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8.4 Handling Local Customs
The second problem of internationalization is the task of following
local customs and conventions in areas such as date and time
formatting. The java.text package defines classes
to help with this duty.The NumberFormat class formats numbers, monetary
amounts, and percentages in a locale-dependent way for display to the
user. This is necessary because different locales have different
conventions for number formatting. For example, in France, a comma is
used as a decimal separator instead of a period, as in many
English-speaking countries. A NumberFormat object
can use the default locale or any locale you specify.
NumberFormat has factory methods for obtaining
instances that are suitable for different purposes, such as
displaying monetary quantities or percentages. In Java 1.4 and later,
the java.util.Currency class can be used with
NumberFormat object so that it can correctly print
an appropriate currency symbol. The DateFormat
class formats dates and times in a locale-dependent way for display
to the user. Different countries have different conventions. Should
the month or day be displayed first? Should periods or colons
separate fields of the time? What are the names of the months in the
language of the locale? A DateFormat object can
simply use the default locale, or it can use any locale you specify.
The DateFormat class is used in conjunction with
the TimeZone and Calendar
classes of java.util. The
TimeZone object tells the
DateFormat what time zone the date should be
interpreted in, while the Calendar object
specifies how the date itself should be broken down into days, weeks,
months, and years. Almost all locales use the standard
GregorianCalendar.
SimpleDateFormat is a useful subclass of
DateFormat: it allows dates to be formatted to or
parsed from a date format specified with a simple template string.The
Collator class compares strings in a
locale-dependent way. This is necessary because different languages
alphabetize strings in different ways (and some languages
don't even use alphabets). In traditional Spanish,
for example, the letters "ch" are
treated as a single character that comes between
"c" and
"d" for the purposes of sorting.
When you need to sort strings or search for a string within Unicode
text, you should use a Collator object, either one
created to work with the default locale or one created for a
specified locale.The
BreakIterator class allows you to locate
character, word, line, and sentence boundaries in a locale-dependent
way. This is useful when you need to recognize such boundaries in
Unicode text, such as when you are implementing a word-wrapping
algorithm.Example 8-3 shows a class that uses the
NumberFormat and DateFormat
classes to display a hypothetical stock portfolio to the user
following local conventions. The program uses various
NumberFormat and DateFormat
objects to format (using the format( ) method)
different types of numbers and dates. These Format
objects all operate using the default locale but could have been
created with an explicitly specified locale. The program displays
information about a hypothetical stock portfolio, formatting dates
and numbers and monetary values according to the current or the
specified locale. Figure 8-2 shows example output
in different locales. The output was produced by running the program
in the default locale, with the arguments "en
GB" and "ja JP".
Figure 8-2. Stock portfolios formatted for U.S., British, and French locales
Example 8-3. Portfolio.java
package je3.i18n;
import java.text.*;
import java.util.*;
import java.io.*;
/**
* A partial implementation of a hypothetical stock portfolio class.
* We use it only to demonstrate number and date internationalization.
**/
public class Portfolio {
EquityPosition[ ] positions; // The positions in the portfolio
Date lastQuoteTime = new Date( ); // Time for current quotes
// Create a Portfolio
public Portfolio(EquityPosition[ ] positions, Date lastQuoteTime) {
this.positions = positions;
this.lastQuoteTime = lastQuoteTime;
}
// A helper class: represents a single stock purchase
static class EquityPosition {
String name; // Name of the stock.
int shares; // Number of shares held.
Date purchased; // When purchased.
Currency currency; // What currency are the prices expressed in?
double bought; // Purchase price per share
double current; // Current price per share
// Format objects like this one are useful for parsing strings as well
// as formatting them. This is for converting date strings to Dates.
static DateFormat dateParser = new SimpleDateFormat("yyyy-MM-dd");
EquityPosition(String n, int s, String date, Currency c,
double then, double now) throws ParseException
{
// Convert the purchased date string to a Date object.
