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Thread: Having trouble with code for my game

  1. #1
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    Default 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


  2. #2
    Member Ada Lovelace's Avatar
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    Default Re: Having trouble with code for my game

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

    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLO SE);
    That line should of thrown an error.

    Wishes Ada xx
    If to Err is human - then programmers are most human of us all.
    "The Analytical Engine offers a new, a vast, and a powerful language . . .
    for the purposes of mankind
    ."
    Augusta Ada Byron, Lady Lovelace (1851)

  3. #3
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    Default Re: Having trouble with code for my game

    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.

  4. #4
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    Default Re: Having trouble with code for my game

    Quote Originally Posted by Ada Lovelace View Post
    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

  5. #5
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    Default Re: Having trouble with code for my game

    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.

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