Why do new lines keep appearing every time I append using "[,\n]" delimiter?

Question

I'm new to java programming, and I currently build a program that updates an information from a user through file handling.

For instance, I have this initially saved in the notepad.

Milo,10,India
Jacob,15,California
Shan,7,France

I want to change the country. So I initialized a scanner to read every line in the file, with the delimiter ("[,\n]"). I was able to change it, but every time I do any changes, new lines appear every after each lines.

The output every time I append is like this: The new lines are appearing randomly, and I don't know why.

Milo,10,Italy
Jacob,15,California



Shan,7,France

Here is my code:

private static Scanner x;
    
    public static void main(String[] args) throws IOException {
        File file = new File("rewrite.txt");
        String nameString = "Milo";
        String newcountry = "Italy";
        
        String tempFile = "temp.txt";
        File oldFile = new File("rewrite.txt");
        File newFile = new File(tempFile);
        String name = ""; 
        String age = "";
        String country = "";
        
        try {
            FileWriter fw = new FileWriter(tempFile, true);
            BufferedWriter bw = new BufferedWriter(fw);
            PrintWriter pw = new PrintWriter(bw);
            x = new Scanner(new File("rewrite.txt"));
            x.useDelimiter("[,\n]");
            
            while(x.hasNext()) {
                name = x.next();
                age = x.next();
                country = x.next();
                
                if (name.equals(nameString)) {
                    
                    pw.println(name + "," + age + "," + newcountry);
                    System.out.println(name + "," + age + "," + newcountry);
                
                } else {
                    pw.println(name + "," + age + "," + country);
                    System.out.println(name + "," + age + "," + country);
                }
            }
            x.close();
            pw.flush();
            pw.close();
            oldFile.delete();
            File dump = new File("rewrite.txt");
            newFile.renameTo(dump);
            
        } catch (Exception e) {
            // TODO: handle exception
        }

Answer 1

Read the whole line, split on the comma. Then assign the values to the variables and write to new file.

public static void main(String[] args) {
    File input = new File("C:\\temp\\input.txt");
    String nameString = "Milo";
    String newcountry = "Italy";

    File output = new File("c:\\temp\\temp.txt");
    String name = "";
    String age = "";
    String country = "";
    try {
        FileWriter fw = new FileWriter(output, true);
        BufferedWriter bw = new BufferedWriter(fw);
        PrintWriter pw = new PrintWriter(bw);
        Scanner x = new Scanner(input);
        while (x.hasNextLine()) {
            String line = x.nextLine();
            String[] split = line.split(",");
            name = split[0];
            age = split[1];
            country = split[2];
            if (name.equals(nameString)) {
                pw.println(name + "," + age + "," + newcountry);
                System.out.println(name + "," + age + "," + newcountry);
            } else {
                pw.println(name + "," + age + "," + country);
                System.out.println(name + "," + age + "," + country);
            }
        }
        x.close();
        pw.flush();
        pw.close();

    } catch (Exception e) {
        // TODO: handle exception
    }
}

Output is:

Milo,10,Italy
Jacob,15,California
Shan,7,France

without any empty lines.

With some debugging, I found the issue, that you are experiencing. You only consume part of the new line delimiter:

Text files created on DOS/Windows machines have different line endings than files created on Unix/Linux. DOS uses carriage return and line feed ("\r\n") as a line ending, which Unix uses just line feed ("\n")

When updating the delimiter to also consume \r, it works just as well

x.useDelimiter(",|\r\n");

This tell the scanner to use , or \r\n as delimiter which consumes the the windows new line characters