java – Using the JOptionPane selection in an if else

I have a JOptionPane with a drop-down selection with resolution pixels as selections and I need to add a multiplier to the selections to use in an if else command. This is what I have and where I am

  String () resolution = new String (4);
  resolution (0) = "1280 x 720";
  resolution (1) = "1920 x 1080";
  resolution (2) = "2560 x 1440";
  resolution (3) = "3840 x 2160";

  Object selectedResolution = JOptionPane.showInputDialog(null, "Choose a Resolution", "Resolution", JOptionPane.QUESTION_MESSAGE, null, resolution, "1280 x 720");