How do I fix a NullPointerException?

Question

I'm making a game but when i tried to launch it it said: java.lang.NullPointerException.

Here is the code:

package com.shinxs.rain.graphics;

import java.awt.Graphics;
import java.awt.Image;
import java.util.Random;
import javax.swing.ImageIcon;

public class Screen {

    private int width, height;
    public int[] pixels;
    Graphics g;

    public int[] tiles = new int[64 * 64];

    private Random random = new Random();

    ImageIcon i = new ImageIcon("Resources/Inventory.png");
    Image image = i.getImage();

    public Screen(int width, int height) {
        this.width = width;
        this.height = height;
        pixels = new int[width * height];

        for (int i = 0; i < 64 * 64; i++) {
            tiles[i] = random.nextInt(0xFFFFFF);
        }
    }

    public void clear() {
        for (int i = 0; i < pixels.length; i++) {
            pixels[i] = 0;
        }       
    }

    public void render() {
        g.drawImage(image, 500, 200, 124, 280, null);
    }
}

Please tell me if you know how to fix it, I've been stuck with it for a long time.

First out, find and study the exception traceback. It will tell you most of what you need to know. — Hot Licks, Nov 03 '12 at 18:16
[Why did you tag this javascript?](http://stackoverflow.com/a/5184356/396458) — NullUserException, Nov 03 '12 at 18:16
Please read some java, default values for object properties for instance... — Vishwanath, Nov 03 '12 at 18:18
If you get any further exceptions, please post it here with a stacktrace. — Roman C, Nov 03 '12 at 18:24

kosa · Answer 1 · 2012-11-03T18:19:12.020

4

 Graphics g;

Your g is pointing to null-reference and you are calling drawImage on null which is resulting in NPE (NullPointerException).

g.drawImage(image, 500, 200, 124, 280, null);

See this tutorial on how to use Graphics in java

edited Nov 03 '12 at 18:19

answered Nov 03 '12 at 18:16

kosa

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score 1 · Answer 2 · answered Nov 03 '12 at 18:30

Your Graphics object is null because you never assign to any other value. Null means that an object is "empty" and contains no data, which is a logical value for objects to be initialized to. In order to use a Graphics object, you need to get access to a pre-made one, as the Graphics class has no public constructor (new Graphics() does not work). The only way I know of to do this is to extend javax.swing.JFrame and override the paint(Graphics g), in which a pre-instantiated Graphics object is passed as an argument. The Graphics object is created by the internal workings of the JFrame.

   class Screen extends javax.swing.JFrame{

         public void paint(Graphics g){
                super.paint(g); //correctly draws background

                //now call methods on g, the graphics object
         }
   }

I would highly recommend looking into the documentation on Swing, to find out more about how it works.

PermGenError · Answer 3 · 2012-11-03T18:48:06.853

0

you never initialiazed your Graphics g;object and calling methods on it, you have to initialize your Graphics object, otherwise it'd be null, as objects default value is null.

Graphics g= Griphics.create();

g.darwLine()

edited Nov 03 '12 at 18:48

answered Nov 03 '12 at 18:19

PermGenError

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8
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How do I fix a NullPointerException?

3 Answers3