Java database application that allow user to insert, update and delete values in a table and manage appropriate exception handling when wrong values are enter

Aim:Write a database application that allow user to insert, update and delete values in a table and manage appropriate exception handling when wrong values are enter.

package bc;

import java.sql.*;

import java.sql.Connection;

import java.sql.DriverManager;

public class database extends javax.swing.JApplet

{

            public void init()

            {

                        setSize(350,250);

                        try

{

                                    java.awt.EventQueue.invokeAndWait(new Runnable()

                                    {

                                                public void run()

                                                {

                                                            initComponents();

                                                }

                                    });

                        }

                        catch (Exception ex)

                        {

                                    ex.printStackTrace();

                        }

            }

private void InsertActionPerformed(java.awt.event.ActionEvent evt)

{                                      

 try

                        {

                                    Connection con=DriverManager.getConnection("jdbc:odbc:DB1");

                                    Statement st= con.createStatement();

String stm="insert into student(Name,Department,Roll_No,Phone_No)     values('"+t1.getText()+"','"+t2.getText()+"','"+t3.getText()+"','"+t4.getText()+"')";

                                    JOptionPane.showMessageDialog(rootPane,"Data is Inserted");

st.executeUpdate(stm);

                        }

                        catch(SQLException sqlEx)

                        {

                                     System.out.println("error");

                        }

             }                                     

    private void deleteActionPerformed(java.awt.event.ActionEvent evt)

   {                                       

  try

            {

                        Connection con=DriverManager.getConnection("jdbc:odbc:DB1");

                        Statement pst= con.createStatement();

                        String stm="delete from student where Roll_No="+t3.getText()+" ";

                        pst.executeUpdate(stm);

 JOptionPane.showMessageDialog(rootPane,"Data is deleted");

             }

            catch(SQLException sqlEx)

            {

                        System.out.println("error");

        }

   }                                     

   private void updateActionPerformed(java.awt.event.ActionEvent evt)

   {                                      

            try

            {

                        Connection con=DriverManager.getConnection("jdbc:odbc:DB1");

                        Statement pst= con.createStatement();

                        String stm=”update student set Name='"+t1.getText()+'",

                                             Department='"+t2.getText()+"',

                                             Phone_No='"+t4.getText()+"',

                                WHERE Roll_No="+t3.getText()+" ";

                         pst.executeUpdate(stm);

                        JOptionPane.showMessageDialog(rootPane,"Data is updated");

            }

            catch(SQLException sqlEx)

            {

                        System.out.println("error");

            }

    }      

Output: