SCJP Java OOP and Inheritance

Question 1

Which keyword is used in Java to prevent a class from being subclassed?

Accepted Answer

final

Answer

The `final` keyword applied to a class prevents any other class from extending it.

Question 2

What is the output of calling a method on an object reference declared as the superclass type but pointing to a subclass instance?

Accepted Answer

Subclass method runs due to dynamic dispatch

Answer

Java uses dynamic method dispatch (runtime polymorphism), so the overridden subclass method is called.

Question 3

Which of the following is true about abstract classes in Java?

Accepted Answer

They can contain both abstract and concrete methods

Answer

Abstract classes can have both abstract methods (no body) and concrete methods (with body).

Question 4

In Java, what is the result if a subclass defines a static method with the same signature as a static method in its superclass?

Accepted Answer

Method hiding occurs

Answer

When a subclass defines a static method with the same signature as the superclass, it hides the superclass method rather than overriding it.

Question 5

Which access modifier allows a method to be accessed within the same package and by subclasses in other packages?

Accepted Answer

protected

Answer

`protected` grants access within the same package and to subclasses regardless of package.

SCJP - Sun Certified Java Programmer Practice Test