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/* |
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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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|
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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.Block; |
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|
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/** |
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* Resizable-array implementation of the {@link Deque} interface. Array |
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* deques have no capacity restrictions; they grow as necessary to support |
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* usage. They are not thread-safe; in the absence of external |
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* synchronization, they do not support concurrent access by multiple threads. |
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* Null elements are prohibited. This class is likely to be faster than |
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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 {@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 {@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 {@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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* 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 {@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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* <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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*/ |
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public class ArrayDeque<E> extends AbstractCollection<E> |
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implements Deque<E>, Cloneable, java.io.Serializable |
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{ |
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/** |
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* The array in which the elements of the deque are stored. |
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* 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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* resized (see doubleCapacity) immediately upon becoming full, |
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* thus avoiding head and tail wrapping around to equal each |
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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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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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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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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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* Must be a power of 2. |
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*/ |
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private static final int MIN_INITIAL_CAPACITY = 8; |
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|
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// ****** Array allocation and resizing utilities ****** |
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|
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/** |
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* Allocates empty array to hold the given number of elements. |
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* |
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* @param numElements the number of elements to hold |
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*/ |
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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 (numElements >= initialCapacity) { |
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initialCapacity = numElements; |
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initialCapacity |= (initialCapacity >>> 1); |
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initialCapacity |= (initialCapacity >>> 2); |
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initialCapacity |= (initialCapacity >>> 4); |
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initialCapacity |= (initialCapacity >>> 8); |
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initialCapacity |= (initialCapacity >>> 16); |
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initialCapacity++; |
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|
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if (initialCapacity < 0) // Too many elements, must back off |
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initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements |
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} |
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elements = new Object[initialCapacity]; |
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} |
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|
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/** |
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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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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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int newCapacity = n << 1; |
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if (newCapacity < 0) |
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throw new IllegalStateException("Sorry, deque too big"); |
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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 = 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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* Copies 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 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 = new Object[16]; |
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} |
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|
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/** |
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* Constructs an empty array deque with an initial capacity |
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* sufficient to hold the specified number of elements. |
