--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/java.base/share/classes/java/util/ArrayDeque.java Sun Aug 17 15:54:13 2014 +0100
@@ -0,0 +1,985 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Josh Bloch of Google Inc. and released to the public domain,
+ * as explained at http://creativecommons.org/publicdomain/zero/1.0/.
+ */
+
+package java.util;
+
+import java.io.Serializable;
+import java.util.function.Consumer;
+
+/**
+ * Resizable-array implementation of the {@link Deque} interface. Array
+ * deques have no capacity restrictions; they grow as necessary to support
+ * usage. They are not thread-safe; in the absence of external
+ * synchronization, they do not support concurrent access by multiple threads.
+ * Null elements are prohibited. This class is likely to be faster than
+ * {@link Stack} when used as a stack, and faster than {@link LinkedList}
+ * when used as a queue.
+ *
+ * <p>Most {@code ArrayDeque} operations run in amortized constant time.
+ * Exceptions include {@link #remove(Object) remove}, {@link
+ * #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
+ * removeLastOccurrence}, {@link #contains contains}, {@link #iterator
+ * iterator.remove()}, and the bulk operations, all of which run in linear
+ * time.
+ *
+ * <p>The iterators returned by this class's {@code iterator} method are
+ * <i>fail-fast</i>: If the deque is modified at any time after the iterator
+ * is created, in any way except through the iterator's own {@code remove}
+ * method, the iterator will generally throw a {@link
+ * ConcurrentModificationException}. Thus, in the face of concurrent
+ * modification, the iterator fails quickly and cleanly, rather than risking
+ * arbitrary, non-deterministic behavior at an undetermined time in the
+ * future.
+ *
+ * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
+ * as it is, generally speaking, impossible to make any hard guarantees in the
+ * presence of unsynchronized concurrent modification. Fail-fast iterators
+ * throw {@code ConcurrentModificationException} on a best-effort basis.
+ * Therefore, it would be wrong to write a program that depended on this
+ * exception for its correctness: <i>the fail-fast behavior of iterators
+ * should be used only to detect bugs.</i>
+ *
+ * <p>This class and its iterator implement all of the
+ * <em>optional</em> methods of the {@link Collection} and {@link
+ * Iterator} interfaces.
+ *
+ * <p>This class is a member of the
+ * <a href="{@docRoot}/../technotes/guides/collections/index.html">
+ * Java Collections Framework</a>.
+ *
+ * @author Josh Bloch and Doug Lea
+ * @since 1.6
+ * @param <E> the type of elements held in this collection
+ */
+public class ArrayDeque<E> extends AbstractCollection<E>
+ implements Deque<E>, Cloneable, Serializable
+{
+ /**
+ * The array in which the elements of the deque are stored.
+ * The capacity of the deque is the length of this array, which is
+ * always a power of two. The array is never allowed to become
+ * full, except transiently within an addX method where it is
+ * resized (see doubleCapacity) immediately upon becoming full,
+ * thus avoiding head and tail wrapping around to equal each
+ * other. We also guarantee that all array cells not holding
+ * deque elements are always null.
+ */
+ transient Object[] elements; // non-private to simplify nested class access
+
+ /**
+ * The index of the element at the head of the deque (which is the
+ * element that would be removed by remove() or pop()); or an
+ * arbitrary number equal to tail if the deque is empty.
+ */
+ transient int head;
+
+ /**
+ * The index at which the next element would be added to the tail
+ * of the deque (via addLast(E), add(E), or push(E)).
+ */
+ transient int tail;
+
+ /**
+ * The minimum capacity that we'll use for a newly created deque.
+ * Must be a power of 2.
+ */
+ private static final int MIN_INITIAL_CAPACITY = 8;
+
+ // ****** Array allocation and resizing utilities ******
+
+ /**
+ * Allocates empty array to hold the given number of elements.
+ *
+ * @param numElements the number of elements to hold
+ */
+ private void allocateElements(int numElements) {
+ int initialCapacity = MIN_INITIAL_CAPACITY;
+ // Find the best power of two to hold elements.
+ // Tests "<=" because arrays aren't kept full.
