public static void conf(){
    try{
        Class.forName("com.mysql.jdbc.Driver");
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost/seriales","root","");
        PreparedStatement ps = con.prepareStatement("SELECT usado FROM serial WHERE serial = ?");
        ps.setString(1, numSerial);
        ResultSet rs = ps.executeQuery();

        System.out.println("Esto lo imprime");

        while(rs.next()){
            if(rs.equals(0)){
                System.out.println("No usado");
            }else if(rs.equals(1)){
                System.out.println("Usado");
            }
        }
        con.close();
    }catch(Exception ex){
        System.out.println(ex);
    }
}