Adjacency list representation of directed graph in kotlin

Kotlin program for Adjacency list representation of directed graph. Here problem description and explanation.

/*
    Kotlin Program for 
    Directed graph representation using adjacency list
*/
class AjlistNode
{
	// Vertices node key
	var id: Int;
	var next: AjlistNode ? ;
	constructor(id: Int)
	{
		// Set value of node key
		this.id = id;
		this.next = null;
	}
}
class Vertices
{
	var data: Int;
	var next: AjlistNode ? ;
	var last: AjlistNode ? ;
	constructor(data: Int)
	{
		this.data = data;
		this.next = null;
		this.last = null;
	}
}
class Graph
{
	// Number of Vertices
	var size: Int;
	var node: Array < Vertices ? > ;
	constructor(size: Int)
	{
		// Set value
		this.size = size;
		this.node = Array(size)
		{
			null
		};
		this.setData();
	}
	// Set initial node value
	fun setData(): Unit
	{
		if (this.size <= 0)
		{
			println("\nEmpty Graph");
		}
		else
		{
			var index: Int = 0;
			while (index < this.size)
			{
				// Set initial node value
				this.node[index] = Vertices(index);
				index += 1;
			}
		}
	}
	// Connect two nodes
	fun connect(start: Int, last: Int): Unit
	{
		val edge: AjlistNode = AjlistNode(last);
		if (this.node[start]?.next == null)
		{
			this.node[start]?.next = edge;
		}
		else
		{
			// Add edge at the end
			this.node[start]?.last?.next = edge;
		}
		// Get last edge 
		this.node[start]?.last = edge;
	}
	//  Handling the request of adding new edge
	fun addEdge(start: Int, last: Int): Unit
	{
		if (start >= 0 && start < this.size && 
            last >= 0 && last < this.size)
		{
			// Safe connection
			this.connect(start, last);
		}
		else
		{
			// When invalid nodes
			println("\nHere Something Wrong");
		}
	}
	fun printGraph(): Unit
	{
		if (this.size > 0)
		{
			var index: Int = 0;
			// Print graph ajlist Node value
			while (index < this.size)
			{
				print("\nAdjacency list of vertex " + index + " :");
				var temp: AjlistNode ? = this.node[index]?.next;
				while (temp != null)
				{
					// Display graph node 
					print("  " + this.node[temp.id]?.data);
					// visit to next edge
					temp = temp.next;
				}
				index += 1;
			}
		}
	}
}
fun main(args: Array < String > ): Unit
{
	// 5 implies the number of nodes in graph
	val g: Graph = Graph(5);
	// Connect node with an edge
	g.addEdge(0, 1);
	g.addEdge(1, 2);
	g.addEdge(1, 4);
	g.addEdge(2, 0);
	g.addEdge(2, 3);
	g.addEdge(4, 3);
	// print graph element
	g.printGraph();
}

Output

Adjacency list of vertex 0 :  1
Adjacency list of vertex 1 :  2  4
Adjacency list of vertex 2 :  0  3
Adjacency list of vertex 3 :
Adjacency list of vertex 4 :  3