In ABAP OOP, we can nest classes in three ways:
- A class as an attribute of the class
- Inheritance
- Using interfaces
Interfaces are not really a full class. This is due to the fact that, in interfaces, we have only a definition of a class without any implementation. This is important because interfaces in ABAP allow us to implement multi-inheritance. However, we'll turn to that in a moment, in the Inheritance and Interfaces section.
All examples will be shown as a global class created in SE24.
We can create a class as an attribute of the class. To create that attribute, we need to add an attribute, which is typed as TYPE REF TO. In our example, we'll create an attribute as a reference to the ZCL_ENGINE class:
In the preceding example, we created an attribute named GR_ENGINE as an attribute of the ZCL_AUTO class. After the instantiation of ZCL_AUTO and the initialization of its GR_ENGINE attribute, a new object of the ZCL_ENGINE class is created inside...