Develop Reference

I want to present the username from database JAVA Jframe

I have two JFrame windows one for the login and the second for the welcome. Now I want to present the Firstname and the Lastname of the connected user near to the hello in the welcome screen.
I tried many things but none of them worked so I'm asking for you help. I just started to learn GUI:
The login code:
import java.awt.EventQueue;
import java.sql.*;
import javax.swing.*;
import java.awt.Font;
import java.awt.Image;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class Login {
private JFrame frame;
private JLabel MainLogo;
String Firstname=null;
String Lastname=null;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Login window = new Login();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the application.
*/
Connection connected = null;
private JTextField UsernameFiled;
private JPasswordField passwordField;
public Login() {
initialize();
connected = DBConnection.DBconnector();
}
/**
* Initialize the contents of the frame.
*/
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 560, 256);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(null);
JLabel lblNewLabel = new JLabel("UserName: ");
lblNewLabel.setFont(new Font("Tahoma", Font.BOLD, 20));
lblNewLabel.setBounds(160, 11, 140, 50);
frame.getContentPane().add(lblNewLabel);
JLabel lblPassword = new JLabel("PassWord: ");
lblPassword.setFont(new Font("Tahoma", Font.BOLD, 20));
lblPassword.setBounds(160, 72, 140, 40);
frame.getContentPane().add(lblPassword);
JButton Loginbtn = new JButton("Login");
Loginbtn.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
try {
String query = "Select * from Users where nickname=? and password=?";
PreparedStatement pst = connected.prepareStatement(query);
pst.setString(1, UsernameFiled.getText());
pst.setString(2, passwordField.getText());
ResultSet res = pst.executeQuery();
Firstname = res.getString("Firstname");
Lastname = res.getString("Lastname");
int c=0;
while(res.next()) {
c++;
}
if(c == 0) {
JOptionPane.showMessageDialog(null, "You didnt put any username or password!");
}
else if(c == 1) {
JOptionPane.showMessageDialog(null, "Hello to you, " + Firstname +" "+ Lastname);
frame.dispose();
UserPage UserFrame = new UserPage();
UserFrame.setVisible(true);
}else if( c > 1) {
JOptionPane.showMessageDialog(null, "Duplicate Username and Password");
}else {
JOptionPane.showMessageDialog(null, "Username and Password are inncorect...Try agian!");
}
pst.close();
res.close();
}catch(Exception LoginError) {
JOptionPane.showMessageDialog(null, LoginError);
}
}
});
Loginbtn.setFont(new Font("Tahoma", Font.BOLD, 20));
Loginbtn.setBounds(160, 148, 186, 40);
frame.getContentPane().add(Loginbtn);
UsernameFiled = new JTextField();
UsernameFiled.setFont(new Font("Tahoma", Font.BOLD, 16));
UsernameFiled.setBounds(310, 28, 186, 25);
frame.getContentPane().add(UsernameFiled);
UsernameFiled.setColumns(10);
passwordField = new JPasswordField();
passwordField.setFont(new Font("Tahoma", Font.BOLD, 16));
passwordField.setBounds(310, 84, 186, 25);
frame.getContentPane().add(passwordField);
MainLogo = new JLabel("");
Image imgs = new ImageIcon(this.getClass().getResource("/login.png")).getImage();
MainLogo.setIcon(new ImageIcon(imgs));
MainLogo.setBounds(10, 11, 128, 128);
frame.getContentPane().add(MainLogo);
}
}
The Welcome Code:
import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import net.proteanit.sql.DbUtils;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import java.awt.Font;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.*;
import javax.swing.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class UserPage extends JFrame {
private JPanel contentPane;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
UserPage frame = new UserPage();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
Connection connected=null;
private JTable table;
public UserPage() {
connected=DBConnection.DBPreconnector();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 576, 410);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
JButton bntLoadData = new JButton("Show Users Data");
bntLoadData.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
try {
String query = "Select ID,Age,Password,Firstname,Lastname from users";
PreparedStatement pst = connected.prepareStatement(query);
ResultSet res = pst.executeQuery();
table.setModel(DbUtils.resultSetToTableModel(res));
} catch (Exception Error) {
Error.printStackTrace();
}
}
});
JLabel lblNewLabel = new JLabel("Hello, " + "The Username name");
lblNewLabel.setFont(new Font("Tahoma", Font.BOLD, 18));
lblNewLabel.setBounds(10, 11, 280, 19);
contentPane.add(lblNewLabel);
bntLoadData.setFont(new Font("Tahoma", Font.BOLD, 20));
bntLoadData.setBounds(162, 102, 238, 23);
contentPane.add(bntLoadData);
table = new JTable();
table.setBounds(28, 136, 508, 221);
contentPane.add(table);
}
}

