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OO ABAP – Interfaces and Polymorphism

May 2, 2016March 18, 2016 by Carlos Mendoza

Interfaces are simply superclasses that cannot be instantiated, do not have an implementation part, and only have public components.
This video will teach you how to define and implement interfaces to use polymorphism in ABAP.

Interfaces

The only real difference between interfaces and inheritance is the role they play. The programming advantages are thus the same as for inheritance.
Interfaces differ from regular inheritance in their area of use. In terms of programming, there are hardly any differences, however.
From a technical point of view, interfaces are simply superclasses that:
- cannot be instantiated,
- do not have an implementation part,
- and only have public components
In ABAP Objects, interfaces primarily serve to define uniform interfaces for services.
Interfaces contain no implementations.
In ABAP Objects, the same components can generally be defined in interfaces and in classes.

Use of Interfaces

Some typical use cases of interfaces are:
- You want to allow for the option of having multiple classes implementing a service in different
  ways, but using the same method names.
  - With regular inheritance, you would define such a method in the shared superclass. However, if you cannot model a superclass suitably for inheritance, you need to define an interface and then define this method there.
- Classes implement interfaces as follows:
  - The interface name is listed in the definition part of the class with the INTERFACES statement. This must be in the PUBLIC SECTION, that is, interfaces can only be implemented publicly.
  - The interface methods must be implemented in the implementation part of the class.
  - The components defined in the interface can be addressed in the implementation part of the class.

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Preview – OO ABAP: Inheritance & Casting

May 2, 2016March 11, 2016 by Carlos Mendoza

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Inheritance is an implementation relationship that emphasizes similarities of the classes. In this video you will learn how to create class hierarchies using ABAP Objects.
After watching this video you will be able to:
1. Define inheritance relationships between classes
2. Redefine methods
3. Understand the basics of casting

Introduction to OO Concepts

Object oriented concepts are the basic programming techniques common to all object-oriented languages.
As far as these concepts are concerned, the only difference between ABAP Objects and other languages like Java or C++ is the syntax.
You can only capitalize on the strengths of object-oriented programming if you use all of the concepts in the intended manner.

Inheritance & Casting

What is Inheritance?

Different kinds of objects often have a certain amount in common with each other.
Cars, trucks, and buses, for example, all share the characteristics of vehicles (current speed, current gear).
Yet each also defines additional features that make them different:
- For example, trucks carry cargo and have more tires than a car
- Buses carry more passengers than trucks and cars.

Inheritance: is the concept that when a class is defined, any subclass that is defined can inherit the definitions of that class.

There is no multiple inheritance in ABAP Objects. However, you can use interfaces in ABAP Objects to simulate multiple inheritance.

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Preview – OO ABAP: Constructors

May 2, 2016March 9, 2016 by Carlos Mendoza

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Constructors are methods that are generally called implicitly when a class is instantiated or defined.
This video will teach you about instance and static constructors in ABAP.

Constructors

Constructors are methods that are not generally called explicitly (CALL METHOD or its short form), but are called implicitly.
The constructor is a special instance method in a class and is always named CONSTRUCTOR. This abbreviated term actually means the instance constructor.
The constructor is automatically called at runtime with the CREATE OBJECT statement.

A constructor is necessary when, after the instantiation of a class:

You need to allocate resources
You need to initialize attributes
You need to modify static attributes
You need to send messages containing the information that a new object was created

Instance Constructors

Each class can have no more than one (instance) constructor
The constructor must be defined in the public area
The constructor’s signature can only have importing parameters and exceptions
When exceptions are raised in the constructor, instances are not created, so no main memory space is occupied
Except for one exceptional case, you cannot normally call the constructor explicitly
There is no destructor in ABAP Objects.