+ if (numElements >= initialCapacity) {
+ initialCapacity = numElements;
+ initialCapacity |= (initialCapacity >>> 1);
+ initialCapacity |= (initialCapacity >>> 2);
+ initialCapacity |= (initialCapacity >>> 4);
+ initialCapacity |= (initialCapacity >>> 8);
+ initialCapacity |= (initialCapacity >>> 16);
+ initialCapacity++;
+
+ if (initialCapacity < 0) // Too many elements, must back off
+ initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
+ }
+ elements = new Object[initialCapacity];
+ }
+
+ /**
+ * Doubles the capacity of this deque. Call only when full, i.e.,
+ * when head and tail have wrapped around to become equal.
+ */
+ private void doubleCapacity() {
+ assert head == tail;
+ int p = head;
+ int n = elements.length;
+ int r = n - p; // number of elements to the right of p
+ int newCapacity = n << 1;
+ if (newCapacity < 0)
+ throw new IllegalStateException("Sorry, deque too big");
+ Object[] a = new Object[newCapacity];
+ System.arraycopy(elements, p, a, 0, r);
+ System.arraycopy(elements, 0, a, r, p);
+ elements = a;
+ head = 0;
+ tail = n;
+ }
+
+ /**
+ * Copies the elements from our element array into the specified array,
+ * in order (from first to last element in the deque). It is assumed
+ * that the array is large enough to hold all elements in the deque.
+ *
+ * @return its argument
+ */
+ private <T> T[] copyElements(T[] a) {
+ if (head < tail) {
+ System.arraycopy(elements, head, a, 0, size());
+ } else if (head > tail) {
+ int headPortionLen = elements.length - head;
+ System.arraycopy(elements, head, a, 0, headPortionLen);
+ System.arraycopy(elements, 0, a, headPortionLen, tail);
+ }
+ return a;
+ }
+
+ /**
+ * Constructs an empty array deque with an initial capacity
+ * sufficient to hold 16 elements.
+ */
+ public ArrayDeque() {
+ elements = new Object[16];
+ }
+
+ /**
+ * Constructs an empty array deque with an initial capacity
+ * sufficient to hold the specified number of elements.
+ *
+ * @param numElements lower bound on initial capacity of the deque
+ */
+ public ArrayDeque(int numElements) {
+ allocateElements(numElements);
+ }
+
+ /**
+ * Constructs a deque containing the elements of the specified
+ * collection, in the order they are returned by the collection's
+ * iterator. (The first element returned by the collection's
+ * iterator becomes the first element, or <i>front</i> of the
+ * deque.)
+ *
+ * @param c the collection whose elements are to be placed into the deque
+ * @throws NullPointerException if the specified collection is null
+ */
+ public ArrayDeque(Collection<? extends E> c) {
+ allocateElements(c.size());
+ addAll(c);
+ }
+
+ // The main insertion and extraction methods are addFirst,
+ // addLast, pollFirst, pollLast. The other methods are defined in
+ // terms of these.
+
+ /**
+ * Inserts the specified element at the front of this deque.
+ *
+ * @param e the element to add
+ * @throws NullPointerException if the specified element is null
+ */
+ public void addFirst(E e) {
+ if (e == null)
+ throw new NullPointerException();
+ elements[head = (head - 1) & (elements.length - 1)] = e;
+ if (head == tail)
+ doubleCapacity();
+ }
+
+ /**
+ * Inserts the specified element at the end of this deque.
+ *
+ * <p>This method is equivalent to {@link #add}.
+ *
+ * @param e the element to add
+ * @throws NullPointerException if the specified element is null
+ */
+ public void addLast(E e) {
+ if (e == null)
+ throw new NullPointerException();
+ elements[tail] = e;
+ if ( (tail = (tail + 1) & (elements.length - 1)) == head)
+ doubleCapacity();
+ }
+
+ /**
+ * Inserts the specified element at the front of this deque.
+ *
+ * @param e the element to add
+ * @return {@code true} (as specified by {@link Deque#offerFirst})
+ * @throws NullPointerException if the specified element is null
+ */
+ public boolean offerFirst(E e) {
+ addFirst(e);
+ return true;
+ }
+
+ /**
+ * Inserts the specified element at the end of this deque.
