Locale getExtensionKeys() Method in Java with Examples

The getExtensionKeys() method of Locale class in Java is used to return a set of extension keys associated with this locale which cannot be modified and the keys remains in lower-case. If there is no extension then the method returns an empty set.

Syntax:

public Set <Character> getExtensionKeys()

Parameters: This method does not take any parameters.

Return Value: This method either returns a set of extension keys associated with this locale or an empty set if it has no extensions.

Below programs illustrate the working of getExtensionKeys() method:
Program 1:

// Java code to illustrate
// getExtensionKeys() method

import java.util.*;

public class Locale_Demo {
    public static void main(String[] args)
    {

        // Creating a new locale
        Locale first_locale
            = new Locale("th", "TH", "TH");

        // Displaying first locale
        System.out.println("Locale: "
                           + first_locale);

        // Displaying the set
        System.out.println("The KeySet: "
                           + first_locale.getExtensionKeys());
    }
}

Output:

Locale: th_TH_TH_#u-nu-thai
The KeySet: [u]

Program 2:

// Java code to illustrate
// getExtensionKeys() method

import java.util.*;

public class Locale_Demo {
    public static void main(String[] args)
    {

        // Creating a new locale
        Locale first_locale
            = new Locale("en", "US");

        // Displaying first locale
        System.out.println("Locale: "
                           + first_locale);

        // Displaying the set
        System.out.println("The KeySet: "
                           + first_locale.getExtensionKeys());
    }
}

Output:

Locale: en_US
The KeySet: []

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/Locale.html#getExtensionKeys()