Sorted order insertion of linked list in scala

Scala program for Sorted order insertion of linked list. Here problem description and explanation.

/*
    Scala program for
    Add node in sorted order of linked list
*/
// Linked list node
class LinkNode(var data: Int,
	var next: LinkNode)
{
	def this(data: Int)
	{
		this(data, null);
	}
}
class SingleLL(var head: LinkNode)
{
	def this()
	{
		this(null);
	}
	// Add new node in sorted order
	def sortedAdd(data: Int): Unit = {
		// Create new node
		var node: LinkNode = new LinkNode(data);
		if (this.head == null || 
            this.head.data >= data)
		{
			// When linked list empty
			// or new nodes are adding at beginning
			node.next = this.head;
			this.head = node;
		}
		else
		{
			var temp: LinkNode = this.head;
			// Find position to add new node
			while (temp.next != null && 
                   temp.next.data < data)
			{
				// Visit to next node
				temp = temp.next;
			}
			node.next = temp.next;
			// Add new node
			temp.next = node;
		}
	}
	// Display linked list element
	def display(): Unit = {
		if (this.head == null)
		{
			return;
		}
		var temp: LinkNode = this.head;
		// Iterating linked list elements
		while (temp != null)
		{
			print(""+ temp.data + " → ");
			// Visit to next node
			temp = temp.next;
		}
		print(" NULL\n");
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		var sll: SingleLL = new SingleLL();
		// Add Linked list node
		sll.sortedAdd(1);
		sll.sortedAdd(-3);
		sll.sortedAdd(9);
		sll.sortedAdd(4);
		sll.sortedAdd(11);
		sll.sortedAdd(-7);
		print(" Linked List \n");
		// -7 → -3 → 1 → 4 → 9 → 11 → NULL
		sll.display();
	}
}

Output

 Linked List
-7 → -3 → 1 → 4 → 9 → 11 →  NULL