ReverseLinkedList.java

class Node {
    int data;
    Node next;

    Node(int data) {
        this.data = data;
        this.next = null;
    }
}

class LinkedList {
    Node head;

    LinkedList() {
        head = null;
    }

    void insert(int data) {
        Node newNode = new Node(data);
        if (head == null) {
            head = newNode;
        } else {
            Node current = head;
            while (current.next != null) {
                current = current.next;
            }
            current.next = newNode;
        }
    }

    void reverse() {
        Node prev = null;
        Node current = head;
        Node next = null;
        while (current != null) {
            next = current.next; // Store the next node
            current.next = prev; // Reverse the current node's pointer
            prev = current;      // Move prev to the current node
            current = next;     // Move current to the next node
        }
        head = prev; // The new head is the last node (prev)
    }

    void display() {
        Node current = head;
        while (current != null) {
            System.out.print(current.data + " -> ");
            current = current.next;
        }
        System.out.println("null");
    }
}

public class ReverseLinkedList {
    public static void main(String[] args) {
        LinkedList list = new LinkedList();
        list.insert(1);
        list.insert(2);
        list.insert(3);
        list.insert(4);

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

        list.reverse();

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