NullPointerException on update button java. Tried all the solutions but no luck

Question

I have followed several solutions here in stack overflow and implemented the practice. But the problem is not getting solved. Actually I am getting a NullPointException when I click on the detail update button. Here's the code:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Statement;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JInternalFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class EditStdReg extends JInternalFrame implements ActionListener {

private JPanel panel;
private JButton btnUpdate,  btnCancel,  btnView;
private JLabel lblName,  lblAdNo,  lblPhNo,  lblSex,  lblFatherName,  lblOccupation;
private JLabel lblMotherName,  lblDOB,  lblAge,  lblCaste,  lblReligion,  lblHouseName;
private JLabel lblCity,  lblDistrict,  lblState,  lblPin,  lblYear,  lblQualification;
private JTextField txtName,  txtAdNo,  txtPhNo,  txtFatherName,  txtOccupation;
private JTextField txtMotherName,  txtDOB,  txtAge,  txtCaste,  txtReligion,  txtHouseName;
private JTextField txtCity,  txtDistrict,  txtState,  txtPin,  txtYear,  txtQualification;
private JComboBox cmbSex;
private Connection con;
private Statement st;
private PreparedStatement ps;
private int adno;

public EditStdReg() {
    super("Edit Student Registration", true, true, true, true);
    this.setDefaultCloseOperation(DISPOSE_ON_CLOSE);
    this.setSize(1000, 1000);

    panel = new JPanel();
    lblAdNo = new JLabel("Admission no");
    lblName = new JLabel("Name");
    lblPhNo = new JLabel("Phone no");
    lblSex = new JLabel("Sex");
    lblFatherName = new JLabel("Father's name");
    lblOccupation = new JLabel("Occupation");
    lblMotherName = new JLabel("Mother's name");
    lblDOB = new JLabel("DOB");
    lblAge = new JLabel("Age");
    lblCaste = new JLabel("Caste");
    lblReligion = new JLabel("Religion");
    lblHouseName = new JLabel("House Name");
    lblCity = new JLabel("City");
    lblDistrict = new JLabel("District");
    lblState = new JLabel("State");
    lblPin = new JLabel("Pin");
    lblYear = new JLabel("Year");
    lblQualification = new JLabel("Qualification");

    txtName = new JTextField();
    txtAdNo = new JTextField();
    txtPhNo = new JTextField();
    //txtSex = new JTextField();                   
    cmbSex = new JComboBox();
    cmbSex.addItem("MALE");
    cmbSex.addItem("FEMALE");
    cmbSex.setSelectedIndex(0);
    txtFatherName = new JTextField();
    txtOccupation = new JTextField();
    txtMotherName = new JTextField();
    txtDOB = new JTextField();
    txtAge = new JTextField();
    txtCaste = new JTextField();
    txtReligion = new JTextField();
    txtHouseName = new JTextField();
    txtCity = new JTextField();
    txtDistrict = new JTextField();
    txtState = new JTextField();
    txtPin = new JTextField();
    txtQualification = new JTextField();
    txtYear = new JTextField();

    btnUpdate = new JButton("Update", new ImageIcon(ClassLoader.getSystemResource("src/images/update.png")));
    btnCancel = new JButton("Cancel", new ImageIcon(ClassLoader.getSystemResource("src/images/cancel.png")));
    btnView = new JButton("View", new ImageIcon(ClassLoader.getSystemResource("src/images/view.png")));
    btnUpdate.addActionListener(this);
    btnCancel.addActionListener(this);
    btnView.addActionListener(this);

    panel.setLayout(null);

    lblAdNo.setBounds(100, 50, 150, 25);
    txtAdNo.setBounds(200, 50, 200, 25);
    lblName.setBounds(100, 90, 150, 25);
    txtName.setBounds(200, 90, 200, 25);
    lblPhNo.setBounds(100, 130, 150, 25);
    txtPhNo.setBounds(200, 130, 200, 25);
    lblSex.setBounds(100, 170, 150, 25);
    cmbSex.setBounds(200, 170, 200, 25);
    lblFatherName.setBounds(100, 210, 150, 25);
    txtFatherName.setBounds(200, 210, 200, 25);
    lblOccupation.setBounds(100, 250, 100, 25);
    txtOccupation.setBounds(200, 250, 200, 25);
    lblMotherName.setBounds(100, 290, 100, 25);
    txtMotherName.setBounds(200, 290, 200, 25);
    lblDOB.setBounds(100, 330, 150, 25);
    txtDOB.setBounds(200, 330, 200, 25);
    lblCaste.setBounds(100, 370, 150, 25);
    txtCaste.setBounds(200, 370, 200, 25);

