1Z0-811 Inheritance and Polymorphism 3

Question 1

Which statement is true about abstract classes in Java?

Accepted Answer

Abstract classes can have both abstract and concrete methods

Answer

Abstract classes can contain both abstract methods (with no implementation) and concrete methods (with full implementation).

Question 2

What does the 'instanceof' operator return in Java?

Accepted Answer

A boolean indicating if an object is an instance of a given type

Answer

The 'instanceof' operator returns true if the object on the left is an instance of the class or interface on the right, enabling safe type checking before casting.

Question 3

What exception is thrown when an invalid cast is attempted at runtime?

Accepted Answer

ClassCastException

Answer

A ClassCastException is thrown at runtime when an object cannot be cast to the specified type because it is not an instance of that type.

Question 4

What is a covariant return type in method overriding?

Accepted Answer

The overriding method may return a subtype of the parent method's return type

Answer

A covariant return type allows an overriding method to return a more specific (subtype) type than the parent method's declared return type.

Question 5

Which of the following is a valid polymorphic variable assignment, where Dog extends Animal?

Accepted Answer

Animal a = new Dog();

Answer

A reference variable of a parent type can hold an object of any subtype — Animal a = new Dog() is valid because Dog is-a Animal.

(1Z0-811) Oracle Java SE11 Programmer Practice Test

(1Z0-811) Oracle Java SE11 Programmer Practice Test

1Z0-811 Inheritance and Polymorphism 3