OOP Core Concept

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Object Oriented Programming
OOP……. Not OOPS!!
Core Concepts
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Java Primitive Data Types
Primitive Data Types:
o boolean true or false
o char unicode (16 bits)
o byte signed 8 bit integer
o short signed 16 bit integer
o int signed 32 bit integer
o long signed 64 bit integer
o float,double floating point values
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Other Data Types
Reference types (composite)
o objects
o arrays
strings are supported by a built-in class named String
(java.lang.String).
string literals are supported by the language (as a special
case).
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Custom Data Type
public class Shape {
private String color = null;
private int borderWidth = 0;
public int getBorderWidth() {
return borderWidth;
}
public void setBorderWidth(int bw){
borderWidth = bw;
}
public String getColor() {
return color;
}
public void setColor(String color) {
this.color = color;
}
}
:Shape
-color :String
-borderWidth:int
+getColor():String
+setColor()
+getBorderWidth():int
+setBorderWidth()
Members
Member
variables
Member
methods

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Define attribute/variable
 public class TestShape {
o public static void main(String[] args){
 Shape s; //Declaration
 s = new Shape(); //Instantiation
 s.setColor(“Red”);
 s.setBorderWidth(3);
 ….
 int borderW =s.getBorderWidth();
 System.out.println(borderW) ;
o }
 }
S is an object here
S is an instance
here

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Encapsulation
Gathering all related methods and attributes in a Class
is called encapsulation.

Real World Entities – More Classes
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:Automobile
-color :String
-speed:int
-make:String
+$NO_OF_GEARS
+getColor():String
+setColor()
+getMake():String
+setMake()
+break()
+changeGear()
+accelerator()
+getSpeed():int
:Person
-name:String
-dob : Date
-address:String
+$AVG_AGE
+getName():String
+setName()
+getAdress():String
+setAddress()
+getDob (): Date
+setDob ()
+getAge() : int
:Account
-number:String
-accountType : String
-balance:double
+getNumber():String
+setNumber()
+getAccountType():String
+setAccountType()
+deposit ()
+withdrawal ()
+getBalance():double
+fundTransfer()
+payBill()

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Define A Class - Shape
public static final float PI = 3.14;
public int getBorderWidth() {
return borderWidth;
}
public void setBorderWidth(int bw) {
borderWidth = bw;
}
public String getColor() {
return color;
}
public void setColor(String color) {
this.color = color;
}
:Shape
-color :String
-borderWidth:int
+$PI=3.14
+getColor():String
+setColor()
+getBorderWidth():int
+setBorderWidth()
Shape s1 = new Shape();
Shape s2 = new Shape();
S.o.p( s1.PI );
S.o.p( s2.PI );
S.o.p( Shape.PI );

Object initialization at the time of memory
allocation
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Constructor
public Shape(){
System.out.println(
“This is default constructor”);
}
……………
Shape s = new Shape();
 Constructor is just like a method.
 It does not have return type.
 Its name is same as Class name.
 It is called at the time of object
instantiation (new Shape()).
 Constructors are used to initialize
instance/class variables.
 A class may have multiple
constructors with different number
of parameters.

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Multiple Constructors
One class may have more than one constructors.
Multiple constructors are used to initialize different sets
of class attributes.
When a class has more than one constructors, it is called
Constructor Overloading.
Constructors those receive parameters are called
Parameterized Constructors.

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Constructors Overloading
public Shape(){
System.out.println(“This is
default constuctor”)
}
public Shape (String c, int w){
color=c;
borderWidth=w;
}
Shape s = new Shape()
s.setColor(“Red”);
s.setBorderWidth(5);
Or
Shape s = new
Shape(“Red”,5)

Inheritance:
o Creates Specialized Classes.
 Q: Does every class have child?
 A: No, class those have specialised behaviour can have child like Shape,
Person, Automobile, Account etc. Otherwise that will be final class like Math,
String etc.
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Inheritance
:Shape
color :String
borderWidth:int
getColor():String
setColor()
getBorderWidth():int
setBorderWidth()
:Rectangle
length :int
width:int
area()
getLength()
setLength()
:Circle
radius : int
area()
getRadius()
setRadius()
:Triangle
base:int
hight:int
area()
getBase()
setBase()
Circle c =new Circle();
c.getColor();
c.getBorderWidth();
c.area();
:Object
UML Notation

