OOP Orientation 1

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INTERNAL

March 23, 2009

OOP Orientation 1

Object Oriented Programming Concepts


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OOP Orientation

INTERNAL- 1 -

Course Objective Object Oriented Programming Concepts

Basic Concepts

(Introduction to classes, objects ,messaging, class

relationships)

Advanced Concepts

(Concepts like Inheritance, Polymorphism, Encapsulation ..)


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OOP Orientation

INTERNAL- 2 -

Overview

Introduction

Object Oriented Paradigm

Keys of OO Technology

Objects

Characteristics of Objects

Class

Message Passing

Classes Vs. Objects

Advantages of OOP


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OOP Orientation

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Software A Complex World!

~ 8,000 new or modified SLOC*/developer/year (2005)

~ 800,000,000,000 cumulative SLOC (1950-2005)

* SLOC : Source Lines of Code

This complexity has led to many problems with large software projects ,termed

as Software Crisis

The software crisis manifests itself in

cost overrunsuser dissatisfaction with the final product

buggy software

brittle software


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OOP Orientation

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How to deal with complexity

How do humans cope with complexity in everyday life?

Abstraction

Humans deal with complexity by abstracting details away.

Examples:

Driving a car doesnt require knowledge of internal combustion engine; sufficient to

think of a car as simple transport.


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OOP Orientation

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OO Object Orientation

In OO

the main focus is to form abstractions called objects

Well put our abstractions into a hierarchy to keep them organized

natural way to divide and conquer (OO Decomposition)

our implementation decisions are easier to postpone since they arent visible.

fidelity of the abstraction to the real world. (Computing as Simulation)

First OO Language - Simula

Best current means of dealing with complexity.

OO has strong historical roots in other paradigms and practices. It came about

to address the software crisis.


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OOP OrientationINTERNAL

- 6 -

oving from a procedure-oriented to an object-oriented mindset

Modules are nested into a calling tree:

The topology of a structure program is inherently different than the topology of an OO program.

Objects cluster together by those which

communicate most frequently.Less ordered.

The algorithms still exist but they are encapsulated into an object which represents the thing

in the problem domain most closely associated with that algorithm.


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Physical Entity

White Tata Truck

An object is an entity (tangible or intangible) that has well defined structure and behavior

Examples of Objects :

Tata Truck

Black Parker Pen

Dr.John

Red Color

Point(3,0)

H+ + OH- > H2O (neutralization)

Linked List

What is an Object??

Conceptual Entity

Chemical Process Linked List

In OOP, a program is seen as comprising of a collection ofobjects, that act on

each other.

Each object having a distinct role or responsibility.


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The responsibility of an object is the role it serves within the system

Consider the object Ishanths Blue Alto

Every Object has a distinct Role or Responsibility

Responsibility of this Alto could be :To carry Ishanth from One place to Another


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How it achieves this responsibility ?

Each part of the car having its own

responsibility

.


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Responsibilities 2 Types

Car Operations

Accelerate

Apply Breaks

Change Gear

.


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Characteristics of Objects

Object has following characteristics

Responsibility

State

Behavior

Identity


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State What an object knows

It is a set of properties which can take different values at different times in the objects life.

Model = LXI

Fuel type = Petrol

Speed = 45 km/hr

Fuel level = Full

Tyre pressure = 30Gear Position = 4

Constant/Static

Dynamic

Lets have a look into The Blue Altos properties

Knowing Responsibilty ~ State


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Behavior What an object does

Behavior is how an object reacts, in terms of its state changes, in response to operations

performed upon it.

Car Operations

Accelerate

Apply Brake

Change Gear

.

Totality of operations we can perform using a car and consequent changes in state

defines behavior of a car.

Doing Responsibilty ~ Behavior


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Identity

Identity is that property of an object which distinguishes it from all other objects

IDENTITY

Reg. No. uniquely identifies a car among all others

Car

Reg. No

Color

MakeFuel type

Speed

Fuel level

Tyre pressure

Gear


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How you define the Software Objects

Class Globe { }

A Class defines the capabilities or behavior of an object


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Class

A class characterizes a set of objects that share a common structure and a common behavior

A class is used as a template for the creation of similar objects

An object is said to be an instance of a class

A class is the blueprint from which individual objects are created.

The attributes/ Fields defined in a class defines the state of an object

The methods of the class defines the object behavior.


