programming-for-dummies

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How Object-Oriented Programming Works
There’s no single “right” way to divide a large program into objects. Two programmers
tackling the same problem will likely divide the same program
into different objects. The way you define your objects reflects how you view
a particular problem.
Every object consists of two parts, as shown in Figure 7-3:
✦ Data (also called properties)
✦ Subprograms (also called methods)
Object
Figure 7-3:
The parts of
a typical
object.
Data
Subprograms
Objects contain two types of data:
✦ Public data is accessible by other parts of the program.
✦ Private data within the object is hidden from the rest of the program.
Objects contain two types of subprograms:
✦ Public subprograms allow other parts of a program to control an object.
✦ Private subprograms are used by an object to calculate a result needed
by its public subprograms (methods).
The difference between public and private data and subprograms is
accessibility:
✦ Public data and subprograms are what the rest of a program can “see”
and use in an object:
• Public data typically describes the object in some way. For example,
a video game program might create an object that represents a monster.
This object may need data, representing X and Y coordinates, to
define the monster’s location on-screen.
• Public subprograms (methods) allow other parts of a program to
manipulate an object. For example, an object representing a monster