Insertion sort on doubly linked list in scala

Scala program for Insertion sort on doubly linked list. Here more information.

// Scala program for
// Perform insertion sort on doubly linked list
class LinkNode(var data: Int,
	var next: LinkNode,
		var prev: LinkNode)
{
	def this(data: Int)
	{
		this(data, null, null);
	}
}
class DoublyLinkedList(var head: LinkNode,
	var tail: LinkNode)
{
	def this()
	{
		this(null, null);
	}
	// Insert new node at end position
	def insert(value: Int): Unit = {
		// Create a node
		var node: LinkNode = new LinkNode(value);
		if (this.head == null)
		{
			// Add first node
			this.head = node;
			this.tail = node;
			return;
		}
		// Add node at last position
		this.tail.next = node;
		node.prev = this.tail;
		this.tail = node;
	}
	// Display node element of doubly linked list
	def display(): Unit = {
		if (this.head == null)
		{
			println("Empty Linked List");
		}
		else
		{
			print("\nLinked List Head to Tail :");
			// 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;
			}
			print("\nLinked List Tail to Head :");
			// Get last node of linked list
			temp = this.tail;
			// iterate linked list 
			while (temp != null)
			{
				// Display node value
				print("  " + temp.data);
				// Visit to prev node
				temp = temp.prev;
			}
			print("\n");
		}
	}
	// Swap value of given node
	def swapData(first: LinkNode, second: LinkNode): Unit = {
		var value: Int = first.data;
		first.data = second.data;
		second.data = value;
	}
	// Sort elements using insertion sort
	def insertionSort(): Unit = {
		// Get first node
		var front: LinkNode = this.head;
		var back: LinkNode = null;
		while (front != null)
		{
			// Get next node
			back = front.next;
			// Update node value when consecutive nodes are not sort
			while (back != null && 
                   back.prev != null && 
                   back.data < back.prev.data)
			{
				// Modified node data
				swapData(back, back.prev);
				// Visit to previous node
				back = back.prev;
			}
			// Visit to next node
			front = front.next;
		}
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		var dll: DoublyLinkedList = new DoublyLinkedList();
		//Insert element of linked list
		dll.insert(25);
		dll.insert(2);
		dll.insert(6);
		dll.insert(14);
		dll.insert(12);
		dll.insert(9);
		dll.insert(16);
		dll.insert(3);
		print("\n Before Sort");
		dll.display();
		// Display all node
		dll.insertionSort();
		print("\n After Sort");
		dll.display();
	}
}

Output

 Before Sort
Linked List Head to Tail :  25  2  6  14  12  9  16  3
Linked List Tail to Head :  3  16  9  12  14  6  2  25

 After Sort
Linked List Head to Tail :  2  3  6  9  12  14  16  25
Linked List Tail to Head :  25  16  14  12  9  6  3  2