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* |
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* @param numElements lower bound on initial capacity of the deque |
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*/ |
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public ArrayDeque(int numElements) { |
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allocateElements(numElements); |
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} |
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|
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/** |
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* Constructs a deque containing the elements of the specified |
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* collection, in the order they are returned by the collection's |
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* iterator. (The first element returned by the collection's |
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* iterator becomes the first element, or <i>front</i> of the |
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* deque.) |
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* |
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* @param c the collection whose elements are to be placed into the deque |
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* @throws NullPointerException if the specified collection is null |
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*/ |
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public ArrayDeque(Collection<? extends E> c) { |
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allocateElements(c.size()); |
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addAll(c); |
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} |
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|
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// The main insertion and extraction methods are addFirst, |
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// addLast, pollFirst, pollLast. The other methods are defined in |
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// terms of these. |
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|
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/** |
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* Inserts the specified element at the front of this deque. |
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* |
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* @param e the element to add |
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* @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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doubleCapacity(); |
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} |
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|
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/** |
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* Inserts the specified element at the end of this deque. |
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* |
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* <p>This method is equivalent to {@link #add}. |
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* |
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* @param e the element to add |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public void addLast(E e) { |
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if (e == null) |
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throw new NullPointerException(); |
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elements[tail] = e; |
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if ( (tail = (tail + 1) & (elements.length - 1)) == head) |
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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 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 {@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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return true; |
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} |
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|
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/** |
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* Inserts the specified element at the end of this deque. |
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* |
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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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return true; |
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} |
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|
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/** |
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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E removeFirst() { |
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E x = pollFirst(); |
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if (x == null) |
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throw new NoSuchElementException(); |
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return x; |
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} |
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|
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/** |
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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E removeLast() { |
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E x = pollLast(); |
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if (x == null) |
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throw new NoSuchElementException(); |
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return x; |
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} |
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|
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public E pollFirst() { |
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int h = head; |
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@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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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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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E getFirst() { |
