Why are style classes stored in a List instead of a Set?

[David Grieve]

The bottom line answer is poor design of the API. There has been 
discussion about how to handle this, such as having a List 
implementation that rejects duplicates (but that would break the List 
contract), or adding new API.

You might be interested to know that, on the CSS implementation side, 
this List<String> is turned into a Set<StyleClass>.

On 5/21/15 1:17 AM, Roland C wrote:
> I was recently toying around with CSS in JavaFX and noticed that I got the
> same style multiple times in the style list of my node.
>
> Since the order of the styles is defined by the order in the css file and
> not by the order of the list that getStyleClass() of a node returns, I was
> wondering if there is a special reason for that.
>
> Example:
>
> application.css
>
> .bg-color-1 {
>      -fx-background-color:red; }.bg-color-2 {
>      -fx-background-color:green;}
>
> Main.java
>
> public class Main extends Application {
>      @Override
>      public void start(Stage primaryStage) {
>          try {
>              BorderPane root = new BorderPane();
>
>              root.getStyleClass().add( "bg-color-1");
>              root.getStyleClass().add( "bg-color-2");
>
>              Scene scene = new Scene(root,400,400);
>              scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
>              primaryStage.setScene(scene);
>              primaryStage.show();
>          } catch(Exception e) {
>              e.printStackTrace();
>          }
>      }
>
>      public static void main(String[] args) {
>          launch(args);
>      }}
>
> It doesn't matter if you write
>
>      root.getStyleClass().add( "bg-color-1");
>      root.getStyleClass().add( "bg-color-2");
>
> or change the order to
>
>      root.getStyleClass().add( "bg-color-2");
>      root.getStyleClass().add( "bg-color-1");
>
> The used style will always be the last in the css file, i. e. "bg-color-2".
>
> *Question*
>
> Why is a List used instead of a Set? A list is less performing than a Set
> and it clutters the code if you always have to make a contains-check first.
>
>
> Thank you very much!