--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/java/util/ArrayDeque.java Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,1227 @@
+/*
+ * 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;
+import java.util.function.Predicate;
+import java.util.function.UnaryOperator;
+
+/**
+ * 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 {@link #iterator() iterator}
+ * method are <em>fail-fast</em>: 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}/java/util/package-summary.html#CollectionsFramework">
+ * Java Collections Framework</a>.
+ *
+ * @author Josh Bloch and Doug Lea
+ * @param <E> the type of elements held in this deque
+ * @since 1.6
+ */
+public class ArrayDeque<E> extends AbstractCollection<E>
+ implements Deque<E>, Cloneable, Serializable
+{
+ /*
+ * VMs excel at optimizing simple array loops where indices are
+ * incrementing or decrementing over a valid slice, e.g.
+ *
+ * for (int i = start; i < end; i++) ... elements[i]
+ *
+ * Because in a circular array, elements are in general stored in
+ * two disjoint such slices, we help the VM by writing unusual
+ * nested loops for all traversals over the elements. Having only
+ * one hot inner loop body instead of two or three eases human
+ * maintenance and encourages VM loop inlining into the caller.
+ */
+
+ /**
+ * The array in which the elements of the deque are stored.
+ * All array cells not holding deque elements are always null.
+ * The array always has at least one null slot (at tail).
+ */
+ transient Object[] elements;
+
+ /**
+ * 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 0 <= head < elements.length 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));
+ * elements[tail] is always null.
+ */
+ transient int tail;
+
+ /**
+ * The maximum size of array to allocate.
+ * Some VMs reserve some header words in an array.
+ * Attempts to allocate larger arrays may result in
+ * OutOfMemoryError: Requested array size exceeds VM limit
+ */
+ private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
+
+ /**
+ * Increases the capacity of this deque by at least the given amount.
+ *
+ * @param needed the required minimum extra capacity; must be positive
+ */
+ private void grow(int needed) {
+ // overflow-conscious code
+ final int oldCapacity = elements.length;
+ int newCapacity;
+ // Double capacity if small; else grow by 50%
+ int jump = (oldCapacity < 64) ? (oldCapacity + 2) : (oldCapacity >> 1);
+ if (jump < needed
+ || (newCapacity = (oldCapacity + jump)) - MAX_ARRAY_SIZE > 0)
+ newCapacity = newCapacity(needed, jump);
+ final Object[] es = elements = Arrays.copyOf(elements, newCapacity);
+ // Exceptionally, here tail == head needs to be disambiguated
+ if (tail < head || (tail == head && es[head] != null)) {
+ // wrap around; slide first leg forward to end of array
+ int newSpace = newCapacity - oldCapacity;
+ System.arraycopy(es, head,
+ es, head + newSpace,
+ oldCapacity - head);
+ for (int i = head, to = (head += newSpace); i < to; i++)
+ es[i] = null;
+ }
+ }
+
+ /** Capacity calculation for edge conditions, especially overflow. */
+ private int newCapacity(int needed, int jump) {
+ final int oldCapacity = elements.length, minCapacity;
+ if ((minCapacity = oldCapacity + needed) - MAX_ARRAY_SIZE > 0) {
+ if (minCapacity < 0)
+ throw new IllegalStateException("Sorry, deque too big");
+ return Integer.MAX_VALUE;
+ }
+ if (needed > jump)
+ return minCapacity;
+ return (oldCapacity + jump - MAX_ARRAY_SIZE < 0)
+ ? oldCapacity + jump
+ : MAX_ARRAY_SIZE;
+ }
+
+ /**
+ * 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) {
+ elements =
+ new Object[(numElements < 1) ? 1 :
+ (numElements == Integer.MAX_VALUE) ? Integer.MAX_VALUE :
+ numElements + 1];
+ }
+
+ /**
+ * 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) {
+ this(c.size());
+ addAll(c);
+ }
+
+ /**
+ * Increments i, mod modulus.