Inheritance
public class Shape{ .. }
public class Circle extends Shape{ .. }
public class Rectangle extends Shape{ .. }
public class Triangle extends Shape{ .. }
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Method Overriding – area()
:Shape
Color :String
borderWidth:int
getColor():String
setColor()
getBorderWidth():int
setBorderWidth()
area()
:Rectangle
length :int
width:int
area()
getLength()
setLength()
:Circle
radius
area()
getRadius()
setRadius()
:Triangle
base:int
hight:int
area()
getBase()
setBase()
Shape s= new Circle();
s.getColor();
s.getBorderWidth();
s.area();

Polymorphism - Method Overriding
 public class Shape{
 public double area(){}
 }
 public class Circle extends Shape{
 public double area(){ ……..}
 }
 public class Rectangle extends Shape{
 public double area(){……..}
 }
 public class Triangle extends Shape{
 public double area(){……..}
 }
In Method Overriding
o Method signature
(name, return
type,no of
parameters) should
be same
o Applies only in case
of Inheritance
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Polymorphism - Method Overloading
 public class Addition{
 public void sum(int a, int b){..}
 public void sum(int a, int b, int c){..}
 public double sum(double a, int b){..}
 public float sum(float a, int b){..}
 }
In Overloading
o Method name should be
same
o Method Parameter should
be different in no and type
both
o Return type can be same or
different
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Data Abstration – Abstract Class
public abstract class Shape {
public abstract double area();
}
public class Circle extends Shape{
public double area(){
double circleArea = 3.14*radius*radius;
return circleArea;
}
public static void main(){
Shape s = new Circle();
double area = s.area();
System.out.println(area);
}
}

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Data Abstraction - interface Richman
public interface Richman {
o public void earnMoney();
o public void donation();
o public void party();
}

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interface SocialWorker
public interface SocialWorker{
o public void helpToOthers();
}

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interface SocialWorker
 public class Businessman extends Person implements Richman,
SocialWorker {
 public void donation() {..}
 public void earnMoney() {..}
 public void party() {..}
 public void helpToOthers() {..}
 }

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Explicit constructor calling using this()
 public Person() {
 System.out.println("Person Default Con");
 }
 public Person(String fn, String ln) {
o firstName = fn;
o lastName = ln;
o System.out.println("2 params constructor is called");
 }
 public Person(String fn, String ln, String address) {
1. this(fn,ln) ;
2. this.address = address;
3. System.out.println(“3 params constructor is called");
 }

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Explicit constructor calling using super()
 public class Employee extends Person {
 private String designation = null;
 public Employee() {
 System.out.println("Default Constructor");
 }
 public Employee(String fn, String ln, String des) {
 super(fn, ln);
 designation = des;
 System.out.println(“3 params constructor is called");
 }

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Method Definition
..
public void setBorderWidth(int bw)
{
borderWidth = bw;
}
}
Method

Default Constructor
 Default constructor does not receive any parameter.
o public Shape(){ .. }
 If User does not define any constructor then Default Constructor
will be created by Java Compiler.
 But if user defines single or multiple constructors then default
constructor will not be generated by Java Compiler.
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Abstract Class
 What code can be written in Shape.area() method?
o Nothing, area() method is defined by child classes. It should have only
declaration.
 Is Shape a concrete class?
o NO, Rectangle, Circle and Triangle are concrete classes.
 If it has only area declaration then
o Method will be abstract and class will be abstract as well.
 Benefit?
o Parent will enforce child to implement area() method.
o Child has to mandatorily define (implement) area method.
o This will achieve polymorphism.

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Interface
When all methods are abstract then interface is created.
It has abstract methods and constants.
It represents a role (abstract view) for a class.
One interface can extend another interface using extends
keyword.
One Class can implement multiple interfaces using
implements keyword.

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Interfaces
Richman
earnMony()
donation()
party()
Businessman
name
address
earnMony()
donation()
party()
Richman rm = new Businessman();
SocialWorker sw = new Businessman();
Businessman bm = new Businessman();
SocialWorker
helpToOthers()
Businessman
name
address
earnMony()
donation()
party()
helpToOthers()
Businessman
name
address
helpToOthers()

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Interface
It declares APIs.
Specifications are defined as interfaces.
o JDBC
o Collection
o EJB
o JNI
o etc.

