public class Main{
    public interface FunctionalInterface {
    public void prvni();
}
    public interface Potomek extends FunctionalInterface{
    @Override
    public void prvni();
}

    public static void main(String[] args) throws InterruptedException {

    FunctionalInterface funkcionalniInterface = new FunctionalInterface() {
        @Override
        public void prvni() {
            System.out.println("Funkcionalni rozhrani");
        }
    };

    Potomek potomek = () -> System.out.println("Potomek");
    }

}