What is the Java Implementation for This?

[Fudgie Braun]

I have a Windows text file with the following info inside it:

25 05 38 26 53 04
07 45 50 33 19 34
55 25 21 30 09 39
26 11 30 12 13 41
32 23 44 11 50 39
45 30 07 44 55 54
21 10 35 46 48 27
52 41 05 53 11 50
40 38 17 43 10 54
45 27 29 12 39 31
24 42 38 02 18 09
13 43 28 06 53 30
45 47 29 30 53 13
38 45 28 48 47 36
25 34 18 06 07 55

How can I code them to break that info apart into six columns and put each column into their own array? (Like in the image below...)


{If you can't still see the image, kindly click on this link.. - webpage )

[Stephan van Hulst]

Keep track of a list of columns, and repeatedly iterate over the columns while you have input:

List<List<Integer>> columns = new ArrayList<>(NUMBER_OF_COLUMNS);

for (var i = 0; i < NUMBER_OF_COLUMNS; i++)
  columns.add(new ArrayList<Integer>());

while (scanner.hasNextInt()) {
  for (var column: columns) {
    if (!scanner.hasNextInt())
      break;

    column.add(scanner.nextInt());
  }
}

Now that you have a list of columns (with each column being a list of integers), you can convert them all to arrays if you really wanted to, but I would prefer keeping them as lists.

[Fudgie Braun]

By the way, where does the text file reading part come in?

Please bear with me - I don't seem to see it in the code...
So sorry :-(

[Stephan van Hulst]

It's the scanner variable. You create it like this:

private static List<List<Integer>> readIntegerColumns(Path path, int numberOfColumns) throws IOException {
  List<List<Integer>> columns = new ArrayList<>(numberOfColumns);
 
  for (var i = 0; i < numberOfColumns; i++)
    columns.add(new ArrayList<Integer>());

  try (
    var reader  = Files.newBufferedReader(path);
    var scanner = new Scanner(reader);
  ) {
    while (scanner.hasNextInt()) {
      for (var column: columns) {
        if (!scanner.hasNextInt())
          break;
 
        column.add(scanner.nextInt());
      }
    }
  }

  return columns;
}

public static void main(String... args) throws Exception {
  var columns = readIntegerColumns(Paths.get("columns.txt"), 6);
}

By default, a Scanner will split the input into tokens that are delimited by whitespace, no matter whether the whitespace is a space or a new line. This will cause scanner.nextInt() to return the next token as an int, no matter how your file is formatted, as long as each individual token is a valid integer and they are separated by whitespace and nothing else.

Be sure to declare the scanner and the reader inside the parentheses of the try-statement. It will ensure that the file is closed after you're done reading it.

[Campbell Ritchie]

Nice bit of code, but I think I would change this:-if (!scanner.hasNextInt()) {    break; }toif (!scanner.hasNextInt()) {    throw new IllegalArgumentException(            "Number out of sequence in file."); }If you get any situation where you don't have a next int, that means the file has a line with 5 or 7 numbers in, or a non‑number, so the file is corrupt and you should stop reading. Should I throw a different sort of exception?

[Stephan van Hulst]

Campbell Ritchie wrote:If you get any situation where you don't have a next int, that means the file has a line with 5 or 7 numbers in, or a non‑number, so the file is corrupt and you should stop reading.

I don't agree. The formatting of the file itself is inconsequential. It's just a bunch of integers that get distributed over different lists.

If you want to deduce the number of columns from the formatting, you should probably perform some special processing on the first line first.

If you don't care that the number of integers is a multiple of the number of columns, but you still want to check that the input doesn't contain invalid tokens, you should probably do it like this:

if (scanner.hasNextInt())
  column.add(scanner.nextInt());

else if (scanner.hasNext())
  throw new InputMismatchException("The input may only contain integers.");

else
  break;

Should I throw a different sort of exception?

InputMismatchException or an appropriate custom exception.