tail |
615 |
> |
* for fence. |
616 |
> |
*/ |
617 |
> |
private class DescendingIterator implements Iterator<E> { |
618 |
> |
private int cursor = tail; |
619 |
> |
private int fence = head; |
620 |
> |
private int lastRet = -1; |
621 |
> |
|
622 |
> |
public boolean hasNext() { |
623 |
> |
return cursor != fence; |
624 |
> |
} |
625 |
> |
|
626 |
> |
public E next() { |
627 |
> |
if (cursor == fence) |
628 |
> |
throw new NoSuchElementException(); |
629 |
> |
cursor = (cursor - 1) & (elements.length - 1); |
630 |
> |
@SuppressWarnings("unchecked") |
631 |
> |
E result = (E) elements[cursor]; |
632 |
> |
if (head != fence || result == null) |
633 |
> |
throw new ConcurrentModificationException(); |
634 |
> |
lastRet = cursor; |
635 |
> |
return result; |
636 |
> |
} |
637 |
> |
|
638 |
> |
public void remove() { |
639 |
> |
if (lastRet < 0) |
640 |
> |
throw new IllegalStateException(); |
641 |
> |
if (!delete(lastRet)) { |
642 |
> |
cursor = (cursor + 1) & (elements.length - 1); |
643 |
> |
fence = head; |
644 |
> |
} |
645 |
> |
lastRet = -1; |
646 |
> |
} |
647 |
> |
} |
648 |
> |
|
649 |
> |
/** |
650 |
> |
* Returns {@code true} if this deque contains the specified element. |
651 |
> |
* More formally, returns {@code true} if and only if this deque contains |
652 |
> |
* at least one element {@code e} such that {@code o.equals(e)}. |
653 |
|
* |
654 |
|
* @param o object to be checked for containment in this deque |
655 |
< |
* @return <tt>true</tt> if this deque contains the specified element |
655 |
> |
* @return {@code true} if this deque contains the specified element |
656 |
|
*/ |
657 |
|
public boolean contains(Object o) { |
658 |
< |
if (o == null) |
659 |
< |
return false; |
660 |
< |
int mask = elements.length - 1; |
661 |
< |
int i = head; |
662 |
< |
E x; |
663 |
< |
while ( (x = elements[i]) != null) { |
664 |
< |
if (o.equals(x)) |
639 |
< |
return true; |
640 |
< |
i = (i + 1) & mask; |
658 |
> |
if (o != null) { |
659 |
> |
int mask = elements.length - 1; |
660 |
> |
int i = head; |
661 |
> |
for (Object x; (x = elements[i]) != null; i = (i + 1) & mask) { |
662 |
> |
if (o.equals(x)) |
663 |
> |
return true; |
664 |
> |
} |
665 |
|
} |
666 |
|
return false; |
667 |
|
} |
668 |
|
|
669 |
|
/** |
670 |
|
* Removes a single instance of the specified element from this deque. |
671 |
< |
* This method is equivalent to {@link #removeFirstOccurrence}. |
671 |
> |
* If the deque does not contain the element, it is unchanged. |
672 |
> |
* More formally, removes the first element {@code e} such that |
673 |
> |
* {@code o.equals(e)} (if such an element exists). |
674 |
> |
* Returns {@code true} if this deque contained the specified element |
675 |
> |
* (or equivalently, if this deque changed as a result of the call). |
676 |
|
* |
677 |
< |
* @param e element to be removed from this deque, if present |
678 |
< |
* @return <tt>true</tt> if this deque contained the specified element |
677 |
> |
* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}. |
678 |
> |
* |
679 |
> |
* @param o element to be removed from this deque, if present |
680 |
> |
* @return {@code true} if this deque contained the specified element |
681 |
|
*/ |
682 |
< |
public boolean remove(Object e) { |
683 |
< |
return removeFirstOccurrence(e); |
682 |
> |
public boolean remove(Object o) { |
683 |
> |
return removeFirstOccurrence(o); |
684 |
|
} |
685 |
|
|
686 |
|
/** |
687 |
|
* Removes all of the elements from this deque. |
688 |
+ |
* The deque will be empty after this call returns. |
689 |
|
*/ |
690 |
|
public void clear() { |
691 |
|
int h = head; |
697 |
|
do { |
698 |
|
elements[i] = null; |
699 |
|
i = (i + 1) & mask; |
700 |
< |
} while(i != t); |
700 |
> |
} while (i != t); |
701 |
|
} |
702 |
