java.util

Class LinkedList<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractList<E>

java.util.AbstractSequentialList<E>

java.util.LinkedList<E>

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>, Queue<E>, Cloneable, Serializable

LinkedList is an implementation of List, backed by a doubly-linked list. All optional operations including adding, removing, and replacing elements are supported.

All elements are permitted, including null.

This class is primarily useful if you need queue-like behavior. It may also be useful as a list if you expect your lists to contain zero or one element, but still require the ability to scale to slightly larger numbers of elements. In general, though, you should probably use ArrayList if you don't need the queue-like behavior.

Since:

1.2

See Also:

Serialized Form

Field Summary

Fields inherited from class java.util.AbstractList

modCount

Constructor Summary

Constructors

Constructor and Description
LinkedList() Constructs a new empty instance of LinkedList.
LinkedList(Collection<? extends E> collection) Constructs a new instance of LinkedList that holds all of the elements contained in the specified collection.

Method Summary

Modifier and Type	Method and Description
boolean	add(E object) Adds the specified object at the end of this LinkedList.
void	add(int location, E object) Inserts the specified object into this LinkedList at the specified location.
boolean	addAll(Collection<? extends E> collection) Adds the objects in the specified Collection to this LinkedList.
boolean	addAll(int location, Collection<? extends E> collection) Inserts the objects in the specified collection at the specified location in this LinkedList.
void	addFirst(E object) Adds the specified object at the beginning of this LinkedList.
void	addLast(E object) Adds the specified object at the end of this LinkedList.
void	clear() Removes all elements from this LinkedList, leaving it empty.
Object	clone() Returns a new LinkedList with the same elements and size as this LinkedList.
boolean	contains(Object object) Searches this LinkedList for the specified object.
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 of the queue represented by this deque (in other words, the first element of this deque).
E	get(int location) Returns the element at the specified location in this list.
E	getFirst() Returns the first element in this LinkedList.
E	getLast() Returns the last element in this LinkedList.
int	indexOf(Object object) Searches this list for the specified object and returns the index of the first occurrence.
int	lastIndexOf(Object object) Searches this LinkedList for the specified object and returns the index of the last occurrence.
ListIterator<E>	listIterator(int location) Returns a ListIterator on the elements of this LinkedList.
boolean	offer(E o) Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available.
boolean	offerFirst(E e) Inserts the specified element at the front of this deque unless it would violate capacity restrictions.
boolean	offerLast(E e) Inserts the specified element at the end of this deque unless it would violate capacity restrictions.
E	peek() Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.
E	peekFirst() Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.
E	peekLast() Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.
E	poll() Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.
E	pollFirst() Retrieves and removes the first element of this deque, or returns null if this deque is empty.
E	pollLast() Retrieves and removes the last element of this deque, or returns null if this deque is empty.
E	pop() Pops an element from the stack represented by this deque.
void	push(E e) Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available.
E	remove() Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque).
E	remove(int location) Removes the object at the specified location from this LinkedList.
boolean	remove(Object object) Removes one instance of the specified object from this Collection if one is contained (optional).
E	removeFirst() Removes the first object from this LinkedList.
boolean	removeFirstOccurrence(Object o) Removes the first occurrence of the specified element from this deque.
E	removeLast() Removes the last object from this LinkedList.
boolean	removeLastOccurrence(Object o) Removes the last occurrence of the specified element from this deque.
E	set(int location, E object) Replaces the element at the specified location in this LinkedList with the specified object.
int	size() Returns the number of elements in this LinkedList.
Object[]	toArray() Returns a new array containing all elements contained in this LinkedList.
<T> T[]	toArray(T[] contents) Returns an array containing all elements contained in this LinkedList.

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, copyOf, equals, hashCode, isEmpty, iterator, listIterator, of, of, of, of, of, of, of, of, of, of, of, of, removeAll, replaceAll, retainAll, sort, spliterator, subList

Methods inherited from interface java.util.Deque

iterator

Methods inherited from interface java.util.Collection

forEach, parallelStream, removeIf, stream, toArray

Constructor Detail

LinkedList

public LinkedList()

Constructs a new empty instance of LinkedList.

