DEV Community: R.Shobika CSE

INHERITANCE IN JAVA

R.Shobika CSE — Mon, 05 Oct 2026 15:33:51 +0000

INHERITANCE:

Inheritance in Java is a core OOP concept that allows a class to acquire properties and behaviors from another class
A subclass can reuse the fields and methods of the parent class without rewriting the code
A subclass can add its own fields and methods or modify existing ones to extend functionality.

public class Animal { ----->super class/ parent class

    public void sound() {
        System.out.println("animal sound");
    }

    public static void main(String[] args) {
        Dog d = new Dog();
        d.sound();
    }
}

class Dog extends Animal { ---->sub class/child class

}

Output:
animal sound

what happened if we print object ?

if we print the object means its give the hash code

class Student{
public void name(){
System.out.println("abc");
}
}
public static void main (String[] args){
Student s = new Student();
System.out.println(s)
}

output:
Student@5e91993f

if we print the object means it will show the hashcode value because each class have the toString() method in java the inbuild function have the own toString() method in some in bulid function does not have so that time that method call the their immediate parent .

Method overriding:

Method overriding in Java allows a subclass to provide a specific implementation of a method that is already defined in its parent class
It is one of the key features of runtime polymorphism in object-oriented programming.

Same method name same no of arguments same return type is called method overriding

public class Student{
String name ="abc";
public static void main(String[] args){
Student s = new Student();
System.out.println(s);
}
public String toString(){
return name;

}
}

output:
abc

Here the object s is search for toString() method for printing so the object s is going to check the object s class "Student" it check whether there is a toString method or not if method is in the Student class means it need not to go for parent class if method not in the class means it go and check the object class , so we can write the same method same argument in the child class also that is called a method overriding

ENCAPSULATION - JAVA

R.Shobika CSE — Tue, 29 Sep 2026 15:24:29 +0000

ENCAPSULATION:
Encapsulation in java is a object oriented concept that bundles data and methods in a single unit.

Example:

Does not use the encapsulation concept

class Student{
String name = "Murugan";
int age = 21;

class Class1{
public static void main(String[] args){
Student s = new Student();
System.out.println(s.name);
System.out.println(s.age);
s.name="kannan";
System.out.println(s.name);

output:
Murugan
21
kannan

In the above program they change the value for the student

class Student{
private String name = "Murugan";
private int age = 21;
public String  getName(){
return name;
}
public int getAge(){
return age;
}
public String setName(String name){
this.name=name;
}
public int setAge(int age){
this.age=age;
}

class Class1{
public static void main (String[] args){
Student s = new String();
System.out.println(s.getName());
System.out.println(s.getAge());

output:
Murugan
21

METHODS IN JAVA

R.Shobika CSE — Fri, 25 Sep 2026 15:03:20 +0000

METHODS:

Methods is a block of code
Methods is used for code reusability
Methods are used to perform certain actions, and they are also known as functions.

Why methods? ---> To Reduce the code

HOW TO DEFINED A METHOD?

class Calc{
public static void main (String[] args){
Calc casio = new Calc(); ----->object creation
casio.add()  ------> method calling
public void add(){    ---------> method define
int i=10;
int j=20;
int res=i+j;
System.out.println(res)  -------> method define
}
}
}

output:
30
METHOD OVERLOADING:

Same method name but different type of arguments / different number of arguments is called method overloading

example:

class Calc{
public static void main (String[] args){
Calc casio = new Calc(); ----->object creation
casio.add(10,20);  ------> method calling
casio.add(10,20,30);  
public void add(int i,intj){    ---------> method define
int res=i+j;
System.out.println(res)  -------> method define
}
public void add(int i,intj,intk){    ---------> method define
int res=i+j+k;
System.out.println(res)  -------> method define
}
}
}

output:
30
60

Return type:
Void ---> void does not return any value

public void add(){
---
---
}

Primitive data type ---> It will return the value

public int add(){
----
----
}

In Java System.out.println() ---> is also a method overloading

System.out.println(10);
System.out.println();
System.out.println(10.0);
System.out.println(True);
System.out.println("abc");

Because it contain same method name but different type of argument

Method overloading is also called as compile- time polymorphism

Constructor in Java

R.Shobika CSE — Thu, 24 Sep 2026 15:35:18 +0000

Constructor:

Constructor in java is a special member that is called when the object is created.
constructor name should be in same class name
It is used to set a default value to the object.

