public database(){
        this.url = "jdbc:mysql://localhost/"+this.db;
       try{
         //obtenemos el driver de para mysql
         Class.forName("com.mysql.jdbc.Driver");
         //obtenemos la conexión
         conn = DriverManager.getConnection( this.url, this.user , this.password );
         if (conn!=null){
            System.out.println("OK base de datos "+this.db+" listo");
         }
      }catch(SQLException e){
         System.err.println( e.getMessage() );
      }catch(ClassNotFoundException e){
         System.err.println( e.getMessage() );
      }
   }