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OOP

TEXT BOOKS :

Java; the complete reference, 7th edition, Herbert schildt, TMH.

UnderstandingOOP with Java, updated edition, T. Budd, pearson

education.

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Unit-I

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Object-Oriented thinking

Need of oop paradigm / model:-

Object-oriented programming is a newprogramming

model.A model helps you understandhow the system works.

For example, the Newton model of physics explains whyapples fall to the ground.

In computer science , a model explains how theelements that go into a program are organizedand howthey interactwith one another.

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A Way of Viewing/Understanding the World

To understand the major ideas in object

oriented programming

Let us see how we handle a real worldsituation.

Then we will see how can we make computerto

model the techniques used in the situation.

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Real world situation

I want to send some flowers to my friend sally

who lives in a city many miles away.

Because of the distance, I cannot pick up the

flowers and carry them to sallys door myself.I will go to Flora, my local florist, tell her the type

and quantity of flowers I wish to send and sallys

address.

I can be assured that the flowers will bedelivered automatically.

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Contd..

Me

Flora

Sallys Florist

Delivery person

Sally

FlowerArranger

Wholesaler

Grower

Gardeners

The community of agents helping me

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Agents and communities

I find an appropriate agent(Flora) and pass to her amessage containing a request.

It is the responsibilityofFlora to satisfymy request.

There is some method-- some algorithm or a set of

operations -- used by Flora to do this.I do not need to know theparticular methodthat Flora will

use, this information is hidden from me.

The General Principle

An object oriented program is structuredas acommunityof interacting agents called objects. Each

object provides a service that is used by other members

of the community.

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Messages andMethods

Action is initiated in object oriented programming by the

transmission of a message to an agent(an object).

The message contains the request foraction and is

accompaniedby additional information (arguments)

needed to carry out the request.

The receiveris the agent to which the message is sent.

If the receiveraccepts the message it accepts the

responsibilityto carry out the indicated action.

In response to a message the receiverwill perform

some methodto satisfy the request.

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In what sense is a message different from a

procedure call?

In both cases there is a set of well-defined steps that will

be executed following the request. But, there are two

important differences.

The first is that a message has a specific receiver. In a

procedure call, there is no specificreceiver.

The second is that the interpretation of the message ( that is, the

method used to respond to the message ) is dependenton thereceiverand can vary with differentreceivers.

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Contd..

The specific receiverfor any given message will not be known untilrun time. There is a late bidingbetween the message and code

fragment( method ) used to respond to the message.

In a function or procedure call, binding name to code fragment will

be done at compile time only. There is an early binding.

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Classes andInstances

A class is the template or blueprintfrom which objects

are actually created.

All objects are instances of a class.

All objects of thesame class use the same methodin response to the

same message.

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Class Hierarchies-Inheritance

The principle thatknowledge of more general category is

also applicable to a more specificcategory is called

inheritance.

Employee

name

salary

hire_date

Professor

bonus

Programmer

contract_period

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Classes can be organized into a hierarchicalinheritance

structure. Achildclass (or subclass) will inheritattributes

from a parent class higher in the tree.

An abstractclass is a class for which there are no direct

instances; it is used only to create subclass.

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Flash Flora Elizabeth Kenneth Phyl Sallys flowers

Florist Potter

Shopkeeper Artist Dentist

HumanDog Platypus

Mammal

Animal

Carnation

Flower

Plant

Material Objects

A class hierarchy for various material objects

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Contd..

Flora

Material Object

Animal

Mammal

Human

Shopkeeper

Florist

Categories surrounding Flora

Flora is a florist, but Florist is a

specialized form of the category

Shopkeeper.

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Method Binding, Overriding and Exceptions

Phyl the platypus presents aproblem for our simplestructure.

We know that mammals give birth to live babies.

But Phyl lays eggs.

To accommodate this variation, we need to find atechnique to convert exceptions to a general rule.

We do this by overridingthe information inherited fromparent class in subclass.

Name of the method in the subclass is same as in theparent class.

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The search for a method to invoke in response to a given

message starts with the class of the receiver.

