JavaTM 2 Platform Std. Ed. v1.6.0
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>, Deque<E>, List<E>, Queue<E>
public class LinkedList<E> - extends AbstractSequentialList<E>
- implements List<E>, Deque<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.
The class implements the Deque interface, providing
first-in-first-out queue operations for add,
poll, along with other stack and deque 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 linked 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 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 ,
Serialized Form
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 e)
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 e)
Inserts the specified element at the beginning of this list. |
void |
addLast(E e)
Appends the specified 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. |
Iterator<E> |
descendingIterator()
Returns an iterator over the elements in this deque in reverse
sequential order. |
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 of the first occurrence of the specified element
in this list, or -1 if this list does not contain the element. |
int |
lastIndexOf(Object o)
Returns the index of the last occurrence of the specified element
in this list, or -1 if this list does not contain the 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 e)
Adds the specified element as the tail (last element) of this list. |
boolean |
offerFirst(E e)
Inserts the specified element at the front of this list. |
boolean |
offerLast(E e)
Inserts the specified element at the end of this list. |
E |
peek()
Retrieves, but does not remove, the head (first element) of this list. |
E |
peekFirst()
Retrieves, but does not remove, the first element of this list,
or returns null if this list is empty. |
E |
peekLast()
Retrieves, but does not remove, the last element of this list,
or returns null if this list is empty. |
E |
poll()
Retrieves and removes the head (first element) of this list |
E |
pollFirst()
Retrieves and removes the first element of this list,
or returns null if this list is empty. |
E |
pollLast()
Retrieves and removes the last element of this list,
or returns null if this list is empty. |
E |
pop()
Pops an element from the stack represented by this list. |
void |
push(E e)
Pushes an element onto the stack represented by 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 from this list,
if it is present. |
E |
removeFirst()
Removes and returns the first element from this list. |
boolean |
removeFirstOccurrence(Object o)
Removes the first occurrence of the specified element in this
list (when traversing the list from head to tail). |
E |
removeLast()
Removes and returns the last element from this list. |
boolean |
removeLastOccurrence(Object o)
Removes the last occurrence of the specified element in this
list (when traversing the list from head to tail). |
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 proper sequence (from first to last element). |
|
toArray(T[] a)
Returns an array containing all of the elements in this list in
proper sequence (from first to last element); the runtime type of
the returned array is that of the specified array. |
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
getFirst
public E getFirst()
- Returns the first element in this list.
- Specified by:
getFirst in interface Deque<E>
- 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.
- Specified by:
getLast in interface Deque<E>
- 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.
- Specified by:
removeFirst in interface Deque<E>
- 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.
- Specified by:
removeLast in interface Deque<E>
- Returns:
- the last element from this list
- Throws:
NoSuchElementException - if this list is empty
addFirst
public void addFirst(E e)
- Inserts the specified element at the beginning of this list.
- Specified by:
addFirst in interface Deque<E>
- Parameters:
e - the element to add
addLast
public void addLast(E e)
- Appends the specified element to the end of this list.
This method is equivalent to add(E) .
- Specified by:
addLast in interface Deque<E>
- Parameters:
e - the element to add
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 Deque<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 Deque<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 e)
- Appends the specified element to the end of this list.
This method is equivalent to addLast(E) .
- Specified by:
add in interface Collection<E> - Specified by:
add in interface Deque<E> - Specified by:
add in interface List<E> - Specified by:
add in interface Queue<E> - Overrides:
add in class AbstractList<E>
- Parameters:
e - element to be appended to this list
- Returns:
- true (as specified by
Collection.add(E) )
remove
public boolean remove(Object o)
- Removes the first occurrence of the specified element from this list,
if it is present. If this 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). Returns true if this list
contained the specified element (or equivalently, if this list
changed as a result of the call).
- Specified by:
remove in interface Collection<E> - Specified by:
remove in interface Deque<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 this 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. (Note that this will occur if the specified collection is
this list, and it's nonempty.)
- Specified by:
addAll in interface Collection<E> - Specified by:
addAll in interface List<E> - Overrides:
addAll in class AbstractCollection<E>
- Parameters:
c - collection containing elements to be added to 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 the first element
from the specified collectionc - collection containing elements to be added to this list
- Returns:
- true if this list changed as a result of the call
- Throws:
IndexOutOfBoundsException - if the 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<E>
get
public E get(int index)
- Returns the element at the specified position in this list.
