_o = (Set) (new HashSet());
	public DGraph() {		_e = (Set) (new HashSet());		_v = (Set) (new HashSet());		_o = (Set) (new HashSet());		_shortestPaths = new Dijkstra(this);		_minEdgeLengthCache = 0;		_shortestPathsCache = false;		_apspSource = null;	}