/*
 * Copyright (c) 2010, 2019, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 */

package javafx.application;

import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.List;
import java.util.Map;

import javafx.application.Preloader.PreloaderNotification;
import javafx.scene.Scene;
import javafx.stage.Stage;

import com.sun.javafx.application.LauncherImpl;
import com.sun.javafx.application.ParametersImpl;
import com.sun.javafx.application.PlatformImpl;
import com.sun.javafx.css.StyleManager;

Application class from which JavaFX applications extend.
Life-cycle

The entry point for JavaFX applications is the Application class. The
JavaFX runtime does the following, in order, whenever an application is
launched:


Starts the JavaFX runtime, if not already started (see Platform.startup(Runnable) for more information)
Constructs an instance of the specified Application class
Calls the init method
Calls the start method
Waits for the application to finish, which happens when either of
the following occur:

the application calls Platform.exit
the last window has been closed and the implicitExit attribute on Platform is true

Calls the stop method

Note that the start method is abstract and must be overridden. The init and stop methods have concrete implementations that do nothing.
The Application subclass must be declared public and must have a public no-argument constructor.
Calling Platform.exit is the preferred way to explicitly terminate a JavaFX Application. Directly calling System.exit is an acceptable alternative, but doesn't allow the Application stop method to run. 
A JavaFX Application should not attempt to use JavaFX after the FX toolkit has terminated or from a ShutdownHook, that is, after the stop method returns or System.exit is called. 
Deploying an Application as a Module
 If the Application subclass is in a named module then that class must be accessible to the javafx.graphics module. Otherwise, an exception will be thrown when the application is launched. This means that in addition to the class itself being declared public, the module must export (or open) the containing package to at least the javafx.graphics module. 
 For example, if com.foo.MyApplication is in the foo.app module, the module-info.java might look like this: 
module foo.app {
exports com.foo to javafx.graphics;

Parameters
 Application parameters are available by calling the getParameters method from the init method, or any time after the init method has been called. 
Threading
 JavaFX creates an application thread for running the application start method, processing input events, and running animation timelines. Creation of JavaFX Scene and Stage objects as well as modification of scene graph operations to live objects (those objects already
attached to a scene) must be done on the JavaFX application thread.


The Java launcher loads and initializes the specified Application class
on the JavaFX Application Thread. If there is no main method in the
Application class, or if the main method calls Application.launch(), then
an instance of the Application is then constructed on the JavaFX Application
Thread.

 The init method is called on the launcher thread, not on the JavaFX Application Thread. This means that an application must not construct a Scene or a Stage in the init method. An application may construct other JavaFX objects in the init method. 
 All the unhandled exceptions on the JavaFX application thread that occur during event dispatching, running animation timelines, or any other code, are forwarded to the thread's uncaught
exception handler. 
Example
The following example will illustrate a simple JavaFX application.

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
public class MyApp extends Application {
public void start(Stage stage) {
Circle circ = new Circle(40, 40, 30);
Group root = new Group(circ);
Scene scene = new Scene(root, 400, 300);
stage.setTitle("My JavaFX Application");
stage.setScene(scene);
stage.show();
 }

The above example will produce the following:

