AP CSA Interfaces and Abstract Classes

Question 1

Which keyword is used to declare an interface in Java?

Accepted Answer

interface

Answer

The `interface` keyword declares an interface in Java, defining a contract of method signatures without implementations.

Question 2

Which keyword does a class use to adopt an interface?

Accepted Answer

implements

Answer

A class uses the `implements` keyword to adopt one or more interfaces and provide concrete implementations for their methods.

Question 3

By default, all methods declared inside an interface are:

Accepted Answer

public and abstract

Answer

Interface methods are implicitly public and abstract, meaning any implementing class must provide a concrete implementation.

Question 4

What happens if a class implements an interface but does not override all of its abstract methods?

Accepted Answer

The class must be declared abstract

Answer

If a class does not implement all abstract methods of an interface, it must itself be declared abstract; otherwise, the code will not compile.

Question 5

Can a single class in Java implement more than one interface?

Accepted Answer

Yes, by listing them separated by commas after implements

Answer

Java allows a class to implement multiple interfaces by listing them after the `implements` keyword, separated by commas.

AP CSA - Advanced Placement Computer Science A Practice Test