Write the contents of Arraylist to txt file in Java

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

Is the question 'how to get rid of the last comma' or 'How to insert an enter after 4 fields' or even something else? — Veger
– Veger, Commented Mar 2, 2012 at 9:46
I think you should use a different structure. I suppose that your 1 and 2 are "rows" in the output. — dacwe
– dacwe, Commented Mar 2, 2012 at 9:47
I would like to get rid of the comma and to insert enter after 4 fields too — user745475
– user745475, Commented Mar 2, 2012 at 9:56

amit · Accepted Answer · 2012-03-02 09:47:12Z

3

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()

answered Mar 2, 2012 at 9:47

amit

179k27 gold badges245 silver badges348 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

neorc · Accepted Answer · 2012-03-02 10:01:27Z

2

You can also try org.apache.commons.lang.StringUtils, it has a join method that meets your need.

StringUtils.join(obj.toArray(), ',');

Or you can only determine whether it's the first element or the last element.

answered Mar 2, 2012 at 10:01

neorc

2771 gold badge3 silver badges11 bronze badges

Collectives™ on Stack Overflow

Write the contents of Arraylist to txt file in Java

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related