3. Some important basic concepts of 
the object-oriented programming 
languages 
The object-oriented programming (OOP) language is 
usually called "4th generation language" (4GL) in 
computer science, some various languages are available 
in the market now, such as: Smalltalk, Turbo Pascal for 
Windows, Borland C++, MS Visual C++, MS Visual 
Basic,..., etc. Because OOP languages have developed 
in the last ten years, it is rather new and it has not yet 
reached a common standard recognized. Therefore, 
some of them have more OOP mechanisms, some less. 
Although the "Visual Basic" is not à complete OOP 
language, it has touched some key concepts of the 
OOP, and it is developing further in this direction and will 
have more OOP mechanisms). It is said that the "Visual 
Basic' is the best language compared with many other 
languages which he has ever seen and used. The reason 
is that it has made the full use of the windows' graphic 
user interface (GUI). 
The "Visual Basic" (VB) language is used and some 
important basic concepts of it compared with the other 
OOP languages are briefly introduced: 
3.4 Object 
Object includes data and procedure that are manipulated 
by the object and are encapsulated in the object, that is, 
the window or window body in the VB. In traditional 
programming, sequence of the procedure and control 
mechanism determine the control flow of the program. 
This flow then provides the method for how to organize 
the whole program in the programming creation period. 
Therefore, it is quite unrealistic and cumbersome when 
the dynamic world entities are involved in the programs. 
The world is changing rapidly. Therefore, we should 
adapt our thought and the data model to the changeful 
world. To grasp the logical relationships between the 
objects is the better choice. The OOP has precisely 
grasped the relationships between the objects. To send 
and receive the messages to and from the objects 
determine the control flow of the programs of the OOP. 
The object can understand the communication 
relationships between each unit in the program through 
the messages sent. The object responds the message 
sent, and sends the message to the other object. it is the 
message flow in the whoie system rather than the data. 
it is not “to cali a function to act to some data” 
(traditional viewpoint), but it is "to send a message to an 
object” (OOP viewpoint) For example, many 
programming mechanisms in the VB are to change the 
properties of the object, to send the message to the 
other object and to write programming codes for 
responding. Although it sounds quite complex, you will 
find that they simplify the programming efforts by using 
the GUI very well. 
3.2 Encapsulation 
Encapsulation has two different viewpoints: one is from 
the programming itself and one is from the programming 
users. 
(a) From the viewpoint of OOP itself 
The use range of the data in the object is limited in the 
OOP. in most circumstances a datum is designed to aim 
at some special conditions or functions, and is not 
intended to be used by any functions or statements. if 
you do not limit the data used, when the program is 
getting bigger, programmer may use the data elsewhere 
in the program unintentionally because of carelessness. 
in this way the data may be appeared elsewhere in the 
program, and there may be no relation at all between 
these data with the same name. The biggest bug of this 
method will take place in the following situation: if the 
program should be modified, added or deleted in some 
day later, then the programmer will have very big 
problem, because there is no way to find out where the 
data will be in the program and You have to distinguish 
them when you find them. You have to find them all over 
the program continuously. That is why you should avoid 
this bug in order to reduce the opportunities to introduce 
such bugs. This is the main purpose of the 
encapsulation. 
( b) From the viewpoint of the users 
The object includes the data and the procedure (or 
method), the data are its property, and the procedure is 
its behaviour. The encapsulation means to put the 
property and the behaviour of the object together in the 
object, this is à very popular term used in the OOP. To 
encapsulate the property and the behaviour of the object 
in the unique source code is more convenient and safe 
than to put them eisewhere separately in the program. 
3.3 Inheritance 
A serious backward of the traditional programming 
languages are unable to adapt the changes orf the world, 
that is, you can not reuse the program designed when 
changes take place. The only way is to modify even to 
rewrite the whole program and leading to the resources 
and programmer's efforts waste. 
in OOP the advanced concepts, such as: object, 
encapsulation, inheritance or reusability (in VB),... etc. 
can be used to design the programs which can be 
adapted to the changes of the world. The object can be 
simply modified or extended for adapting to the new 
situations. This is called the object inheritance or the 
object reusability. 
3.4 Dynamic application program with the automatic 
responding event in real time 
in the VB the “change” event can automatically respond 
the change of the other control item. This means that the 
program designed can follow the changes automatically. 
Therefore, it is very useful for designing the dynamic 
application programs that follow the changes 
automatically. 
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996 
  
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