/**
 * Representation of an undirected graph edge
 */
public class Edge {
  
  // instance variables
  public Vertex vertex1, vertex2;  // vertices at either end of this edge
  public double weight;            // distance between vertices (weight)
  
  /**
   * Construct a new edge
   * @param v1 vertex at one end of this edge
   * @param v2 vertex at the other end of this edge
   * @param wt the distance or weight of this edge
   */
  public Edge(Vertex v1, Vertex v2, double wt) {
    vertex1 = v1;
    vertex2 = v2;
    weight = wt;
  }
  
  /**
   * Return the other vertex associated with this edge
   * @param v one of the vertices on this edge
   * @return the other vertix on this edge
   * @throws IllegalArgumentException if v is not one of the
   *         vertices on this edge
   */
  public Vertex opposite(Vertex v) {
    throw new UnsupportedOperationException();
  }
}