|
} |
703 |
|
|
704 |
|
/** |
705 |
< |
* Returns an array containing all of the elements in this list |
706 |
< |
* in the correct order. |
705 |
> |
* Returns an array containing all of the elements in this deque |
706 |
> |
* in proper sequence (from first to last element). |
707 |
> |
* |
708 |
> |
* <p>The returned array will be "safe" in that no references to it are |
709 |
> |
* maintained by this deque. (In other words, this method must allocate |
710 |
> |
* a new array). The caller is thus free to modify the returned array. |
711 |
> |
* |
712 |
> |
* <p>This method acts as bridge between array-based and collection-based |
713 |
> |
* APIs. |
714 |
|
* |
715 |
< |
* @return an array containing all of the elements in this list |
678 |
< |
* in the correct order |
715 |
> |
* @return an array containing all of the elements in this deque |
716 |
|
*/ |
717 |
|
public Object[] toArray() { |
718 |
< |
return copyElements(new Object[size()]); |
718 |
> |
final int head = this.head; |
719 |
> |
final int tail = this.tail; |
720 |
> |
boolean wrap = (tail < head); |
721 |
> |
int end = wrap ? tail + elements.length : tail; |
722 |
> |
Object[] a = Arrays.copyOfRange(elements, head, end); |
723 |
> |
if (wrap) |
724 |
> |
System.arraycopy(elements, 0, a, elements.length - head, tail); |
725 |
> |
return a; |
726 |
|
} |
727 |
|
|
728 |
|
/** |
729 |
< |
* Returns an array containing all of the elements in this deque in the |
730 |
< |
* correct order; the runtime type of the returned array is that of the |
731 |
< |
* specified array. If the deque fits in the specified array, it is |
732 |
< |
* returned therein. Otherwise, a new array is allocated with the runtime |
733 |
< |
* type of the specified array and the size of this deque. |
729 |
> |
* Returns an array containing all of the elements in this deque in |
730 |
> |
* proper sequence (from first to last element); the runtime type of the |
731 |
> |
* returned array is that of the specified array. If the deque fits in |
732 |
> |
* the specified array, it is returned therein. Otherwise, a new array |
733 |
> |
* is allocated with the runtime type of the specified array and the |
734 |
> |
* size of this deque. |
735 |
> |
* |
736 |
> |
* <p>If this deque fits in the specified array with room to spare |
737 |
> |
* (i.e., the array has more elements than this deque), the element in |
738 |
> |
* the array immediately following the end of the deque is set to |
739 |
> |
* {@code null}. |
740 |
> |
* |
741 |
> |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
742 |
> |
* array-based and collection-based APIs. Further, this method allows |
743 |
> |
* precise control over the runtime type of the output array, and may, |
744 |
> |
* under certain circumstances, be used to save allocation costs. |
745 |
> |
* |
746 |
> |
* <p>Suppose {@code x} is a deque known to contain only strings. |
747 |
> |
* The following code can be used to dump the deque into a newly |
748 |
> |
* allocated array of {@code String}: |
749 |
> |
* |
750 |
> |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
751 |
|
* |
752 |
< |
* <p>If the deque fits in the specified array with room to spare (i.e., |
753 |
< |
* the array has more elements than the deque), the element in the array |
693 |
< |
* immediately following the end of the collection is set to <tt>null</tt>. |
752 |
> |
* Note that {@code toArray(new Object[0])} is identical in function to |
753 |
> |
* {@code toArray()}. |
754 |
|
* |
755 |
|
* @param a the array into which the elements of the deque are to |
756 |
< |
* be stored, if it is big enough; otherwise, a new array of the |
757 |
< |
* same runtime type is allocated for this purpose |
758 |
< |
* @return an array containing the elements of the deque |
