Insert node at beginning of doubly linked list in kotlin

Kotlin program for Insert node at beginning of doubly linked list. Here problem description and other solutions.

// Kotlin Program For
// Insert new node at beginning of doubly linked list

// Define class of linked list Node
class LinkNode
{
	var data: Int;
	var next: LinkNode ? ;
	var prev: LinkNode ? ;
	constructor(data: Int)
	{
		this.data = data;
		this.next = null;
		this.prev = null;
	}
}
class DoublyLinkedList
{
	var head: LinkNode ? ;
	constructor()
	{
		this.head = null;
	}
	// Insert new node at beginning position
	fun insert(value: Int): Unit
	{
		// Create a node
		val node: LinkNode = LinkNode(value);
		node.next = this.head;
		// When linked list is not empty
		if (this.head != null)
		{
			this.head?.prev = node;
		}
		// Make new head
		this.head = node;
	}
	// Display node element of doubly linked list
	fun display(): Unit
	{
		if (this.head == null)
		{
			println("Empty Linked List");
		}
		else
		{
			println("  Doubly Linked List Element :");
			// Get first node of linked list
			var temp: LinkNode ? = this.head;
			// iterate linked list 
			while (temp != null)
			{
				// Display node value
				print("  " + temp.data);
				// Visit to next node
				temp = temp.next;
			}
		}
	}
}
fun main(args: Array < String > ): Unit
{
	val dll: DoublyLinkedList = DoublyLinkedList();
	// Insert following linked list nodes
	dll.insert(70);
	dll.insert(60);
	dll.insert(50);
	dll.insert(40);
	dll.insert(30);
	dll.insert(20);
	dll.insert(10);
	//  NULL <- 10 <--> 20 <--> 30 <--> 40 <--> 50 <--> 60 <--> 70->NULL
	dll.display();
}

Output

  Doubly Linked List Element :
  10  20  30  40  50  60  70