Which of the following cannot be an abstract class?

• A. A class without any methods
• B. A class that is final
• C. A class with all methods defined
• D. A class that does not inherit

Answer: (C)

An abstract class in Java is designed to be subclassed and contains one or more abstract methods that do not have an implementation. The purpose of an abstract class is to provide a common blueprint for other classes.

A class with all methods defined cannot be an abstract class because an abstract class must include at least one abstract method. If all methods in the class are concretely defined (i.e., implemented with body), then there is no need for the class to be abstract. An abstract class signifies that it is intended for inheritance and may not provide complete functionality by itself, thereby needing subclasses to provide implementations for its abstract methods.

On the other hand, a class without any methods can still be abstract if it is designed that way for future subclassing. A final class cannot be abstract because final classes cannot be subclassed at all; hence, it does not fit into the purpose of an abstract class. Similarly, a class that does not inherit can still be abstract, as inheritance is not a requirement for being abstract, but rather the presence of an abstract method is what classifies it as such.