Insert node at beginning of linked list in scala

Write a program which is create and add new node at the beginning of linked list in scala.

Here given of code implementation process.

/*
    Scala program for
    Insert node at beginning 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);
    }
    // Adding new node at beginning of linked list
    def addNode(data: Int): Unit = {
        // Create new node
        var node: LinkNode = new LinkNode(data);
        // Connect current node to previous head
        node.next = this.head;
        this.head = 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();
        // Linked list
        // 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → NULL
        sll.addNode(8);
        sll.addNode(7);
        sll.addNode(6);
        sll.addNode(5);
        sll.addNode(4);
        sll.addNode(3);
        sll.addNode(2);
        sll.addNode(1);
        sll.display();
    }
}

 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → NULL

Time complexity of above program is O(1).