+ * Precondition and postcondition: 0 <= i < modulus.
+ */
+ static final int inc(int i, int modulus) {
+ if (++i >= modulus) i = 0;
+ return i;
+ }
+
+ /**
+ * Decrements i, mod modulus.
+ * Precondition and postcondition: 0 <= i < modulus.
+ */
+ static final int dec(int i, int modulus) {
+ if (--i < 0) i = modulus - 1;
+ return i;
+ }
+
+ /**
+ * Circularly adds the given distance to index i, mod modulus.
+ * Precondition: 0 <= i < modulus, 0 <= distance <= modulus.
+ * @return index 0 <= i < modulus
+ */
+ static final int add(int i, int distance, int modulus) {
+ if ((i += distance) - modulus >= 0) i -= modulus;
+ return i;
+ }
+
+ /**
+ * Subtracts j from i, mod modulus.
+ * Index i must be logically ahead of index j.
+ * Precondition: 0 <= i < modulus, 0 <= j < modulus.
+ * @return the "circular distance" from j to i; corner case i == j
+ * is disambiguated to "empty", returning 0.
+ */
+ static final int sub(int i, int j, int modulus) {
+ if ((i -= j) < 0) i += modulus;
+ return i;
+ }
+
+ /**
+ * Returns element at array index i.
+ * This is a slight abuse of generics, accepted by javac.
+ */
+ @SuppressWarnings("unchecked")
+ static final <E> E elementAt(Object[] es, int i) {
+ return (E) es[i];
+ }
+
+ /**
+ * A version of elementAt that checks for null elements.
+ * This check doesn't catch all possible comodifications,
+ * but does catch ones that corrupt traversal.
+ */
+ static final <E> E nonNullElementAt(Object[] es, int i) {
+ @SuppressWarnings("unchecked") E e = (E) es[i];
+ if (e == null)
+ throw new ConcurrentModificationException();
+ return e;
+ }
+
+ // 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();
+ final Object[] es = elements;
+ es[head = dec(head, es.length)] = e;
+ if (head == tail)
+ grow(1);
+ }
+
+ /**
+ * 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();
+ final Object[] es = elements;
+ es[tail] = e;
+ if (head == (tail = inc(tail, es.length)))
+ grow(1);
+ }
+
+ /**
+ * Adds all of the elements in the specified collection at the end
+ * of this deque, as if by calling {@link #addLast} on each one,
+ * in the order that they are returned by the collection's iterator.
+ *
+ * @param c the elements to be inserted into this deque
+ * @return {@code true} if this deque changed as a result of the call
+ * @throws NullPointerException if the specified collection or any
+ * of its elements are null
+ */
+ public boolean addAll(Collection<? extends E> c) {
+ final int s, needed;
+ if ((needed = (s = size()) + c.size() + 1 - elements.length) > 0)
+ grow(needed);
+ c.forEach(this::addLast);
+ return size() > s;
+ }
+
+ /**
+ * 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 e = pollFirst();
+ if (e == null)
+ throw new NoSuchElementException();
+ return e;
+ }
+
+ /**
+ * @throws NoSuchElementException {@inheritDoc}
+ */
+ public E removeLast() {
+ E e = pollLast();
+ if (e == null)
+ throw new NoSuchElementException();
+ return e;
+ }
+
+ public E pollFirst() {
+ final Object[] es;
+ final int h;
+ E e = elementAt(es = elements, h = head);
+ if (e != null) {
+ es[h] = null;
+ head = inc(h, es.length);
+ }
+ return e;
+ }
+
+ public E pollLast() {
