Basically if the Jump function takes an Animal interface, the package that defines the jump function is the one that defines the Animal.Jump method. So if you p

Basically if the Jump function takes an Animal interface, the package that defines the jump function is the one that defines the Animal.Jump method. So if you provide it with whatever entity that has this method, it will just work. You don’t have to define the Animal interface in your Cat package. But if your cat does not Jump, it won’t be accepted. Of course you can also pass in a box that Jumps.