/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.lang.reflect.Array;
/**
* LinkedList is an implementation of {@link List}, backed by a doubly-linked list.
* All optional operations including adding, removing, and replacing elements are supported.
*
* <p>All elements are permitted, including null.
*
* <p>This class is primarily useful if you need queue-like behavior. It may also be useful
* as a list if you expect your lists to contain zero or one element, but still require the
* ability to scale to slightly larger numbers of elements. In general, though, you should
* probably use {@link ArrayList} if you don't need the queue-like behavior.
*
* @since 1.2
*/
public class LinkedList<E> extends AbstractSequentialList<E> implements
List<E>, Deque<E>, Queue<E>, Cloneable, Serializable {
private static final long serialVersionUID = 876323262645176354L;
transient int size = 0;
transient Link<E> voidLink;
private static final class Link<ET> {
ET data;
Link<ET> previous, next;
Link(ET o, Link<ET> p, Link<ET> n) {
data = o;
previous = p;
next = n;
}
}
private static final class LinkIterator<ET> implements ListIterator<ET> {
int pos, expectedModCount;
final LinkedList<ET> list;
Link<ET> link, lastLink;
LinkIterator(LinkedList<ET> object, int location) {
list = object;
expectedModCount = list.modCount;
if (location >= 0 && location <= list.size) {
// pos ends up as -1 if list is empty, it ranges from -1 to
// list.size - 1
// if link == voidLink then pos must == -1
link = list.voidLink;
if (location < list.size / 2) {
for (pos = -1; pos + 1 < location; pos++) {
link = link.next;
}
} else {
for (pos = list.size; pos >= location; pos--) {
link = link.previous;
}
}
} else {
throw new IndexOutOfBoundsException();
}
}
public void add(ET object) {
if (expectedModCount == list.modCount) {
Link<ET> next = link.next;
Link<ET> newLink = new Link<ET>(object, link, next);
link.next = newLink;
next.previous = newLink;
link = newLink;
lastLink = null;
pos++;
expectedModCount++;
list.size++;
list.modCount++;
} else {
throw new ConcurrentModificationException();
}
}
public boolean hasNext() {
return link.next != list.voidLink;
}
public boolean hasPrevious() {
return link != list.voidLink;
}
public ET next() {
if (expectedModCount == list.modCount) {
LinkedList.Link<ET> next = link.next;
if (next != list.voidLink) {
lastLink = link = next;
pos++;
return link.data;
}
throw new NoSuchElementException();
}
throw new ConcurrentModificationException();
}
public int nextIndex() {
return pos + 1;
}
public ET previous() {
if (expectedModCount == list.modCount) {
if (link != list.voidLink) {
lastLink = link;
link = link.previous;
pos--;
return lastLink.data;
}
throw new NoSuchElementException();
}
throw new ConcurrentModificationException();
}
public int previousIndex() {
return pos;
}
public void remove() {
if (expectedModCount == list.modCount) {
if (lastLink != null) {
Link<ET> next = lastLink.next;
Link<ET> previous = lastLink.previous;
next.previous = previous;
previous.next = next;
if (lastLink == link) {
pos--;
}
link = previous;
lastLink = null;
expectedModCount++;
list.size--;
list.modCount++;
} else {
throw new IllegalStateException();
}
} else {
throw new ConcurrentModificationException();
}
}
public void set(ET object) {
if (expectedModCount == list.modCount) {
if (lastLink != null) {
lastLink.data = object;
} else {
throw new IllegalStateException();
}
} else {
throw new ConcurrentModificationException();
}
}
}
/*
* NOTES:descendingIterator is not fail-fast, according to the documentation
* and test case.
*/
private class ReverseLinkIterator<ET> implements Iterator<ET> {
private int expectedModCount;
private final LinkedList<ET> list;
private Link<ET> link;
private boolean canRemove;
ReverseLinkIterator(LinkedList<ET> linkedList) {
list = linkedList;
expectedModCount = list.modCount;
link = list.voidLink;
canRemove = false;
}
public boolean hasNext() {
return link.previous != list.voidLink;
}
public ET next() {
if (expectedModCount == list.modCount) {
if (hasNext()) {
link = link.previous;
canRemove = true;
return link.data;
}
throw new NoSuchElementException();
}
throw new ConcurrentModificationException();
}
public void remove() {
if (expectedModCount == list.modCount) {
if (canRemove) {
Link<ET> next = link.previous;
Link<ET> previous = link.next;
next.next = previous;
previous.previous = next;
link = previous;
list.size--;
list.modCount++;
expectedModCount++;
canRemove = false;
return;
}
throw new IllegalStateException();
}
throw new ConcurrentModificationException();
}
}
/**
* Constructs a new empty instance of {@code LinkedList}.
