OOPs: Object-Oriented Programming
Examples:
- Java
- .Net
- Python
- C++
- Ruby
Object-Oriented Programming (OOP) is a
programming paradigm that uses objects and classes to design and develop
application
If any Programming language,
which supports OOPs features like
OOPS Features:
1. Class and
Object
2. Inheritance
3. Polymorphism
4. Abstraction
5. Encapsulation
1. Class and Object :
Without Defining class , we
cannot write any simple java program
without writing class , "" ""
Define class :
class is predefined k/w in java to define class /
write class
Syntax:
class someName
{
}
class A
{
public static void main (String args [] )
{
}
}
Class:
A blueprint or template for creating objects
Class is blue print (or)
pre-defined template, which describes Object characteristics + functionality of
an object
Technically class contains
instance variables + methods.
Ex: Blueprint for a House:
A house needs a detailed plan in a chart, which includes various
sections and their sizes. Below is an example blueprint for a house:
House Blueprint
1. Hall:
- Size: 12 feet x 6 feet
- Purpose: Living area for
family gatherings, entertainment, and relaxation.
2. Bedroom:
- Size: Specify the size
based on your requirement (e.g., 10 feet x 12 feet)
- Purpose: Private room for
sleeping and personal activities.
3. Store Water:
- Size: Specify the size
based on your requirement (e.g., 4 feet x 4 feet)
- Purpose: Storage area for
water tanks and other related utilities.
4. Bathrooms:
- Size: Specify the size based
on your requirement (e.g., 6 feet x 8 feet)
- Purpose: Area for bathing,
showering, and other personal hygiene activities.
blue print : house --> need some plan in chart
hall
--> size 12*6
bedroom
-->
store water -->
bathrooms -->
Without defining class, we cannot
create object.
If we want to create object, we
must create class.
Object :
An object is an instance of a
class.
It is anything that is visible
and has some properties (or characteristics or attributes) along with behaviors
(or functionalities).
+
ex 1: Dog
Properties
of the Object:
- Color: black/white
- Weight: 20 grams
- Breed: some breed
Behavior/Functionality
of the Object:
- barking()
- jump()
- run()
- identifyPerson()
Example 2: Pen
Characteristics of Pen:
- Name: Reynold, Cello
- Shape:
- Height:
- Width:
- Color: black/red
- Nib size: 0.2mm
Behavior/Functionality of Pen:
- writingOnPaper()
- writingOnPlasticPaper()
- writingOnDabba()
- changeRiffle()
- changeInk()
Summary
- Object: An instance of a
class with properties and behaviors.
- Properties: Attributes
that describe the object (e.g., name, shape, height, width, color, nib
size).
- Behaviors: Functions or
methods that the object can perform (e.g., writingOnPaper,
writingOnPlasticPaper, writingOnDabba, changeRiffle, changeInk).
Example 3: Student
Properties of Student Object:
- name: Ramu
- color: black/white
- height: 5.5 ft
- gender: M or F (char data
type)
Behavior/Functionality of Student Object:
- playCricket()
- run()
- jump()
- getMarks()
In programming, object properties are defined in the form
of variables:
· name:
Ramu → String
name;
· color:
black/white → String
color;
· height:
5.5 ft → double
height;
·
gender: M or F → char gender;
ex4 : HW
employee
Properties of object:
------------------------
behaviour of Object:
--------------------
Behavior or functionality of an
object is usually described in the form of methods in programming languages:
M1()
{
}
barking()
{
System.out.println("bow -
bow");
}
IdentifyPersons()
{
System.out.println("Identify
Persons");
}
playCricket()
{
}
Run()
{
Object Definition
·
Object
is an instance of a class or a copy of a class (copy of variables + copy of
methods).
·
To create an object, you must first define or
write a class.
·
Without defining a class, you cannot create an
object.
A class
describes the characteristics and behavior of an object:
- Characteristics
(Attributes):
Represented as variables.
- Behavior (Functionality): Represented as methods.
A class describes the properties
of object and functionality of an object:
So, a class contains both the
properties (variables) and the behaviour (methods) of an object.
variables +
Methods
class A
{
Variables
Methods
}
Example: Defining a Class with Variables and Methods
class Dog
{
// variables =
String name ;
String color;
float weight;
// Methods
barking()
{
System.out.println("bow - bow");
}
}
Create
object :
first we should write class
Syntax:
className objName (or) ObjRefvariable = new className();
className:
The name of the class (e.g., A, Dog, Employee).
objName
(or objRefVariable): A meaningful variable name that references
the object.
new:
A predefined keyword in Java used to create an object for the given class name.
