ResourceBundle and ListResourceBundle class in Java with Examples

The ResourceBundle and ListResourceBundle classes are part java.util package. These classes are designed to aid in the internationalization of programs. 

ResourceBundle: The class ResourceBundle is an abstract class. It defines methods that enable you to manage a collection of locale-sensitive resources. Resource bundles are identified by their family name. To the family name is added a two-character lowercase language code that specifies the language. We can also specify a country code after the language code. It is a two-character uppercase identifier and is preceded by an underscore when linked to a resource bundle name. 

Class Hierarchy:

java.lang.Object
↳java.util.ResourceBundle

Constructors:

1. ResourceBundle(): The default constructor which is mainly designed for use by the subclasses and the factory methods. 

public ResourceBundle()

Methods:

1. clearCache(): This method deletes all resource bundles from the cache that were loaded by the default class loader. 

static final void clearCache()

2. containsKey(): This method returns true if the passed string argument is a key within the invoking resource bundle. 

boolean containsKey(String k)

3. getBundle(): This method loads the resource bundle with the given name and the specified locale. 

static final ResourceBundle getBundle(String familyName)
static final ResourceBundle getBundle(String familyName, Locale loc)

4. setParent(): This method sets the passed bundle as parent of the invoking bundle. In case of a lookup, if the key is not found in the invoking object, then it is looked up in the parent bundle. 

protected void setParent(ResourceBundle parent)

5. getObject(): This method retrieves and returns the Object associated with the key passed as argument either from the current resource bundle or the parent. 

public final Object getObject(String key)

6. getHandleObject(): This method returns the object associated with the given key from the resource bundle. If no object is available null is returned. 

protected abstract Object handleGetObject(String key)

7. getString(): This method retrieves and returns the string associated with the key passed as argument either from the current resource bundle or the parent. 

public final String getString(String key)

8. getStringArray(): This method retrieves and returns the string array associated with the key passed as argument either from the current resource bundle or the parent. 

public final String[] getStringArray(String key)

9. getLocale(): This method returns the Locale associated with the current bundle. 

public Locale getLocale()

10. containsKey(): This method checks whether a given key exists within a resource bundle or its parent or not. 

public boolean containsKey(String key)

11. keySet(): This method returns the set of all the keys in the current bundle or its parent bundle. 

public Set keySet()

ListResourceBundle: It is a subclass of ResourceBundle. It is an abstract class, which manages the resources in an array of key/value pairs. It adds only one new method getContents(), which must be implemented by every subclass.

Constructors:

1. ListResourceBundle(): The default constructor to create an object. 

public ListResourceBundle()

Methods:

1. getContents(): This method returns a two dimensional array that contains key/value pairs that represent resources. 

protected abstract Object[][] getContents()

2. handleGetObject(): This method returns the object associated with the key in the current bundle if it exists. 

public final Object handleGetObject(String key)

3. getKeys(): This method returns an enumeration of the keys in the resource bundle.

public Enumeration getKeys()

4. handleKeySet(): This method returns the set of all the keys in the current resource bundle. 

protected Set handleKeySet()

Example to demonstrate the use of a ResourceBundle

Java

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

class SampleRB extends ListResourceBundle {
    protected Object[][] getContents()
    {
        Object[][] resources = new Object[3][2];

        resources[0][0] = "title";
        resources[0][1] = "My Program";

        resources[1][0] = "StopText";
        resources[1][1] = "Stop";

        resources[2][0] = "StartText";
        resources[2][1] = "Start";

        return resources;
    }
}
class SampleRB_de extends ListResourceBundle {
    protected Object[][] getContents()
    {
        Object[][] resources = new Object[3][2];

        resources[0][0] = "title";
        resources[0][1] = "Mein Program";

        resources[1][0] = "StopText";
        resources[1][1] = "Anschlag";

        resources[2][0] = "StartText";
        resources[2][1] = "Anfang";

        return resources;
    }
}
public class LRBDemo {
    public static void main(String[] args)
    {
        ResourceBundle rd
            = ResourceBundle
                  .getBundle("SampleRB",
                             Locale.ENGLISH);
        System.out.println("English Version:");
        System.out.println("String for Title key: "
                           + rd.getString("title"));
        System.out.println("String for StopText key: "
                           + rd.getString("StopText"));
        System.out.println("String for StartText key: "
                           + rd.getString("StartText"));

        rd = ResourceBundle
                 .getBundle("SampleRB",
                            Locale.GERMAN);
        System.out.println("\nGerman Version");
        System.out.println("String for Title key: "
                           + rd.getString("title"));
        System.out.println("String for StopText key: "
                           + rd.getString("StopText"));
        System.out.println("String for StartText key: "
                           + rd.getString("StartText"));
    }
}

Output:

English Version:
String for Title key: My Program
String for StopText key: Stop
String for StartText key: Start

German Version
String for Title key: Mein Program
String for StopText key: Anschlag
String for StartText key: Anfang

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/ResourceBundle.html