如何在每第 5 个数字后开始一个新行？

Question

I'd like get some help to solve the issue with having a new line after every fifth number. I put random numbers between 1 and 90 into an array list and then write it into a file. (Later I'd like to sort the list and everything like that hence I'm using an ArrayList instead of writing the numbers immediately into the file.)

public class Lotto {

    static ArrayList<Integer> list = new ArrayList();


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


          randomNumber();
          fileReader();
    }

    public static void printHeader() {
        System.out.println("Week"
                + "|Numbers                           "
                + "\n"
                + "----+"
                + "-----------------------+");
    }

    public static void randomNumber() {
        int num;
        int n = 5;

      //  String str = String.valueOf(num);

        list = new ArrayList<>();
        try {


            FileWriter writer = new FileWriter("/Users/xyz/desktop/lotto2010.txt");
            BufferedWriter bw = new BufferedWriter(writer);

            for (int i = 1; i <= 260; i++) {
            double number = Math.random() * 90;

            num = (int) number;


            list.add(num);
            if((i % n) == 0) bw.newLine();

            }

            bw.write(list.toString());
            bw.close();

        } catch (IOException ex) {
            System.out.println("Couldn't write the file or directory doesn't exist" + ex.getMessage());
        }
    }

    public static void fileReader() throws IOException {


        FileReader fileReader = new FileReader("/Users/xyz/desktop/lotto2010.txt");
        String allText;
        try (PrintWriter writer = new PrintWriter("/Users/xyz/desktop/lotto2011.txt")) {
            BufferedReader br = new BufferedReader(fileReader);


            allText = br.readLine();

                writer.print(allText);            

        }
        System.out.println(allText);

    }
}

Answer 1

添加一个loop ，检查i % 5 == 0 ，添加/n或bw.newLine();

Answer 2

PsuedoCode :

for (int i = 0; i < array.size(); i++{
    println(array(i));
    if(i % 5 == 0){
        println();
    }
}

Answer 3

This will do the needful, what you are doing is that, while generating numbers you are adding it to the list and writing a newline at the same time after every 5 numbers. Though you should do it while iterating through the array. Before iteration, you can modify your array using sorting or anything

FileWriter writer = new FileWriter("/Users/xyz/desktop/lotto2010.txt");
BufferedWriter bw = new BufferedWriter(writer);

for (int i = 1; i <= 260; i++) {
    double number = Math.random() * 90;
    num = (int) number;
    list.add(num);
}

// optional step like sorting, as per your question
Collections.sort(list);

for (int i = 0; i < list.size(); i++) {
     bw.write(list.get(i).toString());
     if(i!=0 && i % n == 0) {
         bw.newLine();
     } else {
         bw.write(", ");
     }
}

bw.close();

getting output like this -

9, 10, 10, 10, 11
11, 11, 12, 12, 13
13, 13, 13, 13, 13
14, 14, 14, 14, 15
16, 16, 17, 17, 17
18, 18, 19, 19, 19
19, 20, 21, 21, 21
22, 23, 23, 23, 23
23, 24, 24, 24, 25
26, 26, 26, 26, 26
.............