Append the last n nodes of a linked list to the beginning of the list

import java.util.*;

public class Main
{

  public static void main (String[]args) throws Exception
  {
    LinkedList ll = new LinkedList ();
      ll.addFirst (60);
      ll.addFirst (50);
      ll.addFirst (40);
      ll.addFirst (30);
      ll.addFirst (20);
      ll.addFirst (10);

      ll.display ();

      ll.appendToFront (3);

      ll.display ();
  }

}

class LinkedList
{
  private class Node
  {
    int data;
    Node next;

    // Node constructor
// There are two fields in the node- data and address of next node
    public Node (int data, Node next)
    {
      this.data = data;
      this.next = next;
    }
  }

  private Node head;
  private Node tail;
  private int size;

  // Linked list constructor
  public LinkedList ()
  {
    this.head = null;
    this.tail = null;
    this.size = 0;

  }

  // Function to find the size of linked list
  public int size ()
  {
    return this.size;
  }

  // Function to check whether linked list is empty or not
  public boolean isEmpty ()
  {
    return this.size () == 0;
  }

  // Function to traverse and print the linked list
  public void display ()
  {
    Node temp = head;
    while (temp != null)
      {
	System.out.print (temp.data + ">");
// Set temp to point to the next node
	temp = temp.next;
      }
    System.out.println ("END");
  }

  // Function to add a node in beginning of linked list
  public void addFirst (int item)
  {
// Create a temp node which points to head
    Node temp = new Node (item, head);

// If linked list is empty, temp is the head and tail node both
    if (this.size == 0)
      {
	this.head = this.tail = temp;
      }

// else set the head such that it now points to temp node
    else
      {
	this.head = temp;

      }

    this.size++;
  }

  public int kthFromLast (int k)
  {
    return this.kthNodeFromLast (k).data;

  }

  // Function to find kth node from last
  private Node kthNodeFromLast (int k)
  {

// Take slow and fast pointers
    Node slow = this.head;
    Node fast = this.head;

// First move fast pointer k nodes from the head
    for (int i = 0; i < k; i++)
      {
	fast = fast.next;
      }

// Move both slow and fast by one till fast becomes null
    while (fast != null)
      {
	fast = fast.next;
	slow = slow.next;

      }

// Slow pointer points to the nth node from last
    return slow;
  }

  public void appendToFront (int n)
  {

// Find (n+1)th node from last
    Node np1 = this.kthNodeFromLast (n + 1);

// Find the nth node from beginning
    Node nth = np1.next;

// Set the pointers of node
    np1.next = null;
    this.tail.next = this.head;

    this.head = nth;
    this.tail = np1;
  }
}

Output: 
10–>20–>30–>40–>50–>60–>END
40–>50–>60–>10–>20–>30–>END