programming-for-dummies

Organizing a Program with Object-Oriented Programming 45
this task involves flying a rocket to the moon, driving a car down a road, or
controlling a walking robot to an electric outlet to recharge its batteries.
Book I
Chapter 2
The more you divide a larger task into smaller tasks, the harder it can be to
understand what problem you’re even trying to solve. This gets even worse
when you start writing actual program commands.
The two parts of most programs are the commands that tell the computer
what to do and the data that the program manipulates. So if you wrote a program
to identify the current speed and direction of a rocket, the commands
would tell the computer how to retrieve this information and the speed and
direction would be the actual data the program uses.
Different Methods
for Writing
Programs
Essentially, program commands are separate from the data that they manipulate.
If one part of a program manipulates data incorrectly, the rest of the
program winds up using that contaminated data and you, as the programmer,
won’t know which part of the program screwed up the data. This is like
sitting in a baseball game, ordering a hot dog from a vendor, and having six
people pass your hot dog down to you. When you see fingerprints all over
your hot dog, can you tell which person touched your food?
Objects isolate data
Object-oriented programming avoids this problem by combining data and the
commands that manipulate them into a single entity called (surprise!) an object.
With object-oriented programming in the hot dog vendor analogy, instead of
passing your hot dog to half a dozen other people, the hot dog vendor comes
directly to your seat and hands you your hot dog. Now if you saw fingerprints
all over your hot dog, you’d know that the fingerprints could only have come
from the hot dog vendor.
Besides keeping data isolated from other parts of your program, object-oriented
programming also helps you divide a large program into smaller ones.
Although structured programming divides a large program into the tasks
that need to be performed, object-oriented programming divides a large program
into real-life objects.
So if you were designing a program to launch a rocket to the moon, objectoriented
programming would let you divide the program into objects. One
object might be the rocket, a second object might be the moon, and a
third object might be the Earth.
You can also divide a large object into smaller ones. So the rocket object
might be divided into an engine object and a guidance object. The engine
object could be further divided into a fuel pump object, a nozzle object,
and a fuel tank object.