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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 result; |
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} |
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|
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/** |
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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E getLast() { |
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@SuppressWarnings("unchecked") |
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E result = (E) elements[(tail - 1) & (elements.length - 1)]; |
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if (result == null) |
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throw new NoSuchElementException(); |
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return result; |
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} |
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|
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@SuppressWarnings("unchecked") |
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public E peekFirst() { |
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// elements[head] is null if deque empty |
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return (E) elements[head]; |
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} |
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|
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@SuppressWarnings("unchecked") |
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public E peekLast() { |
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return (E) elements[(tail - 1) & (elements.length - 1)]; |
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} |
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|
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/** |
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* Removes the first occurrence of the specified element in this |
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* deque (when traversing the deque from head to tail). |
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* If the deque does not contain the element, it is unchanged. |
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* More formally, removes the first element {@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 {@code true} if the deque contained the specified element |
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*/ |
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public boolean removeFirstOccurrence(Object o) { |
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if (o == null) |
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return false; |
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int mask = elements.length - 1; |
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int i = head; |
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Object x; |
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while ( (x = elements[i]) != null) { |
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if (o.equals(x)) { |
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delete(i); |
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return true; |
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} |
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i = (i + 1) & mask; |
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} |
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return false; |
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} |
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|
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/** |
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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 {@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 {@code true} if the deque contained the specified element |
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*/ |
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public boolean removeLastOccurrence(Object o) { |
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if (o == null) |
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return false; |
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int mask = elements.length - 1; |
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int i = (tail - 1) & mask; |
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Object x; |
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while ( (x = elements[i]) != null) { |
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if (o.equals(x)) { |
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delete(i); |
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return true; |
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} |
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i = (i - 1) & mask; |
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} |
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return false; |
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} |
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|
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// *** Queue methods *** |
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|
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/** |
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* Inserts the specified element at the end of this deque. |
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* |
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* <p>This method is equivalent to {@link #addLast}. |
385 |
* |
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* @param e the element to 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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addLast(e); |
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return true; |
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} |
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|
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/** |
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* Inserts the specified element at the end of this deque. |
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* |
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* <p>This method is equivalent to {@link #offerLast}. |
399 |
* |