+ *
+ * @param e the element to add
+ * @return {@code true} (as specified by {@link Deque#offerLast})
+ * @throws NullPointerException if the specified element is null
+ */
+ public boolean offerLast(E e) {
+ addLast(e);
+ return true;
+ }
+
+ /**
+ * @throws NoSuchElementException {@inheritDoc}
+ */
+ public E removeFirst() {
+ E x = pollFirst();
+ if (x == null)
+ throw new NoSuchElementException();
+ return x;
+ }
+
+ /**
+ * @throws NoSuchElementException {@inheritDoc}
+ */
+ public E removeLast() {
+ E x = pollLast();
+ if (x == null)
+ throw new NoSuchElementException();
+ return x;
+ }
+
+ public E pollFirst() {
+ int h = head;
+ @SuppressWarnings("unchecked")
+ E result = (E) elements[h];
+ // Element is null if deque empty
+ if (result == null)
+ return null;
+ elements[h] = null; // Must null out slot
+ head = (h + 1) & (elements.length - 1);
+ return result;
+ }
+
+ public E pollLast() {
+ int t = (tail - 1) & (elements.length - 1);
+ @SuppressWarnings("unchecked")
+ E result = (E) elements[t];
+ if (result == null)
+ return null;
+ elements[t] = null;
+ tail = t;
+ return result;
+ }
+
+ /**
+ * @throws NoSuchElementException {@inheritDoc}
+ */
+ public E getFirst() {
+ @SuppressWarnings("unchecked")
+ E result = (E) elements[head];
+ if (result == null)
+ throw new NoSuchElementException();
+ return result;
+ }
+
+ /**
+ * @throws NoSuchElementException {@inheritDoc}
+ */
+ public E getLast() {
+ @SuppressWarnings("unchecked")
+ E result = (E) elements[(tail - 1) & (elements.length - 1)];
+ if (result == null)
+ throw new NoSuchElementException();
+ return result;
+ }
+
+ @SuppressWarnings("unchecked")
+ public E peekFirst() {
+ // elements[head] is null if deque empty
+ return (E) elements[head];
+ }
+
+ @SuppressWarnings("unchecked")
+ public E peekLast() {
+ return (E) elements[(tail - 1) & (elements.length - 1)];
+ }
+
+ /**
+ * Removes the first occurrence of the specified element in this
+ * deque (when traversing the deque from head to tail).
+ * If the deque does not contain the element, it is unchanged.
+ * More formally, removes the first element {@code e} such that
+ * {@code o.equals(e)} (if such an element exists).
+ * Returns {@code true} if this deque contained the specified element
+ * (or equivalently, if this deque changed as a result of the call).
+ *
+ * @param o element to be removed from this deque, if present
+ * @return {@code true} if the deque contained the specified element
+ */
+ public boolean removeFirstOccurrence(Object o) {
+ if (o == null)
+ return false;
+ int mask = elements.length - 1;
+ int i = head;
+ Object x;
+ while ( (x = elements[i]) != null) {
+ if (o.equals(x)) {
+ delete(i);
+ return true;
+ }
+ i = (i + 1) & mask;
+ }
+ return false;
+ }
+
+ /**
+ * Removes the last occurrence of the specified element in this
+ * deque (when traversing the deque from head to tail).
+ * If the deque does not contain the element, it is unchanged.
+ * More formally, removes the last element {@code e} such that
+ * {@code o.equals(e)} (if such an element exists).
+ * Returns {@code true} if this deque contained the specified element
+ * (or equivalently, if this deque changed as a result of the call).
+ *
+ * @param o element to be removed from this deque, if present
+ * @return {@code true} if the deque contained the specified element
+ */
+ public boolean removeLastOccurrence(Object o) {
+ if (o == null)
+ return false;
+ int mask = elements.length - 1;
+ int i = (tail - 1) & mask;
+ Object x;
+ while ( (x = elements[i]) != null) {
+ if (o.equals(x)) {
+ delete(i);
+ return true;
+ }
+ i = (i - 1) & mask;
+ }
+ return false;
+ }
+
+ // *** Queue methods ***
+
+ /**
+ * Inserts the specified element at the end of this deque.
+ *
+ * <p>This method is equivalent to {@link #addLast}.
+ *
+ * @param e the element to add
+ * @return {@code true} (as specified by {@link Collection#add})
+ * @throws NullPointerException if the specified element is null
+ */
+ public boolean add(E e) {
+ addLast(e);
+ return true;
+ }
+
+ /**
+ * Inserts the specified element at the end of this deque.
