Database

package database;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class DataBase {

    Connection con;
    PreparedStatement pst2;
    PreparedStatement pst;
    PreparedStatement pst3;
    java.sql.Statement stm;

    public DataBase() throws SQLException, ClassNotFoundException {
        Class.forName("com.mysql.jdbc.Driver");
        con = DriverManager.getConnection("jdbc:mysql://localhost:3306/company", "root", "");
        stm = con.createStatement();
    }

    void insert() throws SQLException {
        pst = con.prepareStatement("INSERT INTO `employee` (`Fname`, `Minit`, `Lname`, `Ssn`, `Bdate`, `Address`,"
                + " `Sex`, `Salary`, `Super_ssn`, `Dno`) VALUES ('alla', 'e', 'emad', '159442648', "
                + "'2019-11-14', 'dubai', 'F', '5000', '123456789', '1');");

    }

    void update() throws SQLException {
        pst2 = con.prepareStatement("UPDATE `employee` SET `Fname` = 'Salwa' WHERE `Fname` = 'alla';");
    }

    void delete() throws SQLException {
        pst3 = con.prepareStatement("DELETE FROM `employee` WHERE SSN ='159442648';");
    }

    String select() throws SQLException {
        String s = "";
        ResultSet rs = stm.executeQuery("select * from `employee`");
        while (rs.next()) {
            s += (rs.getString(1) + " " + rs.getString(2) + " " + rs.getString(3) + "\n"); //getInt()
        }
        return s;

    }

    void mailSent(){
        final String username = "username@gmail.com";
        final String password = "password";

        Properties prop = new Properties();
        prop.put("mail.smtp.host", "smtp.gmail.com");
        prop.put("mail.smtp.port", "465");
        prop.put("mail.smtp.auth", "true");
        prop.put("mail.smtp.socketFactory.port", "465");
        prop.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");

        Session session;
        session = Session.getInstance(prop,
                new javax.mail.Authenticator() {
                    @Override
                    protected PasswordAuthentication getPasswordAuthentication() {
                        return new PasswordAuthentication(username, password);
                    }
                });

        try {

            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress("from@gmail.com"));
            message.setRecipients(
                    Message.RecipientType.TO,
                    InternetAddress.parse("to_username_a@gmail.com, to_username_b@yahoo.com")
            );
            message.setSubject("Testing Mail");
            message.setText("Email Sent!");

            Transport.send(message);

            System.out.println("Done");

        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }

}