how to resolve error "java.lang.NullPointerException"?

Question

when I try to INSERT RECORD(like username and password) in database on clicking register button it shows error through JOptionPane "java.lang.NullPointerException"...please tell me the solution how to INSERT RECORD**

import java.sql.*;
import javax.swing.*;

public class Newuser extends javax.swing.JInternalFrame {
Connection cn;
PreparedStatement st;
ResultSet rs;
String url,sql;
public Newuser() {
    initComponents();
}

public void MyConnection()
{
    try
    {
        Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
        url="jdbc:sqlserver://localhost;instance=LALLYDB;databaseName=Menu;user=kd;password=123";
        cn=DriverManager.getConnection(url);     //above instance ,i.e,LALLYDB is DatabaseServer Name
    }
    catch(Exception ee)
    {
        JOptionPane.showMessageDialog(this, ee);
    }
}

public void Insert_Record(String username,String passwd)
{
    try
    {
        MyConnection();      //calling MyConnection function 
        st=cn.prepareStatement(sql,ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
        rs=st.executeQuery();
        sql="Insert into Project values(?,?)";
        st=cn.prepareStatement(sql);
        st.setString(1,username);
        st.setString(2,passwd);
        st.executeUpdate();
        JOptionPane.showMessageDialog(this,"Record successfully inserted");
        cn.close();
    }

    catch(Exception ee)
    {
        JOptionPane.showMessageDialog(this, ee);
    }
}

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

    nlbl1 = new javax.swing.JLabel();
    nlbl2 = new javax.swing.JLabel();
    ntxt1 = new javax.swing.JTextField();
    ntxt2 = new javax.swing.JTextField();
    nlbl3 = new javax.swing.JLabel();
    nlbl4 = new javax.swing.JLabel();
    nlbl5 = new javax.swing.JLabel();
    ntxt3 = new javax.swing.JTextField();
    ntxt4 = new javax.swing.JTextField();
    regitser = new javax.swing.JButton();
    jcombo1 = new javax.swing.JComboBox<>();

    setClosable(true);
    setIconifiable(true);
    setMaximizable(true);
    setResizable(true);
    setTitle("New User Registration");
    setPreferredSize(new java.awt.Dimension(488, 425));
    setVisible(true);
    getContentPane().setLayout(new org.netbeans.lib.awtextra.AbsoluteLayout());

    nlbl1.setText("Username");
    getContentPane().add(nlbl1, new org.netbeans.lib.awtextra.AbsoluteConstraints(84, 44, -1, -1));

    nlbl2.setText("Password");
    getContentPane().add(nlbl2, new org.netbeans.lib.awtextra.AbsoluteConstraints(80, 80, -1, -1));
    getContentPane().add(ntxt1, new org.netbeans.lib.awtextra.AbsoluteConstraints(210, 40, 140, -1));
    getContentPane().add(ntxt2, new org.netbeans.lib.awtextra.AbsoluteConstraints(210, 80, 140, -1));

    nlbl3.setText("Email-id");
    getContentPane().add(nlbl3, new org.netbeans.lib.awtextra.AbsoluteConstraints(90, 120, -1, -1));

    nlbl4.setText("Hint Question");
    getContentPane().add(nlbl4, new org.netbeans.lib.awtextra.AbsoluteConstraints(80, 160, -1, -1));

    nlbl5.setText("Hint Answer");
    getContentPane().add(nlbl5, new org.netbeans.lib.awtextra.AbsoluteConstraints(80, 200, -1, -1));
    getContentPane().add(ntxt3, new org.netbeans.lib.awtextra.AbsoluteConstraints(210, 120, 140, -1));
    getContentPane().add(ntxt4, new org.netbeans.lib.awtextra.AbsoluteConstraints(210, 200, 140, -1));

    regitser.setText("Register");
    regitser.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            regitserActionPerformed(evt);
        }
    });
    getContentPane().add(regitser, new org.netbeans.lib.awtextra.AbsoluteConstraints(390, 200, -1, -1));

    jcombo1.setModel(new javax.swing.DefaultComboBoxModel<>(new String[] { "Select", "What is your pet name ?", "What is your school name ?", "What is your favourite sport ?" }));
    getContentPane().add(jcombo1, new org.netbeans.lib.awtextra.AbsoluteConstraints(210, 160, -1, -1));

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


private void regitserActionPerformed(java.awt.event.ActionEvent evt) {                                         
    Insert_Record(ntxt1.getText(),ntxt2.getText());
}                                        


// Variables declaration - do not modify                     
private javax.swing.JComboBox<String> jcombo1;
private javax.swing.JLabel nlbl1;
private javax.swing.JLabel nlbl2;
private javax.swing.JLabel nlbl3;
private javax.swing.JLabel nlbl4;
private javax.swing.JLabel nlbl5;
private javax.swing.JTextField ntxt1;
private javax.swing.JTextField ntxt2;
private javax.swing.JTextField ntxt3;
private javax.swing.JTextField ntxt4;
private javax.swing.JButton regitser;
// End of variables declaration

}

You haven't needed the `Class.forName()` line since 2007. – user207421 Apr 07 '16 at 00:04 — user207421, Apr 07 '16 at 00:04

score 0 · Answer 1 · answered Apr 06 '16 at 21:56

The error you get through JOptionPane contains a linenumber, where the Exception occurs (you are catching it and showing it). Either look that linenumber in the MessageDialog up and see what line is the reason, or type ee.printStackTrace() inside the catch-blocks and you can then see the statement throwing the Exception. Also at st=cn.prepareStatement(sql,...); the variable sql has not been set, is this intentional ?

NullPointerException in general means, that you are trying to access a variable that hasn't been initialized before.

how to resolve error "java.lang.NullPointerException"?

1 Answers1