Using a ListResourceBundle

This section illustrates the use of a ListResourceBundle object with a sample program called ListDemo. The text that follows explains each step involved in creating the ListDemo program, along with the ListResourceBundle subclasses that support it.

1. Create the ListResourceBundle Subclasses

A ListResourceBundle is backed up by a class file. Therefore the first step is to create a class file for every supported Locale. In the ListDemo program the base name of the ListResourceBundle is StatsBundle. Since ListDemo supports three Locale objects, it requires the following three class files:

StatsBundle_en_CA.class
StatsBundle_fr_FR.class
StatsBundle_ja_JP.class

The StatsBundle class for Japan is defined in the source code that follows. Note that the class name is constructed by appending the language and country codes to the base name of the ListResourceBundle. Inside the class the two-dimensional contents array is initialized with the key-value pairs. The keys are the first element in each pair: GDP, Population, and Literacy. The keys must be String objects and they must be the same in every class in the StatsBundle set. The values can be any type of object. In this example the values are two Integer objects and a Double object.

import java.util.*;
public class StatsBundle_ja_JP extends ListResourceBundle {
    public Object[][] getContents() {
        return contents;
    }

    private Object[][] contents = {
        { "GDP", new Integer(21300) },
        { "Population", new Integer(125449703) },
        { "Literacy", new Double(0.99) },
    };
}

2. Specify the Locale

The ListDemo program defines the Locale objects as follows:

Locale[] supportedLocales = {
    new Locale("en", "CA"),
    new Locale("ja", "JP"),
    new Locale("fr", "FR")
};

Each Locale object corresponds to one of the StatsBundle classes. For example, the Japanese Locale, which was defined with the ja and JP codes, matches StatsBundle_ja_JP.class.

3. Create the ResourceBundle

To create the ListResourceBundle, invoke the getBundle method. The following line of code specifies the base name of the class (StatsBundle) and the Locale:

ResourceBundle stats = ResourceBundle.getBundle("StatsBundle", currentLocale);

The getBundle method searches for a class whose name begins with StatsBundle and is followed by the language and country codes of the specified Locale. If the currentLocale is created with the ja and JP codes, getBundle returns a ListResourceBundle corresponding to the class StatsBundle_ja_JP, for example.

4. Fetch the Localized Objects

Now that the program has a ListResourceBundle for the appropriate Locale, it can fetch the localized objects by their keys. The following line of code retrieves the literacy rate by invoking getObject with the Literacy key parameter. Since getObject returns an object, cast it to a Double:

Double lit = (Double)stats.getObject("Literacy");

5. Run the Demo Program

ListDemo program prints the data it fetched with the getBundle method:

Locale = en_CA
GDP = 24400
Population = 28802671
Literacy = 0.97

Locale = ja_JP
GDP = 21300
Population = 125449703
Literacy = 0.99

Locale = fr_FR
GDP = 20200
Population = 58317450
Literacy = 0.99