+ final Object[] es;
+ final int t;
+ E e = elementAt(es = elements, t = dec(tail, es.length));
+ if (e != null)
+ es[tail = t] = null;
+ return e;
+ }
+
+ /**
+ * @throws NoSuchElementException {@inheritDoc}
+ */
+ public E getFirst() {
+ E e = elementAt(elements, head);
+ if (e == null)
+ throw new NoSuchElementException();
+ return e;
+ }
+
+ /**
+ * @throws NoSuchElementException {@inheritDoc}
+ */
+ public E getLast() {
+ final Object[] es = elements;
+ E e = elementAt(es, dec(tail, es.length));
+ if (e == null)
+ throw new NoSuchElementException();
+ return e;
+ }
+
+ public E peekFirst() {
+ return elementAt(elements, head);
+ }
+
+ public E peekLast() {
+ final Object[] es;
+ return elementAt(es = elements, dec(tail, es.length));
+ }
+
+ /**
+ * 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) {
+ final Object[] es = elements;
+ for (int i = head, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ if (o.equals(es[i])) {
+ delete(i);
+ return true;
+ }
+ if (to == end) break;
+ }
+ }
+ 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) {
+ final Object[] es = elements;
+ for (int i = tail, end = head, to = (i >= end) ? end : 0;
+ ; i = es.length, to = end) {
+ for (i--; i > to - 1; i--)
+ if (o.equals(es[i])) {
+ delete(i);
+ return true;
+ }
+ if (to == end) break;
+ }
+ }
+ 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();
+ }
+
+ /**
+ * Removes the element at the specified position in the elements array.
+ * This can result in forward or backwards motion of array elements.
+ * We optimize for least element motion.
+ *
+ * <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 near tail moved backwards
+ */
+ boolean delete(int i) {
+ final Object[] es = elements;
+ final int capacity = es.length;
+ final int h, t;
+ // number of elements before to-be-deleted elt
+ final int front = sub(i, h = head, capacity);
+ // number of elements after to-be-deleted elt
+ final int back = sub(t = tail, i, capacity) - 1;
+ if (front < back) {
+ // move front elements forwards
+ if (h <= i) {
+ System.arraycopy(es, h, es, h + 1, front);
+ } else { // Wrap around
+ System.arraycopy(es, 0, es, 1, i);
+ es[0] = es[capacity - 1];
+ System.arraycopy(es, h, es, h + 1, front - (i + 1));
+ }
+ es[h] = null;
+ head = inc(h, capacity);
+ return false;
+ } else {
+ // move back elements backwards
+ tail = dec(t, capacity);
+ if (i <= tail) {
+ System.arraycopy(es, i + 1, es, i, back);
+ } else { // Wrap around
+ System.arraycopy(es, i + 1, es, i, capacity - (i + 1));
+ es[capacity - 1] = es[0];
+ System.arraycopy(es, 1, es, 0, t - 1);
+ }
+ es[tail] = null;
+ return true;
+ }
+ }
+
+ // *** Collection Methods ***
+
+ /**
+ * Returns the number of elements in this deque.
+ *
+ * @return the number of elements in this deque
+ */
+ public int size() {
+ return sub(tail, head, elements.length);
+ }
+
+ /**
+ * 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. */
+ int cursor;
+
+ /** Number of elements yet to be returned. */
+ int remaining = size();
+
+ /**
+ * Index of element returned by most recent call to next.
+ * Reset to -1 if element is deleted by a call to remove.
