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Cannot invoke "Object.getClass()" because "obj" is null - JavaFX [duplicate]

So basically I began a dummy JavaFX project just to achieve a minimalistic example for my actual problem. But now I am not even able to run that minimalistic project anymore and do not receive enough error information to actually google it myself out. So right now, when I run the code, I receive the given error stack, which does not lead me anywhere.
I am using IntelliJ. JavaFX libraries are set correctly and VM Options set to:
--module-path "C:\Program Files\Java\javafx-sdk-11.0.2\lib" --add-modules javafx.controls,javafx.fxml
On top, when I run the code, those errors pop up in console, but the application seems to still be running, because I need to press the Red Stop Button of IntelliJ to actually stop it.
Has anyone some guess, what goes wrong here? I am not experienced enough to follow those errors, since they do not point into my code, but rather into some Deep Java code.
The Exception:
Exception in thread "main" java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1051)
Caused by: java.lang.NullPointerException
at java.base/java.lang.reflect.Method.invoke(Method.java:559)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:464)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:363)
... 5 more
Main.java:
package sample;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
import java.io.IOException;
public class Main extends Application {
private Stage rootStage;
public BorderPane mainWindow;
public AnchorPane left;
public AnchorPane bottom;
#Override
public void start(Stage primaryStage) throws Exception {
this.rootStage = primaryStage;
loadMainWindow();
}
public void loadMainWindow() throws IOException {
FXMLLoader loaderMainWindow = new FXMLLoader(Main.class.getResource("MainWindow.fxml"));
mainWindow = loaderMainWindow.load();
FXMLLoader loaderLeft = new FXMLLoader(Main.class.getResource("Left.fxml"));
left = loaderLeft.load();
mainWindow.setLeft(left);
//mainWindow.setBottom(bottom);
Scene scene = new Scene(mainWindow);
rootStage.setScene(scene);
rootStage.show();
}
public void main(String[] args) {
launch(args);
}
}
MainWindow.fxml:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.BorderPane?>
<BorderPane prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/10.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.MainWindowController" />
MainWindowController:
package sample;
import javafx.fxml.Initializable;
import java.net.URL;
import java.util.ResourceBundle;
public class MainWindowController implements Initializable {
private Main main;
#Override
public void initialize(URL url, ResourceBundle resourceBundle) {
}
public void setMain(Main main) {
this.main = main;
}
}
Left.fxml:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.layout.AnchorPane?>
<AnchorPane prefHeight="400.0" prefWidth="100.0" xmlns="http://javafx.com/javafx/10.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.LeftController">
<children>
<Button fx:id="button" layoutX="237.0" layoutY="169.0" mnemonicParsing="false" onAction="#buttonClick" text="Button" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" />
</children>
</AnchorPane>
LeftController.java:
package sample;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Button;
import java.awt.event.ActionEvent;
import java.net.URL;
import java.util.ResourceBundle;
public class LeftController implements Initializable {
#FXML
private Button button;
#Override
public void initialize(URL url, ResourceBundle resourceBundle) {
}
public void buttonClick(javafx.event.ActionEvent actionEvent) {
System.out.println("Some Stuff");
}
}

Solution
The error you're getting is caused by your main(String[]) method not being static. If you make it static then the error will go away.
Some Explanation
JavaFX offers the ability to launch applications without providing a main method, so long as the main class is a subclass of Application. However, developers can still include a main method which means this special launch functionality has to handle that situation gracefully. In other words, an explicit main method present in the Application subclass must act like the entry point of the application from the developer's point of view. Nonetheless, behind the scenes some deep internal class has become the "real" main class.
To do this, the main method is located—if present at all—via Class#getMethod(String,Class...) which, while only returning public methods, doesn't distinguish between static and non-static methods. If found, Method#invoke(Object,Object...) is used to invoke the main method reflectively. The first argument of invoke is the instance that the method should be invoked on; in the case of static methods the value is null. Unfortunately, the code assumes the method it found is static which causes a NullPointerException to be thrown—you can't call an instance method on a null "instance".
Update: This issue has been submitted on GitHub (#570) and subsequently JBS (JDK-8230119). The current idea is to emit a warning rather than throw the NullPointerException. However, the functionality that allows launching without a main method may be deprecated in a future release, which will affect how this issue is addressed.

