IT1202Fundamentals Of Programming Object Oriented Concepts and Techniques

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IT1202-Fundamentals Of ProgrammingObject
Oriented Concepts and Techniques
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Introduction to Object Oriented Programming

• The idea of Object Oriented
• Programming is
• organize your programs in a way
• that mirrors the way objects are
• organized in the real world

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Thinking in terms of Objects

• This is a way to look at a program as a set of
  objects that work together in predefined ways to
  accomplish tasks
• Using OOP, your overall program is made up of
  different components called objects

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An Object ?

• An object is a self-contained element of a
  computer program that represents a related group
  of features and is designed to accomplish
  specific tasks
• Also known as instances
• Each object has a specific role in a program, and
  all objects can work with other objects in
  defined ways

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Object

• An Employee object (say employee1)
• will have the following
• attributes (what it knows)
• Name
• age
• salary
• It will have the following
• behavior (what it can do)
• set salary
• get salary
• set name
• set age

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A Class

• Definition A template used to create
• multiple objects with
  similar
• features.
• Classes embody all features (attributes
  behaviour) of a particular set of objects
• When writing a program in an OO language, you do
  not need to define individual objects
• Instead, define classes of objects (template)

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A Class

• eg A Tree that describes the features of all
  trees
• Has leaves roots
• Grows
• Creates chlorophyll
• The Tree class serves as an abstract model for
  the concept of a tree

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Class.

• Some objects that
• will be in tree class

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Class..
WashingMachine
Attributes
brandName modelName serialNumber capacity
Objects
A Class
addClothes() addDetergent() removeClothes()
methods
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Attributes and Behavior

• Every class written in java is made up of two
  components
• Attributes and Behavior
• Attributes
• Individual things that differentiate one class
  of objects from another
• Determine the appearance, state and other
  qualities of that class
• eg Color orange, raw amber, lemon yellow, maize

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Attributes and Behavior.

• Behavior of a Class of Objects
• Behavior is the way that a class of objects can
  act to change their attributes

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Behavior.

• Examples for behavior
• Get angry
• Calm down
• Eat an ice cream
• Behavior for a class of objects is done by
• using methods

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Example of a class (template for an object)

• public class Employee
• private String name
• private int age
• private float salary
• public void setName(String tName)
• Name tName
• public void setSalary (float tSalary)
• salary tSalary
• public float getSalary ()
• return salary

Attributes
Methods
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Creating a Class..

• Open the text editor to create Java programs.
• Start with class definition
• eg
• class Jabberwock
• Then create instance variables
• eg
• String color
• boolean hungry

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Creating a Class.

• After that the programmer can add behavior to the
  class by adding methods
• eg
• void feedJabberwock()
• if (hungry true)
• System.out.println(yum an ice
  cream)
• hungry false
• else
• System.out.println(No, thanks I
  have already eaten)

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Creating Objects

• Objects are created by instantiating
• classes
• To use a class in a program, you must first
  create an instance of it
• Objects of a class can be created using the new
  operator

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Creating objects..

• Example
• Employee newEmp new Employee()

Constructor
Variable containing an Object reference
Class Name
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Methods

• Methods are group of related statements in a
  class of objects that act on themselves and on
  other classes of objects
• Used to accomplish specific tasks
• Objects communicate with each other using methods

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Defining methods
Can be any primitive type or a class Name or void
(no return statement)
Optional
modifier returnType MethodName (parameter List)
statement(s)
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Methods..

• The return Type, Method Name, and the
  parameter list defines the Signature of the
  method
• It is possible to define two or more methods
  with the same name within the same class (Method
  Overloading) with different signatures
• Methods are two types - instance methods and
  class methods

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Methods..
1.public void CreatePoint( ) 2.public void
CreatePoint(int x , int y)
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Methods..

• Accessing methods

An instance method can be accessed using the
dot(.) operator as shown below.
ObjectName.method()
A class method can be accessed by using the class
name followed by a period and then the method
name
Integer.parseInt(25)
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What is a constructor?

