java.java

class Node {
    int data;
    Node next;

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

class LinkedList {
    Node head;

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

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

    public void reverse() {
        Node prev = null;
        Node current = head;
        Node next;
        while (current != null) {
            next = current.next;
            current.next = prev;
            prev = current;
            current = next;
        }
        head = prev;
    }
}

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

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

        list.reverse();

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