See Also:
Platform
Since:
JavaFX 2.0/**
 * Application class from which JavaFX applications extend.
 *
 * <p><b>Life-cycle</b></p>
 * <p>
 * The entry point for JavaFX applications is the Application class. The
 * JavaFX runtime does the following, in order, whenever an application is
 * launched:
 * </p>
 * <ol>
 * <li>Starts the JavaFX runtime, if not already started
 * (see {@link Platform#startup(Runnable)} for more information)</li>
 * <li>Constructs an instance of the specified Application class</li>
 * <li>Calls the {@link #init} method</li>
 * <li>Calls the {@link #start} method</li>
 * <li>Waits for the application to finish, which happens when either of
 * the following occur:
 * <ul>
 * <li>the application calls {@link Platform#exit}</li>
 * <li>the last window has been closed and the {@code implicitExit}
 * attribute on {@code Platform} is true</li>
 * </ul></li>
 * <li>Calls the {@link #stop} method</li>
 * </ol>
 * <p>Note that the {@code start} method is abstract and must be overridden.
 * The {@code init} and {@code stop} methods have concrete implementations
 * that do nothing.</p>
 * <p>The {@code Application} subclass must be declared public and must have a
 * public no-argument constructor.</p>
 *
 * <p>Calling {@link Platform#exit} is the preferred way to explicitly terminate
 * a JavaFX Application. Directly calling {@link System#exit} is
 * an acceptable alternative, but doesn't allow the Application {@link #stop}
 * method to run.
 * </p>
 *
 * <p>A JavaFX Application should not attempt to use JavaFX after the
 * FX toolkit has terminated or from a ShutdownHook, that is, after the
 * {@link #stop} method returns or {@link System#exit} is called.
 * </p>
 *
 * <p><b>Deploying an Application as a Module</b></p>
 * <p>
 * If the {@code Application} subclass is in a named module then that class
 * must be accessible to the {@code javafx.graphics} module.
 * Otherwise, an exception will be thrown when the application is launched.
 * This means that
 * in addition to the class itself being declared public, the module must
 * {@link Module#isExported(String,Module) export}
 * (or {@link Module#isOpen(String,Module) open}) the containing package to
 * at least the {@code javafx.graphics} module.
 * </p>
 * <p>
 * For example, if {@code com.foo.MyApplication} is in the {@code foo.app}
 * module, the {@code module-info.java} might look like this:
 * </p>
<pre>{@code module foo.app {
    exports com.foo to javafx.graphics;
}}</pre>
*
 * <p><b>Parameters</b></p>
 * <p>
 * Application parameters are available by calling the {@link #getParameters}
 * method from the {@link #init} method, or any time after the {@code init}
 * method has been called.
 * </p>
 *
 * <p><b>Threading</b></p>
 * <p>
 * JavaFX creates an application thread for running the application start
 * method, processing input events, and running animation timelines. Creation
 * of JavaFX {@link Scene} and {@link Stage} objects as well as modification of
 * scene graph operations to <em>live</em> objects (those objects already
 * attached to a scene) must be done on the JavaFX application thread.
 * </p>
 *
 * <p>
 * The Java launcher loads and initializes the specified Application class
 * on the JavaFX Application Thread. If there is no main method in the
 * Application class, or if the main method calls Application.launch(), then
 * an instance of the Application is then constructed on the JavaFX Application
 * Thread.
 * </p>
 *
 * <p>
 * The {@code init} method is called on the launcher thread, not on the
 * JavaFX Application Thread.
 * This means that an application must not construct a {@link Scene}
 * or a {@link Stage} in the {@code init} method.
 * An application may construct other JavaFX objects in the {@code init}
 * method.
 * </p>
 *
 * <p>
 * All the unhandled exceptions on the JavaFX application thread that occur during
 * event dispatching, running animation timelines, or any other code, are forwarded
 * to the thread's {@link java.lang.Thread.UncaughtExceptionHandler uncaught
 * exception handler}.
 * </p>
 *
 * <p><b>Example</b></p>
 * <p>The following example will illustrate a simple JavaFX application.</p>
 * <pre>{@code
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;

public class MyApp extends Application {
    public void start(Stage stage) {
        Circle circ = new Circle(40, 40, 30);
        Group root = new Group(circ);
        Scene scene = new Scene(root, 400, 300);

        stage.setTitle("My JavaFX Application");
        stage.setScene(scene);
        stage.show();
    }
}
 * }</pre>
 *
 * <p>The above example will produce the following:</p>
 * <p><img src="doc-files/Application.png" alt="A black circle in the top left
 * corner of scene"></p>
 *
 * @see Platform
 *
 * @since JavaFX 2.0
 */
public abstract class Application {
    
Constant for user agent stylesheet for the "Caspian" theme. Caspian
is the theme that shipped as default in JavaFX 2.x.
Since:
JavaFX 8.0/**
     * Constant for user agent stylesheet for the "Caspian" theme. Caspian
     * is the theme that shipped as default in JavaFX 2.x.
     * @since JavaFX 8.0
     */
    public static final String STYLESHEET_CASPIAN = "CASPIAN";
    
Constant for user agent stylesheet for the "Modena" theme. Modena
is the default theme for JavaFX 8.x.
Since:
JavaFX 8.0/**
     * Constant for user agent stylesheet for the "Modena" theme. Modena
     * is the default theme for JavaFX 8.x.
     * @since JavaFX 8.0
     */
    public static final String STYLESHEET_MODENA = "MODENA";

    
Launch a standalone application. This method is typically called from the main method. It must not be called more than once or an exception will be thrown. 
 The launch method does not return until the application has exited, either via a call to Platform.exit() or all of the application windows have been closed. The class specified by the appClass argument must be a public subclass of Application with a public no-argument constructor, in a package that is exported (or open) to at least the javafx.graphics module, or a RuntimeException will be thrown. 

Typical usage is:
    public static void main(String[] args) {
        Application.launch(MyApp.class, args);
    }

where MyApp is a subclass of Application.
Params:
appClass – the application class that is constructed and executed
       by the launcher.
args – the command line arguments passed to the application. An application may get these parameters using the getParameters() method.
Throws:
IllegalStateException – if this method is called more than once.
IllegalArgumentException – if appClass is not a
        subclass of Application.
RuntimeException – if there is an error launching the
JavaFX runtime, or if the application class cannot be constructed
(e.g., if the class is not public or is not in an exported package), or
if an Exception or Error is thrown by the Application constructor, init
method, start method, or stop method./**
     * Launch a standalone application. This method is typically called
     * from the {@code main} method. It must not be called more than once or an
     * exception will be thrown.
     *
     * <p>
     * The launch method does not return until the application has exited,
     * either via a call to {@link Platform#exit()} or all of the application windows
     * have been closed.
     * The class specified by the {@code appClass} argument must be
     * a public subclass of {@code Application}
     * with a public no-argument constructor, in a package that is
     * {@link Module#isExported(String,Module) exported}
     * (or {@link Module#isOpen(String,Module) open}) to at least the
     * {@code javafx.graphics} module, or a RuntimeException will be thrown.
     *
     * <p>
     * Typical usage is:
     * <pre>
     *     public static void main(String[] args) {
     *         Application.launch(MyApp.class, args);
     *     }
     * </pre>
     * where <code>MyApp</code> is a subclass of Application.
     *
     * @param appClass the application class that is constructed and executed
     *        by the launcher.
     * @param args the command line arguments passed to the application.
     *             An application may get these parameters using the
     *             {@link #getParameters()} method.
     *
     * @throws IllegalStateException if this method is called more than once.
     * @throws IllegalArgumentException if <code>appClass</code> is not a
     *         subclass of <code>Application</code>.
     * @throws RuntimeException if there is an error launching the
     * JavaFX runtime, or if the application class cannot be constructed
     * (e.g., if the class is not public or is not in an exported package), or
     * if an Exception or Error is thrown by the Application constructor, init
     * method, start method, or stop method.
     */
    public static void launch(Class<? extends Application> appClass, String... args) {
        LauncherImpl.launchApplication(appClass, args);
    }

    
Launch a standalone application. This method is typically called from the main method. It must not be called more than once or an exception will be thrown. This is equivalent to launch(TheClass.class, args) where TheClass is the immediately enclosing class of the method that called launch. It must be a public subclass of Application with a public no-argument constructor, in a package that is exported (or open) to at least the javafx.graphics module, or a RuntimeException will be thrown. 
 The launch method does not return until the application has exited, either via a call to Platform.exit() or all of the application windows have been closed. 

Typical usage is:
    public static void main(String[] args) {
        Application.launch(args);
    }

Params:
args – the command line arguments passed to the application. An application may get these parameters using the getParameters() method.
Throws:
IllegalStateException – if this method is called more than once.
RuntimeException – if there is an error launching the
JavaFX runtime, or if the application class cannot be constructed
(e.g., if the class is not public or is not in an exported package), or
if an Exception or Error is thrown by the Application constructor, init
method, start method, or stop method./**
     * Launch a standalone application. This method is typically called
     * from the {@code main} method. It must not be called more than once or an
     * exception will be thrown.
     * This is equivalent to {@code launch(TheClass.class, args)} where
     * {@code TheClass} is the
     * immediately enclosing class of the method that called launch.
     * It must be a public subclass of {@code Application}
     * with a public no-argument constructor, in a package that is
     * {@link Module#isExported(String,Module) exported}
     * (or {@link Module#isOpen(String,Module) open}) to at least the
     * {@code javafx.graphics} module, or a RuntimeException will be thrown.
     *
     * <p>
     * The launch method does not return until the application has exited,
     * either via a call to {@link Platform#exit()} or all of the application windows
     * have been closed.
     *
     * <p>
     * Typical usage is:
     * <pre>
     *     public static void main(String[] args) {
     *         Application.launch(args);
     *     }
     * </pre>
     *
     * @param args the command line arguments passed to the application.
     *             An application may get these parameters using the
     *             {@link #getParameters()} method.
     *
     * @throws IllegalStateException if this method is called more than once.
     * @throws RuntimeException if there is an error launching the
     * JavaFX runtime, or if the application class cannot be constructed
     * (e.g., if the class is not public or is not in an exported package), or
     * if an Exception or Error is thrown by the Application constructor, init
     * method, start method, or stop method.
     */
    public static void launch(String... args) {
        // Figure out the right class to call
        StackTraceElement[] cause = Thread.currentThread().getStackTrace();

        boolean foundThisMethod = false;
        String callingClassName = null;
        for (StackTraceElement se : cause) {
            // Skip entries until we get to the entry for this class
            String className = se.getClassName();
            String methodName = se.getMethodName();
            if (foundThisMethod) {
                callingClassName = className;
                break;
            } else if (Application.class.getName().equals(className)
                    && "launch".equals(methodName)) {

                foundThisMethod = true;
            }
        }

        if (callingClassName == null) {
            throw new RuntimeException("Error: unable to determine Application class");
        }

        try {
            Class theClass = Class.forName(callingClassName, false,
                               Thread.currentThread().getContextClassLoader());
            if (Application.class.isAssignableFrom(theClass)) {
                Class<? extends Application> appClass = theClass;
                LauncherImpl.launchApplication(appClass, args);
            } else {
                throw new RuntimeException("Error: " + theClass
                        + " is not a subclass of javafx.application.Application");
            }
        } catch (RuntimeException ex) {
            throw ex;
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

    
Constructs a new Application instance. /**
     * Constructs a new {@code Application} instance.
     */
    public Application() {
    }

    
The application initialization method. This method is called immediately
after the Application class is loaded and constructed. An application may
override this method to perform initialization prior to the actual starting
of the application.

The implementation of this method provided by the Application class does nothing.


NOTE: This method is not called on the JavaFX Application Thread. An
application must not construct a Scene or a Stage in this
method.
An application may construct other JavaFX objects in this method.

Throws:
Exception – if something goes wrong/**
     * The application initialization method. This method is called immediately
     * after the Application class is loaded and constructed. An application may
     * override this method to perform initialization prior to the actual starting
     * of the application.
     *
     * <p>
     * The implementation of this method provided by the Application class does nothing.
     * </p>
     *
     * <p>
     * NOTE: This method is not called on the JavaFX Application Thread. An
     * application must not construct a Scene or a Stage in this
     * method.
     * An application may construct other JavaFX objects in this method.
     * </p>
     * @throws java.lang.Exception if something goes wrong
     */
    public void init() throws Exception {
    }

    
The main entry point for all JavaFX applications.
The start method is called after the init method has returned,
and after the system is ready for the application to begin running.

NOTE: This method is called on the JavaFX Application Thread.

