reverse a doubly circular linked list by swapping node value in scala

Scala program for reverse a doubly circular linked list by swapping node value. Here more information.

/*
  Scala Program
  Reverse a doubly circular linked list by swapping value
*/
// Linked list node
class LinkNode(var data: Int,
	var next: LinkNode,
		var back: LinkNode);

class CircularDoublyLL(var front: LinkNode,
	var tail: LinkNode)
{
	def this()
	{
		this(null, null);
	}
	// Add new node at the end of linked list
	def addNode(data: Int): Unit = {
		var node: LinkNode = new LinkNode(data, null, null);
		// When new node is successfully created
		if (this.front == null)
		{
			// Add first node of linked list
			this.front = node;
			this.tail = node;
		}
		else
		{
			// Add node at last position
			this.tail.next = node;
			node.back = this.tail;
			this.tail = node;
		}
		// Connect the last node in the linked list to front
		this.tail.next = this.front;
		this.front.back = this.tail;
		// Set node data
		node.data = data;
	}
	// Print linked list nodes
	def printElement(): Unit = {
		if (this.front == null)
		{
			print("\n Empty Linked List \n");
		}
		else
		{
			var temp: LinkNode = this.front;
			print("\n Linked List from Front to Tail \n");
			// Display doubly linked list from start to last node
			while (temp != null)
			{
				print("  " + temp.data);
				if (temp == this.tail)
				{
					// When get last node
					temp = null;
				}
				else
				{
					temp = temp.next;
				}
			}
			temp = this.tail;
			print("\n Linked List from Tail to Front \n");
			// Display doubly linked list from last to start node
			while (temp != null)
			{
				print("  " + temp.data);
				if (temp == this.front)
				{
					// When get first node
					temp = null;
				}
				else
				{
					temp = temp.back;
				}
			}
		}
	}
	// Reverses the elements of doubly linked list
	// using swap node values
	def reverseElement(): Unit = {
		// Get first node
		var first: LinkNode = this.front;
		// Get last node
		var last: LinkNode = this.tail;
		var temp: Int = 0;
		// Reverse operation
		while (first != null && last != null)
		{
			if (first != last)
			{
				// Swap the node value
				temp = first.data;
				first.data = last.data;
				last.data = temp;
				if (first.next == last)
				{
					// Stop reverse operation, or use break
					first = null;
					last = null;
				}
				else
				{
					first = first.next;
					last = last.back;
				}
			}
			else
			{
				// Stop reverse operation, or use break
				first = null;
				last = null;
			}
		}
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		var cll: CircularDoublyLL = new CircularDoublyLL();
		// Add linked list node
		cll.addNode(1);
		cll.addNode(2);
		cll.addNode(3);
		cll.addNode(4);
		cll.addNode(5);
		cll.addNode(6);
		print("\n Before reverse linked list");
		cll.printElement();
		cll.reverseElement();
		print("\n\n After reverse linked list");
		cll.printElement();
	}
}

Output

 Before reverse linked list
 Linked List from Front to Tail
  1  2  3  4  5  6
 Linked List from Tail to Front
  6  5  4  3  2  1

 After reverse linked list
 Linked List from Front to Tail
  6  5  4  3  2  1
 Linked List from Tail to Front
  1  2  3  4  5  6