By invoking the methods provided by the
NumberFormat
class, you can format numbers, currencies, and percentages according to
Locale
. The material that follows demonstrates formatting techniques with a sample program called
NumberFormatDemo.java
.
You can use the
NumberFormat
methods to format primitive-type numbers, such as double
, and their corresponding wrapper objects, such as
Double
.
The following code example formats a
Double
according to
Locale
. Invoking the
getNumberInstance
method returns a locale-specific instance of
NumberFormat
. The
format
method accepts the
Double
as an argument and returns the formatted number in a
String
.
static public void displayNumber(Locale currentLocale) { Integer quantity = new Integer(123456); Double amount = new Double(345987.246); NumberFormat numberFormatter; String quantityOut; String amountOut; numberFormatter = NumberFormat.getNumberInstance(currentLocale); quantityOut = numberFormatter.format(quantity); amountOut = numberFormatter.format(amount); System.out.println(quantityOut + " " + currentLocale.toString()); System.out.println(amountOut + " " + currentLocale.toString()); }
This example prints the following; it shows how the format of the same number varies with
Locale
:
123 456 fr_FR 345 987,246 fr_FR 123.456 de_DE 345.987,246 de_DE 123,456 en_US 345,987.246 en_US
By default, when text contains numeric values, those values are displayed using Arabic digits. When other Unicode digit shapes are preferred, use the
java.awt.font.NumericShaper
class. The NumericShaper
API enables you to display a numeric value represented internally as an ASCII value in any Unicode digit shape. See
Converting Latin Digits to Other Unicode Digits for more information.
In addition, some locales have variant codes that specify that Unicode digit shapes be used in place of Arabic digits, such as the locale for the Thai language. See the section Variant Code in Creating a Locale for more information.
If you are writing business applications, you will probably need to format and display currencies. You format currencies in the same manner as numbers, except that you call
getCurrencyInstance
to create a formatter. When you invoke the
format
method, it returns a
String
that includes the formatted number and the appropriate currency sign.
This code example shows how to format currency in a locale-specific manner:
static public void displayCurrency( Locale currentLocale) { Double currencyAmount = new Double(9876543.21); Currency currentCurrency = Currency.getInstance(currentLocale); NumberFormat currencyFormatter = NumberFormat.getCurrencyInstance(currentLocale); System.out.println( currentLocale.getDisplayName() + ", " + currentCurrency.getDisplayName() + ": " + currencyFormatter.format(currencyAmount)); }
The output generated by the preceding lines of code is as follows:
French (France), Euro: 9 876 543,21 € German (Germany), Euro: 9.876.543,21 € English (United States), US Dollar: $9,876,543.21
At first glance, this output may look wrong to you because the numeric values are all the same. Of course, 9 876 543,21 € is not equivalent to $9,876,543.21. However, bear in mind that the
NumberFormat
class is unaware of exchange rates. The methods belonging to the
NumberFormat
class format currencies but do not convert them.
Note that the
Currency
class is designed so that there is never more than one
Currency
instance for any given currency. Therefore, there is no public constructor. As demonstrated in the previous code example, you obtain a
Currency
instance using the
getInstance
methods.
The sample
InternationalizedMortgageCalculator.java
also demonstrates how to use the
Currency
class. (Note that this sample does not convert currency values.) The following uses the en-US locale:
The following uses the en-UK locale:
The sample
InternationalizedMortgageCalculator.java
requires the following resource files:
The
Currency
class contains other methods to retrieve currency related information:
getAvailableCurrencies
: Returns all available currencies in the JDK
getCurrencyCode
: Returns the ISO 4217 numeric code for a
Currency
instance
getSymbol
: Returns the symbol for a
Currency
instance. You can optionally specify as an argument a
Locale
object. Consider the following excerpt:
Locale enGBLocale = new Locale.Builder().setLanguage("en").setRegion("GB").build(); Locale enUSLocale = new Locale.Builder().setLanguage("en").setRegion("US").build(); Currency currencyInstance = Currency.getInstance(enUSLocale); System.out.println( "Symbol for US Dollar, en-US locale: " + currencyInstance.getSymbol(enUSLocale)); System.out.println( "Symbol for US Dollar, en-UK locale: " + currencyInstance.getSymbol(enGBLocale));
The excerpt prints the following:
Symbol for US Dollar, en-US locale: $ Symbol for US Dollar, en-UK locale: USD
This excerpt demonstrates that the symbol of a currency can vary depending on the locale.
getDisplayName
: Returns the display name for a
Currency
instance. Like the
getSymbol
method, you can optionally specify a
Locale
object.
ISO 4217 is a standard published by the International Standards Organization. It specifies three-letter codes (and equivalent three-digit numeric codes) to represent currencies and funds. This standard is maintained by an external agency and is released independent of the Java SE platform.
Suppose that a country adopts a different currency and the ISO 4217 maintenance agency releases a currency update. To implement this update and thereby supercede the default currency at runtime, create a properties file named <JAVA_HOME>/lib/currency.properties
. This file contains the key/value pairs of the
ISO 3166 country code, and the ISO 4217 currency data. The value part consists of three comma-separated ISO 4217 currency values: an alphabetic code, a numeric code, and a minor unit. Any lines beginning with the hash character (#
), are treated as comment lines. For example:
# Sample currency property for Canada CA=CAD,124,2
CAD
stands for the Canadian dollar; 124
is the numeric code for the Canadian dollar; and 2
is the minor unit, which is the number of decimal places the currency requires to represent fractional currencies. For example, the following properties file will supercede the default Canadian currency to a Canadian dollar that does not have any units smaller than the dollar:
CA=CAD,124,0
You can also use the methods of the
NumberFormat
class to format percentages. To get the locale-specific formatter, invoke the
getPercentInstance
method. With this formatter, a decimal fraction such as 0.75 is displayed as 75%.
The following code sample shows how to format a percentage.
static public void displayPercent(Locale currentLocale) { Double percent = new Double(0.75); NumberFormat percentFormatter; String percentOut; percentFormatter = NumberFormat.getPercentInstance(currentLocale); percentOut = percentFormatter.format(percent); System.out.println(percentOut + " " + currentLocale.toString()); }
This sample prints the following:
75 % fr_FR 75% de_DE 75% en_US