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1

Introduction to OO Concepts andUML



2

Overview

Introduction to Classes and Objects

Introduction to UML

Features of Object Oriented Paradigm

Encapsulation

Data Abstraction

Inheritance

Polymorphism

Association

Persistence



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From Procedural to OO

All programming languages support four basic concepts.

Calculation constants, variables, operators, expressions

Selection - if-else, switch, ?

Iteration - while, do, for Abstraction The process of creating self-contained units of

software that allows the solution to be parameterized andtherefore more general purpose.

Abstraction is the fundamental concept that differentiatesprocedural programming languages such as C from OO languagessuch as Java, C++.



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Abstraction in Procedural Languages

Abstraction in procedural languages is provided through functionsor procedures.

Functions modify external data by performing a particularoperation.

e.g. A c function to calculate the average of two numbers.

float calculate_average (float a, float b) {

float result;

result = (a + b)/2;

return result;

}



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Abstraction in OO Languages

Abstraction in OO languages is provided through an abstract datatype (ADT), which contains data and procedures that operate ondata.

Abstract Data Type (ADT) is a definition that contains data and

procedures that operate on the data. In Java, class is an implementation on an abstract data type.

In OO terminology;

data is referred to as fields, parameters or attributes

procedures are referred to as methods or operations

A class contains attributes and methods that operate on theattributes.

A class is a generalization of a real world entity that is used in aOO program depending on the application.

e.g. animal, student, car, account etc.



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Account Class Example

account name

Account

account number

withdraw cash

deposit cash

check account balance

Data

Methods



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Account Class

// Pseudo Code for Account class

class Account {

String accountName;double accountBalance;

withdrawCash();

depositCash();

checkBalance();} // Class Account



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Circle Class Example

centre

Circle

radius

area

move

circumference

Data

Methods



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Circle Class

// Pseudo Code for Circle class

class Circle {

double cetreX, centreY;double radius;

area();

circumference();

move();

} // Class Circle



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Class vs Object

An Object is an instance of a class.e.g. The object: Zahids Account is an instance of Account class.

The object: Zahids Account is another instance of the Account class.

Objects hold state information while classes do not.e.g. Zahids Account

Account Name = Zahid Account Balance = 15,000

A class represents a template for several objects that havecommon properties.

An Object Oriented system is a collection of interacting Objects.



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Examples of Objects

Figure 1.9: Examples of objects

CAR

VDU

BOY GIRL

TREEBOOK

CLOCK

TRIANGLE



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Classes: Objects with the sameattributes and behaviorPerson Objects

Vehicle Objects

Polygon Objects

Abstract Person Class

Attributes:

Operations:

Name, Age, Sex

Speak(), Listen(), Walk()Into

Abstract Vehicle Class

Attributes:

Operations:

Name, Model, Color

Start(), Stop(), Accelerate()Into

AbstractPolygon Class

Attributes:

Operations: Draw(), Erase(), Move()

Vertices, Border,

Color, FillColorInto

Figure 1.12: Objects and classes



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Introduction to UML

UML Unified Modeling Language

A graphical modeling language that can be used to represent artifacts of object oriented analysis, design and implementation.

It is a standard that has international support.

Was developed by Rational Software

Grady Booch, Jim Rumbaugh and Ivar Jacobson



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UML History

1994 Grady Booch and Jim Rumbaugh started at Rationalcreating the new notation

Grandy Booch Booch Method

Jim Rumbaugh Object Modeling Technique

1995 Ivar Jacobson Joined the team Object-Oriented Software Engineering

First Version of UML 0.8

1995 Object Management Group (OMG) agreed to make UMLthe standard.

1996 Additional companies got involved.

Current version of UML is 2.0



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UML Notations

In the next few weeks, UML notation will be introduced alongwith java to represent Object Oriented concepts.

And Thats your Assignment



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Encapsulation

All information (attributes and methods) in an object orientedsystem is stored/hidden within objects/classes.

Information can be manipulated through operations performed on

the object/class interface to the class. Implementation is hiddenfrom the user.

Objects support Information Hiding Some attributes andmethods can be hidden from the user.

This information hiding capability is called Encapsulation.



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Encapsulation - Example

accountName

accountBalance

checkBalance()

message

message

message



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Encapsulation - Example

Only methods withdrawCash(), depositCash() and checkBalance()have access to (can read or modify) accountName andaccountBalance.

class Account {

private String accountName;

private double accountBalance;

public withdrawCash();

public depositCash();

public checkBalance();

} // Class Account



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Data Abstraction

The technique of creating new data types that are well suited to anapplication.

done by defining new classes.

It allows the creation of user defined data types, having theproperties of built in data types and more.

Example : Creating new classes Account and Circle creates new datatypes Account and Circle that can be used any application.



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class Account {

private String accountName;

private double accountBalance;

public withdrawCash();

public depositCash();

public checkBalance();

} // Class Account

Abstraction - Example

Creates a datatype Account

Account acctX; Account acctY;



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Inheritance

New data types (classes) can be defined as extensions topreviously defined types.