+ *
+ * <p>This method is equivalent to {@link #offerLast}.
+ *
+ * @param e the element to add
+ * @return {@code true} (as specified by {@link Queue#offer})
+ * @throws NullPointerException if the specified element is null
+ */
+ public boolean offer(E e) {
+ return offerLast(e);
+ }
+
+ /**
+ * Retrieves and removes the head of the queue represented by this deque.
+ *
+ * This method differs from {@link #poll poll} only in that it throws an
+ * exception if this deque is empty.
+ *
+ * <p>This method is equivalent to {@link #removeFirst}.
+ *
+ * @return the head of the queue represented by this deque
+ * @throws NoSuchElementException {@inheritDoc}
+ */
+ public E remove() {
+ return removeFirst();
+ }
+
+ /**
+ * Retrieves and removes the head of the queue represented by this deque
+ * (in other words, the first element of this deque), or returns
+ * {@code null} if this deque is empty.
+ *
+ * <p>This method is equivalent to {@link #pollFirst}.
+ *
+ * @return the head of the queue represented by this deque, or
+ * {@code null} if this deque is empty
+ */
+ public E poll() {
+ return pollFirst();
+ }
+
+ /**
+ * Retrieves, but does not remove, the head of the queue represented by
+ * this deque. This method differs from {@link #peek peek} only in
+ * that it throws an exception if this deque is empty.
+ *
+ * <p>This method is equivalent to {@link #getFirst}.
+ *
+ * @return the head of the queue represented by this deque
+ * @throws NoSuchElementException {@inheritDoc}
+ */
+ public E element() {
+ return getFirst();
+ }
+
+ /**
+ * Retrieves, but does not remove, the head of the queue represented by
+ * this deque, or returns {@code null} if this deque is empty.
+ *
+ * <p>This method is equivalent to {@link #peekFirst}.
+ *
+ * @return the head of the queue represented by this deque, or
+ * {@code null} if this deque is empty
+ */
+ public E peek() {
+ return peekFirst();
+ }
+
+ // *** Stack methods ***
+
+ /**
+ * Pushes an element onto the stack represented by this deque. In other
+ * words, inserts the element at the front of this deque.
+ *
+ * <p>This method is equivalent to {@link #addFirst}.
+ *
+ * @param e the element to push
+ * @throws NullPointerException if the specified element is null
+ */
+ public void push(E e) {
+ addFirst(e);
+ }
+
+ /**
+ * Pops an element from the stack represented by this deque. In other
+ * words, removes and returns the first element of this deque.
+ *
+ * <p>This method is equivalent to {@link #removeFirst()}.
+ *
+ * @return the element at the front of this deque (which is the top
+ * of the stack represented by this deque)
+ * @throws NoSuchElementException {@inheritDoc}
+ */
+ public E pop() {
+ return removeFirst();
+ }
+
+ private void checkInvariants() {
+ assert elements[tail] == null;
+ assert head == tail ? elements[head] == null :
+ (elements[head] != null &&
+ elements[(tail - 1) & (elements.length - 1)] != null);
+ assert elements[(head - 1) & (elements.length - 1)] == null;
+ }
+
+ /**
+ * Removes the element at the specified position in the elements array,
+ * adjusting head and tail as necessary. This can result in motion of
+ * elements backwards or forwards in the array.
+ *
+ * <p>This method is called delete rather than remove to emphasize
+ * that its semantics differ from those of {@link List#remove(int)}.
+ *
+ * @return true if elements moved backwards
+ */
+ private boolean delete(int i) {
+ checkInvariants();
+ final Object[] elements = this.elements;
+ final int mask = elements.length - 1;
+ final int h = head;
+ final int t = tail;
+ final int front = (i - h) & mask;
+ final int back = (t - i) & mask;
+
+ // Invariant: head <= i < tail mod circularity
+ if (front >= ((t - h) & mask))
+ throw new ConcurrentModificationException();
+
+ // Optimize for least element motion
+ if (front < back) {
+ if (h <= i) {
+ System.arraycopy(elements, h, elements, h + 1, front);
+ } else { // Wrap around
+ System.arraycopy(elements, 0, elements, 1, i);
+ elements[0] = elements[mask];
+ System.arraycopy(elements, h, elements, h + 1, mask - h);
+ }
+ elements[h] = null;
+ head = (h + 1) & mask;
+ return false;
+ } else {
+ if (i < t) { // Copy the null tail as well
+ System.arraycopy(elements, i + 1, elements, i, back);
+ tail = t - 1;
+ } else { // Wrap around
+ System.arraycopy(elements, i + 1, elements, i, mask - i);
+ elements[mask] = elements[0];
+ System.arraycopy(elements, 1, elements, 0, t);
+ tail = (t - 1) & mask;
+ }
+ return true;
+ }
+ }
+
+ // *** Collection Methods ***
+
+ /**
+ * Returns the number of elements in this deque.