+ */
+ int lastRet = -1;
+
+ DeqIterator() { cursor = head; }
+
+ public final boolean hasNext() {
+ return remaining > 0;
+ }
+
+ public E next() {
+ if (remaining <= 0)
+ throw new NoSuchElementException();
+ final Object[] es = elements;
+ E e = nonNullElementAt(es, cursor);
+ cursor = inc(lastRet = cursor, es.length);
+ remaining--;
+ return e;
+ }
+
+ void postDelete(boolean leftShifted) {
+ if (leftShifted)
+ cursor = dec(cursor, elements.length);
+ }
+
+ public final void remove() {
+ if (lastRet < 0)
+ throw new IllegalStateException();
+ postDelete(delete(lastRet));
+ lastRet = -1;
+ }
+
+ public void forEachRemaining(Consumer<? super E> action) {
+ Objects.requireNonNull(action);
+ int r;
+ if ((r = remaining) <= 0)
+ return;
+ remaining = 0;
+ final Object[] es = elements;
+ if (es[cursor] == null || sub(tail, cursor, es.length) != r)
+ throw new ConcurrentModificationException();
+ for (int i = cursor, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ action.accept(elementAt(es, i));
+ if (to == end) {
+ if (end != tail)
+ throw new ConcurrentModificationException();
+ lastRet = dec(end, es.length);
+ break;
+ }
+ }
+ }
+ }
+
+ private class DescendingIterator extends DeqIterator {
+ DescendingIterator() { cursor = dec(tail, elements.length); }
+
+ public final E next() {
+ if (remaining <= 0)
+ throw new NoSuchElementException();
+ final Object[] es = elements;
+ E e = nonNullElementAt(es, cursor);
+ cursor = dec(lastRet = cursor, es.length);
+ remaining--;
+ return e;
+ }
+
+ void postDelete(boolean leftShifted) {
+ if (!leftShifted)
+ cursor = inc(cursor, elements.length);
+ }
+
+ public final void forEachRemaining(Consumer<? super E> action) {
+ Objects.requireNonNull(action);
+ int r;
+ if ((r = remaining) <= 0)
+ return;
+ remaining = 0;
+ final Object[] es = elements;
+ if (es[cursor] == null || sub(cursor, head, es.length) + 1 != r)
+ throw new ConcurrentModificationException();
+ for (int i = cursor, end = head, to = (i >= end) ? end : 0;
+ ; i = es.length - 1, to = end) {
+ // hotspot generates faster code than for: i >= to !
+ for (; i > to - 1; i--)
+ action.accept(elementAt(es, i));
+ if (to == end) {
+ if (end != head)
+ throw new ConcurrentModificationException();
+ lastRet = end;
+ break;
+ }
+ }
+ }
+ }
+
+ /**
+ * 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();
+ }
+
+ final class DeqSpliterator implements Spliterator<E> {
+ private int fence; // -1 until first use
+ private int cursor; // current index, modified on traverse/split
+
+ /** Constructs late-binding spliterator over all elements. */
+ DeqSpliterator() {
+ this.fence = -1;
+ }
+
+ /** Constructs spliterator over the given range. */
+ DeqSpliterator(int origin, int fence) {
+ // assert 0 <= origin && origin < elements.length;
+ // assert 0 <= fence && fence < elements.length;
+ this.cursor = origin;
+ this.fence = fence;
+ }
+
+ /** Ensures late-binding initialization; then returns fence. */
+ private int getFence() { // force initialization
+ int t;
+ if ((t = fence) < 0) {
+ t = fence = tail;
+ cursor = head;
+ }
+ return t;
+ }
+
+ public DeqSpliterator trySplit() {
+ final Object[] es = elements;
+ final int i, n;
+ return ((n = sub(getFence(), i = cursor, es.length) >> 1) <= 0)
+ ? null
+ : new DeqSpliterator(i, cursor = add(i, n, es.length));
+ }
+
+ public void forEachRemaining(Consumer<? super E> action) {
+ if (action == null)
+ throw new NullPointerException();
+ final int end = getFence(), cursor = this.cursor;
+ final Object[] es = elements;
+ if (cursor != end) {
+ this.cursor = end;
+ // null check at both ends of range is sufficient
+ if (es[cursor] == null || es[dec(end, es.length)] == null)
+ throw new ConcurrentModificationException();
+ for (int i = cursor, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ action.accept(elementAt(es, i));
+ if (to == end) break;
+ }
+ }
+ }
+
+ public boolean tryAdvance(Consumer<? super E> action) {
+ Objects.requireNonNull(action);
+ final Object[] es = elements;
+ if (fence < 0) { fence = tail; cursor = head; } // late-binding
