Not able to add XML content to existing JEditorPane

I am currently working on a Java application and the aim is to design a simple interface for asking some questions on Java. So far I have programmed a JEditorPane and a button.

I am using sax to read xml data stored in a folder. I am able to retrieve the the content of the xml and display it in the console log and it prints as expected, however when I try to set this to the JEditorPane (in SetXml class), I fail miserably. The idea is to click on a button and display the xml output to a JEdiorPane. I have spent hours on this and cannot seem to work out what the issue is. I have pasted the code below. I would very much appreciate if anyone could guide me of how to resolve this.

Controller.java

public class Controller {
static JButton btnFirst = new JButton("First Question");
static SetXml xmlObj = new SetXml();

public static void main (String[] args)
{
    JFrame frame = new JFrame();
    MainWin mainObj = new MainWin();

    frame.setSize(500, 500);
    frame.add(mainObj.mainWin());
    frame.add(btnFirst, BorderLayout.WEST);
    btnFirst.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) 
        {
            xmlObj.readXml();
        }
    });
    frame.setVisible(true);
}}

MainWin.java

public class MainWin {

JPanel qPanel = new JPanel();
questionWin qObj = new questionWin();

public JComponent mainWin()
{
            qPanel.setLayout(new BorderLayout());
            qPanel.add(qObj.questionWindow(), BorderLayout.CENTER);
            return qPanel;

}}

questionWin.java

public class questionWin {

JEditorPane editorPane = new JEditorPane();
JPanel panel = new JPanel();
/**
 * @wbp.parser.entryPoint
 */
public JComponent questionWindow() {

    GroupLayout groupLayout = new GroupLayout(panel);
    groupLayout.setHorizontalGroup(
        groupLayout.createParallelGroup(Alignment.LEADING)
            .addGroup(groupLayout.createSequentialGroup()
                .addGap(36)
                .addComponent(editorPane, GroupLayout.PREFERRED_SIZE, 357,      GroupLayout.PREFERRED_SIZE)
                .addContainerGap(41, Short.MAX_VALUE))
    );
    groupLayout.setVerticalGroup(
        groupLayout.createParallelGroup(Alignment.LEADING)
            .addGroup(groupLayout.createSequentialGroup()
                .addGap(26)
                .addComponent(editorPane, GroupLayout.PREFERRED_SIZE, 106, GroupLayout.PREFERRED_SIZE)
                .addContainerGap(129, Short.MAX_VALUE))
    );
    panel.setLayout(groupLayout);
    return panel;
}}

SetXml.java

public class SetXml 
{
questionWin questWinObj = new questionWin();

public JComponent readXml()
{

    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    try 
    {
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse("Questions/q1.xml");
        NodeList questionList = doc.getElementsByTagName("Question");
            for(int i=0; i<questionList.getLength();i++) 
            {
                Node q = questionList.item(i);
                    Element a = (Element)q;
                    questWinObj.editorPane.setText(a.getTextContent());
                    System.out.print(a.getTextContent());
            }       
    }

    catch (ParserConfigurationException e) 
    {
        e.printStackTrace();
    }

    catch (SAXException e) 
    {

        e.printStackTrace();
    } catch (IOException e) 
    {

        e.printStackTrace();
    } 

    return null;

}}