+ *
+ * @return the number of elements in this deque
+ */
+ public int size() {
+ return (tail - head) & (elements.length - 1);
+ }
+
+ /**
+ * Returns {@code true} if this deque contains no elements.
+ *
+ * @return {@code true} if this deque contains no elements
+ */
+ public boolean isEmpty() {
+ return head == tail;
+ }
+
+ /**
+ * Returns an iterator over the elements in this deque. The elements
+ * will be ordered from first (head) to last (tail). This is the same
+ * order that elements would be dequeued (via successive calls to
+ * {@link #remove} or popped (via successive calls to {@link #pop}).
+ *
+ * @return an iterator over the elements in this deque
+ */
+ public Iterator<E> iterator() {
+ return new DeqIterator();
+ }
+
+ public Iterator<E> descendingIterator() {
+ return new DescendingIterator();
+ }
+
+ private class DeqIterator implements Iterator<E> {
+ /**
+ * Index of element to be returned by subsequent call to next.
+ */
+ private int cursor = head;
+
+ /**
+ * Tail recorded at construction (also in remove), to stop
+ * iterator and also to check for comodification.
+ */
+ private int fence = tail;
+
+ /**
+ * Index of element returned by most recent call to next.
+ * Reset to -1 if element is deleted by a call to remove.
+ */
+ private int lastRet = -1;
+
+ public boolean hasNext() {
+ return cursor != fence;
+ }
+
+ public E next() {
+ if (cursor == fence)
+ throw new NoSuchElementException();
+ @SuppressWarnings("unchecked")
+ E result = (E) elements[cursor];
+ // This check doesn't catch all possible comodifications,
+ // but does catch the ones that corrupt traversal
+ if (tail != fence || result == null)
+ throw new ConcurrentModificationException();
+ lastRet = cursor;
+ cursor = (cursor + 1) & (elements.length - 1);
+ return result;
+ }
+
+ public void remove() {
+ if (lastRet < 0)
+ throw new IllegalStateException();
+ if (delete(lastRet)) { // if left-shifted, undo increment in next()
+ cursor = (cursor - 1) & (elements.length - 1);
+ fence = tail;
+ }
+ lastRet = -1;
+ }
+
+ public void forEachRemaining(Consumer<? super E> action) {
+ Objects.requireNonNull(action);
+ Object[] a = elements;
+ int m = a.length - 1, f = fence, i = cursor;
+ cursor = f;
+ while (i != f) {
+ @SuppressWarnings("unchecked") E e = (E)a[i];
+ i = (i + 1) & m;
+ if (e == null)
+ throw new ConcurrentModificationException();
+ action.accept(e);
+ }
+ }
+ }
+
+ private class DescendingIterator implements Iterator<E> {
+ /*
+ * This class is nearly a mirror-image of DeqIterator, using
+ * tail instead of head for initial cursor, and head instead of
+ * tail for fence.
+ */
+ private int cursor = tail;
+ private int fence = head;
+ private int lastRet = -1;
+
+ public boolean hasNext() {
+ return cursor != fence;
+ }
+
+ public E next() {
+ if (cursor == fence)
+ throw new NoSuchElementException();
+ cursor = (cursor - 1) & (elements.length - 1);
+ @SuppressWarnings("unchecked")
+ E result = (E) elements[cursor];
+ if (head != fence || result == null)
+ throw new ConcurrentModificationException();
+ lastRet = cursor;
+ return result;
+ }
+
+ public void remove() {
+ if (lastRet < 0)
+ throw new IllegalStateException();
+ if (!delete(lastRet)) {
+ cursor = (cursor + 1) & (elements.length - 1);
+ fence = head;
+ }
+ lastRet = -1;
+ }
+ }
+
+ /**
+ * Returns {@code true} if this deque contains the specified element.
