Reason for”Exception in thread “AWT-EventQueue-0″ java.lang.NullPointerException”

This question already has answers here: What is a NullPointerException, and how do I fix it? (12 answers) Closed 4 years ago.

i am creating to create a hotel reservation system ,but evey time i run my project i recieve “Exception in thread “AWT-EventQueue-0″ java.lang.NullPointerException” and i have not been able to find why . here is the error report i recieve

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at hotelreservation.Reservation.fill(Reservation.java:389)  at hotelreservation.Reservation.fill(Reservation.java:389)
at hotelreservation.Reservation.<init>(Reservation.java:31)
at hotelreservation.main.jMenuItem1ActionPerformed(main.java:502)
at hotelreservation.main.access$600(main.java:29)
at hotelreservation.main$6.actionPerformed(main.java:277)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.AbstractButton.doClick(AbstractButton.java:376)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:833)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:877)
at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:289)
at java.awt.Component.processMouseEvent(Component.java:6535)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6300)
at java.awt.Container.processEvent(Container.java:2236)
at java.awt.Component.dispatchEventImpl(Component.java:4891)
at java.awt.Container.dispatchEventImpl(Container.java:2294)
at java.awt.Component.dispatchEvent(Component.java:4713)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
at java.awt.Container.dispatchEventImpl(Container.java:2280)
at java.awt.Window.dispatchEventImpl(Window.java:2750)
at java.awt.Component.dispatchEvent(Component.java:4713)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

and here is the class

package hotelreservation;

import java.awt.event.KeyEvent;
//import java.sql.Date;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.Vector;
import javax.swing.JOptionPane;
import javax.swing.JTextField;
import javax.swing.table.DefaultTableModel;
import java.util.Date;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**

*
 * @author TOSHIBA
 */
public class Reservation extends javax.swing.JInternalFrame {

    /**
     * Creates new form Reservation
     */
public Reservation() {
    initComponents();
  fill();
    //idgenerate();
    username();
    Date date = new Date();
    txt_date.setDate(date);
}

public void username() {
    dbconnection db = new dbconnection();
    try {
        db.connect();
        db.stm = db.con.createStatement();
        db.rs = db.stm.executeQuery("select User_name from Users where Status='Active'");
        while (db.rs.next()) {
            txt_user.setText(db.rs.getString(1));
        }
    } catch (SQLException e) {
        JOptionPane.showMessageDialog(this, e.toString());
    }
}

public void idgenerate() {

    dbconnection db = new dbconnection();
    int IDincrement = 0;

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