@FunctionalInterface
interface Verifikasi {
    boolean periksa(String teks);

    // Method abstrak kedua merusak status single abstract method
    void laporkan(String teks);
}

public class KontrakGanda {
    public static void main(String[] args) {
        Verifikasi v = teks -> teks.isEmpty();
        System.out.println(v.periksa("halo"));
    }
}