Ifno appropriate method is found, the search continues

up theparentclass chain until either a method is found

or the parent class chain is exhausted.

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Summary of oop concepts Everything is an object.

Computation is performed by communicatingobjectswith each other.

Objects communicate by sending and receivingmessages. A message is a request for action bundled

with whatever arguments may be necessary to completethe task.

Each object has its own memory.

Every object is an instance of a class.

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All objects that are instances of the same class canperform the same actions.

Classes are organized into a single rooted tree structure,called the inheritance hierarchy.

Properties ofsuper class are automatically available tosubclasses.

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Dealing /Coping with Complexity

Complexity of programming projects is non-linear Two programmers cannot do in one month what one

programmer can do in 2 months

Adding more men/women to a project often lengthens,not shortens, the schedule.

Interconnectedness, the dependence of oneportion of code on another portion, is responsiblefor this situation.

Abstraction mechanisms are used to deal with thiscomplexity and abstraction layers in objectoriented software design provides someassistance to reduce complexity.

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Abstraction

Abstraction is thepurposefulsuppression orhidingof some details of a process in order to

bring out more clearly other aspects.

For example, data is stored in 512B blocks on a disk but

users are presented with the higher level file abstraction.

We are given variables to enter the data, but actually data

will be stored in the form of 1s and 0s.

Similarly header files, ex- math.h in c

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Abstraction mechanisms in

programming languages.

Procedures and Functions

It increases readability of the code

Easy to maintain the code.

Easy to find errors.

Header files and Packages

Easy to write the code.

It reduces the code size.

It reduces the time.

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Contd..

Abstract Data Types ( classes )Separates interface and implementation

Easy to understand the functionality .

Provides security.

polymorphismIncreases readability of the code.

InheritanceIt reduces the code size .

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Abstraction layers in Object-OrientedSoftware

Design

At the highest levela program is viewed as a communityofcooperatingobjects. At this highest level the importantfeatures to stress are the services provided by eachobject and the lines of communication between them.

The next level of abstraction places a group of objectsworking together in a single unit.

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Contd..

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Contd..

The next level of abstraction deals with the interaction

between 2 individualobjects where one uses services from

the other.

The last level of abstraction considers a single task inisolation i.e. what are the steps required to implement a

single method.

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Programming in the Small versus

Programming in the Large

Code developed by singleprogrammer or very smallset of programmers.

Every individual

understands all aspectsof the project.

Major effort is the designand development ofalgorithms .

Code developed by alarge team.

No single individual isresponsible for the entire

project or understands allaspects of it

Major effort is themanagement of detailsand the communication ofinformation between

different portions of theproject.

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Week 2 :

a)Write a Java program that prompts the user foran integer and then prints out all prime numbers

up to that integer.b)Write a Java program to multiply two given

matrices.

c)Write a Java Program that reads a line of

integers, and then displays each integer, and thesum of all the integers (Use StringTokenizerclass of java.util)

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Reading data from keyboard using JOptionPane

import java.lang.*;

import java.io.*;

import javax.swing.*;

public class InputFromKeyboardJOptionPane

{

public static void main(String[] args)

{

String str=JOptionPane.showInputDialog("enter data");

System.out.println(str);

}

}

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StringTokenizerStringTokenizeris a class .

It converts the input stringinto a set oftokens.

To use StringTokenizer, you should specify an input stringand a

string that contains delimiters.

Delimiters are characters that separate tokens.

The defaultset ofdelimiters consists of the whitespace characters:

The StringTokenizerconstructors are shown below:

StringTokenizer(String str)

StringTokenizer(String str, String delimiters)

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Method Description

boolean hasMoreTokens( ) Returns true if one ormore tokens remain in

the string and returns

false if there are none.

String nextToken( ) Returns the next token

as a String.

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Arrays

One-Dimensional Arrays :-

General form

type array-var[ ]= new type[size];

Ex:- int a=new int[10];

Two-Dimensional Arrays :-

General form

type array-var[ ][ ]= new type[row_size][col_size];

Ex:- int a[ ][ ]=new int[3][3];