Values are not converted.

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ChoiceBox;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import javafx.util.StringConverter;

public class Main extends Application {

    VBox root;

    @Override
    public void start(Stage stage) {
        stage.setTitle(this.getClass().getSimpleName());
        stage.setScene(new MainScene());
        stage.show();
    }

    public static void main(String[] args) {
        launch(Main.class, args);
    }

    public final class MainScene extends Scene {
        ChoiceBox cb;

        public MainScene() {
            super(root = new VBox(10), 300, 300);

            cb = new ChoiceBox();

            cb.setConverter(new StringConverter() {
                        @Override
                        public String toString(Object t) {
                            return "Converted " + t.toString();
                        }
                        @Override
                        public Object fromString(String string) {
                            return Integer.valueOf(string);
                        }
                    });


            cb.getItems().clear();
            for (int i = 0; i < 10; i++) {
                cb.getItems().add(i);
            }

            Button setConverter = new Button("Set converter");
            setConverter.setOnAction(new EventHandler<ActionEvent>() {
                public void handle(ActionEvent t) {
                    cb.setConverter(new StringConverter() {
                        @Override
                        public String toString(Object t) {
                            return "Converted " + t.toString();
                        }
                        @Override
                        public Object fromString(String string) {
                            return Integer.valueOf(string);
                        }
                    });
                }
            });

            root.getChildren().add(setConverter);
            root.getChildren().add(cb);
        }

        protected void reset() {
            cb.getItems().clear();
            for (int i = 0; i < 10; i++) {
                cb.getItems().add(i);
            }
        }
    }
}