在继承panel类时，如何添加图片

Question

import java.awt.*;
import java.applet.*;

public class picture extends Panel{
Image backGroundImage;

public void init(){

       backGroundImage=getToolkit().getImage("tianjin.gif");

}
public void paint(Graphics g){
   g.drawImage(backGroundImage,0,50,this);

}

}编译没有问题，但在执行时无法加载图片，出现can't be cast to java.applet.Applet