+ final int i;
+ if ((i = cursor) == fence)
+ return false;
+ E e = nonNullElementAt(es, i);
+ cursor = inc(i, es.length);
+ action.accept(e);
+ return true;
+ }
+
+ public long estimateSize() {
+ return sub(getFence(), cursor, elements.length);
+ }
+
+ public int characteristics() {
+ return Spliterator.NONNULL
+ | Spliterator.ORDERED
+ | Spliterator.SIZED
+ | Spliterator.SUBSIZED;
+ }
+ }
+
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ */
+ public void forEach(Consumer<? super E> action) {
+ Objects.requireNonNull(action);
+ final Object[] es = elements;
+ for (int i = head, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ action.accept(elementAt(es, i));
+ if (to == end) {
+ if (end != tail) throw new ConcurrentModificationException();
+ break;
+ }
+ }
+ }
+
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ */
+ public boolean removeIf(Predicate<? super E> filter) {
+ Objects.requireNonNull(filter);
+ return bulkRemove(filter);
+ }
+
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ */
+ public boolean removeAll(Collection<?> c) {
+ Objects.requireNonNull(c);
+ return bulkRemove(e -> c.contains(e));
+ }
+
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ */
+ public boolean retainAll(Collection<?> c) {
+ Objects.requireNonNull(c);
+ return bulkRemove(e -> !c.contains(e));
+ }
+
+ /** Implementation of bulk remove methods. */
+ private boolean bulkRemove(Predicate<? super E> filter) {
+ final Object[] es = elements;
+ // Optimize for initial run of survivors
+ for (int i = head, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ if (filter.test(elementAt(es, i)))
+ return bulkRemoveModified(filter, i);
+ if (to == end) {
+ if (end != tail) throw new ConcurrentModificationException();
+ break;
+ }
+ }
+ return false;
+ }
+
+ // A tiny bit set implementation
+
+ private static long[] nBits(int n) {
+ return new long[((n - 1) >> 6) + 1];
+ }
+ private static void setBit(long[] bits, int i) {
+ bits[i >> 6] |= 1L << i;
+ }
+ private static boolean isClear(long[] bits, int i) {
+ return (bits[i >> 6] & (1L << i)) == 0;
+ }
+
+ /**
+ * Helper for bulkRemove, in case of at least one deletion.
+ * Tolerate predicates that reentrantly access the collection for
+ * read (but writers still get CME), so traverse once to find
+ * elements to delete, a second pass to physically expunge.
+ *
+ * @param beg valid index of first element to be deleted
+ */
+ private boolean bulkRemoveModified(
+ Predicate<? super E> filter, final int beg) {
+ final Object[] es = elements;
+ final int capacity = es.length;
+ final int end = tail;
+ final long[] deathRow = nBits(sub(end, beg, capacity));
+ deathRow[0] = 1L; // set bit 0
+ for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg;
+ ; i = 0, to = end, k -= capacity) {
+ for (; i < to; i++)
+ if (filter.test(elementAt(es, i)))
+ setBit(deathRow, i - k);
+ if (to == end) break;
+ }
+ // a two-finger traversal, with hare i reading, tortoise w writing
+ int w = beg;
+ for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg;
+ ; w = 0) { // w rejoins i on second leg
+ // In this loop, i and w are on the same leg, with i > w
+ for (; i < to; i++)
+ if (isClear(deathRow, i - k))
+ es[w++] = es[i];
+ if (to == end) break;
+ // In this loop, w is on the first leg, i on the second
+ for (i = 0, to = end, k -= capacity; i < to && w < capacity; i++)
+ if (isClear(deathRow, i - k))
+ es[w++] = es[i];
+ if (i >= to) {
+ if (w == capacity) w = 0; // "corner" case
+ break;
+ }
+ }
+ if (end != tail) throw new ConcurrentModificationException();
+ circularClear(es, tail = w, end);
+ return true;
+ }
+
+ /**
+ * 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) {
+ final Object[] es = elements;
+ for (int i = head, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ if (o.equals(es[i]))
+ return true;
+ if (to == end) break;
+ }
+ }
+ 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() {
+ circularClear(elements, head, tail);
+ head = tail = 0;
+ }
+
+ /**
+ * Nulls out slots starting at array index i, upto index end.
