Java

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.text.*;

public class RichTextBox{
  public RichTextBox(){
    JFrame frame = new JFrame();
    JTextPane textPane = new JTextPane();
    JScrollPane scrollPane = new JScrollPane(textPane);

    JPanel north = new JPanel();
    JMenuBar menu = new JMenuBar();
    JMenu boldMenu = new JMenu();
    boldMenu.setText("B");

    JMenu italicMenu = new JMenu();
    italicMenu.setText("I");

    JMenu lineMenu = new JMenu();
    lineMenu.setText("U");

    JMenu fontMenu = new JMenu();
    fontMenu.setText("F");

    JMenu colorMenu = new JMenu();
    colorMenu.setText("A");

    Action boldAction = new BoldAction();
    boldMenu.add(boldAction);

    Action italicAction = new ItalicAction();
    italicMenu.add(italicAction);

    Action uAction = new UnderLineAction();
    lineMenu.add(uAction);

    Action foregroundAction = new ForegroundAction();
    colorMenu.add(foregroundAction);

    Action formatTextAction = new FontAction();
    fontMenu.add(formatTextAction);

    menu.add(boldMenu);
    menu.add(italicMenu);
    menu.add(lineMenu);
    menu.add(fontMenu);
    menu.add(colorMenu);
    north.add(menu);
    frame.getContentPane().setLayout(new BorderLayout());
    frame.getContentPane().add(north, BorderLayout.NORTH);
    frame.getContentPane().add(scrollPane, BorderLayout.CENTER);
    frame.setSize(400, 200);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
  }
  public static void main(String[] args) {
    new RichTextBox();
  }
}
class BoldAction extends StyledEditorKit.StyledTextAction {
  public BoldAction(){
    super("bold");
  }
    public void actionPerformed(ActionEvent e){
    JEditorPane editor = getEditor(e);
    if(editor != null){
      StyledEditorKit kit = getStyledEditorKit(editor);
      MutableAttributeSet attr = kit.getInputAttributes();
      boolean bold = (StyleConstants.isBold(attr)) ? false : true;
      SimpleAttributeSet sas = new SimpleAttributeSet();
      StyleConstants.setBold(sas, bold);
      setCharacterAttributes(editor, sas, false);
    }
  }
}
class UnderLineAction extends StyledEditorKit.StyledTextAction {
   public UnderLineAction(){
    super("underline");
   }
    public void actionPerformed(ActionEvent e) {
    JEditorPane editor = getEditor(e);
    if(editor != null){
      StyledEditorKit kit = getStyledEditorKit(editor);
      MutableAttributeSet attr = kit.getInputAttributes();
      boolean ul = (StyleConstants.isUnderline(attr)) ? false : true;
      SimpleAttributeSet sas = new SimpleAttributeSet();
      StyleConstants.setUnderline(sas, ul);
      setCharacterAttributes(editor, sas, false);
    }
  }
}
class ItalicAction extends StyledEditorKit.StyledTextAction{
  public ItalicAction() {
    super("font-italic");
  }
   public void actionPerformed(ActionEvent e) {
    JEditorPane editor = getEditor(e);
    if (editor != null){
      StyledEditorKit kit = getStyledEditorKit(editor);
      MutableAttributeSet attr = kit.getInputAttributes();
      boolean italic = (StyleConstants.isItalic(attr)) ? false : true;
      SimpleAttributeSet sas = new SimpleAttributeSet();
      StyleConstants.setItalic(sas, italic);
      setCharacterAttributes(editor, sas, false);
    }
  }
}

continue....

class ForegroundAction extends StyledEditorKit.StyledTextAction {
  JColorChooser colorChooser = new JColorChooser();
  JDialog dialog = new JDialog();
  boolean noChange = false;
  boolean cancelled = false;
  public ForegroundAction(){
    super("foreground");
  }
  public void actionPerformed(ActionEvent e){
    JTextPane editor = (JTextPane) getEditor(e);
    int p0 = editor.getSelectionStart();
    StyledDocument doc = getStyledDocument(editor);
    Element paragraph = doc.getCharacterElement(p0);
    AttributeSet as = paragraph.getAttributes();
    fg = StyleConstants.getForeground(as);
    if(fg == null){
    fg = Color.BLACK;
    }
    colorChooser.setColor(fg);
    JButton accept = new JButton("OK");
    accept.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent ae) {
        fg = colorChooser.getColor();
        dialog.dispose();
      }
    });
    JPanel buttons = new JPanel();
    buttons.add(accept);
    dialog.getContentPane().setLayout(new BorderLayout());
    dialog.getContentPane().add(colorChooser, BorderLayout.CENTER);
    dialog.getContentPane().add(buttons, BorderLayout.SOUTH);
    dialog.setModal(true);
    dialog.pack();
    dialog.setVisible(true);
    if(!cancelled){
      MutableAttributeSet attr = null;
      if(editor != null){
        if(fg != null && !noChange){
          attr = new SimpleAttributeSet();
          StyleConstants.setForeground(attr, fg);
          setCharacterAttributes(editor, attr, false);
        }
      }
    }
    noChange = false;
    cancelled = false;
  }
  private Color fg;
}
class FontAction extends StyledEditorKit.StyledTextAction {
  private String family;
  private float fontSize;
  JDialog formatText;
  private boolean accept = false;
  JComboBox fontFamilyChooser;
  JComboBox fontSizeChooser;
  public FontAction(){
    super("Font");
  }
  public void actionPerformed(ActionEvent e){
    JTextPane editor = (JTextPane) getEditor(e);
    int p0 = editor.getSelectionStart();
    StyledDocument doc = getStyledDocument(editor);
    Element paragraph = doc.getCharacterElement(p0);
    AttributeSet as = paragraph.getAttributes();

    family = StyleConstants.getFontFamily(as);
    fontSize = StyleConstants.getFontSize(as);

    formatText = new JDialog(new JFrame(), "Font", true);
    formatText.getContentPane().setLayout(new BorderLayout());

    JPanel choosers = new JPanel();
    choosers.setLayout(new GridLayout(2, 1));

    JPanel fontFamilyPanel = new JPanel();
    fontFamilyPanel.add (new JLabel("Font"));

    GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
    String[] fontNames = ge.getAvailableFontFamilyNames();

    fontFamilyChooser = new JComboBox();
    for (int i = 0; i < fontNames.length; i++) {
      fontFamilyChooser.addItem(fontNames[i]);
    }
    fontFamilyChooser.setSelectedItem(family);
    fontFamilyPanel.add(fontFamilyChooser);
    choosers.add(fontFamilyPanel);
    JButton ok = new JButton("OK");
    ok.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent ae) {
        accept = true;
        formatText.dispose();
        family = (String) fontFamilyChooser.getSelectedItem();
      }
    });
    JPanel buttons = new JPanel();
    buttons.add(ok);
    formatText.getContentPane().add(choosers, BorderLayout.CENTER);
    formatText.getContentPane().add(buttons, BorderLayout.SOUTH);
    formatText.pack();
    formatText.setVisible(true);

    MutableAttributeSet attr = null;
    if(editor != null && accept) {
      attr = new SimpleAttributeSet();
      StyleConstants.setFontFamily(attr, family);
      StyleConstants.setFontSize(attr, (int) fontSize);
      setCharacterAttributes(editor, attr, false);
    }
  }
}