Showing posts with label encapsulation. Show all posts
Showing posts with label encapsulation. Show all posts
Saturday, June 23
Function groups and now Objects in the new ABAP Objects language
The center of
ABAP Objects are Objects. Any object oriented language focuses on objects and
hence maps objects with the real world entities. After release 3.1 of SAP WAS
ABAP, BOR or the business object repository contains objects. Examples of
objects are customers, invoice, order etc. These are contained in the BOR as
examples.
Function Groups
and function modules were like objects in ABAP versions before ABAP objects was
introduced. Function groups contain function modules. FMs can be treated as
services or functions of the objects. Also the global data of function groups
formed the attributes of the objects. For example: an FG which processes Sales
orders has many FMs within it and global data declared. Global data can be
accessed by the FMs within the FG. This ensures encapsulation. The data (global
data) and the services (FMs) are combined within a FG.
ABAP programs
hold a specific amount of memory art runtime. Similarly when a FM is called, it
loads its corresponding FG and global data into memory. One ABAP program can
call multiple FMs from several FGs and hence multiple internal ABAP sessions
can run and memory occupied.
As already
said, When a FM is called, its FG with global data is loaded into memory. This
instance of FG can be treated as Object when we look at this from the Object
orientation perspective. So the instance of function group is an interface
between the user and function module. Function groups global data can be
accessed via function modules only. If Function groups and function modules can
be used for object orientation of a program then why ABAP Objects was introduced?
The answer is below.
In classical
ABAP, a program can work with many instances of different function groups.
But it is not
possible to work on many instances of a single function group at a time.
ABAP Objects
allow the user to work with many instances of a class.
For example :
You are supposed to develop a ABAP program which can process many sales orders
at the same time. It is not possible to do so with function groups philosophy.
You would instead need a class and several objects of that class. Each object at
that time would represent a Sales Order.
So now with the
new ABAP objects, you can load multiple instances of the same Class using
CREATE OBJECT statement. ABAP accesses the interface of the instance using
Object’s reference.
Introduction to Object Orientation
Software systems are defined by data
and functionality. In a non object oriented system, functionality and data and
treated separately. The focus in such a system remains on functionality. On the
other hand, object oriented systems data and functionality are combined
together using objects. Objects are concrete representation of real world
things. So in a object oriented systems, developer need to map real world
things with software objects and they need to define functions a of each object
in such a manner that it reflects its behavior in the real world.
Typical objects in a SAP software
system can be Invoice, Customer, order etc. It is not possible to introduce
Object orientation with this small article.
Objects
Objects are formed out of classes.
Class is the structure of object. For example, cuckoo belongs to the bird
class, Amazon belongs to the river class. Objects have attributes (also called
its characteristics) and functions or services. The services of an object work
upon the attributes of the object to change the value of attributes. Attributes
and services can be private, public or protected.
Classes
As already described, classes are
structure of objects. Any number of objects can be formed out of a class. Each object has its own values of
its attributes.
Object
References
Object references are not the real
objects but their references. So you can very well access data and services of
object using its reference.
Abstraction
The implementation of objects is not
visible to the users. Users see only the data and services of the object. But
how the services manipulate the data is unknown to the user of the object, such
feature is called encapsulation. For example : Tata innova and Maruti are
objects of the car class and Average is a service of car class. Average returns
different value for both these objects. But how it calculates the average of
the car if unknown. User only knows the name of the service, the data it takes
and the result it gives.
Inheritance
New classes can be formed from
existing classes. This feature of object orientation is called inheritance. The
new class thus formed is called derived class. Derived class has data and
functions of the parent class. But it can overwrite data and functions of the
parent class.
Polymorphism
In ABAP Objects, polymorphism is
implemented by redefining methods during inheritance and by using
constructs called interfaces. Identical methods behave differently in
different classes. Polymorphism means same method behaves differently in different classes.
Polymorphism is a great feature of Object oriented technology. Code written using polymorphism is easy to maintain. With polymorphism, the developer writes a general interface and not a concrete implementation. Change in the requirement of the client can be handled very easily if the program developed has polymorphism feature in it.
Polymorphism is a great feature of Object oriented technology. Code written using polymorphism is easy to maintain. With polymorphism, the developer writes a general interface and not a concrete implementation. Change in the requirement of the client can be handled very easily if the program developed has polymorphism feature in it.
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