INTRODUCTION TO OOP Chapter 1 CSC238 1. Objectives 2 At the end of this topic, you should be able to...

INTRODUCTION TO OOP

Chapter 1

CSC238 1

Objectives2

At the end of this topic, you should be able to know the elements of an object. differentiate between objects and classes. understand the characteristics of OOP.

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Object3

Objects are key to understanding object-oriented technology.

In real life, things that you see such as cars, trees, cats, mobile phones and so on are objects. Even, you as a student is an object.

Each object has states , behaviours and identity.

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OBJECT

Attribute /state – properties used to define characteristics.

Behaviour – means the object can perform actions & can have actions performed on it.

Identity – means the object can be called & used as a single unit.

Elements of an Object

Example 1:

State :

Turn on

Current temperature is at 20 degree celcius

Behaviours :

Change the temperature level

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An air-conditioner at MK02

Example 2:

State :

Dark brown colours on its face, ears and feet

Behaviours :

Playing, fighting, hunting

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A Siamese Cat

Example 3:

They are 3 different cats which two of them are of the same type.

What makes them different?

their states , behaviours and identity.

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How about the following cats?

Example 4:8

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Different types of cats Share the same behaviours

Example 5:

Try to identify their common attributes and behaviours .

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How about these cars?

Lesson Learned…10

What can you tell from example 3 to 5? A group of animals or things that are similar in some way. They share the same attributes and behaviours. This group of objects represents a class.

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● a kind of template.● represents the common

structure & behaviour shared by the same type.

● A collection of objects of similar type.

● must be defined before creating an instance of the class.

● a thing, both tangible and intangible.

● is comprised of data & operations that manipulate these data.

● is called an instance of a class.

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Class Object

Class ? Object ?

Example 6:12

● Represents the data/ attributes variables.

● a set of properties

Methods

Variables

• Represents the behaviours.• A sequence of instructions that a class

or an object follows to perform a task.

Student

nameid

setName()setId()

: Student

name=“Sarah”id=“1234”

class

object / instance of the class

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Messages13

● An object can’t exist on its own.● An object communicates with other objects.● Therefore, a message is used to instruct a class or an object to

perform a task.● An object or a class only responds to messages that it can

understand. Messages must match the method that it possess. ● A list of messages is called an interface.

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Abstraction Encapsulation Inheritance Polymorphism

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Characteristics of OOP

Characteristic of OOP

● the act of representing essential features without including the background details or explanations.

● Use to manage complexity● Abstraction can be managed

through the use of hierarchical classifications.

● The mechanism that binds together code and the data it manipulates and keeps both safe from the outside interference and misuse.

● Access to the code & data inside the wrapper is tightly controlled through a well-defined interface.

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Abstraction Encapsulation

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Student

Variables:name student idaddresscourse

Methods:changeAddress(String)changeCourse(String)

INTERFACEchangeAddress(String)changeCourse(String)

Example 7:

● The process by which one object acquires the properties of another object.

● An object need only to define all those qualities that make it unique within its class. It inherits its general attributes from its parent.

● A subclass has at least one attribute/method that differs from its superclass

● Other names :base class-derived class, parent class-child class

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Inheritance

Characteristics of OOP

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Mobile Phone

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MobilePhone

modelmanufacturerprice

…

CameraPhone

modelmanufacturerpricepixel

…

superclass subclass

subclass

PdaPhone

modelmanufacturerpricememoryCap

…

Example 8:

Characteristics of OOP

● From the Greek, meaning “many forms”.● A feature that allows one interface to be used for a general class of

actions.● “one interface, multiple methods”● Can be applied in the overloaded methods (a few methods that

have the same name but with different parameters).

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Polymorphism

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● Class : Rectangle● Variables : length, width, height● Methods : ….

displayShape(char simbol) displayShape(int a)

This class has 2 methods with the same name but with different type of parameters

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Example 9:

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● Elements of an object are attribute, behaviour and identity.● A class is a collection of objects of similar type.● An object is comprised of data and operations that manipulate

these data.● Characteristics of OOP is abstraction, encapsulation, inheritance

and polymorphism.

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Conclusion