LinkedList in Java

LinkedList is a part of the Java Collections Framework and is present in the java.util package. It implements a doubly linked list where elements are stored as nodes containing data and references to the previous and next nodes, rather than in contiguous memory locations.

• The size of the LinkedList can grow or shrink dynamically at runtime.
• Maintains the order in which elements are inserted.
• Multiple duplicate elements can be stored.
• LinkedList is not thread-safe by default; it can be synchronized using Collections.synchronizedList().
• Provides better performance than ArrayList for insertion and deletion operations, especially at the beginning or middle.

[One, Two, Three, Four, Five]

Explanation:

• Creates an empty LinkedList of Strings.
• Adds elements "One" to "Five" using the add() method.
• Prints the LinkedList showing elements in insertion order: [One, Two, Three, Four, Five].

Note: LinkedList nodes cannot be accessed directly by index; elements must be accessed by traversing from the head.

Hierarchy of LinkedList

It implements the List and Deque interfaces, both of which are sub-interfaces of the Collection Interface.

Constructors of 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 list, then it can be created as: 

LinkedList list = new LinkedList();  

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 list, then, it can be created as: 

LinkedList list = new LinkedList(C);

Performing Different Operations on LinkedList

1. Adding Elements

With the help of the add() method, we can add elements to a LinkedList This method can perform multiple operations based on different parameters. They are:  

• add(Object): This method is used to add an element at the end of the LinkedList.
• add(int index, Object): This method is used to add an element at a specific index in the LinkedList.

[Geeks, For, Geeks]

2. Update Elements

With the help of the set() method, we can update an element in a LinkedList. This method takes an index and the updated element which needs to be inserted at that index.

Initial LinkedList [Geeks, Geeks, Geeks]
Updated LinkedList [Geeks, For, Geeks]

3. Removing Elements

Removes the first occurrence of the specified element from the list, if it exists. They are: 

• remove(Object): Removes the first occurrence of the specified object from the LinkedList.
• remove(int index): Removes the element at the given index and shifts subsequent elements.

Initial LinkedList [Geeks, For, Geeks]
After the Index Removal [Geeks, Geeks]
After the Object Removal [Geeks]

4. Iterating a LinkedList

There are multiple ways to iterate through LinkedList. The most famous ways are by using the basic for loop in combination with a get() method to get the element at a specific index and the advanced for-loop.

Geeks For Geeks 
Geeks For Geeks 

Real-World Usage of LinkedList

• Implementing Queues and Deques: LinkedList implements both Queue and Deque interfaces, making it ideal for FIFO or double-ended queue operations.
• Undo/Redo Functionality in Applications: Many text editors or software maintain a history of actions using LinkedLists, allowing fast insertions/removals at the start or end.
• Browser History Management: Forward and backward navigation in browsers can be efficiently managed using a LinkedList, because nodes can be added or removed dynamically.

Methods for Java LinkedList

ArrayList vs LinkedList