Thread: Having trouble with code for my game

I continue to get this error:
Exception in thread "main" java.lang.NullPointerException
at Main.GamePanel.<init>(GamePanel.java:106)
at Main.Game.main(Game.java:10)

This is the code:
Game Panel
<code>package Main;

import java.awt.*;
import java.awt.image.BufferedImage;
import java.awt.event.*;

import javax.swing.JPanel;

import GameState.GameStateManager;


public class GamePanel extends JPanel implements Runnable, KeyListener{

//dimensions
public static final int WIDTH = 320;
public static final int HEIGHT = 240;
public static final int SCALE = 2;

//game thread
private Thread thread;
private boolean running;
private int FPS = 60;
private long targetTime = 1000 / FPS;

//image
private BufferedImage image;
private Graphics2D g;

//game state manager
private GameStateManager gsm;

public GamePanel() {
super();
setPreferredSize (new Dimension(WIDTH * SCALE, HEIGHT * SCALE));
setFocusable(true);
requestFocus();
}

public void addNotify() {
super.addNotify();
if(thread == null) {
thread = new Thread(this);
addKeyListener(this);
thread.start();
}
}

private void init() {

image = new BufferedImage(
WIDTH, HEIGHT,
BufferedImage.TYPE_INT_RGB
);

g = (Graphics2D) image.getGraphics();
running = true;

gsm = new GameStateManager();

}


public void run() {

init();

long start;
long elapsed;
long wait;

//game loop
while(running) {

start = System.nanoTime();

update();
draw();
drawToScreen();

elapsed = System.nanoTime() - start;

wait = targetTime - elapsed / 1000000;


try {
Thread.sleep(wait);
}
catch(Exception e) {
e.printStackTrace();
}

}


}

private void update() {
gsm.update();
}
private void draw() {
gsm.draw();
}

private void drawToScreen() {} {
Graphics g2 = getGraphics();
g2.drawImage(image, 0, 0, null);
g2.dispose();
}


public void keyTyped(KeyEvent key) {}
public void keyPressed(KeyEvent key) {
gsm.keyPressed(key.getKeyCode());
}
public void keyReleased(KeyEvent key) {
gsm.keyReleased(key.getKeyCode());
}


}
</code>
Game
<code>package Main;

import javax.swing.JFrame;

public class Game {

public static void main (String[] args) {

JFrame window = new JFrame("Game");
window.setContentPane(new GamePanel());
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLO SE);
window.setResizable(false);
window.pack();
window.setVisible(true);



}
}
</code>
any help will be greatly appreciated

Welcome to the forum! Please read this topic to learn how to post code in code or highlight tags and other useful info for new members.

Please post your code correctly using code or highlight tags which are explained near the top of the above link.

Originally Posted by Ada Lovelace

Please use code tags when posting code. Use [ ] not < >



That line should of thrown an error.

Wishes Ada xx

I continue to get this error:
Exception in thread "main" java.lang.NullPointerException
at Main.GamePanel.<init>(GamePanel.java:106)
at Main.Game.main(Game.java:10)

This is the code:
Game Panel

package Main;
 
import java.awt.*;
import java.awt.image.BufferedImage;
import java.awt.event.*;
 
import javax.swing.JPanel;
 
import GameState.GameStateManager;
 
 
public class GamePanel extends JPanel implements Runnable, KeyListener{
 
//dimensions
public static final int WIDTH = 320;
public static final int	HEIGHT = 240;
public static final int SCALE = 2;
 
//game thread
private Thread thread;
private boolean running;
private int FPS = 60;
private long targetTime = 1000 / FPS;
 
//image
private BufferedImage image;
private Graphics2D g;
 
//game state manager
private GameStateManager gsm;
 
public GamePanel() {
super();
setPreferredSize (new Dimension(WIDTH * SCALE, HEIGHT * SCALE));
setFocusable(true);
requestFocus();
}
 
public void addNotify() {
super.addNotify();
if(thread == null) {
thread = new Thread(this);
addKeyListener(this);
thread.start();
}
}
 
private void init() {
 
image = new BufferedImage(
WIDTH, HEIGHT,
BufferedImage.TYPE_INT_RGB
);	
 
g = (Graphics2D) image.getGraphics();
running = true;
 
gsm = new GameStateManager();
 
}
 
 
public void run() {
 
init();
 
long start;
long elapsed;
long wait;
 
//game loop
while(running) {
 
start = System.nanoTime();
 
update();
draw();
drawToScreen();
 
elapsed = System.nanoTime() - start;
 
wait = targetTime - elapsed / 1000000;
 
 
try {
Thread.sleep(wait);
}
catch(Exception e) {
e.printStackTrace();
}
 
}
 
 
}
 
private void update() {
gsm.update();
}
private void draw() {
gsm.draw();
}
 
private void drawToScreen() {} {
Graphics g2 = getGraphics();
g2.drawImage(image, 0, 0, null);
g2.dispose();
}
 
 
public void keyTyped(KeyEvent key) {}
public void keyPressed(KeyEvent key) {
gsm.keyPressed(key.getKeyCode());
}
public void keyReleased(KeyEvent key) {
gsm.keyReleased(key.getKeyCode());
}
 
 
}

Game

package Main;
 
import javax.swing.JFrame;
 
public class Game {
 
public static void main (String[] args) {
 
JFrame window = new JFrame("Game");
window.setContentPane(new GamePanel());
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.setResizable(false);
window.pack();
window.setVisible(true);
 
 
 
}
}

Fixed that CLO SE problem but it still outputs the same error

Good job on the code tags, now please post properly indented code.

Your while(true)/Thread.sleep() game loop is not appopriate for a Swing application. You can find several good articles on why this is not a good idea and other articles that walk through the development of a good/better/best game loop with clear justification for each improvement.

Swing is not thread safe, and a Swing app should be run on the Event Dispatch Thread or "EDT". You can find out more about these topics by searching the 'net.

Your error occurs because there is a null object at line 106 of GamePanel. Look at line 106, identify all of the objects in that line, and using print statements or intuition, figure out which of the objects is null. Then work backwards to determine why that object is null and fix it.