public class GravityStateFactory {
public GravityState createGravityState() {
Gravity3DStateFactory gravity3DFactory = new Gravity3DStateFactory();
Gravity3DState gravity3D = gravity3DFactory.createGravity3DState();
Set<TreeLeafState> fallingLeaves = new HashSet<TreeLeafState>();
return new GravityState(gravity3D, fallingLeaves);
}