Params:
primaryStage – the primary stage for this application, onto which
the application scene can be set.
Applications may create other stages, if needed, but they will not be
primary stages.
Throws:
Exception – if something goes wrong/**
     * The main entry point for all JavaFX applications.
     * The start method is called after the init method has returned,
     * and after the system is ready for the application to begin running.
     *
     * <p>
     * NOTE: This method is called on the JavaFX Application Thread.
     * </p>
     *
     * @param primaryStage the primary stage for this application, onto which
     * the application scene can be set.
     * Applications may create other stages, if needed, but they will not be
     * primary stages.
     * @throws java.lang.Exception if something goes wrong
     */
    public abstract void start(Stage primaryStage) throws Exception;

    
This method is called when the application should stop, and provides a
convenient place to prepare for application exit and destroy resources.

The implementation of this method provided by the Application class does nothing.


NOTE: This method is called on the JavaFX Application Thread.

Throws:
Exception – if something goes wrong/**
     * This method is called when the application should stop, and provides a
     * convenient place to prepare for application exit and destroy resources.
     *
     * <p>
     * The implementation of this method provided by the Application class does nothing.
     * </p>
     *
     * <p>
     * NOTE: This method is called on the JavaFX Application Thread.
     * </p>
     * @throws java.lang.Exception if something goes wrong
     */
    public void stop() throws Exception {
    }

    private HostServices hostServices = null;

    
Gets the HostServices provider for this application. This provides
the ability to get the code base and document base for this application,
and to show a web page in a browser.
Returns:
the HostServices provider/**
     * Gets the HostServices provider for this application. This provides
     * the ability to get the code base and document base for this application,
     * and to show a web page in a browser.
     *
     * @return the HostServices provider
     */
    public final HostServices getHostServices() {
        synchronized (this) {
            if (hostServices == null) {
                hostServices = new HostServices(this);
            }
            return hostServices;
        }
    }

    
Retrieves the parameters for this Application, including any arguments
passed on the command line.

NOTE: this method should not be called from the Application constructor,
as it will return null. It may be called in the init() method or any
time after that.

Returns:
the parameters for this Application, or null if called from the
constructor./**
     * Retrieves the parameters for this Application, including any arguments
     * passed on the command line.
     *
     * <p>
     * NOTE: this method should not be called from the Application constructor,
     * as it will return null. It may be called in the init() method or any
     * time after that.
     * </p>
     *
     * @return the parameters for this Application, or null if called from the
     * constructor.
     */
    public final Parameters getParameters() {
        return ParametersImpl.getParameters(this);
    }

    
Notifies the preloader with an application-generated notification. Application code calls this method with a PreloaderNotification that is delivered to the 
Preloader.handleApplicationNotification method. This is primarily useful for cases where an application wants the preloader to show progress during a long application initialization step. 
 NOTE: the notification will be delivered only to the preloader's handleApplicationNotification() method; this means, for example, that if this method is called with a ProgressNotification, that notification will not be delivered to the 
Preloader.handleProgressNotification method. 
Params:
info – the application-generated preloader notification/**
     * Notifies the preloader with an application-generated notification.
     * Application code calls this method with a PreloaderNotification that is
     * delivered to the
     * {@link Preloader#handleApplicationNotification
     * Preloader.handleApplicationNotification} method.
     * This is primarily useful for cases where an application wants the
     * preloader to show progress during a long application initialization
     * step.
     *
     * <p>
     * NOTE: the notification will be delivered only to the preloader's
     * handleApplicationNotification() method; this means, for example, that
     * if this method is called with a ProgressNotification, that notification
     * will not be delivered to the {@link Preloader#handleProgressNotification
     * Preloader.handleProgressNotification}
     * method.
     * </p>
     *
     * @param info the application-generated preloader notification
     */
    public final void notifyPreloader(PreloaderNotification info) {
        LauncherImpl.notifyPreloader(this, info);
    }

    
Encapsulates the set of parameters for an application. This includes
arguments passed on the command line.

Note that the application and the preloader both get the same set
of parameters for a given run of an application.

