abstract class Hond {
    public final void haalKrant() {
        //...        
        blaf();
    }
    public abstract void blaf();
    //...
}

class SintBernard extends Hond {
    public void blaf() {
        System.out.println("Woef woef");
    }
}

class Tekkel extends Hond {
    public void blaf() {
        System.out.println("Kef kef");
    }
}

public class THond1 {
    public void doeJeWerk(Hond h) {
        h.haalKrant();
    }
    public static void main(String[] s) {
        THond1 test=new THond1();
        Tekkel harry=new Tekkel();
        SintBernard bor=new SintBernard();
        for (int i=0; i<10; ++i)
            if (i%3==0)
                test.doeJeWerk(harry);
            else
                test.doeJeWerk(bor);
   }
}