1. @override
void initialize(World world)

Called when the actor is instantiated in the world

Source 

@override
void initialize(World world)
{
    super.initialize(world);
    maxSpeed = 400.0;
    name = "Character";
    this.onLivesChange = _livesChangeEvent.stream.asBroadcastStream();

    new Observable(this.onCollide)
        .where((Actor a) => a is Enemy)
        .throttle(new Duration(seconds: 1))
        .listen( (Actor a) => this._touchedEnemy());
}