java.lang.noclassdeffounderror while testing ButtonDemo.java from Oracle tutorials

[Jiangbo Tang]

Hi guys,

I was trying the BottonDemo.java from Oracel tutorials (the source code is pasted below). It compiled fine, but gave me a java.lang.noclassdeffounderror at run time. I tried to google what this error is about and found this post helpful (http://javaeesupportpatterns.blogspot.com/2012/06/javalangnoclassdeffounderror-how-to.html). I kinda understand what the author says, but I am a complete newbie, so I am still clueless as how to solve this problem.
Since I just started learning Java and CS, so my questions are: what should I do next? (including reading books, tutorials, etc. ???) Should I just leave this problem alone at this point since I just started learning? Thanks a lot!!

the code: http://docs.oracle.com/javase/tutorial/displayCode.html?code=http://docs.oracle.com/javase/tutorial/uiswing/examples/components/ButtonDemoProject/src/components/ButtonDemo.java

package components;
 
import javax.swing.AbstractButton;
import javax.swing.JButton;
import javax.swing.JPanel;
import javax.swing.JFrame;
import javax.swing.ImageIcon;
 
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
 
/* 
 * ButtonDemo.java requires the following files:
 *   images/right.gif
 *   images/middle.gif
 *   images/left.gif
 */
public class ButtonDemo extends JPanel
                        implements ActionListener {
    protected JButton b1, b2, b3;
 
    public ButtonDemo() {
        ImageIcon leftButtonIcon = createImageIcon("images/right.gif");
        ImageIcon middleButtonIcon = createImageIcon("images/middle.gif");
        ImageIcon rightButtonIcon = createImageIcon("images/left.gif");
 
        b1 = new JButton("Disable middle button", leftButtonIcon);
        b1.setVerticalTextPosition(AbstractButton.CENTER);
        b1.setHorizontalTextPosition(AbstractButton.LEADING);
        b1.setMnemonic(KeyEvent.VK_D);
        b1.setActionCommand("disable");
 
        b2 = new JButton("Middle button", middleButtonIcon);
        b2.setVerticalTextPosition(AbstractButton.BOTTOM);
        b2.setHorizontalTextPosition(AbstractButton.CENTER);
        b2.setMnemonic(KeyEvent.VK_M);
 
        b3 = new JButton("Enable middle button", rightButtonIcon);
        //Use the default text position of CENTER, TRAILING (RIGHT).
        b3.setMnemonic(KeyEvent.VK_E);
        b3.setActionCommand("enable");
        b3.setEnabled(false);
 
        //Listen for actions on buttons 1 and 3.
        b1.addActionListener(this);
        b3.addActionListener(this);
 
        b1.setToolTipText("Click this button to disable the middle button.");
        b2.setToolTipText("This middle button does nothing when you click it.");
        b3.setToolTipText("Click this button to enable the middle button.");
 
        //Add Components to this container, using the default FlowLayout.
        add(b1);
        add(b2);
        add(b3);
    }
 
    public void actionPerformed(ActionEvent e) {
        if ("disable".equals(e.getActionCommand())) {
            b2.setEnabled(false);
            b1.setEnabled(false);
            b3.setEnabled(true);
        } else {
            b2.setEnabled(true);
            b1.setEnabled(true);
            b3.setEnabled(false);
        }
    }
 
    /** Returns an ImageIcon, or null if the path was invalid. */
    protected static ImageIcon createImageIcon(String path) {
        java.net.URL imgURL = ButtonDemo.class.getResource(path);
        if (imgURL != null) {
            return new ImageIcon(imgURL);
        } else {
            System.err.println("Couldn't find file: " + path);
            return null;
        }
    }
 
    /**
     * Create the GUI and show it.  For thread safety, 
     * this method should be invoked from the 
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
 
        //Create and set up the window.
        JFrame frame = new JFrame("ButtonDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        //Create and set up the content pane.
        ButtonDemo newContentPane = new ButtonDemo();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);
 
        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }
 
    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI(); 
            }
        });
    }
}

[Rajdeep Biswas]

Welcome to the Ranch, Jiangbo Tang.

First of all do a search for your problem from Search link on top of the page. [link]
A sample search shows up here [java.lang.NoClassDefFoundError]

You will find existing solution to most of your problems and you dont have to reinvent the wheel everytime.

Also have a look at http://javarevisited.blogspot.in/2011/06/noclassdeffounderror-exception-in.html.
Then may be, you can post here what you understood and if it helped!

[Kemal Sokolovic]

Hello and welcome to the Ranch!

Are you compiling your code from the command line? If so, can you please paste the commands you used to both compile and run the example code? Make sure you copy it from the command line so we can see the directory you are currently in, e.g.:

/javaranch/src/$ javac ...