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Java I > Variables, Objects, and Classes > Flashcards

Variables, Objects, and Classes Flashcards

1
Q

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

A

True

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2
Q

A unit within a computer program that combines data and operations

A

Object

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3
Q

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

A

Instance variable

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4
Q

An operation that an object can perform

A

Method

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5
Q

A plan that tells the computer how to build objects

A

Class

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6
Q

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

A

Field declaration

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7
Q

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

A

Method declaration

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8
Q

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

A

Constructor

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9
Q

A constructor that is automatically provided by the compiler

A

Implicit constructor

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10
Q

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

A

Explicit constructor

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11
Q

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

A

Class variable

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12
Q

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

A

Class method

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13
Q

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

A

Static

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14
Q

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

A

An instance

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15
Q

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

A

True

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16
Q

Given this Die class, which is its field?

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

faceUp

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17
Q

Given this Die class, which is its method?

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

roll( )

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18
Q

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); 
}}
A

Implicit

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19
Q

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);
}}
A

Explicit

20
Q

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

A

True

21
Q

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.

A

Primitive variable

22
Q

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

A

Reference variable

23
Q

A __________ is a direct reference to its datum.

A

Primitive variable

24
Q

A __________ is an indirect reference to its data.

A

Reference variable

25
Q

__________ stores its datum immediately within the memory location.

A

A direct reference

26
Q

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

A

An indirect reference

27
Q

__________ variable holds a whole number.

A

An integer

28
Q

__________ variable holds a number with a fractional part.

A

A floating-point

29
Q

What code fragment declares s to be a reference variable?

A

String s;

30
Q

What code fragment declares s to be a primitive variable?

A

double s;

31
Q

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

A

True

32
Q

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

A

True

33
Q

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);
}}
A

Die d = new Die ( );

34
Q

Which part of the code below declares the object’s reference variable?

Scanner in = new Scanner( System.in );

A

Scanner in

35
Q

Which part of the code below calls the class constructor to initialize the object?

Scanner in = new Scanner( System.in );

A

Scanner( System.in );

36
Q

Which part of the code below builds the object?

Scanner in = new Scanner( System.in );

A

new Scanner

37
Q

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 );

A

in = new

38
Q

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; 
}}
A 
HourlyWorker sam = new HourlyWorker( );
sam.hoursWorked = 40.0;
39
Q

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; 
}}
A 
HourlyWorker sam = new HourlyWorker( );
sam.hourlyWage = 12.25;
   -or- 
HourlyWorker sam = new HourlyWorker( );
HourlyWorker.hourlyWage = 12.25;

Although the second option is the best

40
Q

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; 
}}
A 
HourlyWorker sam = new HourlyWorker( );
sam.setWage( 12.25 );
   -or-
HourlyWorker sam = new HourlyWorker( );
HourlyWorker.setWage( 12.25 );

Although the second option is best

41
Q

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; 
}}
A 
HourlyWorker sam = new HourlyWorker( );
sam.setHours( 40.0 );
42
Q

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; 
}}
A 
HourlyWorker sam = new HourlyWorker( );
. . .
double pay = sam.grossPay( 40.0 );
43
Q

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)

A

True

44
Q

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

A

True

45
Q

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

A

True

46
Q

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

A

.class

Java I (4 decks)

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