DAMN NullPointerException !! How do i get rid of it?

Question

Hi,
My code compiles perfect, but when i run my program i get a "NullPointerException". I spent way too long and dont think I'll ever figure it out. Im hoping somebody can see whats wrong. It happens when I try to assign values to my array of objects. here is my code, thanks!!
Here is the code for PointObject.java:
public class PointObject {
        int reference;  //the class number this point references
        int xc;         //the x coordinate
        int yc;         //the y coordinate
    public PointObject() {
        int reference = 0;
        int xc = 0;
        int yc = 0;
}Here is the code for Jtrack.java:
public class Jtrack extends Frame {
        PointObject[] po;
        public class DPanel extends Panel {
                public DPanel() { }
                public void paint(Graphics g) {
                        super.paint(g);
                        g.setColor(Color.black);
                        Random r = new Random ();
                        for (int k = 1; k <= number; k ++) {
                                int x = r.nextInt (getWidth() - 50);
                                int y = r.nextInt (getHeight() - 50);
                                g.drawRect (x, y, 50, 50);
                                g.drawString(""+k,x+15,y+15);
                                setPointObject(k-1, k, x, y); //#problem on this line#
        public void setPointObject (int idx, int ref, int x_c, int y_c){
                po[idx].reference = ref;
                po[idx].xc = x_c;
                po[idx].yc = y_c;
        public static void main (String[] args) throws Exception {
                new Jtrack ();
}

Answer 1

did you size and instantiate the points instances correctly
that you are assigning to if not that is the problem.
if you did then its probably be in your loop
a alternate way to check your loop is to place a conditional
check in thier just before the line that errors out like so
public void setPointObject (int idx, int ref, int x_c, int y_c){
if(po.length <= idx){
System.out.println(" idx element being assigned is "+idx+" however po.length is "+po.length );// that way you can at least figure it out
po[idx].reference = ref;
po[idx].xc = x_c;
po[idx].yc = y_c;
}