Create a new line in Java's FileWriter

If you want to get new line characters used in current OS like \r\n for Windows, you can get them by

• System.getProperty("line.separator");
• since Java7 System.lineSeparator()
• or as mentioned by Stewart generate them via String.format("%n");

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You can also use PrintStream and its println method which will add OS dependent line separator at the end of your string automatically

PrintStream fileStream = new PrintStream(new File("file.txt"));
fileStream.println("your data");
//         ^^^^^^^ will add OS line separator after data 

(BTW System.out is also instance of PrintStream).

Try System.getProperty( "line.separator" )

   writer.write(System.getProperty( "line.separator" ));

Try wrapping your FileWriter in a BufferedWriter:

BufferedWriter bw = new BufferedWriter(writer);
bw.newLine();

Javadocs for BufferedWriter here.