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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
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 collection
-
c - 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 replace
-
element - 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 inserted
-
element - 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