In your code, you does not seem to load the username or password of the logged in user at the welcome frame. Either you will have to pass that from the login frame or you will have to re-query the database and get firstname and lastname.
I suggest, simply pass the firstname and lastname from welcome screen via constructor.
In successful login, simply pass the name in the constructor: Login code addition:
} else if(c == 1) {
JOptionPane.showMessageDialog(null, "Hello to you, " + Firstname +" "+ Lastname);
frame.dispose();
UserPage UserFrame = new UserPage( Firstname, Lastname );
UserFrame.setVisible(true);
}
In the welcome frame, add a constructor to handle this:
public UserPage(String loggedInFirstName, String loggedInLastName){
// your remaining code
JLabel lblNewLabel = new JLabel("Hello, " + loggedInFirstName + " " + loggedInLastName );
// your remaining code.
}
A approach like this might work for your case and don't forget to mark the answer as accepted if this works for you

populate JTable with the value selected in Jcombobox

I have a JCombobox and JTable
and database
jcombobox is filled with the value of first_name of student table from databse.
Whenever I select a name from database I want the value of Course name from course and student_score from score table of the database to be displayed in Jtable.
Basically I want to display the records of selected in JComboBox in Jtable
import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import net.proteanit.sql.DbUtils;
import javax.swing.JLabel;
import java.awt.Font;
import javax.swing.JTable;
import javax.swing.JScrollPane;
import javax.swing.*;
import java.sql.*;
import javax.swing.event.PopupMenuListener;
import javax.swing.event.PopupMenuEvent;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class ShowScore extends JFrame {
private JPanel contentPane;
private JTable table;
private JComboBox comboBox;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
ShowScore frame = new ShowScore();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
Connection con=null;
Score s=new Score();
public ShowScore() {
con=MyConnection.getConnection();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 1238, 761);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
JLabel lblScoreSheet = new JLabel("Score Sheet");
lblScoreSheet.setFont(new Font("Times New Roman", Font.BOLD, 28));
lblScoreSheet.setBounds(500, 33, 155, 50);
contentPane.add(lblScoreSheet);
JPanel panel = new JPanel();
panel.setBounds(24, 259, 720, 426);
contentPane.add(panel);
panel.setLayout(null);
JScrollPane scrollPane = new JScrollPane();
scrollPane.setBounds(12, 13, 675, 452);
panel.add(scrollPane);
comboBox = new JComboBox();
comboBox.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
table = new JTable();
scrollPane.setViewportView(table);
try {
String n=(String)comboBox.getSelectedItem();
String sql="SELECT score.student_id, student.first_name, student.last_name,course.subject, score.student_score FROM ((score INNER JOIN student ON score.student_id=student.id)\r\n" +
" INNER JOIN course ON score.course_id=course.cid WHERE student.first_name=n)";
PreparedStatement ps=con.prepareStatement(sql);
ResultSet rs=ps.executeQuery();
table.setModel(DbUtils.resultSetToTableModel(rs));
JLabel lblName = new JLabel("Name:");
lblName.setFont(new Font("Times New Roman", Font.PLAIN, 18));
lblName.setBounds(102, 107, 56, 16);
contentPane.add(lblName);
} catch (Exception e1) {
e1.printStackTrace();
}
}
});
s.fillScoreCombo(comboBox);
comboBox.setBounds(171, 105, 260, 27);
contentPane.add(comboBox);
table = new JTable();
scrollPane.setViewportView(table);
try {
String n=(String)comboBox.getSelectedItem();
String sql="SELECT score.student_id, student.first_name, student.last_name,course.subject, score.student_score FROM ((score INNER JOIN student ON score.student_id=student.id)\r\n" +
" INNER JOIN course ON score.course_id=course.cid)";
PreparedStatement ps=con.prepareStatement(sql);
ResultSet rs=ps.executeQuery();
table.setModel(DbUtils.resultSetToTableModel(rs));
JLabel lblName = new JLabel("Name:");
lblName.setFont(new Font("Times New Roman", Font.PLAIN, 18));
lblName.setBounds(102, 107, 56, 16);
contentPane.add(lblName);
} catch (Exception e1) {
e1.printStackTrace();
}
}
}

