programming-for-dummies

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How Object-Oriented Programming Works
To overcome the limitations of subprograms, computer scientists invented
object-oriented programming (abbreviated as OOP). Like structured programming,
which encourages you to break a large program into subprograms,
OOP encourages you to break a large program into smaller parts, or
objects.
Object-oriented programming has actually been around since 1962 when two
Norwegian computer scientists Ole-Johan Dahl and Kristen Nygaard developed
a language called SIMULA, which was designed to help simulate realworld
events. It took object-oriented programming nearly 40 more years to
finally get accepted as a practical tool, so just because an idea is proven to
work doesn’t mean people will accept it if they can continue being comfortable
(and getting paid) to keep doing something that doesn’t work.
How Object-Oriented Programming Works
Like subprograms, objects divide a large program into smaller, interchangeable
parts. The main difference is that subprograms divide a program into
separate tasks whereas objects divide a program into real-world items.
For example, consider a hotel reservation program used by the front desk
when a guest checks in. Dividing this problem into tasks might create the
following:
✦ Subprogram #1: RoomAvailable (Checks if a hotel room is available)
✦ Subprogram #2: RoomBeds (Checks if the room has 1 or 2 beds)
✦ Subprogram #3: RoomType (Checks if it’s a smoking or a nonsmoking
room)
✦ Subprogram #4: RoomPrice (Checks the price)
Dividing this problem into objects, you could create the following:
✦ Object #1: Guest
✦ Object #2: Front desk clerk
✦ Object #3: Hotel room
Figure 7-1 shows how a task-oriented solution might break a program into
multiple subprograms. The main program works by running each subprogram,
one at a time, with each subprogram performing a specific task (such
as determining whether a room is smoking or nonsmoking).