# Java - Linked List

A linked list is a linear data structure, in which the elements are stored in the form of a node. Each node contains two sub-elements. A data part that stores the value of the element and next part that stores the link to the next node as shown in the below image:

The first node also known as HEAD is always used as a reference to traverse the list. The last node points to NULL. Linked list can be visualized as a chain of nodes, where every node points to the next node.

## Types of Linked List

The types of linked list are mentioned below:

**Singly Linked List**: can be traversed only in forward direction.**Doubly Linked List**: can be traversed in forward and backward directions.**Circular Singly Linked List**: Last element contains link to the first element as next.**Circular Doubly Linked List**: Last element contains link to the first element as next and the first element contains link of the last element as previous.

## Implementation of Singly Linked List

### Representation:

In Java, singly linked list can be represented as a class and a Node as a separate class. The LinkedList class contains a reference of Node class type.

//node structure class Node { int data; Node next; }; class LinkedList { Node head; //constructor to create an empty LinkedList LinkedList(){ head = null; } };

### Create a Singly Linked List

Let us create a simple singly linked list which contains three data nodes.

//node structure class Node { int data; Node next; }; class LinkedList { Node head; //constructor to create an empty LinkedList LinkedList(){ head = null; } }; // test the code public class Implementation { public static void main(String[] args) { //create an empty LinkedList LinkedList MyList = new LinkedList(); //Add first node. Node first = new Node(); first.data = 10; first.next = null; //linking with head node MyList.head = first; //Add second node. Node second = new Node(); second.data = 20; second.next = null; //linking with first node first.next = second; //Add third node. Node third = new Node(); third.data = 30; third.next = null; //linking with second node second.next = third; } }

### Traverse a Singly Linked List

A singly linked list can be traversed using a temp node. Keep on moving the temp node to the next one and displaying its content. At the end of the list, the temp node will become NULL.

//node structure class Node { int data; Node next; }; class LinkedList { Node head; //constructor to create an empty LinkedList LinkedList(){ head = null; } //display the content of the list void PrintList() { Node temp = new Node(); temp = this.head; if(temp != null) { System.out.print("\nThe list contains: "); while(temp != null) { System.out.print(temp.data + " "); temp = temp.next; } } else { System.out.print("\nThe list is empty."); } } }; // test the code public class Implementation { public static void main(String[] args) { //create an empty LinkedList LinkedList MyList = new LinkedList(); //Add first node. Node first = new Node(); first.data = 10; first.next = null; //linking with head node MyList.head = first; //Add second node. Node second = new Node(); second.data = 20; second.next = null; //linking with first node first.next = second; //Add third node. Node third = new Node(); third.data = 30; third.next = null; //linking with second node second.next = third; //print the content of list MyList.PrintList(); } }

The above code will give the following output:

The list contains: 10 20 30