jaroslav@597: /*
jaroslav@597:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@597:  *
jaroslav@597:  * This code is free software; you can redistribute it and/or modify it
jaroslav@597:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@597:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@597:  * particular file as subject to the "Classpath" exception as provided
jaroslav@597:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@597:  *
jaroslav@597:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@597:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@597:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@597:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@597:  * accompanied this code).
jaroslav@597:  *
jaroslav@597:  * You should have received a copy of the GNU General Public License version
jaroslav@597:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@597:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@597:  *
jaroslav@597:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@597:  * or visit www.oracle.com if you need additional information or have any
jaroslav@597:  * questions.
jaroslav@597:  */
jaroslav@597: 
jaroslav@597: /*
jaroslav@597:  * This file is available under and governed by the GNU General Public
jaroslav@597:  * License version 2 only, as published by the Free Software Foundation.
jaroslav@597:  * However, the following notice accompanied the original version of this
jaroslav@597:  * file:
jaroslav@597:  *
jaroslav@597:  * Written by Josh Bloch of Google Inc. and released to the public domain,
jaroslav@597:  * as explained at http://creativecommons.org/publicdomain/zero/1.0/.
jaroslav@597:  */
jaroslav@597: 
jaroslav@597: package java.util;
jaroslav@597: import java.io.*;
jaroslav@597: 
jaroslav@597: /**
jaroslav@597:  * Resizable-array implementation of the {@link Deque} interface.  Array
jaroslav@597:  * deques have no capacity restrictions; they grow as necessary to support
jaroslav@597:  * usage.  They are not thread-safe; in the absence of external
jaroslav@597:  * synchronization, they do not support concurrent access by multiple threads.
jaroslav@597:  * Null elements are prohibited.  This class is likely to be faster than
jaroslav@597:  * {@link Stack} when used as a stack, and faster than {@link LinkedList}
jaroslav@597:  * when used as a queue.
jaroslav@597:  *
jaroslav@597:  * <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time.
jaroslav@597:  * Exceptions include {@link #remove(Object) remove}, {@link
jaroslav@597:  * #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
jaroslav@597:  * removeLastOccurrence}, {@link #contains contains}, {@link #iterator
jaroslav@597:  * iterator.remove()}, and the bulk operations, all of which run in linear
jaroslav@597:  * time.
jaroslav@597:  *
jaroslav@597:  * <p>The iterators returned by this class's <tt>iterator</tt> method are
jaroslav@597:  * <i>fail-fast</i>: If the deque is modified at any time after the iterator
jaroslav@597:  * is created, in any way except through the iterator's own <tt>remove</tt>
jaroslav@597:  * method, the iterator will generally throw a {@link
jaroslav@597:  * ConcurrentModificationException}.  Thus, in the face of concurrent
jaroslav@597:  * modification, the iterator fails quickly and cleanly, rather than risking
jaroslav@597:  * arbitrary, non-deterministic behavior at an undetermined time in the
jaroslav@597:  * future.
jaroslav@597:  *
jaroslav@597:  * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
jaroslav@597:  * as it is, generally speaking, impossible to make any hard guarantees in the
jaroslav@597:  * presence of unsynchronized concurrent modification.  Fail-fast iterators
jaroslav@597:  * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
jaroslav@597:  * Therefore, it would be wrong to write a program that depended on this
jaroslav@597:  * exception for its correctness: <i>the fail-fast behavior of iterators
jaroslav@597:  * should be used only to detect bugs.</i>
jaroslav@597:  *
jaroslav@597:  * <p>This class and its iterator implement all of the
jaroslav@597:  * <em>optional</em> methods of the {@link Collection} and {@link
jaroslav@597:  * Iterator} interfaces.
jaroslav@597:  *
jaroslav@597:  * <p>This class is a member of the
jaroslav@597:  * <a href="{@docRoot}/../technotes/guides/collections/index.html">
jaroslav@597:  * Java Collections Framework</a>.
jaroslav@597:  *
jaroslav@597:  * @author  Josh Bloch and Doug Lea
jaroslav@597:  * @since   1.6
jaroslav@597:  * @param <E> the type of elements held in this collection
jaroslav@597:  */
jaroslav@597: public class ArrayDeque<E> extends AbstractCollection<E>
jaroslav@597:                            implements Deque<E>, Cloneable, Serializable
jaroslav@597: {
jaroslav@597:     /**
jaroslav@597:      * The array in which the elements of the deque are stored.
