8143577: optimize ArrayList.removeIf
8169679: ArrayList.subList().iterator().forEachRemaining() off-by-one-error
8167202: ArrayDeque improvements
8164793: new ArrayDeque(2**N) allocates backing array of size 2**(N+1)
8169739: LinkedBlockingDeque spliterator needs to support node self-linking
8169738: CopyOnWriteArrayList subList needs more synchronization
Reviewed-by: martin, smarks, psandoz, forax
/*
* 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}/../technotes/guides/collections/index.html">
* 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);
elements = Arrays.copyOf(elements, newCapacity);
// Exceptionally, here tail == head needs to be disambiguated
if (tail < head || (tail == head && elements[head] != null)) {
// wrap around; slide first leg forward to end of array
int newSpace = newCapacity - oldCapacity;
System.arraycopy(elements, head,
elements, head + newSpace,
oldCapacity - head);
Arrays.fill(elements, head, head + newSpace, null);
head += newSpace;
}
}
/** 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 diambiguated 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;
}
}
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.
*/
private static void circularClear(Object[] es, int i, int end) {
for (int to = (i <= end) ? end : es.length;
; i = 0, to = end) {
Arrays.fill(es, i, to, 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;
}
}
}