JavaFX: Exception in thread “JavaFX Application Thread” java.lang.RuntimeException: java.lang.reflect.InvocationTargetException Ask Question

Question

Im trying to create a simple program to take user input in 2 fields, then save it as a string and write it to a file.

Im getting an error that I dont recognize and cant find the problem anywhere, hopefully someone can explain it to me.

My Controller.Java

        import java.io.*;
        import javafx.event.ActionEvent;
        import javafx.fxml.FXML;
        import javafx.scene.control.Button;
        import javafx.scene.control.TextField;


public class Controller {


    @FXML
    private TextField InputEmail;

    @FXML
    private TextField InputName;

    //Output writer String
    public String Output;


    public void handleButtonAction(ActionEvent event) {
        Output = "Student Name: " + InputName.getText() + "|| Student Email: " + InputEmail.getText() + "\n";
    }

    public void Add(ActionEvent event) {
        try {
            FileWriter fw = new FileWriter("D:/Assignment3&4_Output.txt");
            fw.write(Output);
            System.out.println("File updated");
        } catch (IOException e) {
            System.out.println("File could not be found. Please check the file path.");


        }
    }
}

My sample.fxml

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

<?import java.lang.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.text.*?>

<GridPane alignment="center" hgap="10" vgap="10" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
   <children>
      <SplitPane dividerPositions="0.25252525252525254, 0.5252525252525253" orientation="VERTICAL" prefHeight="200.0" prefWidth="160.0">
        <items>
          <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="100.0" prefWidth="160.0">
               <children>
                  <Label layoutX="12.0" layoutY="12.0" text="Create Student" textFill="#32d9ff">
                     <font>
                        <Font name="Arial" size="20.0" />
                     </font>
                  </Label>
               </children>
            </AnchorPane>
          <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="100.0" prefWidth="160.0">
               <children>
                  <TextField id="InputName" fx:id="InputName" layoutX="5.0" layoutY="13.0" onInputMethodTextChanged="#handleButtonAction" promptText="Student Firstname" />
               </children>
            </AnchorPane>
            <AnchorPane layoutX="10.0" layoutY="10.0" minHeight="0.0" minWidth="0.0" prefHeight="68.0" prefWidth="158.0">
               <children>
                  <TextField id="InputEmail" fx:id="InputEmail" layoutX="5.0" layoutY="14.0" onAction="#handleButtonAction" promptText="Student Email" />
                  <Button id = "button" fx:id="button" layoutX="60.0" layoutY="46.0" mnemonicParsing="false" text="Add" onAction="#Add" />
               </children>
            </AnchorPane>
        </items>
      </SplitPane>
   </children>
   <columnConstraints>
      <ColumnConstraints />
   </columnConstraints>
   <rowConstraints>
      <RowConstraints />
   </rowConstraints>
</GridPane>

My Main.Java


import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

import java.io.IOException;

public class Main extends Application {

    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) throws IOException {
        launch(args);
    }
}

And finally the error thats thrown when I try to use the "Add" button and write the form.

    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1787)
    at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1670)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8879)
    at javafx.controls/javafx.scene.control.Button.fire(Button.java:200)
    at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:206)
    at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3851)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.access$1200(Scene.java:3579)
    at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1849)
    at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2588)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:397)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:434)
    at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:390)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:433)
    at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
    at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
    at java.base/java.lang.Thread.run(Thread.java:835)
Caused by: java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:567)
    at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
    at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:567)
    at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:273)
    at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
    at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1782)
    ... 51 more
Caused by: java.lang.NullPointerException
    at java.base/java.io.Writer.write(Writer.java:249)
    at sample.Controller.Add(Controller.java:29)
    ... 62 more

Any help is greatly appreciated as I am new to Java.

After looking at your FXML closer, ignore my other two statements. What you need to do is remove the handleButtonAction from the TextFields. You then need to take the code from the handleButtonAction and make it the first line of code in the Add. — SedJ601
– SedJ601, Commented Apr 9, 2020 at 20:35

Tag Howard · Accepted Answer · 2020-04-09 22:25:21Z

1

By the looks of it your program is never setting the value of Output (confirm with System.out.println(Output) at the top of the method), maybe instead of having a string for Output at all you just put all the logic from the handleButtonAction method in Add like so

public void Add(ActionEvent event) {
        try {
            FileWriter fw = new FileWriter("D:/Assignment3&4_Output.txt");
            fw.append("Student Name: " + InputName.getText() + "|| Student Email: " + InputEmail.getText() + "\n");
            fw.close();
            System.out.println("File updated");
        } catch (IOException e) {
            System.out.println("File could not be found. Please check the file path.");


        }
    }

Or move the output string assignment to add()

public void Add(ActionEvent event) {
    output ="Student Name: " + InputName.getText() + "|| Student Email: " + 
    InputEmail.getText() + "\n"
        try {
            FileWriter fw = new FileWriter("D:/Assignment3&4_Output.txt");
            fw.append(output);
            fw.close();
            System.out.println("File updated");
        } catch (IOException e) {
            System.out.println("File could not be found. Please check the file path.");


        }
    }

The append(String s) method adds rather than overwrites, which you use is optional the close() method flushes the stream into the file (saves it) and closes the stream.

P.S. You should make the first letter of everything except classes lowercase

edited Apr 9, 2020 at 22:25

answered Apr 9, 2020 at 19:41

Tag Howard

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3 Comments

X22431637 Over a year ago

This removed the error, now it compiles properly and prints "File Updated" but doesnt actually write the output in the file.

SedJ601 Over a year ago

@Tag Howard, make Output = "Student Name: " + InputName.getText() + "|| Student Email: " + InputEmail.getText() + "\n"; the first line of code in your Add method.

Tag Howard Over a year ago

@X22431637 Whoops, you need to add fw.close(). And consider using append instead to avoid deleting previous contents. P.S. Consider marking answer as correct.

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