java comparator, how to sort by integer?

Question

Im trying to learn comparator in java and I have found this great example online, my question is how would this code be changed so that the pet names are ordered by age and

Answer 1

public class DogAgeComparator implements Comparator {
    public int compare(Dog o1, Dog o2) {
        return Integer.compare(o1.getAge(), o2.getId());
    }
}