*/
public LinkedList() {
voidLink = new Link<E>(null, null, null);
voidLink.previous = voidLink;
voidLink.next = voidLink;
}
/**
* Constructs a new instance of {@code LinkedList} that holds all of the
* elements contained in the specified {@code collection}. The order of the
* elements in this new {@code LinkedList} will be determined by the
* iteration order of {@code collection}.
*
* @param collection
* the collection of elements to add.
*/
public LinkedList(Collection<? extends E> collection) {
this();
addAll(collection);
}
/**
* Inserts the specified object into this {@code LinkedList} at the
* specified location. The object is inserted before any previous element at
* the specified location. If the location is equal to the size of this
* {@code LinkedList}, the object is added at the end.
*
* @param location
* the index at which to insert.
* @param object
* the object to add.
* @throws IndexOutOfBoundsException
* if {@code location < 0 || location > size()}
*/
@Override
public void add(int location, E object) {
if (location >= 0 && location <= size) {
Link<E> link = voidLink;
if (location < (size / 2)) {
for (int i = 0; i <= location; i++) {
link = link.next;
}
} else {
for (int i = size; i > location; i--) {
link = link.previous;
}
}
Link<E> previous = link.previous;
Link<E> newLink = new Link<E>(object, previous, link);
previous.next = newLink;
link.previous = newLink;
size++;
modCount++;
} else {
throw new IndexOutOfBoundsException();
}
}
/**
* Adds the specified object at the end of this {@code LinkedList}.
*
* @param object
* the object to add.
* @return always true
*/
@Override
public boolean add(E object) {
return addLastImpl(object);
}
private boolean addLastImpl(E object) {
Link<E> oldLast = voidLink.previous;
Link<E> newLink = new Link<E>(object, oldLast, voidLink);
voidLink.previous = newLink;
oldLast.next = newLink;
size++;
modCount++;
return true;
}
/**
* Inserts the objects in the specified collection at the specified location
* in this {@code LinkedList}. The objects are added in the order they are
* returned from the collection's iterator.
*
* @param location
* the index at which to insert.
* @param collection
* the collection of objects
* @return {@code true} if this {@code LinkedList} is modified,
* {@code false} otherwise.
* @throws ClassCastException
* if the class of an object is inappropriate for this list.
* @throws IllegalArgumentException
* if an object cannot be added to this list.
* @throws IndexOutOfBoundsException
* if {@code location < 0 || location > size()}
*/
@Override
public boolean addAll(int location, Collection<? extends E> collection) {
if (location < 0 || location > size) {
throw new IndexOutOfBoundsException();
}
int adding = collection.size();
if (adding == 0) {
return false;
}
Collection<? extends E> elements = (collection == this) ?
new ArrayList<E>(collection) : collection;
Link<E> previous = voidLink;
if (location < (size / 2)) {
for (int i = 0; i < location; i++) {
previous = previous.next;
}
} else {
for (int i = size; i >= location; i--) {
previous = previous.previous;
}
}
Link<E> next = previous.next;
for (E e : elements) {
Link<E> newLink = new Link<E>(e, previous, null);
previous.next = newLink;
previous = newLink;
}
previous.next = next;
next.previous = previous;
size += adding;
modCount++;
return true;
}
/**
* Adds the objects in the specified Collection to this {@code LinkedList}.
*
* @param collection
* the collection of objects.
* @return {@code true} if this {@code LinkedList} is modified,
* {@code false} otherwise.
