Connect Java to MySQl

Assuming you have added the jdbc driver to the library, you would need to add the import of this.

For this you need to create a driver variable like this:

String driverJDBC= "com.mysql.jdbc.Driver";

And then inport the driver before trying to connect, so that:

Class.forName(driverJDBC);

If we put these two steps into your code, it would look something like this:

package hi;

import java.io.*;
import java.sql.*;

public class Hi {

    import java.sql.*;
    import java.io.*;
    public class Mostrar {

        public static void main(String[] args) throws SQLException, IOException{
            BufferedReader key= new BufferedReader (new InputStreamReader(System.in));
            String user, password;
            String driverJDBC= "com.mysql.jdbc.Driver";
            System.out.println("Usuario");
            user=key.readLine();
            System.out.println("contraseña");
            password=key.readLine();

            try {
                Class.forName(driverJDBC);
                Connection conexion = DriverManager.getConnection("jdbc:mysql://localhost:3306/agenda", user, password);
                Statement st = conexion.createStatement();
                st.executeUpdate("DROP TABLE IF EXISTS personal;");
                st.executeUpdate("CREATE TABLE personal ('Identificador' int(11) NOT NULL AUTO_INCREMENT, 'Nombre' varchar(50) NOT NULL, 'Apellidos' varchar(50) NOT NULL, 'Telefono' varchar(9) DEFAULT NULL, 'Email' varchar(60) DEFAULT NULL, PRIMARY KEY ('Identificador'));");
                st.executeUpdate("INSERT INTO personal ('Identificador', 'Nombre', 'Apellidos', 'Telefono', 'Email') VALUES (1, 'José', 'Martínez López', '968112233', '[email protected]'), (2, 'María', 'Gómez Muñoz', '911876876', '[email protected]'), (3, 'Juan', 'Sánchez Fernández', '922111333', '[email protected]'), (4, 'Ana', 'Murcia Rodríguez', '950999888', '[email protected]');");
                ResultSet rs = st.executeQuery("SELECT * FROM personal;");

                if (rs != null) {
                    System.out.println("El listado de persona es el siguiente:");

                    while (rs.next()) {
                        System.out.println("  ID: " + rs.getObject("Identificador"));
                        System.out.println("  Nombre completo: " + rs.getObject("Nombre") + " " + rs.getObject("Apellidos"));
                        System.out.println("  Contacto: " + rs.getObject("Telefono") + " " + rs.getObject("Email"));
                        System.out.println("- ");
                    }
                    rs.close();
                }
                st.close();

            }
            catch(SQLException s)
            {
                System.out.println("Error: SQL.");
                System.out.println("SQLException: " + s.getMessage());
            }
            catch(Exception s)
            {
                System.out.println("Error: Varios.");
                System.out.println("SQLException: " + s.getMessage());
            }
            System.out.println("FIN DE EJECUCIÓN.");
        }

        }

I hope this helps you.