To solve this question, the user needs to know about inheritance in Java and how casting works. The key to answering this question correctly is understanding how casting works between different classes in an inheritance hierarchy.
Now, let's go through each option and explain why it is right or wrong:
A. Alpha a = x; - This code is valid because Beta is a subclass of Alpha, so it can be upcast to an Alpha without issue. This will not cause a ClassCastException
.
B. Foo f= (Delta)x; - This code is invalid because Delta is a subclass of Beta, so it cannot be downcast to Delta from Beta. This will throw a ClassCastException
.
C. Foo f= (Alpha)x; - This code is valid because Beta is a subclass of Alpha, so it can be upcast to an Alpha without issue. This will not cause a ClassCastException
.
D. Beta b = (Beta)(Alpha)x; - This code is invalid because Alpha is a superclass of Beta, so it cannot be downcast to Beta from Alpha. This will throw a ClassCastException
.
Therefore, the correct answer is:
The Answer is: B