How to insert commas into a number?

Question

I've found such an example of using String.format() in a book:

package stringFormat;

public class Main {
    public static void main(String[] args) {
        String test = String.format("%, d", 1000000000);
        System.out.println(test);
    } 
}

According to the book the output should be: 1,000,000,000. But when I run the code I only get 1 000 000 000 without the commas. Why? how can I get it with commas?

Answer 1

Reproduce the problem with Locale.FRANCE:

Locale.setDefault(Locale.FRANCE);

String test = String.format("%, d", 1000000000);
System.out.println(test); //  1 000 000 000

You can avoid this with Locale.US:

String test = String.format(Locale.US, "%, d", 1000000000);

or

Locale.setDefault(Locale.US);
String test = String.format("%, d", 1000000000);