LinkedList - JRE Emulation | JRE Emulation
public class

LinkedList

extends AbstractSequentialList<E>
implements List<E> Deque<E> Cloneable Serializable
java.lang.Object
   ↳ java.util.AbstractCollection<E>
     ↳ java.util.AbstractList<E>
       ↳ java.util.AbstractSequentialList<E>
         ↳ java.util.LinkedList<E>

Class Overview

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.

See Also

Summary

[Expand]
Inherited Fields
From class java.util.AbstractList
Public Constructors
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.
Public Methods
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(int index)
Removes the element at the specified position in this list.
E remove()
Retrieves and removes the head (first element) of 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 Spliterator over the 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).
<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.
Protected Methods
void finalize()
Invoked when the garbage collector has detected that this instance is no longer reachable.
Inherited Methods
[Expand]
From class java.util.AbstractSequentialList
From class java.util.AbstractList
From class java.util.AbstractCollection
From class java.lang.Object
From interface java.util.List
From interface java.util.Collection
From interface java.util.Deque
From interface java.lang.Iterable
From interface java.util.Queue

Public Constructors

public LinkedList ()

Constructs an empty list.

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

Public Methods

public boolean add (E e)

Appends the specified element to the end of this list.

This method is equivalent to addLast(E).

Parameters
e element to be appended to this list
Returns
  • true (as specified by add(E))

public void add (int index, E element)

Inserts the specified element at the specified position in this list. Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices).

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

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.)

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

public boolean addAll (int index, Collection<? extends E> c)

Inserts all of the elements in the specified collection into this list, starting at the specified position. Shifts the element currently at that position (if any) and any subsequent elements to the right (increases their indices). The new elements will appear in the list in the order that they are returned by the specified collection's iterator.

Parameters
index index at which to insert 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
NullPointerException if the specified collection is null

public void addFirst (E e)

Inserts the specified element at the beginning of this list.

Parameters
e the element to add

public void addLast (E e)

Appends the specified element to the end of this list.

This method is equivalent to add(E).

Parameters
e the element to add

public void clear ()

Removes all of the elements from this list. The list will be empty after this call returns.

public Object clone ()

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

Returns
  • a shallow copy of this LinkedList instance

public boolean contains (Object o)

Returns true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)).

Parameters
o element whose presence in this list is to be tested
Returns
  • true if this list contains the specified element

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).

Returns
  • an iterator over the elements in this deque in reverse sequence

public E element ()

Retrieves, but does not remove, the head (first element) of this list.

Returns
  • the head of this list
Throws
NoSuchElementException if this list is empty

public E get (int index)

Returns the element at the specified position in this list.

Parameters
index index of the element to return
Returns
  • the element at the specified position in this list

public E getFirst ()

Returns the first element in this list.

Returns
  • the first element in this list
Throws
NoSuchElementException if this list is empty

public E getLast ()

Returns the last element in this list.

Returns
  • the last element in this list
Throws
NoSuchElementException if this list is empty

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.

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

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.

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

public ListIterator<E> listIterator (int index)

Returns a list-iterator of the elements in this list (in proper sequence), starting at the specified position in the list. Obeys the general contract of List.listIterator(int).

The list-iterator is fail-fast: if the list is structurally modified at any time after the Iterator is created, in any way except through the list-iterator's own remove or add methods, the list-iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Parameters
index index of 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

public boolean offer (E e)

Adds the specified element as the tail (last element) of this list.

Parameters
e the element to add
Returns

public boolean offerFirst (E e)

Inserts the specified element at the front of this list.

Parameters
e the element to insert
Returns

public boolean offerLast (E e)

Inserts the specified element at the end of this list.

Parameters
e the element to insert
Returns

public E peek ()

Retrieves, but does not remove, the head (first element) of this list.

Returns
  • the head of this list, or null if this list is empty

public E peekFirst ()

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

Returns
  • the first element of this list, or null if this list is empty

public E peekLast ()

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

Returns
  • the last element of this list, or null if this list is empty

public E poll ()

Retrieves and removes the head (first element) of this list.

Returns
  • the head of this list, or null if this list is empty

public E pollFirst ()

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

Returns
  • the first element of this list, or null if this list is empty

public E pollLast ()

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

Returns
  • the last element of this list, or null if this list is empty

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().

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

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).

Parameters
e the element to push

public E remove (int index)

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

Parameters
index the index of the element to be removed
Returns
  • the element previously at the specified position

public E remove ()

Retrieves and removes the head (first element) of this list.

Returns
  • the head of this list
Throws
NoSuchElementException if this list is empty

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).

Parameters
o element to be removed from this list, if present
Returns
  • true if this list contained the specified element

public E removeFirst ()

Removes and returns the first element from this list.

Returns
  • the first element from this list
Throws
NoSuchElementException if this list is empty

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.

Parameters
o element to be removed from this list, if present
Returns
  • true if the list contained the specified element

public E removeLast ()

Removes and returns the last element from this list.

Returns
  • the last element from this list
Throws
NoSuchElementException if this list is empty

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.

Parameters
o element to be removed from this list, if present
Returns
  • true if the list contained the specified element

public E set (int index, E element)

Replaces the element at the specified position in this list with the specified element.

Parameters
index index of the element to replace
element element to be stored at the specified position
Returns
  • the element previously at the specified position

public int size ()

Returns the number of elements in this list.

Returns
  • the number of elements in this list

public Spliterator<E> spliterator ()

Creates a late-binding and fail-fast Spliterator over the elements in this list.

The Spliterator reports SIZED and ORDERED. Overriding implementations should document the reporting of additional characteristic values.

Returns
  • a Spliterator over the elements in this list

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.

Returns
  • an array containing all of the elements in this list in proper sequence

public 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().

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

Protected Methods

protected void finalize ()

Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.

Note that objects that override finalize are significantly more expensive than objects that don't. Finalizers may be run a long time after the object is no longer reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup. Note also that finalizers are run on a single VM-wide finalizer thread, so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary for a class that has a native peer and needs to call a native method to destroy that peer. Even then, it's better to provide an explicit close method (and implement Closeable), and insist that callers manually dispose of instances. This works well for something like files, but less well for something like a BigInteger where typical calling code would have to deal with lots of temporaries. Unfortunately, code that creates lots of temporaries is the worst kind of code from the point of view of the single finalizer thread.

If you must use finalizers, consider at least providing your own ReferenceQueue and having your own thread process that queue.

Unlike constructors, finalizers are not automatically chained. You are responsible for calling super.finalize() yourself.

Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.