String.format返回使用逗号作为分隔符的双精度型

Question

I'm making a random file generator that makes a txt with random cartesian points the problem is: when I use the String.format to a number (let's say 4.3), I get "4,3". But I don't want the comma, I don't even know why it makes a comma, there's no use to it at all... The code:

FileWriter fileWriter = new FileWriter(new File("txt.txt"));
BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
Random generator = new Random();
int nPoints = generator.nextInt(10)+10;
bufferedWriter.write(""+nPoints);
for (int n=0; n<nPoints; n++){
    bufferedWriter.newLine();
    String x = String.format("%.1f", generator.nextDouble()*100-50);
    String y = String.format("%.1f", generator.nextDouble()*100-50);
    bufferedWriter.write(x + " " + y);
}
bufferedWriter.close();

I've solved the problem using replace(",", "."), but I kinda think this is not a good solution, and I want to know if there's any reason to have a comma in the format method.

Answer 1

Instead of using a workaround (replace the comma by a dot) you should solve it in a proper way. "There is an API for that."

Locale.setDefault(new Locale("pt", "BR"));
String portuguese = String.format("%.1f", 1.4d);
String english = String.format(Locale.ENGLISH, "%.1f", 1.4d);
System.out.println("pt_BR = " + portuguese);
System.out.println("en_GB = " + english);

produced output

pt_BR = 1,4
en_GB = 1.4

And it's not a nonstandardized function (see the Javadoc) . Standard is use the default locale and if needed you are able to change the behavior .

Answer 2

Try this:

        DecimalFormatSymbols otherSymbols = new DecimalFormatSymbols(Locale.getDefault());
        otherSymbols.setDecimalSeparator('.');
        DecimalFormat formatter = new DecimalFormat("####.0",otherSymbols);

        for (int n=0; n<nPoints; n++){
            bufferedWriter.newLine();
            String x = formatter.format(generator.nextDouble()*100-50);
            String y = formatter.format(generator.nextDouble()*100-50);

The output :

33.1 -37.7