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* @param e the element to add |
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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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return offerLast(e); |
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} |
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|
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/** |
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* Retrieves and removes the head of the queue represented by this deque. |
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* |
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* This method differs from {@link #poll poll} only in that it throws an |
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* exception if this deque is empty. |
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* |
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* <p>This method is equivalent to {@link #removeFirst}. |
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* |
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* @return the head of the queue represented by this deque |
417 |
* @throws NoSuchElementException {@inheritDoc} |
418 |
*/ |
419 |
public E remove() { |
420 |
return removeFirst(); |
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} |
422 |
|
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/** |
424 |
* Retrieves and removes the head of the queue represented by this deque |
425 |
* (in other words, the first element of this deque), or returns |
426 |
* {@code null} if this deque is empty. |
427 |
* |
428 |
* <p>This method is equivalent to {@link #pollFirst}. |
429 |
* |
430 |
* @return the head of the queue represented by this deque, or |
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* {@code null} if this deque is empty |
432 |
*/ |
433 |
public E poll() { |
434 |
return pollFirst(); |
435 |
} |
436 |
|
437 |
/** |
438 |
* Retrieves, but does not remove, the head of the queue represented by |
439 |
* this deque. This method differs from {@link #peek peek} only in |
440 |
* that it throws an exception if this deque is empty. |
441 |
* |
442 |
* <p>This method is equivalent to {@link #getFirst}. |
443 |
* |
444 |
* @return the head of the queue represented by this deque |
445 |
* @throws NoSuchElementException {@inheritDoc} |
446 |
*/ |
447 |
public E element() { |
448 |
return getFirst(); |
449 |
} |
450 |
|
451 |
/** |
452 |
* Retrieves, but does not remove, the head of the queue represented by |
453 |
* this deque, or returns {@code null} if this deque is empty. |
454 |
* |
455 |
* <p>This method is equivalent to {@link #peekFirst}. |
456 |
* |
457 |
* @return the head of the queue represented by this deque, or |
458 |
* {@code null} if this deque is empty |
459 |
*/ |
460 |
public E peek() { |
461 |
return peekFirst(); |
462 |
} |
463 |
|
464 |
// *** Stack methods *** |
465 |
|
466 |
/** |
467 |
* Pushes an element onto the stack represented by this deque. In other |
468 |
* words, inserts the element at the front of this deque. |
469 |
* |
470 |
* <p>This method is equivalent to {@link #addFirst}. |
471 |
* |
472 |
* @param e the element to push |
473 |
* @throws NullPointerException if the specified element is null |
474 |
*/ |
475 |
public void push(E e) { |
476 |
addFirst(e); |
477 |
} |
478 |
|
479 |
/** |
480 |
* Pops an element from the stack represented by this deque. In other |
481 |
* words, removes and returns the first element of this deque. |
482 |
* |
483 |
* <p>This method is equivalent to {@link #removeFirst()}. |
484 |
* |
485 |
* @return the element at the front of this deque (which is the top |
486 |
* of the stack represented by this deque) |
487 |
* @throws NoSuchElementException {@inheritDoc} |
488 |
*/ |
489 |
public E pop() { |
490 |
return removeFirst(); |
491 |
} |
492 |
|
493 |
private void checkInvariants() { |
494 |
assert elements[tail] == null; |
495 |
assert head == tail ? elements[head] == null : |
496 |
(elements[head] != null && |
497 |
elements[(tail - 1) & (elements.length - 1)] != null); |
498 |
assert elements[(head - 1) & (elements.length - 1)] == null; |
499 |
} |
500 |
|
501 |
/** |
502 |
* Removes the element at the specified position in the elements array, |
503 |
* adjusting head and tail as necessary. This can result in motion of |
504 |
* elements backwards or forwards in the array. |
505 |
* |
506 |
* <p>This method is called delete rather than remove to emphasize |
507 |
* that its semantics differ from those of {@link List#remove(int)}. |
508 |
* |
509 |
* @return true if elements moved backwards |
510 |
*/ |
511 |
private boolean delete(int i) { |
512 |
checkInvariants(); |
513 |
final Object[] elements = this.elements; |
514 |
final int mask = elements.length - 1; |
515 |
final int h = head; |
516 |
final int t = tail; |
517 |
final int front = (i - h) & mask; |
518 |
final int back = (t - i) & mask; |
519 |
|
520 |
// Invariant: head <= i < tail mod circularity |
521 |
if (front >= ((t - h) & mask)) |
522 |
throw new ConcurrentModificationException(); |
523 |
|
524 |
// Optimize for least element motion |
525 |
if (front < back) { |
526 |
if (h <= i) { |
527 |
System.arraycopy(elements, h, elements, h + 1, front); |
528 |
} else { // Wrap around |
529 |
System.arraycopy(elements, 0, elements, 1, i); |
530 |
elements[0] = elements[mask]; |
531 |
System.arraycopy(elements, h, elements, h + 1, mask - h); |
532 |
} |
533 |
elements[h] = null; |
534 |
head = (h + 1) & mask; |
535 |
return false; |
536 |
} else { |
537 |
if (i < t) { // Copy the null tail as well |
538 |
System.arraycopy(elements, i + 1, elements, i, back); |
539 |
tail = t - 1; |
540 |
} else { // Wrap around |
541 |
System.arraycopy(elements, i + 1, elements, i, mask - i); |
542 |
elements[mask] = elements[0]; |
543 |
System.arraycopy(elements, 1, elements, 0, t); |
544 |
tail = (t - 1) & mask; |
545 |
} |
546 |
return true; |
547 |
} |
548 |
} |
549 |
|
550 |
// *** Collection Methods *** |
551 |
|
552 |
/** |
553 |
* Returns the number of elements in this deque. |
554 |
* |
555 |
* @return the number of elements in this deque |
556 |
*/ |
557 |
public int size() { |
558 |
return (tail - head) & (elements.length - 1); |
559 |
} |
560 |
|
561 |
/** |
562 |
* Returns {@code true} if this deque contains no elements. |
563 |
* |
