Bubble Sort On Doubly Linked List

class GFG 
{ 
  
// structure of a node  
static class Node 
{  
    int data;  
    Node prev;  
    Node next;  
};  
  
// Function to insert a node at the beginning of a linked list  
static Node insertAtTheBegin( Node start_ref, int data)  
{  
    Node ptr1 = new Node();  
    ptr1.data = data;  
    ptr1.next = start_ref;  
    if (start_ref != null)  
    (start_ref).prev = ptr1;  
    start_ref = ptr1; 
    return start_ref; 
}  
  
// Function to print nodes in a given linked list  
static void printList( Node start)  
{  
    Node temp = start;  
    System.out.println();  
    while (temp != null)  
    {  
        System.out.print( temp.data + " ");  
        temp = temp.next;  
    }  
}  
  
// Bubble sort the given linked list  
static Node bubbleSort( Node start)  
{  
    int swapped, i;  
    Node ptr1;  
    Node lptr = null;  
  
    // Checking for empty list  
    if (start == null)  
        return null;  
  
    do
    {  
        swapped = 0;  
        ptr1 = start;  
  
        while (ptr1.next != lptr)  
        {  
            if (ptr1.data > ptr1.next.data)  
            {  
                int t = ptr1.data; 
                ptr1.data = ptr1.next.data; 
                ptr1.next.data = t; 
                swapped = 1;  
            }  
            ptr1 = ptr1.next;  
        }  
        lptr = ptr1;  
    }  
    while (swapped != 0);  
        return start; 
}  
  
// Driver code 
public static void main(String args[]) 
{  
    int arr[] = {12, 56, 2, 11, 1, 90};  
    int list_size, i;  
  
    // start with empty linked list  
    Node start = null;  
  
    // Create linked list from the array arr[].  
    //Created linked list will be 1->11->2->56->12  
    for (i = 0; i < 6; i++)  
        start=insertAtTheBegin(start, arr[i]);  
  
    // print list before sorting  
    System.out.printf("\n Linked list before sorting ");  
    printList(start);  
  
    // sort the linked list  
    start = bubbleSort(start);  
  
    // print list after sorting  
    System.out.printf("\n Linked list after sorting ");  
    printList(start);  
}  
}