Before diving into object-oriented programming let try to understand some concepts that will help you later in the articles.
Encapsulation
Encapsulation is the process of combining logically related procedure and data in one class/objects. This way, each object is insulated (separated, protected) from the rest of the program. Because the object is only using data contained within it or passed to it. And it executes only internal procedures. It does not contain any global or public variables, and does not require any external procedures to execute its members. The data and behaviors of an encapsulated object can only be accessed and manipulated through its properties and public methods. Thus encapsulation provides several advantages for you as a programmer. You can protect data from corruption by other objects or parts of the program. You can hide low-level, complex implementation details from the rest of the program, which results in the ability to implement a simple public interface to a more complex set of private member. It is also easier to maintain legacy code or add new members to the object without affecting any procedures that currently call the object. You can to debug individual object and ensure that a bug in one object will not affect some other part of the system in an apparently unconnected way. And lastly, you can reuse the object or by other programmer, improving the productivity.
Polymorphism
Polymorphism is the ability of different classes to expose similar (or identical) interfaces to the outside. The most unmistakable kind of polymorphism in Visual Basic is forms and controls. For example, TextBox and PictureBox controls are completely different objects, but they have some properties and methods in common, such as Left property and Move method. As a programmer, you don't need to worry about how they implement its functionality, instead, all you have to do is to apply it to a supported object and pass a correct value as arguments.
Inheritance
Inheritance is the ability to derive a new class (the derived or
inherited class) from another class (the base class). The derived class automatically
inherits the properties and methods of the base class. For example, you could
define a generic Person class with properties such as FirstName and
Lastname and
then use it as a base for more specific classes (for example, Student, Faculty,
and so on) that inherit all those generic properties. You could then add
specific members, such as BirthDate and StudentID for the
Student class and
FacultyID for the Faculty class. Thus it reduce the amount of code
on your class itself, therefore simplifies
the job of the class author. Unfortunately, Visual Basic doesn't support
inheritance, at least not in its more mature form of implementation inheritance.
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