Вопрос по Java — swing?

package com.jenkov.javafx;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;

import org.w3c.dom.Document;
import org.w3c.dom.Element;

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.concurrent.Worker;
import javafx.concurrent.Worker.State;
import javafx.scene.Scene;
import javafx.scene.layout.VBox;
import javafx.scene.web.WebEngine;
import javafx.scene.web.WebView;
import javafx.stage.Stage;

public class WebViewExample extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    public void start(Stage primaryStage) throws IOException {
        primaryStage.setTitle("JavaFX WebView Example");


        String content = new String(Files.readAllBytes(Paths.get("/home/console/French_pc_keyboard.svg")));
        WebView webView = new WebView();

        WebEngine engine = webView.getEngine();
        engine.loadContent(content);
        engine.getLoadWorker().stateProperty().addListener(
                new ChangeListener<State>() {
                  @Override public void changed(ObservableValue ov, State oldState, State newState) {

                      if (newState == Worker.State.SUCCEEDED) {
                        System.out.println("called");
	                      Document document = webView.getEngine().getDocument();
	                      Element element = document.getElementById("rect2354");
	                      String style = element.getAttribute("style");
	                      element.setAttribute("style", "fill:#00ff00;");
                    }
                      
                    }
                });
        
        VBox vBox = new VBox(webView);
        Scene scene = new Scene(vBox, 960, 600);

        primaryStage.setScene(scene);
        primaryStage.show();
    }
}