// The string must be in the format yyyy-mm-dd
purchased = dateParser.parse(date);
// And store the rest of the fields, too.
name = n; shares = s; currency = c;
bought = then; current = now;
}
}
// Return a localized HTML-formatted string describing the portfolio
public String toString( ) {
StringBuffer b = new StringBuffer( );
// Obtain NumberFormat and DateFormat objects to format our data.
NumberFormat number = NumberFormat.getInstance( );
NumberFormat price = NumberFormat.getCurrencyInstance( );
NumberFormat percent = NumberFormat.getPercentInstance( );
DateFormat shortdate = DateFormat.getDateInstance(DateFormat.MEDIUM);
DateFormat fulldate = DateFormat.getDateTimeInstance(DateFormat.LONG,
DateFormat.LONG);
// Print some introductory data.
b.append("<html><body>");
b.append("<i>Portfolio value at ").
append(fulldate.format(lastQuoteTime)).append("</i>");
b.append("<table border=1>");
b.append("<tr><th>Symbol<th>Shares<th>Purchased<th>At<th>" +
"Quote<th>Change</tr>");
// Display the table using the format( ) methods of the Format objects.
for(int i = 0; i < positions.length; i++) {
b.append("<tr><td>");
b.append(positions[i].name).append("<td>");
b.append(number.format(positions[i].shares)).append("<td>");
b.append(shortdate.format(positions[i].purchased)).append("<td>");
// Set the currency to use when printing the following prices
price.setCurrency(positions[i].currency);
b.append(price.format(positions[i].bought)).append("<td>");
b.append(price.format(positions[i].current)).append("<td>");
double change =
(positions[i].current-positions[i].bought)/positions[i].bought;
b.append(percent.format(change)).append("</tr>");
}
b.append("</table></body></html>");
return b.toString( );
}
/**
* This is a test program that demonstrates the class
**/
public static void main(String[ ] args) throws ParseException {
Currency dollars = Currency.getInstance("USD");
Currency pounds = Currency.getInstance("GBP");
Currency euros = Currency.getInstance("EUR");
Currency yen = Currency.getInstance("JPY");
// This is the portfolio to display.
EquityPosition[ ] positions = new EquityPosition[ ] {
new EquityPosition("WWW", 400, "2003-01-03", dollars, 11.90,13.00),
new EquityPosition("XXX", 1100, "2003-02-02", pounds, 71.09,27.25),
new EquityPosition("YYY", 6000, "2003-04-17", euros, 23.37,89.12),
new EquityPosition("ZZZ", 100, "2003-8-10", yen, 100000,121345)
};
// Create the portfolio from these positions
Portfolio portfolio = new Portfolio(positions, new Date( ));
// Set the default locale using the language code and country code
// specified on the command line.
if (args.length == 2) Locale.setDefault(new Locale(args[0], args[1]));
// Now display the portfolio.
// We use a Swing dialog box to display it because the console may
// not be able to display non-ASCII characters like currency symbols
// for Pounds, Euros, and Yen.
javax.swing.JOptionPane.showMessageDialog(null, portfolio,
Locale.getDefault( ).getDisplayName( ),
javax.swing.JOptionPane.INFORMATION_MESSAGE);
// The modal dialog starts another thread running, so we have to exit
// explictly when the user dismisses it.
System.exit(0);
}
}
8.4.1 Setting the Locale
Example 8-3 contains
code that explicitly sets the locale using the language code and the
country code specified on the command line. If these arguments are
not specified, it uses the default locale for your system. When
experimenting with internationalization, you may want to change the
default locale for the entire platform so you can see what happens.
How you do this is platform-dependent. On Unix platforms, you
typically set the locale by setting the LANG
environment variable. For example, to set the locale for Canadian
French, using a Unix csh-style shell, use this
command:
% setenv LANG fr_CA
Or, to set the locale to English as spoken in Great Britain when
using a Unix sh-style shell, use this command:
$ export LANG=en_GB
To set the locale in Windows, use the Regional Settings control on
the Windows Control Panel.
