I got three classes for MySQL Database access/manipulation:

1. Conector. It has got methods for connecting, disconnecting, querying and updating db.
2. ConectorCliente. It simply extends first and got its constructor receiving user, password, host, port and db.
3. I have written has several different methods per each DB, depending on data which will be needed to be selected, updated or deleted.

These are my classes in the mentioned order:

First class

public class Conector {

    private Connection  connection  = null;
    private Statement   statement   = null;
    private ResultSet   set         = null;

    String host;
    String port;
    String login;
    String password;
    String url;

    public Conector (String login, String password, String db, String host, String port) {
        this.login = login;
        this.password = password;
        this.host = host;
        this.port = port;
        url = "jdbc:mysql://"+host+":"+port+"/"+db;
        Conectar ();
    }

    public void Desconectar () {
        connection = null;
    }

    private void Conectar() {
        try {
            DriverManager.registerDriver(new com.mysql.jdbc.Driver ());
        } catch (SQLException ex) {
            Logger.getLogger(Conector.class.getName()).log(Level.SEVERE, null, ex);
        }
        try {
            connection = DriverManager.getConnection(url, login, password);
            statement = connection.createStatement();
        }

        catch (SQLException e) {
            Logger logger = Logger.getLogger(Conector.class.getName());
            logger.log(Level.SEVERE, e.getSQLState(), e);
        }
    }

    public ResultSet Query(String query){

        try {
            statement = connection.createStatement();
            set = statement.executeQuery(query);
        }
        catch (Exception e) {
            System.out.println("Exception in query method:\n" + e.getMessage());
        }
        return set;
    }

    public boolean Update (String update) {

        try {
            statement = connection.createStatement();
            statement.executeUpdate(update);

        }
        catch (SQLException e) {
            System.out.println("Exception in update method:\n" + e.getMessage());
            return false;
        }

        return true;
    }

    public void cierraConexion(){

        try {
            connection.close();
            connection = null;
        }
        catch(Exception e)         {
            System.out.println("Problema para cerrar la conexión a la base de datos ");
        }
    }

}

Second class

public class ConectorCliente extends Conector {

    public ConectorCliente(String login, String password, String db, String host, String port)  {

        // Con super llamamos y ocupamos el constructor de la clase padre
        super(login, password, db, host, port);

    }
}

Example of third class

public class InteraccionDB {


    private static final ConectorCliente conector = new ConectorCliente("user", "pass","db", "127.0.0.1", "3306");


    public static int obtenerNumRegistros() {

        ResultSet resultado = conector.Query("SELECT COUNT(*) FROM tweets;");

        try {
            while (resultado.next()) {

                return resultado.getInt("COUNT(*)");


            }
        } catch (SQLException ex) {
            Logger.getLogger(InteraccionDB.class.getName()).log(Level.SEVERE, null, ex);
        }

        return -1;
    }

    public static void insertarTweet(String id) {


        conector.Update("INSERT INTO tweets (id) VALUES ('"+id+"')");
    }


    public static void eliminarTweet(String id) {

        conector.Update("DELETE FROM tweets WHERE id = '"+id+"'");        
    }

    public static HashMap<String, Integer> obtenerHoraTweet(String id) {

        HashMap<String, Integer> resultados = new HashMap<>();

        ResultSet resultado = conector.Query("SELECT hora, min FROM tweets WHERE id = '"+id+"'");

        try {
            while (resultado.next()) {

                resultados.put("Hora", resultado.getInt(1));
                resultados.put("Minuto", resultado.getInt("min"));

            }
        } catch (SQLException ex) {
            Logger.getLogger(InteraccionDB.class.getName()).log(Level.SEVERE, null, ex);
        }

        return resultados;

    }

    public static ArrayList<String> obtenerIdsRetweets(int retweets) {


        ArrayList<String> resultados = new ArrayList<>();

        ResultSet resultado = conector.Query("SELECT id FROM tweets WHERE retweets > "+retweets);

        try {
            while (resultado.next()) {
                resultados.add(resultado.getString("id"));
            }
        } catch (SQLException ex) {
            Logger.getLogger(InteraccionDB.class.getName()).log(Level.SEVERE, null, ex);
        }

        return resultados;
    }
}

In my case, I prefer to make third class to return structures like ArrayList's or HashTable's making code cleaner at invocation side.

I care to improve:

• Exception handling (I know I'm not doing nothing for it so far)
• Going for Interfaces
• Security
• Java / OOP stuffs