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/*
 *  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.
 *
 * 

All elements are permitted, including null. * *

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 extends AbstractSequentialList implements List, Deque, Queue, Cloneable, Serializable { transient int size = 0; transient Link voidLink; private static final class Link { ET data; Link previous, next; Link(ET o, Link p, Link n) { data = o; previous = p; next = n; } } private static final class LinkIterator implements ListIterator { int pos, expectedModCount; final LinkedList list; Link link, lastLink; LinkIterator(LinkedList 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 next = link.next; Link newLink = new Link(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 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 next = lastLink.next; Link 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 implements Iterator { private int expectedModCount; private final LinkedList list; private Link link; private boolean canRemove; ReverseLinkIterator(LinkedList 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 next = link.previous; Link 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(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 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 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 previous = link.previous; Link newLink = new Link(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 oldLast = voidLink.previous; Link newLink = new Link(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 collection) { if (location < 0 || location > size) { throw new IndexOutOfBoundsException(); } int adding = collection.size(); if (adding == 0) { return false; } Collection elements = (collection == this) ? new ArrayList(collection) : collection; Link 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 next = previous.next; for (E e : elements) { Link newLink = new Link(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 collection) { int adding = collection.size(); if (adding == 0) { return false; } Collection elements = (collection == this) ? new ArrayList(collection) : collection; Link previous = voidLink.previous; for (E e : elements) { Link newLink = new Link(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 oldFirst = voidLink.next; Link newLink = new Link(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 Cloneable */ @SuppressWarnings("unchecked") @Override public Object clone() { try { LinkedList l = (LinkedList) super.clone(); l.size = 0; l.voidLink = new Link(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 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 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 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 last = voidLink.previous; if (last != voidLink) { return last.data; } throw new NoSuchElementException(); } @Override public int indexOf(Object object) { int pos = 0; Link 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 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 listIterator(int location) { return new LinkIterator(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 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 previous = link.previous; Link 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 first = voidLink.next; if (first != voidLink) { Link 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 last = voidLink.previous; if (last != voidLink) { Link previous = last.previous; voidLink.previous = previous; previous.next = voidLink; size--; modCount++; return last.data; } throw new NoSuchElementException(); } /** * {@inheritDoc} * * @see Deque#descendingIterator() * @since 1.6 */ public Iterator descendingIterator() { return new ReverseLinkIterator(this); } /** * {@inheritDoc} * * @see Deque#offerFirst(Object) * @since 1.6 */ public boolean offerFirst(E e) { return addFirstImpl(e); } /** * {@inheritDoc} * * @see Deque#offerLast(Object) * @since 1.6 */ public boolean offerLast(E e) { return addLastImpl(e); } /** * {@inheritDoc} * * @see Deque#peekFirst() * @since 1.6 */ public E peekFirst() { return peekFirstImpl(); } /** * {@inheritDoc} * * @see Deque#peekLast() * @since 1.6 */ public E peekLast() { Link last = voidLink.previous; return (last == voidLink) ? null : last.data; } /** * {@inheritDoc} * * @see Deque#pollFirst() * @since 1.6 */ public E pollFirst() { return (size == 0) ? null : removeFirstImpl(); } /** * {@inheritDoc} * * @see Deque#pollLast() * @since 1.6 */ public E pollLast() { return (size == 0) ? null : removeLastImpl(); } /** * {@inheritDoc} * * @see Deque#pop() * @since 1.6 */ public E pop() { return removeFirstImpl(); } /** * {@inheritDoc} * * @see Deque#push(Object) * @since 1.6 */ public void push(E e) { addFirstImpl(e); } /** * {@inheritDoc} * * @see Deque#removeFirstOccurrence(Object) * @since 1.6 */ public boolean removeFirstOccurrence(Object o) { return removeFirstOccurrenceImpl(o); } /** * {@inheritDoc} * * @see Deque#removeLastOccurrence(Object) * @since 1.6 */ public boolean removeLastOccurrence(Object o) { Iterator iter = new ReverseLinkIterator(this); return removeOneOccurrence(o, iter); } private boolean removeFirstOccurrenceImpl(Object o) { Iterator iter = new LinkIterator(this, 0); return removeOneOccurrence(o, iter); } private boolean removeOneOccurrence(Object o, Iterator 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 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 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 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[] toArray(T[] contents) { int index = 0; if (size > contents.length) { Class ct = contents.getClass().getComponentType(); contents = (T[]) Array.newInstance(ct, size); } Link 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 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(null, null, null); Link link = voidLink; for (int i = size; --i >= 0;) { Link nextLink = new Link((E) stream.readObject(), link, null); link.next = nextLink; link = nextLink; } link.next = voidLink; voidLink.previous = link; } }





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