AP CSA Inheritance and Polymorphism 3

Question 1

What is a 'has-a' relationship in OOP (as opposed to 'is-a')?

Accepted Answer

Composition — one class contains a reference to another class

Answer

A 'has-a' relationship is composition: a class holds a reference to another class as a field, rather than inheriting from it.

Question 2

What does the `final` keyword do when applied to a method in Java?

Accepted Answer

Prevents the method from being overridden in subclasses

Answer

A `final` method cannot be overridden by any subclass, locking its implementation for the entire inheritance hierarchy.

Question 3

Which of the following correctly performs a downcast from Animal to Dog?

Accepted Answer

Dog d = (Dog) a;

Answer

A downcast requires an explicit cast operator `(Dog)` to convert a superclass reference to a subclass reference.

Question 4

What is the role of an interface in Java's type system for AP CSA purposes?

Accepted Answer

It defines a contract of methods that implementing classes must provide

Answer

A Java interface specifies a set of method signatures that any implementing class must define, establishing a contract without providing implementations.

Question 5

If a subclass constructor does not explicitly call `super()`, what happens in Java?

Accepted Answer

Java automatically inserts a call to the no-argument superclass constructor

Answer

If no explicit super() call is made, Java implicitly calls the superclass's no-argument constructor as the first action of the subclass constructor.

AP CSA - Advanced Placement Computer Science A Practice Test

AP CSA - Advanced Placement Computer Science A Practice Test

AP CSA Inheritance and Polymorphism 3