LinkedList

public LinkedList(Collection<? extends E> collection)

Constructs a new instance of LinkedList that holds all of the elements contained in the specified collection. The order of the elements in this new LinkedList will be determined by the iteration order of collection.

Parameters:

collection - the collection of elements to add.

Method Detail

add

public void add(int location,
                E object)

Inserts the specified object into this LinkedList at the specified location. The object is inserted before any previous element at the specified location. If the location is equal to the size of this LinkedList, the object is added at the end.

Specified by:

add in interface List<E>

Overrides:

add in class AbstractSequentialList<E>

Parameters:

location - the index at which to insert.

object - the object to add.

Throws:

IndexOutOfBoundsException - if location < 0 || location > size()

add

public boolean add(E object)

Adds the specified object at the end of this LinkedList.

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:

object - the object to add.

Returns:

always true

addAll

public boolean addAll(int location,
                      Collection<? extends E> collection)

Inserts the objects in the specified collection at the specified location in this LinkedList. The objects are added in the order they are returned from the collection's iterator.

Specified by:

addAll in interface List<E>

Overrides:

addAll in class AbstractSequentialList<E>

Parameters:

location - the index at which to insert.

collection - the collection of objects

Returns:

true if this LinkedList is modified, false otherwise.

Throws:

ClassCastException - if the class of an object is inappropriate for this list.

IllegalArgumentException - if an object cannot be added to this list.

IndexOutOfBoundsException - if location < 0 || location > size()

addAll

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

Adds the objects in the specified Collection to this LinkedList.

Specified by:

addAll in interface Collection<E>

Specified by:

addAll in interface Deque<E>

Specified by:

addAll in interface List<E>

Overrides:

addAll in class AbstractCollection<E>

Parameters:

collection - the collection of objects.

Returns:

true if this LinkedList is modified, false otherwise.

See Also:

Collection.add(Object)

addFirst

public void addFirst(E object)

Adds the specified object at the beginning of this LinkedList.

Specified by:

addFirst in interface Deque<E>

Parameters:

object - the object to add.

addLast

public void addLast(E object)

Adds the specified object at the end of this LinkedList.

Specified by:

addLast in interface Deque<E>

Parameters:

object - the object to add.

clear

public void clear()

Removes all elements from this LinkedList, leaving it empty.

Specified by:

clear in interface Collection<E>

Specified by:

clear in interface List<E>

Overrides:

clear in class AbstractList<E>

See Also:

List.isEmpty(), size

clone

public Object clone()

Returns a new LinkedList with the same elements and size as this LinkedList.

Overrides:

clone in class Object

Returns:

a shallow copy of this LinkedList.

See Also:

Cloneable

contains

public boolean contains(Object object)

Searches this LinkedList for the specified object.

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:

object - the object to search for.

Returns:

true if object is an element of this LinkedList, false otherwise

get

public E get(int location)

Description copied from class: AbstractList

Returns the element at the specified location in this list.

Specified by:

get in interface List<E>

Overrides:

get in class AbstractSequentialList<E>

Parameters:

location - the index of the element to return.

Returns:

the element at the specified index.

getFirst

public E getFirst()

Returns the first element in this LinkedList.

Specified by:

getFirst in interface Deque<E>

Returns:

the first element.

Throws:

NoSuchElementException - if this LinkedList is empty.

getLast

public E getLast()

Returns the last element in this LinkedList.

Specified by:

getLast in interface Deque<E>

Returns:

the last element

Throws:

NoSuchElementException - if this LinkedList is empty

indexOf

public int indexOf(Object object)

Description copied from class: AbstractList

Searches this list for the specified object and returns the index of the first occurrence.

Specified by:

indexOf in interface List<E>

Overrides:

indexOf in class AbstractList<E>

Parameters:

object - the object to search for.

Returns:

the index of the first occurrence of the object, or -1 if it was not found.

lastIndexOf

public int lastIndexOf(Object object)

Searches this LinkedList for the specified object and returns the index of the last occurrence.

Specified by:

lastIndexOf in interface List<E>

Overrides:

lastIndexOf in class AbstractList<E>

Parameters:

object - the object to search for

Returns:

the index of the last occurrence of the object, or -1 if it was not found.

listIterator

public ListIterator<E> listIterator(int location)

Returns a ListIterator on the elements of this LinkedList. The elements are iterated in the same order that they occur in the LinkedList. The iteration starts at the specified location.

