/*
* Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*
*
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*/
package java.util;
import java.util.function.
Consumer;
/**
* Doubly-linked list implementation of the {@code List} and {@code Deque}
* interfaces. Implements all optional list operations, and permits all
* elements (including {@code null}).
*
* <p>All of the operations perform as could be expected for a doubly-linked
* list. Operations that index into the list will traverse the list from
* the beginning or the end, whichever is closer to the specified index.
*
* <p><strong>Note that this implementation is not synchronized.</strong>
* If multiple threads access a linked list concurrently, and at least
* one of the threads modifies the list structurally, it <i>must</i> be
* synchronized externally. (A structural modification is any operation
* that adds or deletes one or more elements; merely setting the value of
* an element is not a structural modification.) This is typically
* accomplished by synchronizing on some object that naturally
* encapsulates the list.
*
* If no such object exists, the list should be "wrapped" using the
* {@link Collections#synchronizedList Collections.synchronizedList}
* method. This is best done at creation time, to prevent accidental
* unsynchronized access to the list:<pre>
* List list = Collections.synchronizedList(new LinkedList(...));</pre>
*
* <p>The iterators returned by this class's {@code iterator} and
* {@code listIterator} methods are <i>fail-fast</i>: if the list is
* structurally modified at any time after the iterator is created, in
* any way except through the Iterator's own {@code remove} or
* {@code add} methods, the iterator will 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 is a member of the
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @author Josh Bloch
* @see List
* @see ArrayList
* @since 1.2
* @param <E> the type of elements held in this collection
*/
public class
LinkedList<E>
extends
AbstractSequentialList<E>
implements
List<E>,
Deque<E>,
Cloneable, java.io.
Serializable
{
transient int
size = 0;
/**
* Pointer to first node.
* Invariant: (first == null && last == null) ||
* (first.prev == null && first.item != null)
*/
transient
Node<E>
first;
/**
* Pointer to last node.
* Invariant: (first == null && last == null) ||
* (last.next == null && last.item != null)
*/
transient
Node<E>
last;
/**
* Constructs an empty list.
*/
public
LinkedList() {
}
/**
* Constructs a list containing the elements of the specified
* collection, in the order they are returned by the collection's
* iterator.
*
* @param c the collection whose elements are to be placed into this list
* @throws NullPointerException if the specified collection is null
*/
public
LinkedList(
Collection<? extends E>
c) {
this();
addAll(
c);
}
/**
* Links e as first element.
*/
private void
linkFirst(E
e) {
final
Node<E>
f =
first;
final
Node<E>
newNode = new
Node<>(null,
e,
f);
first =
newNode;
if (
f == null)
last =
newNode;
else
f.
prev =
newNode;
size++;
modCount++;
}
/**
* Links e as last element.
*/
void
linkLast(E
e) {
final
Node<E>
l =
last;
final
Node<E>
newNode = new
Node<>(
l,
e, null);
last =
newNode;
if (
l == null)
first =
newNode;
else
l.
next =
newNode;
size++;
modCount++;
}
/**
* Inserts element e before non-null Node succ.
*/
void
linkBefore(E
e,
Node<E>
succ) {
// assert succ != null;
final
Node<E>
pred =
succ.
prev;
final
Node<E>
newNode = new
Node<>(
pred,
e,
succ);
succ.
prev =
newNode;
if (
pred == null)
first =
newNode;
else
pred.
next =
newNode;
size++;
modCount++;
}
/**
* Unlinks non-null first node f.
*/
private E
unlinkFirst(
Node<E>
f) {
// assert f == first && f != null;
final E
element =
f.
item;
final
Node<E>
next =
f.
next;
f.
item = null;
f.
next = null; // help GC
first =
next;
if (
next == null)
last = null;
else
next.
prev = null;
size--;
modCount++;
return
element;
}
/**
* Unlinks non-null last node l.
*/
private E
unlinkLast(
Node<E>
l) {
// assert l == last && l != null;
final E
element =
l.
item;
final
Node<E>
prev =
l.
prev;
l.
item = null;
l.
prev = null; // help GC
last =
prev;
if (
prev == null)
first = null;
else
prev.
next = null;
size--;
modCount++;
return
element;
}
/**
* Unlinks non-null node x.
