Deck 10: Object-Oriented Programming, Part 3: Inheritance, Polymorphism, and Interfaces

Question 1

The extends keyword specifies that the subclass inherits members of the superclass, so:

A) the base class begins with a set of predefined methods and fields inherited from its hierarchy of superclasses.
B) the derived class begins with a set of predefined methods and fields inherited from its hierarchy of superclasses.
C) the derived class begins with a set of predefined methods inherited from its hierarchy of fields.
D) the base class begins with a set of predefined methods inherited from its hierarchy of derived classes.

Answer 1

B

Question 2

Which of the following would make the subclass Clubs more functional than its superclass Extracurriculars?

A) Define new fields and methods.
B) Create another instance variable (?) that includes intramural sports.
C) Add a variable that identifies whether clubs are available only by students.
D) All of these would make the subclass more functional.

Answer 2

D

Question 3

Which of the options listed will happen if the following code segment is run, assuming the remainder of the program is coded correctly?
10 public class Circle extends Figure
11 {
12 private int radius;
13 public Circle( )
14 {
15 super( );
16 radius = 0;

A) The default constructor of the Figure class will be called (line 15).
B) The default constructor of Radius class will set radius to 0.
C) The attempt to instantiate an object of the abstract class will generate a compiler error.
D) All of these are correct.

Answer 3

A

Question 4

Why does Java provide a protected access modifier?

A) To hide methods from the client classes
B) To hide fields from client classes
C) So fields and methods can be inherited by subclasses
D) All of these are correct.

Question 5

An interface can contain one or more abstract methods.

Question 6

A class must implement at least one interface.

Question 7

A class can implement more than one interface.

Question 8

If a class has an abstract method, then that class is automatically an interface.

Question 9

We can instantiate an object from an interface.

Question 10

Inheritance is useful for which of the following?

A) It declares the hierarchy of methods that are not common to all classes so they can be reused.
B) It allows superclasses to override subclasses.
C) It allows related classes to be organized into levels of functionality so they can be reused.
D) None of these is correct.

Question 11

Some OOP developers call a subclass the base class and call a superclass the derived class.

Question 12

Which of the following are not inherited by subclasses?

A) public fields and public methods
B) private fields and private methods
C) protected fields and protected methods
D) All of these are correct.

Question 13

Why does Java provide a protected access modifier?

A) To hide methods from the client classes
B) To hide fields from client classes
C) So that fields and methods can be inherited by subclasses
D) All of these are correct.

Question 14

Why would you want to override a method?

A) It allows you to hide features of the subclass using the super keyword.
B) It allows you to hide features of the superclass that you want to change.
C) It allows you to make the inherited version of the method visible to the client of the subclass.
D) It allows you to invoke the base case method.

Question 15

The extends keyword specifies that the subclass inherits members of the superclass.

Question 16

If the call to the direct superclass constructor was not the first statement in the constructor, a compiler error will be generated.

Question 17

When a class extends another class, the default constructor of the subclass automatically calls the default constructor of the superclass. This is called explicit invocation.

Question 18

Why does using the protected access modifier compromise encapsulation?

A) Multiple classes can set the value of an instance variable defined in another class.
B) When a class does change a protected value, there is added maintenance complexity.
C) Subclass methods that directly set the value of a protected instance variable need to be verified.
D) When high performance is essential, superclass methods can be used to change the value of protected variables.

Question 19

Typically, an abstract class is a class that is not completely implemented.

Question 20

Several classes implement an interface, but all of them implement the same method using the same code. To provide a common method for all of these classes, you would create an abstract class.

Question 21

The following code will run without errors:
// Figure is an abstract class
Figure f = new Figure( );

Question 22

Which of the following is true of polymorphism?

A) It simplifies the processing of various elements in the same class hierarchy.
B) To use polymorphism, the classes must be in a different hierarchy.
C) In Greek, the term means "many changes."
D) All of these are correct.

