NoSuchElementException and more

Question

My assignment is:

• Create a file that has 2 columns of numbers: Distance and Speed.
• Write a class TravelInfo which has three pieces of information: Speed, Time, Distance.
• The class should also have a method calcTime() which calculates the time it will take to reach a destination based on the distance and speed (recall: Time = Distance/Speed)
• Write a main program that:
  • Creates an ArrayList of TravelInfo objects of size 10.
  • Prompts the user for the name of the file and reads the data into TravelInfo objects
  • Calls the calcTime() method on each TravelInfo object.
  • Creates an output file with the data written in the format: Distance, Time, Speed

Every time I run my program I get an error

Exception in thread "main" java.util.NoSuchElementException

Other than this error I think I have done everything right except maybe calling my method, and I still haven't formatted the output file yet (not quite sure how). I can't continue while I get this error.

Here is my main() method:

public static void main(String[] args) throws IOException {

    Scanner keyboard = new Scanner(System.in);
    ArrayList<TravelInfo> list = new ArrayList<>();

    System.out.println("What is the name of the file?");
    String filename = keyboard.nextLine();
    File f = new File(filename);
    Scanner inputFile = new Scanner(f);
    while(inputFile.hasNext()) {
        int s = inputFile.nextInt();
        int d = inputFile.nextInt();
        int t = inputFile.nextInt();


        TravelInfo p = new TravelInfo(s, d, t);
        list.add(p);
        TravelInfo cls = new TravelInfo(s,d,t);
        cls.calcTime(t);
        cls.calcTime(s);
        cls.calcTime(d);

       // System.out.println("Time is " + cls.calcTime(t));

       /*for(int i=0; i<list.size(); i++) {
           list.get(i).print();
      */ }
        for(TravelInfo k : list)
            System.out.println(k);

        PrintWriter outputFile = new PrintWriter("Data.txt");
        outputFile.println(list);
        //outputFile.println();
        outputFile.close();
    }

}

And my TravelInfo class

public class TravelInfo {
    private int speed;
    private int distance;
    private int time;

    public TravelInfo(int s, int d, int t) {
        speed = s;
        distance = d;
        time = t;
    }
    public int calcTime(int time) {
        time = distance/speed;
        return time;
    }
}

Answer 1

You shall do some more validation, and never use the nextXXX() methods blindly - something like

while(true)
{
    if (!inputFile.hasNextInt()) {
       System.err.println("Reading file failed - invalid format (s)");
       break;
    }
    int s = inputFile.nextInt();
    System.out.println("Reading s = " + s);

    if (!inputFile.hasNextInt()) {
       System.err.println("Reading file failed - invalid format (d)");
       break;
    }
    int d = inputFile.nextInt();
    System.out.println("Reading d = " + d);


    if (!inputFile.hasNextInt()) {
       System.err.println("Reading file failed - invalid format (t)");
       break;
    }
    int t = inputFile.nextInt();
    System.out.println("Reading t = " + t);
    // Do some stuff
}

This way, you will avoid the NoSuchElementException, and the application will terminate gracefully. You will get the debugging output on the console. It will also print out what exactly has been read from the file.

Answer 2

As Dorian said, you're missing some validation:

while(inputFile.hasNext()) // Tells you there is "at least" 1 more element.
{
    int s = inputFile.nextInt();   // Good
    int d = inputFile.nextInt();   // Not good if 's' has taken the last element
    int t = inputFile.nextInt();   // Same as above

    // rest of the code here...
}

I personnally don't like the 'while(true)' stuff, so here is my version.

while(inputFile.hasNextInt())  // I would use 'hasNextInt()' rather than 'hasNext()'
                               // This will make sure the next data can be cast to an Integer
{
    Integer d = null;
    Integer t = null;
    Integer s = inputFile.nextInt();

    if( inputFile.hasNextInt() {
        d = inputFile.nextInt();
        if( inputFile.hasNextInt() {
            t = inputFile.nextInt();
        }
    }

    // 's' will never be null.
    if( d != null && t != null ) {
        TravelInfo p = new TravelInfo(s, d, t);
        list.add(p);
        TravelInfo cls = new TravelInfo(s,d,t);
        cls.calcTime(t);
        cls.calcTime(s);
        cls.calcTime(d);

       // System.out.println("Time is " + cls.calcTime(t));

       /*for(int i=0; i<list.size(); i++)
       {
           list.get(i).print();
      */ }
        for(TravelInfo k : list)
            System.out.println(k);

        PrintWriter outputFile = new PrintWriter("Data.txt");
        outputFile.println(list);
        //outputFile.println();
        outputFile.close();
    }
    else if( inputFile.hasNext()) {
        // At this point, you there the remaining data cannot be safely cast to an Integer.
    }
    else {
       // Not enough data to process.
    }
}

public class TravelInfo {
    private int speed;
    private int distance;
    private int time;

    public TravelInfo(int s, int d, int t) {
        speed = s;
        distance = d;
        time = t;
    }
    public int calcTime(int time) {
        time = distance/speed;
        return time;
    }

    // Override toString() instead of using the default Object.toString()
    @Override
    public String toString() {
        // Return whatever 'String' you want
        return String.format( "%d, %d, %d", speed, distance, time );
    }
}