*/
E
unlink(
Node<E>
x) {
// assert x != null;
final E
element =
x.
item;
final
Node<E>
next =
x.
next;
final
Node<E>
prev =
x.
prev;
if (
prev == null) {
first =
next;
} else {
prev.
next =
next;
x.
prev = null;
}
if (
next == null) {
last =
prev;
} else {
next.
prev =
prev;
x.
next = null;
}
x.
item = null;
size--;
modCount++;
return
element;
}
/**
* Returns the first element in this list.
*
* @return the first element in this list
* @throws NoSuchElementException if this list is empty
*/
public E
getFirst() {
final
Node<E>
f =
first;
if (
f == null)
throw new
NoSuchElementException();
return
f.
item;
}
/**
* Returns the last element in this list.
*
* @return the last element in this list
* @throws NoSuchElementException if this list is empty
*/
public E
getLast() {
final
Node<E>
l =
last;
if (
l == null)
throw new
NoSuchElementException();
return
l.
item;
}
/**
* Removes and returns the first element from this list.
*
* @return the first element from this list
* @throws NoSuchElementException if this list is empty
*/
public E
removeFirst() {
final
Node<E>
f =
first;
if (
f == null)
throw new
NoSuchElementException();
return
unlinkFirst(
f);
}
/**
* Removes and returns the last element from this list.
*
* @return the last element from this list
* @throws NoSuchElementException if this list is empty
*/
public E
removeLast() {
final
Node<E>
l =
last;
if (
l == null)
throw new
NoSuchElementException();
return
unlinkLast(
l);
}
/**
* Inserts the specified element at the beginning of this list.
*
* @param e the element to add
*/
public void
addFirst(E
e) {
linkFirst(
e);
}
/**
* Appends the specified element to the end of this list.
*
* <p>This method is equivalent to {@link #add}.
*
* @param e the element to add
*/
public void
addLast(E
e) {
linkLast(
e);
}
/**
* Returns {@code true} if this list contains the specified element.
* More formally, returns {@code true} if and only if this list contains
* at least one element {@code e} such that
* <tt>(o==null ? e==null : o.equals(e))</tt>.
*
* @param o element whose presence in this list is to be tested
* @return {@code true} if this list contains the specified element
*/
public boolean
contains(
Object o) {
return
indexOf(
o) != -1;
}
/**
* Returns the number of elements in this list.
*
* @return the number of elements in this list
*/
public int
size() {
return
size;
}
/**
* Appends the specified element to the end of this list.
*
* <p>This method is equivalent to {@link #addLast}.
*
* @param e element to be appended to this list
* @return {@code true} (as specified by {@link Collection#add})
*/
public boolean
add(E
e) {
linkLast(
e);
return true;
}
/**
* Removes the first occurrence of the specified element from this list,
* if it is present. If this list does not contain the element, it is
* unchanged. More formally, removes the element with the lowest index
* {@code i} such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
* (if such an element exists). Returns {@code true} if this list
* contained the specified element (or equivalently, if this list
* changed as a result of the call).
*
* @param o element to be removed from this list, if present
* @return {@code true} if this list contained the specified element
*/
public boolean
remove(
Object o) {
if (
o == null) {
for (
Node<E>
x =
first;
x != null;
x =
x.
next) {
if (
x.
item == null) {
unlink(
x);
return true;
}
}
} else {
for (
Node<E>
x =
first;
x != null;
x =
x.
next) {
if (
o.
equals(
x.
item)) {
unlink(
x);
return true;
}
}
}
return false;
}
/**
* Appends all of the elements in the specified collection to the end of
* this list, in the order that they are returned by the specified
* collection's iterator. The behavior of this operation is undefined if
* the specified collection is modified while the operation is in
* progress. (Note that this will occur if the specified collection is
* this list, and it's nonempty.)
