/** Changes the font and tabsize for the document. */
public final void do_setFont(String fontName, int fontSize, int tabSize) {
    if (tabSize < 1)
        tabSize = 1;
    else if (tabSize > 100)
        tabSize = 100;
    if (fontName.equals(this.font) && fontSize == this.fontSize && tabSize == this.tabSize)
        return;
    this.font = fontName;
    this.fontSize = fontSize;
    this.tabSize = tabSize;
    for (MutableAttributeSet s : all) {
        StyleConstants.setFontFamily(s, fontName);
        StyleConstants.setFontSize(s, fontSize);
    }
    do_reapplyAll();
    BufferedImage im = new BufferedImage(10, 10, BufferedImage.TYPE_INT_RGB); // this
                                                                             // is
                                                                             // used
                                                                             // to
                                                                             // derive
                                                                             // the
                                                                             // tab
                                                                             // width
    int gap = tabSize * im.createGraphics().getFontMetrics(new Font(fontName, Font.PLAIN, fontSize)).charWidth('X');
    TabStop[] pos = new TabStop[100];
    for (int i = 0; i < 100; i++) {
        pos[i] = new TabStop(i * gap + gap);
    }
    StyleConstants.setTabSet(tabset, new TabSet(pos));
    setParagraphAttributes(0, getLength(), tabset, false);
}
 

@SuppressWarnings("PMD.AvoidInstantiatingObjectsInLoops")
@Override public void install(JEditorPane c) {
  FontMetrics fm = c.getFontMetrics(c.getFont());
  int tabLength = fm.charWidth('m') * 4;
  TabStop[] tabs = new TabStop[100];
  for (int j = 0; j < tabs.length; j++) {
    tabs[j] = new TabStop((j + 1f) * tabLength);
  }
  TabSet tabSet = new TabSet(tabs);
  StyleConstants.setTabSet(ATTRS, tabSet);
  super.install(c);
}
 

private MainPanel() {
  super(new BorderLayout());
  JTextPane textPane = new JTextPane();
  textPane.setFont(new Font(Font.MONOSPACED, Font.PLAIN, 12));
  FontMetrics fm = textPane.getFontMetrics(textPane.getFont());
  float charWidth = fm.charWidth('m');
  float tabWidth = charWidth * 4f;
  TabStop[] tabs = new TabStop[10];
  for (int j = 0; j < tabs.length; j++) {
    tabs[j] = createTabStop((j + 1) * tabWidth);
  }
  TabSet tabSet = new TabSet(tabs);
  // MutableAttributeSet attributes = new SimpleAttributeSet();
  MutableAttributeSet attributes = textPane.getStyle(StyleContext.DEFAULT_STYLE);
  StyleConstants.setTabSet(attributes, tabSet);
  // int length = textPane.getDocument().getLength();
  // textPane.getStyledDocument().setParagraphAttributes(0, length, attributes, false);
  textPane.setParagraphAttributes(attributes, false);
  textPane.setText("JTextPane\n0123\n\t4567\n\t\t89ab\n");

  JTextArea textArea = new JTextArea();
  textArea.setTabSize(4);
  textArea.setText("JTextArea\n0123\n\t4567\n\t\t89ab\n");

  add(new JScrollPane(textArea), BorderLayout.NORTH);
  add(new JScrollPane(textPane));
  setPreferredSize(new Dimension(320, 240));
}
 

@Override public void updateUI() {
  super.updateUI();
  setOpaque(false);
  putClientProperty(JEditorPane.HONOR_DISPLAY_PROPERTIES, Boolean.TRUE);
  EventQueue.invokeLater(() -> {
    // MutableAttributeSet attr = new SimpleAttributeSet();
    Style attr = getStyle(StyleContext.DEFAULT_STYLE);
    TabStop[] ts = {new TabStop(25f, TabStop.ALIGN_DECIMAL, TabStop.LEAD_NONE)};
    StyleConstants.setTabSet(attr, new TabSet(ts));
    setParagraphAttributes(attr, false);
  });
}
 

public JavaSourceDocument(String title, Reader in, SourceFile theSource) throws IOException {
    doc = new DefaultStyledDocument();
    this.title = title;
    this.sourceFile = theSource;
    Debug.println("Created JavaSourceDocument for " + title);
    try {
        dek.read(in, doc, 0);
    } catch (BadLocationException e) {
        throw new RuntimeException(e);
    }
    in.close();
    doc.putProperty(Document.TitleProperty, title);
    //        root = doc.getDefaultRootElement();
    Toolkit toolkit = Toolkit.getDefaultToolkit();
    FontMetrics fontMetrics = toolkit.getFontMetrics(sourceFont);
    TabStop[] tabs = new TabStop[50];
    float width = fontMetrics.stringWidth(" ");

    int tabSize = GUISaveState.getInstance().getTabSize();
    for (int i = 0; i < tabs.length; i++) {
        tabs[i] = new TabStop(width * (tabSize + tabSize * i));
    }
    TAB_SET = new TabSet(tabs);
    StyleConstants.setTabSet(commentAttributes, TAB_SET);
    StyleConstants.setTabSet(javadocAttributes, TAB_SET);

