Using Minimum Fractional Digits with JDK 12 Compact Number Formatting

The post "Compact Number Formatting Comes to JDK 12" demonstrated the support added to NumberFormat in JDK 12 to support compact number formatting. The examples shown in that post only used the instances of NumberFormat returned by invocations of NumberFormat's new overloaded getCompactNumberInstance(-) methods and so therefore did not specify characteristics such as minimum fractional digits and maximum fractional digits. The results, in some cases, are less than desirable. Fortunately, NumberFormat does allow for minimum and maximum fractional digits to be specified and this post demonstrates how that can improve the output of the compact number formatting available with JDK 12.

The Javadoc documentation for new class java.text.CompactNumberFormat (currently available at https://download.java.net/java/early_access/jdk12/docs/api/java.base/java/text/CompactNumberFormat.html, but this location will change when JDK 12 is officially released in March) includes a section "Formatting" that states: "The default formatting behavior returns a formatted string with no fractional digits, however users can use the setMinimumFractionDigits(int) method to include the fractional part."

The code listing introduced in the original "Compact Number Formatting Comes to JDK 12" post (and which is available on GitHub) has been updated to demonstrate use of NumberFormat.setMinimumFractionDigits(int). An excerpt of that code is shown next and is followed by the accompanying output.

/**
 * Generates standardized map of labels to Compact Number Format
 * instances described by the labels. The instances of {@code NumberFormat}
 * are created with Locale and Style only and with the provided number
 * of minimum fractional digits.
 *
 * @return Mapping of label to an instance of a Compact Number Format
 *    consisting of a Locale, Style, and specified minimum number of fractional
 *    digits that is described by the label.
 */
private static Map<String, NumberFormat> generateCompactNumberFormats(
   final int minimumNumberFractionDigits)
{
   var numberFormats = generateCompactNumberFormats();
   numberFormats.forEach((label, numberFormat) ->
      numberFormat.setMinimumFractionDigits(minimumNumberFractionDigits));
   return numberFormats;
}


/**
 * Demonstrates compact number formatting in a variety of locales
 * and number formats against the provided {@code long} value and
 * with a minimum fractional digits of 1 specified.
 * @param numberToFormat Value of type {@code long} that is to be
 *    formatted using compact number formatting and a variety of
 *    locales and number formats and with a single minimal fractional
 *    digit.
 */
private static void demonstrateCompactNumberFormattingOneFractionalDigitMinimum(
   final long numberToFormat)
{
   final Map<String, NumberFormat> numberFormats = generateCompactNumberFormats(1);
   out.println(
      "Demonstrating Compact Number Formatting on long '" + numberToFormat
         + "' with 1 minimum fraction digit:");
   numberFormats.forEach((label, numberFormat) ->
      out.println("\t" +  label + ": " + numberFormat.format(numberToFormat))
   );
}

Demonstrating Compact Number Formatting on long '15' with 1 minimum fraction digit:
 Default: 15
 US/Long: 15
 UK/Short: 15
 UK/Long: 15
 FR/Short: 15
 FR/Long: 15
 DE/Short: 15
 DE/Long: 15
 IT/Short: 15
 IT/Long: 15
Demonstrating Compact Number Formatting on long '150' with 1 minimum fraction digit:
 Default: 150
 US/Long: 150
 UK/Short: 150
 UK/Long: 150
 FR/Short: 150
 FR/Long: 150
 DE/Short: 150
 DE/Long: 150
 IT/Short: 150
 IT/Long: 150
Demonstrating Compact Number Formatting on long '1500' with 1 minimum fraction digit:
 Default: 1.5K
 US/Long: 1.5 thousand
 UK/Short: 1.5K
 UK/Long: 1.5 thousand
 FR/Short: 1,5 k
 FR/Long: 1,5 millier
 DE/Short: 1.500
 DE/Long: 1,5 Tausend
 IT/Short: 1.500
 IT/Long: 1,5 mille
Demonstrating Compact Number Formatting on long '15000' with 1 minimum fraction digit:
 Default: 15.0K
 US/Long: 15.0 thousand
 UK/Short: 15.0K
 UK/Long: 15.0 thousand
 FR/Short: 15,0 k
 FR/Long: 15,0 mille
 DE/Short: 15.000
 DE/Long: 15,0 Tausend
 IT/Short: 15.000
 IT/Long: 15,0 mila
Demonstrating Compact Number Formatting on long '150000' with 1 minimum fraction digit:
 Default: 150.0K
 US/Long: 150.0 thousand
 UK/Short: 150.0K
 UK/Long: 150.0 thousand
 FR/Short: 150,0 k
 FR/Long: 150,0 mille
 DE/Short: 150.000
 DE/Long: 150,0 Tausend
 IT/Short: 150.000
 IT/Long: 150,0 mila
Demonstrating Compact Number Formatting on long '1500000' with 1 minimum fraction digit:
 Default: 1.5M
 US/Long: 1.5 million
 UK/Short: 1.5M
 UK/Long: 1.5 million
 FR/Short: 1,5 M
 FR/Long: 1,5 million
 DE/Short: 1,5 Mio.
 DE/Long: 1,5 Million
 IT/Short: 1,5 Mln
 IT/Long: 1,5 milione
Demonstrating Compact Number Formatting on long '15000000' with 1 minimum fraction digit:
 Default: 15.0M
 US/Long: 15.0 million
 UK/Short: 15.0M
 UK/Long: 15.0 million
 FR/Short: 15,0 M
 FR/Long: 15,0 million
 DE/Short: 15,0 Mio.
 DE/Long: 15,0 Millionen
 IT/Short: 15,0 Mln
 IT/Long: 15,0 milioni

As the example and output shown above demonstrate, use of NumberFormat.setMinimumFractionDigits(int) leads to compact number formatted output that is likely to be more aesthetically pleasing in many cases. There is a recent discussion "Compact Number Formatting and Fraction Digits" on the OpenJDK core-libs-dev mailing list that also discusses this ability to customize the compact number formatting output.