Javafx实际打开Gui示例时的java问题

Question

我对javafx（惊喜大笑）有问题。出于某种原因，我的代码似乎正在运行，但实际的gui从未出现在我的屏幕上，它被卡在了右下角。当我在示例控制器类中取出“implements initializable”时，gui就会出现。我将非常感激任何人能给我的帮助！！ 谢谢

主课

package application;

import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ListView;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.FlowPane;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;


public class Main extends Application {


        @Override

        public void start(Stage primaryStage) {
            try {
                Parent root = FXMLLoader.load(getClass().getResource("Sample.fxml"));
                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);
        }
    }

示例控制器类

package application;

import java.awt.Label;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.ResourceBundle;

import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.Event;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.Node;
import javafx.scene.control.Alert;
import javafx.scene.control.ListView;
import javafx.scene.control.Alert.AlertType;
import javafx.stage.Popup;
import javafx.stage.Stage;

public class SampleController{

    @FXML 
    private ListView<String>mainListView;






    /**
     * Initializing the class
     */
    public void initialize(URL url, ResourceBundle rb) {

        ObservableList<String>thisMainListView = FXCollections.observableArrayList("SPY","QQQ","Rus2000");

        mainListView.setItems(thisMainListView);

    }








}