Data Types and Data Objects
Together with classes and objects, data types and data objects are the
essentials of ABAP programming.
Data Type
A data type describes a data object, just as a class describes an
object. In this sense, a data type is comparable with a class without
methods. ABAP interprets the content of a data object in accordance
with its data type. Data types exist either bound as a property of data
objects or independently. Independent data types can be defined either
in ABAP Dictionary or using the TYPES statement in an ABAP
program.
Data Object
A data object is an instance of a data type, just as an object is an
instance of a class. It exists in the internal session of an ABAP
program or as a shared object in the shared memory and
occupies memory there for the contained data. A data object is generated
either implicitly when a program or procedure is loaded (named data
object), or by using the CREATE DATA statement (anonymous data
object). Named data objects are either variables ( DATA ,
CLASS-DATA statements, and so on) or constants ( CONSTANTS
statement).
A data type describes the technical properties of a data object (for
example, the elementary types it is comprised of, its length) and
semantic properties (what type of entity is represented by the data
object). Types that are defined in ABAP dictionary have additional
properties, for example for input/output on a classic dynpro or in Web
Dynpro.
As far as the ABAP runtime environment is concerned, only the technical
properties of a data object are of interest for program execution.
However, the semantic information, which is linked to the appropriate
use of types, is essential for the legibility of the source code. For
this reason, some of the rules covered in this section could also fall
under the heading Structure and Style ,
since this covers not only robustness, but also good style, which,
although it does not affect program execution, is nevertheless
significant for readability and maintainability.
Bound and Standalone Data Types
Declaration of Data Types and
Constants
Declaration of Variables
Inline Declarations
Including Structures
Using Types
Reference to Data Types or Data Objects
Table Work Areas
Literals
Strings
Start Values
Data Objects for Truth Values
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