Narrrow casting and Wide Casting in ABAP OOPs

REPORT  zcl_oops_test.

*----------------------------------------------------------------------*
*       CLASS cl_super DEFINITION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS cl_super DEFINITION.
  PUBLIC SECTION.

    DATA: sum TYPE i,
          mul TYPE i.

    METHODS:
      calci IMPORTING num1 TYPE i
                     num2 TYPE i.

ENDCLASS.                   

*----------------------------------------------------------------------*
*       CLASS cl_super IMPLEMENTATION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS cl_super IMPLEMENTATION.
  METHOD calci.
    sum = num1 + num2.

    WRITE:/ 'Addition of two numbers = '.
    WRITE: sum.
  ENDMETHOD.                   
ENDCLASS.                    

*----------------------------------------------------------------------*
*       CLASS cl_sub DEFINITION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS cl_sub DEFINITION INHERITING FROM cl_super.
  PUBLIC SECTION.
    DATA: num3 TYPE i.
    METHODS:
    calci REDEFINITION.

ENDCLASS.                    

*----------------------------------------------------------------------*
*       CLASS cl_sub IMPLEMENTATION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS cl_sub IMPLEMENTATION.
  METHOD calci.
    mul = num1 * num2 * num3.
    WRITE:/ 'multiplication of three numbers ='.
    WRITE: mul.
  ENDMETHOD.                   
ENDCLASS.                    

DATA:
  obj_super  TYPE REF TO cl_super,
  obj_sub    TYPE REF TO cl_sub,
  obj1_super TYPE REF TO cl_super.

START-OF-SELECTION.
  CREATE OBJECT obj_super.
  CREATE OBJECT obj_sub.
  CREATE OBJECT obj1_super.

  CALL METHOD obj_super->calci
    EXPORTING
      num1 = 10
      num2 = 10.


******Narrow casting
  obj_sub->num3 = 5.
  obj_super = obj_sub. 


  CALL METHOD obj_super->calci
    EXPORTING
      num1 = 10
      num2 = 5.


****** Wide casting
  obj_super ?= obj1_super.

  CALL METHOD obj_super->calci
    EXPORTING
      num1 = 10
      num2 = 10.

Output