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Thread: GUI problem

  1. #1
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    Default GUI problem

    Hello everyone

    I have this code and whenever i run it i get this error message. I tried to fix it but i dont know what is wrong with it.
    HTML Code:
    package D;
    
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;
    
    public class D extends JFrame implements ActionListener {
    
        JButton Exit, Name;
        String fn,ln;
        
        public D() {
        
            this.setSize(400,300);
            this.setTitle("Celsius and Fahrenheit conversion");
            this.setVisible(true);
            this.setLocationRelativeTo(null);
            this.setLayout(new FlowLayout());
            
            Container content = getContentPane();
            
            Exit = new JButton("Close Program");
            Exit.setActionCommand("Exit");
            
            
            Name = new JButton("Enter Name");
            Name.setActionCommand("Name");
            
            Exit.addActionListener(this);
            Name.addActionListener(this);
            
            content.add(Exit, BorderLayout.NORTH);
            content.add(Name, BorderLayout.WEST);
        }
        
        public void Actions(ActionEvent Action) {
            if(Action.getActionCommand().contains("Exit")) {
                System.exit(0);
            }
            
            if(Action.getActionCommand().equals("Name")) {
                
                fn = JOptionPane.showInputDialog("Enter First Name: ");
                ln = JOptionPane.showInputDialog("Enter Last Name: ");
                
                JOptionPane.showMessageDialog(null, "Hello " + fn + " " + ln);
            }
        }
        public static void main(String[] args) {
            D();
        }
    }
    Error Message:-
    HTML Code:
    run:
    java.lang.NoClassDefFoundError: d/D (wrong name: D/D)
    	at java.lang.ClassLoader.defineClass1(Native Method)
    	at java.lang.ClassLoader.defineClass(ClassLoader.java:791)
    	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    	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)
    Exception in thread "main" Java Result: 1
    BUILD SUCCESSFUL (total time: 1 second)


  2. #2
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    Default Re: GUI problem

    Though this probably isn't it, I thought to implement ActionListener, you had to override the method actionPerformed() and it appears that you don't. However, I've done this before and it doesn't give that error message you posted when you do it.

    I'm going to run that.

    Found another problem.

    It would be

    new D();

    not

    D();

    That also is causing a problem.

    I changed the name of the method Actions to actionPerformed as you have to have an actionPerformed method in order to have the class implement ActionListener().

    I think with you calling

    D(); It was confused as to what that meant.

    I've gotten it to work now:

    package D;
     
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;
     
    public class D extends JFrame implements ActionListener {
     
        JButton Exit, Name;
        String fn,ln;
     
        public D() {
     
            this.setSize(400,300);
            this.setTitle("Celsius and Fahrenheit conversion");
            this.setVisible(true);
            this.setLocationRelativeTo(null);
            this.setLayout(new FlowLayout());
     
            Container content = getContentPane();
     
            Exit = new JButton("Close Program");
            Exit.setActionCommand("Exit");
     
     
            Name = new JButton("Enter Name");
            Name.setActionCommand("Name");
     
            Exit.addActionListener(this);
            Name.addActionListener(this);
     
            content.add(Exit, BorderLayout.NORTH);
            content.add(Name, BorderLayout.WEST);
        }
     
        public void actionPerformed(ActionEvent Action) {
            if(Action.getActionCommand().contains("Exit")) {
                System.exit(0);
            }
     
            if(Action.getActionCommand().equals("Name")) {
     
                fn = JOptionPane.showInputDialog("Enter First Name: ");
                ln = JOptionPane.showInputDialog("Enter Last Name: ");
     
                JOptionPane.showMessageDialog(null, "Hello " + fn + " " + ln);
            }
        }
        public static void main(String[] args) {
           new D();
        }
    }
    Last edited by javapenguin; October 21st, 2011 at 09:10 PM.

  3. #3
    Super Moderator copeg's Avatar
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    Default Re: GUI problem

    Suggested reading:
    Creating Objects (The Java™ Tutorials > Learning the Java Language > Classes and Objects)
    How to write an ActionListener
    Code Conventions for the Java Programming Language