Graphics problem

[luke24]

Hi trying to draw a circle on my frame.

Getting the error

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at SuperStarTrekGame.paint(SuperStarTrekGame.java:44)

import java.awt.Graphics;
import javax.swing.JFrame;


public class SuperStarTrekGame extends JFrame{

    private int numberOfKlingons, numberOfRomulans;
    private boolean setSuperCommander;
    private int timeRemaining;
    private int numberOfStarBases, numberOfBlackHoles;
    private String difficulty;
    private Quadrant[] galaxy = new Quadrant[7];
    private int arrayPos;

   

    public void prepareGame(){

     
        arrayPos = 5;
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(800,600);
        setVisible(true);

    }

    public void adjustTime(){

    }

    
    public void paint(Graphics g){

        galaxy[arrayPos].paint(g);

    }

    public void checkGame(){

    }

    public static void main(String[] args){

        SuperStarTrekGame game = new SuperStarTrekGame();
        game.prepareGame();
        
        

    }

}



import java.awt.Color;
import java.awt.Graphics;


public class Quadrant{

    public Quadrant(){

    }

   

   
    public void paint(Graphics g){

        g.setColor(Color.green);
        g.drawOval(40, 40, 100, 100);
        g.fillOval(40, 40, 100, 100);
        
        
    }

    



}

The error is on
galaxy[arrayPos].paint(g);

Any ideas?

[m00nchile]

I see a declared and initialized array of Quadrants, but nowhere do I see the Quadrants being initialized, so the array galaxy contains null values. That's probably the error, but it's possible you're not showing us the whole code. Also, instance variables should be initialized in the constructor, not at declaration.

[luke24]

Ah ofcourse, I need a for loop to initialise each Quadrant in the array.

thx !

[JosAH]

Also, instance variables should be initialized in the constructor, not at declaration.

Care to elaborate on that? because I think it doesn't matter (much) where those member variables are initialized.

kind regards,

Jos

[luke24]

Just a quick question, I am drawing my image fine, but as far as I know, I should be using paintComponent rather then paint since use Jframe. But when I use paintComponent, the circle is not drawn, it works fine with paint tho?

[JosAH]

Just a quick question, I am drawing my image fine, but as far as I know, I should be using paintComponent rather then paint since use Jframe. But when I use paintComponent, the circle is not drawn, it works fine with paint tho?

A JFrame isn't a JComponent so it hasn't a paintComponent( ... ) method and you can't override it. Add a JPanel to your frame and paint on that.

kind regards,

Jos

[luke24]

So should I instead extend Jpanel and create a JFrame in the constructor, since paintComponent will need to override?

[m00nchile]

Care to elaborate on that? because I think it doesn't matter (much) where those member variables are initialized.

kind regards,

Jos

It's more of a good practice thing in my eyes. Perhaps my wording was a bit too strong with the should.