Download Code Listing 8-3 - CS Course Webpages

Starting Out with Java:
From Control Structures
through Objects
5th edition
By Tony Gaddis
Source Code: Chapter 8
Code Listing 8-1 (Countable.java)
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/**
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This class demonstrates a static
*/
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public class Countable
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field.
{
private static int instanceCount = 0;
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9 /**
10 The constructor increments the static
// What category of variable?
// What is it’s scope?
11 field instanceCount. This keeps track
12 of the number of instances of this
13 class that are created.
14 */
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16 public
17 {
Countable()
18 instanceCount++;
19 }
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(Continued)
21 /**
The getInstanceCount method returns
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the number of instances of this class
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that have been created.
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@return The value in the instanceCount field.
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26 */
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28 public
29 {
int getInstanceCount()
30 return
31 }
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instanceCount;
Code Listing 8-2 (StaticDemo.java)
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/**
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public class StaticDemo
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public static void main(String[] args)
{
This program demonstrates the Countable class.
*/
{
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int objectCount;
11 // Create
three instances
13 Countable object1 = new Countable();
14 Countable object2 = new Countable();
15 Countable object3 = new Countable();
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23 }
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objectCount = object1.getInstanceCount();
System.out.println(objectCount +
" instances of the class " +
"were created.");
Program Output
3 instances of the class were created.
Code Listing 8-3 (Metric.java)
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/**
This class demonstrates static
methods.
*/
5 public class Metric
6 {
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/**
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The milesToKilometers method converts a
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distance in miles to kilometers.
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@param m The distance in miles.
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@return The distance in kilometers.
12 */
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public static double milesToKilometers( double m )
{
return m * 1.609;
}
(Continued)
(Continued) Code Listing 8-3 (Metric.java)
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/**
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public static double kilometersToMiles( double k )
The kilometersToMiles method converts
a distance in kilometers to miles.
@param k The distance in kilometers.
@return The distance in miles.
*/
{
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return k / 1.609;
Code Listing 8-4 (MetricDemo.java)
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import javax.swing.JOptionPane;
import java.text.DecimalFormat;
/**
This program demonstrates the Metric class.
*/
public class MetricDemo
{
public static void main(String[] args)
{
String input;
double miles;
double kilos;
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DecimalFormat fmt = new DecimalFormat("0.00");
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input = JOptionPane.showInputDialog("Enter " +
"a distance in miles.");
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miles = Double.parseDouble(input);
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kilos = Metric.milesToKilometers(miles);
JOptionPane.showMessageDialog(null,
fmt.format(miles) + " miles equals " +
fmt.format(kilos) + " kilometers.");
input = JOptionPane.showInputDialog("Enter " +
"a distance in kilometers:");
kilos = Double.parseDouble(input);
Metric.kilometersToMiles(kilos);
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miles =
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JOptionPane.showMessageDialog(null,
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43 }
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// Invoked thru?
fmt.format(kilos) + " kilometers equals " +
fmt.format(miles) + " miles.");
System.exit(0);
// Invoked thru?
Code Listing 8-5 (PassObject.java)
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/**
This program passes an object as an argument.
*/
public class PassObject
{
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public static void
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{
main(String[] args)
Rectangle box = new Rectangle(12.0, 5.0);
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// Pass a reference to the object to
// the displayRectangle method.
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displayRectangle(box);
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// Where defined?
}
/**
The displayRectangle method displays the
length and width of a rectangle.
@param r A reference to a Rectangle
object.
*/
(Continued)
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public static void displayRectangle(Rectangle r)
{
// Display the length and width.
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System.out.println("Length : " +
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" Width : " +
}
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Program Output
Length : 12.0 Width : 5.0
r.getLength() + // Calls an Instance Method
r.getWidth()); // from a static method
Code Listing 8-6 (PassObject2.java)
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/**
This program passes an object as an argument.
The object is modified by the receiving method.
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*/
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public class PassObject2
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{
public
{
static void main(String[] args)
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Rectangle box = new Rectangle(12.0, 5.0);
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System.out.println("Contents of the box object:");
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System.out.println("Length : " + box.getLength() +
" Width : " +
box.getWidth());
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// Pass a reference to the object to the
// changeRectangle method.
