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java.util
public class: LinkedList [javadoc | source]
java.lang.Object
   java.util.AbstractCollection<E>
      java.util.AbstractList<E>
         java.util.AbstractSequentialList<E>
            java.util.LinkedList

All Implemented Interfaces:
    Cloneable, Deque, List, java$io$Serializable, Collection

Doubly-linked list implementation of the {@code List} and {@code Deque} interfaces. Implements all optional list operations, and permits all elements (including {@code 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 {@code iterator} and {@code 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 {@code remove} or {@code 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 {@code 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.

Field Summary
transient  int size     
transient  Node<E> first    Pointer to first node. Invariant: (first == null && last == null) || (first.prev == null && first.item != null) 
transient  Node<E> last    Pointer to last node. Invariant: (first == null && last == null) || (last.next == null && last.item != null) 
Fields inherited from java.util.AbstractList:
modCount
Constructor:
 public 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 from java.util.LinkedList Summary:
add,   add,   addAll,   addAll,   addFirst,   addLast,   clear,   clone,   contains,   descendingIterator,   element,   get,   getFirst,   getLast,   indexOf,   lastIndexOf,   linkBefore,   linkLast,   listIterator,   node,   offer,   offerFirst,   offerLast,   peek,   peekFirst,   peekLast,   poll,   pollFirst,   pollLast,   pop,   push,   remove,   remove,   remove,   removeFirst,   removeFirstOccurrence,   removeLast,   removeLastOccurrence,   set,   size,   toArray,   toArray,   unlink
Methods from java.util.AbstractSequentialList:
add,   addAll,   get,   iterator,   listIterator,   remove,   set
Methods from java.util.AbstractList:
add,   add,   addAll,   clear,   equals,   get,   hashCode,   indexOf,   iterator,   lastIndexOf,   listIterator,   listIterator,   remove,   removeRange,   set,   subList
Methods from java.util.AbstractCollection:
add,   addAll,   clear,   contains,   containsAll,   isEmpty,   iterator,   remove,   removeAll,   retainAll,   size,   toArray,   toArray,   toString
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from java.util.LinkedList Detail:
 public boolean add(E e) 
    Appends the specified element to the end of this list.

    This method is equivalent to #addLast .

 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).
 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.)
 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.
 public  void addFirst(E e) 
    Inserts the specified element at the beginning of this list.
 public  void addLast(E e) 
    Appends the specified element to the end of this list.

    This method is equivalent 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 {@code LinkedList}. (The elements themselves are not cloned.)
 public boolean contains(Object o) 
    Returns {@code true} if this list contains the specified element. More formally, returns {@code true} if and only if this list contains at least one element {@code e} such that (o==null ? e==null : o.equals(e)).
 public Iterator<E> descendingIterator() 
 public E element() 
    Retrieves, but does not remove, the head (first element) of this list.
 public E get(int index) 
    Returns the element at the specified position in this list.
 public E getFirst() 
    Returns the first element in this list.
 public E getLast() 
    Returns the last element in this list.
 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 {@code i} such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.
 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 {@code i} such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.
  void linkBefore(E e,
    Node<E> succ) 
    Inserts element e before non-null Node succ.
  void linkLast(E e) 
    Links e as last 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 {@code 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 {@code remove} or {@code add} methods, the list-iterator will throw a {@code 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.

 Node<E> node(int index) 
    Returns the (non-null) Node at the specified element index.
 public boolean offer(E e) 
    Adds the specified element as the tail (last element) of this list.
 public boolean offerFirst(E e) 
    Inserts the specified element at the front of this list.
 public boolean offerLast(E e) 
    Inserts the specified element at the end of this list.
 public E peek() 
    Retrieves, but does not remove, the head (first element) of this list.
 public E peekFirst() 
    Retrieves, but does not remove, the first element of this list, or returns {@code null} if this list is empty.
 public E peekLast() 
    Retrieves, but does not remove, the last element of this list, or returns {@code null} if this list is empty.
 public E poll() 
    Retrieves and removes the head (first element) of this list.
 public E pollFirst() 
    Retrieves and removes the first element of this list, or returns {@code null} if this list is empty.
 public E pollLast() 
    Retrieves and removes the last element of this list, or returns {@code 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() .

 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 .

 public E remove() 
    Retrieves and removes the head (first element) of this list.
 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 {@code i} such that (o==null ? get(i)==null : o.equals(get(i))) (if such an element exists). Returns {@code true} if this list contained the specified element (or equivalently, if this list changed as a result of the call).
 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.
 public E removeFirst() 
    Removes and returns the first element from this list.
 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.
 public E removeLast() 
    Removes and returns the last element from this list.
 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.
 public E set(int index,
    E element) 
    Replaces the element at the specified position in this list with the specified element.
 public int size() 
    Returns the number of 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.

 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 {@code 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 {@code 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 {@code String}:

        String[] y = x.toArray(new String[0]);
    Note that {@code toArray(new Object[0])} is identical in function to {@code toArray()}.
 E unlink(Node<E> x) 
    Unlinks non-null node x.