Since:
JavaFX 2.0/**
     * Encapsulates the set of parameters for an application. This includes
     * arguments passed on the command line.
     *
     * <p>
     * Note that the application and the preloader both get the same set
     * of parameters for a given run of an application.
     * </p>
     * @since JavaFX 2.0
     */
    public static abstract class Parameters {

        
Constructs a new Parameters instance. /**
         * Constructs a new {@code Parameters} instance.
         */
        public Parameters() {
        }

        
Retrieves a read-only list of the raw arguments. This list
may be empty, but is never null. In the case of a standalone
application, it is the ordered list of arguments specified on the
command line.
For
named parameters, each <name,value> pair is represented as
a single argument of the form: "--name=value".
Returns:
a read-only list of raw application arguments/**
         * Retrieves a read-only list of the raw arguments. This list
         * may be empty, but is never null. In the case of a standalone
         * application, it is the ordered list of arguments specified on the
         * command line.
         * For
         * named parameters, each &lt;name,value&gt; pair is represented as
         * a single argument of the form: "--name=value".
         *
         * @return a read-only list of raw application arguments
         */
        public abstract List<String> getRaw();

        
Retrieves a read-only list of the unnamed parameters. This list
may be empty, but is never null. The named parameters, that is
the parameters that are represented as <name,value> pairs, are
filtered out.
Returns:
a read-only list of unnamed parameters./**
         * Retrieves a read-only list of the unnamed parameters. This list
         * may be empty, but is never null. The named parameters, that is
         * the parameters that are represented as &lt;name,value&gt; pairs, are
         * filtered out.
         *
         * @return a read-only list of unnamed parameters.
         */
        public abstract List<String> getUnnamed();

        
Retrieves a read-only map of the named parameters. It may be
empty, but is never null.
Named parameters include any command line
arguments of the form: "--name=value".
Returns:
a read-only map of named parameters./**
         * Retrieves a read-only map of the named parameters. It may be
         * empty, but is never null.
         * Named parameters include any command line
         * arguments of the form: "--name=value".
         *
         * @return a read-only map of named parameters.
         */
        public abstract Map<String, String> getNamed();

    }

    private static String userAgentStylesheet = null;

    
Get the user agent stylesheet used by the whole application. This is
used to provide default styling for all ui controls and other nodes.
A value of null means the platform default stylesheet is being used.

NOTE: This method must be called on the JavaFX Application Thread.

Returns:
The URL to the stylesheet as a String.
Since:
JavaFX 8.0/**
     * Get the user agent stylesheet used by the whole application. This is
     * used to provide default styling for all ui controls and other nodes.
     * A value of null means the platform default stylesheet is being used.
     * <p>
     * NOTE: This method must be called on the JavaFX Application Thread.
     * </p>
     *
     * @return The URL to the stylesheet as a String.
     * @since JavaFX 8.0
     */
    public static String getUserAgentStylesheet() {
        return userAgentStylesheet;
    }

    
Set the user agent stylesheet used by the whole application. This is used to provide default styling for all ui controls and other nodes. Each release of JavaFX may have a new default value for this so if you need to guarantee consistency you will need to call this method and choose what default you would like for your application. A value of null will restore the platform default stylesheet. This property can also be set on the command line with -Djavafx.userAgentStylesheetUrl=[URL] Setting it on the command line overrides anything set using this method in code. 

NOTE: This method must be called on the JavaFX Application Thread.

Params:
url – The URL to the stylesheet as a String.
Since:
JavaFX 8.0/**
     * Set the user agent stylesheet used by the whole application. This is used
     * to provide default styling for all ui controls and other nodes. Each
     * release of JavaFX may have a new default value for this so if you need
     * to guarantee consistency you will need to call this method and choose
     * what default you would like for your application. A value of null will
     * restore the platform default stylesheet. This property can also be set
     * on the command line with {@code -Djavafx.userAgentStylesheetUrl=[URL]}
     * Setting it on the command line overrides anything set using this method
     * in code.
     * <p>
     * NOTE: This method must be called on the JavaFX Application Thread.
     * </p>
     *
     *
     * @param url The URL to the stylesheet as a String.
     * @since JavaFX 8.0
     */
    public static void setUserAgentStylesheet(String url) {
        userAgentStylesheet = url;
        if (url == null) {
            PlatformImpl.setDefaultPlatformUserAgentStylesheet();
        } else {
            PlatformImpl.setPlatformUserAgentStylesheet(url);
        }
    }
}