String n=(String)comboBox.getSelectedItem();
String sql="SELECT .... WHERE student.first_name=n)";
That code doesn't do anything with the variable "n". You can't just include "n" as part of the String because all the have is the character "n", not the value of the variable.
You were given a link to a tutorial on using a PreparedStatement in your last question (Populate JTable with the value in JCombobox).
So where do you use the "?" which indicates you want to provide a dynamic value to the SQL statement?
Your basic code should be:
String sql="SELECT ..... where student.first_name = ?)";
PreparedStatement ps = con.prepareStatement(sql);
ps.setString(1, n);
ResultSet rs = ps.executeQuery();
Now the value of the variable "n" will replace the "?" in the SQL string.
Assuming the rest of your SQL is correct then it should work.

SQL Syntax Error In Java and MySql SELECT Query

I am developing a basic program that has 3 JFrames. A log-in, a registration and a Dashboard to be opened after successful log-in attempt. However, I am getting an error after typing in the username and password and clicking log-in button.
Here's the error:
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ' password='1234'' at line 1
And here's my code:
import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import com.mysql.jdbc.Statement;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.ImageIcon;
import java.awt.Font;
import javax.swing.JTextField;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.awt.event.ActionEvent;
public class Login extends JFrame {
private JPanel contentPane;
private JTextField txtUsrName;
private JTextField txtPAss;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Login frame = new Login();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public Login() {
setDefaultCloseOperation(JFrame.HIDE_ON_CLOSE);
setBounds(100, 100, 450, 348);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
JLabel lblLogin = new JLabel("Welcome To TechApp");
lblLogin.setFont(new Font("Tekton Pro", Font.PLAIN, 18));
lblLogin.setBounds(135, 19, 163, 28);
contentPane.add(lblLogin);
JLabel lblUsername = new JLabel("UserName:");
lblUsername.setFont(new Font("Alaska", Font.PLAIN, 15));
lblUsername.setBounds(174, 58, 88, 28);
contentPane.add(lblUsername);
txtUsrName = new JTextField();
txtUsrName.setBounds(145, 90, 132, 20);
contentPane.add(txtUsrName);
txtUsrName.setColumns(10);
JLabel lblPassword = new JLabel("Password:");
lblPassword.setFont(new Font("Alaska", Font.PLAIN, 15));
lblPassword.setBounds(182, 118, 95, 46);
contentPane.add(lblPassword);
txtPAss = new JTextField();
txtPAss.setColumns(10);
txtPAss.setBounds(145, 156, 132, 20);
contentPane.add(txtPAss);
JButton btnNewButton = new JButton("login");
btnNewButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
String _username = txtUsrName.getText();
String _password = txtPAss.getText();
String url = "jdbc:mysql://127.0.0.1:3306/javabase";
String user = "java";
String passw = "password";
try{
// 1.Get a connection To Database
Connection myConn = DriverManager.getConnection(url, user, passw);
// 2.Create a statement
Statement myStmt = (Statement) myConn.createStatement();
// 3.Execute SQL Query
String sql = "SELECT userame, password FROM registration WHERE userame='"+_username+"', password='"+_password+"' ";
ResultSet result = myStmt.executeQuery(sql);
//myStmt.executeUpdate(sql);
int count = 0;
while(result.next()){
count = count + 1;
}
if(count == 1){
Dashboard frame = new Dashboard();
frame.setVisible(true);
}
else if(count > 1){
JOptionPane.showMessageDialog(null, "Duplicate User! Access Denied!");
}
else{
JOptionPane.showMessageDialog(null, "User Not Found!");
}
}
catch(Exception ex)
{
ex.printStackTrace();
}
}
});
btnNewButton.setBounds(169, 202, 89, 49);
contentPane.add(btnNewButton);
JButton btnRegister = new JButton("Register");
btnRegister.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Main frame = new Main();
frame.setVisible(true);
}
});
btnRegister.setBounds(168, 264, 89, 23);
contentPane.add(btnRegister);
JLabel lblNewLabel = new JLabel("");
lblNewLabel.setFont(new Font("Alaska", Font.PLAIN, 16));
lblNewLabel.setIcon(new ImageIcon("D:\\ExploitGate\\MAS-9831-Offwhite2.jpg"));
lblNewLabel.setBounds(0, 0, 434, 310);
contentPane.add(lblNewLabel);
}
}
I've searched the stackoverflow forum and carried out the possible solution given here
Can anyone please guide me how to handle this error?
Thanks In Advance :)

