ALV programming in ABAP

What is ALV programming in ABAP?  When is this grid used in ABAP? - 

• ALV is Application List viewer. Sap provides a set of ALV (ABAP LIST VIEWER) function modules which  can be put into use to embellish the output of a report. This set of ALV functions is used to enhance the readability and functionality of any report output. Cases arise in sap when the output of a report contains columns extending more than 255 characters in length. In such cases, this set of ALV functions can help choose selected columns and arrange the different columns from a report output and also save different variants for report display. This is a very efficient tool for dynamically sorting and arranging the columns from a report output. The report output can contain up to 90 columns in the display with the wide array of display options.

Sap provides a set of ALV (ABAP LIST VIEWER) function modules which can be put into use to embellish the output of a report. This set of ALV functions is used to enhance the readability and functionality of any report output. Cases arise in sap when the output of a report contains columns extending more than 255 characters in length. 
In such cases, this set of ALV functions can help choose selected columns and arrange the different columns from a report output and also save different variants for report display. This is a very efficient tool for dynamically sorting and arranging the columns from a report output. 
The report output can contain up to 90 columns in the display with the wide array of display options.
The commonly used ALV functions used for this purpose are;
1. REUSE_ALV_VARIANT_DEFAULT_GET
2. REUSE_ALV_VARIANT_F4
3. REUSE_ALV_VARIANT_EXISTENCE
4. REUSE_ALV_EVENTS_GET
5. REUSE_ALV_COMMENTARY_WRITE
6. REUSE_ALV_FIELDCATALOG_MERGE
7. REUSE_ALV_LIST_DISPLAY
8. REUSE_ALV_GRID_DISPLAY
9. REUSE_ALV_POPUP_TO_SELECT
Purpose of the above Functions are differ not all the functions are required in all the ALV Report. 
But either no.7 or No.8 is there in the Program. 
How you call this function in your report?
After completion of all the data fetching from the database and append this data into an Internal Table. say I_ITAB.
Then use follwing function module.
CALL FUNCTION 'REUSE_ALV_GRID_DISPLAY'
       EXPORTING
            I_CALLBACK_PROGRAM       = 'Prog.name'
            I_STRUCTURE_NAME         = 'I_ITAB'
            I_DEFAULT                = 'X'
            I_SAVE                   = 'A'
       TABLES
            T_OUTTAB                 = I_ITAB.
  IF SY-SUBRC <> 0.
    WRITE: 'SY-SUBRC: ', SY-SUBRC .
  ENDIF.
ENDFORM.                    " GET_FINAL_DATA

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