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Lesson 2 Companion — Internal Tables, Loops & Methods ​

1. Internal table vs database table ​

An internal table is program memory. A database table is persistent storage. Students should not call internal-table operations database CRUD.

text
Internal table → temporary ABAP data
Database table → persistent data (introduced later)

2. Why WITH EMPTY KEY ​

For simple lists where no table-key lookup is intended, an explicit empty key avoids accidental dependence on ABAP's standard-key rules.

3. VALUE vs APPEND ​

VALUE is excellent for construction. A loop with procedural updates is often easier to debug than a dense expression. Modern ABAP is not a competition to remove every statement.

4. sy-tabix ​

It is valid for index-table processing. It is not a stable business identifier and behaves differently with hashed keys.

5. Table expressions ​

abap
itab[ 2 ]

is modern and concise. Missing lines can raise CX_SY_ITAB_LINE_NOT_FOUND; code should only assume success when the contract guarantees the line.

6. Functional methods ​

A method with exactly one RETURNING result can be used in expressions:

abap
DATA(total) = sum_numbers( numbers ).

Named parameters remain preferable when several parameters could be confused.

7. Reference implementation ​

abap
CLASS zcl_abap_l02_### DEFINITION
  PUBLIC
  FINAL
  CREATE PUBLIC.

  PUBLIC SECTION.
    INTERFACES if_oo_adt_classrun.

    TYPES tt_numbers TYPE STANDARD TABLE OF i WITH EMPTY KEY.

    METHODS sum_numbers
      IMPORTING numbers TYPE tt_numbers
      RETURNING VALUE(total) TYPE i.

    METHODS rectangle_area
      IMPORTING width TYPE decfloat34 height TYPE decfloat34
      RETURNING VALUE(area) TYPE decfloat34.

ENDCLASS.

CLASS zcl_abap_l02_### IMPLEMENTATION.

  METHOD sum_numbers.
    LOOP AT numbers INTO DATA(number).
      total += number.
    ENDLOOP.
  ENDMETHOD.

  METHOD rectangle_area.
    area = width * height.
  ENDMETHOD.

  METHOD if_oo_adt_classrun~main.
    DATA(numbers) = VALUE tt_numbers( ( 5 ) ( 10 ) ( 15 ) ( 20 ) ).
    out->write( |Total: { sum_numbers( numbers ) }| ).

    DATA(area) = rectangle_area(
      width  = CONV decfloat34( '5.5' )
      height = CONV decfloat34( '4' )
    ).
    out->write( |Area: { area }| ).
  ENDMETHOD.

ENDCLASS.

8. Empty-table design ​

For min/max methods, decide the contract for an empty table. Options later include returning an optional result structure or raising a class-based exception. Do not silently rely on line 1 if empty input is possible.

SAP references ​