*
* @param c collection containing elements to be added to this list
* @return {@code true} if this list changed as a result of the call
* @throws NullPointerException if the specified collection is null
*/
public boolean
addAll(
Collection<? extends E>
c) {
return
addAll(
size,
c);
}
/**
* Inserts all of the elements in the specified collection into this
* list, starting at the specified position. Shifts the element
* currently at that position (if any) and any subsequent elements to
* the right (increases their indices). The new elements will appear
* in the list in the order that they are returned by the
* specified collection's iterator.
*
* @param index index at which to insert the first element
* from the specified collection
* @param c collection containing elements to be added to this list
* @return {@code true} if this list changed as a result of the call
* @throws IndexOutOfBoundsException {@inheritDoc}
* @throws NullPointerException if the specified collection is null
*/
public boolean
addAll(int
index,
Collection<? extends E>
c) {
checkPositionIndex(
index);
Object[]
a =
c.
toArray();
int
numNew =
a.length;
if (
numNew == 0)
return false;
Node<E>
pred,
succ;
if (
index ==
size) {
succ = null;
pred =
last;
} else {
succ =
node(
index);
pred =
succ.
prev;
}
for (
Object o :
a) {
@
SuppressWarnings("unchecked") E
e = (E)
o;
Node<E>
newNode = new
Node<>(
pred,
e, null);
if (
pred == null)
first =
newNode;
else
pred.
next =
newNode;
pred =
newNode;
}
if (
succ == null) {
last =
pred;
} else {
pred.
next =
succ;
succ.
prev =
pred;
}
size +=
numNew;
modCount++;
return true;
}
/**
* Removes all of the elements from this list.
* The list will be empty after this call returns.
*/
public void
clear() {
// Clearing all of the links between nodes is "unnecessary", but:
// - helps a generational GC if the discarded nodes inhabit
// more than one generation
// - is sure to free memory even if there is a reachable Iterator
for (
Node<E>
x =
first;
x != null; ) {
Node<E>
next =
x.
next;
x.
item = null;
x.
next = null;
x.
prev = null;
x =
next;
}
first =
last = null;
size = 0;
modCount++;
}
// Positional Access Operations
/**
* Returns the element at the specified position in this list.
*
* @param index index of the element to return
* @return the element at the specified position in this list
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E
get(int
index) {
checkElementIndex(
index);
return
node(
index).
item;
}
/**
* Replaces the element at the specified position in this list with the
* specified element.
*
* @param index index of the element to replace
* @param element element to be stored at the specified position
* @return the element previously at the specified position
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E
set(int
index, E
element) {
checkElementIndex(
index);
Node<E>
x =
node(
index);
E
oldVal =
x.
item;
x.
item =
element;
return
oldVal;
}
/**
* Inserts the specified element at the specified position in this list.
* Shifts the element currently at that position (if any) and any
* subsequent elements to the right (adds one to their indices).
*
* @param index index at which the specified element is to be inserted
* @param element element to be inserted
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public void
add(int
index, E
element) {
checkPositionIndex(
index);
if (
index ==
size)
linkLast(
element);
else
linkBefore(
element,
node(
index));
}
/**
* Removes the element at the specified position in this list. Shifts any
* subsequent elements to the left (subtracts one from their indices).
* Returns the element that was removed from the list.
*
* @param index the index of the element to be removed
* @return the element previously at the specified position
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E
remove(int
index) {
checkElementIndex(
index);
return
unlink(
node(
index));
}
/**
* Tells if the argument is the index of an existing element.
*/
private boolean
isElementIndex(int
index) {
return
index >= 0 &&
index <
size;
}
/**
* Tells if the argument is the index of a valid position for an
* iterator or an add operation.
*/
private boolean
isPositionIndex(int
index) {
return
index >= 0 &&
index <=
size;
}
/**
* Constructs an IndexOutOfBoundsException detail message.
* Of the many possible refactorings of the error handling code,
* this "outlining" performs best with both server and client VMs.
*/
private
String outOfBoundsMsg(int
index) {
return "Index: "+
index+", Size: "+
size;
}
private void
checkElementIndex(int
index) {
if (!
isElementIndex(
index))
throw new
IndexOutOfBoundsException(
outOfBoundsMsg(
index));
}
private void
checkPositionIndex(int
index) {
if (!
isPositionIndex(
index))
throw new
IndexOutOfBoundsException(
outOfBoundsMsg(
index));
}
/**
* Returns the (non-null) Node at the specified element index.
