Rule Definition
This is one of the main benefit and principle of Object-Oriented design and coding: Encapsulation. If direct access to object members is allowed through Public members, there is a significant increase of the cost and risk of changes as well as an increase of security risks. However, a public member can be flagged with the READ-ONLY attribute in order to avoid external modification.

Remediation
General way is to implement methods to access Data Members. However, if the member is mainly read by external methods, then you can use the READ-ONLY attribute.

Violation Code Sample

CLASS table_content DEFINITION.
  PUBLIC SECTION.
     METHODS: calc_spfli,
                       calc__sflight.
     DATA: wa_spfli TYPE spfli,
                 wa_sflight TYPE sflight.
                 wa_disp TYPE i.
ENDCLASS

Fixed Code Sample

CLASS table_content DEFINITION.
  PUBLIC SECTION.
     METHODS: calc_spfli,
                         calc__sflight,
* Define accessors to members
                         get_spfli,
                         get_sflight.
     DATA: wa_disp TYPE i read-only.
  PRIVATE SECTION.
     DATA: wa_spfli TYPE spfli,
                 wa_sflight TYPE sflight.
ENDCLASS

ABAP Objects - An Introduction to Programming SAP Applications Horst Keller & Sascha Kreger SAP PRESS