How to apply more constraints on an interface declaration in Java?

Question

Let's say I have following interface:

interface Mammal {     void marry(Mammal m);     Mammal giveBirthTo(); } 

However, this doesn't say quite exactly what I want.

Obviously, a human can't marry a dog, nor give birth to a cat. So how can I embed this information into the interface, such that the input type and output type can be changed automatically as it gets implemented?

Answer 1

You could use generics and change your design.

Something in the lines of:

interface Marriable<T extends Mammal> {     void marry(T sweetHalf);     T giveBirthTo(); } 

... where Mammal is your top interface or abstract class, and Human, Dog, Unicorn etc. extend / implement it.