Swing/TextFieldOnReadOnlyTextPane のバックアップ(No.1)

void insertQuestion(final JTextPane textPane, String str) {
  Document doc = textPane.getDocument();
  try{
    doc.insertString(doc.getLength(), str, null);
    final int pos = doc.getLength();
    System.out.println(pos);
    final JTextField field = new JTextField(4) {
      @Override public Dimension getMaximumSize() {
        return getPreferredSize();
      }
    };
    field.setBorder(BorderFactory.createMatteBorder(0,0,1,0,Color.BLACK));
    field.addFocusListener(new FocusListener() {
      @Override public void focusGained(FocusEvent e) {
        try{
          Rectangle rect = textPane.modelToView(pos);
          rect.grow(0, 4);
          rect.setSize(field.getSize());
          textPane.scrollRectToVisible(rect);
        }catch(BadLocationException ex) {
          ex.printStackTrace();
        }
      }
      @Override public void focusLost(FocusEvent e) {}
    });
    Dimension d = field.getPreferredSize();
    int baseline = field.getBaseline(d.width, d.height);
    field.setAlignmentY(baseline/(float)d.height);

    SimpleAttributeSet a = new SimpleAttributeSet();
    StyleConstants.setLineSpacing(a, 1.5f);
    textPane.setParagraphAttributes(a, true);

    textPane.insertComponent(field);
    doc.insertString(doc.getLength(), "\n", null);
  }catch(BadLocationException e) {
    e.printStackTrace();
  }
}