[SOLVED] Gotten easy code by proffessor that I don't understand, do you?

Gotten easy code by proffessor that I don't understand, do you?

Hi everyone,

I'm very, very new to java, but since i'm a girl studying a master in technologies I've been assigned to create several computer codes to solve optimization problems in a course of applied optimization. My problem is, I don't even understand some of the code given to us... :/ Can you help me? The only help I have gotten is that I have to use the functions readGraph, readLine, readInteger and readString. Can you comment it and tell me what the functions do? The meaning of them is to read in a example file of the format below. This represents a network directed graph. The first row (8) is the number of nodes. The second row and down represents bows/arcs between nodes. Eg, from node 1 goes an arc to node 3. Thank you so very much, would really appreciate it! :)

8
1 3
1 4
1 7
1 8
3 2
3 7
4 3
5 1
5 4
6 1
6 5
7 2
7 8
8 6

Code :

private static MyDigraph readGraph(String fileName)
  {
    MyDigraph G = null;
 
    int lineNum = 0;
    String line = null;
    StringTokenizer temp;
    BufferedReader inFile = null;
 
    try {
      inFile = new BufferedReader(new FileReader(fileName));
    }
    catch (FileNotFoundException e) {
      System.out.println("?? file not found");
      return null;
    }
 
    if ((line = readLine(inFile)) == null) {
      System.out.println("?? file is empty");
      return null;
    }
    else {
      lineNum++;
      temp = new StringTokenizer(line);
      try {
        if (temp.countTokens() != 1) {
          throw new IllegalArgumentException();
        }
        int n = Integer.parseInt(temp.nextToken());
        G = new MyDigraph(n);
      }
      catch (IllegalArgumentException e) {
        System.out.println("?? format error on line #" + lineNum);
        return null;
      }
    }
 
    while ((line = readLine(inFile)) != null) {
      lineNum++;
      temp = new StringTokenizer(line);
      try {
        if (temp.countTokens() != 2) {
          throw new IllegalArgumentException();
        }
        int u = Integer.parseInt(temp.nextToken());
        int v = Integer.parseInt(temp.nextToken());
        G.insertEdge(u, v);
      }
      catch (IllegalArgumentException e) {
        System.out.println("?? format error on line #" + lineNum);
      }
    }
    return G;
  }
 
  private static int readInteger(String prompt)
  {
    int temp = 0;
 
    while (true) {
      try {
        temp = Integer.parseInt(readString(prompt));
        break;
      }
      catch (NumberFormatException e) {
        System.out.println("?? format error");
      }
    }
    return temp;
  }
 
  private static String readString(String prompt)
  {
    StringTokenizer temp = null;
    BufferedReader stdin = new BufferedReader
			  (new InputStreamReader(System.in));
 
    while (true) {
      System.out.print(prompt);
      System.out.flush();
      temp = new StringTokenizer(readLine(stdin));
      if (temp.countTokens() == 1) break;
      System.out.println("?? format error");
    }
    return temp.nextToken();
  }
 
  private static String readLine(BufferedReader inFile)
  {
    String line = null;
 
    try {
      line = inFile.readLine();
    }
    catch (IOException e) {
      System.err.println("?? beats me ...");
      System.exit(0);
    }
    return line;
  }
}