How to change data(string) from a txt file so I can do mathematical operations on that data?

Question

For my question I saw an reminder that many have already asked this question, but I cant seem to find a decent answer. Or answers are in other programing languages which doesnt help me. So I will ask again :)

I have to read from a txt file, then do some mathematical operations on the data. This data is in 10000 lines and in each line is 20 numbers separated by a semicolon. For reading from txt file I used BufferedReader which gives me string. I probably have to change this string to int. So far so good. Then I have to make it into an array...how? Does the array need to be two dimensional or one dimension is enough?

Then in the end I have to write results in different txt files. I have to write to different files numbers that are dividable by 3, 11 and 5, then I have to sum each row in txt file and make the sum of whole txt numbers. Is what I wrote until now ok? Should I delete something or?

class Assignment {

    public static void main (String[] args) {

        String nameFile = "numbers.txt";
        String contentFile = readFromFile(nameFile);
        List<Integer> divideNumber = stringToIntList(contentFile);

        List<Integer> divisibleNo = processedData(divideNumber);

        System.out.println(divideNumber);
    }

    private static String readFromFile(String nameFile) {
        String content = "";
        try {
            File file = new File(nameFile);
            BufferedReader read = new BufferedReader(new FileReader(file));

            String line = read.readLine();
            while(line != null) {
                System.out.println(line);
                line = read.readLine();
                content = line;
            }
            read.close();
        } catch (IOException e) {
            System.out.println("There was an error reading from the file");
        }
        return content;
    }

    private static List<Integer> stringToIntList(String contentFile) {
        return Arrays
            .stream(contentFile.split("; "))
            .map(Integer::parseInt)
            .collect(Collectors.toList());
    }

    private static int processedData(int divideNumber) {
        try {
            for(int i = 0; i < divideNumber; i++) {
                if((divideNumber % 3 == 0) || (divideNumber % 5 == 0) || (divideNumber % 11 == 0)) {
                System.out.println(divideNumber);
                }
            }
        }
        catch(NumberFormatException e){
            System.out.println("It is not a number"); 
        }
        return divideNumber;
    }
}

Answer 1

Use a Scanner with appropriate delimiter:

List<Integer> list = new ArrayList<>();
Scanner scanner = new Scanner(new FileInputStream(nameFile))
   .useDelimiter("\\D+");
while (scanner.hasNext()) {
    int i = scanner.nextInt();
    list.add(i);
}