All of the above code is basically useless. It's an SQL syntax error, which means it's this one line:
... WHERE userame='"+_username+"', password='"+_password+"' ";
^---
you don't use , to separate where clause arguments. You use boolean operations. and, or, etc...
And note that you're vulnerable to sql injection attacks

You were using a comma , between your WHERE clauses rather than an AND.
String sql = "SELECT userame, password FROM registration WHERE userame='"+_username+"' AND password='"+_password+"' ";

How can I make my table update?

I use SQLite. I have 2 JFrames. 1st is consists of table and "Load data", "Edit data". Click on Edit make the new, 2nd JFrame to appear. I want my table to be updated after I make some changes with a help of class Edit. How do I make it? One idea is to use ActionListener so that after I click save, delete or update buttons in JFrame2 method of Jframe 1, which stays for updating of the table(using query), is called. I have tried, but it does not work. I do not want the method of the 1 Jframe to be called in 2nd Jframe, I want this method to be called in 1st Jframe. What are possible solutions?
import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import net.proteanit.sql.DbUtils;
import javax.swing.JTable;
import javax.swing.JScrollPane;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.sql.*;
import javax.swing.*;
public class Diary extends JFrame {
private JPanel contentPane;
JTable table;
private JButton btnLoadData;
public void refreshTabel(){
try {
String query = "select * from Diary";
PreparedStatement pst = connection.prepareStatement(query);
ResultSet rs = pst.executeQuery();
table.setModel(DbUtils.resultSetToTableModel(rs));
pst.close();
rs.close();
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Diary frame = new Diary();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
Connection connection = null;
/**
* Create the frame.
*/
public Diary() {
setResizable(false);
connection = Main.dbConnector();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 1250, 650);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
JScrollPane scrollPane = new JScrollPane();
scrollPane.setBounds(34, 58, 1182, 530);
contentPane.add(scrollPane);
table = new JTable();
scrollPane.setViewportView(table);
btnLoadData = new JButton("Load data");
btnLoadData.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
try {
String query = "select * from Diary";
PreparedStatement pst = connection.prepareStatement(query);
ResultSet rs = pst.executeQuery();
table.setModel(DbUtils.resultSetToTableModel(rs));
pst.close();
rs.close();
} catch (Exception e) {
e.printStackTrace();
}
}
});
btnLoadData.setBounds(33, 17, 117, 29);
contentPane.add(btnLoadData);
JButton btnAddData = new JButton("Edit");
btnAddData.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
AddData nw = new AddData();
nw.addData();
refreshTabel();
}
});
btnAddData.setBounds(153, 17, 117, 29);
contentPane.add(btnAddData);
}
}
import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import com.sun.glass.events.WindowEvent;
import net.proteanit.sql.DbUtils;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.JList;
import javax.swing.JOptionPane;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.awt.event.ActionEvent;
public class AddData extends JFrame {
private JPanel contentPane;
private JTextField Date;
private JTextField ExerciseName;
private JTextField Weight;
private JTextField Sets;
private JTextField Reps;
/**
* Launch the application.
* #return
*/