Question 23

To use polymorphism, the classes must be in a different hierarchy.

Question 24

Which of the following cannot be an interface member?

A) A class
B) A constant
C) A mutator method
D) An abstract method

Question 25

An interface can contain one or more static constants.

Question 26

Which Java keyword do we use in the constructor of a class inheriting from another class if we want to call the constructor of the inherited class?

A) call
B) super
C) constructor
D) clone

Question 27

Which of the following is correct regarding constructors?

A) Constructors are inherited but cannot be accessed.
B) Constructors are inherited and can be accessed.
C) Constructors are accessible but are not inherited.
D) Constructors are not inherited and cannot be accessed.

Question 28

An abstract method:

A) has a "do-nothing" body.
B) does not have a body.
C) has a body that operates like any other method.

Question 29

When is it determined which method is called when using polymorphism?

A) At compile time
B) At the time of writing code
C) At runtime

Question 30

Which of the following is the correct definition of polymorphism?

A) One form only
B) Two forms only
C) Multiple forms
D) No form

Question 31

A method in a subclass overriding a method in a superclass cannot call the superclass method.

Question 32

Overriding a method and overloading a method mean the same thing.

Question 33

Abstract methods can be static.

Question 34

Abstract methods can be private.

Question 35

Abstract methods can be overridden.

Question 36

A constructor can be declared abstract.

Question 37

An interface can contain instance variables.

Question 38

An interface can contain a constructor.

Question 39

_________ allows us to use the same method call for any object in a class hierarchy.

Question 40

Which keyword do we use in the header of a class that inherits from another class?

A) inherits
B) extends
C) protected
D) modifies

Question 41

When class B inherits from class A:

A) A is the superclass and B is the subclass.
B) A is the subclass and B is the superclass.

Question 42

Assuming that class B inherits from class A and method foo belongs to class A, what do we mean by overriding method foo in class B?

A) We are calling method foo in class B.
B) We are not using method foo in class B.
C) We are replacing the superclass version of the foo method with a new foo method with the same signature.

Question 43

Assuming that class B inherits from class A, which of the following is correct?

A) An object of class B is an object of class A.
B) An object of class A is an object of class B.
C) An object of class B is an object of class A and an object of class A is an object of class B.
D) None of these is correct.

Question 44

What keyword do we use in the class header that inherits from an interface?

A) inherits
B) interfaces
C) implements
D) modifies

Question 45

When a class implements an interface:

A) it does not have to implement the abstract methods of the interface.
B) it has to implement at least one of the abstract methods of the interface, but not all of them.
C) it has to implement all of the abstract methods of the interface.

Question 46

Private fields and methods are inherited.

Question 47

Private fields and methods are part of the inheriting class object.

Question 48

Public fields and methods are inherited.

Question 49

Protected fields and methods are inherited.

Question 50

When calling the constructor of a superclass from the constructor of the subclass, the call to that superclass constructor must be the first statement in the subclass constructor.

Question 51

Typically, an abstract class is a class that is not completely implemented.

Question 52

Usually, an abstract class contains at least one abstract method.

Question 53

We can instantiate an object from an abstract class.

Question 54

If a class has an abstract method, then that class must be declared abstract.

Question 55

Abstract methods can be called.

Question 56

Inheritance helps organize related classes into __________.

Question 57

An abstract class is declared to be abstract by including the __________ keyword in the class header.

Question 58

The interface concept is Java's way of implementing __________ inheritance.

Question 59

Because the private instance variables of a class are not inherited, how can the methods of a subclass access the values of these private instance variables?

Question 60

Suppose you write a program in which you attempt to use a subclass to directly access a private password field in a superclass. Predict what will happen, and suggest a solution that would result in a different outcome.

Question 61

You have written a SavingsAccount class based on the BankAccount class in the textbook. You wish to instantiate a SavingsAccount object with a starting balance of $2,175.25. Theorize why you would need to provide an overloaded constructor for the SavingsAccount class.