Hello, I am to create a Java application that validates ISBN-10 number entered i

Question

Hello, I am to create a Java application that validates ISBN-10 number entered into a custom Textfield object and then using a custom exception class to validate it as a string. I have compiled the classes but everytime i "validate" a number It always comes back as valid.below are the classes i have created please advice me in what I am missing so that my custom exception is called these are

some valid ISBN numbers for testing

031224665X, 0973778709, 0195424409, 0465054676

ISBNVerifierGUI

import java.awt.*;
import javax.swing.*;

public class ISBNVerifierGUI extends JPanel
{
/**
* fields
*/
protected JPanel isbnPanel, // A panel for ISBN label and textfield
buttonPanel; // A panel for the buttons

// Replace the textfield with your custom control
protected ISBNTextField isbn; // A custom control for the ISBN number
protected JTextArea status; // Used to display status and error messages
protected JButton validateButton, // Validates the entered ISBN #
exitButton; // Exits the application
//add custom handler
ISBNHandler handler = new ISBNHandler(this);
  
/**
Constructor
*/
  
public ISBNVerifierGUI()
{
// Set JPanel layout as Border
setLayout(new BorderLayout());
  
// Build the three components for the North, Center and South
buildISBNPanel();
JScrollPane sPane = new JScrollPane( status= new JTextArea(20, 20) );
buildButtonPanel();
  
// Add the components to the JPanel
add(isbnPanel, BorderLayout.NORTH);
add(sPane, BorderLayout.CENTER);
add(buttonPanel, BorderLayout.SOUTH);
}

/**
The buildISBNPanel method creates a panel containing the
ISBN prompt label and textfield
*/

private void buildISBNPanel()
{
// create the panel with a FlowLayout
isbnPanel = new JPanel(new FlowLayout());

// Add label and custom control to the panel
isbnPanel.add(new JLabel("Enter ISBN-10 #: "));
isbnPanel.add(isbn= new ISBNTextField(20));

}// end buildISBNPanel() method

/**
The buildButtonPanel method creates a panel containing
buttons.
*/

private void buildButtonPanel()
{
//Create the button pannel, buttons & add buttons
buttonPanel = new JPanel();
buttonPanel.add( validateButton= new JButton("Validate ISBN") );
buttonPanel.add( exitButton = new JButton("Exit") );

// Add an action listener to the validate and exit buttons.
validateButton.addActionListener(handler);
exitButton.addActionListener(handler);

}// end buildButtonPanel() method

}// end ISBNVerifierGUI class

ISBNHandler

public class ISBNHandler implements ActionListener
{
protected ISBNVerifierGUI gui;
  
public ISBNHandler(ISBNVerifierGUI gui)
{
this.gui = gui;
}
  
public void actionPerformed(ActionEvent e)
{
if(e.getSource() == gui.validateButton)
{
try
{
gui.isbn.getISBN();
}
catch(ISBNException error)
{
System.out.println(error);
}
gui.status.append("Valid ISBN");
}
if(e.getSource() == gui.exitButton)
{
System.exit(0);
}
}

}

ISBNVerifierClient

import java.awt.*; import javax.swing.*;

public class ISBNVerifierClient extends JFrame
{
final static private int WIDTH= 450, HEIGHT= 200;//Window width & height
private Container c; // A reference to the frame's content pane
private ISBNVerifierGUI gui; // A reference to the GUI class

/**
Constructor
*/
  
public ISBNVerifierClient()
{
// Get an instance of the content pane
c = getContentPane();   
  
// Add the GUI to the content pane
c.add(gui= new ISBNVerifierGUI());

// JFrame setup parms:
setTitle("ISBN Validator");
setSize(WIDTH,HEIGHT);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLocationRelativeTo(null);
setVisible(true);

}

public static void main(String[] args) { new ISBNVerifierClient(); }

}// end ISBNVerifierClient class

ISBNTextField

import javax.swing.*;
import java.awt.*;

public class ISBNTextField extends JTextField
{
protected String text;
protected String error;
  
protected ISBNVerifierGUI gui;
  
/**
* constructor for objects of class ISBNText
*/
public ISBNTextField(int size)
{
super(size);
}
  
public String getISBN() throws ISBNException
{
this.text = text;
text = getText();
text = validateISBN(text);
return text;
}
  
private String validateISBN(String text) throws ISBNException
{
int count = 0;
for(int i = 0; i < text.length(); i++)
{
if(text.charAt(i) != '-')
{
count++;
}
}
  
if(count != 10)
{
checkDigit(text);
error = ("isbn " + text + " must be 10 chars long");
throw new ISBNException(error);
}
if((text.charAt(text.length() -1) == 'x'))
{
this.checkDigit(text);
error = ("isbn " + text + " must be a digit or an X");
throw new ISBNException(error);
}
if((text.charAt(text.length() -1) != 'x'))
{
checkDigit(text);
}
return text;
}
  
private boolean checkDigit(String text) throws ISBNException
{
int n = 0;
for(int i = 0; i < text.length() -1; i++)
{
n += text.indexOf(i + 1) * text.charAt(i);
}
if(n % 11 == text.indexOf(text.length() -1))
{
return true;
}
else if(n % 11 == 10)
{
return true;
}
else
{
return false;
}
}
}

ISBNException

public class ISBNException extends Exception
{
public ISBNException(String error)
{
super(error);
}
}

Explanation / Answer

When you insert invalid numbers in a table using the weak mode, the number

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