// Textbook fragment 13.06
/** This class specializes DFS to determine whether the graph is connected. */
public class ConnectivityDFS<V, E> extends DFS <V, E, Object, Boolean> {
  protected int reached;
  protected void setup() { reached = 0; }
  protected void startVisit(Vertex<V> v) { reached++; }
  protected Boolean finalResult(Boolean dfsResult) {
    return new Boolean(reached == graph.numVertices());
  }
}