Grund für "Ausnahme im Thread" AWT-EventQueue-0 "java.lang.NullPointerException"

Question

Ich erstelle ein Hotel-Reservierungssystem, aber jedes Mal, wenn ich mein Projekt starte, bekomme ich "Exception in thread" AWT-EventQueue- 0 "java.lang.NullPointerException" und ich konnte den Grund nicht finden. hier ist der Fehlerbericht i

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) 

und hier ist die Klasse

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; 
    try { 
     db.connect(); 
     db.stm = db.con.createStatement(); 

     db.rs = db.stm.executeQuery("select MAX(Res_ID)from Reservation"); 

     while(db.rs.next()) { 
      if (db.rs.first() == false) { 
       txt_id.setText("Res000001"); 
      } else { 
       db.rs.last(); 
       int autoID = db.rs.getInt(1) + 1; 
       String no = String.valueOf(autoID); 
       int nolong = no.length(); 
       for (int a = 0; a < 3 - nolong; a++) { 
        no = "0" + no; 
       } 
       txt_id.setText("Res" + no); 

      } 
      /* db.rs.next(); 
      if (db.rs != null) { 
       IDincrement = db.rs.getInt(1) + 1; 
       IDincrement++; 
      } else { 
       IDincrement = 1; 
      } 
      txt_id.setText("CS" + IDincrement);*/ 
     } 

    } catch (SQLException e) { 

     JOptionPane.showMessageDialog(this,"Error \n"+ e.getMessage(),"warning",JOptionPane.WARNING_MESSAGE); 
    } 

} 

@SuppressWarnings("unchecked") 
// <editor-fold defaultstate="collapsed" desc="Generated Code">       
private void initComponents() { 

    jPanel1 = new javax.swing.JPanel(); 
    jScrollPane1 = new javax.swing.JScrollPane(); 
    jTable1 = new javax.swing.JTable(); 
    jPanel3 = new javax.swing.JPanel(); 
    jButton4 = new javax.swing.JButton(); 
    jButton1 = new javax.swing.JButton(); 
    txt_user = new javax.swing.JTextField(); 
    txt_date = new com.toedter.calendar.JDateChooser(); 
    jLabel6 = new javax.swing.JLabel(); 
    jLabel9 = new javax.swing.JLabel(); 
    jLabel5 = new javax.swing.JLabel(); 
    txt_rrate = new javax.swing.JTextField(); 
    txt_rid = new javax.swing.JTextField(); 
    jLabel4 = new javax.swing.JLabel(); 
    txt_id = new javax.swing.JTextField(); 
    jLabel1 = new javax.swing.JLabel(); 
    jLabel2 = new javax.swing.JLabel(); 
    jLabel7 = new javax.swing.JLabel(); 
    jLabel3 = new javax.swing.JLabel(); 
    txtlname = new javax.swing.JTextField(); 
    txt_fname = new javax.swing.JTextField(); 
    txt_tel = new javax.swing.JTextField(); 
    filler1 = new javax.swing.Box.Filler(new java.awt.Dimension(0, 0), new java.awt.Dimension(0, 0), new java.awt.Dimension(0, 0)); 
    jPanel2 = new javax.swing.JPanel(); 
    jLabel8 = new javax.swing.JLabel(); 

    setBackground(new java.awt.Color(204, 204, 204)); 
    setClosable(true); 
    setTitle("Reservation Form"); 
    setFont(new java.awt.Font("Arial", 1, 14)); // NOI18N 
    setFrameIcon(new javax.swing.ImageIcon(getClass().getResource("/images/Icon-Edit-Reservations1.png"))); // NOI18N 
    setName(""); // NOI18N 
    setVisible(false); 

    jPanel1.setBackground(new java.awt.Color(255, 204, 51)); 
    jPanel1.setBorder(new javax.swing.border.SoftBevelBorder(javax.swing.border.BevelBorder.LOWERED, java.awt.Color.black, new java.awt.Color(204, 255, 0), java.awt.Color.red, java.awt.Color.black)); 

