FORM vs Method vs Function Module

Explanation

FORM subroutines are procedural, share the program's global state and cannot be unit-tested cleanly — reserved for legacy maintenance. Methods (in local or global classes) support encapsulation, exceptions and ABAP Unit tests. Function modules are still required for RFC/BAPI/tRFC/qRFC and update tasks. New code should default to classes.

Code example

CLASS lcl_order DEFINITION.  PUBLIC SECTION.    METHODS confirm IMPORTING iv_id TYPE vbeln_va                    RAISING zcx_order.ENDCLASS.

Real project scenario

Rewriting order-confirmation FORMs as service class methods enabled ABAP Unit tests and cut regression bugs.

Common mistakes

Creating new FORMs; using FMs for pure in-system logic; putting business logic in includes.

Best practices

Use classes for new code; keep FMs only for RFC and update-task boundaries.

Interview angle

Why is dependency injection easier with classes?