Java NumberFormat
Jakob Jenkov |
The java.text.NumberFormat class is used to format numbers according to
a specific Locale. Different countries have different standards for
how they format numbers. In Denmark fractions of a number are separated from the
integer part using a comma. In England they use a dot.
Creating a NumberFormat
Creating a NumberFormat for a specific Locale is done like this:
Locale locale = new Locale("da", "DK");
NumberFormat numberFormat = NumberFormat.getInstance(locale);
Formatting Numbers
Formatting a number using a NumberFormatter is done using the format() method.
Here is an example:
String number = numberFormat.format(100.99); System.out.println(number);
Using a Danish Locale, the output printed from this code would be:
100,99
Notice that numbers like 100.00 might be formatted without the decimals, as 100.
Formatting Currencies
To format a number as currency you need a currency NumberFormat instance.
You create a currency NumberFormat using the getCurrencyInstance()
like this:
NumberFormat currencyFormat = NumberFormat.getCurrencyInstance(locale);
Formatting a number as a currency is still done using the format() method. Here
is an example:
String currency = currencyFormat.format(100.999); System.out.println(currency);
The output printed from this code would be:
kr 101,00
Notice how the localized Danish currency code is written in front of the number. Other countries might have the currency code after the number instead. Notice also that the amount is rounded.
It is also possible to obtain the Currency object representing the currency used to format
the number. You do so using the getCurrency() method. Here is an example:
Currency currency = currencyFormat.getCurrency();
From the Currency instance you can get the name, symbol etc. of the currency, using its
getDisplayName() and getCurrencyCode() etc. methods.
You can also set the Currency object to use for formatting a number as a currency,
using the setCurrency() method on the NumberFormat class. Here is
an example:
NumberFormat numberFormat =
NumberFormat.getCurrencyInstance(new Locale("da", "DK"));
numberFormat.setCurrency(Currency.getInstance("EUR"));
String currencyString = numberFormat.format(120.99);
System.out.println(currencyString);
This code create a currency formatter using a Danish locale, then exchanges the currency to use for formatting with EURO. The output printed from this code would be:
€ 120,99
Formatting Percentages
To format a number as percentage you need a percentage NumberFormat instance.
You create that using the getPercentageInstance() like this:
NumberFormat percentageFormat = NumberFormat.getPercentInstance(locale);
Formatting a number as a percentage is also done using the format() method.
Here is an example:
String percentage = percentageFormat.format(99.999); System.out.println(percentage);
The output printed from this code would be:
10.000%
Notice the % character after the number. Notice also that the number is rounded.
Minimum and Maximum Number of Digits
You can set both the minimum and maximum number of digits to use both for the integer part and the fractional part of the number. You do so using these methods:
numberFormat.setMinimumIntegerDigits(int digits) numberFormat.setMaximumIntegerDigits(int digits) numberFormat.setMinimumFractionDigits(int digits) numberFormat.setMaximumFractionDigits(int digits)
You can also obtain these values again, using these methods:
int digits = numberFormat.getMinimumIntegerDigits(); int digits = numberFormat.getMaximumIntegerDigits(); int digits = numberFormat.getMinimumFractionDigits(); int digits = numberFormat.getMaximumFractionDigits();
Rounding Mode
As you may have noticed earlier, the formatted numbers are rounded.
You can set the rounding mode using the setRoundingMode() method
of the NumberFormat class. Here is an example:
NumberFormat numberFormat =
NumberFormat.getInstance(new Locale("da", "DK"));
numberFormat.setRoundingMode(RoundingMode.HALF_DOWN);
numberFormat.setMinimumFractionDigits(0);
numberFormat.setMaximumFractionDigits(0);
String number = numberFormat.format(99.50);
System.out.println(number);
The output from this code would be 99. The fraction part would be
rounded down because of the rounding mode, and to 0 fraction digits.
Parsing Numbers
You can also use the NumberFormat class to parse numbers. Here is an example:
NumberFormat numberFormat =
NumberFormat.getInstance(new Locale("da", "DK"));
Number parse = numberFormat.parse("100,00");
System.out.println(parse.intValue());
The output printed from running this code would be:
100
As you can see, the number in the parsed string uses a comma (,) as separator between the
integer part and the fraction part of the number. Since the NumberFormat is
created using a Danish Locale instance, this string is parsed correctly to
the value 100.
Had the NumberFormat instance been created using a UK Locale
instance, the number had been parsed to 10000, because the comma would have been
interpreted as a integer separator (e.g. thousand separator), and not a fraction separator.
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Jakob Jenkov | |
