* Animals by their animal class. Order doesn't matter, but we want to 
         * ensure that animals are grouped by their animal class property.
         */
        Arrays.sort(animals, new Comparator() {
            public int compare(Object t, Object t1) {
                Animal firstAnimal = (Animal) t;
                Animal secondAnimal = (Animal) t1;
                return firstAnimal.getAnimalClass().hashCode() - 
                        secondAnimal.getAnimalClass().hashCode();
            }
        });
        for (Animal animal : animals) {
            System.out.println(animal.toString());