759 |
< |
* @throws ArrayStoreException if the runtime type of a is not a supertype |
760 |
< |
* of the runtime type of every element in this deque |
756 |
> |
* be stored, if it is big enough; otherwise, a new array of the |
757 |
> |
* same runtime type is allocated for this purpose |
758 |
> |
* @return an array containing all of the elements in this deque |
759 |
> |
* @throws ArrayStoreException if the runtime type of the specified array |
760 |
> |
* is not a supertype of the runtime type of every element in |
761 |
> |
* this deque |
762 |
> |
* @throws NullPointerException if the specified array is null |
763 |
|
*/ |
764 |
+ |
@SuppressWarnings("unchecked") |
765 |
|
public <T> T[] toArray(T[] a) { |
766 |
< |
int size = size(); |
767 |
< |
if (a.length < size) |
768 |
< |
a = (T[])java.lang.reflect.Array.newInstance( |
769 |
< |
a.getClass().getComponentType(), size); |
770 |
< |
copyElements(a); |
771 |
< |
if (a.length > size) |
772 |
< |
a[size] = null; |
766 |
> |
final int head = this.head; |
767 |
> |
final int tail = this.tail; |
768 |
> |
boolean wrap = (tail < head); |
769 |
> |
int size = (tail - head) + (wrap ? elements.length : 0); |
770 |
> |
int firstLeg = size - (wrap ? tail : 0); |
771 |
> |
int len = a.length; |
772 |
> |
if (size > len) { |
773 |
> |
a = (T[]) Arrays.copyOfRange(elements, head, head + size, |
774 |
> |
a.getClass()); |
775 |
> |
} else { |
776 |
> |
System.arraycopy(elements, head, a, 0, firstLeg); |
777 |
> |
if (size < len) |
778 |
> |
a[size] = null; |
779 |
> |
} |
780 |
> |
if (wrap) |
781 |
> |
System.arraycopy(elements, 0, a, firstLeg, tail); |
782 |
|
return a; |
783 |
|
} |
784 |
|
|
790 |
|
* @return a copy of this deque |
791 |
|
*/ |
792 |
|
public ArrayDeque<E> clone() { |
793 |
< |
try { |
793 |
> |
try { |
794 |
> |
@SuppressWarnings("unchecked") |
795 |
|
ArrayDeque<E> result = (ArrayDeque<E>) super.clone(); |
796 |
< |
// These two lines are currently faster than cloning the array: |
724 |
< |
result.elements = (E[]) new Object[elements.length]; |
725 |
< |
System.arraycopy(elements, 0, result.elements, 0, elements.length); |
796 |
> |
result.elements = Arrays.copyOf(elements, elements.length); |
797 |
|
return result; |
798 |
< |
|
728 |
< |
} catch (CloneNotSupportedException e) { |
798 |
> |
} catch (CloneNotSupportedException e) { |
799 |
|
throw new AssertionError(); |
800 |
|
} |
801 |
|
} |
802 |
|
|
733 |
– |
/** |
734 |
– |
* Appease the serialization gods. |
735 |
– |
*/ |
803 |
|
private static final long serialVersionUID = 2340985798034038923L; |
804 |
|
|
805 |
|
/** |
806 |
< |
* Serialize this deque. |
806 |
> |
* Saves this deque to a stream (that is, serializes it). |
807 |
|
* |
808 |
< |
* @serialData The current size (<tt>int</tt>) of the deque, |
808 |
> |
* @param s the stream |
809 |
> |
* @throws java.io.IOException if an I/O error occurs |
810 |
> |
* @serialData The current size ({@code int}) of the deque, |
811 |
|
* followed by all of its elements (each an object reference) in |
812 |
|
* first-to-last order. |
813 |
|
*/ |
814 |
< |
private void writeObject(ObjectOutputStream s) throws IOException { |
814 |
> |
private void writeObject(java.io.ObjectOutputStream s) |
815 |
> |
throws java.io.IOException { |
816 |
|
s.defaultWriteObject(); |
817 |
|
|
818 |
|
// Write out size |
819 |
< |
int size = size(); |
750 |
< |
s.writeInt(size); |
819 |
> |
s.writeInt(size()); |
820 |
|
|
821 |
|
// Write out elements in order. |
753 |
– |
int i = head; |
822 |
|
int mask = elements.length - 1; |
823 |
< |
for (int j = 0; j < size; j++) { |
823 |
> |
for (int i = head; i != tail; i = (i + 1) & mask) |
824 |
|
s.writeObject(elements[i]); |
757 |
– |
i = (i + 1) & mask; |
758 |
– |
} |
825 |
|
} |