564 |
* @return {@code true} if this deque contains no elements |
565 |
*/ |
566 |
public boolean isEmpty() { |
567 |
return head == tail; |
568 |
} |
569 |
|
570 |
/** |
571 |
* Returns an iterator over the elements in this deque. The elements |
572 |
* will be ordered from first (head) to last (tail). This is the same |
573 |
* order that elements would be dequeued (via successive calls to |
574 |
* {@link #remove} or popped (via successive calls to {@link #pop}). |
575 |
* |
576 |
* @return an iterator over the elements in this deque |
577 |
*/ |
578 |
public Iterator<E> iterator() { |
579 |
return new DeqIterator(); |
580 |
} |
581 |
|
582 |
public Iterator<E> descendingIterator() { |
583 |
return new DescendingIterator(); |
584 |
} |
585 |
|
586 |
private class DeqIterator implements Iterator<E> { |
587 |
/** |
588 |
* Index of element to be returned by subsequent call to next. |
589 |
*/ |
590 |
private int cursor = head; |
591 |
|
592 |
/** |
593 |
* Tail recorded at construction (also in remove), to stop |
594 |
* iterator and also to check for comodification. |
595 |
*/ |
596 |
private int fence = tail; |
597 |
|
598 |
/** |
599 |
* Index of element returned by most recent call to next. |
600 |
* Reset to -1 if element is deleted by a call to remove. |
601 |
*/ |
602 |
private int lastRet = -1; |
603 |
|
604 |
public boolean hasNext() { |
605 |
return cursor != fence; |
606 |
} |
607 |
|
608 |
public E next() { |
609 |
if (cursor == fence) |
610 |
throw new NoSuchElementException(); |
611 |
@SuppressWarnings("unchecked") |
612 |
E result = (E) elements[cursor]; |
613 |
// This check doesn't catch all possible comodifications, |
614 |
// but does catch the ones that corrupt traversal |
615 |
if (tail != fence || result == null) |
616 |
throw new ConcurrentModificationException(); |
617 |
lastRet = cursor; |
618 |
cursor = (cursor + 1) & (elements.length - 1); |
619 |
return result; |
620 |
} |
621 |
|
622 |
public void remove() { |
623 |
if (lastRet < 0) |
624 |
throw new IllegalStateException(); |
625 |
if (delete(lastRet)) { // if left-shifted, undo increment in next() |
626 |
cursor = (cursor - 1) & (elements.length - 1); |
627 |
fence = tail; |
628 |
} |
629 |
lastRet = -1; |
630 |
} |
631 |
} |
632 |
|
633 |
private class DescendingIterator implements Iterator<E> { |
634 |
/* |
635 |
* This class is nearly a mirror-image of DeqIterator, using |
636 |
* tail instead of head for initial cursor, and head instead of |
637 |
* tail for fence. |
638 |
*/ |
639 |
private int cursor = tail; |
640 |
private int fence = head; |
641 |
private int lastRet = -1; |
642 |
|
643 |
public boolean hasNext() { |
644 |
return cursor != fence; |
645 |
} |
646 |
|
647 |
public E next() { |
648 |
if (cursor == fence) |
649 |
throw new NoSuchElementException(); |
650 |
cursor = (cursor - 1) & (elements.length - 1); |
651 |
@SuppressWarnings("unchecked") |
652 |
E result = (E) elements[cursor]; |
653 |
if (head != fence || result == null) |
654 |
throw new ConcurrentModificationException(); |
655 |
lastRet = cursor; |
656 |
return result; |
657 |
} |
658 |
|
659 |
public void remove() { |
660 |
if (lastRet < 0) |
661 |
throw new IllegalStateException(); |
662 |
if (!delete(lastRet)) { |
663 |
cursor = (cursor + 1) & (elements.length - 1); |
664 |
fence = head; |
665 |
} |
666 |
lastRet = -1; |
667 |
} |
668 |
} |
669 |
|
670 |
/** |
671 |
* Returns {@code true} if this deque contains the specified element. |
672 |
* More formally, returns {@code true} if and only if this deque contains |
673 |
* at least one element {@code e} such that {@code o.equals(e)}. |
674 |
* |
675 |
* @param o object to be checked for containment in this deque |
676 |
* @return {@code true} if this deque contains the specified element |
677 |
*/ |
678 |
public boolean contains(Object o) { |
679 |
if (o == null) |
680 |
return false; |
681 |
int mask = elements.length - 1; |
682 |
int i = head; |
683 |
Object x; |
684 |
while ( (x = elements[i]) != null) { |
685 |
if (o.equals(x)) |
686 |
return true; |
687 |
i = (i + 1) & mask; |
688 |
} |
689 |
return false; |
690 |
} |
691 |
|
692 |
/** |
693 |
* Removes a single instance of the specified element from this deque. |
694 |
* If the deque does not contain the element, it is unchanged. |
695 |
* More formally, removes the first element {@code e} such that |
696 |
* {@code o.equals(e)} (if such an element exists). |
697 |
* Returns {@code true} if this deque contained the specified element |
698 |
* (or equivalently, if this deque changed as a result of the call). |
699 |
* |
700 |
* <p>This method is equivalent to {@link #removeFirstOccurrence}. |
701 |
* |
702 |
* @param o element to be removed from this deque, if present |
703 |
* @return {@code true} if this deque contained the specified element |
704 |
*/ |
705 |
public boolean remove(Object o) { |
706 |
return removeFirstOccurrence(o); |
707 |
} |
708 |
|
709 |
/** |
710 |
* Removes all of the elements from this deque. |
711 |
* The deque will be empty after this call returns. |
712 |
*/ |
713 |
public void clear() { |
714 |
int h = head; |
715 |
int t = tail; |
716 |
if (h != t) { // clear all cells |
717 |
head = tail = 0; |
718 |
int i = h; |
719 |
int mask = elements.length - 1; |
720 |
do { |
721 |
elements[i] = null; |
722 |
i = (i + 1) & mask; |
723 |
} while (i != t); |
724 |
} |
725 |
} |
726 |
|
727 |
/** |
728 |
* Returns an array containing all of the elements in this deque |
729 |
* in proper sequence (from first to last element). |
730 |
* |
731 |
* <p>The returned array will be "safe" in that no references to it are |
732 |
* maintained by this deque. (In other words, this method must allocate |
733 |
* a new array). The caller is thus free to modify the returned array. |
734 |
* |
735 |
* <p>This method acts as bridge between array-based and collection-based |
736 |
* APIs. |
737 |
* |
738 |
* @return an array containing all of the elements in this deque |
739 |
*/ |
740 |
public Object[] toArray() { |
741 |
return copyElements(new Object[size()]); |
742 |
} |
743 |
|
744 |
/** |
745 |
* Returns an array containing all of the elements in this deque in |
746 |
* proper sequence (from first to last element); the runtime type of the |
747 |
* returned array is that of the specified array. If the deque fits in |
748 |
