Question

I’m writing a program in Java and one of the things that I need to do is to create a set of every valid location for a shortest path problem. The locations are defined in a .txt file that follows a strict pattern (one entry per line, no extra whitespace) and is perfect for using .nextLine to get the data. My problem is that 241 lines into the file (out of 432) the scanner stops working 3/4 of the way through an entry and doesn’t recognize any new lines.

My code:

    //initialize state space
private static Set<String> posible(String posLoc) throws FileNotFoundException {
    Scanner s = new Scanner(new File(posLoc));
    Set<String> result = new TreeSet<String>();
    String availalbe;
    while(s.hasNextLine()) {
        availalbe = s.nextLine();
        result.add(availalbe);
    }
    s.close();
    return result;
}

The Data

Shenlong Gundam
Altron Gundam
Tallgee[scanner stops reading here]se
Tallgeese II
Leo (Ground)
Leo (Space)

Of course, “scanner stops reading here” is not in the data, I’m just marking where scanner stops reading the file. This is 3068 bytes into the file, but that shouldn’t affect anything because in the same program, with nearly identical code, I’m reading a 261-line, 14KB .txt file that encodes the paths. Any help would be appreciated.

Thank you.

Answer 1

There’s a problem with Scanner reading your file but I’m not sure what it is. It mistakenly believes that it’s reached the end of file when it has not, possibly due to some funky String encoding. Try using a BufferedReader object that wraps a FileReader object instead.

e.g.,

   private static Set<String> posible2(String posLoc) {
      Set<String> result = new TreeSet<String>();
      BufferedReader br = null;
      try {
         br = new BufferedReader(new FileReader(new File(posLoc)));
         String availalbe;
         while((availalbe = br.readLine()) != null) {
             result.add(availalbe);            
         }
      } catch (FileNotFoundException e) {
         e.printStackTrace();
      } catch (IOException e) {
         e.printStackTrace();
      } finally {
         if (br != null) {
            try {
               br.close();
            } catch (IOException e) {
               e.printStackTrace();
            }
         }
      }
      return result;
  }

Edit
I tried reducing your problem to its bare minimum, and just this was enough to elicit the problem:

   public static void main(String[] args) {
      try {
         Scanner scanner = new Scanner(new File(FILE_POS));
         int count = 0;
         while (scanner.hasNextLine()) {
            String line = scanner.nextLine();
            System.out.printf("%3d: %s %n", count, line );
            count++;
         }

I checked the Scanner object with a printf:

System.out.printf("Str: %-35s size%5d; Has next line? %b%n", availalbe, result.size(), s.hasNextLine());

and showed that it thought that the file had ended. I was in the process of progressively deleting lines from the data to file to see which line(s) caused the problem, but will leave that to you.