Difference between Dynamic and Static type assignments in Java

Question

Given the follow class hierarchy what are the dynamic and static types for the following statements?

Class hierarchy:

class Alpha {}         


        

Answer 1

The concrete, runtime type of f is Fruit (as you correctly stated in your question).

So Beta b = f; initilalizes a variable whose declared, compile-time type is Beta, and whose runtime type is Fruit. This won't compile though, because the compile-time type of f is Fruit, and Fruit is not a subclass of Beta, so f can't be assigned to a variable of type Beta.

In a = b;, b, whose runtime type is Fruit (see above) is assigned to the variable a, declared as Alpha a. So a's compile-time type is Alpha and its runtime type is Fruit.