Question

Suppose I have ArrayList with following contents

public void add() {

    obj.add(1);
    obj.add(123456789);
    obj.add(1.222);
    obj.add(2.333);  

    obj.add(2);
    obj.add(9876541);
    obj.add(4.555);
    obj.add(7.888);



}

I want the contents of the ArrayList to be written in the txt file as follows

1,123456789,1.222,2.333
2,9876541,4.555,7,888 

I have following code to write the contents to the file

  public void createCSV() {

    try {
        FileWriter fos = new FileWriter(
                "/home/data.txt");
        PrintWriter out = new PrintWriter(fos);

        for (int i = 0; i < obj.size(); i++) {

            out.write(String.valueOf(obj.get(i)));
            out.write(",");

        }
        out.close();

    } catch (Exception e) {

    }
}

public static void main(String[] args) {

    JavaOp_CSV x = new JavaOp_CSV();
    x.add();
    x.createCSV();

}

As of now the contents in the file is

1,123456789,1.222,2.333,

Can anybody provide me with a logic to get the o/p as mention above??
Thanks in advance

Answer 1

Use a StringBuilder to build the string you will later write to file, and keep a count i on the elements.

if i % 4 == 0 – add a line break

else: add a ','.

Note: You need to avoid adding the new line at the first element, and possibly the last as well if total_num_elements % 4 != 0

It can be easily done duing post processing using StringBuilder.deleteCharAt()