Specified by:

listIterator in interface List<E>

Specified by:

listIterator in class AbstractSequentialList<E>

Parameters:

location - the index at which to start the iteration

Returns:

a ListIterator on the elements of this LinkedList

Throws:

IndexOutOfBoundsException - if location < 0 || location > size()

See Also:

ListIterator

remove

public E remove(int location)

Removes the object at the specified location from this LinkedList.

Specified by:

remove in interface List<E>

Overrides:

remove in class AbstractSequentialList<E>

Parameters:

location - the index of the object to remove

Returns:

the removed object

Throws:

IndexOutOfBoundsException - if location < 0 || location >= size()

remove

public boolean remove(Object object)

Description copied from class: AbstractCollection

Removes one instance of the specified object from this Collection if one is contained (optional). This implementation iterates over this Collection and tests for each element e returned by the iterator, whether e is equal to the given object. If object != null then this test is performed using object.equals(e), otherwise using object == null. If an element equal to the given object is found, then the remove method is called on the iterator and true is returned, false otherwise. If the iterator does not support removing elements, an UnsupportedOperationException is thrown.

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:

object - the object to remove.

Returns:

true if this Collection is modified, false otherwise.

removeFirst

public E removeFirst()

Removes the first object from this LinkedList.

Specified by:

removeFirst in interface Deque<E>

Returns:

the removed object.

Throws:

NoSuchElementException - if this LinkedList is empty.

removeLast

public E removeLast()

Removes the last object from this LinkedList.

Specified by:

removeLast in interface Deque<E>

Returns:

the removed object.

Throws:

NoSuchElementException - if this LinkedList is empty.

descendingIterator

public Iterator<E> descendingIterator()

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

See Also:

Deque.descendingIterator()

offerFirst

public boolean offerFirst(E e)

Inserts the specified element at the front of this deque unless it would violate capacity restrictions. When using a capacity-restricted deque, this method is generally preferable to the Deque.addFirst(E) method, which can fail to insert an element only by throwing an exception.

Specified by:

offerFirst in interface Deque<E>

Parameters:

e - the element to add

Returns:

true if the element was added to this deque, else false

Since:

1.6

See Also:

Deque.offerFirst(java.lang.Object)

offerLast

public boolean offerLast(E e)

Inserts the specified element at the end of this deque unless it would violate capacity restrictions. When using a capacity-restricted deque, this method is generally preferable to the Deque.addLast(E) method, which can fail to insert an element only by throwing an exception.

Specified by:

offerLast in interface Deque<E>

Parameters:

e - the element to add

Returns:

true if the element was added to this deque, else false

Since:

1.6

See Also:

Deque.offerLast(java.lang.Object)

peekFirst

public E peekFirst()

Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.

Specified by:

peekFirst in interface Deque<E>

Returns:

the head of this deque, or null if this deque is empty

Since:

1.6

See Also:

Deque.peekFirst()

peekLast

public E peekLast()

Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.

Specified by:

peekLast in interface Deque<E>

Returns:

the tail of this deque, or null if this deque is empty

Since:

1.6

See Also:

Deque.peekLast()

pollFirst

public E pollFirst()

Retrieves and removes the first element of this deque, or returns null if this deque is empty.

Specified by:

pollFirst in interface Deque<E>

Returns:

the head of this deque, or null if this deque is empty

Since:

1.6

See Also:

Deque.pollFirst()

pollLast

public E pollLast()

Retrieves and removes the last element of this deque, or returns null if this deque is empty.

Specified by:

pollLast in interface Deque<E>

Returns:

the tail of this deque, or null if this deque is empty

Since:

1.6

See Also:

Deque.pollLast()

pop

public E pop()

Pops an element from the stack represented by this deque. In other words, removes and returns the first element of this deque.

This method is equivalent to Deque.removeFirst().

Specified by:

pop in interface Deque<E>

Returns:

the element at the front of this deque (which is the top of the stack represented by this deque)

Since:

1.6

See Also:

Deque.pop()

push

public void push(E e)

Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available.

