dynamicsWorld.setInternalTickCallback(new InternalTickCallback() {
                @Override
                public void internalTick(DynamicsWorld dynamicsWorld, float timeStep) {
                    try{
                    Dispatcher dispatcher = dynamicsWorld.getDispatcher();
                    int manifoldCount = dispatcher.getNumManifolds();
                    System.out.println(manifoldCount);
                    for (int i = 0; i < manifoldCount; i++) {
                        PersistentManifold manifold = dispatcher.getManifoldByIndexInternal(i);
                        // The following two lines are optional.
                        RigidBody object1 = (RigidBody)manifold.getBody0();
                        RigidBody object2 = (RigidBody)manifold.getBody1();
                        if (object1 != object2){
                        RigidBody physicsObject1 = (RigidBody)object1.getUserPointer();
                        RigidBody physicsObject2 = (RigidBody)object2.getUserPointer();
                        boolean hit = false;
                        javax.vecmath.Vector3f normal = null;
                        for (int j = 0; j < manifold.getNumContacts(); j++) {
                            ManifoldPoint contactPoint = manifold.getContactPoint(j);
                            if (contactPoint.getDistance() < 0.0f) {
                                hit = true;
                                normal = contactPoint.normalWorldOnB;
                                break;
                            }
                        }
                        if (hit) {

                            // Collision happened between physicsObject1 and physicsObject2. Collision normal is in variable 'normal'.
                            System.out.println("Collided!");
                        }
                    }
                    }
                    }catch (Exception e){
                        System.out.println("Much exception. Wow.");
                        e.printStackTrace();
                    }
                }
            }, null);