Thread: Not sure what is wrong with this code?? Please help

I am learning java from videos online, I wont post the link because i'm not sure if I would be allows but I can do if anybody wants.

From the video I have copied the code exactly. My code compiles but when I run it, it doesn't work. The person online runs his and it works. No idea what's wrong:

I am using practicing using sprites:

Sprite class:

import java.awt.Image;
 
public class Sprite {
 
    private Animation a;
    private float x;
    private float y;
    private float vx;
    private float vy;
 
    //Constructor    
    public Sprite(Animation a)
    {
        this.a = a;
    }
 
    //Chnage position
    public void update(long timePassed)
    {
        x += vx * timePassed;
        y += vy * timePassed;
        a.update(timePassed);
    }
 
    //Get x position
    public float getX()
    {
        return x;
    }
 
    //Get y position
    public float getY()
    {
        return y;
    }
 
    //Set sprite x position
    public void setX(float x)
    {
        this.x = 0;
    }
 
    //Set sprite y position
    public void setY(float y)
    {
        this.y = 0;
    }
 
    //Get sprite width
    public int getWidth()
    {
        return a.getImage().getWidth(null);
    }
 
    //Get sprite height
    public int getHeight()
    {
        return a.getImage().getHeight(null);
    }
 
    //get horizontal velocity
    public float getVelocityX()
    {
        return vx;
    }
 
    //get vertical velocity
    public float getVelocityY()
    {
        return vy;
    }
 
    //set horizontal velocity
    public void setVelocityX(float vx)
    {
        this.vx = vx;
    }
 
    //set vertical velocity
    public void setVelocityY(float vy)
    {
        this.vy = vy;
    }
 
    //get sprite / image
    public Image getImage()
    {
        return a.getImage();
    }
 
}

Animation class:

import java.awt.Image;
import java.util.ArrayList;
 
public class Animation{
 
    private ArrayList scenes;
    private int sceneIndex;
    private long movieTime;
    private long totalTime;
 
    //CONSTRUCTOR
    public Animation(){
        scenes = new ArrayList();
        totalTime = 0;
        start();
    }
 
    //Add scene to ArrayList and set time for each scene
    public synchronized void addScene(Image i, long t)
    {
        totalTime += t;
        scenes.add(new oneScene(i, totalTime));
    }
 
    //Start aimation from begining
    public synchronized void start()
    {
        movieTime = 0;
        sceneIndex = 0;
    }
 
    //Change scenes
    public synchronized void update(long timePassed)
    {
        if(scenes.size()>1){
            movieTime += timePassed;
            if(movieTime >= totalTime){
                movieTime = 0;
                sceneIndex = 0;
            }
            while(movieTime > getScene(sceneIndex).endTime){
                sceneIndex++;
            }
        }
    }
 
    //get animations current scene AKA image
    public synchronized Image getImage()
    {
        if(scenes.size()==0){
            return null;
        }else{
            return getScene(sceneIndex).pic;
        }
    }
 
    //get scene
    private oneScene getScene(int x)
    {
        return (oneScene) scenes.get(x);
    }
 
    //Private inner class//
 
    private class oneScene{
        Image pic;
        long endTime;
 
        public oneScene(Image pic, long endTime)
        {
            this.pic = pic;
            this.endTime = endTime;
        }
    }
}

Screen Manager class:

 
import java.awt.*;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;
import java.lang.reflect.InvocationTargetException;
import javax.swing.JFrame;
 
public class ScreenManager {
 
    private GraphicsDevice vc;
 
    //Give vc acces to moniter screen
    public ScreenManager()
    {
        GraphicsEnvironment e = GraphicsEnvironment.getLocalGraphicsEnvironment();
        vc = e.getDefaultScreenDevice();
    }
 
    //Get all compatible display modes
    public DisplayMode[] getCompatibleDisaplyModes()
    {
        return vc.getDisplayModes();
    }
 
    //Compares display modes passed in to vc display modes and see if they match
    public DisplayMode findFirstCompatibleMode(DisplayMode modes[])
    {
        DisplayMode goodModes[] = vc.getDisplayModes();
        for(int x=0; x<modes.length; x++){
            for(int y = 0; y<goodModes.length; y++){
                if(displayModesMatch(modes[x], goodModes[y])){
                    return modes[x];
                }
            }
        }
        return null;
    }
 
    //Get current displayMode
    public DisplayMode getCurrentDisplayMode()
    {
        return vc.getDisplayMode();
    }
 
    //Checks if two modes match each other
    public boolean displayModesMatch(DisplayMode m1, DisplayMode m2)
    {
        if(m1.getWidth() != m2.getWidth() || m1.getHeight() != m2.getHeight())
        {
            return false;
        }
        if(m1.getBitDepth() != DisplayMode.BIT_DEPTH_MULTI && m2.getBitDepth() != DisplayMode.BIT_DEPTH_MULTI && m1.getBitDepth() != m2.getBitDepth())
        {
            return false;
        }
        if(m1.getRefreshRate() != DisplayMode.REFRESH_RATE_UNKNOWN && m2.getRefreshRate() != DisplayMode.REFRESH_RATE_UNKNOWN && m1.getRefreshRate() != m2.getRefreshRate())
        {
            return false;
        }
 
        return true;
    }
 
    //Make frame full screen
    public void setFullScreen(DisplayMode dm)
    {
        JFrame f = new JFrame();
        f.setUndecorated(true);
        f.setIgnoreRepaint(true);
        f.setResizable(false);
        vc.setFullScreenWindow(f);
 
        if(dm != null && vc.isDisplayChangeSupported())
        {
            try{
                vc.setDisplayMode(dm);
            }catch(Exception ex) {}
        }
 
        f.createBufferStrategy(2);
    }
 
    //Set graphics object = to this
    public Graphics2D getGraphics()
    {
        Window w = vc.getFullScreenWindow();
        if(w != null){
            BufferStrategy s = w.getBufferStrategy();
            return (Graphics2D)s.getDrawGraphics();
        } else{
            return null;
        }
    }
 
