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

  1. #1
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    Default 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



    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;
      }
    }


  2. #2
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    Default Re: Gotten easy code by proffessor that I don't understand, do you?

    That isn't really how this works. How about you tell us what the functions do and we'll tell you how close you are. Have you stepped through this with a debugger? Have you stepped through it with a piece of paper and a pencil, manually tracing what it's doing? If not, those are your first steps.
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    matitorn (October 8th, 2012)

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

    Why it took such mental gymnastics to do what shouldn't need to be this complicated, though, I don't know.
    Last edited by jps; October 9th, 2012 at 10:41 AM. Reason: Spoonfeeding

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

    Quote Originally Posted by Fazan View Post
    Why it took such mental gymnastics to do what shouldn't need to be this complicated, though, I don't know.
    This was the point of the assignment. I have edited your above post and removed the spoilers.

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    KevinWorkman (October 9th, 2012)

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

    Fair enough. Apologies for breaking the rules. I didn't think I said too much, but I defer to your judgement.

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

    I think I have managed to solve this one on my own now Tried to find where I can put this thread as [SOLVED] so that noone puts energy into it anymore. Where can I find it?

  9. #7
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    Default Re: Gotten easy code by proffessor that I don't understand, do you?

    The announcements page describes how to mark your thread as solved as well as other forum related useful information.

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    matitorn (October 9th, 2012)

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

    Great, thanks!

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