Producing a read-only copy of a class, howto

Question

Given the following UML representation, how can i get an instance of a BullDog , that only has getter methods exposed?

• Instance of the BullDog should not have any of the setter methods available.
• Instance of the BullDog should only have getter methods (3 of them) available

Basically the question is .. what do i cast new BullDog to?

Answer 1

Since HealthyPet and Pet are unrelated there's nothing you can cast to that will give you all 3 getter methods(getMetabolism(),getName() and getAge()). Now if HealthyPet extended Pet (and I'm really not sure why it doesn't) you'd be in business. Because then you could cast to HealthyPet, return that interface, and a caller would only see the 3 getter methods (of course I'm talking without fancy introspection which should allow them to discover everything).

Answer 2

You need HealthyPet to extend Pet. Then you cast your BullDog instance to HealthyPet.