Why does \n and (String)System.getProperty("line.separator"); act differently?

Question

My program takes a input of a text file that has words each separated by a newline and my program takes it and deals with the data, and then I am required to output to a new file whilst keeping the console output.

Now I am wondering why when I append "\n" to my stringBuilder that it prints it out as it were to have a new line in the console, but in the file output, it doesn't take it as a new line and just puts all the words in one line.

When I use newLine, then only does it give a new line in both my console output and my output file. Why is that? What does (String)System.getProperty("line.separator") do that causes this?

String newLine = (String)System.getProperty("line.separator");

 try{
     BufferedReader fileIn = new BufferedReader(new FileReader(fileName));

     stringBuilder.append(newLine);
     while((s = fileIn.readLine()) != null){
        stringBuilder.append(s);
        stringBuilder.append(newLine);//using newLine, 
     }
        String a = stringBuilder.toString();

     if(s== null){
        fileIn.close();
     }

Because on some systems (think OSX or Windows), `\n` is not the line separator? — , Nov 03 '15 at 17:47
you should use `System.lineSeparator()` and no need to cast the result to `String` — Manos Nikolaidis, Nov 03 '15 at 17:51

Brent C · Accepted Answer · 2018-10-19T20:31:03.910

3

Because on some systems (Linux/Unix) a new line is defined as \n while on others (Windows) it is \r\n. Depending on the software reading the text, it may chose to adhere to this or be more "forgiving" recognizing either or even \r individually.

Relevant Wikipedia text (https://en.wikipedia.org/wiki/Newline):

Systems based on ASCII or a compatible character set use either LF (Line feed, '\n', 0x0A, 10 in decimal) or CR (Carriage return, '\r', 0x0D, 13 in decimal) individually, or CR followed by LF (CR+LF, '\r\n', 0x0D0A)

This is also why you can retrieve the system-defined line separater from the System class as you did, instead of, for example, having it be some constant in the String class.

edited Oct 19 '18 at 20:31

answered Nov 03 '15 at 17:53

Brent C

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This answer is wholly incorrect. On Windows systems, the newline String is \r\n and on Unix systems it is \n (LF or ASCII char 10). – Darrell Teague Oct 01 '18 at 17:50
@DarrellTeague Thank you for catching the error. I have edited the answer to reflect. – Brent C Oct 19 '18 at 20:32

score 1 · Answer 2 · answered Nov 03 '15 at 17:57

System.getProperty("line.separator") is different from "\n" in that the former returns the OS line separator (not always \n). \n is just a line feed, and when you open your output file in a program that does not interpret \n as a new line (say, Notepad on Windows) you won't see that new line.

Why does \n and (String)System.getProperty("line.separator"); act differently?

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