    //Updates display
    public void update()
    {
        Window w = vc.getFullScreenWindow();
        if(w != null){
            BufferStrategy s = w.getBufferStrategy();
            if(!s.contentsLost()){
                s.show();
            }
        }
    }
 
    //Return full screen window
    public Window getFullScreenWindow()
    {
        return vc.getFullScreenWindow();
    }
 
    //Get width of window
    public int getWidth()
    {
        Window w = vc.getFullScreenWindow();
        if(w != null){
            return w.getWidth();
        }else{
            return 0;
        }
    }
 
    //Get hieght of window
    public int getHeight()
    {
        Window w = vc.getFullScreenWindow();
        if(w != null){
            return w.getHeight();
        }else{
            return 0;
        }
    }
 
    //Get out of full screen
    public void restoreScreen()
    {
        Window w = vc.getFullScreenWindow();
        if(w != null){
            w.dispose();
        }
        vc.setFullScreenWindow(null);
    }
 
    //Create image compatible with monitor
    public BufferedImage createCompatibleImage(int w, int h, int t)
    {
        Window win = vc.getFullScreenWindow();
        if(win != null){
            GraphicsConfiguration gc = win.getGraphicsConfiguration();
            return gc.createCompatibleImage(w,h,t);
        }
        return null;
    }
}

bucky class:

import java.awt.*;
import javax.swing.JFrame;
import javax.swing.ImageIcon;
import javax.swing.*;
 
public class bucky2{
 
    public static void main(String args[]) {
        bucky2 b = new bucky2();
        b.run();
    }
 
    private Sprite sprite;
    private Animation a;
    private ScreenManager s;
    private Image bg;
    private static final DisplayMode modes1[] = {
        new DisplayMode(800,600,32,0),
        new DisplayMode(800,600,24,0),
        new DisplayMode(800,600,16,0),
        new DisplayMode(640,480,32,0),
        new DisplayMode(640,480,24,0),
        new DisplayMode(640,480,16,0),
    };
 
    //Load images and add scenes
    public void loadImages()
    {
        bg = new ImageIcon("C:\\temp\background1.jpg").getImage();
        Image face1 = new ImageIcon("C:\\temp\face1.png").getImage();
        Image face2 = new ImageIcon("C:\\temp\face2.png").getImage();
 
        a = new Animation();
        a.addScene(face1, 250);
        a.addScene(face2, 250);
 
        sprite = new Sprite(a);
        sprite.setVelocityX(0.3f);
        sprite.setVelocityY(0.3f);
    }
 
    //Main method called from main
    public void run()
    {
        s = new ScreenManager();
        try{
            DisplayMode dm = s.findFirstCompatibleMode(modes1);
            s.setFullScreen(dm);
            movieLoop();
        }finally{
            s.restoreScreen();
        }
    }
 
    //Play movie
    public void movieLoop()
    {
        long startingTime = System.currentTimeMillis();
        long cumTime = startingTime;
        while(cumTime - startingTime < 5000){
            long timePassed = System.currentTimeMillis() - cumTime;
            cumTime += timePassed;
            update(timePassed);
 
            //draw and update screen
            Graphics2D g = s.getGraphics();
            draw(g);
            g.dispose();
            s.update();
 
            try{
                Thread.sleep(200);
            }catch (Exception ex){}
        }
    }
 
    //Draws graphics
    public void draw(Graphics g)
    {
        g.drawImage(bg, 0,0, null);
        g.drawImage(sprite.getImage(), Math.round(sprite.getX()), Math.round(sprite.getY()), null);        
    }
 
    //Update sprite positioning
    public void update(long timePassed)
    {
        if(sprite.getX() < 0){
            sprite.setVelocityX(Math.abs(sprite.getVelocityX()));
        }else if(sprite.getX() + sprite.getWidth() >= s.getWidth()){
            sprite.setVelocityX(-Math.abs(sprite.getVelocityX()));
        }
 
        if(sprite.getY() < 0){
            sprite.setVelocityY(Math.abs(sprite.getVelocityY()));
        }else if(sprite.getY() + sprite.getHeight() >= s.getHeight()){
            sprite.setVelocityY(-Math.abs(sprite.getVelocityY()));
        }
 
        sprite.update(timePassed);
    }
}

When I run my code, in the bucky class on the update method :

public void update(long timePassed)
    {
        if(sprite.getX() < 0){

That is what gives me a null pointer exception. I have tried many things but I can't think of anything.
I have attached my code so if anybody wants to try it, I have done it in both blueJ and Eclipse.

Sorry about the long code!

Thank you.

The method loadImages gives sprite a value of a.

Is my problem that loadImages in the bucky2 class is never called??

Originally Posted by sim18

Is my problem...?

If that is the only place in the code where the sprite can be given a non-null value, and the NPE is generated because sprite has a null value when it is used, then I think you have found the reason for the NPE.

Cheers!

Z