Visual Basic 2012 Programmer's Reference

CLASSES

A class is a programming entity that gathers together all of the data and behavior that characterizes some sort of programming abstraction. It wraps the abstraction in a nice, neat package with well-defined interfaces to outside code. Those interfaces determine exactly how code outside of the class can interact with the class. A class determines which data values are visible outside of the class and which are hidden. It determines the routines that the class supports and their availability (visible or hidden).

A class defines properties, methods, and events that let the program work with the class:

• A property is some sort of data value. It may be a simple value (such as a name or number), or it may be a more complex item (such as an array, collection, or object containing its own properties, methods, and events).
• A method is a subroutine or function. It is a piece of code that makes the object defined by the class do something.
• An event is a notification defined by the class. An event calls some other piece of code to tell it that some condition in a class object has occurred.

For a concrete example, imagine a Job class that represents a piece of work to be done by an employee. This class might have the properties shown in the following table.

PROPERTY	PURPOSE
JobDescription	A string describing the job
EstimatedHours	The number of hours initially estimated for the job
ActualHours	The actual number of hours spent on the job
Status	The job’s status (New, Assigned, ...