Adjacency list representation of undirected graph in java

Java program for Adjacency list representation of undirected graph. Here problem description and explanation.

/*
    Java Program for 
    Undirected graph representation by using adjacency list 
*/
class AjlistNode
{
    // Vertices node key
    public int id;
    public AjlistNode next;
    public AjlistNode(int id)
    {
        // Set value of node key
        this.id = id;
        this.next = null;
    }
}
class Vertices
{
    public int data;
    public AjlistNode next;
    public AjlistNode last;
    public Vertices(int data)
    {
        this.data = data;
        this.next = null;
        this.last = null;
    }
}
public class Graph
{
    // Number of Vertices
    public int size;
    public Vertices[] node;
    public Graph(int size)
    {
        // Set value
        this.size = size;
        this.node = new Vertices[size];
        this.setData();
    }
    // Set initial node value
    public void setData()
    {
        if (size <= 0)
        {
            System.out.println("\nEmpty Graph");
        }
        else
        {
            for (int index = 0; index < size; index++)
            {
                node[index] = new Vertices(index);
            }
        }
    }
    // Connect two nodes
    public void connect(int start, int last)
    {
        AjlistNode edge = 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
    public void addEdge(int start, int last)
    {
        if (start >= 0 && start < size && 
            last >= 0 && last < size )
        {
            connect(start, last);
            if(start==last)
            {
                // When self loop
                return;
            }
            connect(last,start);
        }
        else
        {
            // When invalid nodes
            System.out.println("\nHere Something Wrong");
        }
    }
    public void printGraph()
    {
        if (size > 0 )
        {
            // Print graph ajlist Node value
            for (int index = 0; index < size; ++index)
            {
                System.out.print("\nAdjacency list of vertex " + index + " :");
                AjlistNode temp = node[index].next;
                while (temp != null)
                {
                    // Display graph node 
                    System.out.print("  " + node[temp.id].data);
                    // Visit to next edge
                    temp = temp.next;
                }
            }
        }
    }
    public static void main(String[] args)
    {
        // 5 implies the number of nodes in graph
        Graph g = new Graph(5);
        // Connect node with an edge
        g.addEdge(0,1);
        g.addEdge(0,2);
        g.addEdge(0,4);
        g.addEdge(1,2);
        g.addEdge(1,4);
        g.addEdge(2,3);
        g.addEdge(3,4);
        // print graph element
        g.printGraph();
    }
}

Output

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