Ignoring back edges in an undirected graph...

Question

let's say i have a graph with 3 vertices. then let's say i have 2 edges connecting vertex 1 (v1) with vertex 2 (v2), and there's one edge connecting v2 with vertex 3 (v3). i want only to print edges going to each vertex, not 'back' edges. how do i do that?
//given - Graph 'g'
Iterator it = g.vertices();
while(it.hasNext()){
Vertex v = (Vertex)it.next();
VertexElement a = v.element();
System.out.println(vertexElement);
Iterator fit = g.incidentEdges(v);
while(fit.hasNext()){
Edge e = (Edge)fit.next();
EdgeElement = e.element();
System.out.println(EdgeElement);
this prints out every edge associated with each vertex.

Answer 1

alright guys, sorry for the previous confusion... i guess i'll go ahead and show all the code associated so you can get a good idea on what i'm trying to do. we're making an airline reservation system built upon a graph in which the vertices are 'airports' and the edges are 'flights'
the information is stored in a text file, which a certain format for airports and a slightly different format for flights. we read the text file, read in the airports and assign them as vertices, then read in the flights, and assign those to edges on the corresponding vertices (there are 'destination' and 'origin' values so we can keep track of which edge to place the elements) the format of the text file is described in detail in the class code, but i'll give an example at the bottom.
here are the classes
AIRPORT CLASS
* Airport information in text file...
* the information in the text file has 2 sections of data, each section is
* separated by a bang (!) line:
*                � Airport Information
*                � Flight Information
* the information is presented in padded fields of known length. ex. the first
* 3 characters in the airport section is the unique airport abbreviation.
* Fields:                                (variable associated)
* #3 - Airport abbreviation           :  'airportID'
* #1 <padding>                        :
* #5 - Time Zone (offset from GMT)    :  'timeZone'
* #1 <padding>                        :
* #3 - X Coordinate on map            :  'xCoord'
* #1 <padding>                        :
* #3 - Y Coordinate on map            :  'yCoord'
* #1 <padding>                        :
* # remainder - Name of City/Airport  :  'airportCity'
public class Airport {
  private int timeZone, xCoord, yCoord;
  private String airportID = "[UNASSIGNED]", airportCity = "[UNASSIGNED]";
// blank constructor
  public Airport(){
  public Airport(String airportID, int timeZone, int xCoord, int yCoord,
                 String airportCity) {
    this.airportID = airportID;
    this.timeZone = timeZone;
    this.xCoord = xCoord;
    this.yCoord = yCoord;
    this.airportCity = airportCity;
  // accessor methods
  public String getID(){
      return airportID; }
  public int getTimeZone(){
      return timeZone; }
  public int getX(){
      return xCoord; }
  public int getY(){
      return yCoord; }
  public String getCity(){
    return airportCity; }
  // mutator methods
  public void setID(String airportID){
    this.airportID = airportID; }
  public void setTimeZone(int timeZone){
    this.timeZone = timeZone; }
  public void setXcoord(int xCoord){
    this.xCoord = xCoord; }
  public void setYcoord(int yCoord){
    this.yCoord = xCoord; }
  public void setCity(String airportCity){
    this.airportCity = airportCity; }
  // toString
  public String toString(){
    return ("AIRPORT ID: " + airportID + '\n' +
            "TIME ZONE: " + timeZone + '\n' +
            "X/Y: " + xCoord + "/" + yCoord + '\n' +
            "CITY: " + airportCity); }
}FLIGHT CLASS
package lab06;
* Airline Flight Schedule - USA: Starts after the '!' delimiter.