+ * More formally, returns {@code true} if and only if this deque contains
+ * at least one element {@code e} such that {@code o.equals(e)}.
+ *
+ * @param o object to be checked for containment in this deque
+ * @return {@code true} if this deque contains the specified element
+ */
+ public boolean contains(Object o) {
+ if (o == null)
+ return false;
+ int mask = elements.length - 1;
+ int i = head;
+ Object x;
+ while ( (x = elements[i]) != null) {
+ if (o.equals(x))
+ return true;
+ i = (i + 1) & mask;
+ }
+ return false;
+ }
+
+ /**
+ * Removes a single instance of the specified element from this deque.
+ * If the deque does not contain the element, it is unchanged.
+ * More formally, removes the first element {@code e} such that
+ * {@code o.equals(e)} (if such an element exists).
+ * Returns {@code true} if this deque contained the specified element
+ * (or equivalently, if this deque changed as a result of the call).
+ *
+ * <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
+ *
+ * @param o element to be removed from this deque, if present
+ * @return {@code true} if this deque contained the specified element
+ */
+ public boolean remove(Object o) {
+ return removeFirstOccurrence(o);
+ }
+
+ /**
+ * Removes all of the elements from this deque.
+ * The deque will be empty after this call returns.
+ */
+ public void clear() {
+ int h = head;
+ int t = tail;
+ if (h != t) { // clear all cells
+ head = tail = 0;
+ int i = h;
+ int mask = elements.length - 1;
+ do {
+ elements[i] = null;
+ i = (i + 1) & mask;
+ } while (i != t);
+ }
+ }
+
+ /**
+ * Returns an array containing all of the elements in this deque
+ * in proper sequence (from first to last element).
+ *
+ * <p>The returned array will be "safe" in that no references to it are
+ * maintained by this deque. (In other words, this method must allocate
+ * a new array). The caller is thus free to modify the returned array.
+ *
+ * <p>This method acts as bridge between array-based and collection-based
+ * APIs.
+ *
+ * @return an array containing all of the elements in this deque
+ */
+ public Object[] toArray() {
+ return copyElements(new Object[size()]);
+ }
+
+ /**
+ * Returns an array containing all of the elements in this deque in
+ * proper sequence (from first to last element); the runtime type of the
+ * returned array is that of the specified array. If the deque fits in
+ * the specified array, it is returned therein. Otherwise, a new array
+ * is allocated with the runtime type of the specified array and the
+ * size of this deque.
+ *
+ * <p>If this deque fits in the specified array with room to spare
+ * (i.e., the array has more elements than this deque), the element in
+ * the array immediately following the end of the deque is set to
+ * {@code null}.
+ *
+ * <p>Like the {@link #toArray()} method, this method acts as bridge between
+ * array-based and collection-based APIs. Further, this method allows
+ * precise control over the runtime type of the output array, and may,
+ * under certain circumstances, be used to save allocation costs.
+ *
+ * <p>Suppose {@code x} is a deque known to contain only strings.
+ * The following code can be used to dump the deque into a newly
+ * allocated array of {@code String}:
+ *
+ * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
+ *
+ * Note that {@code toArray(new Object[0])} is identical in function to
+ * {@code toArray()}.
+ *
+ * @param a the array into which the elements of the deque are to
+ * be stored, if it is big enough; otherwise, a new array of the
+ * same runtime type is allocated for this purpose
+ * @return an array containing all of the elements in this deque
+ * @throws ArrayStoreException if the runtime type of the specified array
+ * is not a supertype of the runtime type of every element in
+ * this deque
+ * @throws NullPointerException if the specified array is null
+ */
+ @SuppressWarnings("unchecked")
+ public <T> T[] toArray(T[] a) {
+ int size = size();
+ if (a.length < size)
+ a = (T[])java.lang.reflect.Array.newInstance(
+ a.getClass().getComponentType(), size);
+ copyElements(a);
+ if (a.length > size)
+ a[size] = null;
+ return a;
+ }
+
+ // *** Object methods ***
+
+ /**
+ * Returns a copy of this deque.