* the specified array, it is returned therein. Otherwise, a new array |
749 |
* is allocated with the runtime type of the specified array and the |
750 |
* size of this deque. |
751 |
* |
752 |
* <p>If this deque fits in the specified array with room to spare |
753 |
* (i.e., the array has more elements than this deque), the element in |
754 |
* the array immediately following the end of the deque is set to |
755 |
* {@code null}. |
756 |
* |
757 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
758 |
* array-based and collection-based APIs. Further, this method allows |
759 |
* precise control over the runtime type of the output array, and may, |
760 |
* under certain circumstances, be used to save allocation costs. |
761 |
* |
762 |
* <p>Suppose {@code x} is a deque known to contain only strings. |
763 |
* The following code can be used to dump the deque into a newly |
764 |
* allocated array of {@code String}: |
765 |
* |
766 |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
767 |
* |
768 |
* Note that {@code toArray(new Object[0])} is identical in function to |
769 |
* {@code toArray()}. |
770 |
* |
771 |
* @param a the array into which the elements of the deque are to |
772 |
* be stored, if it is big enough; otherwise, a new array of the |
773 |
* same runtime type is allocated for this purpose |
774 |
* @return an array containing all of the elements in this deque |
775 |
* @throws ArrayStoreException if the runtime type of the specified array |
776 |
* is not a supertype of the runtime type of every element in |
777 |
* this deque |
778 |
* @throws NullPointerException if the specified array is null |
779 |
*/ |
780 |
@SuppressWarnings("unchecked") |
781 |
public <T> T[] toArray(T[] a) { |
782 |
int size = size(); |
783 |
if (a.length < size) |
784 |
a = (T[])java.lang.reflect.Array.newInstance( |
785 |
a.getClass().getComponentType(), size); |
786 |
copyElements(a); |
787 |
if (a.length > size) |
788 |
a[size] = null; |
789 |
return a; |
790 |
} |
791 |
|
792 |
// *** Object methods *** |
793 |
|
794 |
/** |
795 |
* Returns a copy of this deque. |
796 |
* |
797 |
* @return a copy of this deque |
798 |
*/ |
799 |
public ArrayDeque<E> clone() { |
800 |
try { |
801 |
@SuppressWarnings("unchecked") |
802 |
ArrayDeque<E> result = (ArrayDeque<E>) super.clone(); |
803 |
result.elements = Arrays.copyOf(elements, elements.length); |
804 |
return result; |
805 |
} catch (CloneNotSupportedException e) { |
806 |
throw new AssertionError(); |
807 |
} |
808 |
} |
809 |
|
810 |
private static final long serialVersionUID = 2340985798034038923L; |
811 |
|
812 |
/** |
813 |
* Saves this deque to a stream (that is, serializes it). |
814 |
* |
815 |
* @serialData The current size ({@code int}) of the deque, |
816 |
* followed by all of its elements (each an object reference) in |
817 |
* first-to-last order. |
818 |
*/ |
819 |
private void writeObject(java.io.ObjectOutputStream s) |
820 |
throws java.io.IOException { |
821 |
s.defaultWriteObject(); |
822 |
|
823 |
// Write out size |
824 |
s.writeInt(size()); |
825 |
|
826 |
// Write out elements in order. |
827 |
int mask = elements.length - 1; |
828 |
for (int i = head; i != tail; i = (i + 1) & mask) |
829 |
s.writeObject(elements[i]); |
830 |
} |
831 |
|
832 |
/** |
833 |
* Reconstitutes this deque from a stream (that is, deserializes it). |
834 |
*/ |
835 |
private void readObject(java.io.ObjectInputStream s) |
836 |
throws java.io.IOException, ClassNotFoundException { |
837 |
s.defaultReadObject(); |
838 |
|
839 |
// Read in size and allocate array |
840 |
int size = s.readInt(); |
841 |
allocateElements(size); |
842 |
head = 0; |
843 |
tail = size; |
844 |
|
845 |
// Read in all elements in the proper order. |
846 |
for (int i = 0; i < size; i++) |
847 |
elements[i] = s.readObject(); |
848 |
} |
849 |
|
850 |
public Stream<E> stream() { |
851 |
int flags = Streams.STREAM_IS_ORDERED | Streams.STREAM_IS_SIZED; |
852 |
return Streams.stream |
853 |
(() -> new DeqSpliterator<E>(this, head, tail), flags); |
854 |
} |
855 |
public Stream<E> parallelStream() { |
856 |
int flags = Streams.STREAM_IS_ORDERED | Streams.STREAM_IS_SIZED; |
857 |
return Streams.parallelStream |
858 |
(() -> new DeqSpliterator<E>(this, head, tail), flags); |
859 |
} |
860 |
|
861 |
|
862 |
static final class DeqSpliterator<E> implements Spliterator<E> { |
863 |
private final ArrayDeque<E> deq; |
864 |
private final int fence; // initially tail |
865 |
private int index; // current index, modified on traverse/split |
866 |
|
867 |
/** Create new spliterator covering the given array and range */ |
868 |
DeqSpliterator(ArrayDeque<E> deq, int origin, int fence) { |
869 |
this.deq = deq; this.index = origin; this.fence = fence; |
870 |
} |
871 |
|
872 |
public DeqSpliterator<E> trySplit() { |
873 |
int n = deq.elements.length; |
874 |
int h = index, t = fence; |
875 |
if (h != t && ((h + 1) & (n - 1)) != t) { |
876 |
if (h > t) |
877 |
t += n; |
878 |
int m = ((h + t) >>> 1) & (n - 1); |
879 |
return new DeqSpliterator<E>(deq, h, index = m); |
880 |
} |
881 |
return null; |
882 |
} |
883 |
|
884 |
public void forEach(Block<? super E> block) { |
885 |
if (block == null) |
886 |
throw new NullPointerException(); |
887 |
Object[] a = deq.elements; |
888 |
int m = a.length - 1, f = fence, i = index; |
889 |
index = f; |
890 |
while (i != f) { |
891 |
@SuppressWarnings("unchecked") E e = (E)a[i]; |
892 |
i = (i + 1) & m; |
893 |
if (e == null) |
894 |
throw new ConcurrentModificationException(); |
895 |
block.accept(e); |
896 |
} |
897 |
} |
898 |
|
899 |
public boolean tryAdvance(Block<? super E> block) { |
900 |
if (block == null) |
901 |
throw new NullPointerException(); |
902 |
Object[] a = deq.elements; |
903 |
int m = a.length - 1, i = index; |
904 |
if (i != fence) { |
905 |
@SuppressWarnings("unchecked") E e = (E)a[i]; |
906 |
index = (i + 1) & m; |
907 |
if (e == null) |
908 |
throw new ConcurrentModificationException(); |
909 |
block.accept(e); |
910 |
return true; |
911 |
} |
912 |
return false; |
913 |
} |
914 |
|
915 |
// Other spliterator methods |
916 |
public long estimateSize() { |
917 |
int n = fence - index; |
918 |
if (n < 0) |
919 |
n += deq.elements.length; |
920 |
return (long)n; |
921 |
} |
922 |
public boolean hasExactSize() { return true; } |
923 |
public boolean hasExactSplits() { return true; } |
924 |
} |
925 |
|
926 |
} |