Q1. How to implement circular linked list in Java ?

Sure, here is a simple implementation of a circular linked list in Java:

public class Node {
    int data;
    Node next;

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

public class CircularLinkedList {
    Node head = null;
    Node tail = null;

    public void addNode(int data) {
        Node newNode = new Node(data);

        if (head == null) {
            head = newNode;
        } else {
            tail.next = newNode;
        }

        tail = newNode;
        tail.next = head;
    }

    public void display() {
        Node current = head;
        if (head == null) {
            System.out.println("List is empty");
            return;
        } else {
            do {
                System.out.print(" " + current.data);
                current = current.next;
            } while (current != head);
            System.out.println();
        }
    }

    public static void main(String[] args) {
        CircularLinkedList circularLinkedList = new CircularLinkedList();

        circularLinkedList.addNode(1);
        circularLinkedList.addNode(2);
        circularLinkedList.addNode(3);
        circularLinkedList.addNode(4);

        circularLinkedList.display();
    }
}

This code first defines a Node class, which represents a node in the linked list. Each node contains some data and a reference to the next node.

The CircularLinkedList class contains methods to add a node to the list (addNode) and to display the contents of the list (display). The addNode method adds a new node to the end of the list and updates the next reference of the last node to point to the first node, creating a circular structure. The display method prints the data in each node, starting from the head and continuing until it reaches the head again.

The main method creates a CircularLinkedList, adds some nodes to it, and then displays its contents.