programming-for-dummies

136
Dividing a Program into Objects
User Interface
Changing this subprogram . . .
Figure 1-7:
Changing
one part of a
program
can affect
other parts
of that same
program.
Examine hard disk
Displaying report
Printing
Save report
. . . could affect this subprogram,
which can affect . . .
. . . all of these other subprograms.
When subprograms are highly dependent on each other, they’re high, strong,
or tight coupling. When subprograms aren’t dependent on each other, they’re
low, weak, or loose coupling. You want your subprograms to have low, weak,
or loose coupling. That way, changing one part of your program doesn’t accidentally
affect another part of your program.
To enforce weak coupling, computer scientists have created object-oriented
programming (OOP). The main idea behind OOP is to divide a large program
into objects.
Objects act like “super” subprograms. Whereas subprograms give programmers
the choice of making a tightly or loosely coupled subprogram, objects
force programmers to create loosely coupled subprograms.
By forcing programmers to create loosely coupled subprograms, objects
make it easy to modify a program without worrying about any unintended
side effects. OOP lets you yank out an object, modify it, and plug it back in
without worrying if your changes might affect the rest of the program.
Objects offer another advantage over subprograms. Whereas subprograms
typically represent a specific action, objects represent specific physical
items in the real world.
For example, if you’re writing a program to control a robot, you could divide
the program into the following subprograms that make the robot:
✦ Move
✦ Sense obstacles (through sight and touch) in its way
✦ Navigate