code: static final String getPayloadAsType(int typeInfo, ConstantPool pool) {
      if (getTag(typeInfo) == OBJECT_TAG) {
        return (String) pool.getConstantData(getPayload(typeInfo));
      }
      throw new IllegalArgumentException("expecting object type");
    }
docs: Treat the result of getPayload as a constant pool index and fetch the
  corresponding String mapped to it.
  
  Only works on OBJECT types.