问使用JavaFX时出错

EN

    *xception in Application start method
    java.lang.reflect.InvocationTargetException
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.base/java.lang.reflect.Method.invoke(Unknown Source)
        at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(Unknown Source)
        at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(Unknown Source)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.base/java.lang.reflect.Method.invoke(Unknown Source)
        at java.base/sun.launcher.LauncherHelper$FXHelper.main(Unknown Source)
    Caused by: java.lang.RuntimeException: Exception in Application start method
        at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(Unknown Source)
        at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(Unknown Source)
        at java.base/java.lang.Thread.run(Unknown Source)
    Caused by: java.lang.NullPointerException: Location is required.
        at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(Unknown Source)
        at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(Unknown Source)
        at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(Unknown Source)
        at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(Unknown Source)
        at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(Unknown Source)
        at javafx.fxml/javafx.fxml.FXMLLoader.load(Unknown Source)
        at ProvaGrafica2.start(ProvaGrafica2.java:29)
        at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(Unknown Source)
        at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$11(Unknown Source)
        at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$9(Unknown Source)
        at java.base/java.security.AccessController.doPrivileged(Native Method)
        at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(Unknown Source)
        at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
        at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(Unknown Source)
        ... 1 more
    Exception running application ProvaGrafica2*

import java.io.File;

import javafx.application.*;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class ProvaGrafica2 extends Application {


public static void main(String[] args) {
    // TODO Auto-generated method stub
    launch(args);
}
@Override
public void start (Stage stage) throws Exception
{
    System.out.println("prova");

    File file = new File("C:\\Users\\u5ex\\Desktop\\eclipse\\Grafica2\\src\\a.fxml");
    if (file.exists())
        System.out.println("il file esiste");


    Parent root = FXMLLoader.load(getClass().getResource("C:\\Users\\u5ex\\Desktop\\eclipse\\Grafica2\\src\\a.fxml"));
    Scene scene=new Scene (root);
    stage.setTitle("Login");
    stage.setScene(scene);

    stage.show();

}