Anticlockwise spiral conversion of doubly linked list in scala

Scala program for Anticlockwise spiral conversion of doubly linked list. Here problem description and explanation.

// Scala program for
// Convert a doubly linked list anticlockwise spiral form

// This is Linked List Node
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("Linked 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;
			}
		}
	}
	def spiralTransform(): Unit = {
		if (this.head == null || this.head.next == null)
		{
			return;
		}
		var last: LinkNode = this.tail;
		var current: LinkNode = this.head;
		var auxiliary: LinkNode = null;
		var temp: LinkNode = null;
		var back: LinkNode = null;
		// Set new head
		this.head = this.tail;
		while (current != null && last != null)
		{
			if (current == last)
			{
				current.next = null;
				current.prev = back;
				this.tail = current;
				// Set new last node
				return;
			}
			else if (current.next == last)
			{
				current.next = null;
				current.prev = last;
				last.next = current;
				last.prev = back;
				// Set new last node
				this.tail = current;
				return;
			}
			// Swap link
			auxiliary = current.next;
			temp = last.prev;
			current.prev = last;
			last.next = current;
			current.next = temp;
			last.prev = back;
			back = current;
			current = auxiliary;
			last = temp;
		}
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		var dll: DoublyLinkedList = new DoublyLinkedList();
		// Insert following linked list nodes
		dll.insert(1);
		dll.insert(2);
		dll.insert(3);
		dll.insert(4);
		dll.insert(5);
		dll.insert(6);
		dll.insert(7);
		dll.insert(8);
		dll.insert(9);
		println("\nBefore anticlockwise spiral conversion");
		// Display all node
		dll.display();
		println("\nAfter anticlockwise spiral conversion");
		dll.spiralTransform();
		dll.display();
	}
}

Output

Before anticlockwise spiral conversion
Linked List Head to Tail :  1  2  3  4  5  6  7  8  9
Linked List Tail to Head :  9  8  7  6  5  4  3  2  1
After anticlockwise spiral conversion
Linked List Head to Tail :  9  1  8  2  7  3  6  4  5
Linked List Tail to Head :  5  4  6  3  7  2  8  1  9