programming-for-dummies

Organizing a Program with Object-Oriented Programming 47
in the original subprogram and also in the modified subprogram. If
you made 20 different modifications to a subprogram, you now have
the problem of not only correcting the error in every copy of the
original subprogram, but also fixing that same error in all your
modified versions of that original subprogram.
But after you modify a subprogram, will you remember which subprogram
you copied and modified originally? Even worse, you could copy a subprogram
and modify it, and then copy your modified subprogram and modify
that copy. Do this several times and you’ll wind up with several slightly
different versions of the same subprogram, but now you may not have any
idea which subprogram you copied originally.
Book I
Chapter 2
Different Methods
for Writing
Programs
So now if you find an error in the original subprogram, how can you find and
fix that same error in any modified copies of that subprogram? Most likely,
you can’t because you won’t know for sure which modified versions of the
subprogram you (or another programmer) might have created.
Because programmers are always going to copy an existing program that
works, object-oriented programming helps manage the copying process by
using inheritance. The whole idea behind inheritance is that rather than
making physical copies of a subprogram, you have only one copy of a subprogram
at all times.
Instead of physically copying a subprogram, objects inherit a subprogram by
essentially pointing to the subprogram that they want to copy. Not only does
this save physical space by eliminating the need to make copies of a subprogram,
but this also makes it easy to modify subprograms.
If you find an error in a subprogram, just correct the error in the original
subprogram and that’s it. Any objects that have inherited commands from
that subprogram now point automatically to the modified version of the original
subprogram, as shown in Figure 2-8.
By isolating commands in objects and using inheritance, objects can get the
advantages of copying subprograms without the disadvantages of having
multiple physical copies scattered all over the place.
Object-oriented programming makes programs easier to write (by dividing a
large program into parts), easier to understand (by organizing subprograms
into objects that mimic the actual problem the program is trying to solve),
and easier to modify (by automatically updating any copies of subprograms).
All these advantages allow you, as the programmer, to focus more on solving
problems and less on keeping track of trivial details.