AP CSA Inheritance and Polymorphism 2

Question 1

What is dynamic dispatch (dynamic method lookup) in Java?

Accepted Answer

The JVM determines which overridden method to call based on the actual runtime type of the object

Answer

Dynamic dispatch means the JVM uses the actual object type at runtime (not the declared reference type) to decide which overridden method to invoke.

Question 2

If class Dog extends Animal and both have a `speak()` method, what does `Animal a = new Dog(); a.speak();` call?

Accepted Answer

Dog's speak() method

Answer

Due to dynamic dispatch, the JVM looks at the actual object type (Dog) at runtime and calls Dog's speak() method, not Animal's.

Question 3

What does it mean for a class to be `abstract`?

Accepted Answer

It cannot be instantiated and may contain abstract methods

Answer

An abstract class cannot be instantiated directly and can declare abstract methods that subclasses must implement.

Question 4

What must a concrete (non-abstract) subclass do with abstract methods it inherits?

Accepted Answer

Implement (override) all of them

Answer

A concrete subclass must provide implementations for all abstract methods inherited from its abstract superclass, or itself be declared abstract.

Question 5

Can a subclass inherit from multiple superclasses in Java?

Accepted Answer

No, Java only supports single inheritance for classes

Answer

Java supports single class inheritance only — a class can extend only one superclass, though it can implement multiple interfaces.

AP CSA - Advanced Placement Computer Science A Practice Test