/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* 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
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*/
/*
* 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/.
*/
/**
* 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 <tt>ArrayDeque</tt> 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 <tt>iterator</tt> 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 <tt>remove</tt>
* 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 <tt>ConcurrentModificationException</tt> 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
*/
{
/**
* 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.
*/
private transient E[] 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 equal to tail if the deque is empty.
*/
private 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)).
*/
private transient int tail;
/**
* The minimum capacity that we'll use for a newly created deque.
* Must be a power of 2.
*/
// ****** Array allocation and resizing utilities ******
/**
* Allocate empty array to hold the given number of elements.
*
* @param numElements the number of elements to hold
*/
// Find the best power of two to hold elements.
// Tests "<=" because arrays aren't kept full.
if (numElements >= initialCapacity) {
}
}
/**
* Double the capacity of this deque. Call only when full, i.e.,
* when head and tail have wrapped around to become equal.
*/
private void doubleCapacity() {
int p = head;
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");
elements = (E[])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) {
}
return a;
}
/**
* Constructs an empty array deque with an initial capacity
* sufficient to hold 16 elements.
*/
public ArrayDeque() {
}
/**
* 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
*/
}
/**
* 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
*/
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();
}
/**
* 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();
}
/**
* Inserts the specified element at the front of this deque.
*
* @param e the element to add
* @return <tt>true</tt> (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 <tt>true</tt> (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;
return null;
return result;
}
public E pollLast() {
return null;
tail = t;
return result;
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public E getFirst() {
if (x == null)
throw new NoSuchElementException();
return x;
}
/**
* @throws NoSuchElementException {@inheritDoc}
*/
public E getLast() {
if (x == null)
throw new NoSuchElementException();
return x;
}
public E peekFirst() {
}
public E peekLast() {
}
/**
* 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 <tt>e</tt> such that
* <tt>o.equals(e)</tt> (if such an element exists).
* Returns <tt>true</tt> 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 <tt>true</tt> if the deque contained the specified element
*/
if (o == null)
return false;
int i = head;
E x;
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 <tt>e</tt> such that
* <tt>o.equals(e)</tt> (if such an element exists).
* Returns <tt>true</tt> 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 <tt>true</tt> if the deque contained the specified element
*/
if (o == null)
return false;
E x;
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 <tt>true</tt> (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 <tt>true</tt> (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
* <tt>null</tt> if this deque is empty.
*
* <p>This method is equivalent to {@link #pollFirst}.
*
* @return the head of the queue represented by this deque, or
* <tt>null</tt> 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 <tt>null</tt> if this deque is empty.
*
* <p>This method is equivalent to {@link #peekFirst}.
*
* @return the head of the queue represented by this deque, or
* <tt>null</tt> 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() {
}
/**
* 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) {
final int h = head;
final int t = tail;
// Invariant: head <= i < tail mod circularity
throw new ConcurrentModificationException();
// Optimize for least element motion
if (h <= i) {
} else { // Wrap around
}
return false;
} else {
if (i < t) { // Copy the null tail as well
tail = t - 1;
} else { // Wrap around
}
return true;
}
}
// *** Collection Methods ***
/**
* Returns the number of elements in this deque.
*
* @return the number of elements in this deque
*/
public int size() {
}
/**
* Returns <tt>true</tt> if this deque contains no elements.
*
* @return <tt>true</tt> if this deque contains no elements
*/
public boolean isEmpty() {
}
/**
* 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
*/
return new DeqIterator();
}
return new DescendingIterator();
}
/**
* Index of element to be returned by subsequent call to next.
*/
/**
* Tail recorded at construction (also in remove), to stop
* iterator and also to check for comodification.
*/
/**
* Index of element returned by most recent call to next.
* Reset to -1 if element is deleted by a call to remove.
*/
public boolean hasNext() {
}
public E next() {
throw new NoSuchElementException();
// This check doesn't catch all possible comodifications,
// but does catch the ones that corrupt traversal
throw new ConcurrentModificationException();
return result;
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
}
lastRet = -1;
}
}
/*
* This class is nearly a mirror-image of DeqIterator, using
* tail instead of head for initial cursor, and head instead of
* tail for fence.
*/
public boolean hasNext() {
}
public E next() {
throw new NoSuchElementException();
throw new ConcurrentModificationException();
return result;
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
}
lastRet = -1;
}
}
/**
* Returns <tt>true</tt> if this deque contains the specified element.
* More formally, returns <tt>true</tt> if and only if this deque contains
* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
*
* @param o object to be checked for containment in this deque
* @return <tt>true</tt> if this deque contains the specified element
*/
if (o == null)
return false;
int i = head;
E x;
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 <tt>e</tt> such that
* <tt>o.equals(e)</tt> (if such an element exists).
* Returns <tt>true</tt> 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}.
*
* @param o element to be removed from this deque, if present
* @return <tt>true</tt> if this deque contained the specified element
*/
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
int i = h;
do {
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
*/
}
/**
* 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
* <tt>null</tt>.
*
* <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 <tt>x</tt> is a deque known to contain only strings.
* The following code can be used to dump the deque into a newly
* allocated array of <tt>String</tt>:
*
* <pre>
* String[] y = x.toArray(new String[0]);</pre>
*
* Note that <tt>toArray(new Object[0])</tt> is identical in function to
* <tt>toArray()</tt>.
*
* @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
*/
public <T> T[] toArray(T[] a) {
copyElements(a);
return a;
}
// *** Object methods ***
/**
* Returns a copy of this deque.
*
* @return a copy of this deque
*/
try {
return result;
} catch (CloneNotSupportedException e) {
throw new AssertionError();
}
}
/**
* Appease the serialization gods.
*/
/**
* Serialize this deque.
*
* @serialData The current size (<tt>int</tt>) of the deque,
* followed by all of its elements (each an object reference) in
* first-to-last order.
*/
s.defaultWriteObject();
// Write out size
// Write out elements in order.
s.writeObject(elements[i]);
}
/**
* Deserialize this deque.
*/
throws IOException, ClassNotFoundException {
s.defaultReadObject();
// Read in size and allocate array
head = 0;
// Read in all elements in the proper order.
for (int i = 0; i < size; i++)
elements[i] = (E)s.readObject();
}
}