    StyleConstants.setTabSet(quotesAttributes, TAB_SET);

    StyleConstants.setTabSet(keywordsAttributes, TAB_SET);

    StyleConstants.setTabSet(commentAttributes, TAB_SET);

    StyleConstants.setTabSet(whiteAttributes, TAB_SET);
    StyleConstants.setFontFamily(whiteAttributes, sourceFont.getFamily());
    StyleConstants.setFontSize(whiteAttributes, sourceFont.getSize());
    StyleConstants.setLeftIndent(whiteAttributes, NumberedParagraphView.NUMBERS_WIDTH);

    doc.setParagraphAttributes(0, doc.getLength(), whiteAttributes, true);
    JavaScanner parser = new JavaScanner(new DocumentCharacterIterator(doc));
    while (parser.next() != JavaScanner.EOF) {
        int kind = parser.getKind();
        switch (kind) {
        case JavaScanner.COMMENT:
            doc.setCharacterAttributes(parser.getStartPosition(), parser.getLength(), commentAttributes, true);
            break;

        case JavaScanner.KEYWORD:
            doc.setCharacterAttributes(parser.getStartPosition(), parser.getLength(), keywordsAttributes, true);
            break;

        case JavaScanner.JAVADOC:
            doc.setCharacterAttributes(parser.getStartPosition(), parser.getLength(), javadocAttributes, true);
            break;

        case JavaScanner.QUOTE:
            doc.setCharacterAttributes(parser.getStartPosition(), parser.getLength(), quotesAttributes, true);
            break;

        default:
            break;
        }

    }

}
 

private static TabStop createTabStop(float pos) {
  return new TabStop(pos);
}
 

private MainPanel() {
  super(new BorderLayout());
  JCheckBox check = new JCheckBox("vertical grid lines", true);
  check.addActionListener(e -> repaint());

  JTextPane textPane = new JTextPane() {
    @Override protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      if (check.isSelected()) {
        int ox = getInsets().left;
        int h = getHeight();
        g.setColor(Color.RED);
        g.drawLine(ox, 0, ox, h);
        g.drawLine(ox + 100, 0, ox + 100, h);
        g.drawLine(ox + 200, 0, ox + 200, h);
        g.drawLine(ox + 300, 0, ox + 300, h);
        g.setColor(Color.ORANGE);
        g.drawLine(ox + 50, 0, ox + 50, h);
        g.drawLine(ox + 150, 0, ox + 150, h);
        g.drawLine(ox + 250, 0, ox + 250, h);
      }
    }
  };
  textPane.setText(String.join("\n",
      String.join("\t", "LEFT1", "CENTER1", "RIGHT1", "3.14"),
      String.join("\t", "LEFT22", "CENTER22", "RIGHT22", "12.3"),
      String.join("\t", "LEFT333", "CENTER333", "RIGHT333", "123.45"),
      String.join("\t", "LEFT4444", "CENTER4444", "RIGHT4444", "0.9876")));

  // MutableAttributeSet attr = new SimpleAttributeSet();
  Style attr = textPane.getStyle(StyleContext.DEFAULT_STYLE);
  StyleConstants.setTabSet(attr, new TabSet(new TabStop[] {
      new TabStop(0f, TabStop.ALIGN_LEFT, TabStop.LEAD_NONE),
      new TabStop(100f, TabStop.ALIGN_CENTER, TabStop.LEAD_NONE),
      new TabStop(200f, TabStop.ALIGN_RIGHT, TabStop.LEAD_NONE),
      new TabStop(250f, TabStop.ALIGN_DECIMAL, TabStop.LEAD_NONE)
      // new TabStop(300f, TabStop.ALIGN_BAR, TabStop.LEAD_NONE)
  }));
  textPane.setParagraphAttributes(attr, false);
  // textPane.getStyledDocument().setParagraphAttributes(0, textPane.getDocument().getLength(), attr, false);

  add(new JScrollPane(textPane));
  add(check, BorderLayout.SOUTH);
  setPreferredSize(new Dimension(320, 240));
}