Data Hiding ( Cont. )
Data Hiding is an aspect of Object Oriented
Programming (OOP) that allows developers to
protect private data and hide implementation
details.
Developers can hide class members from other
classes. Access of class members can be
restricted or hide with the help of access
modifiers.
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How a constructor can call another constructor ?
 public class Person {
 protected String firstName = null;
 protected String lastName = null;
 protected String address = null;
 public Person() {
 System.out.println("Person Default Con");
 }
 public Person(String fn, String ln) {
o firstName = fn;
o lastName = ln;
o System.out.println(“2 params constructor is called");
 }

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How a constructor can call another constructor ?
 public Person(String fn, String ln, String address) {
o firstName = fn;
o lastName = ln;
o this.address = address;
 }

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Super default constructor
 If Child constructor does not call parent’s constructor then Parent’s default
constructor is automatically called.
 }
 Is Equal to
 super();
 }

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Super default constructor (cont.)
o designation = des;
o System.out.println(“3 params constructor is called ");
 }
 Is Equal to
o super();
o designation = des;
 }

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How to call Parent’s overridden method?
 public class Person {
 public void changeAddress() {
o System.out.println("Person change Address");
 }
 …
 public class Employee extends Person {
 public void changeAddress() {
o System.out.println("*****");
o super.changeAddress();
o System.out.println("Employee change Address");
 }
 …

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Interesting facts - Overriding
 public class Account{
o public int getAmount() {
o return 5;
o }
 }
 public class SavingAccount extends Account {
 return 10;
o }
 }

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What is Output Of
 public class Test {
 public static void main(String[] args) {
o SavingAccount s = new SavingAccount ();
o Account a = new Account ();
o Account sa = new SavingAccount ();
o System.out.println(s.getAmount());
o System.out.println(a.getAmount());
o System.out.println(sa.getAmount());
o }
 }

Interesting facts - Overriding
 public class Account{
o return 5;
o }
 }
 public class SavingAccount extends Account{
 int i = super.getAmount() + 10;
 return i;
o }
 }
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Polymorphism
 Three Common Uses of Polymorphism:
o Using Polymorphism in Arrays.
o Using Polymorphism for Method Arguments.
o Using Polymorphism for Method Return Type.
 Ways to Provide polymorphism:
o Through Interfaces.
o Method Overriding.
o Method Overloading.

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1) Using Polymorphism in Arrays
Shape s[] = new Shape[3];
s[0] = new Rectangle()
s[1] = new Circle()
s[2] = new Triangle()
s[0]:Rectangle
color
borderWidth
length = 17
Width = 35
s[1]:Circle
color
borderWidth
radius = 11
s[2]:Triangle
color
borderWidth
base:15
hight:7

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2) Using Polymorphism for Method Arguments
public static void main(String[] args) {
Shape[] s = new Shape[3];
s[0] = new Rectangle();
s[1] = new Circle();
s[2] = new Triangle();
double totalArea = calcArea(s);
System.out.println(totalArea);
}
public static double calcArea(Shape[] s) {
double totalArea = 0;
for(int i =0;i<s.length; i++){
totalArea += s[i].area();
}
return totalArea;
}
*The method overriding is an example of runtime polymorphism.

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3) Polymorphism using Return Type
public static Shape getShape(int i) {
if (i == 1) return new Rectangle();
if (i == 2) return new Circle();
if (i == 3) return new Triangle();
}

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Method Overloading
PrintWriter
o println(String)
o println(int)
o println(double)
o println(boolean)
o println()

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The Final modifier
Class :
o Final classes can not have Children.
o public final class Math
Method:
o Final Methods can not be overridden.
o public final double sqrt(int i);
Attribute:
o Final attributes can be assigned a value once in a life.
o public final float PI = 3.14;

Disclaimer
This is an educational presentation to enhance the skill
of computer science students.
This presentation is available for free to computer
science students.
Some internet images from different URLs are used in
this presentation to simplify technical examples and
correlate examples with the real world.
We are grateful to owners of these URLs and pictures.
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Thank You!
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OOP Core Concept

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