Creating a Button with I18N Resources

Problem

You want your program to take “sensitivity lessons” so it can communicate well internationally.

Solution

Your program must obtain all control and message strings via the internationalization software. Here’s how:

  1. Get a ResourceBundle. 

    ResourceBundle b = ResourceBundle.getBundle("Menus");

    I’ll talk about ResourceBundle in Section 14.7, but briefly, a ResourceBundle represents a collection of name-value pairs (resources). The names are names you assign to each GUI control or other user interface text, and the values are the text to assign to each control in a given language.

  2. Use this ResourceBundle to fetch the localized version of each control name.

    Old way:

    somePanel.add(new JButton("Exit"));

    New way:

    rb = ResourceBundle.getBundle("Widgets");
try { label = rb.getString("exit.label"); }
catch (MissingResourceException e) { label="Exit"; } // fallback
somePanel.add(new JButton(label));

    This is quite a bit of code for one button, but distributed over all the widgets (buttons, menus, etc.) in a program, it can be as little as one line with the use of convenience routines, which I’ll show in Section 14.4.

What happens at runtime?

The default locale is used, since we didn’t specify one. The default locale is platform-dependent:

  • Unix/POSIX: LANG environment variable (per user)

  • Windows 95: Start->Control Panel->Regional Settings

  • Others: see platform documentation

ResourceBundle.getBundle( ) locates a file with the named resource bundle name (Menus in the previous example), plus an underscore and the locale name (if any locale is set), plus another underscore and the locale variation (if any variation is set), plus the extension .properties . If a variation is set but the file can’t be found, it falls back to just the country code. If that can’t be found, it falls back to the original default. Table 14-1 shows some examples for various locales.

Table 14-1. Property filenames for different locales

Locale

Filename

Default locale

Menus.Properties

Swedish

Menus_sv.properties

Spanish

Menus_es.properties

French

Menus_fr.properties

French-Canadian

Menus_fr_CA.properties

Locale names are two-letter ISO language codes (lowercase); locale variations are two-letter ISO country codes (uppercase)

Setting the locale

On Windows, go into the Control Panel. Changing this setting entails a reboot, so exit any editor windows.

On Unix, set your LANG environment variable. For example, a Korn shell user in Mexico might have this line in his or her .profile : 

export LANG=es_MX

On either system, for testing a different locale, you need only define the locale in the System Properties at runtime using the command-line option -D, as in: 

java -Duser.language=es Browser

to run the program named Browser in the Spanish locale.

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