    jScrollPane1.setBackground(new java.awt.Color(255, 204, 51)); 
    jScrollPane1.setBorder(javax.swing.BorderFactory.createTitledBorder(null, "Available Rooms", javax.swing.border.TitledBorder.DEFAULT_JUSTIFICATION, javax.swing.border.TitledBorder.DEFAULT_POSITION, new java.awt.Font("Tahoma", 0, 18), new java.awt.Color(204, 0, 204))); // NOI18N 
    jScrollPane1.setViewportBorder(javax.swing.BorderFactory.createEtchedBorder(javax.swing.border.EtchedBorder.RAISED, null, java.awt.Color.lightGray)); 
    jScrollPane1.setAutoscrolls(true); 

    jTable1.setBackground(new java.awt.Color(153, 0, 153)); 
    jTable1.setModel(new javax.swing.table.DefaultTableModel(
     new Object [][] { 
      {null, null, null, null}, 
      {null, null, null, null}, 
      {null, null, null, null}, 
      {null, null, null, null} 
     }, 
     new String [] { 
      "Room_ID", "Room_Type", "Room_rate", "Status" 
     } 
    )); 
    jTable1.setToolTipText("click on the row you want "); 
    jTable1.setGridColor(new java.awt.Color(255, 255, 255)); 
    jTable1.setSelectionBackground(new java.awt.Color(102, 255, 0)); 
    jTable1.setSelectionForeground(new java.awt.Color(255, 0, 51)); 
    jTable1.addMouseListener(new java.awt.event.MouseAdapter() { 
     public void mouseClicked(java.awt.event.MouseEvent evt) { 
      jTable1MouseClicked(evt); 
     } 
    }); 
    jScrollPane1.setViewportView(jTable1); 

    jPanel3.setBackground(new java.awt.Color(255, 204, 51)); 
    jPanel3.setBorder(javax.swing.BorderFactory.createBevelBorder(javax.swing.border.BevelBorder.LOWERED, new java.awt.Color(204, 0, 204), new java.awt.Color(204, 0, 204), new java.awt.Color(204, 0, 204), new java.awt.Color(204, 0, 204))); 

    jButton4.setBackground(new java.awt.Color(204, 0, 204)); 
    jButton4.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/sav.png"))); // NOI18N 
    jButton4.setText("Reserve"); 
    jButton4.addActionListener(new java.awt.event.ActionListener() { 
     public void actionPerformed(java.awt.event.ActionEvent evt) { 
      jButton4ActionPerformed(evt); 
     } 
    }); 

    jButton1.setBackground(new java.awt.Color(204, 0, 204)); 
    jButton1.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/Clear-icon.png"))); // NOI18N 
    jButton1.setText("Clear"); 
    jButton1.addActionListener(new java.awt.event.ActionListener() { 
     public void actionPerformed(java.awt.event.ActionEvent evt) { 
      jButton1ActionPerformed(evt); 
     } 
    }); 

    txt_user.setEditable(false); 

    txt_date.setDateFormatString("yyyy MMM d"); 
    txt_date.setEnabled(false); 

    jLabel6.setText("Date_In"); 

    jLabel9.setText("User_name"); 

    jLabel5.setText("Room_Rate:"); 

    txt_rrate.setEditable(false); 
    txt_rrate.addActionListener(new java.awt.event.ActionListener() { 
     public void actionPerformed(java.awt.event.ActionEvent evt) { 
      txt_rrateActionPerformed(evt); 
     } 
    }); 
    txt_rrate.addKeyListener(new java.awt.event.KeyAdapter() { 
     public void keyPressed(java.awt.event.KeyEvent evt) { 
      txt_rrateKeyPressed(evt); 
     } 
    }); 

    txt_rid.setEditable(false); 

    jLabel4.setText("Room_ID:"); 

    jLabel1.setText("Res_ID:"); 

    jLabel2.setText("Firstname:"); 

    jLabel7.setText("Lastname"); 

    jLabel3.setText("Telephone:"); 

    txtlname.addKeyListener(new java.awt.event.KeyAdapter() { 
     public void keyTyped(java.awt.event.KeyEvent evt) { 
      txtlnameKeyTyped(evt); 
     } 
    }); 

    txt_fname.addKeyListener(new java.awt.event.KeyAdapter() { 
     public void keyTyped(java.awt.event.KeyEvent evt) { 
      txt_fnameKeyTyped(evt); 
     } 
    }); 

    txt_tel.setToolTipText(" valid number format +252615178484"); 
    txt_tel.addKeyListener(new java.awt.event.KeyAdapter() { 
     public void keyTyped(java.awt.event.KeyEvent evt) { 
      txt_telKeyTyped(evt); 
     } 
    }); 

