import java.util.HashSet; import java.util.Collections; import java.util.Set; public class Main { public static void main(String[] args) { HashSet<String> cars = new HashSet<String>(); cars.add("Volvo"); Set<String> readOnly = Collections.unmodifiableSet(cars); try { readOnly.add("BMW"); } catch (UnsupportedOperationException e) { System.out.println("Error: the set cannot be changed."); } } }