E - the type of elements held in this collectionpublic 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.
modCount 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.
c - the collection whose elements are to be placed into this listNullPointerException - if the specified collection is nullpublic E getFirst()
Returns the first element in this list.
getFirst in interface Deque<E>
NoSuchElementException - if this list is emptypublic E getLast()
Returns the last element in this list.
getLast in interface Deque<E>
NoSuchElementException - if this list is emptypublic E removeFirst()
Removes and returns the first element from this list.
removeFirst in interface Deque<E>
NoSuchElementException - if this list is emptypublic E removeLast()
Removes and returns the last element from this list.
removeLast in interface Deque<E>
NoSuchElementException - if this list is emptypublic 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(E).
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)).
contains in interface Collection<E>
contains in interface Deque<E>
contains in interface List<E>
contains in class AbstractCollection<E>
o - element whose presence in this list is to be testedtrue if this list contains the specified elementpublic int size()
Returns the number of elements in this list.
size in interface Collection<E>
size in interface Deque<E>
size in interface List<E>
size in class AbstractCollection<E>
public boolean add(E e)
Appends the specified element to the end of this list.
This method is equivalent to addLast(E).
add in interface Collection<E>
add in interface Deque<E>
add in interface List<E>
add in interface Queue<E>
add in class AbstractList<E>
e - element to be appended to this listtrue (as specified by Collection.add(E))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).
remove in interface Collection<E>
remove in interface Deque<E>
remove in interface List<E>
remove in class AbstractCollection<E>
o - element to be removed from this list, if presenttrue if this list contained the specified elementpublic 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.)
addAll in interface Collection<E>
addAll in interface List<E>
addAll in class AbstractCollection<E>
c - collection containing elements to be added to this listtrue if this list changed as a result of the callNullPointerException - if the specified collection is nullAbstractCollection.add(Object)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.
addAll in interface List<E>
addAll in class AbstractSequentialList<E>
index - index at which to insert the first element from the specified collectionc - collection containing elements to be added to this listtrue if this list changed as a result of the callIndexOutOfBoundsException - if the index is out of range (index < 0 || index > size())NullPointerException - if the specified collection is nullpublic void clear()
Removes all of the elements from this list. The list will be empty after this call returns.
clear in interface Collection<E>
clear in interface List<E>
clear in class AbstractList<E>
public E get(int index)
Returns the element at the specified position in this list.
get in interface List<E>
get in class AbstractSequentialList<E>
index - index of the element to returnIndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())public E set(int index,
E element) Replaces the element at the specified position in this list with the specified element.
set in interface List<E>
set in class AbstractSequentialList<E>
index - index of the element to replaceelement - element to be stored at the specified positionIndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())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).
add in interface List<E>
add in class AbstractSequentialList<E>
index - index at which the specified element is to be insertedelement - element to be insertedIndexOutOfBoundsException - if the index is out of range (index < 0 || index > size())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.
remove in interface List<E>
remove in class AbstractSequentialList<E>
index - the index of the element to be removedIndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())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.
indexOf in interface List<E>
indexOf in class AbstractList<E>
o - element to search forpublic 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.
lastIndexOf in interface List<E>
lastIndexOf in class AbstractList<E>
o - element to search forpublic E peek()
Retrieves, but does not remove, the head (first element) of this list.
peek in interface Deque<E>
peek in interface Queue<E>
null if this list is emptypublic E element()
Retrieves, but does not remove, the head (first element) of this list.
element in interface Deque<E>
element in interface Queue<E>
NoSuchElementException - if this list is emptypublic E poll()
Retrieves and removes the head (first element) of this list.
poll in interface Deque<E>
poll in interface Queue<E>
null if this list is emptypublic E remove()
Retrieves and removes the head (first element) of this list.
remove in interface Deque<E>
remove in interface Queue<E>
NoSuchElementException - if this list is emptypublic boolean offer(E e)
Adds the specified element as the tail (last element) of this list.
offer in interface Deque<E>
offer in interface Queue<E>
e - the element to addtrue (as specified by Queue.offer(E))public boolean offerFirst(E e)
Inserts the specified element at the front of this list.
offerFirst in interface Deque<E>
e - the element to inserttrue (as specified by Deque.offerFirst(E))public boolean offerLast(E e)
Inserts the specified element at the end of this list.
offerLast in interface Deque<E>
e - the element to inserttrue (as specified by Deque.offerLast(E))public E peekFirst()
Retrieves, but does not remove, the first element of this list, or returns null if this list is empty.
peekFirst in interface Deque<E>
null if this list is emptypublic E peekLast()
Retrieves, but does not remove, the last element of this list, or returns null if this list is empty.
peekLast in interface Deque<E>
null if this list is emptypublic E pollFirst()
Retrieves and removes the first element of this list, or returns null if this list is empty.
pollFirst in interface Deque<E>
null if this list is emptypublic E pollLast()
Retrieves and removes the last element of this list, or returns null if this list is empty.
pollLast in interface Deque<E>
null if this list is emptypublic 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).
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().
pop in interface Deque<E>
NoSuchElementException - if this list is emptypublic 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.
removeFirstOccurrence in interface Deque<E>
o - element to be removed from this list, if presenttrue if the list contained the specified elementpublic 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.
removeLastOccurrence in interface Deque<E>
o - element to be removed from this list, if presenttrue if the list contained the specified elementpublic 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.
listIterator in interface List<E>
listIterator in class AbstractSequentialList<E>
index - index of the first element to be returned from the list-iterator (by a call to next)IndexOutOfBoundsException - if the index is out of range (index < 0 || index > size())List.listIterator(int)public Iterator<E> descendingIterator()
Description copied from interface: Deque
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).
descendingIterator in interface Deque<E>
public Object clone()
Returns a shallow copy of this LinkedList. (The elements themselves are not cloned.)
clone in class Object
LinkedList instanceCloneablepublic 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.
toArray in interface Collection<E>
toArray in interface List<E>
toArray in class AbstractCollection<E>
Arrays.asList(Object[])public <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. 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().toArray in interface Collection<E>
toArray in interface List<E>
toArray in class AbstractCollection<E>
T - the runtime type of the array to contain the collectiona - 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.ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this listNullPointerException - if the specified array is nullpublic Spliterator<E> spliterator()
Creates a late-binding and fail-fast Spliterator over the elements in this list.
The Spliterator reports Spliterator.SIZED and Spliterator.ORDERED. Overriding implementations should document the reporting of additional characteristic values.
spliterator in interface Iterable<E>
spliterator in interface Collection<E>
spliterator in interface List<E>
Spliterator additionally reports Spliterator.SUBSIZED and implements trySplit to permit limited parallelism..Spliterator over the elements in this list
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