Java Program to Find the Length of a Linked List

Introduction

Finding the length of a linked list involves counting the number of nodes present in the list. This operation is fundamental when you need to determine the size of the linked list for various algorithms or applications. This guide will walk you through writing a Java program that calculates the length of a singly linked list.

Problem Statement

Create a Java program that:

Implements a singly linked list.
Calculates and displays the length of the linked list.

Example:

Input: 1 -> 2 -> 3 -> 4 -> 5
Output: Length of the linked list is 5
Input: 10 -> 20 -> 30
Output: Length of the linked list is 3

Solution Steps

Create the Linked List and Node Structure: Define a Node class to represent each element in the linked list and a LinkedList class to manage the list.
Add Nodes to the Linked List: Implement methods to add nodes to the linked list.
Calculate the Length of the Linked List:

Traverse the linked list from the head to the end.
Count the number of nodes during the traversal.

Display the Result: Output the length of the linked list.

Java Program

// Java Program to Find the Length of a Linked List
// Author: https://www.rameshfadatare.com/

class Node {
    int data;
    Node next;

    // Constructor to initialize the node
    public Node(int data) {
        this.data = data;
        this.next = null;
    }
}

class LinkedList {
    Node head;

    // Method to add a new node at the end of the list
    public void add(int data) {
        Node newNode = new Node(data);
        if (head == null) {
            // Step 1: Initialize the head if the list is empty
            head = newNode;
        } else {
            // Step 2: Traverse to the end of the list and add the new node
            Node current = head;
            while (current.next != null) {
                current = current.next;
            }
            current.next = newNode;
        }
    }

    // Method to calculate the length of the linked list
    public int length() {
        int count = 0;
        Node current = head;

        // Step 3: Traverse the list and count the nodes
        while (current != null) {
            count++;
            current = current.next;
        }

        return count;
    }

    // Method to display the linked list
    public void display() {
        Node current = head;
        while (current != null) {
            System.out.print(current.data + " -> ");
            current = current.next;
        }
        System.out.println("null");
    }
}

public class LinkedListLength {
    public static void main(String[] args) {
        LinkedList list = new LinkedList();

        // Adding elements to the linked list
        list.add(1);
        list.add(2);
        list.add(3);
        list.add(4);
        list.add(5);

        System.out.println("Linked List:");
        list.display();

        // Finding the length of the linked list
        int length = list.length();
        System.out.println("Length of the linked list is: " + length);
    }
}

Explanation

Step 1: Initialize the Node Class

The Node class represents a single node in the linked list. Each node contains data and a reference to the next node in the list.
The constructor initializes the node with data and sets the next pointer to null.

Step 2: Initialize the LinkedList Class

The LinkedList class manages the linked list. The class contains the head node that points to the first node in the list.
The add() method appends a new node to the end of the list. If the list is empty, the head node is set to the new node.

Step 3: Traverse the List and Count the Nodes

The length() method calculates the length of the linked list by traversing from the head to the last node.
A counter variable count is initialized to 0 and is incremented for each node encountered during the traversal.

Output Example

Linked List:
1 -> 2 -> 3 -> 4 -> 5 -> null
Length of the linked list is: 5

Example with Different Input

If you modify the input list to:

list.add(10);
list.add(20);
list.add(30);

The output will be:

Linked List:
10 -> 20 -> 30 -> null
Length of the linked list is: 3

Conclusion

This Java program demonstrates how to find the length of a singly linked list by traversing the list and counting the nodes. The program efficiently calculates the size of the linked list, providing a fundamental operation that is useful in various applications and algorithms in Java programming.