*/
Node<E>
node(int
index) {
// assert isElementIndex(index);
if (
index < (
size >> 1)) {
Node<E>
x =
first;
for (int
i = 0;
i <
index;
i++)
x =
x.
next;
return
x;
} else {
Node<E>
x =
last;
for (int
i =
size - 1;
i >
index;
i--)
x =
x.
prev;
return
x;
}
}
// Search Operations
/**
* Returns the index of the first occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the lowest index {@code i} such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*
* @param o element to search for
* @return the index of the first occurrence of the specified element in
* this list, or -1 if this list does not contain the element
*/
public int
indexOf(
Object o) {
int
index = 0;
if (
o == null) {
for (
Node<E>
x =
first;
x != null;
x =
x.
next) {
if (
x.
item == null)
return
index;
index++;
}
} else {
for (
Node<E>
x =
first;
x != null;
x =
x.
next) {
if (
o.
equals(
x.
item))
return
index;
index++;
}
}
return -1;
}
/**
* Returns the index of the last occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the highest index {@code i} such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*
* @param o element to search for
* @return the index of the last occurrence of the specified element in
* this list, or -1 if this list does not contain the element
*/
public int
lastIndexOf(
Object o) {
int
index =
size;
if (
o == null) {
for (
Node<E>
x =
last;
x != null;
x =
x.
prev) {
index--;
if (
x.
item == null)
return
index;
}
} else {
for (
Node<E>
x =
last;
x != null;
x =
x.
prev) {
index--;
if (
o.
equals(
x.
item))
return
index;
}
}
return -1;
}
// Queue operations.
/**
* Retrieves, but does not remove, the head (first element) of this list.
*
* @return the head of this list, or {@code null} if this list is empty
* @since 1.5
*/
public E
peek() {
final
Node<E>
f =
first;
return (
f == null) ? null :
f.
item;
}
/**
* Retrieves, but does not remove, the head (first element) of this list.
*
* @return the head of this list
* @throws NoSuchElementException if this list is empty
* @since 1.5
*/
public E
element() {
return
getFirst();
}
/**
* Retrieves and removes the head (first element) of this list.
*
* @return the head of this list, or {@code null} if this list is empty
* @since 1.5
*/
public E
poll() {
final
Node<E>
f =
first;
return (
f == null) ? null :
unlinkFirst(
f);
}
/**
* Retrieves and removes the head (first element) of this list.
*
* @return the head of this list
* @throws NoSuchElementException if this list is empty
* @since 1.5
*/
public E
remove() {
return
removeFirst();
}
/**
* Adds the specified element as the tail (last element) of this list.
*
* @param e the element to add
* @return {@code true} (as specified by {@link Queue#offer})
* @since 1.5
*/
public boolean
offer(E
e) {
return
add(
e);
}
// Deque operations
/**
* Inserts the specified element at the front of this list.
*
* @param e the element to insert
* @return {@code true} (as specified by {@link Deque#offerFirst})
* @since 1.6
*/
public boolean
offerFirst(E
e) {
addFirst(
e);
return true;
}
/**
* Inserts the specified element at the end of this list.
*
* @param e the element to insert
* @return {@code true} (as specified by {@link Deque#offerLast})
* @since 1.6
*/
public boolean
offerLast(E
e) {
addLast(
e);
return true;
}
/**
* Retrieves, but does not remove, the first element of this list,
* or returns {@code null} if this list is empty.
*
* @return the first element of this list, or {@code null}
* if this list is empty
* @since 1.6
*/
public E
peekFirst() {
final
Node<E>
f =
first;
return (
f == null) ? null :
f.
item;
}
/**
* Retrieves, but does not remove, the last element of this list,
* or returns {@code null} if this list is empty.
*
* @return the last element of this list, or {@code null}
* if this list is empty
* @since 1.6
*/
public E
peekLast() {
final
Node<E>
l =
last;
return (
l == null) ? null :
l.
item;
}
/**
* Retrieves and removes the first element of this list,
* or returns {@code null} if this list is empty.
