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Trail: Internationalization
Lesson: Formatting
Section: Numbers and Currencies
Formatting
Numbers and Currencies
Using Predefined Formats
Customizing Formats
Dates and Times
Using Predefined Formats
Customizing Formats
Changing Date Format Symbols
Messages
Dealing with Compound Messages
Handling Plurals
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Using Predefined Formats

> 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`.

### Numbers

> 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`.

> >     Double amount = new Double(345987.246);
> >     NumberFormat numberFormatter;
> >     String amountOut;

> >     numberFormatter = NumberFormat.getNumberInstance(currentLocale);
> >     amountOut = numberFormatter.format(amount);
> >     System.out.println(amountOut + " " +
> >                        currentLocale.toString());

> The output from this example shows how the format of the same number varies with `Locale`:

> >     345 987,246	 fr_FR
> >     345.987,246	 de_DE
> >     345,987.246	 en_US

### Currencies

> If you're writing business applications, you'll probably need to format and to 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:

> >     Double currency = new Double(9876543.21);
> >     NumberFormat currencyFormatter;
> >     String currencyOut;

> >     currencyFormatter = NumberFormat.getCurrencyInstance(currentLocale);
> >     currencyOut = currencyFormatter.format(currency);
> >     System.out.println(currencyOut + " " +
> >                        currentLocale.toString());

> The output generated by the preceding lines of code is as follows:

> >     9 876 543,21 F	 fr_FR
> >     9.876.543,21 DM	 de_DE
> >     $9,876,543.21	 en_US

> At first glance this output may look wrong to you, because the numeric values are all the same. Of course, 9 876 543,21 F is not equivalent to 9.876.543,21 DM. 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.

### Percentages

> 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.

> >     Double percent = new Double(0.75);
> >     NumberFormat percentFormatter;
> >     String percentOut;

> >     percentFormatter = NumberFormat.getPercentInstance(currentLocale);
> >     percentOut = percentFormatter.format(percent);

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