RevLinkedList.java

class Node {
    int data;
    Node next;

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

class LinkedList {
    Node head;

    public void reverse() {
        Node prev = null;
        Node current = head;
        Node next = null;

        while (current != null) {
            next = current.next;
            current.next = prev;
            prev = current;
            current = next;
        }
        head = prev;
    }

    public void printList() {
        Node temp = head;
        while (temp != null) {
            System.out.print(temp.data + " ");
            temp = temp.next;
        }
        System.out.println();
    }

    public static void main(String[] args) {
        LinkedList list = new LinkedList();
        list.head = new Node(1);
        list.head.next = new Node(2);
        list.head.next.next = new Node(3);
        list.head.next.next.next = new Node(4);

        System.out.println("Original linked list:");
        list.printList();
        list.reverse();
        System.out.println("Reversed linked list:");
        list.printList();
    }
}