LinkedList in Java
Linked List is a part of the Collection framework present in java.util package. This class is an implementation of the LinkedList data structure which is a linear data structure where the elements are not stored in contiguous locations and every element is a separate object with a data part and address part. The elements are linked using pointers and addresses. Each element is known as a node.
Due to the dynamicity and ease of insertions and deletions, they are preferred over the arrays. It also has a few disadvantages like the nodes cannot be accessed directly instead we need to start from the head and follow through the link to reach a node we wish to access.
How Does LinkedList work Internally?
Since a LinkedList acts as a dynamic array and we do not have to specify the size while creating it, the size of the list automatically increases when we dynamically add and remove items. And also, the elements are not stored in a continuous fashion. Therefore, there is no need to increase the size. Internally, the LinkedList is implemented using the doubly linked list data structure.
The main difference between a normal linked list and a doubly LinkedList is that a doubly linked list contains an extra pointer, typically called the previous pointer, together with the next pointer and data which are there in the singly linked list.
Constructors in the LinkedList:
In order to create a LinkedList, we need to create an object of the LinkedList class. The LinkedList class consists of various constructors that allow the possible creation of the list. The following are the constructors available in this class:
1. LinkedList(): This constructor is used to create an empty linked list. If we wish to create an empty LinkedList with the name ll, then, it can be created as:
2. LinkedList(Collection C): This constructor is used to create an ordered list that contains all the elements of a specified collection, as returned by the collection’s iterator. If we wish to create a LinkedList with the name ll, then, it can be created as:
Methods for Java LinkedList:
| Method | Description |
|---|---|
| add(int index, E element) | This method Inserts the specified element at the specified position in this list. |
| add(E e) | This method Appends the specified element to the end of this list. |
| addAll(int index, Collection c) | This method Inserts all of the elements in the specified collection into this list, starting at the specified position. |
| addAll(Collection c) | This method 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. |
| addFirst(E e) | This method Inserts the specified element at the beginning of this list. |
| addLast(E e) | This method Appends the specified element to the end of this list. |
| clear() | This method removes all of the elements from this list. |
| clone() | This method returns a shallow copy of this LinkedList. |
| contains(Object o) | This method returns true if this list contains the specified element. |
| descendingIterator() | This method returns an iterator over the elements in this deque in reverse sequential order. |
| element() | This method retrieves but does not remove, the head (first element) of this list. |
| get(int index) | This method returns the element at the specified position in this list. |
| getFirst() | This method returns the first element in this list. |
| getLast() | This method returns the last element in this list. |
| indexOf(Object o) | This method returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. |
| lastIndexOf(Object o) | This method 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(int index) | This method returns a list-iterator of the elements in this list (in proper sequence), starting at the specified position in the list. |
| offer(E e) | This method Adds the specified element as the tail (last element) of this list. |
| offerFirst(E e) | This method Inserts the specified element at the front of this list. |
| offerLast(E e) | This method Inserts the specified element at the end of this list. |
| peek() | This method retrieves but does not remove, the head (first element) of this list. |
| peekFirst() | This method retrieves, but does not remove, the first element of this list, or returns null if this list is empty. |
| peekLast() | This method retrieves, but does not remove, the last element of this list, or returns null if this list is empty. |
| poll() | This method retrieves and removes the head (first element) of this list. |
| pollFirst() | This method retrieves and removes the first element of this list, or returns null if this list is empty. |
| pollLast() | This method retrieves and removes the last element of this list, or returns null if this list is empty. |
| pop() | This method Pops an element from the stack represented by this list. |
| push(E e) | This method pushes an element onto the stack represented by this list. |
| remove() | This method retrieves and removes the head (first element) of this list. |
| remove(int index) | This method removes the element at the specified position in this list. |
| remove(Object o) | This method removes the first occurrence of the specified element from this list if it is present. |
| removeFirst() | This method removes and returns the first element from this list. |
| removeFirstOccurrence(Object o) | This method removes the first occurrence of the specified element in this list (when traversing the list from head to tail). |
| removeLast() | This method removes and returns the last element from this list. |
| removeLastOccurrence(Object o) | This method removes the last occurrence of the specified element in this list (when traversing the list from head to tail). |
| set(int index, E element) | This method replaces the element at the specified position in this list with the specified element. |
| size() | This method returns the number of elements in this list. |
| spliterator() | This method creates a late-binding and fail-fast Spliterator over the elements in this list. |
| toArray() | This method returns an array containing all of the elements in this list in proper sequence (from first to last element). |
| toArray(T[] a) | This method 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. |
| toString() | This method returns a string containing all of the elements in this list in proper sequence (from first to the last element), each element is separated by commas and the String is enclosed in square brackets. |
Below is the implementation of the above operations:
Link list methods java
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.
Field Summary
Fields inherited from class java.util.AbstractList
Constructor Summary
Constructs a list containing the elements of the specified collection, in the order they are returned by the collection’s iterator.
Method Summary
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.
Inserts all of the elements in the specified collection into this list, starting at the specified position.
Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.
Returns a list-iterator of the elements in this list (in proper sequence), starting at the specified position in the list.
Retrieves, but does not remove, the first element of this list, or returns null if this list is empty.
Retrieves, but does not remove, the last element of this list, or returns null if this list is empty.
Removes the first occurrence of the specified element in this list (when traversing the list from head to tail).
Removes the last occurrence of the specified element in this list (when traversing the list from head to tail).
Returns an array containing all of the elements in this list in proper sequence (from first to last element).
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.
Class LinkedList
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.