How to get array method from another array method from the other class

My apologize, I have a class on my Project, called test01.java. And i used the library from Tadaki Graphlib contained many class. On of them is Graph.java.

Test01.java:

    public class test01 extends Graph{

public test01(String name, int n) {
    super(name);
public test01(String name, int n) {
    super(name);

    graphLib.Vertex vList[] = new graphLib.Vertex[n];
    for (int i = 0; i < n; i++) {
        vList[i] = new graphLib.Vertex(String.valueOf(i));
        addVertex(vList[i]);
    }
    int deg = 0;
    System.out.println("<---------- Random val ---------->");
     addArc(vList[0], vList[1], String.valueOf(0));   deg++;
     addArc(vList[1], vList[0], String.valueOf(1));   deg++;
     System.out.println("Vertex-0 with Vertex-1");
     System.out.println("Vertex-1 with Vertex-0");
    int k = 2;
    int l;
    int m=0;
    Random randomval = new Random();
    int isAvailInt [] = new int[n];
    while (k<n) {
        for(l=0;l<k;l++){
                isAvailInt [l]= Integer.parseInt(vList[l].toString());
                m=isAvailInt[l];            
        }
        int chosen = randomval.nextInt(m);
        addArc(vList[k], vList[chosen], String.valueOf(k));
        System.out.println("Vertex-"+k+" with Vertex-"+chosen+
                " exp = " + String.valueOf(k));

        k++;
    }

}public static void main(String args[]) {
    int n;
    String num = JOptionPane.showInputDialog("Masukkan nilai jumlah iterasi = ");
    String degnum = null;        
    n = Integer.parseInt(num);
    int deg []= new int [n];
    test01 t = new test01("test",n);

    System.out.println("<---------- Vertex-i = Degree-i ------------>");
    graphLib.Graph g= new Graph("test");

    int [][]adj = g.getAdjacent();

    System.out.println(adj[0][0]);
    for (int i=0; i<t.getSize();i++){
        for (int j=0; j<t.getSize();j++){
        }          
    }}

and one other class called Graph.java

public class Graph extends GraphBase { int adjacent[][] = null;

public Graph(String name) {
    this.name = name;
    vertexes = Utils.createVertexList();
    arcs = Utils.createArcList();
    a2vHead = new HashMap<>();
    a2vTail = new HashMap<>();
    v2a = new HashMap<>();
}
public int[][] getAdjacent() {
    int n = vertexes.size();
    adjacent = new int[n][];
    for (int i = 0; i < n; i++) {
        adjacent[i] = new int[n];
        for (int j = 0; j < n; j++) {
            adjacent[i][j] = 0;
        }
    }
    if (directed) {
        for (int i = 0; i < n; i++) {
            Vertex v = vertexes.get(i);
            for (Arc a : v2a.get(v)) {
                Vertex t = a2vTail.get(a);
                int l = vertexes.indexOf(t);
                adjacent[l][i]++;
            }
        }
    } else {
        for (int i = 0; i < n; i++) {
            Vertex v = vertexes.get(i);
            for (Arc a : v2a.get(v)) {
                Vertex t = a2vTail.get(a);
                if (!t.equals(v)) {
                    int l = vertexes.indexOf(t);
                    adjacent[i][l]++;
                    adjacent[l][i]++;
                }
            }
        }

    }
    checkConnectedness();
    return adjacent;
}}

From above, method - int [][] Adjacent() - has an array return value:

return adjacent;

Then I want to received it with array variable declared:

int [][]adj = g.getAdjacent();

But when I run the program, the code :

System.out.println(adj[0][0]);

Has appeared error :

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0

I've declare the variable vertexes in Graph.java that extended from other class, GraphBase.java:

 vertexes = Utils.createVertexList();

How do I obtain an array value form a variable adjacent in Graph.java to test01.java and how do I display it with System.out.println() ?