JavaFX ListView Null Pointer when Adding to List [duplicate]

This question already has answers here:
Passing Parameters JavaFX FXML
(10 answers)
Closed 3 years ago.
Edit: Static's removed. Still getting the same error
I've created a GUI with a Listview in Scene builder and now I'm trying to populate the Listview with some Strings.
I'm using 2 classes at the moment. Here are 2 cut down versions of the scripts for easier reading
MainController:
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
public class MainController extends Application
{
#Override
public void start(Stage primaryStage) throws Exception
{
Parent root = FXMLLoader.load(getClass().getResource("IntelligentSystems.fxml"));
primaryStage.setTitle("Intelligent Systems Agent Program");
primaryStage.setScene(new Scene (root));
primaryStage.show();
GUIController GUIList = new GUIController();
GUIList.DoList.add("agentCtrl");
GUIList.DoList.add("DeliveryAgent");
GUIList.PopulateAgentList();
}
public static void main (String[] args)
{
launch(args);
}
}
and the second Class, GUIController:
import javafx.fxml.FXML;
import javafx.scene.control.ListView;
import javafx.collections.ObservableList;
import javafx.collections.FXCollections;
public class GUIController {
//List View variables.
#FXML
public ListView AgentsList;
#FXML
public ObservableList<String> DoList= FXCollections.observableArrayList();
#FXML
public void PopulateAgentList()
{
AgentsList.setItems(DoList);
}
}
Currently, I've set the fxId of the Listview to "AgentsList" in the fxml file.
<ListView fx:id="AgentsList" layoutX="15.0" layoutY="39.0" prefHeight="200.0" prefWidth="86.0" />
Whenever I run the program in IntelliJ, it always returns a java.lang.NullPointerException around the "AgentsList.setItems(_doList);" line.
I'm completely lost as to why it can't add to the list. Not helped that I haven't been using Java for long as I've mostly worked with C#.
Edit: Exception Stack Trace:
java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:464)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:363)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1051)
Caused by: java.lang.RuntimeException: Exception in Application start method
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:900)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:195)
at java.base/java.lang.Thread.run(Thread.java:830)
Caused by: java.lang.NullPointerException
at GUIController.PopulateAgentList(GUIController.java:26)
at MainController.start(MainController.java:57)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(LauncherImpl.java:846)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$12(PlatformImpl.java:455)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:428)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:427)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
... 1 more
Exception running application MainController
Process finished with exit code 1

Your #FXML annotated fields are static, which is not supported by JavaFX, as it is desinged to create/load multiple instances of the same fxml file/controller class. If you are unfamiliar with what 'static' actually means, you can refer to What is the difference between a static method and a non-static method?.
As for how you get the correct controller instance, you need to load the fxml file a little bit different.
FXMLLoader loader = new FXMLLoader(getClass().getResource("IntelligentSystems.fxml"));
Parent root = loader.load(); // must be called before getting the controller!
GUIController controller = loader.getController();
Now you can use the controller variable to access the fields in a non-static way.

Distinguish between foo(int) and foo(Integer) in java

I haven't been able to find this, though I currently have a usecase where I have a generic type which has a method foo(int) and a method foo(T).
For my usecase said type is instantiated with T = Integer, meaning I have the methods foo(int) and foo(Integer).
Whenever I try to call foo(Integer) it calls foo(int) instead, no matter whether the type is specified, whether I cast or not. The only thing solving it is using a Long instead, which I do not want to do.
Is there any way I can force java to use the foo(Integer) method?
Edit:
For once, to answer the comment, I don't think code was relevant here, as what I described was formable enough to understand what I meant.
Secondly, the error was on my end, I apologise. I didn't have the expected behaviour and thought it'd be because of an issue in that regard, especially since my IDE displayed the usage of the foo(int) method. I'll be closing this now
A MVCE:
Main.java
package sample;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
public class Main extends Application {
#Override
public void start(Stage primaryStage) throws Exception{
Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
primaryStage.setTitle("Hello World");
primaryStage.setScene(new Scene(root, 300, 275));
primaryStage.show();
}
public static void main(String[] args) {
launch(Main,args);
}
}
Controller.java
package sample;
import javafx.collections.FXCollections;
import javafx.fxml.Initializable;
import javafx.scene.control.ListView;
public class Controller implements Initializable {
#Override
public void initialize(URL url, ResourceBundle resourceBundle) {
ListView<Integer> listView = new ListView<>();
listView.setItems(FXCollections.observableArrayList(1, 5, 8, 13));
Integer t = 5;
listView.getSelectionModel().select(t);
System.out.println(listView.getSelectionModel().getSelectedItems());
}
}
sample.fxml
<?import javafx.geometry.Insets?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<GridPane fx:controller="sample.Controller"
xmlns:fx="http://javafx.com/fxml" alignment="center" hgap="10" vgap="10">
</GridPane>
You will notice this code works as expected, what I figured out now though is that, since I'm not using java but rather groovy - switching the file endings to groovy and compiling with a groovy compiler makes this program have my described behaviour, which means the issue is groovy related not java related.