public static void addData() {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
AddData frame = new AddData();
frame.setVisible(true);
frame.setAlwaysOnTop(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
Connection connection = null;
private JTextField Exercise;
private JTextField N;
/**
* Create the frame.
*/
public AddData() {
setTitle("Edit");
setResizable(false);
connection = Main.dbConnector();
setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
setBounds(100, 100, 465, 368);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
JLabel lblDate = new JLabel("Date");
lblDate.setBounds(29, 49, 61, 16);
contentPane.add(lblDate);
JLabel ExerciseLabel = new JLabel("Exercise");
ExerciseLabel.setBounds(29, 88, 90, 16);
contentPane.add(ExerciseLabel);
JLabel lblNewLabel_1 = new JLabel("Sets");
lblNewLabel_1.setBounds(29, 169, 61, 16);
contentPane.add(lblNewLabel_1);
JLabel lblReps = new JLabel("Reps");
lblReps.setBounds(29, 213, 61, 16);
contentPane.add(lblReps);
JLabel lblWeight = new JLabel("Weight");
lblWeight.setBounds(29, 126, 61, 16);
contentPane.add(lblWeight);
Date = new JTextField();
Date.setBounds(169, 56, 150, 26);
contentPane.add(Date);
Date.setColumns(10);
ExerciseName = new JTextField();
ExerciseName.setBounds(169, 60, 150, 26);
contentPane.add(ExerciseLabel);
ExerciseName.setColumns(10);
Weight = new JTextField();
Weight.setBounds(169, 132, 150, 26);
contentPane.add(Weight);
Weight.setColumns(10);
Sets = new JTextField();
Sets.setBounds(169, 170, 150, 26);
contentPane.add(Sets);
Sets.setColumns(10);
Reps = new JTextField();
Reps.setBounds(169, 208, 150, 26);
contentPane.add(Reps);
Reps.setColumns(10);
JButton btnSave = new JButton("Save");
btnSave.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
try {
String query = "insert into Diary (Date, Exercise, Weight, Sets, Reps) values (?,?,?,?,?)";
PreparedStatement pst = connection.prepareStatement(query);
pst.setString(1, Date.getText());
pst.setString(2, Exercise.getText());
pst.setString(3, Weight.getText());
pst.setString(4, Sets.getText());
pst.setString(5, Reps.getText());
pst.execute();
JOptionPane.showMessageDialog(null, "Saved");
pst.close();
} catch (Exception ea) {
ea.printStackTrace();
}
}
});
btnSave.setBounds(29, 261, 117, 29);
contentPane.add(btnSave);
JButton btnUpdate = new JButton("Update");
btnUpdate.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
try {
String query = "update Diary set N ='"+N.getText()+"', Exercise ='"+Exercise.getText()+"', Weight ='"+Weight.getText()+"', Sets ='"+Sets.getText()+"', Reps ='"+Reps.getText()+"' where N ='"+N.getText()+"' ";
PreparedStatement pst = connection.prepareStatement(query);
pst.execute();
JOptionPane.showMessageDialog(null, "Updated");
pst.close();
} catch (Exception ea) {
ea.printStackTrace();
}
}
});
btnUpdate.setBounds(176, 261, 117, 29);
contentPane.add(btnUpdate);
Exercise = new JTextField();
Exercise.setBounds(169, 94, 150, 26);
contentPane.add(Exercise);
Exercise.setColumns(10);
N = new JTextField();
N.setBounds(169, 18, 150, 26);
contentPane.add(N);
N.setColumns(10);
JLabel lblN = new JLabel("N");
lblN.setBounds(29, 23, 61, 16);
contentPane.add(lblN);
JButton Delete = new JButton("Delete");
Delete.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
try {
String query = "delete from Diary where N = '"+N.getText()+"'";
PreparedStatement pst = connection.prepareStatement(query);
pst.execute();
JOptionPane.showMessageDialog(null, "Deleted");
pst.close();
} catch (Exception ea) {
ea.printStackTrace();
}
}
});
Delete.setBounds(305, 261, 117, 29);
contentPane.add(Delete);
}
}

