Introduction to OOP
Structured Programming
▪Emphasis on logic more than data or action
▪The steps of programming (algorithms) are more emphasized
▪C, Pascal, FORTRAN, and similar languages are procedural
languages i.e., each statement in the language tells the
computer to do something
▪A program in a procedural language is a list of instructions:
Get some input, add these numbers, divide by six, display that
output, and so on
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Structured Programming
▪Also known as Modular Approach to Programming
▪Major Feature – Division into Functions
▪Dividing a program into functions and modules is one of the
cornerstones of structured programming
▪The idea of breaking a program into functions can be further
extended by grouping a number of functions together into a
larger entity called a module (which is often a file)
▪Top-down approach of program design
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Procedure Oriented Programming
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Structured Programming
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Problems with Structured Programming
▪Unrestricted Access (of data)
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Problems with Structured Programming
▪Local data is hidden inside a function, and is used exclusively
by the function
▪Local data is closely related to its function and is safe from
modification by other functions
▪However, when two or more functions must access the same
data then the data must be made global
▪Global data can be accessed by any function in the program
▪In a large program, there are many functions and many global
data items which leads to a large number of potential
connections
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Problems with Structured Programming
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Problems with Structured Programming
▪Real World Modeling
▪Arrangement of separate data and functions does a poor job
of modeling things in the real world
▪In the physical world we deal with objects such as people and
cars
▪Such objects aren’t like data and they aren’t like functions
▪Complex real-world objects have both attributes and
behavior
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Problems with Structured Programming
▪Attributes (Characteristics)
▪For people, eye color, job title
▪For cars, horsepower and number of doors
▪Attributes are equivalent to data in a program: they have a
certain specific values, such as blue (for eye color) or four
(for the number of doors)
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Problems with Structured Programming
▪Behavior
▪Behavior is something a real-world object does in response
to some stimulus
▪If you ask your boss for a raise, she will generally say yes or
no
▪If you apply the brakes in a car, it will generally stop
▪Behavior is like a function: you call a function to do
something (display the inventory, for example) and it does it
▪So neither data nor functions, by themselves, model
real-world objects effectively
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Object Oriented Programming
▪Emphasis on data rather than steps or logic
▪Programs are divided into entities called objects
▪The fundamental idea behind object-oriented languages is to
combine into a single unit both data and the functions that
operate on that data
▪Data is hidden and cannot be accessed by external functions
and hence is safe from accidental alteration
▪Objects may communicate with each other through functions
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Object Oriented Programming
▪New data and functions can be easily added whenever
necessary
▪Data encapsulation and data hiding are key terms in the
description of object-oriented languages
▪Bottom-up approach of program design
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Basic Concepts / Characteristics of OOP
▪ Objects
▪ Classes
▪ Data Abstraction and Encapsulation
▪ Inheritance
▪ Polymorphism
▪ Dynamic Binding
▪ Message Passing
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Objects
▪ Objects are basic run-time entities of an object oriented
system
▪ Program objects must be chosen such that they match closely
with real world objects
▪ They may represent a person, place, a bank account, a table
of data or any item that the program has to handle
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Objects
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Classes
▪ Class is a user defined data type
▪ An object is a instance of a class
▪ In simple terms, objects are variable of type class
▪ Once a class has been defined, we can create any number of
objects belonging to that class
▪ A class is thus a collection of objects of similar type
▪ For example, if ‘Brand’ has been defined as a class, then
Brand gucci;
will create an object gucci belonging to the class Brand
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Classes
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Data Abstraction and Encapsulation
▪ The wrapping up of data and functions into a single unit
(called class) is known as encapsulation
▪ The data is not accessible to the outside world, and only
those functions which are wrapped in the class can access it
▪ These functions provide the interface between the object’s
data and the program
▪ The insulation of data from direct access by the program is
called data hiding or information hiding
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Data Abstraction and Encapsulation
▪ Abstraction refers to the concept of representing essential
features without including the background details or
explanations
▪ Classes use the concept of abstraction and are defined as a
list of abstract attributes (data members) and functions to
operate on these attributes (methods or member functions)
▪ Since the classes use the concept of data abstraction, they
are known as Abstract Data Types (ADT)
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Inheritance
▪ Inheritance is the feature by which objects of one class
acquire the properties of objects of another class
▪ It supports the concept of hierarchical classification
▪ The concept of inheritance provides the idea of reusability
▪ This means we can add additional features to an existing class
without modifying it
▪ This is possible by deriving a new class from an existing one
▪ The new derived class will have the features of the existing
class as well as its own unique features
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Inheritance
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Polymorphism
▪ Polymorphism means the ability to take more than one form
▪ Using this feature, an operation may exhibit different behaviors in
different instances
▪ The behavior depends on the types of data used in the operation
▪ Example: Operator Overloading – Consider the addition
operation
▪ For two numbers, the operation would generate a sum
▪ For two strings, the operation would generate a third string which is
the concatenation of the two input strings
▪Another Example: Function Overloading
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Polymorphism
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Dynamic Binding
▪ Binding refers to the linking of a procedure call to the code to
be executed in response to the call
▪ Dynamic Binding (Late Binding) means the code associated
with a given procedure call is not known until the time of the
call at runtime
▪ It is associated with polymorphism and inheritance
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Message Passing
▪ An object oriented program consists of a set of objects that
communicate with each other
▪ The process of programming in an object oriented language
involves the following steps:
▪Creating classes that define objects and their behavior
▪Creating objects from class definitions
▪Establishing communication among objects
▪Objects communicate with one another by sending and
receiving messages
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Message Passing
▪ A message for an object is a request for execution of a
procedure and therefore will invoke a function (procedure) in
the receiving object that generates the desired result
▪ Message passing involves specifying the name of the object,
the name of the function (message) and the information to be
sent
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