public abstract class Dijkstra {
  private static final int INFINITE = Integer.MAX_VALUE;
  protected InspectableGraph graph;
  protected PriorityQueue Q; // priority queue used by the algorithm
  public Object execute(InspectableGraph g, Vertex start) {
    graph = g;
    dijkstraVisit(start);
    return distances();
  }
  // initialization
  abstract void init();
  // create an empty priority queue
  abstract PriorityQueue initPQ(Comparator comp); 
  // return the weight of edge e
  abstract int weight(Edge e); 
  // attach to u its locator loc in Q
  abstract void setLocator(Vertex u, Locator loc); 
  // return the locator attached to u
  abstract Locator getLocator(Vertex u); 
  // attach to u its distance dist
  abstract void setDistance(Vertex u, int dist); 
  // return the vertex distances in a data structure
  abstract Object distances(); 
  // return as an int the key of a vertex in Q
  private int value(Locator u_loc) {
    return ((Integer) u_loc.key()).intValue();
  }