Java JTextPane create rich text processor

import javax.swing.JFrame;
import java.awt.Container;
import javax.swing.JTextPane;
import javax.swing.JButton;
import java.awt.BorderLayout;
import javax.swing.JPanel;
import javax.swing.text.StyledDocument;
import javax.swing.text.BadLocationException;
import javax.swing.text.Style;
import javax.swing.text.StyleContext;
import javax.swing.text.StyleConstants;
import java.awt.Color;

public class Main extends JFrame {
    JTextPane textPane = new JTextPane();

    JButton normalBtn = new JButton("Normal");
    JButton boldBtn = new JButton("Bold");
    JButton italicBtn = new JButton("Italic");
    JButton underlineBtn = new JButton("Underline");
    JButton superscriptBtn = new JButton("Superscript");
    JButton blueBtn = new JButton("Blue");
    JButton leftBtn = new JButton("Left Align");
    JButton rightBtn = new JButton("Right Align");

    public Main(String title) {
        super(title);
        initFrame();//from   w  w w .  j av  a 2 s  . com
    }

    private void initFrame() {
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Container contentPane = this.getContentPane();

        JPanel buttonPanel = this.getButtonPanel();
        contentPane.add(buttonPanel, BorderLayout.NORTH);
        contentPane.add(textPane, BorderLayout.CENTER);

        this.addStyles(); // Add styles to the text pane for later use 
        insertTestStrings(); // Insert some texts to the text pane 
    }

    private JPanel getButtonPanel() {
        JPanel buttonPanel = new JPanel();
        buttonPanel.add(normalBtn);
        buttonPanel.add(boldBtn);
        buttonPanel.add(italicBtn);
        buttonPanel.add(underlineBtn);
        buttonPanel.add(superscriptBtn);
        buttonPanel.add(blueBtn);
        buttonPanel.add(leftBtn);
        buttonPanel.add(rightBtn);

        // Add action event listeners to buttons
        normalBtn.addActionListener(e -> setNewStyle("normal", true));
        boldBtn.addActionListener(e -> setNewStyle("bold", true));
        italicBtn.addActionListener(e -> setNewStyle("italic", true));
        underlineBtn.addActionListener(e -> setNewStyle("underline", true));
        superscriptBtn.addActionListener(e -> setNewStyle("superscript", true));
        blueBtn.addActionListener(e -> setNewStyle("blue", true));
        leftBtn.addActionListener(e -> setNewStyle("left", false));
        rightBtn.addActionListener(e -> setNewStyle("right", false));

        return buttonPanel;
    }

    private void addStyles() {
        // Get the default style 
        StyleContext sc = StyleContext.getDefaultStyleContext();
        Style defaultContextStyle = sc.getStyle(StyleContext.DEFAULT_STYLE);

        // Add some styles to the document, to retrieve and use later 
        StyledDocument document = textPane.getStyledDocument();
        Style normalStyle = document.addStyle("normal", defaultContextStyle);

        // Create a bold style 
        Style boldStyle = document.addStyle("bold", normalStyle);
        StyleConstants.setBold(boldStyle, true);

        // Create an italic style 
        Style italicStyle = document.addStyle("italic", normalStyle);
        StyleConstants.setItalic(italicStyle, true);

        // Create an underline style 
        Style underlineStyle = document.addStyle("underline", normalStyle);
        StyleConstants.setUnderline(underlineStyle, true);

        // Create a superscript style 
        Style superscriptStyle = document.addStyle("superscript", normalStyle);
        StyleConstants.setSuperscript(superscriptStyle, true);

        // Create a blue color style 
        Style blueColorStyle = document.addStyle("blue", normalStyle);
        StyleConstants.setForeground(blueColorStyle, Color.BLUE);

        // Create a left alignment paragraph style 
        Style leftStyle = document.addStyle("left", normalStyle);
        StyleConstants.setAlignment(leftStyle, StyleConstants.ALIGN_LEFT);

        // Create a right alignment paragraph style 
        Style rightStyle = document.addStyle("right", normalStyle);
        StyleConstants.setAlignment(rightStyle, StyleConstants.ALIGN_RIGHT);
    }

    private void setNewStyle(String styleName, boolean isCharacterStyle) {
        StyledDocument document = textPane.getStyledDocument();
        Style newStyle = document.getStyle(styleName);
        int start = textPane.getSelectionStart();
        int end = textPane.getSelectionEnd();
        if (isCharacterStyle) {
            boolean replaceOld = styleName.equals("normal");
            document.setCharacterAttributes(start, end - start,
                    newStyle, replaceOld);
        } else {
            document.setParagraphAttributes(start, end - start, newStyle, false);
        }
    }

    private void insertTestStrings() {
        StyledDocument document = textPane.getStyledDocument();
        try {
            document.insertString(0, "Hello JTextPane\n", null);
        } catch (BadLocationException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        Main frame = new Main("Word Processor");
        frame.setSize(700, 500);
        frame.setVisible(true);
    }
}