Computer Programming Concepts and Visual Basic David I. Schneider

4. Methods can be either Function or Sub procedures. A method that returns a
value must be a Function procedure; otherwise it can be a Sub procedure.
5. A program with a class module has at least three components: a form, form
code, and class module code. Although the View menu gives you access to the
form (Alt/V/B) and the form code (Alt/V/C), only the Project Explorer gives
access to all three. To view the code for a class module, double-click on the
name of the class in the Project Explorer.
6. A class module is saved in a file whose file name has the extension .cls. Therefore,
classes have both a name (Csomething) and a file name (something.cls).
7. To insert an existing (saved) class module into a program, click on Add Class
Module in the Project menu, click on the Existing tab, and enter the filespec for
the class module.
8. To delete a class from a program, right click on the class name in the Project
Explorer and click on Remove className.
9. An object also can be declared with a statement of the form
Private pupil As Object
However, objects so declared require more time and effort for Visual Basic to
access.
10. The set of properties, methods, and events for a class is called the class interface.
The classes CStudent and CPFStudent have the same interface, even
though they carry out the task of computing a grade differently. The programmer
need only be aware of the SemGrade method and needn’t be concerned
about its implementation. The feature that two classes can have behaviors that
are named the same and have essentially the same purpose but different implementations
is called polymorphism.
11. Sometimes you will have difficulty deciding whether an interface item should
be a property or a method. As a rule of thumb, properties should access data and
methods should perform operations.
12. The ByVal (which stands for “by value”) keyword is automatically inserted
before parameters in Property Let statements invoked from the Tools menu.
However, this keyword is optional. The default way of passing an argument to
a parameter is ByRef (which stands for “by reference”). Usually, passing by
value is more efficient than passing by reference.
13. The default parameter name in a Property Let procedure is vNewValue.
Although we usually substitute a meaningful name, we retain the convention of
beginning the name with the prefix v.
14. We could have preceded our member variables with the keyword Public and
allowed direct access to the variables. However, this is considered poor programming
practice. By using Property Let procedures to update the data, we
can enforce constraints and carry out validation.
15. In a class module, a property is implemented by two procedures, one to set and
the other to retrieve the property value. These procedures that access properties
are sometimes referred to as accessor methods.
12.2 COLLECTIONS AND EVENTS
Collections and Events 365
“An object without an event is like a telephone without a ringer.”
Anonymous
A collection is an entity, similar to an array, that is especially well-suited to working with sets
of objects. This section discusses collections of objects and user-defined events for classes.