BACS 287 Basics of Object-Oriented Programming 1

BACS 287 What is Object-Oriented Programming? An approach to programming that combines data and procedures into a single unit (i.e., an object) This produces a tight coupling between the data and the logic that acts upon the data Results in natural modular programs that promote code reuse

BACS 287 What is Object-Oriented Programming? Objects can be grouped into hierarchies (i.e., trees) that share characteristics via inheritance The definition of a type of object is called a class The template of the objects and their inheritance relationships is called the class hierarchy

BACS 287 What is Object-Oriented Programming? Visual Basic is an object-oriented language True object-oriented languages involve 3 core concepts: – Inheritance – Encapsulation – Polymorphism

BACS 287 Object-Oriented Inheritance Enables you to create a new object based upon an existing object merely my stating what is different This is called sub-classing Example: Class: Vehicle – Sub-Classes: Car, Boat, Airplane The sub-classes share the basic attributes of vehicle but have differences. The differences are said to “specialize” the super-class.

BACS 287 Object-Oriented Encapsulation Means hiding the implementation details within an object Only the methods and properties needed to make the object perform are exposed to the application (i.e., the “outside world”) Enables conceptual abstraction Visual Basic supports encapsulation well

BACS 287 Object-Oriented Polymorphism Enables different objects to respond to the same message in different ways Each object type does whatever is most appropriate for the data it contains For Example: the ADD message would produce different results in objects that held dates, times, strings, and numbers

BACS 287 Object-Oriented Terminology Class Sub-class Class Hierarchy Inheritance Object (instance) – Properties – characteristic of the object – Methods – procedure that an object to perform – Events – actions or situations that trigger methods

BACS 287 Object-Oriented Terminology Message – what the event sends to the method to trigger it to execute Encapsulation Polymorphism Conceptual abstraction – hiding unnecessary details Code reuse Collection – group of objects with something in common

BACS 287 Object-Orientation and Event-Driven Programming Event-Driven programming and Object- Oriented programming are closely related The event model of the programming language determines the events that the objects can respond to It is possible to separate the two concepts, but this is normally not done

BACS 287 Quiz What are the 3 key characteristics of an object-oriented language? What is meant by “conceptual abstraction” How is “polymorphism” related to the class hierarchy? What does an “event” trigger? Is Visual Basic a “true” object-oriented language?