public class java.util
LinkedList<E>


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Java SE 6
  
Extends: AbstractCollection > AbstractList > AbstractSequentialList
Implements: List, Deque, Cloneable, Serializable
Details
Linked list implementation of the List interface. Implements all optional list operations, and permits all elements (including null). In addition to implementing the List interface, the LinkedList class provides uniformly named methods to get, remove and insert an element at the beginning and end of the list. These operations allow linked lists to be used as a stack, queue, or double-ended queue.

The class implements the Deque interface, providing first-in-first-out queue operations for add, poll, along with other stack and deque operations.

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.
version1.67, 04/21/06
since1.2
Ethe type of elements held in this collection
See also java.util.List, java.util.ArrayList, java.util.Vector


Constructors
public LinkedList()
Constructs an empty list.
public LinkedList(Collection c) Details
Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.
cthe collection whose elements are to be placed into this list
ThrowsNullPointerException: if the specified collection is null

Methods
public boolean add(Object e) Details
Appends the specified element to the end of this list.

This method is equivalent to #addLast.
eelement to be appended to this list
returntrue (as specified by Collection#add)

public void add(int index, Object element) Details
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).
indexindex at which the specified element is to be inserted
elementelement to be inserted
ThrowsIndexOutOfBoundsException: if the index is out of range (index < 0 || index > size())
public boolean addAll(Collection c) Details
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.)
ccollection containing elements to be added to this list
returntrue if this list changed as a result of the call
ThrowsNullPointerException: if the specified collection is null
public boolean addAll(int index, Collection c) Details
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.
indexindex at which to insert the first element from the specified collection
ccollection containing elements to be added to this list
returntrue if this list changed as a result of the call
ThrowsIndexOutOfBoundsException: if the index is out of range (index < 0 || index > size())
ThrowsNullPointerException: if the specified collection is null
public void addFirst(Object e) Details
Inserts the specified element at the beginning of this list.
ethe element to add
public void addLast(Object e) Details
Appends the specified element to the end of this list.

This method is equivalent to #add.
ethe element to add

public void clear()
Removes all of the elements from this list.
public Object clone() Details
Returns a shallow copy of this LinkedList. (The elements themselves are not cloned.)
returna shallow copy of this LinkedList instance
public boolean contains(Object o) Details
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)).
oelement whose presence in this list is to be tested
returntrue if this list contains the specified element
public Iterator descendingIterator() Details
since1.6
public Object element() Details
Retrieves, but does not remove, the head (first element) of this list.
returnthe head of this list
ThrowsNoSuchElementException: if this list is empty
since1.5
public Object get(int index) Details
Returns the element at the specified position in this list.
indexindex of the element to return
returnthe element at the specified position in this list
ThrowsIndexOutOfBoundsException: if the index is out of range (index < 0 || index >= size())
public int indexOf(Object o) Details
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.
oelement to search for
returnthe 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) Details
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.
oelement to search for
returnthe index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element
public ListIterator listIterator(int index) Details
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.
indexindex of the first element to be returned from the list-iterator (by a call to next)
returna ListIterator of the elements in this list (in proper sequence), starting at the specified position in the list
ThrowsIndexOutOfBoundsException: if the index is out of range (index < 0 || index > size())
See also listIterator(int)

public boolean offer(Object e) Details
Adds the specified element as the tail (last element) of this list.
ethe element to add
returntrue (as specified by Queue#offer)
since1.5
public boolean offerFirst(Object e) Details
Inserts the specified element at the front of this list.
ethe element to insert
returntrue (as specified by Deque#offerFirst)
since1.6
public boolean offerLast(Object e) Details
Inserts the specified element at the end of this list.
ethe element to insert
returntrue (as specified by Deque#offerLast)
since1.6
public Object peek() Details
Retrieves, but does not remove, the head (first element) of this list.
returnthe head of this list, or null if this list is empty
since1.5
public Object peekFirst() Details
Retrieves, but does not remove, the first element of this list, or returns null if this list is empty.
returnthe first element of this list, or null if this list is empty
since1.6
public Object peekLast() Details
Retrieves, but does not remove, the last element of this list, or returns null if this list is empty.
returnthe last element of this list, or null if this list is empty
since1.6
public Object poll() Details
Retrieves and removes the head (first element) of this list
returnthe head of this list, or null if this list is empty
since1.5
public Object pollFirst() Details
Retrieves and removes the first element of this list, or returns null if this list is empty.
returnthe first element of this list, or null if this list is empty
since1.6
public Object pollLast() Details
Retrieves and removes the last element of this list, or returns null if this list is empty.
returnthe last element of this list, or null if this list is empty
since1.6
public Object pop() Details
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().
returnthe element at the front of this list (which is the top of the stack represented by this list)
ThrowsNoSuchElementException: if this list is empty
since1.6

public void push(Object e) Details
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.
ethe element to push
since1.6

public boolean remove(Object o) Details
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).
oelement to be removed from this list, if present
returntrue if this list contained the specified element
public Object remove(int index) Details
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.
indexthe index of the element to be removed
returnthe element previously at the specified position
ThrowsIndexOutOfBoundsException: if the index is out of range (index < 0 || index >= size())
public Object remove() Details
Retrieves and removes the head (first element) of this list.
returnthe head of this list
ThrowsNoSuchElementException: if this list is empty
since1.5
public Object removeFirst() Details
Removes and returns the first element from this list.
returnthe first element from this list
ThrowsNoSuchElementException: if this list is empty
public boolean removeFirstOccurrence(Object o) Details
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.
oelement to be removed from this list, if present
returntrue if the list contained the specified element
since1.6
public Object removeLast() Details
Removes and returns the last element from this list.
returnthe last element from this list
ThrowsNoSuchElementException: if this list is empty
public boolean removeLastOccurrence(Object o) Details
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.
oelement to be removed from this list, if present
returntrue if the list contained the specified element
since1.6
public Object set(int index, Object element) Details
Replaces the element at the specified position in this list with the specified element.
indexindex of the element to replace
elementelement to be stored at the specified position
returnthe element previously at the specified position
ThrowsIndexOutOfBoundsException: if the index is out of range (index < 0 || index >= size())
public int size() Details
Returns the number of elements in this list.
returnthe number of elements in this list
public Object[] toArray() Details
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.
returnan array containing all of the elements in this list in proper sequence

public Object[]<T> toArray(Object[] a) Details
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().
athe 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.
returnan array containing the elements of the list
ThrowsArrayStoreException: if the runtime type of the specified array is not a supertype of the runtime type of every element in this list
ThrowsNullPointerException: if the specified array is null

Properties
public Object getFirst() Details
Returns the first element in this list.
returnthe first element in this list
ThrowsNoSuchElementException: if this list is empty
public Object getLast() Details
Returns the last element in this list.
returnthe last element in this list
ThrowsNoSuchElementException: if this list is empty
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Java SE 6
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