提问：@FAML下控件返回null，如何处理？

Question

我是一个javafx初学者，正在学习fxml
实践中控件startButton总是为null，这是为什么？求指教！
java：

package application;
    
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;

import javafx.fxml.*;
import javafx.scene.Parent;

import javafx.scene.control.*;

public class Main extends Application {
    @Override
    public void start(Stage primaryStage) {
        try {
            FXMLLoader loader = new FXMLLoader(getClass().getResource("/appilcation/welcome_scene.fxml"));
            loader.setController(this);
            Scene scene = new Scene(loader.load(),640,400);
            primaryStage.setScene(scene);
            primaryStage.show();
        } catch(Exception e) {
            e.printStackTrace();
        }
        welcome();
    }
    @FXML
    Button startButton;
    public static void main(String[] args) {
        launch(args);    
    }
    public void welcome() {
        startButton.setOnAction(e -> {
            System.out.println(1);
        });
    }
}

fxml：

<?xml version="1.0" encoding="UTF-8"?>


<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.VBox?>
<?import javafx.scene.text.Font?>

<VBox prefHeight="400.0" prefWidth="640.0" xmlns="http://javafx.com/javafx/16" xmlns:fx="http://javafx.com/fxml/1">
  <children>
    <AnchorPane maxHeight="-1.0" maxWidth="-1.0" prefHeight="-1.0" prefWidth="-1.0" VBox.vgrow="ALWAYS">
      <children>
        <Label alignment="CENTER" layoutX="149.0" layoutY="36.0" style="&#10;" text="MPCB_STAR_WARS" textAlignment="CENTER" textFill="#9f9f9f" wrapText="false">
          <font>
            <Font size="37.0" />
          </font>
        </Label>
            <Button fx:id="startButton" layoutX="409.0" layoutY="107.0" mnemonicParsing="false" prefHeight="47.0" prefWidth="142.0" text="START_GAME" />
            <Button layoutX="409.0" layoutY="189.0" mnemonicParsing="false" prefHeight="47.0" prefWidth="142.0" text="SETTING" />
            <Button layoutX="409.0" layoutY="270.0" mnemonicParsing="false" prefHeight="47.0" prefWidth="142.0" text="HELP" />
      </children>
    </AnchorPane>
  </children>
</VBox>