How to transfer a string to a void from a separate class (Java)...?

Question

Okay, here's this problem I have in my java class. Upon searching, I didn't find any results, so. I have this string value for x, y and z positions in one of my classes named 'statpedia'...

public class Statpedia   
{
    private game conto;

    String car_x = Integer.toString(conto.x / 100     ); String display_car_x  = "X: "+ car_x; 
    String car_y = Integer.toString(conto.y + 27 / 100); String display_car_y  = "Y: "+ car_y;
    String car_z = Integer.toString(conto.z / 100     ); String display_car_z  = "Z: "+ car_z; 

}

And in another class graphimage a void...

public void stateInGame(Statpedia stat)
{
    rd.drawString(stat.display_car_x, 20, 360);
...
}

Now, rd is just graphics2D and drawing strings work perfectly fine, but when the void is called and it tries to draw display_car_x, I get this:

Exception in thread "Thread-2" java.lang.NullPointerException
at applet.xtGraphics.stateInGame(GraphImage.java:716)
at applet.GameSparker.run(MainGame.java:1092)
at java.lang.Thread.run(Thread.java:744)

What is happening? And how can I transfer the strings? Thanks in advance.

Answer 1

Default values of class variables.:

So, you need to initialize conto. So that it is not null.

If you have not written constructor in game class. Do it by calling default constructor like :

private game conto = new game();

Answer 2

Initialise the object as below :

private game conto = new game(); // Please use the class name starting with uppercase

You only create the reference and trying to get the instance variable due to which it throws NPE