// World object in it, the engine can always get to World quickly.
// - ST 1/10/07
public volatile boolean comeUpForAir = false; // NOPMD pmd doesn't like 'volatile'
public World() {
_turtleShapeList = new ShapeList();
_linkShapeList = new ShapeList();
_observer = createObserver();
_observers = new ArrayAgentSet(Observer.class, 1, "observers", false, this);
linkManager = new LinkManager(this);