Object Oriented ABAP

1.6 Inheritance
In OO ABAP we use an existing class to derive a new class (child class). The new class
contains the attributes of the parent class (derives according to the visibility of attributes
and methods) in addition to new attributes and methods added to it. The child class derives
all the attributes and methods declared in parent class as public visibility. The child class
cannot inherit private members. The protected members in parent class are derived in child
class but their visibility changes to private.
1.7 Interfaces
Interfaces are similarly defined as classes. They also contain attributes and methods. But
interfaces do not have implementation part. Their methods are implemented in the class
that implements the interface.
So we provide different implementation to the methods defined in the interface in different
class that implements that interface. This way polymorphism is achieved.
1.8 Binding in Object Oriented languages
It is the concept which determines the object‟s method to be invoked based on the
signature or parameters provided. It is important in case of invoking a method, which is
redefined in subsequent sub classes. As the level of hierarchy increases and the same
method is redefined in subclasses we need to know which method is called. When this
decision is made at run time it is called as Dynamic binding. When this decision is made at
compile time it is known as Static binding. In Java this concept is implemented using
concept of method overriding and in C++ there is concept of virtual functions. They help in
achieving dynamic binding. Similarly in OO ABAP we can redefine methods and use concept
of binding to invoke methods as per required.
Binding in OO ABAP
Suppose we need to redefine or override a method of a class in all sub classes inheriting
from it. We can take a pointer or reference variable to the base or parent class. This parent
class reference variable can take or refer to objects of the sub classes. Now to decide that
which method will be called upon while we are using this parent class reference variable, we
need to know about the concept of binding.
We define a reference variable as
Data : obj_a type ref to .
Here obj_a is a reference variable of type class
Creating the object
create object : obj_a.
Now obj_a refers to an object of class