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
Doubly-linked list implementation of the List
and Deque
interfaces. Implements all optional list operations, and permits all elements (including null
).
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
, Serialized Form
Field Summary
Fields declared in class java.util.AbstractList
modCount
Constructor Summary
Constructor | Description |
---|---|
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
Modifier and Type | Method | Description |
---|---|---|
void | add(int index,
E element) | Inserts the specified element at the specified position in this list. |
boolean | add(E e) | Appends the specified element to the end of this list. |
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. |
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. |
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 |
boolean | contains(Object o) | Returns |
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 |
E | peekLast() | Retrieves, but does not remove, the last element of this list, or returns |
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 |
E | pollLast() | Retrieves and removes the last element of this list, or returns |
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. |
Spliterator<E> | spliterator() | Creates a late-binding and fail-fast |
Object[] | toArray() | Returns an array containing all of the elements in this list in proper sequence (from first to last element). |
<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. |
Methods declared in class java.util.AbstractSequentialList
iterator
Methods declared in class java.util.AbstractList
equals, hashCode, listIterator, removeRange, subList
Methods declared in class java.util.AbstractCollection
containsAll, isEmpty, removeAll, retainAll, toString
Methods declared in class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.Collection
parallelStream, removeIf, stream, toArray
Methods declared in interface java.util.Deque
iterator
Methods declared in interface java.lang.Iterable
forEach
Methods declared in interface java.util.List
containsAll, equals, hashCode, isEmpty, iterator, listIterator, removeAll, replaceAll, retainAll, sort, 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.
- Specified by:
-
getFirst
in interfaceDeque<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 interfaceDeque<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 interfaceDeque<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 interfaceDeque<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.
addLast
public void addLast(E e)
Appends the specified element to the end of this list.
This method is equivalent to add(E)
.
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 Objects.equals(o, e)
.
- Specified by:
-
contains
in interfaceCollection<E>
- Specified by:
-
contains
in interfaceDeque<E>
- Specified by:
-
contains
in interfaceList<E>
- Overrides:
-
contains
in classAbstractCollection<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 interfaceCollection<E>
- Specified by:
-
size
in interfaceDeque<E>
- Specified by:
-
size
in interfaceList<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 interfaceCollection<E>
- Specified by:
-
add
in interfaceDeque<E>
- Specified by:
-
add
in interfaceList<E>
- Specified by:
-
add
in interfaceQueue<E>
- Overrides:
-
add
in classAbstractList<E>
- Parameters:
-
e
- element to be appended to this list - Returns:
-
true
(as specified byCollection.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 Objects.equals(o, 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 interfaceCollection<E>
- Specified by:
-
remove
in interfaceDeque<E>
- Specified by:
-
remove
in interfaceList<E>
- Overrides:
-
remove
in classAbstractCollection<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 interfaceCollection<E>
- Specified by:
-
addAll
in interfaceDeque<E>
- Specified by:
-
addAll
in interfaceList<E>
- Overrides:
-
addAll
in classAbstractCollection<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 interfaceList<E>
- Overrides:
-
addAll
in classAbstractSequentialList<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. The list will be empty after this call returns.
- Specified by:
-
clear
in interfaceCollection<E>
- Specified by:
-
clear
in interfaceList<E>
- Overrides:
-
clear
in classAbstractList<E>
get
public E get(int index)
Returns the element at the specified position in this list.
- Specified by:
-
get
in interfaceList<E>
- Overrides:
-
get
in classAbstractSequentialList<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 interfaceList<E>
- Overrides:
-
set
in classAbstractSequentialList<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 interfaceList<E>
- Overrides:
-
add
in classAbstractSequentialList<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 interfaceList<E>
- Overrides:
-
remove
in classAbstractSequentialList<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 Objects.equals(o, get(i))
, or -1 if there is no such index.
- Specified by:
-
indexOf
in interfaceList<E>
- Overrides:
-
indexOf
in classAbstractList<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 Objects.equals(o, get(i))
, or -1 if there is no such index.
- Specified by:
-
lastIndexOf
in interfaceList<E>
- Overrides:
-
lastIndexOf
in classAbstractList<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 interfaceDeque<E>
- Specified by:
-
peek
in interfaceQueue<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 interfaceDeque<E>
- Specified by:
-
element
in interfaceQueue<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 interfaceDeque<E>
- Specified by:
-
poll
in interfaceQueue<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 interfaceDeque<E>
- Specified by:
-
remove
in interfaceQueue<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 interfaceDeque<E>
- Specified by:
-
offer
in interfaceQueue<E>
- Parameters:
-
e
- the element to add - Returns:
-
true
(as specified byQueue.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 interfaceDeque<E>
- Parameters:
-
e
- the element to insert - Returns:
-
true
(as specified byDeque.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 interfaceDeque<E>
- Parameters:
-
e
- the element to insert - Returns:
-
true
(as specified byDeque.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 interfaceDeque<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 interfaceDeque<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 interfaceDeque<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 interfaceDeque<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)
.
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 interfaceDeque<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 interfaceDeque<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 interfaceDeque<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 interfaceList<E>
- Specified by:
-
listIterator
in classAbstractSequentialList<E>
- Parameters:
-
index
- index of the first element to be returned from the list-iterator (by a call tonext
) - 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 interfaceDeque<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 classObject
- 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 interfaceCollection<E>
- Specified by:
-
toArray
in interfaceList<E>
- Overrides:
-
toArray
in classAbstractCollection<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 interfaceCollection<E>
- Specified by:
-
toArray
in interfaceList<E>
- Overrides:
-
toArray
in classAbstractCollection<E>
- Type Parameters:
-
T
- the component type of the array to contain the collection - 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
spliterator
public Spliterator<E> spliterator()
Creates a late-binding and fail-fast Spliterator
over the elements in this list.
The Spliterator
reports Spliterator.SIZED
and Spliterator.ORDERED
. Overriding implementations should document the reporting of additional characteristic values.
- Specified by:
-
spliterator
in interfaceCollection<E>
- Specified by:
-
spliterator
in interfaceIterable<E>
- Specified by:
-
spliterator
in interfaceList<E>
- Implementation Note:
- The
Spliterator
additionally reportsSpliterator.SUBSIZED
and implementstrySplit
to permit limited parallelism.. - Returns:
- a
Spliterator
over the elements in this list - Since:
- 1.8