The StyleConstants class is full of helper methods to simplify setting attribute sets.
Instead of calling the following to make the SimpleAttributeSet both bold and italic:
attributes.addAttribute(StyleConstants.CharacterConstants.Bold, Boolean.TRUE)
attributes.addAttribute(StyleConstants.CharacterConstants.Italic, Boolean.TRUE)
You could use the following:
StyleConstants.setBold(attributes, true);
StyleConstants.setItalic(attributes, true);