java - How to fix a javafx.fxml.LoadException? -

i'm trying make javafx login window, , followed tutorial, gives me strange bug...

src/main/java/scripter/nukkit/playertool/mainapplication.java

package scripter.nukkit.playertool; import javafx.application.application; import javafx.application.platform; import javafx.event.actionevent; import javafx.event.eventhandler; import javafx.scene.scene; import javafx.scene.control.button; import javafx.scene.layout.stackpane; import javafx.scene.parent; import javafx.stage.stage; import javafx.fxml.*;  @suppresswarnings("restriction") public class mainapplication extends application {      @override     public void start(stage primarystage) throws exception {         parent root = fxmlloader.load(getclass().getclassloader().getresource("mainapplication.fxml"));          scene scene = new scene(root, 300, 275);          primarystage.settitle("fxml welcome");         primarystage.setscene(scene);         primarystage.show();     }  } 

src/main/java/scripter/nukkit/playertool/maincontroller.java

package scripter.nukkit.playertool;  import javafx.event.actionevent; import javafx.fxml.fxml; import javafx.scene.text.text;  @suppresswarnings("restriction") public class maincontroller {     @fxml     private text actiontarget;      @fxml     protected void handlesubmitbuttonaction(actionevent event) {         actiontarget.settext("sign in button pressed");     } } 

src/main/resources/mainapplication.fxml

<?xml version="1.0" encoding="utf-8"?>  <?import java.net.*?> <?import javafx.geometry.*?> <?import javafx.scene.control.*?> <?import javafx.scene.layout.*?> <?import javafx.scene.text.*?>  <gridpane fx:controller="scripter.nukkit.playertool.maincontroller" xmlns:fx="http://javafx.com/fxml" alignment="center" hgap="10" vgap="10">     <padding>         <insets top="25" right="25" bottom="10" left="25"/>     </padding>     <text text="welcome" gridpane.columnindex="0" gridpane.rowindex="0" gridpane.columnspan="2"/>      <label text="user name:" gridpane.columnindex="0" gridpane.rowindex="1"/>      <textfield gridpane.columnindex="1" gridpane.rowindex="1"/>      <label text="password:" gridpane.columnindex="0" gridpane.rowindex="2"/>      <passwordfield fx:id="passwordfield" gridpane.columnindex="1" gridpane.rowindex="2"/>     <hbox spacing="10" alignment="bottom_right" gridpane.columnindex="1" gridpane.rowindex="4">         <button text="sign in" onaction="#handlesubmitbuttonaction"/>     </hbox>     <text fx:id="actiontarget" gridpane.columnindex="1" gridpane.rowindex="6"/> </gridpane> 

error report

exception in thread "thread-7" java.lang.runtimeexception: exception in application start method     @ com.sun.javafx.application.launcherimpl.launchapplication1(launcherimpl.java:917)     @ com.sun.javafx.application.launcherimpl.lambda$launchapplication$155(launcherimpl.java:182) caused by: javafx.fxml.loadexception: n source)       @ javafx.fxml.fxmlloader.constructloadexception(fxmlloader.java:2601)     @ javafx.fxml.fxmlloader.access$700(fxmlloader.java:103)     @ javafx.fxml.fxmlloader$valueelement.processattribute(fxmlloader.java:922)     @ javafx.fxml.fxmlloader$instancedeclarationelement.processattribute(fxmlloader.java:971)     @ javafx.fxml.fxmlloader$element.processstartelement(fxmlloader.java:220)     @ javafx.fxml.fxmlloader$valueelement.processstartelement(fxmlloader.java:744)     @ javafx.fxml.fxmlloader.processstartelement(fxmlloader.java:2707)     @ javafx.fxml.fxmlloader.loadimpl(fxmlloader.java:2527)     @ javafx.fxml.fxmlloader.loadimpl(fxmlloader.java:2441)     @ javafx.fxml.fxmlloader.loadimpl(fxmlloader.java:3214)     @ javafx.fxml.fxmlloader.loadimpl(fxmlloader.java:3175)     @ javafx.fxml.fxmlloader.loadimpl(fxmlloader.java:3148)     @ javafx.fxml.fxmlloader.loadimpl(fxmlloader.java:3124)     @ javafx.fxml.fxmlloader.loadimpl(fxmlloader.java:3104)     @ javafx.fxml.fxmlloader.load(fxmlloader.java:3097)     @ scripter.nukkit.playertool.mainapplication.start(mainapplication.java:19)     @ com.sun.javafx.application.launcherimpl.lambda$launchapplication1$162(launcherimpl.java:863)     @ com.sun.javafx.application.platformimpl.lambda$runandwait$175(platformimpl.java:326)     @ com.sun.javafx.application.platformimpl.lambda$null$173(platformimpl.java:295)     @ java.security.accesscontroller.doprivileged(native method)     @ com.sun.javafx.application.platformimpl.lambda$runlater$174(platformimpl.java:294)     @ com.sun.glass.ui.invokelaterdispatcher$future.run(invokelaterdispatcher.java:95)     @ com.sun.glass.ui.win.winapplication._runloop(native method)     @ com.sun.glass.ui.win.winapplication.lambda$null$148(winapplication.java:191)     ... 1 more caused by: java.lang.classnotfoundexception: scripter.nukkit.playertool.maincontroller     @ java.net.urlclassloader.findclass(unknown source)     @ java.lang.classloader.loadclass(unknown source)     @ sun.misc.launcher$appclassloader.loadclass(unknown source)     @ java.lang.classloader.loadclass(unknown source)     @ javafx.fxml.fxmlloader$valueelement.processattribute(fxmlloader.java:920)     ... 22 more 

and tested

class.forname("scripter.nukkit.playertool.maincontroller") 

but worked. why can't find class?!