This is CD.java
public class CD
{
// Fields (or instance data members)
private String title; // CD's title
private String artist; // CD's artist
private double cost; // CD's cost
private int numberOfTracks; // Number of Tracks
/**
* Constructors: Please describe each of them.
*
*/
public CD ()
{
}
public CD (String title, String artist, double cost, int numberOfTracks)
{
// four statements
}
/**
* The setTitle () method has a parameter. It assigns the value of the parameter to instance field name.
* The method does not return a value.
*/
public void setTitle (String cdTitle)
{
title = cdTitle;
}
/**
* The setArtist () method has a parameter. It assigns the value of the parameter to instance field name.
* The method does not return a value.
*/
public void setArtist (String cdArtist)
{
artist = cdArtist;
}
/**
* The setCost () method has a parameter. It assigns the value of the parameter to instance field name.
* The method does not return a value.
*/
public void setCost (double cdCost)
{
cost = cdCost;
}
/**
* The setNumberOfTracks () method has a parameter. It assigns the value of the parameter to instance field name.
* The method does not return a value.
*/
public void setNumberOfTracks (int cdNumberOfTracks)
{
numberOfTracks = cdNumberOfTracks;
}
/**
* The getTitle method does not accept arguments.
* It simply returns the value of the title field.
*/
public String getTitle ()
{
return title;
}
/**
* The getArtist method does not accept arguments.
* It simply returns the value of the artist field.
*/
public String getArtist ()
{
return artist;
}
/**
* The getCost method does not accept arguments.
* It simply returns the value of the cost field.
*/
public Double getCost ()
{
return cost;
}
/**
* The getNumberofTracks method does not accept arguments.
* It simply returns the value of the numberofTracks field.
*/
public int getNumberOfTracks ()
{
return numberOfTracks;
}
} // End of class CD
This is CDDemo.java
// an import statement needed here for keyboard input
import java.util.Scanner;
public class CDDemo
{
private static CD cd1;
private static CD cd2;
private static CD cd3;
public static void main (String [] args)
{
// Declare ALL necessary variables here,
String title; // CD's title
String artist; // CD's artist
double cost; // CD's cost
int numberOfTracks; // Number of Tracks
// Create a Scanner object
Scanner keyboard = new Scanner(System.in);
// Create the first CD object. Use the no-arg constructor (assuming
// that you added one to the CD class definition).
CD cd = new CD();
// Read the data for First CD from the keyboard
System.out.print("Please enter CD1 Title: ");
title=keyboard.nextLine();
System.out.print("Please enter CD1 Artist: ");
artist=keyboard.nextLine();
System.out.print("Please enter CD1 Cost: ");
cost=keyboard.nextDouble();
// Clear out Double
keyboard.nextLine();
System.out.print("Please enter CD1 number of tracks: ");
numberOfTracks=keyboard.nextInt();
// Clear out int
keyboard.nextLine();
// Call the set methods of the first CD object
// to set its fields with values entered from the keyboard.
// This is how you test the set methods.
cd1.setTitle (title);
cd1.setArtist (artist);
cd1.setCost (cost);
cd1.setNumberOfTracks (numberOfTracks);
// Create the second and third CD objects using the
// constructor that accepts arguments for all of the fields.
cd2 = new CD ("CD Title2", "CD Artist2", 15.50, 5);
cd3 = new CD ("CD Title3", "CD Artist3", 20.00, 8);
// The rest of this class tests get methods (and the successful execution of
// constructors and set methods as well).
// Display the data for CD 1.
System.out.println ("CD #1");
System.out.println ("Title: " + cd1.getTitle());
System.out.println ("Artist: " + cd1.getArtist());
System.out.println ("Cost: " + cd1.getCost());
System.out.println ("Number of Tracks: " + cd1.getNumberOfTracks());
System.out.println ();
// Display the data for CD 2.
System.out.println ("CD #2");
System.out.println ("Title: " + cd2.getTitle());
System.out.println ("Artist: " + cd2.getArtist());
System.out.println ("Cost: " + cd2.getCost());
System.out.println ("Number of Tracks: " + cd2.getNumberOfTracks());
System.out.println ();
// Display the data for CD 3.
System.out.println ("CD #3");
System.out.println ("Title: " + cd3.getTitle());
System.out.println ("Artist: " + cd3.getArtist());
System.out.println ("Cost: " + cd3.getCost());
System.out.println ("Number of Tracks: " + cd3.getNumberOfTracks());
System.out.println ();
} // end of method main ()
} // end of class CDDemo
CMD Entries
Microsoft Windows [Version 6.3.9600]
(c) 2013 Microsoft Corporation. All rights reserved.
C:\Users\fLyBa>cd C:\Users\fLyBa\Desktop\java
C:\Users\fLyBa\Desktop\java>javac CD.java
C:\Users\fLyBa\Desktop\java>javac CDDemo.java
C:\Users\fLyBa\Desktop\java>java CDDemo
Please enter CD1 Title: Title
Please enter CD1 Artist: Artist
Please enter CD1 Cost: 12
Please enter CD1 number of tracks: 12
Exception in thread "main" java.lang.NullPointerException
at CDDemo.main(CDDemo.java:58)
C:\Users\fLyBa\Desktop\java>
When I run this java code I get This error:Exception in thread "main" java.lang.NullPointerException at CDDemo.main(CDDemo.java:58)
Anyone knows how can I fix this? I just want to apply simplest correction without changing the code too much...
