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>, SequencedCollection<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:

  • Field Summary

    Fields declared in class java.util.AbstractList

    modCount

  • Constructor Summary

    Constructors
    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 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).
    LinkedList<E>
    reversed()
    Returns a reverse-ordered view of this collection.
    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.

    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 Details

    • 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 Details

    • getFirst

      public E getFirst()
      Returns the first element in this list.
      Specified by:
      getFirst in interface Deque<E>
      Specified by:
      getFirst in interface List<E>
      Specified by:
      getFirst in interface SequencedCollection<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>
      Specified by:
      getLast in interface List<E>
      Specified by:
      getLast in interface SequencedCollection<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>
      Specified by:
      removeFirst in interface List<E>
      Specified by:
      removeFirst in interface SequencedCollection<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>
      Specified by:
      removeLast in interface List<E>
      Specified by:
      removeLast in interface SequencedCollection<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>
      Specified by:
      addFirst in interface List<E>
      Specified by:
      addFirst in interface SequencedCollection<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>
      Specified by:
      addLast in interface List<E>
      Specified by:
      addLast in interface SequencedCollection<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 Objects.equals(o, 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>
      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 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 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 Deque<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:

    • 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. The list will be empty after this call returns.
      Specified by:
      clear in interface Collection<E>
      Specified by:
      clear in interface List<E>
      Overrides: