import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ListView;
import javafx.scene.layout.VBox;

public class App extends Application {
    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
        ListView<String> list = new ListView<>();
        list.getItems().setAll("alma", "körte", "barack", "szilva");

        Button button = new Button("Mehet");
        button.setOnAction(e -> {
            System.out.println(list.getSelectionModel().getSelectedIndex());
            System.out.println(list.getSelectionModel().getSelectedItem());
        });

        VBox vbox = new VBox(10);
        vbox.setPadding(new Insets(10, 10, 10, 10));
        vbox.getChildren().addAll(list, button);

        Scene scene = new Scene(vbox, 300, 250);
        primaryStage.setScene(scene);

        primaryStage.show();
    }

}