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CS304-Handouts
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LECTURE NO.45 .............................................................................................................................. 343
45.1. RESOURCE MANAGEMENT ............................................................................................. 343
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Lecture No.
01.1. Introduction
Course Objective:
Objective of this course is to make students familiar with the concepts of
object oriented programming. These concepts will be reinforced by their
implementation in C++.
Course Contents:
The main topics that we will study in the 45 lectures of this course are given
below,
- Object Orientation
- Objects and Classes
- Overloading
- Inheritance
- Polymorphism
- Generic Programming
- Exception Handling
- Introduction to Design Patterns
Recommended Text Book:
C++ How to Program ( Deitel & Deitel )
Reference Books:
1. Object-Oriented Software Engineering
By Jacobson, Christerson, Jonsson, Overgaard
(For object oriented programming introductory concepts)
2. The C++ Programming Language
By Bjarne Stroustrup
(For better c++ understanding)
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Suppose we want to develop a fee collection system for a school for this we will need
to find out related objects and their interactions as happens in real life.
In this way we can say that object orientation makes it easier for us to solve our real
world problems by thinking solution of the problem in terms of real world objects.
So we can say that in our daily life everything can be taken as an object that behaves in a
certain way and has certain attributes.
In object orientation we move our concentration to objects in contrast to procedural
paradigm in which we simply write our code in functions and call them in our main
program.
01.2. What is a Model?
A model is an abstraction of something real or conceptual.
We need models to understand an aspect of reality.
Model Examples
Teacher Student School Bag
Book Pen Playground
Parents Classroom Library
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Highway maps
Architectural models
Mechanical models
01.3. OO Models:
In the context of programming models are used to understand the problem before
starting developing it.
We make Object Oriented models showing several interacting objects to understand
a system given to us for implementation.
Example 1– Object Oriented Model
Objects
Ali, Car, House, Tree
Interactions
Ali lives in the house
Ali drives the car
Example 2– Object Oriented Model (A School Model)
Ali
Car
House
Tree
lives-in
drives
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Ali is a tangible object, having some characteristics (attributes) and behavior as given
below,
Ali
Characteristics (attributes) Behaviour (operations)
Name
Age
Walks
Eats
We will identify Ali using his name.
Car is also a tangible object having some characteristics (attributes) and behavior
given below,
Car
State (attributes) Behavior (operations)
Color
Model
Accelerate
Start Car
Change Gear
We can identify Car using its registration number
Examples of Intangible Objects (also called as conceptual objects):
Time is an intangible (conceptual) object
Time
State (attributes) Behavior (operations)
Hours
Seconds
Minutes
Set/Get Hours
Set/Get Seconds
Set/Get Minutes
We will assign our own generated unique ID in the model for Time object
Date is also an intangible (conceptual) object
State (attributes)
Year
Day
Month
Behavior (operations)
Set/Get Year
Set/Get Day
Set/Get Month
We will assign our own generated unique ID in the model for Date object.
01.7. Summary:
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- Model is the abstraction of some real word scenario. It helps us to understand
that scenario.
- Object oriented model of any scenario (problem) describes that scenario
(problem) in the form of interacting objects.
- We use Object Orientation because it helps us in mapping real world problem
in a programming language.
- Object Orientation is achieved using objects and their relationships.
- Properties of an object are described using its data members and behavior of an
object is described using its functions.
- Objects may be tangible (physical) or intangible (also called conceptual or
virtual).
- Generally when we have given a certain problem description, nouns in that
problem description are candidates for becoming objects of our system.
- There may be more than one aspects of an object
- It is not necessary that every object has a specific role in implementation of a
problem there may be some objects without any role, like school parking in
our school.
- It is easier to develop programs using Object Oriented Programming because
it is closer to real life.
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- All information related to an object is stored within the object
- It is hidden from the outside world
- It can only be manipulated by the object itself
Advantages of Information Hiding
Following are two major advantages of information hiding,
It simplifies our Object Oriented Model:
As we saw earlier that our object oriented model only had objects and their
interactions hiding implementation details so it makes it easier for everyone to
understand our object oriented model.
It is a barrier against change propagation
As implementation of functions is limited to our class and we have only given the
name of functions to user along with description of parameters so if we change
implementation of function it doesn’t affect the object oriented model.
We can achieve information hiding using Encapsulation and Abstraction, so we see
these two concepts in detail now,
02.2. Encapsulation
Encapsulation means “we have enclosed all the characteristics of an object in the object
itself”
Encapsulation and information hiding are much related concepts (information
hiding is achieved using Encapsulation)
We have seen in previous lecture that object characteristics include data members
and behavior of the object in the form of functions.
So we can say that Data and Behavior are tightly coupled inside an object and
both the information structure and implementation details of its operations are
hidden from the outer world.
Examples of Encapsulation
Consider the same example of object Ali of previous lecture we described it as
follows,
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You can see that Ali stores his personal information in itself and its behavior is
also implemented in it.
Now it is up to object Ali whether he wants to share that information with
outside world or not. Same thing stands for its behavior if some other object in
real life wants to use his behavior of walking it can not use it without the
permission of Ali.
So we say that attributes and behavior of Ali are encapsulated in it.
Any other object don’t know about these things unless Ali share this information
with that object through an interface,
Same concept also applies to phone which has some data and behavior of
showing that data to user we can only access the information stored in the phone
if phone interface allow us to do so.
Advantages of Encapsulation
The following are the main advantages of Encapsulation,
a. Simplicity and clarity
As all data and functions are stored in the objects so there is no data or function
around in program that is not part of any object and is this way it becomes very
easy to understand the purpose of each data member and function in an object.
b. Low complexity
As data members and functions are hidden in objects and each object has a
specific behavior so there is less complexity in code there will be no such
situations that a functions is using some other function and that functions is
using some other function.
c. Better understanding
Everyone will be able to understand whole scenario by simple looking into object
diagrams without any issue as each object has specific role and specific relation
with other objects.
02.3. Interface
Ali
Characteristics
(attributes)
Behavior
(operations)
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So it has,
- Data Structure in the form of Mechanical structure of gear box
- Functionality mechanism to change gear
b. Address Book in a Phone
Similarly take the example of contact details saved in the SIM of a phone,
In that case we can say physical structure of SIM card as Data Structure
And Read/write operations provided by the phone as Functionality.
02.5. Separation of Interface & Implementation
As discussed earlier we only show interface of an object to outside world and
hide actual implementation from outside world. The benefit of using this
approach is that our object interface to outside word becomes independent
from inside implementation of that interface.
This is achieved through the concepts of encapsulation and information
hiding.
Real Life example of separation of interface and implementations
Driver has a standard interface to drive a car and using that interface
he drive can drive any car regardless of its model or type whatever
engine type it has or whatever type of fuel it is using.
02.6. Messages
Objects communicate through messages they send messages (stimuli) by
invoking appropriate operations on the target object. The number and kind of
messages that can be sent to an object depends upon its interface
Examples – Messages
A Person sends message (stimulus) “stop” to a Car by applying brakes
A Person sends message “place call” to a Phone by pressing appropriate button
02.7. Summary
- Information hiding is achieved through encapsulation.
- Encapsulation and Information Hiding are related to each other.
- Interface of an object provides us the list of available functions.
- An object may have more than one interface.
- Interface and implementation are separated from each other to achieve
Information Hiding.
- Objects communicate with each other using messages.
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