jaroslav@597:      * The capacity of the deque is the length of this array, which is
jaroslav@597:      * always a power of two. The array is never allowed to become
jaroslav@597:      * full, except transiently within an addX method where it is
jaroslav@597:      * resized (see doubleCapacity) immediately upon becoming full,
jaroslav@597:      * thus avoiding head and tail wrapping around to equal each
jaroslav@597:      * other.  We also guarantee that all array cells not holding
jaroslav@597:      * deque elements are always null.
jaroslav@597:      */
jaroslav@597:     private transient E[] elements;
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * The index of the element at the head of the deque (which is the
jaroslav@597:      * element that would be removed by remove() or pop()); or an
jaroslav@597:      * arbitrary number equal to tail if the deque is empty.
jaroslav@597:      */
jaroslav@597:     private transient int head;
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * The index at which the next element would be added to the tail
jaroslav@597:      * of the deque (via addLast(E), add(E), or push(E)).
jaroslav@597:      */
jaroslav@597:     private transient int tail;
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * The minimum capacity that we'll use for a newly created deque.
jaroslav@597:      * Must be a power of 2.
jaroslav@597:      */
jaroslav@597:     private static final int MIN_INITIAL_CAPACITY = 8;
jaroslav@597: 
jaroslav@597:     // ******  Array allocation and resizing utilities ******
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Allocate empty array to hold the given number of elements.
jaroslav@597:      *
jaroslav@597:      * @param numElements  the number of elements to hold
jaroslav@597:      */
jaroslav@597:     private void allocateElements(int numElements) {
jaroslav@597:         int initialCapacity = MIN_INITIAL_CAPACITY;
jaroslav@597:         // Find the best power of two to hold elements.
jaroslav@597:         // Tests "<=" because arrays aren't kept full.
jaroslav@597:         if (numElements >= initialCapacity) {
jaroslav@597:             initialCapacity = numElements;
jaroslav@597:             initialCapacity |= (initialCapacity >>>  1);
jaroslav@597:             initialCapacity |= (initialCapacity >>>  2);
jaroslav@597:             initialCapacity |= (initialCapacity >>>  4);
jaroslav@597:             initialCapacity |= (initialCapacity >>>  8);
jaroslav@597:             initialCapacity |= (initialCapacity >>> 16);
jaroslav@597:             initialCapacity++;
jaroslav@597: 
jaroslav@597:             if (initialCapacity < 0)   // Too many elements, must back off
jaroslav@597:                 initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
jaroslav@597:         }
jaroslav@597:         elements = (E[]) new Object[initialCapacity];
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Double the capacity of this deque.  Call only when full, i.e.,
jaroslav@597:      * when head and tail have wrapped around to become equal.
jaroslav@597:      */
jaroslav@597:     private void doubleCapacity() {
jaroslav@597:         assert head == tail;
jaroslav@597:         int p = head;
jaroslav@597:         int n = elements.length;
jaroslav@597:         int r = n - p; // number of elements to the right of p
jaroslav@597:         int newCapacity = n << 1;
jaroslav@597:         if (newCapacity < 0)
jaroslav@597:             throw new IllegalStateException("Sorry, deque too big");
jaroslav@597:         Object[] a = new Object[newCapacity];
jaroslav@597:         System.arraycopy(elements, p, a, 0, r);
jaroslav@597:         System.arraycopy(elements, 0, a, r, p);
jaroslav@597:         elements = (E[])a;
jaroslav@597:         head = 0;
jaroslav@597:         tail = n;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Copies the elements from our element array into the specified array,
jaroslav@597:      * in order (from first to last element in the deque).  It is assumed
jaroslav@597:      * that the array is large enough to hold all elements in the deque.
jaroslav@597:      *
jaroslav@597:      * @return its argument
jaroslav@597:      */
jaroslav@597:     private <T> T[] copyElements(T[] a) {
jaroslav@597:         if (head < tail) {
jaroslav@597:             System.arraycopy(elements, head, a, 0, size());
jaroslav@597:         } else if (head > tail) {
jaroslav@597:             int headPortionLen = elements.length - head;
jaroslav@597:             System.arraycopy(elements, head, a, 0, headPortionLen);
jaroslav@597:             System.arraycopy(elements, 0, a, headPortionLen, tail);
jaroslav@597:         }
jaroslav@597:         return a;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Constructs an empty array deque with an initial capacity
jaroslav@597:      * sufficient to hold 16 elements.
