How to insert a node in Linked List at a given position in Java ?

In this post, we will learn How to insert a node in Linked List at a given position in Java?

Program Logic Explanation

Case 1: If the insertion position is zero(o) then assign head to newNode.next and newNode to head.

Case 2: If the insertion position >0 then

We have to traverse the Linked list upto position-1 nodes.
Once we traverse the position-1 nodes then allocate memory and the given data to the new node.
Assign the next pointer of the new node to the next of the current node.
Assign the next pointer of the current node to the new node.

Exception Handling:

Throw Exception if node insert position is less than zero.
Throw Exception if node insertion position is greater than the number of nodes in the Linked List

package com.kkjavatutorials.util;

/**
 * How to insert a node in Linked List at a given position in Java ?
 * @author KK JavaTutorials
 */
public class LinkedList<T> {
	
	private Node<T> head;
	
	//This internal class represents Node in Linked List
	private static class Node<T>{
		
		private T data;
		private Node<T> next;
		public Node(T data) {
			super();
			this.data = data;
			this.next = null;
		}
	}
	
	/**
	 * This method insert a node at given position
	 * (Position start from zero(0))
	 * @param data Node value has to insert
	 * @param position 
	 */
	public void insertAtPosition(T data,int position) {
		
		/**
		 * if insert position is negative then throw
		 * IllegalArgumentException
		 */
		if(position<0) {
			throw new IllegalArgumentException("Invalid Value of position ="+position);
		}
		Node<T> newNode = new Node<T>(data);

		if(position == 0) {
			newNode.next = head;
			head = newNode;
			return;
		}
	
		Node<T> currentNode = head;
		for (int i = 0; i < position-1; i++) {
			currentNode = currentNode.next;
			/**
			 * if node insertion position is greater
			 * than number of nodes then
			 *  throw IllegalArgumentException
			 */
			if(currentNode == null) {
				throw new IllegalArgumentException("Valus of position ="+position+" is greater than number of nodes in the list!!");
			}
		}
		
		newNode.next = currentNode.next;
		currentNode.next = newNode;
	}
	
	/**
	 * This method insert a Node in Linked List
	 * @param data has to insert in the List
	 */
	public void insert(T data) {
		Node<T> newNode = new Node<T>(data);
		if(head == null) {
			head = newNode;
		}else {
			Node<T> currentNode = head;
			while (currentNode.next != null) {
				currentNode = currentNode.next;
			}
			 currentNode.next = newNode;
		}
	}
	
	/**
	 * Method which traverse Linked List and display all data.
	 */
	public void displayLinkedList() {
		Node<T> currentNode = head;
		while(currentNode!= null) {
			System.out.print(currentNode.data+" ");
			currentNode = currentNode.next;
		}
	}
	
	public static void main(String[] args) {
		
		LinkedList<Integer> linkedList = new LinkedList<>();
		linkedList.insert(10);
		linkedList.insert(20);
		linkedList.insert(30);
		linkedList.insert(40);
		linkedList.insert(50);
		linkedList.insert(60);
		
		System.out.println("Original LinkedList:");
		linkedList.displayLinkedList();
		System.out.println();
		
		int position = 2;
		int nodeValue = 80;
		System.out.println("Adding a Node with Value:"+nodeValue+" at position:"+position);
		linkedList.insertAtPosition(nodeValue, position);
		linkedList.displayLinkedList();
		
	}
}

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