Insert node at beginning of linked list in kotlin

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

Here given of code implementation process.

/*
    Kotlin program for
    Insert node at beginning of linked list
*/
// Linked list node
class LinkNode
{
    var data: Int;
    var next: LinkNode ? ;
    constructor(data: Int)
    {
        this.data = data;
        this.next = null;
    }
}
class SingleLL
{
    var head: LinkNode ? ;
    constructor()
    {
        this.head = null;
    }
    // Adding new node at beginning of linked list
    fun addNode(data: Int): Unit
    {
        // Create new node
        val node: LinkNode = LinkNode(data);
        // Connect current node to previous head
        node.next = this.head;
        this.head = node;
    }
    // Display linked list element
    fun 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");
    }
}
fun main(args: Array < String > ): Unit
{
    val sll: SingleLL = 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).