    javax.swing.GroupLayout jPanel3Layout = new javax.swing.GroupLayout(jPanel3); 
    jPanel3.setLayout(jPanel3Layout); 
    jPanel3Layout.setHorizontalGroup(
     jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
     .addGroup(jPanel3Layout.createSequentialGroup() 
      .addGap(18, 18, 18) 
      .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING) 
       .addGroup(jPanel3Layout.createSequentialGroup() 
        .addComponent(jButton4, javax.swing.GroupLayout.PREFERRED_SIZE, 110, javax.swing.GroupLayout.PREFERRED_SIZE) 
        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED) 
        .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 123, javax.swing.GroupLayout.PREFERRED_SIZE) 
        .addGap(175, 175, 175)) 
       .addGroup(jPanel3Layout.createSequentialGroup() 
        .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
         .addGroup(jPanel3Layout.createSequentialGroup() 
          .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
           .addComponent(jLabel2) 
           .addComponent(jLabel7) 
           .addComponent(jLabel3)) 
          .addGap(24, 24, 24) 
          .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false) 
           .addComponent(txtlname, javax.swing.GroupLayout.DEFAULT_SIZE, 175, Short.MAX_VALUE) 
           .addComponent(txt_id) 
           .addComponent(txt_fname) 
           .addComponent(txt_tel))) 
         .addComponent(jLabel1)) 
        .addGap(18, 18, 18) 
        .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
         .addComponent(jLabel5, javax.swing.GroupLayout.PREFERRED_SIZE, 60, javax.swing.GroupLayout.PREFERRED_SIZE) 
         .addComponent(jLabel4) 
         .addComponent(jLabel6) 
         .addComponent(jLabel9)) 
        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED) 
        .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false) 
         .addComponent(txt_rid) 
         .addComponent(txt_date, javax.swing.GroupLayout.DEFAULT_SIZE, 155, Short.MAX_VALUE) 
         .addComponent(txt_rrate) 
         .addComponent(txt_user)))) 
      .addContainerGap(43, Short.MAX_VALUE)) 
    ); 
    jPanel3Layout.setVerticalGroup(
     jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
     .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel3Layout.createSequentialGroup() 
      .addContainerGap(40, Short.MAX_VALUE) 
      .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) 
       .addComponent(txt_id, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
       .addComponent(jLabel1) 
       .addComponent(txt_rid, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
       .addComponent(jLabel4)) 
      .addGap(18, 18, 18) 
      .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) 
       .addComponent(txt_fname, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
       .addComponent(jLabel2) 
       .addComponent(txt_rrate, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
       .addComponent(jLabel5)) 
      .addGap(18, 18, 18) 
      .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
       .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) 
        .addComponent(txtlname, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
        .addComponent(jLabel7) 
        .addComponent(jLabel6)) 
       .addComponent(txt_date, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)) 
      .addGap(18, 18, 18) 
      .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
       .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) 
        .addComponent(jLabel3) 
        .addComponent(jLabel9) 
        .addComponent(txt_tel, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)) 
       .addComponent(txt_user, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)) 
      .addGap(30, 30, 30) 
      .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) 
       .addComponent(jButton4, javax.swing.GroupLayout.PREFERRED_SIZE, 31, javax.swing.GroupLayout.PREFERRED_SIZE) 
       .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 31, javax.swing.GroupLayout.PREFERRED_SIZE)) 
      .addContainerGap()) 
    ); 

    javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1); 
    jPanel1.setLayout(jPanel1Layout); 
    jPanel1Layout.setHorizontalGroup(
     jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING) 
     .addGroup(jPanel1Layout.createSequentialGroup() 
      .addGap(20, 20, 20) 
      .addComponent(jPanel3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
      .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) 
      .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 0, Short.MAX_VALUE)) 
    ); 
    jPanel1Layout.setVerticalGroup(
     jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
     .addGroup(jPanel1Layout.createSequentialGroup() 
      .addContainerGap() 
      .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
       .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 216, javax.swing.GroupLayout.PREFERRED_SIZE) 
       .addComponent(jPanel3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)) 
      .addContainerGap(24, Short.MAX_VALUE)) 
    ); 

    jPanel2.setBackground(new java.awt.Color(153, 0, 153)); 

