Convert singly linked list to circular list in kotlin

Kotlin program for Convert singly linked list to circular list. Here more information.

// Kotlin program for
// Convert singly linked list into circular list

// Define class of linked list Node
class LinkNode
{
	var data: Int;
	var next: LinkNode ? ;
	constructor(data: Int)
	{
		this.data = data;
		this.next = null;
	}
}
class LinkedList
{
	var head: LinkNode ? ;
	// Class constructor
	constructor()
	{
		this.head = null;
	}
	// Check circular linked list or not
	// Note that this function is not capable to detect loop
	fun isCircular(): Boolean
	{
		if (this.head == null)
		{
			// Case when linked list is empty
			return false;
		}
		else
		{
			var temp: LinkNode ? = this.head;
			while (temp != null)
			{
				// Visit to next node
				temp = temp.next;
				if (temp == this.head)
				{
					// When detecting circular node
					return true;
				}
			}
			// When not circular linked list
			return false;
		}
	}
	// Display node element of linked list
	fun display(): Unit
	{
		if (this.head == null)
		{
			println("Empty Linked List");
		}
		else
		{
			print("Linked List Element :");
			var temp: LinkNode ? = this.head;
			// Iterate linked list
			while (temp != null)
			{
				// Display node
				print("  " + temp.data);
				// Visit to next node
				temp = temp.next;
				if (temp == this.head)
				{
					// Stop iteration
					return;
				}
			}
			println();
		}
	}
	// Coverted circular Linked list
	fun makeCircular(): Unit
	{
		if (this.head == null)
		{
			println("Empty Linked List");
		}
		else
		{
			var temp: LinkNode ? = this.head;
			// Find last node
			while (temp?.next != null)
			{
				temp = temp.next;
				if (temp == this.head)
				{
					// Already circular Linked list
					return;
				}
			}
			// Connect last node to first node
			temp?.next = this.head;
		}
	}
}
fun main(args: Array < String > ): Unit
{
	val ll: LinkedList = LinkedList();
	// Insert element of linked list
	ll.head = LinkNode(1);
	ll.head?.next = LinkNode(2);
	ll.head?.next?.next = LinkNode(3);
	ll.head?.next?.next?.next = LinkNode(4);
	ll.head?.next?.next?.next?.next = LinkNode(5);
	ll.head?.next?.next?.next?.next?.next = LinkNode(6);
	ll.head?.next?.next?.next?.next?.next?.next = LinkNode(7);
	ll.display();
	if (ll.isCircular())
	{
		println("Circular Yes");
	}
	else
	{
		println("Circular No");
	}
	println("After Convert");
	ll.makeCircular();
	if (ll.isCircular())
	{
		println("Circular Yes");
	}
	else
	{
		println("Circular No");
	}
}

Output

Linked List Element :  1  2  3  4  5  6  7
Circular No
After Convert
Circular Yes