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changeRectangle(box);
(Continued)
System.out.println("\nNow the contents of the " +
"box object are:");
System.out.println("Length : " + box.getLength() +
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" Width : " +
box.getWidth());
}
/**
The changeRectangle method sets a Rectangle
object's length and width to 0.
@param r The Rectangle object to change.
*/
public
static void changeRectangle( Rectangle r )
{
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r.setLength(0.0);
r.setWidth(0.0);
Program Output
Contents of the box object:
Length : 12.0 Width : 5.0
Now the contents of the box object are:
Length : 0.0 Width : 0.0
Code Listing 8-7 (ReturnObject.java)
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import javax.swing.JOptionPane;
/**
This program demonstrates how a method
can return a reference to an object.
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*/
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public class ReturnObject
{
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public static void
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{
main(String[] args)
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BankAccount account;
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account = getAccount();
JOptionPane.showMessageDialog(null,
"The account has a balance of $" +
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account.getBalance());
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System.exit(0);
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}
// Returns what?
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/**
The getAccount method creates a BankAccount
object with the balance specified by the
user.
@return A reference to the object.
*/
public
static BankAccount getAccount()
{
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String input;
double balance;
// To hold input
// Account balance
input = JOptionPane.showInputDialog("Enter " +
"the account balance.");
balance = Double.parseDouble(input);
return new BankAccount(balance);
Code Listing 8-8 (Stock.java)
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/**
The Stock class holds data about a stock.
*/
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public class Stock
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private String
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private double
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public Stock( String
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{
{
// Trading symbol of stock
// Current price per share
/**
Constructor
@param sym The stock's trading symbol.
@param price The stock's share price.
*/
sym, double price )
symbol = sym;
sharePrice = price;
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symbol;
sharePrice;
}
(Continued)
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/**
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public String getSymbol()
{
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getSymbol method
@return The stock's trading symbol.
*/
return symbol;
}
/**
getSharePrice method
@return The stock's share price
*/
public double getSharePrice()
{
return sharePrice;
}
(Continued)
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/**
toString method
@return A string indicating the object's
trading symbol and share price.
*/
public String toString()
//
{
// Create a string describing the stock.
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String
str = "Trading symbol: " + symbol +
"\nShare price: " + sharePrice;
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return str;
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EXPLICIT toString()
}
}
Code Listing 8-9 (StockDemo1.java)
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/**
This program demonstrates the Stock class's
3 toString method.
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*/
public class StockDemo1
{
public static void main(String[] args)
{
// Create
a Stock object for the XYZ Company.
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Stock xyzCompany = new Stock ("XYZ", 9.62);
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System.out.println(xyzCompany);
// Display the object's values.
// What method is called?
}
}
Program Output
Trading symbol: XYZ
Share price: 9.62
// Auto call under what 2
// conditions?
Code Listing 8-10 (StockCompare.java)
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/**
This program uses the Stock class's equals
method to compare two Stock objects. See 514-515 for “equals”.
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*/
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public class StockCompare
{
public static void main(String[] args)
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{
Stock company1 = new Stock("XYZ", 9.62);
Stock company2 = new Stock("XYZ", 9.62);
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if (company1.equals(company2))
System.out.println("Both objects are the same.");
else
System.out.println("The objects are different.");
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}
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Program Output
Both objects are the same.
Code Listing 8-11 (ObjectCopy.java)
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/**
This program uses the Stock class's copy method
to create a copy of a Stock object. ( see pg. 517)
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*/
public class ObjectCopy
{
public static void main(String[] args)
{
Stock company1 = new Stock("XYZ", 9.62);
Stock company2;
// copy()- makes a new stock object-uses IV’s of company1.
// returns addr of new object
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company2 = company1.copy();
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System.out.println();
System.out.println("Company 2:\n" + company2);
// Display the contents of both objects.
System.out.println("Company 1:\n" + company1);
// Calls toString()
// implicitly
(Continued)
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// Confirm that we actually have two objects.
if (company1 == company2)
{
System.out.println("The company1 and company2 " +
"variables reference the same object.");
}
else
{
System.out.println("The company1 and company2 " +
"variables reference different objects.");
}
36 }
37 }
Program Output
Company 1:
Trading symbol: XYZ
Share price: 9.62
Company 2:
Trading symbol: XYZ
Share price: 9.62
The company1 and company2 variables reference different objects.