java sql queries

I have a query. I have a database, and I am trying to write code, so that a record in the database can be created from the java software.
I have a connector class that connects to the database, then a registerStudent class, that lets the user type in value into 2 textfields. then the values should be used to create a record in the database table.
when i hit the submit button it gives me this error code:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at RegisterStudent$2.actionPerformed(RegisterStudent.java:99)
FYI - Line 99 Code =
con.stmt.executeUpdate("INSERT INTO staff (Name, Profession)"+"VALUES"+"("+"'"+name+"',"+"'"+profession+"')");
This is my code for the registerStudent class:
import java.awt.Component;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.Border;
import javax.swing.border.LineBorder;
import javax.swing.JLabel;
import java.awt.Font;
import javax.swing.JTextField;
import javax.swing.JButton;
import javax.swing.JOptionPane;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.sql.SQLException;
public class RegisterStudent
{
public RegisterStudent() {
initialize();
}
public JFrame frmRegisterStudent;
Connector con;
private JTextField textField_1;
private JTextField textField_2;
// initialise the frame
private void initialize() {
frmRegisterStudent = new JFrame();
frmRegisterStudent.setTitle("LEC AdminPro: RegisterStudents");
frmRegisterStudent.setBounds(100, 100, 413, 225);
frmRegisterStudent.setDefaultCloseOperation(JFrame.HIDE_ON_CLOSE);
frmRegisterStudent.setLocationRelativeTo(null);
Border border = LineBorder.createGrayLineBorder();
frmRegisterStudent.getContentPane().setLayout(null);
con = new Connector();
JPanel panel_1 = new JPanel();
panel_1.setBounds(0, 0, 397, 189);
frmRegisterStudent.getContentPane().add(panel_1);
panel_1.setBorder(border);
panel_1.setLayout(null);
JLabel lblRegister = new JLabel("Register Student");
lblRegister.setFont(new Font("Tahoma", Font.BOLD, 12));
lblRegister.setBounds(10, 11, 124, 20);
panel_1.add(lblRegister);
JLabel lblSurname = new JLabel("Name");
lblSurname.setFont(new Font("Arial", Font.PLAIN, 11));
lblSurname.setBounds(10, 63, 69, 14);
panel_1.add(lblSurname);
JLabel lblDob = new JLabel("Profession");
lblDob.setFont(new Font("Arial", Font.PLAIN, 11));
lblDob.setBounds(10, 88, 69, 14);
panel_1.add(lblDob);
textField_1 = new JTextField();
textField_1.setColumns(10);
textField_1.setBounds(104, 63, 266, 20);
panel_1.add(textField_1);
textField_2 = new JTextField();
textField_2.setColumns(10);
textField_2.setBounds(104, 88, 266, 20);
panel_1.add(textField_2);
JButton btnNewButton = new JButton("Cancel");
btnNewButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
Object[] options = {"Yes", "No"};
Component form = null;
int n = JOptionPane.showOptionDialog(form, "Would you like to cancel the new Registration?", "Exit Confirmation", JOptionPane.YES_NO_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE, null, options, options);
if(n == JOptionPane.YES_OPTION) {
frmRegisterStudent.setVisible(false);
}
}
});
btnNewButton.setBounds(280, 119, 89, 23);
panel_1.add(btnNewButton);
JButton button = new JButton("Submit");
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
String name = textField_1.getText();
String profession = textField_1.getText();
try {
con.stmt.executeUpdate("INSERT INTO staff (Name, Profession)"+"VALUES"+"("+"'"+name+"',"+"'"+profession+"')");
JOptionPane.showMessageDialog(frmRegisterStudent, "New Record has been added");
} catch (SQLException e) {
System.out.println("Record couldn't be added!");
e.printStackTrace();
}
}
});
button.setBounds(181, 119, 89, 23);
panel_1.add(button);
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
RegisterStudent window = new RegisterStudent();
window.frmRegisterStudent.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
public void setVisible(boolean b) {
frmRegisterStudent.setVisible(true);
}
}

It looks like the problem is in the Connector class, which has a stmt field that does not get initialized.
Use this instead of the line with the NullPointerException
con.stmt = con.conn.prepareStatement("insert into staff (name, profession) values (?, ?)");
con.stmt.setString(1, name);
con.stmt.setString(2, profession);
con.stmt.executeUpdate();
But note that this is pretty bad design.

Is your connector null? I see the stmt is a field in the connector, have you initialized it?
By the way using a prepared statement is much better in your case, because it will escape the Strings (for example if they have "'" in them).
PreparedStatement pstmt = connection.prepareStatement("insert into staff (name, profession) values (?, ?)");
pstmt.setString(1, name);
pstmt.setString(2, profession);
pstmt.executeUpdate();