为什么我的obj档无法显示出来

主题内容： import java.applet.Applet;
import java.awt.BorderLayout;
import java.awt.Frame.css;
import java.awt.event._.css;
import com.sun.j3d.utils.applet.MainFrame;
import com.sun.j3d.utils.universe._.css;
import com.sun.j3d.utils.geometry.ColorCube.css;
import javax.media.j3d._.css;
import javax.vecmath.*;
import java.awt.GraphicsConfiguration.css;

import com.sun.j3d.loaders.objectfile.ObjectFile.css;
import com.sun.j3d.loaders.Scene.css;
import java.net.URL.css;
import java.net.MalformedURLException.css;

import java.awt.*;

public class applet3D extends Applet {

private URL filename=null;

private boolean spin=false;
private SimpleUniverse u;
private BoundingSphere bounds;


public applet3D() {


}
public BranchGroup createSceneGraph() {

BranchGroup objRoot = new BranchGroup();

TransformGroup objScale = new TransformGroup();
Transform3D t3d = new Transform3D();

t3d.setScale(0.5);
objScale.setTransform(t3d);
objRoot.addChild(objScale);


TransformGroup objTrans = new TransformGroup();

objTrans.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);


objTrans.setCapability(TransformGroup.ALLOW_TRANSFORM_READ);
objScale.addChild(objTrans);

int flags=ObjectFile.RESIZE;
ObjectFile f=new ObjectFile(flags);
Scene s=null;
try{
s=f.load(filename);
}
catch (Exception e)
{
System.out.println("a.obj");
e.printStackTrace();
}



Transform3D yAxis = new Transform3D();
Alpha rotationAlpha = new Alpha(-1, 4000);

RotationInterpolator rotator =
new RotationInterpolator(rotationAlpha, objTrans, yAxis,
0.0f, (float) Math.PI*2.0f);


BoundingSphere bounds = new BoundingSphere();
rotator.setSchedulingBounds(bounds);
objTrans.addChild(rotator);

return objRoot;

}

public void init() {

if (filename == null)
{
try
{
URL path = getCodeBase();
filename = new URL("./a.obj");
System.out.println("filename:" + filename);
}
catch (MalformedURLException e)
{
//System.out.println(filename);
System.err.println(e);
System.exit(1);
}
}

setLayout(new BorderLayout());
GraphicsConfiguration config =
SimpleUniverse.getPreferredConfiguration();
Canvas3D canvas3D = new Canvas3D(config);
add("Center", canvas3D);

BranchGroup scene = createSceneGraph();
scene.compile();


SimpleUniverse simpleU = new SimpleUniverse(canvas3D);



simpleU.getViewingPlatform().setNominalViewingTransform();
simpleU.addBranchGraph(scene);
}


public static void main(String[] args) {
Frame frame = new MainFrame(new applet3D(), 500, 500);
}

}


好像是URL 那边有点小出错 各位老手们 能为我解答一下吗??