* Fields:                               (variable associated)
* #2 - Airline                       :  'airline'
* #4 - Flight                        :  'flightNum'
* #2 <padding>                       :
* #3 - Origin Airport                :  'originAirport'
* #1 <padding>                       :
* #5 - Departure Time                :  'departTime'
* #2 <padding>                       :
* #3 - Destination Airport           :  'destinationAirport'
* #1 <padding>                       :
* #5 - Arrival Time                  :  'arriveTime'
* #2 <padding>                       :
* #2 - Meals (S=snack/L=lunch/       :
*             D=dinner/B=b-fast/     :
*             #=depends on class)    :  'meals'
* #4 <padding>                       :
* #1 - # of stops during flight      :  'stops'
* #4 <padding>                       :
* #3 - Aircraft type                 :  'aircraftType'
* #12 <padding>                      :
* # remainder - Booking classes      :
*               [IGNORE THIS DATA]   :
public class Flight {
  private int flightNum, stops;
  private String
  airline = "[UNASSIGNED]", originAirport = "[UNASSIGNED]",
  departTime = "[UNASSIGNED]", destinationAirport = "[UNASSIGNED]",
  arriveTime = "[UNASSIGNED]", meals = "[UNASSIGNED]",
  aircraftType = "[UNASSIGNED]";
// blank constructor
  public Flight(){
  public Flight(String airline, int flightNum, String originAirport,
                String departTime, String destinationAirport, String arriveTime,
                String meals, int stops, String aircraftType) {
    this.airline = airline;
    this.flightNum = flightNum;
    this.originAirport = originAirport;
    this.departTime = departTime;
    this.destinationAirport = destinationAirport;
    this.arriveTime = arriveTime;
    this.meals = meals;
    this.stops = stops;
    this.aircraftType = aircraftType;
  // accessor methods
  public String getAirline(){
      return airline; }
  public int getFlightNum(){
      return flightNum; }
  public String getOrigin(){
      return originAirport; }
  public String getDepartTime(){
      return departTime; }
  public String getDestination(){
    return destinationAirport; }
  public String getArriveTime(){
    return arriveTime; }
  public String getMeals(){
    return meals; }
  public int getStops(){
    return stops; }
  public String getAircraftType(){
    return aircraftType; }
  // mutator methods
  public void setAirline(String airline){
    this.airline = airline; }
  public void setFlightNum(int flightNum){
    this.flightNum = flightNum; }
  public void setOrigin(String origin){
    this.originAirport = origin; }
  public void setDepartTime(String departTime){
    this.departTime = departTime; }
  public void setDestination(String destination){
    this.destinationAirport = destination; }
  public void setArriveTime(String arriveTime){
    this.arriveTime = arriveTime; }
  public void setMeals(String meals){
    this.meals = meals; }
  public void setStops(int stops){
    this.stops = stops; }
  public void setAircraftType(String aircraftType){
    this.aircraftType = aircraftType; }
  // toString
  public String toString(){
      return ('\n' + "FLIGHT #" + airline + flightNum + '\n' +
              "ORIGIN AIRPORT: " + originAirport + '\n' +
              "DESTINATION: " + destinationAirport + '\n' +
              "DEPARTS: " + departTime + " ARRIVES: " + arriveTime + '\n' +
              "MEAL ON FLIGHT: " + meals + '\n' +
              "NUMBER OF STOPS: " + stops + '\n' +
              "AIRCRAFT TYPE: " + aircraftType); }
}and here's my driver - it selects the text file (which must be formatted appropriately) and reads in each flight/airport and creates the graph.
MAIN CLASS
import java.io.*;
import java.util.StringTokenizer;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.filechooser.*;
import java.util.Iterator;
import net.datastructures.*;
import java.util.Vector;
public class Driver extends JComponent{
  public static void main(String args[]){
    JPanel contentHolder;
    int status;
    StringTokenizer tokenizer;
    String first_, second_, third_, fourth_, fifth_, sixth_, seventh_,
    eighth_, ninth_, rest_, temp_, airportID, timeZone, xCoord, yCoord, airportCity;
    //create initially empty graph
    Graph g = new AdjacencyListGraph();
    //hash table to store information
    HashTable h = new HashTable();
    //display file chooser
    JFileChooser chooser = new JFileChooser();
    status = chooser.showOpenDialog(null);
    if(status != JFileChooser.APPROVE_OPTION)
      System.out.println("NO FILE CHOSEN.");
    else {
      //read file selected...
      try {
      File x = chooser.getSelectedFile();
      FileReader fr = new FileReader(x);
      BufferedReader inFile = new BufferedReader(fr);
      String info = "";
      String line = inFile.readLine();
      int numLines = 0; //keep track of # of lines in our file (if desired)
      boolean readingFlights = false;
      while(line != null){
        if (line.equals("!")) {  //we found the bang line, and now start reading
                                 //flight objects.
