在JDK 12精简数字格式中使用最小分数数字

帖子“ 紧凑数字格式出现在JDK 12中 ”演示了对JDK 12中 NumberFormat的支持，以支持紧凑数字格式。该帖子中显示的示例仅使用NumberFormat的调用重载了NumberFormat的新重载getCompactNumberInstance(-)方法返回的NumberFormat实例，因此没有指定诸如最小小数位和最大小数位之类的特征。在某些情况下，结果不理想。幸运的是， NumberFormat确实允许指定最小和最大小数位，并且本文演示了如何改善JDK 12提供的紧凑数字格式的输出。

原始“ 紧凑型数字格式来到JDK 12 ”一文中介绍的代码清单（可在GitHub上找到）已更新，以演示NumberFormat.setMinimumFractionDigits（int）的使用。接下来是该代码的摘录，然后是随附的输出。

/*** 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: 15US/Long: 15UK/Short: 15UK/Long: 15FR/Short: 15FR/Long: 15DE/Short: 15DE/Long: 15IT/Short: 15IT/Long: 15
Demonstrating Compact Number Formatting on long '150' with 1 minimum fraction digit:Default: 150US/Long: 150UK/Short: 150UK/Long: 150FR/Short: 150FR/Long: 150DE/Short: 150DE/Long: 150IT/Short: 150IT/Long: 150
Demonstrating Compact Number Formatting on long '1500' with 1 minimum fraction digit:Default: 1.5KUS/Long: 1.5 thousandUK/Short: 1.5KUK/Long: 1.5 thousandFR/Short: 1,5 kFR/Long: 1,5 millierDE/Short: 1.500DE/Long: 1,5 TausendIT/Short: 1.500IT/Long: 1,5 mille
Demonstrating Compact Number Formatting on long '15000' with 1 minimum fraction digit:Default: 15.0KUS/Long: 15.0 thousandUK/Short: 15.0KUK/Long: 15.0 thousandFR/Short: 15,0 kFR/Long: 15,0 milleDE/Short: 15.000DE/Long: 15,0 TausendIT/Short: 15.000IT/Long: 15,0 mila
Demonstrating Compact Number Formatting on long '150000' with 1 minimum fraction digit:Default: 150.0KUS/Long: 150.0 thousandUK/Short: 150.0KUK/Long: 150.0 thousandFR/Short: 150,0 kFR/Long: 150,0 milleDE/Short: 150.000DE/Long: 150,0 TausendIT/Short: 150.000IT/Long: 150,0 mila
Demonstrating Compact Number Formatting on long '1500000' with 1 minimum fraction digit:Default: 1.5MUS/Long: 1.5 millionUK/Short: 1.5MUK/Long: 1.5 millionFR/Short: 1,5 MFR/Long: 1,5 millionDE/Short: 1,5 Mio.DE/Long: 1,5 MillionIT/Short: 1,5 MlnIT/Long: 1,5 milione
Demonstrating Compact Number Formatting on long '15000000' with 1 minimum fraction digit:Default: 15.0MUS/Long: 15.0 millionUK/Short: 15.0MUK/Long: 15.0 millionFR/Short: 15,0 MFR/Long: 15,0 millionDE/Short: 15,0 Mio.DE/Long: 15,0 MillionenIT/Short: 15,0 MlnIT/Long: 15,0 milioni

如上面的示例和输出所示，使用NumberFormat.setMinimumFractionDigits(int)可以生成紧凑的数字格式输出，在许多情况下，从美学上讲更令人愉悦。 OpenJDK core-libs-dev邮件列表上最近有一个讨论“ 紧凑数字格式和小数位数 ”，该讨论还讨论了自定义紧凑数字格式输出的功能。