static String isField(ClassPool pool, ConstPool cp, CtClass fclass,
                          String fname, boolean is_private, int index) {
        if (!cp.getFieldrefName(index).equals(fname))
            return null;

        try {
            CtClass c = pool.get(cp.getFieldrefClassName(index));
            if (c == fclass || (!is_private && isFieldInSuper(c, fclass, fname)))
                return cp.getFieldrefType(index);
        }
        catch (NotFoundException e) {}
        return null;
    }