            line = inFile.readLine();
            readingFlights = true; }
        tokenizer = new StringTokenizer(line);
        int numTokens = tokenizer.countTokens();
        if (readingFlights) {
            first_ = tokenizer.nextToken();   //airline
            second_ = tokenizer.nextToken();  //flightNum
            third_ = tokenizer.nextToken();   //originAirport
            fourth_ = tokenizer.nextToken();  //departTime
            fifth_ = tokenizer.nextToken();   //destinationAirport
            sixth_ = tokenizer.nextToken();   //arriveTime
            //'meals' is a special case, since not all flights even have a meal
            //designated in the text file. those flights w/out meals can throw
            //our tokenizer off track, so we use a substring methods from here.
            seventh_ = line.substring(30,35); //meals
            eighth_ = line.substring(36,37);  //stops
            ninth_ = line.substring(41,44);   //aircraftType
            rest_ = line.substring(56,69);    //read rest of line
          //a test to see if the substrings are lined up right...
          //System.out.println("1st " + first_ + '\n' + "2nd " + second_ + '\n'
          //                 + "3rd " + third_ + '\n' + "4th " + fourth_ + '\n'
          //                 + "5th " + fifth_ + '\n' + "6th " + sixth_ + '\n'
          //                 + "7th " + seventh_ + '\n' + "8th " + eighth_ +
          //                 '\n' + "9th " + ninth_ + '\n' + "rest: " + rest_);
            //create flight object from this information
            //if(seventh_ == ""){
            Flight f1 = new Flight(first_, (Integer).parseInt(second_), third_,
                                   fourth_, fifth_, sixth_, seventh_,
                                   (Integer).parseInt(eighth_), ninth_);
            Vertex v1 = (Vertex)h.get(f1.getOrigin());
            Vertex v2 = (Vertex)h.get(f1.getDestination());
            Edge e1 = g.insertEdge(v1, v2, f1);
    } else {
        first_ = tokenizer.nextToken();       //airportID
        second_ = tokenizer.nextToken();      //timeZone
        third_ = tokenizer.nextToken();       //xCoord
        fourth_ = tokenizer.nextToken();      //yCoord
        fifth_ = tokenizer.nextToken("");     //airportCity (reads rest of line)
        //create airport object from this information
        Airport a1 = new Airport(first_, (Integer).parseInt(second_), (Integer).
                                 parseInt(third_), (Integer).parseInt(fourth_),
                                 fifth_);
        Vertex v1 = g.insertVertex(a1);
        h.put(a1.getID(), v1);
    } //close else
        line = inFile.readLine();
        numLines++; } //stop reading file
       //show info on screen
        Iterator it = g.vertices();
          while(it.hasNext()){
          Vertex v = (Vertex)it.next();
          Airport a = (Airport)v.element();
          System.out.println(a.getID());
        Iterator fit = g.incidentEdges(v);
          while(fit.hasNext()){
          Edge e = (Edge)fit.next();
          Flight curFlight = (Flight)e.element();
          //if the origin of the current flight is the same as the current
          //airport's ID then we wanna list those because those are the outgoing
          //flights from the current airport
          //System.out.println(curFlight.getOrigin().compareTo(a.getID()));
          System.out.println(curFlight);
          System.out.println("--------------------------------------" + '\n');
    catch(FileNotFoundException exception)
    { System.out.println("The file " + chooser.getSelectedFile() +
                         " was not found."); }
    catch(IOException exception)
    { System.out.println(exception); }
}an example text file would look like this...
ABQ -0800 195 275 Albuquerque, New Mexico
DEN -0800 215 205 Denver, Colorado
DTW -0600 445 140 Detroit, Michigan
UA 785  ABQ  645A  DEN  757A  S     0    733            F  Y  B  M  Q
CO 195  DEN  251P  ABQ  410P        0    73S            F  A  Y  Q  H
AA 305  DTW  105P  ABQ  446P  #     1    72S            F  Y  H  B  Mthe first three lines are airports, separated by the bang line, then the next three lines are airports...
the way the flights are set up, i want to display only outgoing flights...
for example, under the Alberquerque airport display, the output will show flight UA785 leaving Alberquerque and arriving at Denver, BUT it will also show flights CO195 & AA305 coming INTO Alberquerque from Denver and Detroit, respectively. I don't want to see that. I only want to see the flights LEAVING a given airport.
-Chris