/*
* Copyright 2008 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package java.util;
import java.io.Serializable;
/**
* Linked list implementation. <a
* href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/LinkedList.html">[Sun
* docs]</a>
*
* @param <E> element type.
*/
public class LinkedList<E> extends AbstractSequentialList<E> implements
List<E>, Queue<E>, Serializable {
/*
* This implementation uses a doubly-linked circular list with a header node.
*
* TODO(jat): add more efficient subList implementation.
*/
/**
* Implementation of ListIterator for linked lists.
*/
private final class ListIteratorImpl implements ListIterator<E> {
/**
* The index to the current position.
*/
protected int currentIndex;
/**
* Current node, to be returned from next.
*/
protected Node<E> currentNode;
/**
* The last node returned from next/previous, or null if deleted or never
* called.
*/
protected Node<E> lastNode = null;
/**
* @param index from the beginning of the list (0 = first node)
* @param startNode the initial current node
*/
public ListIteratorImpl(int index, Node<E> startNode) {
currentNode = startNode;
currentIndex = index;
}
public void add(E o) {
addBefore(o, currentNode);
++currentIndex;
lastNode = null;
}
public boolean hasNext() {
return currentNode != header;
}
public boolean hasPrevious() {
return currentNode.prev != header;
}
public E next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
lastNode = currentNode;
currentNode = currentNode.next;
++currentIndex;
return lastNode.value;
}
public int nextIndex() {
return currentIndex;
}
public E previous() {
if (!hasPrevious()) {
throw new NoSuchElementException();
}
lastNode = currentNode = currentNode.prev;
--currentIndex;
return lastNode.value;
}
public int previousIndex() {
return currentIndex - 1;
}
public void remove() {
verifyCurrentElement();
if (currentNode == lastNode) {
// We just did a previous().
currentNode = lastNode.next;
} else {
// We just did a next().
--currentIndex;
}
lastNode.remove();
lastNode = null;
--size;
}
public void set(E o) {
verifyCurrentElement();
lastNode.value = o;
}
protected void verifyCurrentElement() {
if (lastNode == null) {
throw new IllegalStateException();
}
}
}
/**
* Internal class representing a doubly-linked list node.
*
* @param <E> element type
*/
private static class Node<E> {
public Node<E> next;
public Node<E> prev;
public E value;
public Node() {
next = prev = this;
}
public Node(E value) {
this.value = value;
}
/**
* Construct a node containing a value and add it before the specified node.
*
* @param value
* @param nextNode
*/
public Node(E value, Node<E> nextNode) {
this(value);
this.next = nextNode;
this.prev = nextNode.prev;
nextNode.prev.next = this;
nextNode.prev = this;
}
/**
* Remove this node from any list it is in, leaving it with circular
* references to itself.
*/
public void remove() {
this.next.prev = this.prev;
this.prev.next = this.next;
this.next = this.prev = this;
}
}
/**
* Ensures that RPC will consider type parameter E to be exposed. It will be
* pruned by dead code elimination.
*/
@SuppressWarnings("unused")
private E exposeElement;
/**
* Header node - header.next is the first element of the list, and header.prev
* is the last element of the list. If the list is empty, the header node will
* point to itself.
*/
private Node<E> header;
/**
* Number of nodes currently present in the list.
*/
private int size;
public LinkedList() {
clear();
}
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
@Override
public boolean add(E o) {
addLast(o);
return true;
}
public void addFirst(E o) {
new Node<E>(o, header.next);
++size;
}
public void addLast(E o) {
new Node<E>(o, header);
++size;
}
@Override
public void clear() {
header = new Node<E>();
size = 0;
}
public E element() {
return getFirst();
}
public E getFirst() {
throwEmptyException();
return header.next.value;
}
public E getLast() {
throwEmptyException();
return header.prev.value;
}
@Override
public ListIterator<E> listIterator(final int index) {
if (index < 0 || index > size) {
indexOutOfBounds(index, size);
}
Node<E> node;
// start from the nearest end of the list
if (index >= size >> 1) {
node = header;
for (int i = size; i > index; --i) {
node = node.prev;
}
} else {
node = header.next;
for (int i = 0; i < index; ++i) {
node = node.next;
}
}
return new ListIteratorImpl(index, node);
}
public boolean offer(E o) {
return add(o);
}
public E peek() {
if (size == 0) {
return null;
} else {
return getFirst();
}
}
public E poll() {
if (size == 0) {
return null;
} else {
return removeFirst();
}
}
public E remove() {
return removeFirst();
}
public E removeFirst() {
throwEmptyException();
--size;
Node<E> node = header.next;
node.remove();
return node.value;
}
public E removeLast() {
throwEmptyException();
--size;
Node<E> node = header.prev;
node.remove();
return node.value;
}
@Override
public int size() {
return size;
}
private void addBefore(E o, Node<E> target) {
new Node<E>(o, target);
++size;
}
/**
* Throw an exception if the list is empty.
*/
private void throwEmptyException() {
if (size == 0) {
throw new NoSuchElementException();
}
}
}