jaroslav@597:      */
jaroslav@597:     public ArrayDeque() {
jaroslav@597:         elements = (E[]) new Object[16];
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Constructs an empty array deque with an initial capacity
jaroslav@597:      * sufficient to hold the specified number of elements.
jaroslav@597:      *
jaroslav@597:      * @param numElements  lower bound on initial capacity of the deque
jaroslav@597:      */
jaroslav@597:     public ArrayDeque(int numElements) {
jaroslav@597:         allocateElements(numElements);
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Constructs a deque containing the elements of the specified
jaroslav@597:      * collection, in the order they are returned by the collection's
jaroslav@597:      * iterator.  (The first element returned by the collection's
jaroslav@597:      * iterator becomes the first element, or <i>front</i> of the
jaroslav@597:      * deque.)
jaroslav@597:      *
jaroslav@597:      * @param c the collection whose elements are to be placed into the deque
jaroslav@597:      * @throws NullPointerException if the specified collection is null
jaroslav@597:      */
jaroslav@597:     public ArrayDeque(Collection<? extends E> c) {
jaroslav@597:         allocateElements(c.size());
jaroslav@597:         addAll(c);
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     // The main insertion and extraction methods are addFirst,
jaroslav@597:     // addLast, pollFirst, pollLast. The other methods are defined in
jaroslav@597:     // terms of these.
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Inserts the specified element at the front of this deque.
jaroslav@597:      *
jaroslav@597:      * @param e the element to add
jaroslav@597:      * @throws NullPointerException if the specified element is null
jaroslav@597:      */
jaroslav@597:     public void addFirst(E e) {
jaroslav@597:         if (e == null)
jaroslav@597:             throw new NullPointerException();
jaroslav@597:         elements[head = (head - 1) & (elements.length - 1)] = e;
jaroslav@597:         if (head == tail)
jaroslav@597:             doubleCapacity();
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Inserts the specified element at the end of this deque.
jaroslav@597:      *
jaroslav@597:      * <p>This method is equivalent to {@link #add}.
jaroslav@597:      *
jaroslav@597:      * @param e the element to add
jaroslav@597:      * @throws NullPointerException if the specified element is null
jaroslav@597:      */
jaroslav@597:     public void addLast(E e) {
jaroslav@597:         if (e == null)
jaroslav@597:             throw new NullPointerException();
jaroslav@597:         elements[tail] = e;
jaroslav@597:         if ( (tail = (tail + 1) & (elements.length - 1)) == head)
jaroslav@597:             doubleCapacity();
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Inserts the specified element at the front of this deque.
jaroslav@597:      *
jaroslav@597:      * @param e the element to add
jaroslav@597:      * @return <tt>true</tt> (as specified by {@link Deque#offerFirst})
jaroslav@597:      * @throws NullPointerException if the specified element is null
jaroslav@597:      */
jaroslav@597:     public boolean offerFirst(E e) {
jaroslav@597:         addFirst(e);
jaroslav@597:         return true;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Inserts the specified element at the end of this deque.
jaroslav@597:      *
jaroslav@597:      * @param e the element to add
jaroslav@597:      * @return <tt>true</tt> (as specified by {@link Deque#offerLast})
jaroslav@597:      * @throws NullPointerException if the specified element is null
jaroslav@597:      */
jaroslav@597:     public boolean offerLast(E e) {
jaroslav@597:         addLast(e);
jaroslav@597:         return true;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@597:      */
jaroslav@597:     public E removeFirst() {
jaroslav@597:         E x = pollFirst();
jaroslav@597:         if (x == null)
jaroslav@597:             throw new NoSuchElementException();
jaroslav@597:         return x;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@597:      */
jaroslav@597:     public E removeLast() {
jaroslav@597:         E x = pollLast();
jaroslav@597:         if (x == null)
jaroslav@597:             throw new NoSuchElementException();
jaroslav@597:         return x;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     public E pollFirst() {
jaroslav@597:         int h = head;
jaroslav@597:         E result = elements[h]; // Element is null if deque empty
jaroslav@597:         if (result == null)
jaroslav@597:             return null;
jaroslav@597:         elements[h] = null;     // Must null out slot
jaroslav@597:         head = (h + 1) & (elements.length - 1);
jaroslav@597:         return result;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     public E pollLast() {
jaroslav@597:         int t = (tail - 1) & (elements.length - 1);
jaroslav@597:         E result = elements[t];
jaroslav@597:         if (result == null)
jaroslav@597:             return null;
jaroslav@597:         elements[t] = null;
jaroslav@597:         tail = t;
jaroslav@597:         return result;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@597:      */
jaroslav@597:     public E getFirst() {
jaroslav@597:         E x = elements[head];
jaroslav@597:         if (x == null)
jaroslav@597:             throw new NoSuchElementException();
jaroslav@597:         return x;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@597:      */
jaroslav@597:     public E getLast() {
jaroslav@597:         E x = elements[(tail - 1) & (elements.length - 1)];
jaroslav@597:         if (x == null)
jaroslav@597:             throw new NoSuchElementException();
jaroslav@597:         return x;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     public E peekFirst() {
jaroslav@597:         return elements[head]; // elements[head] is null if deque empty
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     public E peekLast() {
jaroslav@597:         return elements[(tail - 1) & (elements.length - 1)];
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Removes the first occurrence of the specified element in this
jaroslav@597:      * deque (when traversing the deque from head to tail).