+ *
+ * @return a copy of this deque
+ */
+ public ArrayDeque<E> clone() {
+ try {
+ @SuppressWarnings("unchecked")
+ ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
+ result.elements = Arrays.copyOf(elements, elements.length);
+ return result;
+ } catch (CloneNotSupportedException e) {
+ throw new AssertionError();
+ }
+ }
+
+ private static final long serialVersionUID = 2340985798034038923L;
+
+ /**
+ * Saves this deque to a stream (that is, serializes it).
+ *
+ * @serialData The current size ({@code int}) of the deque,
+ * followed by all of its elements (each an object reference) in
+ * first-to-last order.
+ */
+ private void writeObject(java.io.ObjectOutputStream s)
+ throws java.io.IOException {
+ s.defaultWriteObject();
+
+ // Write out size
+ s.writeInt(size());
+
+ // Write out elements in order.
+ int mask = elements.length - 1;
+ for (int i = head; i != tail; i = (i + 1) & mask)
+ s.writeObject(elements[i]);
+ }
+
+ /**
+ * Reconstitutes this deque from a stream (that is, deserializes it).
+ */
+ private void readObject(java.io.ObjectInputStream s)
+ throws java.io.IOException, ClassNotFoundException {
+ s.defaultReadObject();
+
+ // Read in size and allocate array
+ int size = s.readInt();
+ allocateElements(size);
+ head = 0;
+ tail = size;
+
+ // Read in all elements in the proper order.
+ for (int i = 0; i < size; i++)
+ elements[i] = s.readObject();
+ }
+
+ /**
+ * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
+ * and <em>fail-fast</em> {@link Spliterator} over the elements in this
+ * deque.
+ *
+ * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
+ * {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and
+ * {@link Spliterator#NONNULL}. Overriding implementations should document
+ * the reporting of additional characteristic values.
+ *
+ * @return a {@code Spliterator} over the elements in this deque
+ * @since 1.8
+ */
+ public Spliterator<E> spliterator() {
+ return new DeqSpliterator<>(this, -1, -1);
+ }
+
+ static final class DeqSpliterator<E> implements Spliterator<E> {
+ private final ArrayDeque<E> deq;
+ private int fence; // -1 until first use
+ private int index; // current index, modified on traverse/split
+
+ /** Creates new spliterator covering the given array and range */
+ DeqSpliterator(ArrayDeque<E> deq, int origin, int fence) {
+ this.deq = deq;
+ this.index = origin;
+ this.fence = fence;
+ }
+
+ private int getFence() { // force initialization
+ int t;
+ if ((t = fence) < 0) {
+ t = fence = deq.tail;
+ index = deq.head;
+ }
+ return t;
+ }
+
+ public DeqSpliterator<E> trySplit() {
+ int t = getFence(), h = index, n = deq.elements.length;
+ if (h != t && ((h + 1) & (n - 1)) != t) {
+ if (h > t)
+ t += n;
+ int m = ((h + t) >>> 1) & (n - 1);
+ return new DeqSpliterator<>(deq, h, index = m);
+ }
+ return null;
+ }
+
+ public void forEachRemaining(Consumer<? super E> consumer) {
+ if (consumer == null)
+ throw new NullPointerException();
+ Object[] a = deq.elements;
+ int m = a.length - 1, f = getFence(), i = index;
+ index = f;
+ while (i != f) {
+ @SuppressWarnings("unchecked") E e = (E)a[i];
+ i = (i + 1) & m;
+ if (e == null)
+ throw new ConcurrentModificationException();
+ consumer.accept(e);
+ }
+ }
+
+ public boolean tryAdvance(Consumer<? super E> consumer) {
+ if (consumer == null)
+ throw new NullPointerException();
+ Object[] a = deq.elements;
+ int m = a.length - 1, f = getFence(), i = index;
+ if (i != fence) {
+ @SuppressWarnings("unchecked") E e = (E)a[i];
+ index = (i + 1) & m;
+ if (e == null)
+ throw new ConcurrentModificationException();
+ consumer.accept(e);
+ return true;
+ }
+ return false;
+ }
+
+ public long estimateSize() {
+ int n = getFence() - index;
+ if (n < 0)
+ n += deq.elements.length;
+ return (long) n;
+ }
+
+ @Override
+ public int characteristics() {
+ return Spliterator.ORDERED | Spliterator.SIZED |
+ Spliterator.NONNULL | Spliterator.SUBSIZED;
+ }
+ }
+
+}