*/
@Override
public boolean addAll(Collection<? extends E> collection) {
int adding = collection.size();
if (adding == 0) {
return false;
}
Collection<? extends E> elements = (collection == this) ?
new ArrayList<E>(collection) : collection;
Link<E> previous = voidLink.previous;
for (E e : elements) {
Link<E> newLink = new Link<E>(e, previous, null);
previous.next = newLink;
previous = newLink;
}
previous.next = voidLink;
voidLink.previous = previous;
size += adding;
modCount++;
return true;
}
/**
* Adds the specified object at the beginning of this {@code LinkedList}.
*
* @param object
* the object to add.
*/
public void addFirst(E object) {
addFirstImpl(object);
}
private boolean addFirstImpl(E object) {
Link<E> oldFirst = voidLink.next;
Link<E> newLink = new Link<E>(object, voidLink, oldFirst);
voidLink.next = newLink;
oldFirst.previous = newLink;
size++;
modCount++;
return true;
}
/**
* Adds the specified object at the end of this {@code LinkedList}.
*
* @param object
* the object to add.
*/
public void addLast(E object) {
addLastImpl(object);
}
/**
* Removes all elements from this {@code LinkedList}, leaving it empty.
*
* @see List#isEmpty
* @see #size
*/
@Override
public void clear() {
if (size > 0) {
size = 0;
voidLink.next = voidLink;
voidLink.previous = voidLink;
modCount++;
}
}
/**
* Returns a new {@code LinkedList} with the same elements and size as this
* {@code LinkedList}.
*
* @return a shallow copy of this {@code LinkedList}.
* @see java.lang.Cloneable
*/
@SuppressWarnings("unchecked")
@Override
public Object clone() {
try {
LinkedList<E> l = (LinkedList<E>) super.clone();
l.size = 0;
l.voidLink = new Link<E>(null, null, null);
l.voidLink.previous = l.voidLink;
l.voidLink.next = l.voidLink;
l.addAll(this);
return l;
} catch (CloneNotSupportedException e) {
throw new AssertionError(e);
}
}
/**
* Searches this {@code LinkedList} for the specified object.
*
* @param object
* the object to search for.
* @return {@code true} if {@code object} is an element of this
* {@code LinkedList}, {@code false} otherwise
*/
@Override
public boolean contains(Object object) {
Link<E> link = voidLink.next;
if (object != null) {
while (link != voidLink) {
if (object.equals(link.data)) {
return true;
}
link = link.next;
}
} else {
while (link != voidLink) {
if (link.data == null) {
return true;
}
link = link.next;
}
}
return false;
}
@Override
public E get(int location) {
if (location >= 0 && location < size) {
Link<E> link = voidLink;
if (location < (size / 2)) {
for (int i = 0; i <= location; i++) {
link = link.next;
}
} else {
for (int i = size; i > location; i--) {
link = link.previous;
}
}
return link.data;
}
throw new IndexOutOfBoundsException();
}
/**
* Returns the first element in this {@code LinkedList}.
*
* @return the first element.
* @throws NoSuchElementException
* if this {@code LinkedList} is empty.
*/
public E getFirst() {
return getFirstImpl();
}
private E getFirstImpl() {
Link<E> first = voidLink.next;
if (first != voidLink) {
return first.data;
}
throw new NoSuchElementException();
}
/**
* Returns the last element in this {@code LinkedList}.
*
* @return the last element
* @throws NoSuchElementException
* if this {@code LinkedList} is empty
*/
public E getLast() {
Link<E> last = voidLink.previous;
if (last != voidLink) {
return last.data;
}
throw new NoSuchElementException();
}
@Override
public int indexOf(Object object) {
int pos = 0;
Link<E> link = voidLink.next;
if (object != null) {
while (link != voidLink) {
if (object.equals(link.data)) {
return pos;
}
link = link.next;
pos++;
}
} else {
while (link != voidLink) {
if (link.data == null) {
return pos;
}
link = link.next;
pos++;
}
}
return -1;
}
/**
* Searches this {@code LinkedList} for the specified object and returns the
* index of the last occurrence.
*
* @param object
* the object to search for
* @return the index of the last occurrence of the object, or -1 if it was
* not found.
*/
@Override
public int lastIndexOf(Object object) {
int pos = size;
Link<E> link = voidLink.previous;
if (object != null) {
while (link != voidLink) {
pos--;
if (object.equals(link.data)) {
return pos;
}
link = link.previous;
}
} else {
while (link != voidLink) {
pos--;
if (link.data == null) {
return pos;
}
link = link.previous;
}
}
return -1;
}
/**
* Returns a ListIterator on the elements of this {@code LinkedList}. The
* elements are iterated in the same order that they occur in the
* {@code LinkedList}. The iteration starts at the specified location.