+ * Condition i == end means "empty" - nothing to do.
+ */
+ private static void circularClear(Object[] es, int i, int end) {
+ // assert 0 <= i && i < es.length;
+ // assert 0 <= end && end < es.length;
+ for (int to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++) es[i] = null;
+ if (to == end) break;
+ }
+ }
+
+ /**
+ * 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 toArray(Object[].class);
+ }
+
+ private <T> T[] toArray(Class<T[]> klazz) {
+ final Object[] es = elements;
+ final T[] a;
+ final int head = this.head, tail = this.tail, end;
+ if ((end = tail + ((head <= tail) ? 0 : es.length)) >= 0) {
+ // Uses null extension feature of copyOfRange
+ a = Arrays.copyOfRange(es, head, end, klazz);
+ } else {
+ // integer overflow!
+ a = Arrays.copyOfRange(es, 0, end - head, klazz);
+ System.arraycopy(es, head, a, 0, es.length - head);
+ }
+ if (end != tail)
+ System.arraycopy(es, 0, a, es.length - head, tail);
+ return a;
+ }
+
+ /**
+ * 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) {
+ final int size;
+ if ((size = size()) > a.length)
+ return toArray((Class<T[]>) a.getClass());
+ final Object[] es = elements;
+ for (int i = head, j = 0, len = Math.min(size, es.length - i);
+ ; i = 0, len = tail) {
+ System.arraycopy(es, i, a, j, len);
+ if ((j += len) == size) break;
+ }
+ if (size < a.length)
+ 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).
+ *
+ * @param s the stream
+ * @throws java.io.IOException if an I/O error occurs
+ * @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.
+ final Object[] es = elements;
+ for (int i = head, end = tail, to = (i <= end) ? end : es.length;
+ ; i = 0, to = end) {
+ for (; i < to; i++)
+ s.writeObject(es[i]);
+ if (to == end) break;
+ }
+ }
+
+ /**
+ * Reconstitutes this deque from a stream (that is, deserializes it).
+ * @param s the stream
+ * @throws ClassNotFoundException if the class of a serialized object
+ * could not be found
+ * @throws java.io.IOException if an I/O error occurs
+ */
+ private void readObject(java.io.ObjectInputStream s)
+ throws java.io.IOException, ClassNotFoundException {
+ s.defaultReadObject();
+
+ // Read in size and allocate array
+ int size = s.readInt();
+ elements = new Object[size + 1];
+ this.tail = size;
+
+ // Read in all elements in the proper order.
+ for (int i = 0; i < size; i++)
+ elements[i] = s.readObject();
+ }
+
+ /** debugging */
+ void checkInvariants() {
+ // Use head and tail fields with empty slot at tail strategy.
+ // head == tail disambiguates to "empty".
+ try {
+ int capacity = elements.length;
+ // assert 0 <= head && head < capacity;
+ // assert 0 <= tail && tail < capacity;
+ // assert capacity > 0;
+ // assert size() < capacity;
+ // assert head == tail || elements[head] != null;
+ // assert elements[tail] == null;
+ // assert head == tail || elements[dec(tail, capacity)] != null;
+ } catch (Throwable t) {
+ System.err.printf("head=%d tail=%d capacity=%d%n",
+ head, tail, elements.length);
+ System.err.printf("elements=%s%n",
+ Arrays.toString(elements));
+ throw t;
+ }
+ }
+
+}