SAP CLASS TYPES CONSTANTS documentation, setup help and example usage

ARTICLE

Data Types and Constants

Data Types

Independent Types
You can use the TYPES statement to define any number of your own ABAP data types within a class. Types are not instance-specific and are only available once for all the objects in the class.
In particular, it is possible to define data types in the public visibility section of global classes, which makes the use of type groups in this context obsolete.

Bound Data Types
Bound data types that occur as properties of instance or static attributes also belong to the static attributes of a class. After a LIKE addition, the class name can be used to access the properties of instance attributes (exceptions to this rule are the statements ASSIGN ... CASTING and
SELECT-OPTIONS ... FOR ). In addition, a reference variable can be used with an object component selector without the object having previously been generated.

Constants
Constants are special static attributes
for which values are specified when they are declared. These values cannot be changed later. Use the CONSTANTS

statement to declare constants. Constants are not instance-specific - they are only available once for all the objects in the class.
In particular, it is possible to declare constants in the public visibility section of global classes, which makes the use of type groups in this context obsolete.