i generate a jar file for my project but when i try to run it by d-clicking it i found this massage
java Virtual Machine Launcher
could not find the main class.program will exit

[quote=wegdan;454015]i generate a jar file for my project but when i try to run it by d-clicking it i found this massage
java Virtual Machine Launcher
could not find the main class.program will exit[/i am using netbeans 6.0 and it generate the jar file automatically but it didnot work and give me the previous message what is wrong]

Verify that you have the main class set. There is an an entry in the jar manifest.mf file Main-Class: that specifies the main entry point class when the jar is run. If you have specified the main class in your project properties, this entry will be made automatically when you build the project.

I had some weird problem some times ago when jar created on my desktop will not run, but when I tried on laptop I had no problem at all.
On the end I changed JAR file settings in Folder Options>File Types and cahnge it execution of javaw.exe from jre to jdk and it worked fine. However it shouldn't make any differences if javaw.exe is called from jre or jdk, so

i have specified the main class in my project properties and the main class i have is this class
[\
/*
* Start.java
*
* Created on October 16, 2007, 1:48 PM
*/
package attaxxgame;
/**
*
* @author User
*/
public class Start extends javax.swing.JFrame {

/** Creates new form Start */
public Start() {
initComponents();
}

/** This method is called from within the constructor to
* initialize the form.
* WARNING: Do NOT modify this code. The content of this method is
* always regenerated by the Form Editor.
*/
// <editor-fold defaultstate="collapsed" desc=" Generated Code ">
private void initComponents() {
jLabel1 = new javax.swing.JLabel();
jLabel2 = new javax.swing.JLabel();
jLabel3 = new javax.swing.JLabel();
jLabel4 = new javax.swing.JLabel();
jLabel5 = new javax.swing.JLabel();
jLabel6 = new javax.swing.JLabel();
jLabel7 = new javax.swing.JLabel();
jLabel8 = new javax.swing.JLabel();
jLabel9 = new javax.swing.JLabel();
jLabel10 = new javax.swing.JLabel();
jLabel11 = new javax.swing.JLabel();
jTextField1 = new javax.swing.JTextField();
jRadioButton1 = new javax.swing.JRadioButton();
jRadioButton2 = new javax.swing.JRadioButton();
jRadioButton3 = new javax.swing.JRadioButton();
jRadioButton4 = new javax.swing.JRadioButton();
jButton1 = new javax.swing.JButton();
jButton2 = new javax.swing.JButton();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
setBackground(new java.awt.Color(204, 204, 204));
jLabel1.setText("Name");
jLabel2.setText("Won");
jLabel3.setText("Lost");
jLabel4.setText("Tied");
jLabel5.setText("Rating");
jLabel6.setText("Rating");
jLabel7.setText((new Integer(AttaxxBoard.humanwin )).toString());
jLabel8.setText((new Integer(AttaxxBoard.compwin)).toString());
jLabel8.setToolTipText((new Integer(AttaxxBoard.compwin)).toString());
jLabel9.setText((new Integer(AttaxxBoard.ties )).toString());
jLabel10.setText("792");
jLabel11.setText("1000");
jRadioButton1.setText("Beginner");
jRadioButton1.setBorder(javax.swing.BorderFactory.createEmptyBorder(0, 0, 0, 0));
jRadioButton1.setMargin(new java.awt.Insets(0, 0, 0, 0));
jRadioButton2.setText("Intermediate");
jRadioButton2.setBorder(javax.swing.BorderFactory.createEmptyBorder(0, 0, 0, 0));
jRadioButton2.setMargin(new java.awt.Insets(0, 0, 0, 0));
jRadioButton3.setText("Advanced");
jRadioButton3.setBorder(javax.swing.BorderFactory.createEmptyBorder(0, 0, 0, 0));
jRadioButton3.setEnabled(false);
jRadioButton3.setMargin(new java.awt.Insets(0, 0, 0, 0));
jRadioButton4.setText("Professional");
jRadioButton4.setBorder(javax.swing.BorderFactory.createEmptyBorder(0, 0, 0, 0));
jRadioButton4.setEnabled(false);
jRadioButton4.setMargin(new java.awt.Insets(0, 0, 0, 0));
jButton1.setText("OK");
jButton1.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
Start.this.actionPerformed(evt);
}
});
jButton2.setText("Reset score");
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(20, 20, 20)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jLabel1, javax.swing.GroupLayout.DEFAULT_SIZE, 68, Short.MAX_VALUE)
.addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, 68, javax.swing.GroupLayout.PREFERRED_SIZE)))
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(jRadioButton4)))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addComponent(jLabel2, javax.swing.GroupLayout.PREFERRED_SIZE, 66, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(18, 18, 18)
.addComponent(jLabel3, javax.swing.GroupLayout.PREFERRED_SIZE, 66, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addComponent(jLabel4, javax.swing.GroupLayout.PREFERRED_SIZE, 66, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(2, 2, 2)
.addComponent(jLabel5, javax.swing.GroupLayout.PREFERRED_SIZE, 66, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addComponent(jLabel6, javax.swing.GroupLayout.PREFERRED_SIZE, 66, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED))
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addComponent(jLabel7, javax.swing.GroupLayout.PREFERRED_SIZE, 66, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(jLabel8, javax.swing.GroupLayout.PREFERRED_SIZE, 66, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addComponent(jLabel9, javax.swing.GroupLayout.PREFERRED_SIZE, 66, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(14, 14, 14)
.addComponent(jLabel10, javax.swing.GroupLayout.PREFERRED_SIZE, 66, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(2, 2, 2)
.addComponent(jLabel11, javax.swing.GroupLayout.PREFERRED_SIZE, 66, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(layout.createSequentialGroup()
.addComponent(jButton2)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(jButton1)
.addGap(37, 37, 37))))))
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(jRadioButton3))
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(jRadioButton2))
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(jRadioButton1)))
.addContainerGap())
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel6, javax.swing.GroupLayout.PREFERRED_SIZE, 29, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel5, javax.swing.GroupLayout.PREFERRED_SIZE, 29, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel4, javax.swing.GroupLayout.PREFERRED_SIZE, 29, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel3, javax.swing.GroupLayout.PREFERRED_SIZE, 29, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel2, javax.swing.GroupLayout.PREFERRED_SIZE, 29, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 29, javax.swing.GroupLayout.PREFERRED_SIZE))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel11, javax.swing.GroupLayout.PREFERRED_SIZE, 29, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel10, javax.swing.GroupLayout.PREFERRED_SIZE, 29, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel7, javax.swing.GroupLayout.PREFERRED_SIZE, 29, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel8, javax.swing.GroupLayout.PREFERRED_SIZE, 29, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel9, javax.swing.GroupLayout.PREFERRED_SIZE, 29, javax.swing.GroupLayout.PREFERRED_SIZE))
.addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 24, Short.MAX_VALUE)
.addComponent(jRadioButton1)
.addGap(31, 31, 31)
.addComponent(jRadioButton2)
.addGap(35, 35, 35)
.addComponent(jRadioButton3)
.addGap(28, 28, 28)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jRadioButton4)
.addComponent(jButton2)
.addComponent(jButton1))
.addGap(23, 23, 23))
);
pack();
}// </editor-fold>
private void actionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
String butname;
butname=evt.getActionCommand();
if(butname.equals("OK"))
{
this.setVisible(false);
AttaxxBoard game=new AttaxxBoard();
}
else if(butname.equals("Reset score"))
{
Reset_Score reset=new Reset_Score();
}

