Q:

How can switch on main screen after successfully login in JavaFX

I am new in JavaFX.  I am trying to load another FXML file after successfully login:
<BorderPane id="BorderPane" maxHeight="-Infinity"
  maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity"
  prefHeight="700.0" prefWidth="1370.0" styleClass="anchor_background"
  stylesheets="@index.css" xmlns="javafx.com/javafx/8.0.141"; xmlns:fx="javafx.com/fxml/1";
  fx:controller="properties. Admin_homepageController">

It's showing error in this line:
Parent admin_homepage = FXMLLoader.load(getClass().getResource("Admin_homepage.fxml"));

The error is:

javafx.fxml. LoadException: file:/C:/Users/Arpit%20Singh/Documents/NetBeansProjects/Properties/dist/run1802424867/Properties.jar!/properties/Admin_homepage.fxml at javafx.fxml. FXMLLoader.constructLoadException(FXMLLoader.java:2601) at javafx.fxml. FXMLLoader.loadImpl(FXMLLoader.java:2543) at javafx.fxml. FXMLLoader.loadImpl(FXMLLoader.java:2441) at javafx.fxml. FXMLLoader.loadImpl(FXMLLoader.java:3214) at javafx.fxml. FXMLLoader.loadImpl(FXMLLoader.java:3175) at javafx.fxml. FXMLLoader.loadImpl(FXMLLoader.java:3148) at javafx.fxml. FXMLLoader.loadImpl(FXMLLoader.java:3124)

A:

The stack-trace contains:
javafx.fxml. LoadException:
file:/C:/Users/Arpit%20Singh/Documents/NetBeansProjects/Mulani_Properties/dist/run90454756/Mulani_Properties.jar!/mulani_properties/Admin_homepage.fxml

...

Caused by: javax.xml.stream. XMLStreamException: ParseError at [row,col]:[1,7]
Message: The processing instruction target matching "[xX][mM][lL]" is not allowed. 

Now you should search for Message: The processing instruction target matching "[xX][mM][lL]" is not allowed.  and find this question Error: The processing instruction target matching “[xX][mM][lL]” is not allowed. 
The reason is that you have other characters before <? xml version="1.0" encoding="UTF-8"? > in Admin_homepage.fxml, remove them and put <? xml version="1.0" encoding="UTF-8"? > into the first line.