Error while using swing

Question

I'm trying to create panel with some button which would enables disable the other button What's the problem with the codes its compiled perfectly but while running shows the error. I'm not able to debug this.

Exception in thread "main" java.lang.NoClassDefFoundError: buttondemo (wrong nam
e: components/buttondemo)
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:791)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:14
2)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
        at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:472)

Here's the code

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;

public class buttondemo extends JPanel implements ActionListener {
    private JButton b1, b2, b3;

    public buttondemo() {
        ImageIcon Left = createImageIcon("C:\\Users\\nco\\Desktop\\Swing\\components\\images\\left.png");
        ImageIcon Right = createImageIcon("C:\\Users\\nco\\Desktop\\Swing\\components\\images\\right.jpg");
        ImageIcon Middle = createImageIcon("C:\\Users\\nco\\Desktop\\Swing\\components\\images\\middle.jpg");
        b1 = new JButton("Disable middle button", Left);
        b1.setVerticalTextPosition(AbstractButton.CENTER);
        b1.setMnemonic(KeyEvent.VK_D);// shortcut D
        b1.setActionCommand("disable");
        b2 = new JButton("middle button", Middle);
        b2.setVerticalTextPosition(AbstractButton.BOTTOM);
        b2.setVerticalTextPosition(AbstractButton.CENTER);
        b3.setMnemonic(KeyEvent.VK_M);// shortcut M
        b3 = new JButton("Enable middle button", Right);
        b3.setVerticalTextPosition(AbstractButton.RIGHT);
        b3.setMnemonic(KeyEvent.VK_E);// shortcut E
        b3.setActionCommand("enable");
        b3.setEnabled(false);
        b1.addActionListener(this);
        b3.addActionListener(this);
        b1.setToolTipText("click on the middle button to " + "disable middle");
        b3.setToolTipText("click on the middle button to " + "enable middle");
        b2.setToolTipText("click disable");
        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);
        }
    }

    protected static ImageIcon createImageIcon(String path) {
        java.net.URL img = buttondemo.class.getResource(path);
        if (img != null) {
            return new ImageIcon(img);
        } else {
            System.err.println("could not find path" + path);
            return null;
        }
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("Button demso");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        buttondemo Contentpane = new buttondemo();
        Contentpane.setOpaque(true);
        frame.setContentPane(Contentpane);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String args[]) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }

}

Answer 1

• b3.setMnemonic(KeyEvent.VK_M);// shortcut M is code line to the non_initalized JButton (initialized in the next code line)

• not all combinations for Text and Icon can be matched together , without an exceptions from AbstractButton

• use only constants for BorderLayout

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingConstants;
import javax.swing.UIManager;

public class buttondemo extends JPanel implements ActionListener {

    private JButton b1, b2, b3;

    public buttondemo() {
        Icon Left = UIManager.getIcon("OptionPane.errorIcon");
        Icon Right = UIManager.getIcon("OptionPane.informationIcon");
        Icon Middle = UIManager.getIcon("OptionPane.warningIcon");
        b1 = new JButton("Disable middle button", Left);
        b1.setVerticalTextPosition(SwingConstants.TOP);
        b1.setHorizontalTextPosition(SwingConstants.CENTER);
        b1.setMnemonic(KeyEvent.VK_D);//shortcut D
        b1.setActionCommand("disable");
        b2 = new JButton("middle button", Middle);
        b2.setVerticalTextPosition(SwingConstants.BOTTOM);
        b2.setHorizontalTextPosition(SwingConstants.LEFT);
        b3 = new JButton("Enable middle button", Right);
        b3.setMnemonic(KeyEvent.VK_M);//shortcut M
        b2.setVerticalTextPosition(SwingConstants.EAST);
        b2.setHorizontalTextPosition(SwingConstants.CENTER);
        b3.setActionCommand("enable");
        b3.setEnabled(false);
        b1.addActionListener(this);
        b3.addActionListener(this);
        b1.setToolTipText("click on the middle button to " + "disable middle");
        b3.setToolTipText("click on the middle button to " + "enable middle");
        b2.setToolTipText("click disable");
        add(b1);
        add(b2);
        add(b3);
    }

    @Override
    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);
        }
    }

    protected static ImageIcon createImageIcon(String path) {
        java.net.URL img = buttondemo.class.getResource(path);
        if (img != null) {
            return new ImageIcon(img);
        } else {
            System.err.println("could not find path" + path);
            return null;
        }
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("Button demso");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        buttondemo Contentpane = new buttondemo();
        Contentpane.setOpaque(true);
        frame.setContentPane(Contentpane);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String args[]) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

EDIT

Java6 on WinXP caused the with same exception

java.lang.NoClassDefFoundError: JButton/ButtonDemo Caused by: java.lang.ClassNotFoundException: JButton.ButtonDemo at java.net.URLClassLoader$1.run(URLClassLoader.java:202) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:248) Could not find the main class: JButton.ButtonDemo. Program will exit. Exception in thread "main" Java Result: 1

• but have to use the proper private to use instead of protected static ImageIcon createImageIcon(String path) { caused am exception

@see

private ImageIcon createImageIcon(String path) {
    java.net.URL img = ButtonDemo.class.getResource(path);
    if (img != null) {
        return new ImageIcon(img);
    } else {
        System.err.println("could not find path" + path);
        return null;
    }
}