java - Add commas (grouping separator) to number without modifying decimals?

Question

I'm trying to format a string to add commas between 3 digit groups

EG:

1200.20 >> 1,200.20
15000   >> 15,000

I'm trying to figure out how to do it with DecimalFormat, to this point I have been using a script of my own that seems overly complicated. I cannot figure out how to do it, using # simply hides trailing zeroes and using 0 adds them to the number.

This is what I'm trying right now:

DecimalFormat df = new DecimalFormat("###,###.####", new DecimalFormatSymbols(Locale.US));
resultStr = df.format(Double.valueOf(resultStr));

I'm sure it must be easy but I'm not sure how to do it. I don't have to do it with DecimalFormat, I just thought it would be the easier way. How can I simply add the commas without modifying the decimals in any way?

Answer 1

You should use a NumberFormat object and set it to use grouping. Something like

import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.util.Locale;

public class NumberFormatEg {
   public static void main(String[] args) {
      NumberFormat myFormat = NumberFormat.getInstance();
      myFormat.setGroupingUsed(true);

      double[] numbers = { 11220.00, 232323232.24, 121211.55, 102.121212 };

      for (double d : numbers) {
         System.out.println(myFormat.format(d));
      }
      System.out.println();

      DecimalFormat decimalFormat = new DecimalFormat("#.00");
      decimalFormat.setGroupingUsed(true);
      decimalFormat.setGroupingSize(3);

      for (double d : numbers) {
         System.out.println(decimalFormat.format(d));
      }

      System.out.println("
For Germany");

      NumberFormat anotherFormat = NumberFormat
            .getNumberInstance(Locale.GERMAN);
      if (anotherFormat instanceof DecimalFormat) {
         DecimalFormat anotherDFormat = (DecimalFormat) anotherFormat;
         anotherDFormat.applyPattern("#.00");
         anotherDFormat.setGroupingUsed(true);
         anotherDFormat.setGroupingSize(3);

         for (double d : numbers) {
            System.out.println(anotherDFormat.format(d));
         }

      }

      System.out.println("
For US:");

      anotherFormat = NumberFormat.getNumberInstance(Locale.US);
      if (anotherFormat instanceof DecimalFormat) {
         DecimalFormat anotherDFormat = (DecimalFormat) anotherFormat;
         anotherDFormat.applyPattern("#.00");
         anotherDFormat.setGroupingUsed(true);
         anotherDFormat.setGroupingSize(3);

         for (double d : numbers) {
            System.out.println(anotherDFormat.format(d));
         }

      }
   }
}

which returns:

11,220
232,323,232.24
121,211.55
102.121

11,220.00
232,323,232.24
121,211.55
102.12

For Germany
11.220,00
232.323.232,24
121.211,55
102,12

For US:
11,220.00
232,323,232.24
121,211.55
102.12

An advantage of this is that the solution can be locale specific.

Edited
Now shows an example with a DecimalFormat object. Note that you should set the grouping size if you use this.