Though the problem in your case was basically because you used comma on your SQL query which is wrong you can use AND or OR for condition fulfillment when using WHERE clause but also
I would suggest you to use PreparedStatement over Statement.
String query = "Select * from Ombrellone where PosizioneX = ? and PosizioneY = ?"
PreparedStatement statement = conn.prepareStatement(query);
statement.setString(1,c.getX());
statement.setString(2,c.getY());
ResultSet resultSet = statement.executeQuery();
Refer difference between statement and preparedstatement