Adjacency list representation of directed graph in scala

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

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