package OOPSBasics;
public class Dog {
// properties
//
Declare variables name, color, weight
String
name;
String
color;
float
weight;
// behaviour of dog- Define method- barking
public
void barking()
{
System.out.println("bow
- bow");
}
public
static void main(String[] args)
{
// create obj
for 'dog' class
// Syntax: ClassName
objRefName = new ClassName();
Dog
d1 = new Dog();
//
new predefined k.w in java
//
which can be used to create obj for the
given class i.e Dog class
}
}
Creating an Object for the Student Class:
package OOPSBasics;
public class Student {
//
Declare variables - name, address, gender
String
name;
String
address;
char
gender;
//
Define playCricket()
public
void playCricket()
{
System.out.println("plays
cricket");
}
public
static void main(String[] args) {
// create obj for 'student' class
// synatx:
classname objref= new className();
Student
s1 = new Student();
}
}
HW Create Employee class and create obj
HW Create Pen
class and Create obj
Creating object inside Same class:
Access Variables and Methods Using Object name or object reference
variable:
package OOPSBasics;
public class Dog {
// properties
//
Declare variables name, color, weight
String
name;
String
color;
float
weight;
// behaviour of dog- Define method- barking
public
void barking()
{
System.out.println("bow
- bow");
}
public
static void main(String[] args)
{
// create obj
for dog class
// Synatx: ClassName
objRefName = new ClassName();
Dog
d1 = new Dog();
//
new predefined k.w in java
//
which can be used to create obj for the
given class i.e Dog class
//
access variables and store
"Dolly" in name, color = "white";weight = 20.5f;
// syntax: refVar.VariableName
d1.name
= "Dolly";
d1.color
="white";
d1.weight
= 20.5f;
//
display name
//
display color
//
display weight
System.out.println("d1
name="+ d1.name);
System.out.println("d1
color ="+ d1.color);
System.out.println("d1
weght ="+ d1.weight);
// 20.5
// call methods using refVar
// synatx: referVar.MethodName();
// call barking();
d1.barking();
}
}
o/p:
d1 name=Dolly
d1 color =white
d1 weght =20.5
bow - bow
ex2:
package
OOPSBasics;
public
class Student {
//
Declare variables - name, address, gender
String
name;
String
address;
char
gender;
//
Define playCricket()
public
void playCricket()
{
System.out.println("plays
cricket");
}
public
static void main(String[] args) {
// create obj for 'student' class
// synatx:
classname objref= new className();
Student
s1 = new Student();
// store name = "Ram";gender = 'M';
Address = "BNG";
s1.name
= "Ram";
s1.gender
= 'M';
s1.address
= "BNG";
// display s1 name and s1 gender
System.out.println("s1
name="+ s1.name);
System.out.println("s1
gender="+ s1.gender);
// call PlayCricket()
s1.playCricket();
}
}
o/p:
s1 name=Ram
s1 gender=M
plays cricket
Creating object inside other class:
package OOPSBasics;
public class Dog
{
// variables ( properties)
//
Declare variables name, color, weight
String
name;
String
color;
float
weight;
// behaviour of dog---> Define method- barking
public
void barking()
{
System.out.println("bow
- bow");
}
}
----------------------
package OOPSBasics;
public class TestDog {
public
static void main(String[] args) {
//
create obj for 'Dog' class
Dog
d1 = new Dog();
//
name = "Dolly";
d1.name = "Dolly";
// display d1 name
System.out.println("d1
name="+ d1.name);
// call Methods of Dog -class -barking();
d1.barking();
//
note :If we want to access variable and Methods of 'Dog'Class inside other
classes,
//first
we must create obj and by using reference variable name or By using object
name,
//we
can access all instance variables
// and also instance methods of Class
}
}
Create Multiple objects for the same class:
package OOPSBasics;
public class TestDog {
public
static void main(String[] args) {
//
create obje for 'Dog' class with ref variable d3 and call barking method
Dog d3 = new Dog();
d3.name
= "D3";
d3.weight
= 3.5f;
d3.barking();
// create multiple objects for Dog class inside
the same class or other classes
//
create obje for Dog class with ref variable d4
and name =" D4 ";weight
= 4.5f;
Dog
d4 = new Dog();
d4.name
= "D4";
d4.weight
= 4.5f;
//
call barking method
d4.barking();
////
create obje for Dog class with ref variable d5
and name =" D5 ";weight
= 5.2f;
Dog
d5 = new Dog();
d5.name
= "D5";
d5.weight
= 5.2f;
//
// call barking method
d5.barking();
}
}
-----------------------------
package OOPSBasics;
public class TestStudent {
public
static void main(String[] args) {
//
TODO Auto-generated method stub
//
creating object For 'Student'class with ref variable s1 and name =
"Ramu",gender = 'M';
//Address
= "Bng";
// ex: classname
Student
s1 = new Student();
s1.name
= "Ramu";
s1.gender
= 'M';
// address =
"BNG";/ error as we did not
use refer variable name i.e s1.address
s1.address
= "Bng";
//
display s1 name
System.out.println("s1
name="+ s1.name);
// Ramu
//
call playCricket();
// playCricket();//
error as we did not use refer variable name
i.e s1.playCricket();
s1.playCricket();
//
create obj of student class with ref variable
s1
// can we create
duplicate ref variable s1 ?
// Student s1 = new Student();// Error :
Duplicate variable name s1 is not allowed
// int a;
// int a;// error
//
create obj of student class with ref variable
s2 and
//name
= "Sita";gender = 'F';Address = "Chennai";
Student
s2 = new Student();
s2.name=
"Sita";
s2.gender
= 'F';
s2.address
= "Chennai";
//
display s2 name
System.out.println("s2
name="+ s2.name);
// call playCricket();
s2.playCricket();
//we
can create obj for any class, Dog,
employee..etc
}
}
o/p:
-----
s1 name=Ramu
plays cricket
s2 name=Sita
plays cricket
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