Parent Class (Super Class) Child Class (Sub Class)

Subclass inherits properties from the parent class.

Parent

Child

Inheritedcapability



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Inheritance - Examples

Account Class

Account class in our example had two attributes :accountName and accountBalance.

A check account:

has attributes accountName and accountBalance. In addition: number of cheques issued (numChecks). This

attribute may not be applicable to all types of accounts.

Instead of creating a new class CheckAccount which has allthree attributes, inheritence allows CheckAccount to be definedas a sub class of Account class

thus inheriting attributes accountName and accountBalancefrom the Account class.

Account is the Super Class and CheckAccount is the Sub Class.



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Inheritance in UML

CheckingAccount is a subclass (inherited from ) of a parent class Account.

Account

CheckAccount



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Inheritance - Examples

Circle Class

Circle class in our example has attributes centre and radius.

Consider a Rectangle class. Can have an attribute centre.

However, radius in not an applicable attribute.

Rectangle class should have attributes height and width. Height and width not applicable to circle.

The methods area(), circumference() and move() defines inthe Circle Class are applicable to the Rectangle class.

Do not define a new class Rectangle holding all three attributesand methods.

Define a parent class Shape.

Move common properties to class Shape.

Circle class and Rectangle class can be then be defined assub classes of Shape class.



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Uses of Inheritance - Reuse

If multiple classes have common attributes/methods, thesemethods can be moved to a common class - parent class.

This allows reuse since the implementation is not repeated.

Example : Rectangle and Circle method have a common method move(),which requires changing the centre coordinate.



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Uses of Inheritance - Specialisation

Specialised behaviour can be added to child classes.

In this case the behaviour will be implemented in the child class.

E.g. The implementation of area() method in the Circle class isdifferent from the Rectangle class.

area() method in the child classes override defintions of themethod in parent classes.



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Uses of Inheritance Common Interface

Not all operations supported for Rectangle and Circle are thesame.

Some methods have common implementation and others dont. move() operation is common to classes and can be

implemented in parent. circumference(), area() operations are significantly different

and have to be implemented in the respective classes.

The Shape class provides a common interface where all 3 operations move(), circumference() and area().



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Uses of Inheritance - Extension

Extend functionality of a class.

Child class adds new operations to the parent class but does not change the inherited behaviour.

E.g. Rectangle class might have a special operation that maynot be meaningful to the Circle class - rotate90degrees()



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Uses of Inheritance Multiple Iinheritance

Inherit properties from more than one class.

This is called Multiple Inheritance.

Shape

Circle

Graphics



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Uses of Multiple Inheritance

This is done when a class resides in more than one inheritenceheirarchy.

The class inherits behaviour from multiple parent classes.

Eg. Circle class can inherit move() from the Shape class andpaint() from the Graphics class.

Multiple inheritance is not supported in JAVA but is supported inC++.



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Polymorphism

Polymorphic which means many forms Poly many Morphos - forms.

In OOP, polymorphism itself has many forms.

Polymorphism allows a single object, method, operator to bedefined differently depending on the type of data passed to it.



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Polymorphism

An object of type Circle or Rectangle can be assigned to a Shapeobject. The behaviour of the object will depend on the object passed.

circleA = new Circle(); Create a new circle object

Shape shape = circleA;shape.area(); area() for circle class will be executed

rectangleA = new Rectangle(); Create a new rectangle object

shape= rectangleA;shape.area() area() method for rectangle will be executed.



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Polymorphism Method Overloading

Multiple methods can be defined with the same name, acceptingdifferent input arguments.

Method 1 - initialize(int a)

Method 2 - initialize(int a, int b)

The Appropriate method will be called based on the input arguments.

initialize(2) Method 1 will be called.

initialize(2,4) Method 2 will be called.



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Polymorphism Operator Overloading

Allows regular operators such as +, -, *, / to have different meanings based on the type.

E.g. + operator for Circle can re-defined

Circle c = c +2;

Not supported in JAVA. C++ does support it.



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Association

A class can maintain a relationship with another class which willallow the class to communicate with the other class.

This type of relationship is called an association.

Example :

The Circle and Rectangle objects may be contained in a Diagram

class. This creates and association between the Diagram class and

Circle class and also Diagram and Rectangle class.

Circle

Rectangle

Diagram

contains>

contains>



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A simple class diagram

A Class diagram shown classes and their relationships.

Draw a simple class diagram for the following description.

A student can be an undergraduate or a graduate.

An undergraduate student can be a type of tutor.

A tutor tutors a student.

A teacher and a professor are two types of instructors.

A teacher assistant is a type of graduate student who assists a

teacher.



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Why OOP?

Greater Reliability

Break complex software projects into small, self-contained, andmodular objects

Maintainability

Modular objects make locating bugs easier, with less impact onthe overall project

Greater Productivity through Reuse!

Faster Design and Modelling

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