ProblemSolving Introduction to OOP Objectsv1.0

8/12/2019 ProblemSolving Introduction to OOP Objectsv1.0

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INTERNAL

March 23, 2009

Problem Solving

Introduction to Objects


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Topic Objective

Understand Objects

Existence

Identity Responsibilities

Understand Classes

Message Passing

Abstraction

Encapsulation

Class Relationships


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Elements of Programming

Data

Programs are set of instructions that act upon data that is received (input) and transforms

it into required information.

Expressions

Instructions that carry out required operations on the given data.

Functions/Methods

A block of instructions that accept some data, carry out some operations and returns an

output.

Calculate Gross

Salary

Basic Pay, DA Rate,

HRA RateGross Salary

Data

Function

Inside Calculate Gross Salary

DA = Basic Pay * DA Rate/100

HRA = Basic Pay * HRA

Rate/100Gross Salary = Basic Pay +

DA+ HRA

Return Gross Salary

Expressions


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Structured approach to programming

Structured approach to programming, implements a system as a collection of functions that

accepts data, processes it and returns an output.

A function some times calls another function, when it wants to make use of the functionality

defined in the other function.A program to calculate salary of an employee might look some what like this. A function to

calculate salary, calling another two functions that calculates HRA and DA. The values

returned by these modules is added up in the module that calculates salary,

Calculate Salary

Calculate HRA Calculate DA

Basic pay,

HRA Rate, DA

Rate salary

Basic pay,

HRA RateHRA

Basic pay,DA Rate

DA

CalculateSalary(Basic Pay, HRA Rate, DA Rate)

{

DA = call CalculateDA(Basic Pay, DA Rate)

HRA = call CalulateHRA(Basic Pay, HRA Rate)

Salary = DA+HRA

Return Salary

}

Calculate DA(Basic Pay, DA Rate)

{

Return DA Rate*Basic Pay /100

}

Calculate HRA(Basic Pay, HRA Rate)

{

Return HRA Rate * Basic Pay/100

}

Note: This is a pseudo code


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Writing programs that simulate real world domains

Structured approach implements a system as a collection of functions that act upon data

that is passed into it.

We write programs that make up a software to solve a problem in real world. In real world

problem domains we do not find any functions that work on data.

We find objects that are described by some state (data) and having some behaviours

(functions).

Object Oriented Approach to programming is about implementing a system as collection of

objects that have state and behaviours, interacting with each other to achieve expected

functionalities.


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Objects Make the World

An object is a real world entity that has a well defined structure and behaviour.

Characteristics of an object

State Behaviour

Responsibility

Communication

Identity

Examples of objects


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StateWhat an object knows

State of an object is a set of properties that describes the object, which can take different

values during the life time of the object.

Bob is an employee of tech smart, let us havea look into Bobs properties as an employee: Bob

Name: Bob

Emp.No. 2312

Department: Marketing

BasicPay = 10,000

Designation: Manager

Linda

Name: Linda

Emp.No. 3361

Department: Marketing

BasicPay = 9,500

Designation: Executive

Linda is another employee

Knowing Responsibility: It is the responsibility of an object to know its state


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Behaviours

Behaviour is how objects react to its state changes or any other operations performed on it

Bank account

State:

Account number:121XXXXXXX

Account Balance:Rs. XXXXX/-

Opening Date:12/01/2005

Branch:XXXXX

Bank accountBehaviours

Withdraw

Deposit

Generate Transaction Statement

A bank account can perform these responsibilities, by making use of state values or

other data provided to it.

Doing responsibility: It is the responsibility of object to behave according

the operations performed on it


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Doing responsibilities

Doing something itself, like creating an object/doing a calculation

Initiating action in other objects Controlling and coordinating activities in other objects

Knowing responsibilities

Knowing about state

Knowing about related objects

Knowing about things it can derive or calculate

Responsibilities


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Communication

Objects can communicate with each other, provided they know each other.

Objects can respond to the message send by another object, by performing an action, or

returning some data.

Account

121XXXX

Please

deposit Rs.

1000/- to

account

121XXXX

Customer

Deposit an

amount of

Rs. 1000/-

Balance

updated

accordingly, new

balance is Rs.

XXXXX/-

Money credited

to your account,

balance is Rs.

XXXXX


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Identifying objects and behaviours

The nouns in the requirements specification would suggest the Objects in the problem

domain.

The verbs from the requirements specification would suggest object behaviors.


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Problem Context - Prepaid Connection manager

A local grocery shop in our society is an authorized distributor for prepaid and post paid

GSM mobile connections for Talk the Talk" service provider. The shop sells new

connections, provide easy recharge and topups. The shop also maintains an inventory of

connections sold, and re-charges and top-ups done from there, for audits and reports.

Identify objects and their responsibilities


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Objects in the scenario

Try to find out the objects involved.

? What could be the possible objects?? Connection, TopUp, anything else?

? The Recharge list itself?

? Each entry in the recharge list?

? Anything missed out?

? What are the attributes of each objects?


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Object Way..

Once you have identified the objects, we need to identify the behaviours ofobjects.

? Which object will take the responsibility of recording a top up made againsta connection?

? Which object will take care of knowing talk-time in a re-charge coupon?

? Which object will know about the details of transaction on connections?

? What are the responsibilities of Connection object?


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Summary

An object is a real world entity that has a well defined structure and

behaviour.

Characteristics of an object

State Behaviour

Responsibility

Communication

Identity


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Happy Learning!

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ProblemSolving Introduction to OOP Objectsv1.0