Load another FXML file when loading one

Question

When I am clicking on Start button of my homepage, I am loading SimulatorWindow.fxml file on the middle of the homepage.

This is the SimulatorWindow.fxml file.

Here into the red marked area of the given image, I need to load another fxml file(named Simulator.fxml).

Here is my SimulatorWindowController.java file

package SortingAlgorithmSimulator.view;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import SortingAlgorithmSimulator.Main;
import javafx.application.Application;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.control.CheckBox;
import javafx.scene.control.TextArea;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
public class SimulatorWindowController extends Application
{
    private HomeController hc=new HomeController();
    @FXML
    private TextArea AlgorithmField;
    @FXML
    private CheckBox screenSize;
    @FXML
    public static BorderPane simu;
    @FXML
    private void initialize() throws IOException
    {   FXMLLoader loader1=new FXMLLoader();
        loader1.setLocation(Main.class.getResource("view/Simulator.fxml"));
        BorderPane mainItems1=loader1.load();
        simu.setCenter(mainItems1);
        BufferedReader buff = null;
          try {
               buff = new BufferedReader(new FileReader(hc.selectedFile));
               String str;
               while ((str = buff.readLine()) != null)
               {
                   AlgorithmField.appendText(str+"\n");
               }
         } catch (IOException e)
          {
          } finally
          {
            try { buff.close(); } catch (Exception ex) { }
          }
    }
    @FXML
    private void goHome() throws IOException
    {
        Main.showHome();
    }
    @FXML
    private void goHelp() throws IOException
    {
        Main.showHelp();
    }
    @FXML
    private void goAboutMe() throws IOException
    {
        Main.showAboutMe();
    }
    @FXML
    private void goScreen() throws IOException
    {
        if(screenSize.isSelected())
        {
            Main.primaryStage.setFullScreen(true);
            screenSize.setText("Exit Full Screen");
        }
        else 
        {
            Main.primaryStage.setFullScreen(false); 
            screenSize.setText("Full Screen");
        }
    }
    @FXML
    private void goExit() throws IOException
    {
        System.exit(0);
    }
    @Override
    public void start(Stage arg0) throws Exception
    {
        // TODO Auto-generated method stub
    }
}

But when I am running this code, it is showing me error NullPointerException.

Here is error report

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException at javafx.fxml.FXMLLoader$MethodHandler.invoke(Unknown Source) at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(Unknown Source) at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source) at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source) at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source) at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source) at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source) at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source) at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source) at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source) at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source) at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source) at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source) at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source) at javafx.event.Event.fireEvent(Unknown Source) at javafx.scene.Node.fireEvent(Unknown Source) at javafx.scene.control.Button.fire(Unknown Source) at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(Unknown Source) at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown Source) at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown Source) at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(Unknown Source) at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source) at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source) at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source) at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source) at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source) at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source) at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source) at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source) at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source) at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source) at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source) at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source) at javafx.event.Event.fireEvent(Unknown Source) at javafx.scene.Scene$MouseHandler.process(Unknown Source) at javafx.scene.Scene$MouseHandler.access$1500(Unknown Source) at javafx.scene.Scene.impl_processMouseEvent(Unknown Source) at javafx.scene.Scene$ScenePeerListener.mouseEvent(Unknown Source) at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source) at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(Unknown Source) at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(Unknown Source) at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(Unknown Source) at com.sun.glass.ui.View.handleMouseEvent(Unknown Source) at com.sun.glass.ui.View.notifyMouse(Unknown Source) at com.sun.glass.ui.win.WinApplication._runLoop(Native Method) at com.sun.glass.ui.win.WinApplication.lambda$null$148(Unknown Source) at java.lang.Thread.run(Unknown Source) Caused by: java.lang.reflect.InvocationTargetException at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at sun.reflect.misc.Trampoline.invoke(Unknown Source) at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at sun.reflect.misc.MethodUtil.invoke(Unknown Source) ... 49 more Caused by: javafx.fxml.LoadException: /D:/Document%20Files/Java%20Programming/bin/SortingAlgorithmSimulator/view/SimulatorWindow.fxml

at javafx.fxml.FXMLLoader.constructLoadException(Unknown Source) at javafx.fxml.FXMLLoader.loadImpl(Unknown Source) at javafx.fxml.FXMLLoader.loadImpl(Unknown Source) at javafx.fxml.FXMLLoader.load(Unknown Source) at SortingAlgorithmSimulator.Main.showSimulatorWindow(Main.java:87) at SortingAlgorithmSimulator.view.HomeController.goSimulatorWindow(HomeController.java:64) ... 58 more Caused by: java.lang.reflect.InvocationTargetException at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at sun.reflect.misc.Trampoline.invoke(Unknown Source) at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at sun.reflect.misc.MethodUtil.invoke(Unknown Source) ... 63 more Caused by: java.lang.NullPointerException at SortingAlgorithmSimulator.view.SimulatorWindowController.initialize(SimulatorWindowController.java:35) ... 72 more

How can I fix it?

Here is the download link of source code

https://drive.google.com/folderview?id=0B7pxly3GctSNQ1FaajY4LTFOQnM&usp=sharing