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Class Vs. Object

Class Object

Class is a type/template for similar

objects

Object is an instance of the class, with

each instance behaving identically

Class is purely a static concept,

represented by program text

Object is dynamic/run-time entity,

occupying space in memory


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Point Class An Example

import java.math.*;

//Class Specification

//Responsibility: Represents a point with x & y coordinates, which can compute the distance from another point

class Point {

//Attributes defines the state: The coordinates of the point

double x;

double y;

//Methods define Behaviours of Objects

Point(double xCor, double yCor) { x = xCor; y = yCor;} // A constructor that initializes the fields

double getx() { return x; } //Getters

double gety() { return y; }

void setx(double xCor) { x = xCor; } //Setters

void sety(double yCor) { y = yCor; }

//Business Behaviors

//Contract: distance-from: Point->Number

//Purpose: Distance between P(x1,y1) & Q(x2,y2) = v (x2-x1)2 + (y2-y1)2

double distanceFrom(Point anotherPoint) {

return Math.sqrt(((anotherPoint.getx() - x)*(anotherPoint.getx() - x))

+ ((anotherPoint.gety() - y)*(anotherPoint.gety() - y))) ;

}

}


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How to identify objects & their behaviors???

The nouns in the requirements specification would suggest the Objects in

the problem domain.

The verbs from the requirements specification would correspond to object

behaviors.


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Consider the following scenario:

Mr. White is married. He teaches OO Software Engineering

classes on Fridays. He is a part-time member of the faculty at the

CS Department of the All-Smart Institute. John is enrolled in the

OOSE class that Mr. White teaches. Mrs. White uses a Nano for

transportation to and from the campus (she teaches Philosophy at

the same institute). Class size is limited at the institute to 14

students. Janet, the sister of John is enrolled for violin course in

the same institute.

All Smart Group Activity


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From the scenario,

1. Identify all the objects

2. Identify their knowing/doing responsibilities

3. Identify the different states and behaviors of each object

4. Identify Similar Objects / Class or Type that defines

the objects

5. Identify attributes and methods of the class corresponding

to the state and behavior of objects identified


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Demo All Smart Institute

Classes

Objects


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Constructors To create objects with proper state

Used to create customized objects of a class.

Customization means, we can initialize the fields/attributes during the creation time. The name of the constructor and class should be same.


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Mr. White When is

your OOSE

session?

Analyze the message sent by John to Mr. White

Identity of the recipient object - Mr. White

Behavior to be invoked by the recipient - Tell when the session isExtra information Required to invoke the behavior OOSE Name of

the session

Now Mr.White responds correctly.

Friday Morning9.00 am

Object Interaction Real World


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Object Interaction Software World

As in real world, Software Objects also interact by passingmessages.

In Software World, messages are dispatched to Methods :

which defines the behavior of the object for a message

Code to be executed by an object (to invoke a behavior of an

object), when a message is sent to it is known as a Method.

Message passing is achieved by invoking the methods of

the objects.


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Types of methods of a class

Constructors (We already discussed)

Accesors /Getters (Accesses, but does not change the state )

Mutators /Setters (Changes the state of the object )

Methods that defines other behaviors

>> Demo


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Why OOP ?

Square

rotate(){

//code

}

playSound(){

//code

}

Triangle

rotate(){

//code

}

playSound(){

//code

}

The spec

Jack proceduralprogrammer

Maria OOprogrammer

Here is my code with rotate & playSound as theprocedures

rotate(shapenum){

//make the shape rotate 360

}

playSound(shapenum){

//use shapenum to find which AIF to play

}

Here's the code for the classes:

Circle

rotate(){

//code

}

playSound(){

//code

}

Well! Let me identifythe procedures

I need. After all what is

a program if not alist of procedures.

Well! Let me identifythe key players.

They can be theclasses of my code


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OOPS!!! The spec has changedWho is more affected???

The modification in the spec

Hmm!! The playSound codehas to be changedwhich

means I will have to rewrite

the code every time thespec changes

playSound(shapenum){

//if the shape is not amoeba, use shapenum to

//find which AIF to play else

//play amoeba.hif sound

}

Cool!! I just have towrite one more class &I dont have to touch

the code alreadywritten.

Amoeba

rotate(){

//code}

playSound(){

//code to play .hif file

}

Oh Great!! Howefficient OOP is with so

manyfeatures.Flexibility,

extensibility.


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Session 2,3 & 4

Session 2 : Model Objects from Problem Domain

Session 3 : First Feel of Objects using Blue J

Session 4 : Message Passing / Mutators / Accessors


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Happy Learning !

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