java.util
Class LinkedList<E>

java.lang.Object   
  java.util.AbstractCollection   <E>
      java.util.AbstractList   <E>
          java.util.AbstractSequentialList   <E>
              java.util.LinkedList<E>

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

Serializable , Cloneable , Iterable <E>, Collection <E>, List <E>, Queue <E>

public class LinkedList<E>
extends AbstractSequentialList   <E>
implements List   <E>, Queue   <E>, Cloneable   , Serializable   

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).

The class implements the Queue interface, providing first-in-first-out queue operations for add, poll, etc. Other stack and 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 beginning 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.

This class is a member of the Java Collections Framework.

Since:

1.2

See Also:

List , ArrayList , Vector , Collections.synchronizedList(List) , Serialized Form

Field Summary

Fields inherited from class java.util.AbstractList

modCount

Constructor Summary

LinkedList ()
Constructs an empty list.

LinkedList (Collection <? extends E> c)
Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.

Method Summary

boolean	add (E o) Appends the specified element to the end of this list.
void	add (int index, E element) Inserts the specified element at the specified position in this list.
boolean	addAll (Collection <? extends E> c) 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.
boolean	addAll (int index, Collection <? extends E> c) Inserts all of the elements in the specified collection into this list, starting at the specified position.
void	addFirst (E o) Inserts the given element at the beginning of this list.
void	addLast (E o) Appends the given element to the end of this list.
void	clear () Removes all of the elements from this list.
Object	clone () Returns a shallow copy of this LinkedList.
boolean	contains (Object o) Returns true if this list contains the specified element.
E	element () Retrieves, but does not remove, the head (first element) of this list.
E	get (int index) Returns the element at the specified position in this list.
E	getFirst () Returns the first element in this list.
E	getLast () Returns the last element in this list.
int	indexOf (Object o) Returns the index in this list of the first occurrence of the specified element, or -1 if the List does not contain this element.
int	lastIndexOf (Object o) Returns the index in this list of the last occurrence of the specified element, or -1 if the list does not contain this element.
ListIterator <E>	listIterator (int index) Returns a list-iterator of the elements in this list (in proper sequence), starting at the specified position in the list.
boolean	offer (E o) Adds the specified element as the tail (last element) of this list.
E	peek () Retrieves, but does not remove, the head (first element) of this list.
E	poll () Retrieves and removes the head (first element) of this list.
E	remove () Retrieves and removes the head (first element) of this list.
E	remove (int index) Removes the element at the specified position in this list.
boolean	remove (Object o) Removes the first occurrence of the specified element in this list.
E	removeFirst () Removes and returns the first element from this list.
E	removeLast () Removes and returns the last element from this list.
E	set (int index, E element) Replaces the element at the specified position in this list with the specified element.
int	size () Returns the number of elements in this list.
Object []	toArray () Returns an array containing all of the elements in this list in the correct order.
<T> T[]	toArray (T[] a) Returns an array containing all of the elements in this list in the correct order; the runtime type of the returned array is that of the specified array.

Methods inherited from class java.util.AbstractSequentialList

iterator

Methods inherited from class java.util.AbstractList

equals , hashCode , listIterator , removeRange , subList

Methods inherited from class java.util.AbstractCollection

containsAll , isEmpty , removeAll , retainAll , toString

Methods inherited from class java.lang.Object

finalize , getClass , notify , notifyAll , wait , wait , wait

Methods inherited from interface java.util.List

containsAll , equals , hashCode , isEmpty , iterator , listIterator , removeAll , retainAll , subList

Constructor Detail

LinkedList

public LinkedList()

Constructs an empty list.

LinkedList

public LinkedList(Collection   <? extends E> c)

Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.

Parameters:

c - the collection whose elements are to be placed into this list.

Throws:

NullPointerException - if the specified collection is null.

Method Detail

getFirst

public E getFirst()

Returns the first element in this list.

Returns:

the first element in this list.

Throws:

NoSuchElementException - if this list is empty.

getLast

public E getLast()

Returns the last element in this list.

Returns:

the last element in this list.

Throws:

NoSuchElementException - if this list is empty.

removeFirst

public E removeFirst()

Removes and returns the first element from this list.

Returns:

the first element from this list.

Throws:

NoSuchElementException - if this list is empty.

removeLast

public E removeLast()

Removes and returns the last element from this list.

Returns:

the last element from this list.

Throws:

NoSuchElementException - if this list is empty.

addFirst

public void addFirst(E o)

Inserts the given element at the beginning of this list.

Parameters:

o - the element to be inserted at the beginning of this list.

addLast

public void addLast(E o)

Appends the given element to the end of this list. (Identical in function to the add method; included only for consistency.)

Parameters:

o - the element to be inserted at the end of this list.

contains

public boolean contains(Object    o)

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)).

Specified by:

contains in interface Collection <E>

Specified by:

contains in interface List <E>

Overrides:

contains in class AbstractCollection <E>

Parameters:

o - element whose presence in this list is to be tested.

Returns:

true if this list contains the specified element.

size

public int size()

Returns the number of elements in this list.

Specified by:

size in interface Collection <E>

Specified by:

size in interface List <E>

Specified by:

size in class AbstractCollection <E>

Returns:

the number of elements in this list.

add

public boolean add(E o)

Appends the specified element to the end of this list.

Specified by:

add in interface Collection <E>

Specified by:

add in interface List <E>

Overrides:

add in class AbstractList <E>

Parameters:

o - element to be appended to this list.

Returns:

true (as per the general contract of Collection.add).

remove

public boolean remove(Object    o)

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).

Specified by:

remove in interface Collection <E>

Specified by:

remove in interface List <E>

Overrides:

remove in class AbstractCollection <E>

Parameters:

o - element to be removed from this list, if present.

Returns:

true if the list contained the specified element.

addAll

public boolean addAll(Collection   <? extends E> c)

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.)

Specified by:

addAll in interface Collection <E>

Specified by:

addAll in interface List <E>

Overrides:

addAll in class AbstractCollection <E>

Parameters:

c - the elements to be inserted into this list.

Returns:

true if this list changed as a result of the call.

Throws:

NullPointerException - if the specified collection is null.

See Also:

AbstractCollection.add(Object)

addAll

public boolean addAll(int index,
                      Collection   <? extends E> 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.

Specified by:

addAll in interface List <E>

Overrides:

addAll in class AbstractSequentialList <E>

Parameters:

index - index at which to insert first element from the specified collection.

c - elements to be inserted into this list.

Returns:

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()).

NullPointerException - if the specified collection is null.

clear

public void clear()

Removes all of the elements from this list.

Specified by:

clear in interface Collection <E>

Specified by:

clear in interface List <E>

Overrides:

clear in class AbstractList