    lblAge.setBounds(500, 90, 150, 25);
    txtAge.setBounds(600, 90, 200, 25);
    lblReligion.setBounds(500, 130, 100, 25);
    txtReligion.setBounds(600, 130, 200, 25);
    lblHouseName.setBounds(500, 170, 100, 25);
    txtHouseName.setBounds(600, 170, 200, 25);
    lblCity.setBounds(500, 210, 150, 25);
    txtCity.setBounds(600, 210, 200, 25);
    lblDistrict.setBounds(500, 250, 100, 25);
    txtDistrict.setBounds(600, 250, 200, 25);
    lblState.setBounds(500, 290, 50, 25);
    txtState.setBounds(600, 290, 200, 25);
    lblPin.setBounds(500, 330, 150, 25);
    txtPin.setBounds(600, 330, 200, 25);
    lblYear.setBounds(500, 370, 100, 25);
    txtYear.setBounds(600, 370, 200, 25);
    lblQualification.setBounds(100, 420, 80, 25);
    txtQualification.setBounds(200, 420, 600, 25);

    btnUpdate.setBounds(300, 470, 100, 25);
    btnCancel.setBounds(450, 470, 100, 25);
    btnView.setBounds(600, 470, 100, 25);
    btnUpdate.setEnabled(false);
    panel.add(lblAdNo);
    panel.add(txtAdNo);
    panel.add(lblName);
    panel.add(txtName);
    panel.add(lblPhNo);
    panel.add(txtPhNo);
    panel.add(lblSex);
    panel.add(cmbSex);
    panel.add(lblFatherName);
    panel.add(txtFatherName);
    panel.add(lblOccupation);
    panel.add(txtOccupation);
    panel.add(lblMotherName);
    panel.add(txtMotherName);
    panel.add(lblDOB);
    panel.add(txtDOB);
    panel.add(lblAge);

    panel.add(txtAge);
    panel.add(lblCaste);
    panel.add(txtCaste);
    panel.add(lblReligion);
    panel.add(txtReligion);

    panel.add(lblHouseName);
    panel.add(txtHouseName);
    panel.add(lblCity);
    panel.add(txtCity);
    panel.add(lblDistrict);
    panel.add(txtDistrict);
    panel.add(lblState);
    panel.add(txtState);
    panel.add(lblPin);
    panel.add(txtPin);
    panel.add(txtYear);
    panel.add(lblYear);
    panel.add(lblQualification);
    panel.add(txtQualification);
    panel.add(btnUpdate);
    panel.add(btnCancel);
    panel.add(btnView);
    add(panel, BorderLayout.CENTER);
    try {
        Class.forName("com.mysql.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/anu?zeroDateTimeBehavior=convertToNull","root","root");
        st = con.createStatement();
    } catch (Exception ex) {
        JOptionPane.showMessageDialog(null, "Error on connection to database, cannot continue updation process", "Error", JOptionPane.ERROR_MESSAGE);
    }//outer try catch closed

}//constructor closed
public void actionPerformed(ActionEvent e) {
    if (e.getActionCommand().equalsIgnoreCase("Update")) {
        try {
            if(adno!=Integer.parseInt(txtAdNo.getText())){
                JOptionPane.showMessageDialog(null,"Roll number cannot be changed","Updation error",JOptionPane.ERROR_MESSAGE);
                return;
            }
            String sql = "UPDATE student SET SName=?,Phno=?,Sex=?,Fname=?,Occupation=?,Mname=?,Dob=?" +
                    ",Age=?,Caste=?,Religion=?,Hname=?,City=?,District=?,State=?,Pin=?,Year=?,Qualification=?" +
                    " WHERE Rollno="+ adno;
            ps=con.prepareStatement(sql);
            ps.setString(1,txtName.getText());
            ps.setString(2,txtPhNo.getText());
            ps.setString(3,cmbSex.getSelectedItem().toString());
            ps.setString(4,txtFatherName.getText());
            ps.setString(5,txtOccupation.getText());
            ps.setString(6,txtMotherName.getText());
            ps.setString(7,txtDOB.getText());                        
            ps.setInt(8,Integer.parseInt(txtAge.getText()));                
            ps.setString(9,txtCaste.getText());
            ps.setString(10,txtReligion.getText());
            ps.setString(11,txtHouseName.getText());
            ps.setString(12,txtCity.getText());
            ps.setString(13,txtDistrict.getText());
            ps.setString(14,txtState.getText());
            ps.setString(15,txtPin.getText());
            ps.setInt(16,Integer.parseInt(txtYear.getText()));
            ps.setString(17,txtQualification.getText());
            ps.executeUpdate();                                                     
            JOptionPane.showMessageDialog(null, "Registration details successfully updated", "Success", JOptionPane.INFORMATION_MESSAGE);
            ClearForm();
            btnUpdate.setEnabled(false);
        } catch (Exception x) {
            //JOptionPane.showMessageDialog(null, "Error on database operation,Updation failure", "Error", JOptionPane.ERROR_MESSAGE);
            x.printStackTrace();
        }//inner try catch closed
    }//if closed
    if (e.getActionCommand().equalsIgnoreCase("View")) {

