Collision related "urgent"

Question

I'm new to Java3D. I'm going to make the object move by a interpolator after collision. However, when run the code below, it always gives an exception: javax.media.j3d.RestrictedAccessException: Group: only a BranchGroup node may be added
at javax.media.j3d.Group.addChild<Group.java:260>
at CollisionDetector.processStimulus<CollisionDetector.java:43>
at javax.media.j3d.BehaviorSceduler.doWork<BehaviorScheduler.java:172>
at javax.media.j3d.J3dThread.run<J3dThread.java:250>
public class CollisionDetector extends Behavior {
private WakeupOnCollisionEntry wEnter;
private WakeupOnCollisionExit wExit;
private boolean wait2Enter;
private Sphere shape;
private PositionPathInterpolator ppi;
private TransformGroup group1;
public CollisionDetector(Sphere s, TransformGroup g, PositionPathInterpolator d) {
     shape = s;
     ppi = d;
     group1 = g;
public void initialize() {
wEnter = new WakeupOnCollisionEntry(shape);
wakeupOn(wEnter);
public void processStimulus(Enumeration criteria) {
System.out.println("Enter!");
     group1.addChild(ppi);
wakeupOn(wEnter);
Thx a lot

Answer 1

The problem there is that you can't add a new PathInterpolator to a live branchgroup. I'm guessing that what you need to do may be to create an object that contains a branchgroup with a pathinterpolator attached to it and change the parameters on the interpolator from your behaviour.