Please help with BufferedImage

Question

hi,
I'm making a space invaders game and need some help with image buffering. I so far have classes for:
ImageHandler - which should handle the loading of images
GameEntities - which contains methods for the ship movements etc
AlienEntitiy - which will draw an alien and have methods for its movement, shooting etc.
SpaceInvaders - which extends Canvas and handles the main game
The problem is that when I create a new alien which has a call to the setImageName(String name) method, which should call the getImage(String imageName) method in ImageHandler, a null pointer exception is thrown.
I have searched my code and can't trace the error (by the way, this is the first ime I've used buffered image). Can someone PLEASE help.
Here's my code:
package InvadersGame;
import java.awt.image.BufferedImage;
import java.io.PrintStream;
import java.util.HashMap;
import javax.imageio.ImageIO;
public class ImageHandler
    private HashMap images;
    public ImageHandler()
        images = new HashMap();
    public BufferedImage loadImage(String name)
        try
            java.net.URL url = null;
            url = getClass().getResource(name);
            return ImageIO.read(url);
        catch(Exception e)
            System.exit(0);
            System.out.println("image not found");
            return null;
    public BufferedImage getImage(String name)
        BufferedImage image = (BufferedImage)images.get(name);
        return image;
    public HashMap getImages()
        return images;
    public void setImages(HashMap val)
        images = val;
}and
package InvadersGame;
import java.awt.Graphics;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.awt.Graphics2D;
public class GameEntities {
    private double x, y;
    private int width, height;
    private String imageName;
    private boolean deletionMark = false;
    private SpaceInvaders invaders;
    private ImageHandler imageHandler;
    public GameEntities(SpaceInvaders invaders)
        this.invaders = invaders;
        imageHandler = invaders.getImageHandler();
    public double getX()
        return x;
    public double getY()
        return y;
    public int getWidth()
        return width;
    public int getHeight()
        return height;
    public Rectangle getBounds()
        return new Rectangle((int)x, (int)y, width, height);
    public void setX(int x)
        this.x = x;
    public void setY(int y)
        this.y = y;
    public void setWidth(int width)
        this.width = width;
    public void setHeight(int height)
        this.height = height;
    public boolean deletionMarked()
        return deletionMark;
    public void setDeletionMarkedTrue(boolean value)
        deletionMark = value;
   public String getImageName()
        return imageName;
    public void setImageName(String name)
        imageName = name;
        BufferedImage image = imageHandler.getImage(imageName);
        height = image.getHeight();
        width = image.getWidth();
    public boolean collidesWith(GameEntities other)
        Rectangle thisEntity = new Rectangle();
        Rectangle otherEntity = new Rectangle();       
        thisEntity.setBounds((int)this.getX(), (int)this.getY(), this.getWidth(), this.getHeight());
        otherEntity.setBounds((int)other.getX(),(int)other.getY(), other.getWidth(), other.getHeight());
        return thisEntity.intersects(otherEntity);
    public void move(){}
    public void paint(Graphics2D g)
         g.drawImage(imageHandler.getImage(imageName), (int)x, (int)y, invaders);
}and
package InvadersGame;
import java.awt.*;
import java.awt.geom.*;
import java.awt.event.*;
import java.awt.Graphics2D;
import java.lang.Math;
import java.util.Random;
public class AlienEntity extends GameEntities {
    double x, y;
    int alienType;
    int speedx = 2;
    int speedy = 2;
    public AlienEntity(SpaceInvaders invaders)
        super(invaders); 
        setImageName("alien4.gif");
    public void move()
        y = y + speedy;      
}and finally..
package InvadersGame;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.Graphics2D;
import java.awt.geom.*;
import java.util.ArrayList;
import java.util.Random;
import java.awt.image.BufferStrategy;
public class SpaceInvaders extends Canvas{
    JPanel panel;
    //AlienEntity al, al2;
    Graphics2D g2;
    boolean gameRunning = true;
    ArrayList<GameEntities> entitiesList;
    AnimationThread thread;
    AlienEntity alien;
    private BufferStrategy buffer;
    ImageHandler imageHandler;
    class AnimationThread extends Thread
        public void run()
            while(true)
                //paintAlien();
                try
                    sleep(50);
                catch(InterruptedException e){}
    public SpaceInvaders()
        super();
        imageHandler = new ImageHandler();
        JFrame window = new JFrame("Space Invaders");
        JPanel panel = (JPanel)window.getContentPane();
        setBounds(0, 0, 800, 600);
        panel.add(this);
        window.setBounds(0, 0, 800, 600);
        window.setVisible(true);         
        window.addWindowListener(new WindowAdapter()
            public void windowClosing(WindowEvent e)
                System.exit(0);
        setFocusable(true);
        this.createBufferStrategy(2);
        buffer = getBufferStrategy();
        thread = new AnimationThread();  
       paintAlien();
    public void paintAlien()
        Graphics2D g = (Graphics2D)buffer.getDrawGraphics();
        g.setColor(Color.black);
        g.fillRect(0, 0, getWidth(), getHeight());
        alien = new AlienEntity(this);
        alien.paint(g);
        buffer.show();
    public void setBufferstrategy(BufferStrategy buffer)
        buffer = buffer;
    public ImageHandler getImageHandler()
        return imageHandler;
    public static void main(String[] args)
        SpaceInvaders canvas = new SpaceInvaders();  
        canvas.thread.start();
}Can someone please take the time an give me some pointers.
Cheers

Answer 1

I've tracked the problem to this bit of the code in the ImageHandler class:
public BufferedImage loadImage(String name)
        try
            java.net.URL url = null;
            url = getClass().getResource(name);
            System.out.println(url); //to check whether the image was found
            return ImageIO.read(url);           
        catch(Exception e)
            System.exit(0);
            System.out.println("image not found");
            return null;
    For some reason the url = getClass().getResource(name); equals null even though the name I supply as an argument is exactly the same as the file name (alien4.gif).
I'm not too sure whether the problem's with my code or the way netbeans is setup. Can someone please help.