You question as stated has a simple answer:
class Foo<T> {
void foo(int i) {
System.out.println("foo(int)");
}
void foo(T t) {
System.out.println("foo(T)");
}
}
private void test() {
Foo<Integer> foo = new Foo<>();
foo.foo(1);
foo.foo((Integer)1);
foo.foo(Integer.valueOf("1"));
}
prints:
foo(int)
foo(T)
foo(T)
However, I suspect you've tried this so please post some example code.
If you like, check out the rules for method selection here: https://docs.oracle.com/javase/specs/jls/se11/html/jls-5.html#jls-5.3.

JavaFX Preloader issue

Hello dear Stackoverflow,
I have several questions regarding the JavaFX class Preloader.
After a long-term research, I haven't found any proper solution to my problem and I think it's not really the issue with my code, but rather the limits of JavaFX itself when it comes to the Preloader class.
Let me get straight up to my point: Is it not possible to use FXML to define the design of a Preloader? It's interesting to see how all the tutorials only guide you throughout creating a preloader by creating new Instances out of the classes. (ProgressBar progressBar = new ProgressBar(); ie)
So, let's take this example code for you to test this with me:
TestPreloader:
import com.sun.javafx.application.LauncherImpl;
import javafx.application.Preloader;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.ProgressBar;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import javafx.stage.StageStyle;
public class TestPreloader extends Preloader {
#FXML
ProgressBar progressBar;
public static void main(String[] args) {
LauncherImpl.launchApplication(TestApplication.class, TestPreloader.class, args);
}
public void initialize() {
System.out.println("initialize printed");
}
#Override
public void start(Stage primaryStage) throws Exception {
primaryStage.initStyle(StageStyle.TRANSPARENT);
Parent root = FXMLLoader.load(getClass().getResource("preloader.fxml"));
Scene scene = new Scene(root);
scene.setFill(Color.TRANSPARENT);
primaryStage.setScene(scene);
primaryStage.setResizable(false);
primaryStage.centerOnScreen();
primaryStage.show();
}
#Override
public void handleProgressNotification(ProgressNotification progressNotification) {
// progressBar.setProgress(progressNotification.getProgress());
}
#Override
public void handleStateChangeNotification(StateChangeNotification notification) {
System.out.println(notification.getType().toString());
switch (notification.getType()) {
case BEFORE_START:
//progressBar.setProgress(1);
break;
case BEFORE_LOAD: //this is where the TestApplication class will be constructed
//progressBar.setProgress(1);
break;
case BEFORE_INIT:
//progressBar.setProgress(1);
break;
}
}
}
FXML
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="TestPreloader">
<children>
<ProgressBar fx:id="progressBar" layoutX="174.0" layoutY="141.0" prefWidth="200.0" progress="0.0" />
</children>
</AnchorPane>
TestApplication
import javafx.application.Application;
import javafx.stage.Stage;
public class TestApplication extends Application {
#Override
public void start(Stage primaryStage) throws Exception {
System.out.println("Application started!");
}
}
The output if you start is in the following order:
initialize printed
BEFORE_LOAD
BEFORE_INIT
BEFORE_START
Application started!
now, as you can see the initialize() method is being called firsthand, then the state of the preloader changes and thus upon every change the notification pops up - all good until now.
Yet what bothers me is, if I call progressBar#setProgress IN the initialize method, the progress actually gets set to 1 and no errors are being thrown. Although the States occur AFTER the Preloader is initialized, NullPointers occur.
To understand what I mean, uncomment setProgress under handleStateNotification (under the BEFORE_LOAD statement would make the most sense to me), and you'll see that a NullPointerException pops up.
Now, why does it occur? What can I do to fix this issue? It just doesn't make any sense for me. If the Preloader is initialized and the ProgresssBar is not null, how can it turn null afterwards? Perhaps maybe there is a new instance of the own class being used separately? But that wouldn't make sense as well to me. Why would you have that?
I'm stuck on this problem for a few days now, I mean I could just go for a Timeline and "hardcode" it, but well, I want to learn what causes these issues.
TLDR;
ProgressBar turns null after initializing the application when using the Preloader class, what causes it and what should I do?
EDIT:
It seems like the class is not being reconstructed somewhere, idk i'm really stuck lol

