The TextAtribute.SUPERSCRIPT does not appear to be super or sub scripting text. To reproduce compile and run the attached program. Snippet :

        as.addAttribute(TextAttribute.SUPERSCRIPT,
                        TextAttribute.SUPERSCRIPT_SUB, 0, 10);
        as.addAttribute(TextAttribute.SUPERSCRIPT,
                        TextAttribute.SUPERSCRIPT_SUPER, 10, s.length());