Traditional programming has the following characteristics:Functions are written sequentially, so that a change in programming can
affect any code that follows it.
If a function is used multiple times in a system (i.e., a piece of code
that manages the date), it is often simply cut and pasted into each
program (i.e., a change log, order function, fulfillment system, etc).
If a date change is needed (i.e., Y2K when the code needed to be changed
to handle four numerical digits instead of two), all these pieces of
code must be found, modified, and tested.
Code (sequences of computer instructions) and data (information on which
the instructions operates on) are kept separate. Multiple sets of code
can access and modify one set of data. One set of code may rely on data
in multiple places. Multiple sets of code and data are required to work
together. Changes made to any of the code sets and data sets can cause
problems through out the system.Object-Oriented programming takes a radically different approach:Code and data are merged into one indivisible item – an object (the
term “component” has also been used to describe an object.) An object is
an abstraction of a set of real-world things (for example, an object may
be created around “date”) The object would contain all information and
functionality for that thing (A date
object it may contain labels like January, February, Tuesday, Wednesday.
It may contain functionality that manages leap years, determines if it
is a business day or a holiday, etc., See Fig. 1). Ideally, information
about a particular thing should reside in only one place in a system.
The information within an object is encapsulated (or hidden) from the
rest of the system.
A system is composed of multiple objects (i.e., date function, reports,
order processing, etc., See Fig 2). When one object needs information
from another object, a request is sent asking for specific information.
(for example, a report object may need to know what today’s date is and
will send a request to the date object) These requests are called
messages and each object has an interface that manages messages.
OO programming languages include features such as “class”, “instance”,
“inheritance”, and “polymorphism” that increase the power and
flexibility of an object.