/* * @(#)LinkedList.java 1.43 01/12/03 * * Copyright 2002 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util; /** * JSR166: Added Queue operations.
* Linked list implementation of the List interface. Implements all * optional list operations, and permits all elements (including * null). In addition to implementing the List interface, * the LinkedList class provides uniformly named methods to * get, remove and insert an element at the * beginning and end of the list. These operations allow linked lists to be * used as a stack, queue, or double-ended queue (deque).
* * All of the stack/queue/deque operations could be easily recast in terms of * the standard list operations. They're included here primarily for * convenience, though they may run slightly faster than the equivalent List * operations.
* * 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 begining or the end, whichever is closer to the specified index.
* * Note that this implementation is not synchronized. If multiple * threads access a list concurrently, and at least one of the threads * modifies the list structurally, it must 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 * Collections.synchronizedList method. This is best done at creation time, * to prevent accidental unsynchronized access to the list:
* List list = Collections.synchronizedList(new LinkedList(...)); *
* * The iterators returned by the this class's iterator and * listIterator methods are fail-fast: if the list is * structurally modified at any time after the iterator is created, in any way * except through the Iterator's own remove or add methods, * the iterator will throw a 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. * *
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 ConcurrentModificationException on a best-effort basis.
* Therefore, it would be wrong to write a program that depended on this
* exception for its correctness: the fail-fast behavior of iterators
* should be used only to detect bugs.
*
* @author Josh Bloch
* @version 1.43, 12/03/01
* @see java.util.List
* @see java.util.ArrayList
* @see java.util.Vector
* @see java.util.Collections#synchronizedList(java.util.List)
* @since 1.2
*/
public class LinkedList extends AbstractSequentialList
implements List, Queue, Cloneable, java.io.Serializable
{
private transient Entry header = new Entry(null, null, null);
private transient int size = 0;
/**
* Constructs an empty list.
*/
public LinkedList() {
header.next = header.previous = header;
}
/**
* 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 c) {
this();
addAll(c);
}
/**
* Returns the first element in this list.
*
* @return the first element in this list.
* @throws NoSuchElementException if this list is empty.
*/
public Object getFirst() {
if (size==0)
throw new NoSuchElementException();
return header.next.element;
}
/**
* Returns the last element in this list.
*
* @return the last element in this list.
* @throws NoSuchElementException if this list is empty.
*/
public Object getLast() {
if (size==0)
throw new NoSuchElementException();
return header.previous.element;
}
/**
* Removes and returns the first element from this list.
*
* @return the first element from this list.
* @throws NoSuchElementException if this list is empty.
*/
public Object removeFirst() {
Object first = header.next.element;
remove(header.next);
return first;
}
/**
* Removes and returns the last element from this list.
*
* @return the last element from this list.
* @throws NoSuchElementException if this list is empty.
*/
public Object removeLast() {
Object last = header.previous.element;
remove(header.previous);
return last;
}
/**
* Inserts the given element at the beginning of this list.
*
* @param o the element to be inserted at the beginning of this list.
*/
public void addFirst(Object o) {
addBefore(o, header.next);
}
/**
* Appends the given element to the end of this list. (Identical in
* function to the add method; included only for consistency.)
*
* @param o the element to be inserted at the end of this list.
*/
public void addLast(Object o) {
addBefore(o, header);
}
/**
* Returns true if this list contains the specified element.
* More formally, returns true if and only if this list contains
* at least one element e such that (o==null ? e==null
* : o.equals(e)).
*
* @param o element whose presence in this list is to be tested.
* @return 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.
*
* @param o element to be appended to this list.
* @return true (as per the general contract of
* Collection.add).
*/
public boolean add(Object o) {
addBefore(o, header);
return true;
}
/**
* Removes the first occurrence of the specified element in this list. If
* the list does not contain the element, it is unchanged. More formally,
* removes the element with the lowest index i such that
* (o==null ? get(i)==null : o.equals(get(i))) (if such an
* element exists).
*
* @param o element to be removed from this list, if present.
* @return true if the list contained the specified element.
*/
public boolean remove(Object o) {
if (o==null) {
for (Entry e = header.next; e != header; e = e.next) {
if (e.element==null) {
remove(e);
return true;
}
}
} else {
for (Entry e = header.next; e != header; e = e.next) {
if (o.equals(e.element)) {
remove(e);
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. (This implies that the behavior of this call is undefined if
* the specified Collection is this list, and this list is nonempty.)
*
* @param c the elements to be inserted into this list.
* @return true if this list changed as a result of the call.
* @throws NullPointerException if the specified collection is null.
*/
public boolean addAll(Collection 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 first element
* from the specified collection.
* @param c elements to be inserted into this list.
* @return true if this list changed as a result of the call.
* @throws IndexOutOfBoundsException if the specified index is out of
* range (index < 0 || index > size()).
* @throws NullPointerException if the specified collection is null.
*/
public boolean addAll(int index, Collection c) {
int numNew = c.size();
if (numNew==0)
return false;
modCount++;
Entry successor = (index==size ? header : entry(index));
Entry predecessor = successor.previous;
Iterator it = c.iterator();
for (int i=0; i
*
* The list-iterator is fail-fast: if the list is structurally
* modified at any time after the Iterator is created, in any way except
* through the list-iterator's own remove or add
* methods, the list-iterator will throw a
* 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 first element to be returned from the
* list-iterator (by a call to next).
* @return a ListIterator of the elements in this list (in proper
* sequence), starting at the specified position in the list.
* @throws IndexOutOfBoundsException if index is out of range
* (index < 0 || index > size()).
* @see java.util.List#listIterator(int)
*/
public ListIterator listIterator(int index) {
return new ListItr(index);
}
private class ListItr implements ListIterator {
private Entry lastReturned = header;
private Entry next;
private int nextIndex;
private int expectedModCount = modCount;
ListItr(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: "+index+
", Size: "+size);
if (index < (size >> 1)) {
next = header.next;
for (nextIndex=0; nextIndex
*
* 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
* collection is set to null. This is useful in determining the length
* of the list only if the caller knows that the list
* does not contain any null elements.
*
* @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 a is not a
* supertype of the runtime type of every element in this list.
* @throws NullPointerException if the specified array is null.
*/
public Object[] toArray(Object a[]) {
if (a.length < size)
a = (Object[])java.lang.reflect.Array.newInstance(
a.getClass().getComponentType(), size);
int i = 0;
for (Entry e = header.next; e != header; e = e.next)
a[i++] = e.element;
if (a.length > size)
a[size] = null;
return a;
}
private static final long serialVersionUID = 876323262645176354L;
/**
* Save the state of this LinkedList instance to a stream (that
* is, serialize 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 synchronized 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 (Entry e = header.next; e != header; e = e.next)
s.writeObject(e.element);
}
/**
* Reconstitute this LinkedList instance from a stream (that is
* deserialize it).
*/
private synchronized 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();
// Initialize header
header = new Entry(null, null, null);
header.next = header.previous = header;
// Read in all elements in the proper order.
for (int i=0; i