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TIA1013 : Introduction ToProgramming

Week 2Introduction to

Object Oriented Programming

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Object, Class, Message, Method &

Attributes

Object-Oriented Programming

Characteristics

Lecture Outlines

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To describe fundamental concepts of OOP.

To state the difference between objects

and classes To identify characteristics of OOP.

To draw a basic of UML class diagram.

Learning Objectives

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Two popular programming design methods:

Structured Programming (SP)

Object-Oriented Programming (OOP)

Introduction to OOP

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Other name: top-down, stepwise, modular

Main problem will be divided into sub-problem

Analyze each sub-problem

All sub-problem solutions will be combinedto solves the main problem

Structured Programming(SP)

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Designs a program as collections of interactingobjects that work together to accomplish tasks.

Model the world as it is.

The main concepts OO:

Objects, Classes and Instances

Attributes and operations (behaviour)

Object State Message-passing and methods


(OOP)

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Identify object as foundation for problemsolving

Identify interaction method for each object

Identify data/attribute for each object

Identify operation for each data

Object will combines data and operation in

one unit An OOP program is a collection of objects

that interacts each other


(OOP)

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An Object is a thing, both tangible andintangible. Account, Vehicle, Employee, etc.

Objects have state, behaviour and identity.

State: the condition of an object at any moment,affecting how it can behave

Behaviour: what an object can do, how it canrespond to events and stimuli

Identity: each object is unique

Objects are categorized into classes

Each individual object is an instance of a class

Objects

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To create an object inside the computerprogram, we must provide a definition forobjectshow they behave and what kindsof information they maintain called a

Class. Class - a category of objects that share the

same:

attributes,

operations/methods

Attribute keeping objects characteristics

Operation represents objects behavior.

Class

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Attribute- a named propertyof a class thatdescribes a range of values that instances ofthe attribute might hold

Attributes are the way classes encapsulatedata

Example:

Class : Employee

Attributes: employee_name, employee_id,

position, department etc..

Attribute

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A behaviorof an object Implemented in classes are methods Methods are identified and invoked by their

signatures, including name, parameters, andreturn type

Example:Class : EmployeeAttributes: employee_name, employee_id,

position, department, salary etc..

Operations: setEmployeeDetailscalculateSalaryprintEmployeeDetails

Operation

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ClassTemplate (blue print) to define specificinstances or objects

ObjectInstantiation of a class

AttributesDescribes the object

Behaviors/Operationspecify what object can do

Methods implement an objects behavior

Analogous to a function or procedure Messages are sent to trigger methods

Procedure call from one object to the next

Summary

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Basic skeleton of Java class

/*Sample program: Displaying Welcome*/

public class Greeting{

public static void main (String[] args){System.out.println(Welcome);

}

}

Class Declaration

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Comments

Reserved words Identifiers

Statements

Blocks

Classes

Methods

The main method

//printing welcome

public class Greeting {

public static void main(String[] args)

{

System.out.println(Welcome!");

}

}

StringMain method signature

Class title Class name

block

block

Java Anatomy

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The Java class declaration takes the followingform:

* class {

**

}

Class Declaration

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public void print(){System.out.println(This CD title is

+ title + and still available

+ no_of_stock + copies);}

}

Method definition

Class Declaration

public class Cd {private String title;private String no_of_stock;

public void setData(){title = Animal Planet;no_of_stock = 45;

}

class

attributes

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The notation we used here is based on the industry standardnotation called UML, which stands for Unified Modeling Language.

Example:

Graphical Representation of a

Class

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Graphical Representation of a

ClassCd

- title

- no_of_stock

+ setData()

+ print()

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To instruct a class or an object to perform a task,we send a messageto it.

You can send a message ONLY TO the classes

and objects that understand the message yousent to them.

A class or an object must possess a matchingmethodto be able to handle the received

message.

Message and Method

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print()

Message print is sent toa Cd object myCd.

myjCd : Cd

Sending Message..

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In Java, instance/object is created by usingnewkeyword.

Basic syntax: = new (parameters);

Example:

Cd myCd = new Cd ();

Creating Object

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We use a rectangle torepresent an object andplace the underlinedname of the objectinside the rectangle.

Example:

myCd This is an object namedmyCd.

Graphical Representation of

an Object

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public class TestCd{

public static void main (String args[ ])

{Cd myCd = new Cd();

myCd.print();

}

}

Accessing print() method (sending message

printto object myCd)

Main method, Object,

Accessing method

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class Cd {

private String title;private int no_of_stock;

public void setData(){title = Animal Planet;no_of_stock = 45;

}void print() {System.out.println(This CD title is

+ title + and still available

+ no_of_stock + copies);

}

}public class TestCd {

public static void main (String args[ ]){

Cd myCd = new Cd();

myCd.print();

}}

Sample of Complete Program

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Abstraction

Encapsulation

Inheritance Polymorphism

Characteristics of OOP

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Abstraction is the process of finding theessential feature set for a class.

Concentrating on what an object isand does

before making any decision about how theobject will be implemented.

Capture the attributes and operation of aobject/real-world deck.

Object in a program is an abstractionof thereal-world object. Example: myCd.

Abstraction..

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Encapsulation is the process of hiding object data andproviding methods for data access (data and behaviorare bundled into a class and hidden from the outsideworld)

Process of hiding the implementation details.

Each object of a class has its own set of instance fields.Instance fields are declared with the access modifierprivate, public or protected.

Access to the data and behavior is provided and

controlled through an objects interface Useful, because programmer can reuse the programcode.

Data, element, and method is being encapsulatedin aclass, and can be use by the other class.

Encapsulation..

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Inheritance is a fundamental object-oriented designtechnique used to create and organize reusableclasses

Inheritanceallows a software developer to derive anew class from an existing one

The existing class is called the parent class, orsuperclass, or base class

The derived class is called the child classorsubclass

As the name implies, the child inheritscharacteristics of the parent

A subclass inherits accessible data fields andmethods from its super class, and may also addnew data fields and methods.

Inheritance..

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Inheritance..

Super class(more general)

Subclass

(morespecialized)

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Inheritance..

Inheritance relationships are shown in a UMLclass diagram using a solid arrow with anunfilled triangular arrowhead pointing to theparent class

Vehicle

Car

Proper inheritance creates an is-arelationship, meaning the child is amorespecific version of the parent

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A is a superclass to BB is a subclass to AB is a superclass to C, D and E.

C, D and E is a subclass to B

Class A

Class B

Class C Class D Class E

Inheritance..

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Inheritance..

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The ability for different classes of objects

to respond to identical messages in

different ways

Polymorphism = having many forms

Different behaviors for the same message

Polymorphism..

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Can be overloading oroverriding.

Overloading methods appear in the same class have the same name but, have different parameter lists, and,

can have different return types

Overriding methods overriding allows a subclass to re-define a method it inherits from

it's superclass overriding methods: appear in subclasses

have the same name as a superclass method have the same parameter list as a superclass method have the same return type as as a superclass method

Polymorphism..

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Here, each

type ofvehicle has

its own

version of

calcPrice()

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Conclusion

Q & A Session

basic - week 02

Documents