Program Structure

• Each ABAP program starts with an introductory statement.

• The functions of an ABAP program are implemented in processing blocks. Processing blocks are defined using modularization statements. You can use declarative statements in processing blocks of the type procedure to define local data types and data objects. The other processing blocks do not have a local data area, and any declarative statements apply to the program globally. Methods play a special role here: Methods are processing blocks that have to be implemented within the implementation section of their class. The order of the processing blocks or implementation sections is irrelevant for program execution, but should be designed to make the program easy to read.

• Every ABAP program provides predefined data types, data object and predefined functions.

• Following the introductory statement, every program contains a global declaration section, in which you implement the definitions and declarations that are valid and visible in the entire program. This includes the declaration of data types and data objects, as well as the definition of interfaces or the declaration section of classes in ABAP Objects. The definitions of interfaces and classes contain the declarations of their components. While the order of the individual definitions and declarations is not specified, you have to take into account that an ABAP statement can only refer to existing definitions and declarations. For example, a reference variable can only refer to a previously defined class, which in turn can only implement a previously defined interface. Once you introduce a procedure, you can declare the data types and data objects that will be visible within that procedure.In the broadest sense, the declaration of data types also includes the typing of objects whose data type is undetermined when the program is written.

• All the other statements of an ABAP program are implementation statements, which can always be assigned to a processing block. You use the implementation statements to implement the functions of a processing block. The functions of all processing blocks are largely implemented using the same statements.

• Since ABAP is a language that has grown over time, it contains several obsolete additions to statements that have been replaced with improved language constructs, but which have not been eliminated in order to ensure downward compatibility. In ABAP Objects - that is, in the implementation of methods -, almost all of the obsolete language elements will fail syntax checks. In general, you should no longer use these language elements in new programs, but you may to encounter them in older programs.