When the FXMLLoader loads your FXML file, it creates a new instance of the specified controller. However, this is not the desired outcome. The object that receives your state callbacks should be the controller of your FXML window.
Replacing your FXMLLoader.load(...) block with
FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("preloader.fxml"));
fxmlLoader.setController(this);
Parent root = fxmlLoader.load();
and removing the controller property from your FXML, causes the FXMLLoader to use the given controller instance (being the one that receives the state callbacks) instead of it constructing a new instance of the specified controller class.

Java FX Exception (Media Player Application)

I'm just starting to use Java FX and cannot for the life of me figure out why this exception keeps occurring.
I have 2 classes. One called Main and the other called Player. Here is what they each look like....
Main Class
package application;
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.scene.paint.Color;
public class Main extends Application {
#Override
public void start(Stage primaryStage) {
Player player = new Player("/Applications/Nacho.mp4");
Scene scene = new Scene (player, 720, 480, Color.BLACK);
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
Player Class
package application;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Pane;
import javafx.scene.media.Media;
import javafx.scene.media.MediaPlayer;
import javafx.scene.media.MediaView;
public class Player extends BorderPane {
Media media;
MediaPlayer player;
MediaView view;
Pane nPane;
public Player(String file){
media = new Media(file);
player = new MediaPlayer(media);
view = new MediaView(player);
nPane = new Pane();
nPane.getChildren().add(view);
setCenter(nPane);
player.play();
}
}
Here is what the compiler spits out when I run the program...
START
Exception in Application start method
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Exception in Application start method
at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$152(LauncherImpl.java:182)
at com.sun.javafx.application.LauncherImpl$$Lambda$51/1323468230.run(Unknown Source)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.IllegalArgumentException: uri.getScheme() == null! uri == 'Applications/Nacho.mp4'
at com.sun.media.jfxmedia.locator.Locator.(Locator.java:211)
at javafx.scene.media.Media.(Media.java:391)
at application.Player.(Player.java:16)
at application.Main.start(Main.java:13)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$159(LauncherImpl.java:863)
at com.sun.javafx.application.LauncherImpl$$Lambda$54/1046396900.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$172(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl$$Lambda$47/186276003.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$null$170(PlatformImpl.java:295)
at com.sun.javafx.application.PlatformImpl$$Lambda$49/287662571.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$171(PlatformImpl.java:294)
at com.sun.javafx.application.PlatformImpl$$Lambda$48/237061348.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
Exception running application application.Main
FINISH
I know that the issue occurs as soon as the Player object is instantiated in Main. As soon the Player object uses it's constructor and creates a Media object, which gets passed the String file location, that's when I get the error. I ran the program with an empty constructor for the Player object and it ran fine so the issue is clearly in my Player Class, again when the Media object is instantiated. Am I passing the correct parameters? "/Applications/Nacho.mp4"
If someone can please tell me how to fix this, I would greatly appreciate it. I literally can't move forward with this project otherwise. Thank you!

Nevermind, I figured it out, the problem was passing the parameter to the Media object. I'm used to C++ syntax and did not realize that the proper way to do it is
media = new Media("file:///Applications/Nacho.mp4");

This error usually occurs due to wrongly input of the file address. The correct way to write the address is file:///C:/abc.mp4.
More clearly:
Object b = new Object("file:///C:/abc.mp4");