jaroslav@597:      * If the deque does not contain the element, it is unchanged.
jaroslav@597:      * More formally, removes the first element <tt>e</tt> such that
jaroslav@597:      * <tt>o.equals(e)</tt> (if such an element exists).
jaroslav@597:      * Returns <tt>true</tt> if this deque contained the specified element
jaroslav@597:      * (or equivalently, if this deque changed as a result of the call).
jaroslav@597:      *
jaroslav@597:      * @param o element to be removed from this deque, if present
jaroslav@597:      * @return <tt>true</tt> if the deque contained the specified element
jaroslav@597:      */
jaroslav@597:     public boolean removeFirstOccurrence(Object o) {
jaroslav@597:         if (o == null)
jaroslav@597:             return false;
jaroslav@597:         int mask = elements.length - 1;
jaroslav@597:         int i = head;
jaroslav@597:         E x;
jaroslav@597:         while ( (x = elements[i]) != null) {
jaroslav@597:             if (o.equals(x)) {
jaroslav@597:                 delete(i);
jaroslav@597:                 return true;
jaroslav@597:             }
jaroslav@597:             i = (i + 1) & mask;
jaroslav@597:         }
jaroslav@597:         return false;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Removes the last occurrence of the specified element in this
jaroslav@597:      * deque (when traversing the deque from head to tail).
jaroslav@597:      * If the deque does not contain the element, it is unchanged.
jaroslav@597:      * More formally, removes the last element <tt>e</tt> such that
jaroslav@597:      * <tt>o.equals(e)</tt> (if such an element exists).
jaroslav@597:      * Returns <tt>true</tt> if this deque contained the specified element
jaroslav@597:      * (or equivalently, if this deque changed as a result of the call).
jaroslav@597:      *
jaroslav@597:      * @param o element to be removed from this deque, if present
jaroslav@597:      * @return <tt>true</tt> if the deque contained the specified element
jaroslav@597:      */
jaroslav@597:     public boolean removeLastOccurrence(Object o) {
jaroslav@597:         if (o == null)
jaroslav@597:             return false;
jaroslav@597:         int mask = elements.length - 1;
jaroslav@597:         int i = (tail - 1) & mask;
jaroslav@597:         E x;
jaroslav@597:         while ( (x = elements[i]) != null) {
jaroslav@597:             if (o.equals(x)) {
jaroslav@597:                 delete(i);
jaroslav@597:                 return true;
jaroslav@597:             }
jaroslav@597:             i = (i - 1) & mask;
jaroslav@597:         }
jaroslav@597:         return false;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     // *** Queue methods ***
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Inserts the specified element at the end of this deque.
jaroslav@597:      *
jaroslav@597:      * <p>This method is equivalent to {@link #addLast}.
jaroslav@597:      *
jaroslav@597:      * @param e the element to add
jaroslav@597:      * @return <tt>true</tt> (as specified by {@link Collection#add})
jaroslav@597:      * @throws NullPointerException if the specified element is null
jaroslav@597:      */
jaroslav@597:     public boolean add(E e) {
jaroslav@597:         addLast(e);
jaroslav@597:         return true;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Inserts the specified element at the end of this deque.
jaroslav@597:      *
jaroslav@597:      * <p>This method is equivalent to {@link #offerLast}.
