java.lang.NullPointerException: Canvas3D: null GraphicsConfiguration
    at javax.media.j3d.Canvas3D.checkForValidGraphicsConfig(Canvas3D.java:982)
    at javax.media.j3d.Canvas3D.<init>(Canvas3D.java:1025)
    at wjg.test.MyCone.<init>(MyCone.java:49)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at java.lang.Class.newInstance0(Unknown Source)
    at java.lang.Class.newInstance(Unknown Source)
    at sun.applet.AppletPanel.createApplet(Unknown Source)
    at sun.applet.AppletPanel.runLoader(Unknown Source)
    at sun.applet.AppletPanel.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

package wjg.test;
import java.applet.Applet;
import java.awt.BorderLayout;
import com.sun.j3d.utils.applet.MainFrame;
import com.sun.j3d.utils.geometry.Cone;    //调用生成Cone的Utility包
import com.sun.j3d.utils.geometry.Primitive;
import com.sun.j3d.utils.universe.*;
import javax.media.j3d.*;
import javax.vecmath.*;

public class MyCone extends Applet{

    public BranchGroup createSceneGraph(){
        BranchGroup objRoot = new BranchGroup();    //创建一个分支节点来包含一组对象
        TransformGroup objTrans = new TransformGroup();        //创建转换节点（生成坐标系）
        objRoot.addChild(objTrans);        //将转换节点（坐标系）添加到根节点上
        BoundingSphere bounds = new BoundingSphere(new Point3d(0.0,0.0,0.0),100.0);        //设置场景的有效范围
        Color3f bgColor = new Color3f(0.0f,0.0f,0.0f);        //定义背景颜色
        Background bg = new Background(bgColor);        //创建背景颜色
        bg.setApplicationBounds(bounds);
        objRoot.addChild(bg);         //将背景添加到场景中
        Color3f directionalColor= new Color3f(1.f,1.f,1.f);
        Vector3f vec = new Vector3f(0.f,0.f,-1.f);
        DirectionalLight directionalLight = new DirectionalLight(directionalColor,vec);
        directionalLight.setInfluencingBounds(bounds);
        objRoot.addChild(directionalLight);
        
        //设置外观
        Appearance app = new Appearance();
        Material material =new Material();
        material.setDiffuseColor(new Color3f(1.0f,1.0f,1.0f));
        app.setMaterial(material);
        
        //生成基本的圆锥体
        Cone cone = new Cone(.5f,1.0f,1,app);
        
        //将生成的圆锥添加到场景中
        objRoot.addChild(cone);
        
        return objRoot;
    }
    
    public MyCone(){
        setLayout(new BorderLayout());
        Canvas3D c = new Canvas3D(null);
        add("Center",c);
        BranchGroup scene = createSceneGraph();
        scene.compile();
        SimpleUniverse u = new SimpleUniverse(c);
        u.getViewingPlatform().setNominalViewingTransform();
        u.addBranchGraph(scene);
    }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        new MainFrame(new MyCone(),400,300);
    }

}