In all Java file there is a default constructor when the object is created
Eg:

class Super{
String pro_name;
int price;
public Super(String pro_name,int price){ -----> constructor
this.pro_name=pro_name;
this.price=price;
}
public static void main(String[] args){
Super pro1=new Super("boost",250); -------> Object creation
Super pro2=new Super("soap",200);----------> Object creation
System.out.println(pro1.pro_name);
System.out.println(pro1.price);
System.out.println(pro2.pro_name);
System.out.println(pro2.price);
}
}

Output:
boost
250
soap
200

In the above program this operator refers to current object

TYPES OF CONSTRUCTOR:

Default constructor
If we doesnot create any constructor in a class the java automatically take a default constructor
Argument constructor
when the object is created with some argument and pass the arguments to the constructor means is a argument constructor
No argument constructor
when the object is created with no argument means is a no argument constructor

same constructor name with different number of arguments /different type(data type ) of argument is called constructor overloading.

JAVA- What is class?

R.Shobika CSE — Thu, 24 Sep 2026 05:17:06 +0000

OOPS:

OOPS - Object Oriented Programming Language
Java is a object oriented programming language
Java is simple and easy to understand

OOPS Concept:

Class
Object
Inheritance
Polymorphism
Abstraction
Encapsulation

Class:

Class is a blue print /template
Class is a container
Class is a collection of objects and methods

Class Home{
--------
--------
}

Class name should start with upper case

class Home{
public static void main (String[] args){
System.out.println("HELLO WORLD!!!!");
}
}

In the above program the classes are

Home
String
System

These three are the class in the above program because it start with uppercase

DATA TYPES IN JAVA:

In java Datatypes are divide into two

Primitive datatype
Non-Primitive datatype

Primitive datatype

byte->1byte=8bit
short->2byte
int->4byte
long->8byte
float->4byte
double->8byte
char->It store only one character
boolean->1 bit [true/false]

Non Primitive datatype:

String
class
array

class Home{
Static string name ="Shobi";
Static int addno=108;
//static keyword is used to store the class information is common for all and it take 1 memory space for whole class
public static void main(String[] args){
System.out.println(Home.name);
System.out.println(Home.age);
}
}

JAVA - Global Variable

R.Shobika CSE — Thu, 24 Sep 2026 04:58:50 +0000

VARIABLES:

In Java there are two types of variable

Global Variable

-> Static Variable
-> Non-Static Varible
Local Variable

Static variable:

A static variable in Java is a class-level variable that is declared using the static keyword
Static variable is used to store the class information.
Unlike instance variables, only one copy of a static variable is created and shared among all objects of the class, making it useful for storing common data.

Public class Super{
Static string name="Murugan";
Static int addno=108;
public static void main(String[] args){
System.out.println(Super.name);
System.out.println(Super.addno);
}
}

Output:
Murugan
108

Static variables take single memory space for the whole class

OBJECT:

In Java Object is a instance of a class
It represents a specific entity created from the class template.

Public class Super{
Static string name="Murugan";
String pro_name="Laptop";
int price=25000;
Static int addno=108;
public static void main(String[] args){
Super product=new Super();   ---------------> This is the object creation 
System.out.println(Super.name);
System.out.println(Super.addno);
}
}

In Object creation it will allocate the space for the some product in the supermarket
Object is a Non- Static Information used to store the object information

What is field ?

In java field is a global variable

if we assign variable in the main method is a local variable otherwise it is a global variable

In java we doesnot assign any value for the variable means it will take a default value as 0

String=null
int=0
double=0.0
boolean=false

example:

Public class Super{
Static string name= "Murugan"
string pro-name;
int addno;
Public Static void main (String[] args){
Super product1=new Super();
Super product2=new Super();
product1.pro_name="Boost";
product1.price=250;
product2.pro_name="soap";
product2.price=300;
}
}

Output:
Boost
250
soap
300

When we create a object means it will take one memory space if we create another object means it will take another memory space.

so non-static variabes are the object information
Static variables are the class information

JAVA INTRO

R.Shobika CSE — Mon, 21 Sep 2026 08:47:02 +0000

JAVA:

Java is a high level programming language.
Java is a secure language
It is a statically type programming language
It is a case sensetive.
First Java was developed in 1991 in the name of Oak then in 1995 Oak change into Java
-Java was developed by James Gosling

JAVA ACHITECTURE

Java does not compile the whole program to the machine code (0,1) there is a two part in compilation

1st part -> Java programming file Translate into class file it is called as a byte code It was translate by a Java Development Kit [JDK] . This is a platform independent.

