从普通图形格式文本文件创建对象。 Java的 dijkstra算法

Question

i want to create objects, vertex and edge, from trivial graph format txt file. one of programmers here suggested that i use trivial graph format to store data for dijkstra algorithm.

the problem is that at the moment all the information, eg, weight, links, is in the sourcecode. i want to have a separate text file for that and read it into the program.

i thought about using a code for scanning through the text file by using scanner. but i am not quite sure how to create different objects from the same file. could i have some help please?

the file is

v0 Harrisburg
v1 Baltimore
v2 Washington
v3 Philadelphia
v4 Binghamton
v5 Allentown
v6 New York
#
v0 v1 79.83
v0 v5 81.15
v1 v0 79.75
v1 v2 39.42
v1 v3 103.00
v2 v1 38.65
v3 v1 102.53
v3 v5 61.44
v3 v6 96.79
v4 v5 133.04
v5 v0 81.77
v5 v3 62.05
v5 v4 134.47
v5 v6 91.63
v6 v3 97.24
v6 v5 87.94

and the dijkstra algorithm code is

Downloaded from: http://en.literateprograms.org/Special:Downloadcode/Dijkstra%27s_algorithm_%28Java%29 */

import java.util.PriorityQueue;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;


class Vertex implements Comparable<Vertex>
{
public final String name;
public Edge[] adjacencies;
public double minDistance = Double.POSITIVE_INFINITY;
public Vertex previous;

public Vertex(String argName) { 
    name = argName;
}

public String toString() {
    return name;
}


public int compareTo(Vertex other)
{
    return Double.compare(minDistance, other.minDistance);
}

}


class Edge
{
public final Vertex target;
public final double weight;

public Edge(Vertex argTarget, double argWeight) { 

    target = argTarget; 
    weight = argWeight; 
}
}


public class Dijkstra
{
public static void computePaths(Vertex source)
{
    source.minDistance = 0.;
    PriorityQueue<Vertex> vertexQueue = new PriorityQueue<Vertex>();
    vertexQueue.add(source);

while (!vertexQueue.isEmpty()) {
    Vertex u = vertexQueue.poll();

        // Visit each edge exiting u
        for (Edge e : u.adjacencies)
        {
            Vertex v = e.target;
            double weight = e.weight;
            double distanceThroughU = u.minDistance + weight;
    if (distanceThroughU < v.minDistance) {
        vertexQueue.remove(v);

        v.minDistance = distanceThroughU ;
        v.previous = u;
        vertexQueue.add(v);

    }

        }
    }
}


public static List<Vertex> getShortestPathTo(Vertex target)
{
    List<Vertex> path = new ArrayList<Vertex>();
    for (Vertex vertex = target; vertex != null; vertex = vertex.previous)
        path.add(vertex);
        Collections.reverse(path);
        return path;
}

public static void main(String[] args)
{

Vertex v0 = new Vertex("Nottinghill_Gate");
Vertex v1 = new Vertex("High_Street_kensignton");
Vertex v2 = new Vertex("Glouchester_Road");
Vertex v3 = new Vertex("South_Kensignton");
Vertex v4 = new Vertex("Sloane_Square");
Vertex v5 = new Vertex("Victoria");
Vertex v6 = new Vertex("Westminster");
v0.adjacencies = new Edge[]{new Edge(v1,  79.83), new Edge(v6,  97.24)};
v1.adjacencies = new Edge[]{new Edge(v2,  39.42), new Edge(v0, 79.83)};
v2.adjacencies = new Edge[]{new Edge(v3,  38.65), new Edge(v1, 39.42)};
v3.adjacencies = new Edge[]{new Edge(v4, 102.53), new Edge(v2,  38.65)};
v4.adjacencies = new Edge[]{new Edge(v5, 133.04), new Edge(v3, 102.53)};
v5.adjacencies = new Edge[]{new Edge(v6,  81.77), new Edge(v4, 133.04)};
v6.adjacencies = new Edge[]{new Edge(v0,  97.24), new Edge(v5, 81.77)};
Vertex[] vertices = { v0, v1, v2, v3, v4, v5, v6 };


    computePaths(v0);
    for (Vertex v : vertices)
{
    System.out.println("Distance to " + v + ": " + v.minDistance);
    List<Vertex> path = getShortestPathTo(v);
    System.out.println("Path: " + path);
}

}
}

and the code for scanning file is

 import java.util.Scanner;
 import java.io.File;
 import java.io.FileNotFoundException;

 public class DataScanner1 {

 //private int total = 0;
 //private int distance = 0; 
 private String vector; 
 private String stations;
 private double [] Edge = new double []; 

 /*public int getTotal(){
    return total;
  }
  */

  /*
  public void getMenuInput(){
    KeyboardInput in = new KeyboardInput;
    System.out.println("Enter the destination? ");
    String val = in.readString();
    return val;
  }
  */


 public void readFile(String fileName) {
   try {
     Scanner scanner =
       new Scanner(new File(fileName));
     scanner.useDelimiter
       (System.getProperty("line.separator")); 
     while (scanner.hasNext()) {
       parseLine(scanner.next()); 
    }
       scanner.close();
   } catch (FileNotFoundException e) {
     e.printStackTrace();
   }
 }



  public void parseLine(String line) {
   Scanner lineScanner = new Scanner(line);
   lineScanner.useDelimiter("\\s*,\\s*");
   vector = lineScanner.next();
   stations = lineScanner.next();
   System.out.println("The current station is " + vector + " and the destination to the next station is " + stations + ".");
   //total += distance;
   //System.out.println("The total distance is " + total);
  }

 public static void main(String[] args) {
  /* if (args.length != 1) {
     System.err.println("usage: java TextScanner2"
       + "file location");
     System.exit(0);
   }
   */
   DataScanner1 scanner = new DataScanner1();
   scanner.readFile(args[0]);
   //int total =+ distance;
   //System.out.println("");
   //System.out.println("The total distance is " + scanner.getTotal());
 }
 }

Answer 1

You are pretty close with it.

To read each line, use String.split(" ") . That will give you an array of Strings for each argument in a line of the file.

For parsing the file, HashMap is your friend here. The source file works with names like "v0", so start by making a HashMap<String, Vertex> which stores "v0" (or whatever key you are looking at) in the key and a new Vertex object initialized with the city name as the value.

In the loop on the second chunk of data (the adjacencies), you want to create an Edge by saying something like new Edge(verticies.get(parsedLine[1]), parsedLine[2])) , then add that to the proper vertex via verticies.get(parsedLine[0]).getAdjacencies().add(..) , substituting the Edge you just created for the ".." in my example.

Note their code defines Vertex.adjacencies as an Edge[], my example requires making it an ArrayList that is initialized in field.