jaroslav@597:      *
jaroslav@597:      * @param e the element to add
jaroslav@597:      * @return <tt>true</tt> (as specified by {@link Queue#offer})
jaroslav@597:      * @throws NullPointerException if the specified element is null
jaroslav@597:      */
jaroslav@597:     public boolean offer(E e) {
jaroslav@597:         return offerLast(e);
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Retrieves and removes the head of the queue represented by this deque.
jaroslav@597:      *
jaroslav@597:      * This method differs from {@link #poll poll} only in that it throws an
jaroslav@597:      * exception if this deque is empty.
jaroslav@597:      *
jaroslav@597:      * <p>This method is equivalent to {@link #removeFirst}.
jaroslav@597:      *
jaroslav@597:      * @return the head of the queue represented by this deque
jaroslav@597:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@597:      */
jaroslav@597:     public E remove() {
jaroslav@597:         return removeFirst();
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Retrieves and removes the head of the queue represented by this deque
jaroslav@597:      * (in other words, the first element of this deque), or returns
jaroslav@597:      * <tt>null</tt> if this deque is empty.
jaroslav@597:      *
jaroslav@597:      * <p>This method is equivalent to {@link #pollFirst}.
jaroslav@597:      *
jaroslav@597:      * @return the head of the queue represented by this deque, or
jaroslav@597:      *         <tt>null</tt> if this deque is empty
jaroslav@597:      */
jaroslav@597:     public E poll() {
jaroslav@597:         return pollFirst();
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Retrieves, but does not remove, the head of the queue represented by
jaroslav@597:      * this deque.  This method differs from {@link #peek peek} only in
jaroslav@597:      * that it throws an exception if this deque is empty.
jaroslav@597:      *
jaroslav@597:      * <p>This method is equivalent to {@link #getFirst}.
jaroslav@597:      *
jaroslav@597:      * @return the head of the queue represented by this deque
jaroslav@597:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@597:      */
jaroslav@597:     public E element() {
jaroslav@597:         return getFirst();
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Retrieves, but does not remove, the head of the queue represented by
jaroslav@597:      * this deque, or returns <tt>null</tt> if this deque is empty.
jaroslav@597:      *
jaroslav@597:      * <p>This method is equivalent to {@link #peekFirst}.
jaroslav@597:      *
jaroslav@597:      * @return the head of the queue represented by this deque, or
jaroslav@597:      *         <tt>null</tt> if this deque is empty
jaroslav@597:      */
jaroslav@597:     public E peek() {
jaroslav@597:         return peekFirst();
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     // *** Stack methods ***
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Pushes an element onto the stack represented by this deque.  In other
jaroslav@597:      * words, inserts the element at the front of this deque.
jaroslav@597:      *
jaroslav@597:      * <p>This method is equivalent to {@link #addFirst}.
jaroslav@597:      *
jaroslav@597:      * @param e the element to push
jaroslav@597:      * @throws NullPointerException if the specified element is null
jaroslav@597:      */
jaroslav@597:     public void push(E e) {
jaroslav@597:         addFirst(e);
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Pops an element from the stack represented by this deque.  In other
jaroslav@597:      * words, removes and returns the first element of this deque.
jaroslav@597:      *
jaroslav@597:      * <p>This method is equivalent to {@link #removeFirst()}.
jaroslav@597:      *
jaroslav@597:      * @return the element at the front of this deque (which is the top
jaroslav@597:      *         of the stack represented by this deque)
jaroslav@597:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@597:      */
jaroslav@597:     public E pop() {
jaroslav@597:         return removeFirst();
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     private void checkInvariants() {
jaroslav@597:         assert elements[tail] == null;
jaroslav@597:         assert head == tail ? elements[head] == null :
jaroslav@597:             (elements[head] != null &&
jaroslav@597:              elements[(tail - 1) & (elements.length - 1)] != null);
jaroslav@597:         assert elements[(head - 1) & (elements.length - 1)] == null;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Removes the element at the specified position in the elements array,
jaroslav@597:      * adjusting head and tail as necessary.  This can result in motion of
jaroslav@597:      * elements backwards or forwards in the array.
jaroslav@597:      *
jaroslav@597:      * <p>This method is called delete rather than remove to emphasize
jaroslav@597:      * that its semantics differ from those of {@link List#remove(int)}.