Code Listing 8-12 (Instructor.java)
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/**
This class stores data about an instructor.
*/
public class Instructor
{
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private String
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private String
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private String
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lastName;
firstName;
officeNumber;
// Last name
// First name
// Office number
/**
This constructor initializes the last name,
first name, and office number.
@param lname The instructor's last name.
@param fname The instructor's first name.
@param office The office number.
*/
public
Instructor(String lname, String fname,
String office)
(Continued)
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{
lastName = lname;
firstName = fname;
officeNumber = office;
}
/**
The copy constructor initializes the object
as a copy of another Instructor object.
@param object2 The object to copy.
*/
public
{
lastName =
object2.lastName;
firstName =
object2.firstName;
officeNumber = object2.officeNumber;
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Instructor( Instructor object2 )
}
/**
The set method sets a value for each field.
@param lname The instructor's last name.
(Continued)
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@param fname The instructor's first name.
@param office The office number.
*/
public void set(String lname, String fname,
String office)
{
lastName = lname;
firstName = fname;
officeNumber = office;
}
/**
toString method
@return A string containing the instructor
information.
*/
(Continued)
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public String toString()
{
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// Create
a string representing the object.
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String str = "Last Name: " + lastName +
"\nFirst Name: " + firstName +
"\nOffice Number: " + officeNumber;
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return str;
Code Listing 8-13 (TextBook.java)
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/**
This class stores data about a textbook.
*/
public class TextBook
{
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private String
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private String
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private String
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title;
author;
publisher;
// Title of the book
// Author's last name
// Name of publisher
/**
This constructor initializes the title,
author, and publisher fields
@param textTitle The book's title.
@param auth The author's name.
@param pub The name of the publisher.
*/
public TextBook(String textTitle, String auth,
String pub)
{
title = textTitle;
author = auth;
(Continued)
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publisher = pub;
}
/**
The copy constructor initializes the object
as a copy of another TextBook object.
@param object2 The object to copy.
*/
public TextBook( TextBook
{
title = object2.title;
author = object2.author;
publisher = object2.publisher;
}
object2 )
/**
The set method sets a value for
@param textTitle The book's title.
@param auth The author's name.
@param pub The name of the publisher.
each field.
*/
public void
set(String textTitle, String auth,
(Continued)
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String pub)
{
title = textTitle;
author = auth;
publisher = pub;
}
/**
toString method
@return A string containing the textbook
information.
*/
public String toString()
{
// Create a string representing the object.
String str = "Title: " + title +
"\nAuthor: " + author +
"\nPublisher: " + publisher;
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return str;
Code Listing 8-14 (Course.java)
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/**
This class stores data about a course. Aggregate data.
*/
public class Course
{
courseName;
private Instructor instructor;
private TextBook textBook;
private String
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11 /**
// Name of the course
// Course “has an” instructor
// Course “has a” textbook
12 This constructor initializes the courseName,
13 instructor, and text fields.
14 @param name The name of the course.
15 @param instructor An Instructor object.
16 @param text A TextBook object.
17 */
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public
Course(String name, Instructor instr,
TextBook text)
{
// Assign the courseName.
courseName = name;
(Continued)
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// Init IV with a “deep copy” of the parameter object.
instructor = new Instructor(instr);
// Init IV with a “deep copy” of the parameter object.
textBook = new TextBook(text);
}
/**
getName method
@return The name of the course.
*/
public String getName()
{
return courseName;
}
/**
getInstructor method
@return A reference to a copy of this course's
(Continued)
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Instructor object.
*/
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public Instructor getInstructor()
{
// Return a copy of the instructor object.
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public TextBook getTextBook()
{
// Return a copy of the textBook object.
}
return new Instructor(instructor); // Returns a copy of object, not
// reference to the object.
// See 527-529, “Shallow” copy and security
/**
getTextBook method
@return A reference to a copy of this course's
TextBook object.
*/
return new TextBook(textBook);
// Same as comments above.
}
/**
toString method
(Continued)
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@return A string containing the course information.
*/
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public String toString()
{
// Create a string representing the object.
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String str = "Course name: " + courseName +
"\nInstructor Information:\n" +
instructor +
"\nTextbook Information:\n" +
textBook;
// “courseName” - String IV
// “instructor” - Instructor class toString()
// “textBook” - Textbook class toString()
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return str;
Code Listing 8-15 (CourseDemo.java)
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/**
This program demonstrates the Course class.