- Specified by:
get in interface List<E> - Overrides:
get in class AbstractSequentialList<E>
- Parameters:
index - index of the element to return
- Returns:
- the element at the specified position in this list
- Throws:
IndexOutOfBoundsException - if the index is out of range
(index < 0 || index >= size())
set
public E set(int index,
E element)
- Replaces the element at the specified position in this list with the
specified element.
- Specified by:
set in interface List<E> - Overrides:
set in class AbstractSequentialList<E>
- Parameters:
index - index of the element to replaceelement - element to be stored at the specified position
- Returns:
- the element previously at the specified position
- Throws:
IndexOutOfBoundsException - if the index is out of range
(index < 0 || index >= size())
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).
- Specified by:
add in interface List<E> - Overrides:
add in class AbstractSequentialList<E>
- Parameters:
index - index at which the specified element is to be insertedelement - element to be inserted
- Throws:
IndexOutOfBoundsException - if the index is out of range
(index < 0 || index > size())
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.
- Specified by:
remove in interface List<E> - Overrides:
remove in class AbstractSequentialList<E>
- Parameters:
index - the index of the element to be removed
- Returns:
- the element previously at the specified position
- Throws:
IndexOutOfBoundsException - if the index is out of range
(index < 0 || index >= size())
indexOf
public int indexOf(Object o)
- Returns the index of the first occurrence of the specified element
in this list, or -1 if this list does not contain the 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.
- Specified by:
indexOf in interface List<E> - Overrides:
indexOf in class AbstractList<E>
- Parameters:
o - element to search for
- Returns:
- the index of the first occurrence of the specified element in
this list, or -1 if this list does not contain the element
lastIndexOf
public int lastIndexOf(Object o)
- Returns the index of the last occurrence of the specified element
in this list, or -1 if this list does not contain the 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.
- Specified by:
lastIndexOf in interface List<E> - Overrides:
lastIndexOf in class AbstractList<E>
- Parameters:
o - element to search for
- Returns:
- the index of the last occurrence of the specified element in
this list, or -1 if this list does not contain the element
peek
public E peek()
- Retrieves, but does not remove, the head (first element) of this list.
- Specified by:
peek in interface Deque<E> - Specified by:
peek in interface Queue<E>
- Returns:
- the head of this list, or null if this list is empty
- Since:
- 1.5
element
public E element()
- Retrieves, but does not remove, the head (first element) of this list.
- Specified by:
element in interface Deque<E> - Specified by:
element in interface Queue<E>
- Returns:
- the head of this list
- Throws:
NoSuchElementException - if this list is empty- Since:
- 1.5
poll
public E poll()
- Retrieves and removes the head (first element) of this list
- Specified by:
poll in interface Deque<E> - Specified by:
poll in interface Queue<E>
- Returns:
- the head of this list, or null if this list is empty
- Since:
- 1.5
remove
public E remove()
- Retrieves and removes the head (first element) of this list.
- Specified by:
remove in interface Deque<E> - Specified by:
remove in interface Queue<E>
- Returns:
- the head of this list
- Throws:
NoSuchElementException - if this list is empty- Since:
- 1.5
offer
public boolean offer(E e)
- Adds the specified element as the tail (last element) of this list.
- Specified by:
offer in interface Deque<E> - Specified by:
offer in interface Queue<E>
- Parameters:
e - the element to add
- Returns:
- true (as specified by
Queue.offer(E) ) - Since:
- 1.5
offerFirst
public boolean offerFirst(E e)
- Inserts the specified element at the front of this list.
- Specified by:
offerFirst in interface Deque<E>
- Parameters:
e - the element to insert
- Returns:
- true (as specified by
Deque.offerFirst(E) ) - Since:
- 1.6
offerLast
public boolean offerLast(E e)
- Inserts the specified element at the end of this list.
- Specified by:
offerLast in interface Deque<E>
- Parameters:
e - the element to insert
- Returns:
- true (as specified by
Deque.offerLast(E) ) - Since:
- 1.6
peekFirst
public E peekFirst()
- Retrieves, but does not remove, the first element of this list,
or returns null if this list is empty.
- Specified by:
peekFirst in interface Deque<E>
- Returns:
- the first element of this list, or null
if this list is empty
- Since:
- 1.6
peekLast
public E peekLast()
- Retrieves, but does not remove, the last element of this list,
or returns null if this list is empty.
