Applet java

Bonjour,

j'ai réaliser une applet java qui permet d'afficher une webcam sous applet mais j'ai une petit erreur pas le corrigé quelqu'un peut m'aider .merci
voila code source:


import java.awt.*;
import java.applet.*;
/**
* This class reads PARAM tags from its HTML host page and sets
* the color and label properties of the applet. Program execution
* begins with the init() method.
*/
public class Applet1 extends Applet implements Runnable
{
Thread tcam;
MediaTracker track = new MediaTracker(this);
Image i;
public void init()
{
}
public void start (){
if(tcam==null){
tcam=new Thread(this);
tcam.start ();
System.out.println("Start Cam()");
}
}
public void stop (){
if(tcam!=null){
tcam=null;
tcam.stop ();
System.out.println("Stop Cam()");
}
}
public void run(){
while(true){
repaint();
try{
tcam.sleep(1000);//pause de 1 seconde
System.out.println("Refresh Cam()");
}catch(InterruptedException e) {
}
}
}
public void paint(Graphics g){
i = getImage(getCodeBase(),"picture.jpg");
track.addImage(i,0); //0 était sencé être l'indice du tableau
try {
track.waitForID(0); //le programme attends le complet chargement de l'image
} catch (InterruptedException e) { }
if((i.getWidth(this)==320) & (i.getHeight(this)==240))
{
g.drawImage(i,0,0,this);
}
i.flush();
}
public void update(Graphics g){
paint(g);
}
private final String labelParam = "label";
private final String backgroundParam = "background";
private final String foregroundParam = "foreground";
/**
* Reads parameters from the applet's HTML host and sets applet
* properties.
*/
private void usePageParams()
{
final String defaultLabel = "Default label";
final String defaultBackground = "C0C0C0";
final String defaultForeground = "000000";
String labelValue;
String backgroundValue;
String foregroundValue;
/**
* Read the <PARAM NAME="label" VALUE="some string">,
* <PARAM NAME="background" VALUE="rrggbb">,
* and <PARAM NAME="foreground" VALUE="rrggbb"> tags from
* the applet's HTML host.
*/
labelValue = getParameter(labelParam);
backgroundValue = getParameter(backgroundParam);
foregroundValue = getParameter(foregroundParam);
if ((labelValue == null) || (backgroundValue == null) ||
(foregroundValue == null))
{
/**
* There was something wrong with the HTML host tags.
* Generate default values.
*/
labelValue = defaultLabel;
backgroundValue = defaultBackground;
foregroundValue = defaultForeground;
}
/**
* Set the applet's string label, background color, and
* foreground colors.
*/
label1.setText(labelValue);
label1.setBackground(stringToColor(backgroundValue));
label1.setForeground(stringToColor(foregroundValue));
this.setBackground(stringToColor(backgroundValue));
this.setForeground(stringToColor(foregroundValue));
}
/**
* Converts a string formatted as "rrggbb" to an awt.Color object
*/
private Color stringToColor(String paramValue)
{
int red;
int green;
int blue;
red = (Integer.decode("0x" + paramValue.substring(0,2))).intValue();
green = (Integer.decode("0x" + paramValue.substring(2,4))).intValue();
blue = (Integer.decode("0x" + paramValue.substring(4,6))).intValue();
return new Color(red,green,blue);
}
/**
* External interface used by design tools to show properties of an applet.
*/
public String[][] getParameterInfo()
{
String[][] info =
{
{ labelParam, "String", "Label string to be displayed" },
{ backgroundParam, "String", "Background color, format \"rrggbb\"" },
{ foregroundParam, "String", "Foreground color, format \"rrggbb\"" },
};
return info;
}
Label label1 = new Label();
/**
* Intializes values for the applet and its components
*/
void initForm()
{
this.setBackground(Color.lightGray);
this.setForeground(Color.black);
label1.setText("label1");
this.setLayout(new BorderLayout());
this.add("North",label1);
}
}



voici l'erreur quand fait run:

java.lang.NullPointerException
at Applet1.stop(Applet1.java:28)
at sun.applet.AppletPanel.run(AppletPanel.java:535)
at java.lang.Thread.run(Thread.java:722)