*
* @return the first element of this list, or {@code null} if
* this list is empty
* @since 1.6
*/
public E
pollFirst() {
final
Node<E>
f =
first;
return (
f == null) ? null :
unlinkFirst(
f);
}
/**
* Retrieves and removes the last element of this list,
* or returns {@code null} if this list is empty.
*
* @return the last element of this list, or {@code null} if
* this list is empty
* @since 1.6
*/
public E
pollLast() {
final
Node<E>
l =
last;
return (
l == null) ? null :
unlinkLast(
l);
}
/**
* Pushes an element onto the stack represented by this list. In other
* words, inserts the element at the front of this list.
*
* <p>This method is equivalent to {@link #addFirst}.
*
* @param e the element to push
* @since 1.6
*/
public void
push(E
e) {
addFirst(
e);
}
/**
* Pops an element from the stack represented by this list. In other
* words, removes and returns the first element of this list.
*
* <p>This method is equivalent to {@link #removeFirst()}.
*
* @return the element at the front of this list (which is the top
* of the stack represented by this list)
* @throws NoSuchElementException if this list is empty
* @since 1.6
*/
public E
pop() {
return
removeFirst();
}
/**
* Removes the first occurrence of the specified element in this
* list (when traversing the list from head to tail). If the list
* does not contain the element, it is unchanged.
*
* @param o element to be removed from this list, if present
* @return {@code true} if the list contained the specified element
* @since 1.6
*/
public boolean
removeFirstOccurrence(
Object o) {
return
remove(
o);
}
/**
* Removes the last occurrence of the specified element in this
* list (when traversing the list from head to tail). If the list
* does not contain the element, it is unchanged.
*
* @param o element to be removed from this list, if present
* @return {@code true} if the list contained the specified element
* @since 1.6
*/
public boolean
removeLastOccurrence(
Object o) {
if (
o == null) {
for (
Node<E>
x =
last;
x != null;
x =
x.
prev) {
if (
x.
item == null) {
unlink(
x);
return true;
}
}
} else {
for (
Node<E>
x =
last;
x != null;
x =
x.
prev) {
if (
o.
equals(
x.
item)) {
unlink(
x);
return true;
}
}
}
return false;
}
/**
* Returns a list-iterator of the elements in this list (in proper
* sequence), starting at the specified position in the list.
* Obeys the general contract of {@code List.listIterator(int)}.<p>
*
* The list-iterator is <i>fail-fast</i>: if the list is structurally
* modified at any time after the Iterator is created, in any way except
* through the list-iterator's own {@code remove} or {@code add}
* methods, the list-iterator will throw a
* {@code 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.
*
* @param index index of the first element to be returned from the
* list-iterator (by a call to {@code next})
* @return a ListIterator of the elements in this list (in proper
* sequence), starting at the specified position in the list
* @throws IndexOutOfBoundsException {@inheritDoc}
* @see List#listIterator(int)
*/
public
ListIterator<E>
listIterator(int
index) {
checkPositionIndex(
index);
return new
ListItr(
index);
}
private class
ListItr implements
ListIterator<E> {
private
Node<E>
lastReturned;
private
Node<E>
next;
private int
nextIndex;
private int
expectedModCount =
modCount;
ListItr(int
index) {
// assert isPositionIndex(index);
next = (
index ==
size) ? null :
node(
index);
nextIndex =
index;
}
public boolean
hasNext() {
return
nextIndex <
size;
}
public E
next() {
checkForComodification();
if (!
hasNext())
throw new
NoSuchElementException();
lastReturned =
next;
next =
next.
next;
nextIndex++;
return
lastReturned.
item;
}
public boolean
hasPrevious() {
return
nextIndex > 0;
}
public E
previous() {
checkForComodification();
if (!
hasPrevious())
throw new
NoSuchElementException();
lastReturned =
next = (
next == null) ?
last :
next.
prev;
nextIndex--;
return
lastReturned.
item;
}
public int
nextIndex() {
return
nextIndex;
}
public int
previousIndex() {
return
nextIndex - 1;
}
public void
remove() {
checkForComodification();
if (
lastReturned == null)
throw new
IllegalStateException();
Node<E>
lastNext =
lastReturned.