jaroslav@597:      *
jaroslav@597:      * @return true if elements moved backwards
jaroslav@597:      */
jaroslav@597:     private boolean delete(int i) {
jaroslav@597:         checkInvariants();
jaroslav@597:         final E[] elements = this.elements;
jaroslav@597:         final int mask = elements.length - 1;
jaroslav@597:         final int h = head;
jaroslav@597:         final int t = tail;
jaroslav@597:         final int front = (i - h) & mask;
jaroslav@597:         final int back  = (t - i) & mask;
jaroslav@597: 
jaroslav@597:         // Invariant: head <= i < tail mod circularity
jaroslav@597:         if (front >= ((t - h) & mask))
jaroslav@597:             throw new ConcurrentModificationException();
jaroslav@597: 
jaroslav@597:         // Optimize for least element motion
jaroslav@597:         if (front < back) {
jaroslav@597:             if (h <= i) {
jaroslav@597:                 System.arraycopy(elements, h, elements, h + 1, front);
jaroslav@597:             } else { // Wrap around
jaroslav@597:                 System.arraycopy(elements, 0, elements, 1, i);
jaroslav@597:                 elements[0] = elements[mask];
jaroslav@597:                 System.arraycopy(elements, h, elements, h + 1, mask - h);
jaroslav@597:             }
jaroslav@597:             elements[h] = null;
jaroslav@597:             head = (h + 1) & mask;
jaroslav@597:             return false;
jaroslav@597:         } else {
jaroslav@597:             if (i < t) { // Copy the null tail as well
jaroslav@597:                 System.arraycopy(elements, i + 1, elements, i, back);
jaroslav@597:                 tail = t - 1;
jaroslav@597:             } else { // Wrap around
jaroslav@597:                 System.arraycopy(elements, i + 1, elements, i, mask - i);
jaroslav@597:                 elements[mask] = elements[0];
jaroslav@597:                 System.arraycopy(elements, 1, elements, 0, t);
jaroslav@597:                 tail = (t - 1) & mask;
jaroslav@597:             }
jaroslav@597:             return true;
jaroslav@597:         }
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     // *** Collection Methods ***
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Returns the number of elements in this deque.
jaroslav@597:      *
jaroslav@597:      * @return the number of elements in this deque
jaroslav@597:      */
jaroslav@597:     public int size() {
jaroslav@597:         return (tail - head) & (elements.length - 1);
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Returns <tt>true</tt> if this deque contains no elements.
jaroslav@597:      *
jaroslav@597:      * @return <tt>true</tt> if this deque contains no elements
jaroslav@597:      */
jaroslav@597:     public boolean isEmpty() {
jaroslav@597:         return head == tail;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Returns an iterator over the elements in this deque.  The elements
jaroslav@597:      * will be ordered from first (head) to last (tail).  This is the same
jaroslav@597:      * order that elements would be dequeued (via successive calls to
jaroslav@597:      * {@link #remove} or popped (via successive calls to {@link #pop}).
jaroslav@597:      *
jaroslav@597:      * @return an iterator over the elements in this deque
jaroslav@597:      */
jaroslav@597:     public Iterator<E> iterator() {
jaroslav@597:         return new DeqIterator();
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     public Iterator<E> descendingIterator() {
jaroslav@597:         return new DescendingIterator();
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     private class DeqIterator implements Iterator<E> {
jaroslav@597:         /**
jaroslav@597:          * Index of element to be returned by subsequent call to next.
jaroslav@597:          */
jaroslav@597:         private int cursor = head;
jaroslav@597: 
jaroslav@597:         /**
jaroslav@597:          * Tail recorded at construction (also in remove), to stop
jaroslav@597:          * iterator and also to check for comodification.
jaroslav@597:          */
jaroslav@597:         private int fence = tail;
jaroslav@597: 
jaroslav@597:         /**
jaroslav@597:          * Index of element returned by most recent call to next.
jaroslav@597:          * Reset to -1 if element is deleted by a call to remove.
