AP CSA Interfaces and Abstract Classes 2

Question 1

Which keyword is used to declare an abstract class in Java?

Accepted Answer

abstract

Answer

The `abstract` keyword is placed before the `class` keyword to declare a class as abstract, meaning it cannot be instantiated directly.

Question 2

Can an abstract class contain non-abstract (concrete) methods?

Accepted Answer

Yes, it can contain both abstract and concrete methods

Answer

An abstract class can have a mix of abstract methods (no body) and concrete methods (with a body), providing partial implementation.

Question 3

What is the result of trying to instantiate an abstract class directly?

Accepted Answer

A compile-time error

Answer

Attempting to instantiate an abstract class results in a compile-time error because abstract classes are incomplete by design.

Question 4

Which relationship does abstract class inheritance use in Java?

Accepted Answer

extends

Answer

A subclass inherits from an abstract class using the `extends` keyword, the same as with concrete class inheritance.

Question 5

Consider: `public abstract class Shape { public abstract double area(); }`. Which of the following correctly creates a subclass?

Accepted Answer

public class Circle extends Shape { public double area() { return 3.14 * r * r; } }

Answer

Circle must extend Shape (not implement) and must provide a concrete `area()` method to avoid being abstract itself.

AP CSA - Advanced Placement Computer Science A Practice Test