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Computing |
Java
Oops…
I did it Again!
This article is going to explain the
object-oriented programming (commonly called OOPS) concepts used in languages
like C++ and Java.
OOP's concepts have simplified
programming like never before. Basically one can write programs in two ways:
One way is the process-oriented
model, where the programs are written in steps of code. C language uses this
approach, and as the programs become lengthy, the code gets more complex.
Other way is the object-oriented
programming (OOP) way. OOP organizes a program around its data (also called
objects) and a set of well-defined interfaces to that data. An object-oriented
program can be called as a data controlling access to code.
Abstraction is an essential element
for this, which manages the complexity. In a sense, when someone works on a
computer, not necessary that he should know the working of each and every part
of the computer. Even without the hardware knowledge, he can e-mail, type or do
other jobs on the computer. Thus people do not think of a computer as a unit
made up of hundreds of cards and chips, but as a well-defined object with its
own unique behavior. This is the advantage of abstraction.
Object-oriented programming is modeled on how, in the real world, objects are
often made up of many kinds of smaller objects. This capability of combining
objects, however, is only one very general aspect of object-oriented
programming.
The Three Oops
Concepts:
1) Encapsulation:
It is the mechanism that binds together code and data in manipulates, and keeps
both safe from outside interference and misuse. In short it isolates a
particular code and data from all other codes and data. A well-defined interface
controls the access to that particular code and data. In Java, the basis of
encapsulation is the class. A class defines the structure and behavior
(data and code) that will be shared by a set of objects. Each object of a given
class contains the structure and behavior defined by the class, as if it were
stamped out of a mold in the shape of a class. A class is a logical construct,
an object has physical reality. When you create a class, you will specify the
code and data that will constitute that class. Collectively, these elements are
called the members of the class. Specifically, the data defined by the
class are referred to as member variables or instance variables.
The code that operates on that data is referred to as member methods or just
methods, which define the use of the member variables.
Since the purpose of a class is to encapsulate complexity, there are mechanisms
for hiding the complexity of the implementation inside the class. Each method or
variable in a class may be marked public or private. The private methods and
data can only be accessed by the code, that is a member of the class. The public
method has all details essential for external users.
2) Inheritance:
It is the process by which one object acquires the properties of another
object. This supports the hierarchical classification. Without the use of
hierarchies, each object would need to define all its characteristics
explicitly. However, by use of inheritance, an object need only define those
qualities that make it unique within its class. It can inherit its general
attributes from its parent. A new sub-class inherits all of the attributes of
all of its ancestors.
3) Polymorphism:
It is a feature that allows one interface to be used for general class of
actions. The specific action is determined by the exact nature of the situation.
In general polymorphism means "one interface, multiple methods", This
means that it is possible to design a generic interface to a group of related
activities. This helps reduce complexity by allowing the same interface to be
used to specify a general class of action. It is the compiler's job to select
the specific action (that is, method) as it applies to each situation.
On the lighter side, extending this analogy to a dog, its sense of smell is
polymorphic. If the dog smells a cat, it will bark and run around it. If the dog
smells its food, it will salivate and run to its bowl. Note that the same sense
of smell is at work in both the cases. The difference is what is being smelled,
that is, the type of data being operated upon by the dog's nose!
– Deepak Chandrasekaran
April 9, 2001
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