• Constructor is also a method
• It is a special method
• Method name same as the class name
• No return type
• It allocates memory for the instance object
• called automatically when an instance is
  created/constructed
• If not defined still and object will be created
• If defined variables can be initialized in your
  own way

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this and super keywords

• this keyword
• this keyword is used to refer to the current
  object

• It can be used to
• Refer to the current objects member variables
• Refer to current objects methods
• Pass a reference to a method of the current
  object
• Return a reference from the current object

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this keyword
Refers to the member variable x in this object
tthis.x this.myMethod(this) return this
Calls the myMethod defined in this class and
pass it to this Object
Return this Object
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super keyword

• super keyword is used to refer to the
• Super or parent class

Invokes super class Constructor
super( ) super(x,y) super.f( )
Invokes super class Constructor with x and y
arguments
Calls the super class function called f( )
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Object Oriented Concepts

• Three basic concepts underlining Object Oriented
  Programming
• Data Abstraction with Encapsulation
• Inheritance
• Polymorphism

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Encapsulation

• Enables you to hide, inside the object, both the
  data fields and the methods that act on that data

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Encapsulation..

• Object CAR
• Attributes
• speed,direction
• Number of people it can carry
• Methods
• Steer() ,
• PressGasPedal(),
• PressBreak()
• Loadpeople()

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Encapsulation..

• Encapsulation is achieved by using Modifiers
• Modifiers are Language Keywords that modify the
  definition of a Class, Method or a Variable
• Access to variables and methods in Java classes
  is accomplished through Access Modifiers
• Access modifiers define varying levels of access
  between class members and the outside world
  (other objects)

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Encapsulation..

• Access modifiers are declared immediately before
  the type of a member variable or the return type
  of a method
• modifier returnType MethodName (parameter List)
• There are four access modifiers
• Default (package access)
• Public
• Protected
• Private

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Inheritance

• One class of objects inheriting the data and
  behavior from another class of objects

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Inheritance

• class for a regular car.

Class Car direction
position speed
Steer() PressGasPedal()
PressBreak()
Data members/ Attributes
Methods
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Inheritance
Suppose you want to create a new car which has a
special passing gear
Class PassingCar inherits from Car
Pass()
Pass() is a method that implements the new
functionality
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Inheritance

• Through inheritance you can express the
  differences among related classes
• You share the functions and member variables that
  implement the common features
• Inheritance also helps you to reuse existing code
  from one or more classes by simply deriving a new
  class from them

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Inheritance

• Inheritance is the creation of one class by
  extending another class so that instances of the
  new class automatically inherit the fields and
  methods of its parent class
• Inheritance promotes the class Reusability
• It is because an existing class can be sub
  classed through inheritance and any modifications
  necessary could be applied to the sub class
  (Overriding)

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Inheritance

• In Java the extends Keyword is used to achieve
  Inheritance

public class threeDPoint extends twoDPoint
sub class
super class
Java does not Support Multiple Inheritance
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Inheritance

• A class that cannot be instantiated is known as
  an Abstract Class
• An Abstract Class
• is defined to be extended to sub classes
• uses abstract Keyword in the Definition

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Inheritance
abstract class Shape abstract Point Center(
) abstract double Diameter( ) abstract double
Area( )
Can be used to create any shape Such as Circle
or Square
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Polymorphism

• Combines Greek Words
• Poly , Morphism
• Poly Many
• Morphism Forms
• The quality of having more than one form

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Polymorphism

• In the context of Object Oriented Programming,
  polymorphism refers to the fact
• A single operation can have different behavior in
  different objects

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Polymorphism

• It allows different forms of the same service to
  be defined
• There are two common ways of implementing
  Polymorphism. Overloading, Overriding
• Overloading - Using the same method name with
  different parameter type lists within the same
  class
• Overriding - Using different implementations of
  the same method in sub classes

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Lets consider some examples which are
illustrating some of the concepts of object
Orientation
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Lets simulate a box in Java
Depth
Height
Width
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Lets simulate a box in Java
Introduce the class
class Box
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Lets simulate a box in Java
Introduce instance variable
class Box double width double height double
depth
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Lets simulate a box in Java
Save and compile
class Box double width double height double
depth
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Lets simulate a box in Java
Some important notes

• In the class the main() method is not written
• Class is just a template
• During designing one creates a class
• During Run time objects are created

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Lets simulate a box in Java
Using the class Box

• Create a class which is having the main() method
  (our program)
• Declare a variable of the class Box
• Use them in the program

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Lets simulate a box in Java
Using the class Box
class BoxDemo public static void main(String
args)


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Lets simulate a box in Java
Declare a variable of Box with values
class BoxDemo public static void main(String
args)
Box myBox new
Box() myBox.width3 myBox.height5 myBox.depth
4

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Lets simulate a box in Java
Using the class Box
class BoxDemo public static void main(String
args)
Box myBox new
Box() myBox.width3 myBox.height5 myBox.depth
4

myBox
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Lets simulate a box in Java
Lets calculate the volume of the myBox
class BoxDemo public static void main(String
args)
Box myBox new Box() myBox.width3 myB
ox.height5 myBox.depth4 System.out.println(myB
ox.width myBox.heightmyBox.depth)


