Using setGroupingSize() method of DecimalFormat, default grouping of numbers can be changed. Following example is illustrating the same.

Example

import java.text.DecimalFormat;

public class I18NTester {
   public static void main(String[] args) {
      double number = 121223232473.4567;

      DecimalFormat decimalFormat = new DecimalFormat();

      System.out.println(number);
      System.out.println(decimalFormat.format(number));   

      decimalFormat.setGroupingSize(4);
      System.out.println(decimalFormat.format(number));
   
   }
}

Output

It will print the following result.

1.212232324734567E11
121,223,232,473.457
1212,2323,2473.457