Help on Error

Question

I was testing one of the example code from the Java Tutorial, PasswordDemo.java, when i run it this error comes out..
+++++++++++++++++++++++++++++++++++++++++++++++
java.lang.NoClassDefFoundError: PasswordDemo (wrong name: components/PasswordDemo)
     at java.lang.ClassLoader.defineClass1(Native Method)
     at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
     at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
     at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
     at java.net.URLClassLoader.access$000(URLClassLoader.java:56)
     at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
     at java.security.AccessController.doPrivileged(Native Method)
     at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:276)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
     at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
Exception in thread "main"
Tool completed with exit code 1
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Can any one tell me why???

Answer 1

Here is the code....
package components;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.Arrays;
/* PasswordDemo.java requires no other files. */
public class PasswordDemo extends JPanel
implements ActionListener {
private static String OK = "ok";
private static String HELP = "help";
private JFrame controllingFrame; //needed for dialogs
private JPasswordField passwordField;
public PasswordDemo(JFrame f) {
//Use the default FlowLayout.
controllingFrame = f;
//Create everything.
passwordField = new JPasswordField(10);
passwordField.setActionCommand(OK);
passwordField.addActionListener(this);
JLabel label = new JLabel("Enter the password: ");
label.setLabelFor(passwordField);
JComponent buttonPane = createButtonPanel();
//Lay out everything.
JPanel textPane = new JPanel(new FlowLayout(FlowLayout.TRAILING));
textPane.add(label);
textPane.add(passwordField);
add(textPane);
add(buttonPane);
protected JComponent createButtonPanel() {
JPanel p = new JPanel(new GridLayout(0,1));
JButton okButton = new JButton("OK");
JButton helpButton = new JButton("Help");
okButton.setActionCommand(OK);
helpButton.setActionCommand(HELP);
okButton.addActionListener(this);
helpButton.addActionListener(this);
p.add(okButton);
p.add(helpButton);
return p;
public void actionPerformed(ActionEvent e) {
String cmd = e.getActionCommand();
if (OK.equals(cmd)) { //Process the password.
char[] input = passwordField.getPassword();
if (isPasswordCorrect(input)) {
JOptionPane.showMessageDialog(controllingFrame,
"Success! You typed the right password.");
} else {
JOptionPane.showMessageDialog(controllingFrame,
"Invalid password. Try again.",
"Error Message",
JOptionPane.ERROR_MESSAGE);
//Zero out the possible password, for security.
Arrays.fill(input, '0');
passwordField.selectAll();
resetFocus();
} else { //The user has asked for help.
JOptionPane.showMessageDialog(controllingFrame,
"You can get the password by searching this example's\n"
+ "source code for the string \"correctPassword\".\n"
+ "Or look at the section How to Use Password Fields in\n"
+ "the components section of The Java Tutorial.");
* Checks the passed-in array against the correct password.
* After this method returns, you should invoke eraseArray
* on the passed-in array.
private static boolean isPasswordCorrect(char[] input) {
boolean isCorrect = true;
char[] correctPassword = { 'b', 'u', 'g', 'a', 'b', 'o', 'o' };
if (input.length != correctPassword.length) {
isCorrect = false;
} else {
isCorrect = Arrays.equals (input, correctPassword);
//Zero out the password.
Arrays.fill(correctPassword,'0');
return isCorrect;
//Must be called from the event dispatch thread.
protected void resetFocus() {
passwordField.requestFocusInWindow();
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event dispatch thread.
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("PasswordDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
final PasswordDemo newContentPane = new PasswordDemo(frame);
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Make sure the focus goes to the right component
//whenever the frame is initially given the focus.
frame.addWindowListener(new WindowAdapter() {
public void windowActivated(WindowEvent e) {
newContentPane.resetFocus();
//Display the window.
frame.pack();
frame.setVisible(true);
public static void main(String[] args) {
//Schedule a job for the event dispatch thread:
//creating and showing this application's GUI.
SwingUtilities.invokeLater(new Runnable() {
public void run() {
//Turn off metal's use of bold fonts
          UIManager.put("swing.boldMetal", Boolean.FALSE);
          createAndShowGUI();
}