Why doesn't the javafx program work?

Question

JavaFX

In controller.java:

package sample;

import javafx.event.EventHandler;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.control.TextArea;
import javafx.scene.input.MouseEvent;

public class Controller {
    @FXML
    private Button btn;
    @FXML
    private TextArea text;

    @FXML
    public void btn_click(){
        text.setText("Hello World");
    }

}

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

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.TextArea?>
<?import javafx.scene.layout.AnchorPane?>


<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8.0.121" xmlns:fx="http://javafx.com/fxml/1">
   <children>
      <Button fx:id="btn" layoutX="202.0" layoutY="339.0" mnemonicParsing="false" prefHeight="25.0" prefWidth="155.0" text="Button" onAction="#btn_click" />
      <TextArea fx:id="text" layoutX="180.0" layoutY="60.0" prefHeight="200.0" prefWidth="200.0" AnchorPane.rightAnchor="220.0" />
   </children>
</AnchorPane>

Error:
Exception 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(NativeMethodAccessorImpl.java :62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at javafx.graphics/ com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:473)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:372)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base
/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java: 941)
Caused by: java.lang.RuntimeException: Exception in Application start method
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:973)
at javafx.graphics/com.sun.javafx. application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:198)
at java.base/java.lang.Thread.run(Thread.java:844)
Caused by: javafx.fxml.LoadException: No controller specified.
/C:/Users/%d0%98%d0%b2%d0%b0%d0%bd%20%d0%94%d0%bc%d0%b8%d1%82%d1%80%d0%b8%d0 %b5%d0%b2%d0%b8%d1%87/IdeaProjects/Atom%20Platform/out/production/Atom%20Platform/sample/sample.fxml:10
at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader .java:2621)
at javafx.fxml/javafx.fxml.FXMLLoader.access$100(FXMLLoader.java:105)
at javafx.fxml/javafx.fxml.FXMLLoader$Element.getControllerMethodHandle(FXMLLoader.java:565)
at javafx.fxml /javafx.fxml.FXMLLoader$Element.processEventHandlerAttributes(FXMLLoader.java:607)
at javafx.fxml/javafx.fxml.FXMLLoader$ValueElement.processEndElement(FXMLLoader.java:778)
at javafx.fxml/javafx.fxml.FXMLLoader.processEndElement(FXMLLoader.java:2838)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2557
) (FXMLLoader.java:2466)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3253)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3210)
at javafx.fxml/ javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3179)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3152)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java: 3129)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3122)
at sample.Main.start(Main.java:13)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(LauncherImpl.java:919)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$11(PlatformImpl.java: 449)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$9(PlatformImpl.java:418)
at java.base/java.security.AccessController.doPrivileged(Native Method)
at javafx.graphics/com .sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:417)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$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:175)
... 1 more
Exception running application sample.Main
Process finished with exit code 1
sees btn_click
I'm new to java so I don't know how to solve it

Answer 1

1. The fxml root element must contain a controller
2. If you want to access btn and text from the code, they must be public
3. The @FXML annotation over the method is optional
In this case, the program does not see the method, but the entire controller - a problem in that