Variables, Objects, and Classes

Question 1

The goal of object technology is to allow you to write software that better models the natural world. (T/F)

Answer 1

True

Question 2

A unit within a computer program that combines data and operations

Answer 2

Object

Question 3

Variables internal to an object that hold data defining the object’s state

Answer 3

Instance variable

Question 4

An operation that an object can perform

Answer 4

Method

Question 5

A plan that tells the computer how to build objects

Answer 5

Class

Question 6

Specifies the variables that are to be included in objects of the class

Answer 6

Field declaration

Question 7

Specifies the methods that are to be included in objects of the class

Answer 7

Method declaration

Question 8

A special method that, when called, initializes the object being built

Answer 8

Constructor

Question 9

A constructor that is automatically provided by the compiler

Answer 9

Implicit constructor

Question 10

A constructor that is written out within the text of the class

Answer 10

Explicit constructor

Question 11

Specified by a static field declaration, a variable shared by all objects of a class

Answer 11

Class variable

Question 12

Specified by a static method declaraion, a method shared by all objects of a class

Answer 12

Class method

Question 13

Indicates that a field or method belongs to the entire class and not to individual objects of the class

Answer 13

Static

Question 14

Object-oriented programmers refer to an object as __________ of a class.

Answer 14

An instance

Question 15

You can always identify an explicit constructor within a class declaration because it has the same identifier as the class. (T/F)

Answer 15

True

Question 16

Given this Die class, which is its field?

public class Die {
     public int faceUp;
     public void roll( ) {
          faceUp = (int) (Math.random( ) * 6 + 1); 
}}

Answer 16

faceUp

Question 17

Given this Die class, which is its method?

public class Die {
     public int faceUp;
     public void roll( ) {
          faceUp = (int) (Math.random( ) * 6 + 1); 
}}

Answer 17

roll( )

Question 18

Given this Die class, does it have an implicit or explicit constructor?

public class Die {
     public int faceUp;
     public void roll( ) {
          faceUp = (int) (Math.random( ) * 6 + 1); 
}}

Answer 18

Implicit

Question 19

Given this Die class, does it have an implicit or explicit constructor?

public class Die {
     public int faceUp;
     public Die ( ) {
          roll( );
     }
     public void roll( ) {
          faceUp = (int) (Math.random( ) * 6 + 1);
}}

Answer 19

Explicit

Question 20

If a class has no constructor explicitly written out, the Java compiler automatically gives it an implicit constructor. (T/F)

Answer 20

True

Question 21

A __________ has as its declared data type one of the eight data types (e.g. int, double, char, etc.) that are built into the Java language.

Answer 21

Primitive variable

Question 22

A __________ has as its declared data type a Java class.

Answer 22

Reference variable

Question 23

A __________ is a direct reference to its datum.

Answer 23

Primitive variable

Question 24

A __________ is an indirect reference to its data.

Answer 24

Reference variable

Question 25

__________ stores its datum immediately within the memory location.

Answer 25

A direct reference

Question 26

__________ stores an address that the computer must travel to in order to find the data.

Answer 26

An indirect reference

Question 27

__________ variable holds a whole number.

Answer 27

An integer

Question 28

__________ variable holds a number with a fractional part.

Answer 28

A floating-point

Question 29

What code fragment declares s to be a reference variable?

Answer 29

String s;

Question 30

What code fragment declares s to be a primitive variable?

Answer 30

double s;

Question 31

Java objects can only be accessed through an associated reference variable. (T/F)

Answer 31

True

Question 32

A reference variable that doesn't refer to any object is called a null pointer. (T/F)

Answer 32

True

Question 33

Given this Die class, what Java statement correctly builds a Die object? ``` public class Die { public int faceUp; public Die ( ) { roll( ); } public void roll( ) { faceUp = (int) (Math.random( ) * 6 + 1); }} ```

Answer 33

Die d = new Die ( );

Question 34

Which part of the code below declares the object's reference variable? Scanner in = new Scanner( System.in );

Answer 34

Scanner in

Question 35

Which part of the code below calls the class constructor to initialize the object? Scanner in = new Scanner( System.in );

Answer 35

Scanner( System.in );

Question 36

Which part of the code below builds the object? Scanner in = new Scanner( System.in );

Answer 36

new Scanner

Question 37

Which part of the code below copys the address where the object is located in memory to the reference variable? Scanner in = new Scanner( System.in );

Answer 37

in = new

Question 38

Given this HourlyWorker class, which code fragment correctly references Sam's hoursWorked? ``` public class HourlyWorker { public static double hourlyWage; public double hoursWorked; public static void setWage( double w ) { hourlyWage = w; } public void setHours( double h) { hoursWorked = h; } public double grossPay( ) { return hoursWorked * hourlyWage; }} ```

Answer 38

``` HourlyWorker sam = new HourlyWorker( ); sam.hoursWorked = 40.0; ```

Question 39

Given this HourlyWorker class, which code fragment correctly references Sam's hourlyWage? ``` public class HourlyWorker { public static double hourlyWage; public double hoursWorked; public static void setWage( double w ) { hourlyWage = w; } public void setHours( double h) { hoursWorked = h; } public double grossPay( ) { return hoursWorked * hourlyWage; }} ```

Answer 39

``` HourlyWorker sam = new HourlyWorker( ); sam.hourlyWage = 12.25; -or- HourlyWorker sam = new HourlyWorker( ); HourlyWorker.hourlyWage = 12.25; ``` Although the second option is the best

Question 40

Given this HourlyWorker class, which code fragment correctly calls setWage? ``` public class HourlyWorker { public static double hourlyWage; public double hoursWorked; public static void setWage( double w ) { hourlyWage = w; } public void setHours( double h) { hoursWorked = h; } public double grossPay( ) { return hoursWorked * hourlyWage; }} ```

Answer 40

``` HourlyWorker sam = new HourlyWorker( ); sam.setWage( 12.25 ); -or- HourlyWorker sam = new HourlyWorker( ); HourlyWorker.setWage( 12.25 ); ``` Although the second option is best

Question 41

Given this HourlyWorker class, which code fragment correctly calls setHours? ``` public class HourlyWorker { public static double hourlyWage; public double hoursWorked; public static void setWage( double w ) { hourlyWage = w; } public void setHours( double h) { hoursWorked = h; } public double grossPay( ) { return hoursWorked * hourlyWage; }} ```

Answer 41

``` HourlyWorker sam = new HourlyWorker( ); sam.setHours( 40.0 ); ```

Question 42

Given this HourlyWorker class, which code fragment correctly calls grossPay? ``` public class HourlyWorker { public static double hourlyWage; public double hoursWorked; public static void setWage( double w ) { hourlyWage = w; } public void setHours( double h) { hoursWorked = h; } public double grossPay( ) { return hoursWorked * hourlyWage; }} ```

Answer 42

``` HourlyWorker sam = new HourlyWorker( ); . . . double pay = sam.grossPay( 40.0 ); ```

Question 43

The easiest way to compile and run a Java program using more than one class is to have all necessary class files contained in the same disk folder. (T/F)

Answer 43

True

Question 44

An external reference is the occurrence in some file A of an identifier x that is declared in another file B. (T/F)

Answer 44

True

Question 45

To resolve an external reference, the Java compiler automatically searches for its declaration, a process called separate compilation. (T/F)

Answer 45

True

Question 46

Each Java class is compiled into a separate file that has __________ as its extension.

Answer 46

.class