        try {
            ResultSet rs = st.executeQuery("SELECT * FROM student WHERE RollNo=" + txtAdNo.getText());
            if (rs.next()) {
                adno = Integer.parseInt(txtAdNo.getText());
                txtName.setText(rs.getString("SName"));
                cmbSex.setSelectedItem(rs.getString("Sex"));
                txtFatherName.setText(rs.getString("FName"));
                txtMotherName.setText(rs.getString("MName"));
                txtAge.setText(rs.getString("Age"));
                txtOccupation.setText(rs.getString("Occupation"));
                txtPhNo.setText(rs.getString("phno"));
                txtReligion.setText(rs.getString("Religion"));
                txtHouseName.setText(rs.getString("Hname"));
                txtCaste.setText(rs.getString("Caste"));
                txtCity.setText(rs.getString("City"));
                txtState.setText(rs.getString("State"));
                txtDOB.setText(rs.getDate("Dob").toString());
                txtDistrict.setText(rs.getString("District"));
                txtPin.setText(rs.getString("Pin"));
                txtYear.setText(rs.getString("Year"));
                txtQualification.setText(rs.getString("Qualification"));
                btnUpdate.setEnabled(true);
            } else {
                JOptionPane.showMessageDialog(null, "Roll No not found in database", "Not found", JOptionPane.INFORMATION_MESSAGE);
                ClearForm();
                btnUpdate.setEnabled(false);
            }//if else closed                
        } catch (Exception x) {
            JOptionPane.showMessageDialog(null, "Error on database operation,Updation failure", "Error", JOptionPane.ERROR_MESSAGE);
        }//inner try catch closed

    }//if closed
    if (e.getActionCommand().equalsIgnoreCase("Cancel")) {
        this.dispose();
    }//if closed
}

private void ClearForm() {
    txtAdNo.setText("");
    txtName.setText("");
    cmbSex.setSelectedIndex(0);
    txtFatherName.setText("");
    txtOccupation.setText("");
    txtMotherName.setText("");
    txtPhNo.setText("");
    txtDOB.setText("");
    txtAge.setText("");
    txtCaste.setText("");
    txtReligion.setText("");
    txtHouseName.setText("");
    txtCity.setText("");
    txtDistrict.setText("");
    txtState.setText("");
    txtPin.setText("");
    txtYear.setText("");
    txtQualification.setText("");
}//clearform() closed
}//class closed

The exception thrown is:

java.lang.NullPointerException
at EditStdReg.actionPerformed(EditStdReg.java:197)
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.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
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)

"Tried all the solutions but no luck" - What have you tried? — Steve Smith, Feb 16 '17 at 15:55
The answer has been practiced the whole day. No luck mate. Need some specific answer. @khelwood — razznitin, Feb 16 '17 at 15:55
@SteveSmith, I have tried this: http://stackoverflow.com/questions/16255724/jbutton-actionperformed-null-pointer-exception and many other answers. — razznitin, Feb 16 '17 at 15:57
The answer to that question is eaxctly the same answer to your question. You are "shadowing" `con` by declaring it twice, so the instance at line 197 hasn't been instanciated. — Steve Smith, Feb 16 '17 at 15:58
You are right@SteveSmith. I basically focused on button part and ignored it. — razznitin, Feb 16 '17 at 16:06

score 1 · Accepted Answer · answered Feb 16 '17 at 15:55

1

Replace in constructor

Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/anu?zeroDateTimeBehavior=convertToNull","root","root");

with

con = DriverManager.getConnection("jdbc:mysql://localhost:3306/anu?zeroDateTimeBehavior=convertToNull","root","root");

Reason

You are declaring a separate local Connection object in the Constructor which is not available to the other methods after the constructor scope is over. You already have another Connection object at an instance level which is available to all the methods including the constructor. Use that.

answered Feb 16 '17 at 15:55

VHS

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This exactly is the solution. Thanks alot. Works now. – razznitin Feb 16 '17 at 16:06
You are welcome @user2983808. – VHS Feb 16 '17 at 16:10

Yousaf · Answer 2 · 2017-02-16T16:13:49.450

Problem:

You have declared Connection object con twice.

Once inside your class and second time in constructor inside try-catch block.

The scope of Connection object initialized inside constructor is limited to that constructor so when you try

ps=con.prepareStatement(sql);

this con is not initialized, hence the infamous NullPointerException

Solution

Change your try-catch block statement

Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/anu?
zeroDateTimeBehavior=convertToNull","root","root");

to

con = DriverManager.getConnection("jdbc:mysql://localhost:3306/anu?
zeroDateTimeBehavior=convertToNull","root","root");

so that you have only one Connection object con that is initialized inside Constructor.

NullPointerException on update button java. Tried all the solutions but no luck

2 Answers2