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

Just replace:

return d.age - d1.age;

By:

return ((Integer)d.age).compareTo(d1.age);

Or invert to reverse the list:

return ((Integer)d1.age).compareTo(d.age);

EDIT:

Fixed the "memory problem".
Indeed, the better solution is change the age field in the Dog class to Integer, because there many benefits, like the null possibility...