*/
public class CourseDemo
{
public static void
{
main(String[] args)
// Create an Instructor object.
Instructor myInstructor = new Instructor("Kramer", "Shawn", "RH3010");
// Create a TextBook object.
TextBook myTextBook = new TextBook("Starting Out with Java",
"Gaddis", "Addison-Wesley");
// Create a Course object.
Course myCourse = new Course("Intro to Java", myInstructor, myTextBook);
// Display the course information.
(Continued)
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System.out.println(myCourse);
}
Program Output
Course name: Intro to Java
Instructor Information:
Last Name: Kramer
First Name: Shawn
Office Number: RH3010
Textbook Information:
Title: Starting Out with Java
Author: Gaddis
Publisher: Addison-Wesley
// Implicit call to ?
Code Listing 8-16 (FullName.java)
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/**
This class stores a person's first, last, and middle
names. The class is dangerous because it does not
prevent operations on null reference fields.
NOTE: No explicit constructor
5 */
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8 {
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private String lastName;
// Last name
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private String firstName;
// First name
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private String middleName;
// Middle name
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/**
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The setLastName method sets the lastName field.
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@param str The String to set lastName to.
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*/
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public void setLastName(String str)
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{
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lastName = str;
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}
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/**
(Continued)
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The setFirstName method sets the firstName field.
@param str The String to set firstName to.
*/
public void setFirstName(String str)
{
firstName = str;
}
/**
The setMiddleName method sets the middleName field.
@param str The String to set middleName to.
*/
public void setMiddleName(String str)
{
middleName = str;
}
/**
The getLength method returns the length of the
full name.
@return The length.
(Continued)
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*/
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public int getLength()
{
return lastName.length() + firstName.length()
+ middleName.length();
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}
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public String toString()
/**
The toString method returns the full name.
@return A reference to a String.
*/
{
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return firstName + " " + middleName + " "
+ lastName;
Code Listing 8-17 (NameTester.java)
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/**
This program creates a FullName object, and then
calls the object's getLength method before values
are established for its reference fields. As a
result, this program will crash.
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*/
public class NameTester
{
public static void main(String[] args)
{
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int len;
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// Create a FullName object.
FullName name = new FullName();
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// To hold the name length
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// Get the length of the full name.
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len = name.getLength(); // Will cause crash! Why?
Code Listing 8-18 (EnumDemo.java)
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/**
This program demonstrates an enumerated type.
*/
public class EnumDemo
{
enum Day { SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
THURSDAY, FRIDAY, SATURDAY }
public static void main(String[] args)
{
Day workDay = Day.WEDNESDAY;
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System.out.println(workDay);
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System.out.println("The ordinal value for " +
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Day.SUNDAY + " is " +
Day.SUNDAY.ordinal());
(Continued)
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System.out.println("The ordinal value for " +
Day.SATURDAY + " is " +
Day.SATURDAY.ordinal());
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if (Day.FRIDAY.compareTo(Day.MONDAY ) > 0)
System.out.println(Day.FRIDAY + " is greater than " +
Day.MONDAY);
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38 }
else
System.out.println(Day.FRIDAY + " is NOT greater than " +
Day.MONDAY);
39 }
Program Output
WEDNESDAY
The ordinal value for SUNDAY is 0
The ordinal value for SATURDAY is 6
FRIDAY is greater than MONDAY
Code Listing 8-19 (CarType.java)
/**
2 CarType enumerated data type
3 */
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5 enum CarType { PORSCHE, FERRARI, JAGUAR }
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Code Listing 8-20 (CarColor.java)
/**
2 CarColor enumerated data type
3 */
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5 enum CarColor { RED, BLACK, BLUE, SILVER }
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Code Listing 8-21 (SportsCar.java)
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import java.text.DecimalFormat;
/**
SportsCar class
*/
public class SportsCar
{
private CarType
make;
private CarColor color;
private double
price;
// The car's make
// The car's color
// The car's price
/**
The constructor initializes the car's make,
color, and price.
@param aMake The car's make.
@param aColor The car's color.
@param aPrice The car's price.
*/
public SportsCar( CarType aMake,
double aPrice)
{
CarColor aColor,
(Continued)
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make = aMake;
color = aColor;
price = aPrice;
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}
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public CarType
{
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/**
getMake method
@return The car's make.