jaroslav@597:          */
jaroslav@597:         private int lastRet = -1;
jaroslav@597: 
jaroslav@597:         public boolean hasNext() {
jaroslav@597:             return cursor != fence;
jaroslav@597:         }
jaroslav@597: 
jaroslav@597:         public E next() {
jaroslav@597:             if (cursor == fence)
jaroslav@597:                 throw new NoSuchElementException();
jaroslav@597:             E result = elements[cursor];
jaroslav@597:             // This check doesn't catch all possible comodifications,
jaroslav@597:             // but does catch the ones that corrupt traversal
jaroslav@597:             if (tail != fence || result == null)
jaroslav@597:                 throw new ConcurrentModificationException();
jaroslav@597:             lastRet = cursor;
jaroslav@597:             cursor = (cursor + 1) & (elements.length - 1);
jaroslav@597:             return result;
jaroslav@597:         }
jaroslav@597: 
jaroslav@597:         public void remove() {
jaroslav@597:             if (lastRet < 0)
jaroslav@597:                 throw new IllegalStateException();
jaroslav@597:             if (delete(lastRet)) { // if left-shifted, undo increment in next()
jaroslav@597:                 cursor = (cursor - 1) & (elements.length - 1);
jaroslav@597:                 fence = tail;
jaroslav@597:             }
jaroslav@597:             lastRet = -1;
jaroslav@597:         }
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     private class DescendingIterator implements Iterator<E> {
jaroslav@597:         /*
jaroslav@597:          * This class is nearly a mirror-image of DeqIterator, using
jaroslav@597:          * tail instead of head for initial cursor, and head instead of
jaroslav@597:          * tail for fence.
jaroslav@597:          */
jaroslav@597:         private int cursor = tail;
jaroslav@597:         private int fence = head;
jaroslav@597:         private int lastRet = -1;
jaroslav@597: 
jaroslav@597:         public boolean hasNext() {
jaroslav@597:             return cursor != fence;
jaroslav@597:         }
jaroslav@597: 
jaroslav@597:         public E next() {
jaroslav@597:             if (cursor == fence)
jaroslav@597:                 throw new NoSuchElementException();
jaroslav@597:             cursor = (cursor - 1) & (elements.length - 1);
jaroslav@597:             E result = elements[cursor];
jaroslav@597:             if (head != fence || result == null)
jaroslav@597:                 throw new ConcurrentModificationException();
jaroslav@597:             lastRet = cursor;
jaroslav@597:             return result;
jaroslav@597:         }
jaroslav@597: 
jaroslav@597:         public void remove() {
jaroslav@597:             if (lastRet < 0)
jaroslav@597:                 throw new IllegalStateException();
jaroslav@597:             if (!delete(lastRet)) {
jaroslav@597:                 cursor = (cursor + 1) & (elements.length - 1);
jaroslav@597:                 fence = head;
jaroslav@597:             }
jaroslav@597:             lastRet = -1;
jaroslav@597:         }
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Returns <tt>true</tt> if this deque contains the specified element.
jaroslav@597:      * More formally, returns <tt>true</tt> if and only if this deque contains
jaroslav@597:      * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
jaroslav@597:      *
jaroslav@597:      * @param o object to be checked for containment in this deque
jaroslav@597:      * @return <tt>true</tt> if this deque contains the specified element
jaroslav@597:      */
jaroslav@597:     public boolean contains(Object o) {
jaroslav@597:         if (o == null)
jaroslav@597:             return false;
jaroslav@597:         int mask = elements.length - 1;
jaroslav@597:         int i = head;
jaroslav@597:         E x;
jaroslav@597:         while ( (x = elements[i]) != null) {
jaroslav@597:             if (o.equals(x))
jaroslav@597:                 return true;
jaroslav@597:             i = (i + 1) & mask;
jaroslav@597:         }
jaroslav@597:         return false;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Removes a single instance of the specified element from this deque.
jaroslav@597:      * If the deque does not contain the element, it is unchanged.
jaroslav@597:      * More formally, removes the first element <tt>e</tt> such that
jaroslav@597:      * <tt>o.equals(e)</tt> (if such an element exists).
jaroslav@597:      * Returns <tt>true</tt> if this deque contained the specified element
jaroslav@597:      * (or equivalently, if this deque changed as a result of the call).
jaroslav@597:      *
jaroslav@597:      * <p>This method is equivalent to {@link #removeFirstOccurrence}.
jaroslav@597:      *
jaroslav@597:      * @param o element to be removed from this deque, if present
jaroslav@597:      * @return <tt>true</tt> if this deque contained the specified element
jaroslav@597:      */
jaroslav@597:     public boolean remove(Object o) {
jaroslav@597:         return removeFirstOccurrence(o);
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Removes all of the elements from this deque.
jaroslav@597:      * The deque will be empty after this call returns.
jaroslav@597:      */
jaroslav@597:     public void clear() {
jaroslav@597:         int h = head;
jaroslav@597:         int t = tail;
jaroslav@597:         if (h != t) { // clear all cells
jaroslav@597:             head = tail = 0;
jaroslav@597:             int i = h;
jaroslav@597:             int mask = elements.length - 1;
jaroslav@597:             do {
jaroslav@597:                 elements[i] = null;
jaroslav@597:                 i = (i + 1) & mask;
jaroslav@597:             } while (i != t);
jaroslav@597:         }
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Returns an array containing all of the elements in this deque
jaroslav@597:      * in proper sequence (from first to last element).