*
* @param location
* the index at which to start the iteration
* @return a ListIterator on the elements of this {@code LinkedList}
* @throws IndexOutOfBoundsException
* if {@code location < 0 || location > size()}
* @see ListIterator
*/
@Override
public ListIterator<E> listIterator(int location) {
return new LinkIterator<E>(this, location);
}
/**
* Removes the object at the specified location from this {@code LinkedList}.
*
* @param location
* the index of the object to remove
* @return the removed object
* @throws IndexOutOfBoundsException
* if {@code location < 0 || location >= size()}
*/
@Override
public E remove(int location) {
if (location >= 0 && location < size) {
Link<E> link = voidLink;
if (location < (size / 2)) {
for (int i = 0; i <= location; i++) {
link = link.next;
}
} else {
for (int i = size; i > location; i--) {
link = link.previous;
}
}
Link<E> previous = link.previous;
Link<E> next = link.next;
previous.next = next;
next.previous = previous;
size--;
modCount++;
return link.data;
}
throw new IndexOutOfBoundsException();
}
@Override
public boolean remove(Object object) {
return removeFirstOccurrenceImpl(object);
}
/**
* Removes the first object from this {@code LinkedList}.
*
* @return the removed object.
* @throws NoSuchElementException
* if this {@code LinkedList} is empty.
*/
public E removeFirst() {
return removeFirstImpl();
}
private E removeFirstImpl() {
Link<E> first = voidLink.next;
if (first != voidLink) {
Link<E> next = first.next;
voidLink.next = next;
next.previous = voidLink;
size--;
modCount++;
return first.data;
}
throw new NoSuchElementException();
}
/**
* Removes the last object from this {@code LinkedList}.
*
* @return the removed object.
* @throws NoSuchElementException
* if this {@code LinkedList} is empty.
*/
public E removeLast() {
return removeLastImpl();
}
private E removeLastImpl() {
Link<E> last = voidLink.previous;
if (last != voidLink) {
Link<E> previous = last.previous;
voidLink.previous = previous;
previous.next = voidLink;
size--;
modCount++;
return last.data;
}
throw new NoSuchElementException();
}
/**
* {@inheritDoc}
*
* @see java.util.Deque#descendingIterator()
* @since 1.6
*/
public Iterator<E> descendingIterator() {
return new ReverseLinkIterator<E>(this);
}
/**
* {@inheritDoc}
*
* @see java.util.Deque#offerFirst(java.lang.Object)
* @since 1.6
*/
public boolean offerFirst(E e) {
return addFirstImpl(e);
}
/**
* {@inheritDoc}
*
* @see java.util.Deque#offerLast(java.lang.Object)
* @since 1.6
*/
public boolean offerLast(E e) {
return addLastImpl(e);
}
/**
* {@inheritDoc}
*
* @see java.util.Deque#peekFirst()
* @since 1.6
*/
public E peekFirst() {
return peekFirstImpl();
}
/**
* {@inheritDoc}
*
* @see java.util.Deque#peekLast()
* @since 1.6
*/
public E peekLast() {
Link<E> last = voidLink.previous;
return (last == voidLink) ? null : last.data;
}
/**
* {@inheritDoc}
*
* @see java.util.Deque#pollFirst()
* @since 1.6
*/
public E pollFirst() {
return (size == 0) ? null : removeFirstImpl();
}
/**
* {@inheritDoc}
*
* @see java.util.Deque#pollLast()
* @since 1.6
*/
public E pollLast() {
return (size == 0) ? null : removeLastImpl();
}
/**
* {@inheritDoc}
*
* @see java.util.Deque#pop()
* @since 1.6
*/
public E pop() {
return removeFirstImpl();
}
/**
* {@inheritDoc}
*
* @see java.util.Deque#push(java.lang.Object)
* @since 1.6
*/
public void push(E e) {
addFirstImpl(e);
}
/**
* {@inheritDoc}
*
* @see java.util.Deque#removeFirstOccurrence(java.lang.Object)
* @since 1.6
*/
public boolean removeFirstOccurrence(Object o) {
return removeFirstOccurrenceImpl(o);
}
/**
* {@inheritDoc}
*
* @see java.util.Deque#removeLastOccurrence(java.lang.Object)
* @since 1.6
*/
public boolean removeLastOccurrence(Object o) {
Iterator<E> iter = new ReverseLinkIterator<E>(this);
return removeOneOccurrence(o, iter);
}
private boolean removeFirstOccurrenceImpl(Object o) {
Iterator<E> iter = new LinkIterator<E>(this, 0);
return removeOneOccurrence(o, iter);
}
private boolean removeOneOccurrence(Object o, Iterator<E> iter) {
while (iter.hasNext()) {
E element = iter.next();
if (o == null ? element == null : o.equals(element)) {
iter.remove();
return true;
}
}
return false;
}
/**
* Replaces the element at the specified location in this {@code LinkedList}
* with the specified object.
