What is Object Orientation?
Object orientation (OO), or to be more precise, object-oriented programming, is a problem-solving method in which the software solution reflects objects in the real world.
A comprehensive introduction to object orientation as a whole would go far beyond the limits of this introduction to ABAP Objects. This documentation introduces a selection of terms that are used universally in object orientation and also occur in ABAP Objects. In subsequent sections, it goes on to discuss in more detail how these terms are used in ABAP Objects. The end of this section contains a list of further reading, with a selection of titles about object orientation.
An object is a section of source code that contains data and provides services. The data forms the attributes of the object. The services are known as methods (also known as operations or functions). Typically, methods operate on private data (the attributes, or state of the object), which is only visible to the methods of the object. Thus the attributes of an object cannot be changed directly by the user, but only by the methods of the object. This guarantees the internal consistency of the object.
Classes describe objects. From a technical point of view, objects are runtime instances of a class. In theory, you can create any number of objects based on a single class. Each instance (object) of a class has a unique identity and its own set of values for its attributes.
In a program, you identify and address objects using unique object references. Object references allow you to access the attributes and methods of an object.
In object-oriented programming, objects usually have the following properties:
Objects restrict the visibility of their resources (attributes and methods) to other users. Every object has an interface, which determines how other objects can interact with it. The implementation of the object is encapsulated, that is, invisible outside the object itself.
Identical (identically-named) methods behave differently in different classes. Object-oriented programming contains constructions called interfaces. They enable you to address methods with the same name in different objects. Although the form of address is always the same, the implementation of the method is specific to a particular class.
You can use an existing class to derive a new class. Derived classes inherit the data and methods of the superclass. However, they can overwrite existing methods, and also add new ones.
Uses of Object Orientation
Below are some of the advantages of object-oriented programming:
Achieving these goals requires:
Object-oriented programming techniques do not necessarily depend on object-oriented programming languages. However, the efficiency of object-oriented programming depends directly on how object-oriented language techniques are implemented in the system kernel.
Object-oriented tools allow you to create object-oriented programs in object-oriented languages. They allow you to model and store development objects and the relationships between them.
The object-orientation modeling of a software system is the most important, most time-consuming, and most difficult requirement for attaining the above goals. Object-oriented design involves more than just object-oriented programming, and provides logical advantages that are independent of the actual implementation.
This section of the ABAP User’s Guide provides an overview of the object-oriented extension of the ABAP language. We have used simple examples to demonstrate how to use the new features. However, these are not intended to be a model for object-oriented design. More detailed information about each of the ABAP Objects statements is contained in the keyword documentation in the ABAP Editor. For a comprehensive introduction to object-oriented software development, you should read one or more of the titles listed below.
There are many books about object orientation, object-oriented programming languages, object-oriented analysis and design, project management for OO projects, patterns and frameworks, and so on. This is a small selection of good books covering the most important topics:
A very good introduction to object orientation for programmers. It provides comprehensive explanations of all essential OO concepts, and contains a procedure model for learning OO quickly and thoroughly. It is easy to read and practical, but still theoretically-founded.
A good book about all of the non-technical aspects of OO that are equally important for effective object-oriented programming. Easy to read and full of practical tips.
An excellent book about UML (Unified Modeling Language - the new standardized OO language and notation for modeling). Assumes knowledge and experience of object orientation.
Provides a pattern, showing how recurring design problems can be solved using objects. This is the first big pattern book, containing many examples of good OO design.
A collection of articles addressing the many questions and problems of OO analysis and design, implementation, dependency management, and so on. Highly recommended.
If you are new to object-orientation, you should read Scott Ambler’s ‘The Object Primer’ and then acquire some practical experience of your own. You should definitely use the CRC techniques described by Ambler and Fowler for object-oriented analysis and design. After this, you should learn UML, since this is the universal OO analysis and design notation. Finally, you should read at least one book about patterns.
At the beginning of a large OO project, the question immediately arises as to the sequence in which things should be done, which phases should be finished at what time, how to divide up and organize the development work, how to minimize risks, how to assemble a good team, and so on and so forth. Many of the best practices of project management have had to be redefined for the object-oriented world, and the opportunities that this has produced are significant. For further information about how to use OO in project management, see Grady Brooch’s book ‘Object solutions’, or the chapter entitles ‘An outline development process’ from Martin Fowler’s book.
There are, of course, many other good books about object orientation. The above list does not claim either to be complete, or necessarily to recommend the best books available.