Warum löst dieser Code eine java.lang.NullPointerException aus?

Question

Ich habe einen Quellcode gefunden und ich habe ihn zu meinem Frame hinzugefügt, nur um zu testen, dass er Java2D verwendet. Aber es wirft eine Ausnahme. Ich verstehe nicht, warum.

meine Klasse:

package ClientGUI;

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.MediaTracker;
import java.awt.RenderingHints;
import java.awt.geom.CubicCurve2D;
import java.awt.geom.PathIterator;
import java.awt.geom.Point2D;
import java.awt.image.BufferedImage;

/**
 *
 * @author ICC
 */

public class SignInFrame extends javax.swing.JFrame implements Runnable {

private static int iw,  ih,  iw2,  ih2;
private static Image img;
private static final int FORWARD = 0;
private static final int BACK = 1;

// the points of the curve
private Point2D pts[];

// initializes direction of movement forward, or left-to-right
private int direction = FORWARD;
private int pNum;
private int x,  y;
private Thread thread;
private BufferedImage bimg;

/** Creates new form SignInFrame */
public SignInFrame() {
    initComponents();
    img = getToolkit().getImage(Image.class.getResource("Yahoo-Messanger.jpg"));
    try {
        MediaTracker tracker = new MediaTracker(this);
        tracker.addImage(img, 0);
        tracker.waitForID(0);
    } catch (Exception e) {
    }
    iw = img.getWidth(this);
    ih = img.getHeight(this);
    iw2 = iw / 2;
    ih2 = ih / 2;

}

public void reset(int w, int h) {
    pNum = 0;
    direction = FORWARD;

    // initializes the cubic curve
    CubicCurve2D cc = new CubicCurve2D.Float(
            w * .2f, h * .5f, w * .4f, 0, w * .6f, h, w * .8f, h * .5f);

    // creates an iterator to define the boundary of the flattened curve
    PathIterator pi = cc.getPathIterator(null, 0.1);
    Point2D tmp[] = new Point2D[200];
    int i = 0;

    // while pi is iterating the curve, adds points to tmp array
    while (!pi.isDone()) {
        float[] coords = new float[6];
        switch (pi.currentSegment(coords)) {
            case PathIterator.SEG_MOVETO:
            case PathIterator.SEG_LINETO:
                tmp[i] = new Point2D.Float(coords[0], coords[1]);
        }
        i++;
        pi.next();
    }
    pts = new Point2D[i];

    // copies points from tmp to pts
    System.arraycopy(tmp, 0, pts, 0, i);
}

public void step(int w, int h) {
    if (pts == null) {
        return;
    }
    x = (int) pts[pNum].getX();
    y = (int) pts[pNum].getY();
    if (direction == FORWARD) {
        if (++pNum == pts.length) {
            direction = BACK;
        }
    }
    if (direction == BACK) {
        if (--pNum == 0) {
            direction = FORWARD;
        }
    }
}

public void drawDemo(int w, int h, Graphics2D g2) {
    g2.drawImage(img,
            0, 0, x, y,
            0, 0, iw2, ih2,
            this);
    g2.drawImage(img,
            x, 0, w, y,
            iw2, 0, iw, ih2,
            this);
    g2.drawImage(img,
            0, y, x, h,
            0, ih2, iw2, ih,
            this);
    g2.drawImage(img,
            x, y, w, h,
            iw2, ih2, iw, ih,
            this);
}

public Graphics2D createGraphics2D(int w, int h) {
    Graphics2D g2 = null;
    if (bimg == null || bimg.getWidth() != w || bimg.getHeight() != h) {
        bimg = (BufferedImage) createImage(w, h);
        reset(w, h);
    }
    g2 = bimg.createGraphics();
    g2.setBackground(getBackground());
    g2.clearRect(0, 0, w, h);
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
    g2.setRenderingHint(RenderingHints.KEY_RENDERING,
            RenderingHints.VALUE_RENDER_QUALITY);
    return g2;
}

@Override
public void paint(Graphics g) {
    Dimension d = getSize();
    step(d.width, d.height);
    Graphics2D g2 = createGraphics2D(d.width, d.height);
    drawDemo(d.width, d.height, g2);
    g2.dispose();
    g.drawImage(bimg, 0, 0, this);
}

public void start() {
    thread = new Thread(this);
    thread.setPriority(Thread.MIN_PRIORITY);
    thread.start();
}

public synchronized void stop() {
    thread = null;
}

public static void main(String argv[]) {

    SignInFrame f = new SignInFrame();

    f.start();
}

public void run() {

    Thread me = Thread.currentThread();
    while (thread == me) {
        repaint();
        try {
            Thread.sleep(10);
        } catch (InterruptedException e) {
            break;
        }
    }
    thread = null;
}}

die Ausnahme:

  init:
  deps-jar:
  Compiling 1 source file to C:\\Users\\ICC\\Documents\\NetBeansProjects\\YahooServer\\build\\classes
  compile-single:
  run-single:
  Uncaught error fetching image:
  java.lang.NullPointerException
          at sun.awt.image.URLImageSource.getConnection(URLImageSource.java:97)
          at sun.awt.image.URLImageSource.getDecoder(URLImageSource.java:107)
          at sun.awt.image.InputStreamImageSource.doFetch(InputStreamImageSource.java:240)
          at sun.awt.image.ImageFetcher.fetchloop(ImageFetcher.java:172)
          at sun.awt.image.ImageFetcher.run(ImageFetcher.java:136)