This method is equivalent to Deque.addFirst(E).

Specified by:

push in interface Deque<E>

Parameters:

e - the element to push

Since:

1.6

See Also:

Deque.push(java.lang.Object)

removeFirstOccurrence

public boolean removeFirstOccurrence(Object o)

Removes the first occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the first element e such that Objects.equals(o, e) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).

Specified by:

removeFirstOccurrence in interface Deque<E>

Parameters:

o - element to be removed from this deque, if present

Returns:

true if an element was removed as a result of this call

Since:

1.6

See Also:

Deque.removeFirstOccurrence(java.lang.Object)

removeLastOccurrence

public boolean removeLastOccurrence(Object o)

Removes the last occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the last element e such that Objects.equals(o, e) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).

Specified by:

removeLastOccurrence in interface Deque<E>

Parameters:

o - element to be removed from this deque, if present

Returns:

true if an element was removed as a result of this call

Since:

1.6

See Also:

Deque.removeLastOccurrence(java.lang.Object)

set

public E set(int location,
             E object)

Replaces the element at the specified location in this LinkedList with the specified object.

Specified by:

set in interface List<E>

Overrides:

set in class AbstractSequentialList<E>

Parameters:

location - the index at which to put the specified object.

object - the object to add.

Returns:

the previous element at the index.

Throws:

ClassCastException - if the class of an object is inappropriate for this list.

IllegalArgumentException - if an object cannot be added to this list.

IndexOutOfBoundsException - if location < 0 || location >= size()

size

public int size()

Returns the number of elements in this LinkedList.

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 LinkedList.

offer

public boolean offer(E o)

Description copied from interface: Deque

Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available. When using a capacity-restricted deque, this method is generally preferable to the Deque.add(E) method, which can fail to insert an element only by throwing an exception.

This method is equivalent to Deque.offerLast(E).

Specified by:

offer in interface Deque<E>

Specified by:

offer in interface Queue<E>

Parameters:

o - the element to add

Returns:

true if the element was added to this deque, else false

poll

public E poll()

Description copied from interface: Deque

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.

This method is equivalent to Deque.pollFirst().

Specified by:

poll in interface Deque<E>

Specified by:

poll in interface Queue<E>

Returns:

the first element of this deque, or null if this deque is empty

remove

public E remove()

Description copied from interface: Deque

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from poll() only in that it throws an exception if this deque is empty.

This method is equivalent to Deque.removeFirst().

Specified by:

remove in interface Deque<E>

Specified by:

remove in interface Queue<E>

Returns:

the head of the queue represented by this deque

peek

public E peek()

Description copied from interface: Deque

Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.

This method is equivalent to Deque.peekFirst().

Specified by:

peek in interface Deque<E>

Specified by:

peek in interface Queue<E>

Returns:

the head of the queue represented by this deque, or null if this deque is empty

element

public E element()

Description copied from interface: Deque

Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from peek only in that it throws an exception if this deque is empty.

This method is equivalent to Deque.getFirst().

Specified by:

element in interface Deque<E>

Specified by:

element in interface Queue<E>

Returns:

the head of the queue represented by this deque

toArray

public Object[] toArray()

Returns a new array containing all elements contained in this LinkedList.

Specified by:

toArray in interface Collection<E>

Specified by:

toArray in interface List<E>

Overrides:

toArray in class AbstractCollection<E>

Returns:

an array of the elements from this LinkedList.

See Also:

Arrays.asList(Object[])

toArray

public <T> T[] toArray(T[] contents)

Returns an array containing all elements contained in this LinkedList. If the specified array is large enough to hold the elements, the specified array is used, otherwise an array of the same type is created. If the specified array is used and is larger than this LinkedList, the array element following the collection elements is set to null.

Specified by:

toArray in interface Collection<E>

Specified by:

toArray in interface List<E>

Overrides:

toArray in class AbstractCollection<E>

Type Parameters:

T - the runtime type of the array to contain the collection

Parameters:

contents - the array.

Returns:

an array of the elements from this LinkedList.

Throws:

ArrayStoreException - if the type of an element in this LinkedList cannot be stored in the type of the specified array.