}

/**
* @param args the command line arguments
*/
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new Start().setVisible(true);
}
});
}

// Variables declaration - do not modify
private javax.swing.JButton jButton1;
private javax.swing.JButton jButton2;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel10;
private javax.swing.JLabel jLabel11;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JLabel jLabel4;
private javax.swing.JLabel jLabel5;
private javax.swing.JLabel jLabel6;
private javax.swing.JLabel jLabel7;
private javax.swing.JLabel jLabel8;
private javax.swing.JLabel jLabel9;
private javax.swing.JRadioButton jRadioButton1;
private javax.swing.JRadioButton jRadioButton2;
private javax.swing.JRadioButton jRadioButton3;
private javax.swing.JRadioButton jRadioButton4;
private javax.swing.JTextField jTextField1;
// End of variables declaration


}
]
is there is some thing wrong in it .because when i tried to import it in another project it gave me this masseage after trying to build it
C:\Documents and Settings\User\Desktop\ggggg\nbproject\build-impl.xml:384: The following error occurred while executing this line:
C:\Documents and Settings\User\Desktop\ggggg\nbproject\build-impl.xml:253: java.lang.ThreadDeath
BUILD FAILED (total time: 49 seconds)

Nothing to do with existing code. NetBeans are complaining about build-impl.xml file. You must done something wrong while importing or copying.