java.util

Class LinkedList<E>

public class LinkedList<E> extends AbstractSequentialList<E> implements List<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).

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.

This class is a member of the Java Collections Framework.

Since: 1.2

Version: 1.53, 06/22/03

Author: Josh Bloch

See Also: List ArrayList Vector synchronizedList

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
booleanadd(E o)
Appends the specified element to the end of this list.
voidadd(int index, E element)
Inserts the specified element at the specified position in this list.
booleanaddAll(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.
booleanaddAll(int index, Collection<? extends E> c)
Inserts all of the elements in the specified collection into this list, starting at the specified position.
voidaddFirst(E o)
Inserts the given element at the beginning of this list.
voidaddLast(E o)
Appends the given element to the end of this list.
voidclear()
Removes all of the elements from this list.
Objectclone()
Returns a shallow copy of this LinkedList.
booleancontains(Object o)
Returns true if this list contains the specified element.
Eget(int index)
Returns the element at the specified position in this list.
EgetFirst()
Returns the first element in this list.
EgetLast()
Returns the last element in this list.
intindexOf(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.
intlastIndexOf(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.
booleanremove(Object o)
Removes the first occurrence of the specified element in this list.
Eremove(int index)
Removes the element at the specified position in this list.
EremoveFirst()
Removes and returns the first element from this list.
EremoveLast()
Removes and returns the last element from this list.
Eset(int index, E element)
Replaces the element at the specified position in this list with the specified element.
intsize()
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.

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

add

public boolean add(E o)
Appends the specified element to the end of this list.

Parameters: o element to be appended to this list.

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

add

public void add(int index, E element)
Inserts the specified element at the specified position in this list. Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices).

Parameters: index index at which the specified element is to be inserted. element element to be inserted.

Throws: IndexOutOfBoundsException if the specified index is out of range (index < 0 || index > size()).

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.)

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.

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.

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.

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.

clear

public void clear()
Removes all of the elements from this list.

clone

public Object clone()
Returns a shallow copy of this LinkedList. (The elements themselves are not cloned.)

Returns: a shallow copy of this LinkedList instance.

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)).

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

Returns: true if this list contains the specified element.

get

public E get(int index)
Returns the element at the specified position in this list.

Parameters: index index of element to return.

Returns: the element at the specified position in this list.

Throws: IndexOutOfBoundsException if the specified index is is out of range (index < 0 || index >= size()).

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.

indexOf

public 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. More formally, returns the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.

Parameters: o element to search for.

Returns: the index in this list of the first occurrence of the specified element, or -1 if the list does not contain this element.

lastIndexOf

public 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. More formally, returns the highest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.

Parameters: o element to search for.

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

public 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. Obeys the general contract of List.listIterator(int).

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.

Parameters: index index of first element to be returned from the list-iterator (by a call to next).

Returns: 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 Also: List

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).

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

Returns: true if the list contained the specified element.

remove

public E remove(int index)
Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices). Returns the element that was removed from the list.

Parameters: index the index of the element to removed.

Returns: the element previously at the specified position.

Throws: IndexOutOfBoundsException if the specified index is out of range (index < 0 || index >= size()).

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.

set

public E set(int index, E element)
Replaces the element at the specified position in this list with the specified element.

Parameters: index index of element to replace. element element to be stored at the specified position.

Returns: the element previously at the specified position.

Throws: IndexOutOfBoundsException if the specified index is out of range (index < 0 || index >= size()).

size

public int size()
Returns the number of elements in this list.

Returns: the number of elements in this list.

toArray

public Object[] toArray()
Returns an array containing all of the elements in this list in the correct order.

Returns: an array containing all of the elements in this list in the correct order.

toArray

public <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. If the list fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this list.

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.

Parameters: 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.

Returns: 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. NullPointerException if the specified array is null.