Learn Java from Scratch - A Beginner's Guide - Step 15 - Java Abstract Class – Puzzles

The video explores puzzles related to abstract classes in programming. It begins by discussing the possibility of creating an abstract class without abstract methods, which is syntactically allowed but not commonly useful. The video then delves into extending abstract classes and the requirement to implement abstract methods unless the subclass is also abstract. It further explains that abstract classes can contain variables and non-abstract methods, providing flexibility in design. The video concludes with a summary of these concepts.

Is it syntactically correct to have an abstract class without any abstract methods?

• No, it is not allowed.

• Yes, it is allowed.

• Only if the class is private.

• Only if the class is final.

What must a class do if it extends an abstract class with abstract methods?

• It must be declared private.

• It must not have any methods.

• It must be declared final.

• It must implement all abstract methods or be declared abstract.

Can an abstract class extend another abstract class without implementing its abstract methods?

• Only if it is a private class.

• Only if it is a final class.

• Yes, it can extend without implementing.

• No, it must implement all methods.

Is it possible for an abstract class to have member variables?

• Only if the variables are final.

• Only if the variables are static.

• Yes, abstract classes can have member variables.

• No, abstract classes cannot have variables.

Can an abstract class contain non-abstract methods?

• Yes, it can have non-abstract methods.

• Only if the methods are private.

• Only if the methods are static.

• No, all methods must be abstract.