jaroslav@597:      *
jaroslav@597:      * <p>The returned array will be "safe" in that no references to it are
jaroslav@597:      * maintained by this deque.  (In other words, this method must allocate
jaroslav@597:      * a new array).  The caller is thus free to modify the returned array.
jaroslav@597:      *
jaroslav@597:      * <p>This method acts as bridge between array-based and collection-based
jaroslav@597:      * APIs.
jaroslav@597:      *
jaroslav@597:      * @return an array containing all of the elements in this deque
jaroslav@597:      */
jaroslav@597:     public Object[] toArray() {
jaroslav@597:         return copyElements(new Object[size()]);
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Returns an array containing all of the elements in this deque in
jaroslav@597:      * proper sequence (from first to last element); the runtime type of the
jaroslav@597:      * returned array is that of the specified array.  If the deque fits in
jaroslav@597:      * the specified array, it is returned therein.  Otherwise, a new array
jaroslav@597:      * is allocated with the runtime type of the specified array and the
jaroslav@597:      * size of this deque.
jaroslav@597:      *
jaroslav@597:      * <p>If this deque fits in the specified array with room to spare
jaroslav@597:      * (i.e., the array has more elements than this deque), the element in
jaroslav@597:      * the array immediately following the end of the deque is set to
jaroslav@597:      * <tt>null</tt>.
jaroslav@597:      *
jaroslav@597:      * <p>Like the {@link #toArray()} method, this method acts as bridge between
jaroslav@597:      * array-based and collection-based APIs.  Further, this method allows
jaroslav@597:      * precise control over the runtime type of the output array, and may,
jaroslav@597:      * under certain circumstances, be used to save allocation costs.
jaroslav@597:      *
jaroslav@597:      * <p>Suppose <tt>x</tt> is a deque known to contain only strings.
jaroslav@597:      * The following code can be used to dump the deque into a newly
jaroslav@597:      * allocated array of <tt>String</tt>:
jaroslav@597:      *
jaroslav@597:      * <pre>
jaroslav@597:      *     String[] y = x.toArray(new String[0]);</pre>
jaroslav@597:      *
jaroslav@597:      * Note that <tt>toArray(new Object[0])</tt> is identical in function to
jaroslav@597:      * <tt>toArray()</tt>.
jaroslav@597:      *
jaroslav@597:      * @param a the array into which the elements of the deque are to
jaroslav@597:      *          be stored, if it is big enough; otherwise, a new array of the
jaroslav@597:      *          same runtime type is allocated for this purpose
jaroslav@597:      * @return an array containing all of the elements in this deque
jaroslav@597:      * @throws ArrayStoreException if the runtime type of the specified array
jaroslav@597:      *         is not a supertype of the runtime type of every element in
jaroslav@597:      *         this deque
jaroslav@597:      * @throws NullPointerException if the specified array is null
jaroslav@597:      */
jaroslav@597:     public <T> T[] toArray(T[] a) {
jaroslav@597:         int size = size();
jaroslav@597:         if (a.length < size)
jaroslav@597:             a = (T[])java.lang.reflect.Array.newInstance(
jaroslav@597:                     a.getClass().getComponentType(), size);
jaroslav@597:         copyElements(a);
jaroslav@597:         if (a.length > size)
jaroslav@597:             a[size] = null;
jaroslav@597:         return a;
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     // *** Object methods ***
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Returns a copy of this deque.
jaroslav@597:      *
jaroslav@597:      * @return a copy of this deque
jaroslav@597:      */
jaroslav@597:     public ArrayDeque<E> clone() {
jaroslav@597:         try {
jaroslav@597:             ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
jaroslav@597:             result.elements = Arrays.copyOf(elements, elements.length);
jaroslav@597:             return result;
jaroslav@597: 
jaroslav@597:         } catch (CloneNotSupportedException e) {
jaroslav@597:             throw new AssertionError();
jaroslav@597:         }
jaroslav@597:     }
jaroslav@597: 
jaroslav@597:     /**
jaroslav@597:      * Appease the serialization gods.
jaroslav@597:      */
jaroslav@597:     private static final long serialVersionUID = 2340985798034038923L;
jaroslav@597: 
jaroslav@597: }