next;
unlink(
lastReturned);
if (
next ==
lastReturned)
next =
lastNext;
else
nextIndex--;
lastReturned = null;
expectedModCount++;
}
public void
set(E
e) {
if (
lastReturned == null)
throw new
IllegalStateException();
checkForComodification();
lastReturned.
item =
e;
}
public void
add(E
e) {
checkForComodification();
lastReturned = null;
if (
next == null)
linkLast(
e);
else
linkBefore(
e,
next);
nextIndex++;
expectedModCount++;
}
public void
forEachRemaining(
Consumer<? super E>
action) {
Objects.
requireNonNull(
action);
while (
modCount ==
expectedModCount &&
nextIndex <
size) {
action.
accept(
next.
item);
lastReturned =
next;
next =
next.
next;
nextIndex++;
}
checkForComodification();
}
final void
checkForComodification() {
if (
modCount !=
expectedModCount)
throw new
ConcurrentModificationException();
}
}
private static class
Node<E> {
E
item;
Node<E>
next;
Node<E>
prev;
Node(
Node<E>
prev, E
element,
Node<E>
next) {
this.
item =
element;
this.
next =
next;
this.
prev =
prev;
}
}
/**
* @since 1.6
*/
public
Iterator<E>
descendingIterator() {
return new
DescendingIterator();
}
/**
* Adapter to provide descending iterators via ListItr.previous
*/
private class
DescendingIterator implements
Iterator<E> {
private final
ListItr itr = new
ListItr(
size());
public boolean
hasNext() {
return
itr.
hasPrevious();
}
public E
next() {
return
itr.
previous();
}
public void
remove() {
itr.
remove();
}
}
@
SuppressWarnings("unchecked")
private
LinkedList<E>
superClone() {
try {
return (
LinkedList<E>) super.clone();
} catch (
CloneNotSupportedException e) {
throw new
InternalError(
e);
}
}
/**
* Returns a shallow copy of this {@code LinkedList}. (The elements
* themselves are not cloned.)
*
* @return a shallow copy of this {@code LinkedList} instance
*/
public
Object clone() {
LinkedList<E>
clone =
superClone();
// Put clone into "virgin" state
clone.
first =
clone.
last = null;
clone.
size = 0;
clone.
modCount = 0;
// Initialize clone with our elements
for (
Node<E>
x =
first;
x != null;
x =
x.
next)
clone.
add(
x.
item);
return
clone;
}
/**
* Returns an array containing all of the elements in this list
* 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 list. (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 list
* in proper sequence
*/
public
Object[]
toArray() {
Object[]
result = new
Object[
size];
int
i = 0;
for (
Node<E>
x =
first;
x != null;
x =
x.
next)
result[
i++] =
x.
item;
return
result;
}
/**
* Returns an array containing all of the elements in this list in
* proper sequence (from first to last element); the runtime type of
* the returned array is that of the specified array. If the list 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 list.
*
* <p>If the list fits in the specified array with room to spare (i.e.,
* the array has more elements than the list), the element in the array
* immediately following the end of the list is set to {@code null}.
* (This is useful in determining the length of the list <i>only</i> if
* the caller knows that the list does not contain any null elements.)
*
* <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 list known to contain only strings.
* The following code can be used to dump the list into a newly
* allocated array of {@code String}:
*
* <pre>
* 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 list 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 the elements of the list
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this list
* @throws NullPointerException if the specified array is null
*/
@
SuppressWarnings("unchecked")
public <T> T[]
toArray(T[]
a) {
if (
a.length <
size)
a = (T[])java.lang.reflect.
Array.
newInstance(
a.
getClass().
getComponentType(),
size);
int
i = 0;
Object[]
result =
a;
for (
Node<E>
x =
first;
x != null;
x =
x.
next)
result[
i++] =
x.
item;
if (
a.length >
size)
a[
size] = null;
return
a;
}
private static final long
serialVersionUID = 876323262645176354L;
/**
* Saves the state of this {@code LinkedList} instance to a stream
* (that is, serializes it).
*
* @serialData The size of the list (the number of elements it
* contains) is emitted (int), followed by all of its
* elements (each an Object) in the proper order.