*/
getMake()
return make;
}
/**
getColor method
@return The car's color.
*/
public CarColor
{
getColor()
return color;
(Continued)
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}
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public double getPrice()
{
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return price;
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/**
getPrice method
@return The car's price.
*/
}
/**
toString method
@return A string indicating the car's make,
color, and price.
*/
public String toString()
{
// Create a DecimalFormat object for
// dollar formatting.
DecimalFormat dollar = new DecimalFormat("#,##0.00");
(Continued)
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78 }
79 }
// Create a string representing the object.
String str = "Make: " + make +
"\nColor: " + color +
"\nPrice: $" + dollar.format(price);
// Return the string.
return str;
Code Listing 8-22 (SportsCarDemo.java)
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/**
This program demonstrates the SportsCar class.
*/
public class SportsCarDemo
{
public static void
{
main(String[] args)
// Create a SportsCar object.
.
SportsCar yourNewCar = new SportsCar (CarType PORSCHE,
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14
System.out.println(yourNewCar);
15 }
16 }
Program Output
Make: PORSCHE
Color: RED
Price: $100,000.00
.
CarColor RED, 100000);
Code Listing 8-23 (SportsCarDemo2.java)
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/**
This program shows that you can switch on an
enumerated type.
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5
*/
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public class SportsCarDemo2
8
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{
public static void main(String[] args)
{
SportsCar yourNewCar = new SportsCar(CarType.PORSCHE,
CarColor.RED, 100000);
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14
.
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switch ( yourNewCar getMake() )
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{
case PORSCHE :
System.out.println("Your car was made in Germany.");
break;
case FERRARI :
System.out.println("Your car was made in Italy.");
break;
case JAGUAR :
System.out.println("Your car was made in England.");
break;
default:
System.out.println("I'm not sure where that car "
+ "was made.");
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}
30 }
31 }
Program Output
Your car was made in Germany.
Code Listing 8-24 (StockPurchase.java)
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/**
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The StockPurchase class represents a stock purchase.
Class collaboration. Uses Stock class.
*/
public class StockPurchase
{
private Stock stock;
private int
// Number of shares owned
/**
Constructor
@param stockObject The stock to purchase.
@param numShares The number of shares.
*/
public StockPurchase(Stock
{
stockObject, int numShares)
// Create a copy of the object referenced by
// stockObject.
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shares;
// The stock that was purchased
stock = new Stock(stockObject);
shares = numShares;
// Creates Stock object copy.
}
(Continued)
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/**
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public Stock getStock()
{
// Return a copy of the object referenced by stock.
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getStock method
@return A copy of the Stock object for the stock
being purchased.
*/
return new Stock(stock);
// Invoke Stock class copy constructor
}
/**
getShares method
@return The number of shares being purchased.
*/
public int getShares()
{
return shares;
}
/**
(Continued)
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getCost method
@return The cost of the stock purchase.
*/
public double getCost()
{
53
54 }
55 }
return shares * stock.getSharePrice(); // Invokes Stock method.
Code Listing 8-25 (StockTrader.java)
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import java.util.Scanner;
/**
This program allows you to purchase shares of XYZ
company's stock.
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7
*/
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9
public class StockTrader
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{
public static void main(String[] args)
{
int sharesToBuy;
// Number of shares to buy.
14
// Create a Stock object for the company stock.
16
// The trading symbol is XYZ and the stock is
// currently $9.62 per share.
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Stock xyzCompany = new Stock("XYZ", 9.62);
23
System.out.printf("XYZ stock is currently $%,.2f.\n",
Scanner keyboard = new Scanner(System.in);
// Display the current share price.
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xyzCompany.getSharePrice());
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// Get the number of shares to purchase.
30
// Create a StockPurchase object for the transaction.
31
StockPurchase buy =
new StockPurchase(xyzCompany, sharesToBuy);
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System.out.print("How many shares do you want to buy? ");
sharesToBuy = keyboard.nextInt();
34
// Display the cost of the transaction.
35
System.out.printf("Cost of the stock: $%,.2f",
36
buy.getCost());
37 }
38 }
Program Output with Example Input Shown in Bold
XYZ stock is currently $9.62.
How many shares do you want to buy? 100 [Enter]
Cost of the stock: $962.00