Starting Out with Java: From Control Structures through Objects

Tony Gaddis

Chapter 10

Inheritance - all with Video Answers

Educators

Chapter Questions

Problem 1

Here is the first line of a class declaration. What is the name of the supcrelass? What is the name of the subclass?
public class Truck extends vehicle

Aditya Sood

Aditya Sood

Numerade Educator

Problem 2

Look at the following class declarations and answer the questions that follow them:
public claaa shape
{
private double area public vold set\Lambdarea(double a)
}
area $=a$
\[
{
\]
public double gethrea()
}
return area:
\[
{
\]
}
public class CLrcle extends shape
{
private double radius? pub1Le vold setRadius (double $x$ )
}
radius $=x_{i}$ set\Lambdarea(Math.PI : $x$ " x)
{
public double getRadius()
}
retura radius?
{
}
a) Which class is the superclass? Which class is the subclass?
b) Draw a UML diagram showing the relationship between these two classes.
c) When a clrcle object is created, what are its public members?
d) What members of the shape class are not accessible to the clrcle class's methods?
c) Assume a program has the following declarations:
shape $s=$ new shape () i circle $c=$ new $c$ ircle (1) ;
Indicate whether the following statements are legal or illegal:
c. set Radius (10.0)
8. set Radius (10.0) Syatem, out .printin(c.gethrea())

Brian Ketelobeter

Brian Ketelobeter

Numerade Educator

Problem 3

Class $B$ extends class $A$. (Class $A$ is the superclass and class $B$ is the subclass.) Describe the order in which the class's constructors exccute when a class B object is created.

Aditya Sood

Numerade Educator

Problem 4

Look at the following classes:
public clasa Ground
{
public Ground()
\[
}
\]
Systen, out .printing "You are on the ground,"
\[
{
\]
}
public class sky extends Ground
{
public sky()
\[
}
\]
Syatem.out.printla("You are in the sky."):
\[
{
\]
}
What will the following program display?
public class Checkpoint
{
public static void main(stringl 1 arga) }
sky object - new sky():
\[
{
\]
}

SS

Sarvesh Somasundaram

Numerade Educator

Problem 5

Look at the following classes:
public class Ground
{
public Ground() 1
System. Out $.$ printla $($ "You are on the ground." )
}
publ Le Ground ( String groundColor)
\[
{
\]
Syatem. Out $.$ print 1 a $(\text { "The ground } 1 \text { s }=+$ groundcolor
\[
}
\]
{
public class sky extends Ground
}
public sky()
{
Syatem, out $\cdot$ print $1 n(\text { "You are } 1 \text { n the aky }, "$ )
}
public sky(string akycolor)
{
super $\left(" \operatorname{green}^{-0}\right)$
}
{
What will the following program display?
public claaa Checkpolat
}
public atatic void main(stringl 1 arga)
{
sky object = new sky("blue")
}

Manik Pulyani

Numerade Educator

Problem 6

Under what circumstances would a subclass need to override a superclass method?

Pawan Yadav

Numerade Educator

Problem 7

How can a subclass method call an overridden superclass method?

Manik Pulyani

Numerade Educator

Problem 8

If a method in a subclass has the same signature as a method in the superclass, does the subclass method overload or override the superclass method?

Aditya Sood

Numerade Educator

Problem 9

If a method in a subclass has the same name as a method in the superclass, but uses a different parameter list, does the subclass method overload or override the superclass method?

Aditya Sood

Numerade Educator

Problem 10

How do you prevent a method from being overridden?

Manik Pulyani

Numerade Educator

Problem 11

When a class member is declared as protected, what code may access it?

Aditya Sood

Numerade Educator

Problem 12

What is the difference between private members and protected members?

Jennifer Stoner

Jennifer Stoner

Numerade Educator

Problem 13

Why should you avoid making class members protected when possible?

SS

Sarvesh Somasundaram

Numerade Educator

Problem 14

What is the difference between private access and package access?

Jennifer Stoner

Jennifer Stoner

Numerade Educator

Problem 15

Why is it casy to give package access to a class member by accident?

SS

Sarvesh Somasundaram

Numerade Educator

Problem 16

Look at the following class definition:
public claaa Clasab extenda ClasaB
{
(Member Declarations $\dots .)$
}
Because clasab inherits from classb, is it true that classb does not inherit from the Object class? Why or why not?

Aditya Sood

Numerade Educator

Problem 17

When you create a class, it automatically has a tostring method and an equals method. Why?

Julie Silva

Numerade Educator

Problem 18

Recall the Rectangle and cube classes discussed carlicr, as shown in Figure $10-18$
a) Is the following starement legal or illegal? If is is illegal, why?
Rectangle $x=$ new Cube (10,12,5)
b) If you determined that the statement in part a is legal, are the following statements legal or illcgal? (Indicate legal or illcgal for cach statement.) Syatem . OUt . Println ( $x$. gettength () ) System.out $.$ print 1 n $(x, \text { getwidth }())$ System . OUt . print $1 n(x . \text { get } \text { Helght }())$ Syatem.out $\cdot$ print $1 n(x \cdot \text { getsurtacentea }())$
c) Is the following statement legal or illegal? If it is illegal, why?
Cube $e$ - new Rectangle (10,12) ?

Vysakh M

Numerade Educator

Problem 19

What is the purpose of an abstract method?

Aditya Sood

Numerade Educator

Problem 20

If a subclass extends a superclass with an abstract method, what must you do in the subclass?

Aditya Sood

Numerade Educator

Problem 21

What is the purpose of an abstract class?

Aditya Sood

Numerade Educator

Problem 22

If a class is defined as abstract, what can you not do with the class?

Aditya Sood

Numerade Educator

Problem 23

What is the purpose of an interface?

Jennifer Stoner

Jennifer Stoner

Numerade Educator

Problem 24

How is an interface similar to an abstract class?

Aditya Sood

Numerade Educator

Problem 24

How is an interface similar to an abstract class?

Aditya Sood

Numerade Educator

Problem 25

How is an interface different from an abstract class, or any class?

Aditya Sood

Numerade Educator

Problem 26

If an interface has ficlds, how are they treated?

Jennifer Stoner

Jennifer Stoner

Numerade Educator

Problem 27

Write the first line of a class named cuatomer, which implements an interface named Relatable.

Manik Pulyani

Numerade Educator

Problem 28

Write the first line of a class named zmployee, which implements interfaces named Payable and Liatable.

SS

Sarvesh Somasundaram

Numerade Educator