*/
private void
writeObject(java.io.
ObjectOutputStream s)
throws java.io.
IOException {
// Write out any hidden serialization magic
s.
defaultWriteObject();
// Write out size
s.
writeInt(
size);
// Write out all elements in the proper order.
for (
Node<E>
x =
first;
x != null;
x =
x.
next)
s.
writeObject(
x.
item);
}
/**
* Reconstitutes this {@code LinkedList} instance from a stream
* (that is, deserializes it).
*/
@
SuppressWarnings("unchecked")
private void
readObject(java.io.
ObjectInputStream s)
throws java.io.
IOException,
ClassNotFoundException {
// Read in any hidden serialization magic
s.
defaultReadObject();
// Read in size
int
size =
s.
readInt();
// Read in all elements in the proper order.
for (int
i = 0;
i <
size;
i++)
linkLast((E)
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
* list.
*
* <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and
* {@link Spliterator#ORDERED}. Overriding implementations should document
* the reporting of additional characteristic values.
*
* @implNote
* The {@code Spliterator} additionally reports {@link Spliterator#SUBSIZED}
* and implements {@code trySplit} to permit limited parallelism..
*
* @return a {@code Spliterator} over the elements in this list
* @since 1.8
*/
@
Override
public
Spliterator<E>
spliterator() {
return new
LLSpliterator<E>(this, -1, 0);
}
/** A customized variant of Spliterators.IteratorSpliterator */
static final class
LLSpliterator<E> implements
Spliterator<E> {
static final int
BATCH_UNIT = 1 << 10; // batch array size increment
static final int
MAX_BATCH = 1 << 25; // max batch array size;
final
LinkedList<E>
list; // null OK unless traversed
Node<E>
current; // current node; null until initialized
int
est; // size estimate; -1 until first needed
int
expectedModCount; // initialized when est set
int
batch; // batch size for splits
LLSpliterator(
LinkedList<E>
list, int
est, int
expectedModCount) {
this.
list =
list;
this.
est =
est;
this.
expectedModCount =
expectedModCount;
}
final int
getEst() {
int
s; // force initialization
final
LinkedList<E>
lst;
if ((
s =
est) < 0) {
if ((
lst =
list) == null)
s =
est = 0;
else {
expectedModCount =
lst.
modCount;
current =
lst.
first;
s =
est =
lst.
size;
}
}
return
s;
}
public long
estimateSize() { return (long)
getEst(); }
public
Spliterator<E>
trySplit() {
Node<E>
p;
int
s =
getEst();
if (
s > 1 && (
p =
current) != null) {
int
n =
batch +
BATCH_UNIT;
if (
n >
s)
n =
s;
if (
n >
MAX_BATCH)
n =
MAX_BATCH;
Object[]
a = new
Object[
n];
int
j = 0;
do {
a[
j++] =
p.
item; } while ((
p =
p.
next) != null &&
j <
n);
current =
p;
batch =
j;
est =
s -
j;
return
Spliterators.
spliterator(
a, 0,
j,
Spliterator.
ORDERED);
}
return null;
}
public void
forEachRemaining(
Consumer<? super E>
action) {
Node<E>
p; int
n;
if (
action == null) throw new
NullPointerException();
if ((
n =
getEst()) > 0 && (
p =
current) != null) {
current = null;
est = 0;
do {
E
e =
p.
item;
p =
p.
next;
action.
accept(
e);
} while (
p != null && --
n > 0);
}
if (
list.
modCount !=
expectedModCount)
throw new
ConcurrentModificationException();
}
public boolean
tryAdvance(
Consumer<? super E>
action) {
Node<E>
p;
if (
action == null) throw new
NullPointerException();
if (
getEst() > 0 && (
p =
current) != null) {
--
est;
E
e =
p.
item;
current =
p.
next;
action.
accept(
e);
if (
list.
modCount !=
expectedModCount)
throw new
ConcurrentModificationException();
return true;
}
return false;
}
public int
characteristics() {
return
Spliterator.
ORDERED |
Spliterator.
SIZED |
Spliterator.
SUBSIZED;
}
}
}