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