public class MethodReferenceDemo1 {

    @FunctionalInterface

    interface StringListFormatter {

        String format(String delimiter, List<String> list);

    }

    public static void formatAndPrint(StringListFormatter formatter,  String delimiter, List<String> list) {

        String formatted = formatter.format(delimiter, list);

        System.out.println(formatted);

    }

   

    public static void main(String[] args) {

        List<String> names = Arrays.asList("Don", "King", "Kong");

        formatAndPrint(String::join, ", ", names);

    }

}