826 |
|
|
827 |
|
/** |
828 |
< |
* Deserialize this deque. |
828 |
> |
* Reconstitutes this deque from a stream (that is, deserializes it). |
829 |
> |
* @param s the stream |
830 |
> |
* @throws ClassNotFoundException if the class of a serialized object |
831 |
> |
* could not be found |
832 |
> |
* @throws java.io.IOException if an I/O error occurs |
833 |
|
*/ |
834 |
< |
private void readObject(ObjectInputStream s) |
835 |
< |
throws IOException, ClassNotFoundException { |
834 |
> |
private void readObject(java.io.ObjectInputStream s) |
835 |
> |
throws java.io.IOException, ClassNotFoundException { |
836 |
|
s.defaultReadObject(); |
837 |
|
|
838 |
|
// Read in size and allocate array |
843 |
|
|
844 |
|
// Read in all elements in the proper order. |
845 |
|
for (int i = 0; i < size; i++) |
846 |
< |
elements[i] = (E)s.readObject(); |
846 |
> |
elements[i] = s.readObject(); |
847 |
> |
} |
848 |
|
|
849 |
+ |
public Spliterator<E> spliterator() { |
850 |
+ |
return new DeqSpliterator<E>(this, -1, -1); |
851 |
|
} |
852 |
+ |
|
853 |
+ |
static final class DeqSpliterator<E> implements Spliterator<E> { |
854 |
+ |
private final ArrayDeque<E> deq; |
855 |
+ |
private int fence; // -1 until first use |
856 |
+ |
private int index; // current index, modified on traverse/split |
857 |
+ |
|
858 |
+ |
/** Creates new spliterator covering the given array and range */ |
859 |
+ |
DeqSpliterator(ArrayDeque<E> deq, int origin, int fence) { |
860 |
+ |
this.deq = deq; |
861 |
+ |
this.index = origin; |
862 |
+ |
this.fence = fence; |
863 |
+ |
} |
864 |
+ |
|
865 |
+ |
private int getFence() { // force initialization |
866 |
+ |
int t; |
867 |
+ |
if ((t = fence) < 0) { |
868 |
+ |
t = fence = deq.tail; |
869 |
+ |
index = deq.head; |
870 |
+ |
} |
871 |
+ |
return t; |
872 |
+ |
} |
873 |
+ |
|
874 |
+ |
public Spliterator<E> trySplit() { |
875 |
+ |
int t = getFence(), h = index, n = deq.elements.length; |
876 |
+ |
if (h != t && ((h + 1) & (n - 1)) != t) { |
877 |
+ |
if (h > t) |
878 |
+ |
t += n; |
879 |
+ |
int m = ((h + t) >>> 1) & (n - 1); |
880 |
+ |
return new DeqSpliterator<>(deq, h, index = m); |
881 |
+ |
} |
882 |
+ |
return null; |
883 |
+ |
} |
884 |
+ |
|
885 |
+ |
public void forEachRemaining(Consumer<? super E> consumer) { |
886 |
+ |
if (consumer == null) |
887 |
+ |
throw new NullPointerException(); |
888 |
+ |
Object[] a = deq.elements; |
889 |
+ |
int m = a.length - 1, f = getFence(), i = index; |
890 |
+ |
index = f; |
891 |
+ |
while (i != f) { |
892 |
+ |
@SuppressWarnings("unchecked") E e = (E)a[i]; |
893 |
+ |
i = (i + 1) & m; |
894 |
+ |
if (e == null) |
895 |
+ |
throw new ConcurrentModificationException(); |
896 |
+ |
consumer.accept(e); |
897 |
+ |
} |
898 |
+ |
} |
899 |
+ |
|
900 |
+ |
public boolean tryAdvance(Consumer<? super E> consumer) { |
901 |
+ |
if (consumer == null) |
902 |
+ |
throw new NullPointerException(); |
903 |
+ |
Object[] a = deq.elements; |
904 |
+ |
int m = a.length - 1, f = getFence(), i = index; |
905 |
+ |
if (i != fence) { |
906 |
+ |
@SuppressWarnings("unchecked") E e = (E)a[i]; |
907 |
+ |
index = (i + 1) & m; |
908 |
+ |
if (e == null) |
909 |
+ |
throw new ConcurrentModificationException(); |
910 |
+ |
consumer.accept(e); |
911 |
+ |
return true; |
912 |
+ |
} |
913 |
+ |
return false; |
914 |
+ |
} |
915 |
+ |
|
916 |
+ |
public long estimateSize() { |
917 |
+ |
int n = getFence() - index; |
918 |
+ |
if (n < 0) |
919 |
+ |
n += deq.elements.length; |
920 |
+ |
return (long) n; |
921 |
+ |
} |
922 |
+ |
|
923 |
+ |
@Override |
924 |
+ |
public int characteristics() { |
925 |
+ |
return Spliterator.ORDERED | Spliterator.SIZED | |
926 |
+ |
Spliterator.NONNULL | Spliterator.SUBSIZED; |
927 |
+ |
} |
928 |
+ |
} |
929 |
+ |
|
930 |
|
} |