j.l.classfile.ClassReader instance is exposed in the Class-File API through j.l.classfile.AttributeMapper::readAttribute method only.
ClassReader only purpose is to serve as a tool for reading content of a custom attribute in a user-provided AttribtueMapper.
It contains useful set of low-level class reading methods for user to implement a custom attribute content parser.

However methods ClassReader::thisClassPos and ClassReader::skipAttributeHolder are not necessary for a custom attribute content parsing and so redundant in the API.
Class-File API implementation internally use these methods, however they should not be exposed in the API.