*
* @param location
* the index at which to put the specified object.
* @param object
* the object to add.
* @return the previous element at the index.
* @throws ClassCastException
* if the class of an object is inappropriate for this list.
* @throws IllegalArgumentException
* if an object cannot be added to this list.
* @throws IndexOutOfBoundsException
* if {@code location < 0 || location >= size()}
*/
@Override
public E set(int location, E object) {
if (location >= 0 && location < size) {
Link<E> link = voidLink;
if (location < (size / 2)) {
for (int i = 0; i <= location; i++) {
link = link.next;
}
} else {
for (int i = size; i > location; i--) {
link = link.previous;
}
}
E result = link.data;
link.data = object;
return result;
}
throw new IndexOutOfBoundsException();
}
/**
* Returns the number of elements in this {@code LinkedList}.
*
* @return the number of elements in this {@code LinkedList}.
*/
@Override
public int size() {
return size;
}
public boolean offer(E o) {
return addLastImpl(o);
}
public E poll() {
return size == 0 ? null : removeFirst();
}
public E remove() {
return removeFirstImpl();
}
public E peek() {
return peekFirstImpl();
}
private E peekFirstImpl() {
Link<E> first = voidLink.next;
return first == voidLink ? null : first.data;
}
public E element() {
return getFirstImpl();
}
/**
* Returns a new array containing all elements contained in this
* {@code LinkedList}.
*
* @return an array of the elements from this {@code LinkedList}.
*/
@Override
public Object[] toArray() {
int index = 0;
Object[] contents = new Object[size];
Link<E> link = voidLink.next;
while (link != voidLink) {
contents[index++] = link.data;
link = link.next;
}
return contents;
}
/**
* Returns an array containing all elements contained in this
* {@code LinkedList}. If the specified array is large enough to hold the
* elements, the specified array is used, otherwise an array of the same
* type is created. If the specified array is used and is larger than this
* {@code LinkedList}, the array element following the collection elements
* is set to null.
*
* @param contents
* the array.
* @return an array of the elements from this {@code LinkedList}.
* @throws ArrayStoreException
* if the type of an element in this {@code LinkedList} cannot
* be stored in the type of the specified array.
*/
@Override
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] contents) {
int index = 0;
if (size > contents.length) {
Class<?> ct = contents.getClass().getComponentType();
contents = (T[]) Array.newInstance(ct, size);
}
Link<E> link = voidLink.next;
while (link != voidLink) {
contents[index++] = (T) link.data;
link = link.next;
}
if (index < contents.length) {
contents[index] = null;
}
return contents;
}
private void writeObject(ObjectOutputStream stream) throws IOException {
stream.defaultWriteObject();
stream.writeInt(size);
Iterator<E> it = iterator();
while (it.hasNext()) {
stream.writeObject(it.next());
}
}
@SuppressWarnings("unchecked")
private void readObject(ObjectInputStream stream) throws IOException,
ClassNotFoundException {
stream.defaultReadObject();
size = stream.readInt();
voidLink = new Link<E>(null, null, null);
Link<E> link = voidLink;
for (int i = size; --i >= 0;) {
Link<E> nextLink = new Link<E>((E) stream.readObject(), link, null);
link.next = nextLink;
link = nextLink;
}
link.next = voidLink;
voidLink.previous = link;
}
}