ResourceBundle (in java.util) is a mechanism for internationalization (i18n) that allows you to load locale-specific resources like text messages, labels, or configuration data from property files or classes.

• Supporting multiple languages in your application.
• Separating locale-specific strings from code.
• Dynamically loading language resources based on user locale.

Suppose you have two property files:

• Messages_en.properties
• Messages_fr.properties

# Messages_en.properties
greeting=Hello
farewell=Goodbye

# Messages_fr.properties
greeting=Bonjour
farewell=Au revoir

Java code to load and use these resources:

import java.util.Locale;
import java.util.ResourceBundle;

public class ResourceBundleExample {
    public static void main(String[] args) {
        ResourceBundle bundle = ResourceBundle.getBundle("Messages", Locale.FRANCE);
        System.out.println(bundle.getString("greeting"));  // Output: Bonjour

        bundle = ResourceBundle.getBundle("Messages", Locale.US);
        System.out.println(bundle.getString("farewell"));  // Output: Goodbye
    }
}

• Resource bundles can be backed by property files or Java classes.
• The getBundle() method chooses the best match for the requested locale.
• Missing keys throw MissingResourceException if not handled.

Using ResourceBundle helps create applications that are easy to adapt to different languages and regions.