- Specified by:
peekLast in interface Deque<E>
- Returns:
- the last element of this list, or null
if this list is empty
- Since:
- 1.6
pollFirst
public E pollFirst()
- Retrieves and removes the first element of this list,
or returns null if this list is empty.
- Specified by:
pollFirst in interface Deque<E>
- Returns:
- the first element of this list, or null if
this list is empty
- Since:
- 1.6
pollLast
public E pollLast()
- Retrieves and removes the last element of this list,
or returns null if this list is empty.
- Specified by:
pollLast in interface Deque<E>
- Returns:
- the last element of this list, or null if
this list is empty
- Since:
- 1.6
push
public void push(E e)
- Pushes an element onto the stack represented by this list. In other
words, inserts the element at the front of this list.
This method is equivalent to addFirst(E) .
- Specified by:
push in interface Deque<E>
- Parameters:
e - the element to push- Since:
- 1.6
pop
public E pop()
- Pops an element from the stack represented by this list. In other
words, removes and returns the first element of this list.
This method is equivalent to removeFirst() .
- Specified by:
pop in interface Deque<E>
- Returns:
- the element at the front of this list (which is the top
of the stack represented by this list)
- Throws:
NoSuchElementException - if this list is empty- Since:
- 1.6
removeFirstOccurrence
public boolean removeFirstOccurrence(Object o)
- Removes the first occurrence of the specified element in this
list (when traversing the list from head to tail). If the list
does not contain the element, it is unchanged.
- Specified by:
removeFirstOccurrence in interface Deque<E>
- Parameters:
o - element to be removed from this list, if present
- Returns:
- true if the list contained the specified element
- Since:
- 1.6
removeLastOccurrence
public boolean removeLastOccurrence(Object o)
- Removes the last occurrence of the specified element in this
list (when traversing the list from head to tail). If the list
does not contain the element, it is unchanged.
- Specified by:
removeLastOccurrence in interface Deque<E>
- Parameters:
o - element to be removed from this list, if present
- Returns:
- true if the list contained the specified element
- Since:
- 1.6
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.
- Specified by:
listIterator in interface List<E> - Specified by:
listIterator in class AbstractSequentialList<E>
- Parameters:
index - index of the 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 the index is out of range
(index < 0 || index > size())- See Also:
List.listIterator(int)
descendingIterator
public Iterator<E> descendingIterator()
- Description copied from interface:
Deque
- Returns an iterator over the elements in this deque in reverse
sequential order. The elements will be returned in order from
last (tail) to first (head).
- Specified by:
descendingIterator in interface Deque<E>
- Returns:
- an iterator over the elements in this deque in reverse
sequence
- Since:
- 1.6
clone
public Object clone()
- Returns a shallow copy of this LinkedList. (The elements
themselves are not cloned.)
- Overrides:
clone in class Object
- Returns:
- a shallow copy of this LinkedList instance
- See Also:
Cloneable
toArray
public Object[] toArray()
- Returns an array containing all of the elements in this list
in proper sequence (from first to last element).
The returned array will be "safe" in that no references to it are
maintained by this list. (In other words, this method must allocate
a new array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based
APIs.
- Specified by:
toArray in interface Collection<E> - Specified by:
toArray in interface List<E> - Overrides:
toArray in class AbstractCollection<E>
- Returns:
- an array containing all of the elements in this list
in proper sequence
- See Also:
Arrays.asList(Object[])
toArray
public <T> T[] toArray(T[] a)
- Returns an array containing all of the elements in this list in
proper sequence (from first to last element); 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 list 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.)
Like the toArray() method, this method acts as bridge between
array-based and collection-based APIs. Further, this method allows
precise control over the runtime type of the output array, and may,
under certain circumstances, be used to save allocation costs.
Suppose x is a list known to contain only strings.
The following code can be used to dump the list into a newly
allocated array of String:
String[] y = x.toArray(new String[0]);
Note that toArray(new Object[0]) is identical in function to
toArray().
- Specified by:
toArray in interface Collection<E> - Specified by:
toArray in interface List<E> - Overrides:
toArray in class AbstractCollection<E>
- 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 the specified array
is not a supertype of the runtime type of every element in
this list
NullPointerException - if the specified array is null
Copyright 2003 Sun Microsystems, Inc. All rights reserved
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