Java Program to Add a Node to a Singly Linked List

In this article we are going to see how we can add a node to a singly linked list by using Java programming language.

Java Program to Add a Node to a Singly Linked List

In a linked list each element is called as a node which is having the actual element and a pointer to next element. You can add a new node at any position of the linked list.

Approach:

Create a linked list add some elements.
Display the list.
Add elements at the beginning by using the addBeg() user defined method that points the head to the new node and links the node to the rest of the list.
Display the list.
Ask the user to enter the position and data to insert.
Pass the values with head to the addPos( ) user defined method. The method iterates to the position and adds the node to the rest of the list.
Display the list.
Insert elements at the end by using insertEnd( ) user defined method. The method updates the tail and links the new node.
Display the list.

Program:

import java.util.*;
// Main class
public class Main
{
    // Class Node that defines the two linked list variables
    class Node
    {
        int data;
        Node nextNode;
        // constructor to create a node
        public Node(int data) 
        {    
            this.data = data;    
            this.nextNode = null;    
        }    
    }

    // Setting the head and end of the node as NULL  
    public Node head = null;    
    public Node tail = null;  

    // Method to add a node to the start of a linked list
    public void addBeg(int data)
    {  
        //Create a new node  
        Node newNode = new Node(data);  
        //Checks if the list is empty  
        if(head == null)
        {  
            // makes the head and tail point to the first node
            head = newNode;  
            tail = newNode;  
        }  
        else
        {
            Node temp = head;  
            //The newNode becomes the head of the linked list
            head = newNode;  
            //the head node now points to the previous head node
            head.nextNode = temp;  
        }  
    }

    // Method to add a node at a specified position
    public void addPos(Node headNode, int pos, int data) 
    {
        Node curr = headNode;
        // Position should be always greater than equals to 1
        if (pos < 1)
            System.out.print("Wrong input");
 
        // if position is 1 then the insertion happens at head
        if (pos == 1) 
        {
            // Setting the newNode as head
            Node newNode = new Node(data);
            newNode.nextNode = headNode;
            curr = newNode;
        } 
        else 
        {
            while (pos-- != 0) 
            {
                if (pos == 1) 
                {
                    Node newNode = new Node(data);
                    // Set the new node to point to the previously existing node
                    newNode.nextNode = headNode.nextNode;
                    headNode.nextNode = newNode;
                    break;
                }
                headNode = headNode.nextNode;
            }
            if (pos != 1)
                System.out.print("Wrong input");
        }
        head = curr;
    }

    // method to add a node to the end of the linked list
    public void add(int data)
    {
        Node newNode = new Node(data);
        // Checks if there was any previous node
        if(head==null)
        {
            head = newNode;
            tail = newNode;
        }
        else
        {
            tail.nextNode = newNode;
            tail = newNode;
        }
    }
    
    // Method to display all the nodes of the linked list
    public void show()
    {
        Node curr = head;
        // If the head is pointing to no node then the linked list is empty
        if(head==null)
            System.out.println("Linked List is empty");
        else
        {
            System.out.println("The nodes are:");
            while(curr!=null)
            {
                System.out.print(curr.data+",");
                curr = curr.nextNode;
            }
            System.out.println();
        }
    }

    public static void main(String[] args) 
    {
        // create an object of the main class
        Main ll = new Main();
        // add elements to the linked list
        ll.add(10);
        ll.add(20);
        ll.add(30);
        ll.add(40);
        ll.add(50);
        // display the nodes
        ll.show();
        // add a node at beginning
        System.out.println("Adding 11 at beginning");
        ll.addBeg(11);
        // Display the nodes
        ll.show();
        // Add a node at a position
        // Taking user input
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the position to enter a node and the data");
        int pos = sc.nextInt(), data = sc.nextInt();
        ll.addPos(ll.head,pos,data);
        // display the nodes
        ll.show();
        // Add a node at the end
        System.out.println("Adding 99 at end");
        ll.add(99);
        // display the nodes
        ll.show();
    }
}

Output:

The nodes are:
10,20,30,40,50,
Adding 11 at beginning
The nodes are:
11,10,20,30,40,50,
Enter the position to enter a node and the data
5 50
The nodes are:
11,10,20,30,50,40,50,
Adding 99 at end
The nodes are:
11,10,20,30,50,40,50,99,

Beginners and experienced programmers can rely on these Best Java Programs Examples and code various basic and complex logics in the Java programming language with ease.

Java Program to Add a Node to a Singly Linked List

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