    jLabel8.setFont(new java.awt.Font("Tw Cen MT", 1, 48)); // NOI18N 
    jLabel8.setForeground(new java.awt.Color(255, 255, 255)); 
    jLabel8.setText("Guest Reservation"); 

    javax.swing.GroupLayout jPanel2Layout = new javax.swing.GroupLayout(jPanel2); 
    jPanel2.setLayout(jPanel2Layout); 
    jPanel2Layout.setHorizontalGroup(
     jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
     .addGroup(jPanel2Layout.createSequentialGroup() 
      .addGap(283, 283, 283) 
      .addComponent(jLabel8) 
      .addContainerGap(305, Short.MAX_VALUE)) 
    ); 
    jPanel2Layout.setVerticalGroup(
     jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
     .addGroup(jPanel2Layout.createSequentialGroup() 
      .addContainerGap() 
      .addComponent(jLabel8) 
      .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)) 
    ); 

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); 
    getContentPane().setLayout(layout); 
    layout.setHorizontalGroup(
     layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
     .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup() 
      .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) 
      .addComponent(filler1, javax.swing.GroupLayout.PREFERRED_SIZE, 7, javax.swing.GroupLayout.PREFERRED_SIZE) 
      .addGap(161, 161, 161)) 
     .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) 
     .addComponent(jPanel2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) 
    ); 
    layout.setVerticalGroup(
     layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
     .addGroup(layout.createSequentialGroup() 
      .addComponent(jPanel2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
      .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) 
      .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
      .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) 
      .addComponent(filler1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)) 
    ); 

    pack(); 
}// </editor-fold>       

private void txt_rrateActionPerformed(java.awt.event.ActionEvent evt) {           
    // TODO add your handling code here: 
}           

public void fill() { 

    dbconnection db = new dbconnection(); 
    try { 
     db.connect(); 
     db.stm = db.con.createStatement(); 
     db.rs = db.stm.executeQuery("select Room_ID,Room_type,Room_Rate,Status from Rooms where Status='Available'ORDER By Room_ID"); 
     ResultSetMetaData rmetadata = db.rs.getMetaData(); 
     int columns = rmetadata.getColumnCount(); 
     DefaultTableModel dtm = new DefaultTableModel(); 
     Vector columns_name = new Vector(); 
     Vector data_rows = new Vector(); 
     for (int i = 1; i <= columns; i++) { 
      columns_name.addElement(rmetadata.getColumnName(i)); 
     } 
     dtm.setColumnIdentifiers(columns_name); 
     // dtm.setColumnIdentifiers(Columns_name); 
     while (db.rs.next()) { 
      data_rows = new Vector(); 
      for (int j = 1; j <= columns; j++) { 
       data_rows.addElement(db.rs.getString(j)); 
      } 
      dtm.addRow(data_rows); 
     } 
     jTable1.setModel(dtm); 

    } catch (SQLException e) { 
     JOptionPane.showMessageDialog(this, e.getMessage()); 
    } 
} 

Answer 1

Diese Linie

at hotelreservation.Reservation.fill(Reservation.java:389) 

der Stack-Trace erzählt, dass die Ausnahme in der Methode fill geschieht() in Zeile 389. Null-Zeiger-Ausnahme im Grunde bedeutet, dass Sie etwas auf ein Null-Objekt aufrufen.

Seine diese Linie denke ich

jTable1.setModel(dtm); 

was bedeutet, dass jTable1 null ist. Wenn Sie Ihren Code betrachten, ist die Variable jTable1, die Sie zuvor in der Methode initComponents() festgelegt haben, lokal für diese Methode, weshalb sie in der Methode null ist

Sie können das beheben, indem Sie die Klassenvariablen jTable1 und using erstellen dass

Answer 2

Es sieht aus wie Sie eine space in der SQL-Abfrage nur knapp verfehlt, nachdem empfangen : whereStatus='Available' in Ihrer fill() Methode.

select Room_ID,Room_type,Room_Rate,Status from Rooms whereStatus='Available'ORDER By Room_ID

Ändern Sie es an:

select Room_ID,Room_type,Room_Rate,Status from Rooms whereStatus='Available' ORDER By Room_ID.

Da die SQL-Anweisung ungültig ist, ist db.rs null, was zu einer NullPointerException führt, wenn Anweisung ausgeführt wird.