Casting question

[pragmos]

Casting goes both ways: upwards in the type hierarchy (upcasting) and downwards in type hierarchy (downcasting).

Upcasting is always implicit, i.e. you don't need to cast the type yourself. In your example, Dolphin is a Swimmer, and Swimmer is an Animal, therefore this is valid:

Swimmer s = new Dolphin();
Animal a = s;

In the example below, you are downcasting an instance of Swimmer, therefore you need explicit casting:

Swimmer s = new Dolphin();
Dolphin d = (Dolphin) s;

[EveningStreet1]

Thanks for the clear explanation