@Override
    public void initialize(AppStateManager stateManager, Application app) {
        super.initialize(stateManager, app);
        this.app = app;
        this.stateManager = stateManager;
        startPhysics();
    }
Initialize this state prior to its 1st update. Should be invoked only by
a subclass or by the AppStateManager.

@param stateManager the manager for this state (not null)
@param app the application which owns this state (not null)
jme3-jbullet/src/main/java/com/jme3/bullet/BulletAppState.java