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Lets simulate a box in Java
new keyword

• Box myBox new Box()
• Java does three things when new is used
• Allocate memory for the object
• Initialize that objects instance variables,
  either to initial values or to a default(0 for
  numbers,null for objects, false for Booleans
  ,\0 for characters)
• Calls the constructor method of the class which
  might be one of several methods

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Lets simulate a box in Java
Initialization

• myBox.width3
• myBox.height5
• myBox.depth4
• When the variables are initialized of the myBox
  instance object
• width 3, height 5, depth 4

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Lets simulate a box in Java
The output

• System.out.println(myBox.width
  myBox.heightmyBox.depth)
• When this statement is executed the volume of my
  box will be calculated and will output to the
  screen

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Lets simulate a box in Java
When the program executed
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Lets simulate a box in Java
Methods

• Methods written to manipulate data
• Methods written to allocate memory(constructors)

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Lets simulate a box in Java
Add a method to the class Box

• To calculate the volume lets create a method
• Name of the method is calcVol()
• No parameters are used
• No returning values

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Lets simulate a box in Java
Add a method to the class Box
How do we write a method? Return type
methodName(Parameter list) Body of the method
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Lets simulate a box in Java
Add a method to the class Box
void CalcVol( ) System.out.println( width
height depth)
resultant value will be out put to the screen
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Lets simulate a box in Java
Add a method to the class Box
class Box double width double height double
depth void CalcVol() System.out.println( width
height depth)

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Lets simulate a box in Java
Add a method to the class Box

• Save the file Box.java
• Compile the file
• But you can not execute the file
• because this is a class file( no main())

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Lets simulate a box in Java
Add a method to the class Box

• How do we use methods(call methods)
• We have to call methods from our program
• Our program name is BoxDemo
• When we call the method we have to refer to the
  method using the instance name and dot operator

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Lets simulate a box in Java
Use a method in the BoxDemo
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Lets simulate a box in Java
What is a constructor?

• Constructor is also a method
• It is a special method
• Method name same as the class name
• No return type
• It allocates memory for the instance object
• Called automatically when an instance is
  created/constructed
• If not defined an object will be created
• If defined, variables can be initialized
  according to your requirements

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Lets simulate a box in Java
Add a constructor to the class Box
class Box double width double heightdouble
depth void CalcVol() System.out.println( width
height depth ) Box() Width
4 Height 2 Depth 3
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Lets simulate a box in Java
Then our program?
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Lets simulate a box in Java
Add a constructor to the class Box
How do we create our own box with our own
dimension ?
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Lets simulate a box in Java
constructor to the class Box
class Box double width double heightdouble
depth void CalcVol() System.out.println( width
height depth) Box(double w, double h,
double d) Width w Height h
Depth d
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Lets simulate a box in Java
Then our program?
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Lets simulate a box in Java
Inheritance
Box
Box
There are two boxes having different colours
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Lets simulate a box in Java
Inheritance
Box
Box
Other than dimensions the colour is changed
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Lets simulate a box in Java
Template of the class Box
class Box double width double heightdouble
depth double CalcVol() return width height
depth Box(double w, double h, double d)
Width w Height h Depth d

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Lets simulate a box in Java
Template of the class ColorBox
class ColorBox extends Box int
colour ColorBox(double w, double h, double d,
int c) Super(w,h,d) Color c

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Lets simulate a box in Java
Inheritance
height width depth
w , h , d
colour
Box
c
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Lets simulate a box in Java
Template of the class ColorBox
class ColorBox extends Box int
colour ColorBox(double w, double h, double d,
int c) Super(w,h,d) Color c

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Lets simulate a box in Java
Then our program?
class BoxDemo public static void main(String
args) ColorBox myBox new ColorBox(2,4,5,255)
System.out.println(myBox.CalcVol())


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Polymorphism
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Lets simulate a box in Java
Template of the class Box
class Box double width double heightdouble
depth double CalcVol() return width height
depth Box() Box(double w, double h, double
d) Width w Height h Depth
d
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Some URLs

•   Definition of a class
• http//java.sun.com/docs/books/tutorial/java/conce
  pts/class.html
• Creating objects
• http//java.sun.com/docs/books/tutorial/java/data/
  objectcreation.html
•   Defining methods
• http//www.cs.brown.edu/courses/cs015/2002/Referen
  ceGuides/JavaRefGuide/definemethod.html