[java] Create a new line in Java's FileWriter

I have coded the following FileWriter:

try {
    FileWriter writer = new FileWriter(new File("file.txt"), false);

    String sizeX = jTextField1.getText();
    String sizeY = jTextField2.getText();
    writer.write(sizeX);
    writer.write(sizeY);

    writer.flush();
    writer.close();
} catch (IOException ex) {}

Now I want to insert a new line, just like you would do it with \n normally, but it doesn't seem to work.

What can be done to solve this?

Thank you.

One can use PrintWriter to wrap the FileWriter, as it has many additional useful methods.

try(PrintWriter pw = new PrintWriter(new FileWriter(new File("file.txt"), false))){
   pw.println();//new line
   pw.print("text");//print without new line
   pw.println(10);//print with new line
   pw.printf("%2.f", 0.567);//print double to 2 decimal places (without new line)
}

Since 1.8, I thought this might be an additional solution worth adding to the responses:

Path java.nio.file.Files.write(Path path, Iterable lines, OpenOption... options) throws IOException

StringBuilder sb = new StringBuilder();
sb.append(jTextField1.getText());
sb.append(jTextField2.getText());
sb.append(System.lineSeparator());
Files.write(Paths.get("file.txt"), sb.toString().getBytes());

If appending to the same file, perhaps use an Append flag with Files.write()

Files.write(Paths.get("file.txt"), sb.toString().getBytes(), StandardOpenOption.APPEND);

Try wrapping your FileWriter in a BufferedWriter:

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

Javadocs for BufferedWriter here.

Try:

String.format("%n");

See this question for more details.

If you mean use the same code but add a new line so that when you add something to the file it will be on a new line. You can simply use BufferedWriter's newLine().
Here I have Improved you code also: NumberFormatException was unnecessary as nothing was being cast to a number data type, saving variables to use once also was.

try {
    BufferedWriter writer = new BufferedWriter(new FileWriter("file.txt"));
        writer.write(jTextField1.getText());
        writer.write(jTextField2.getText());
        writer.newLine();
        writer.flush();
        writer.close();
} catch (IOException ex) {
    System.out.println("File could not be created");
}

I would tackle the problem like this:

    BufferedWriter output;
    output = new BufferedWriter(new FileWriter("file.txt", true));
    String sizeX = jTextField1.getText();
    String sizeY = jTextField2.getText();
    output.append(sizeX);
    output.append(sizeY);
    output.newLine();
    output.close();

The true in the FileWriter constructor allows to append.
The method newLine() is provided by BufferedWriter
Could be ok as solution?

Try System.getProperty( "line.separator" )

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

Here "\n" is also working fine. But the problem here lies in the text editor(probably notepad). Try to see the output with Wordpad.