2nd part -> the byte code is translate into a binary values(0,1)[machine code] .It was translate by JIT [ Just In Time] compiler basically its a interpreter type , It does not translate directly into the machine code firstly it will translate byte code into a Java Virtual Machine [JVM]

The entire Process is a Java RunTime Environment .

JDK
JDK (Java Development Kit) is a software package used to develop and run Java applications. It provides all the necessary tools required for writing, compiling, debugging, and executing Java programs. JDK is mainly used by Java developers to create Java-based applications.

JIT
The JIT or Just-In-Time compiler is an essential part of the JRE (Java Runtime Environment), that is responsible for performance optimization of java based applications during run time. The compiler is one of the key aspects in deciding the performance of an application for both parties i.e. the end-user and the application developer.

JVM
The Java Virtual Machine (JVM) is an abstract machine that provides the runtime environment for executing Java bytecode. It is a part of the Java Runtime Environment (JRE) and is responsible for loading, verifying, and executing Java class files.

JRE
Java Runtime Environment (JRE) is a software package that provides the environment required to run Java applications. It contains the Java Virtual Machine (JVM), core class libraries, and supporting files needed to execute Java bytecode. JRE is a part of the Java Development Kit (JDK) and is responsible for running Java programs on different platforms.

HOW TO CREATE AND EXECUTE THE JAVA FILE??

1st create the java file file name is "Sample.java"

public class Sample{
public static void main (String[], args){
System.out.println("HELLO WORLD!!!");

the file name and class name should be same and java is a case sensitive

2nd execute the file the commands are

javac Sample.java   ------> java file convert into a class file 
java Sample         ------> execute the program

output:
HELLO WORLD!!!

TASK: error making


class Sample {
    public static void main(String[] args) {
        System.out.println("HELLO WORLD!!!")
    }
}

o/p:
Main.java:6: error: ';' expected
        System.out.println("HELLO WORLD!!!")
                                            ^
1 error


class Sample {
    public static void main(string[] args) {
        System.out.println("HELLO WORLD!!!")
    }
}

o/p:
ERROR!
Main.java:5: error: cannot find symbol
    public static void main(string[] args) {
                            ^
  symbol:   class string
  location: class Main
1 error

class Sample {
    public Static Void Main(String[] args) {
        System.out.println("HELLO WORLD!!!");
    }
}

o/p:
ERROR!
/tmp/EnWS8Elbz1/Main.java:5: error: ';' expected
    public Static Void Main(String[] args) {
                      ^
ERROR!
/tmp/EnWS8Elbz1/Main.java:5: error: invalid method declaration; return type required
    public Static Void Main(String[] args) {
                       ^
2 errors
ERROR!
error: compilation failed


class Sample {
     static void main(String[] args) {
        System.out.println("HELLO WORLD!!!");
    }
}

o/p:
ERROR!
error: can't find main(String[]) method in class: Sample

class Sample {
    public static void main(String[] args) {
        system.out.println("HELLO WORLD!!!");
    }
}
o/p:
ERROR!
/tmp/Ldf0kuboP4/Main.java:6: error: package system does not exist
        system.out.println("HELLO WORLD!!!");
              ^
1 error
ERROR!
error: compilation failed

class Sample {
    public static void main(String[] args) {
        System.println("HELLO WORLD!!!");
    }
}

o/p:
ERROR!
/tmp/2TXFdsDVof/Main.java:6: error: cannot find symbol
        System.println("HELLO WORLD!!!");
              ^
  symbol:   method println(String)
  location: class System
1 error
ERROR!
error: compilation failed


class Sample {
    public static void main(String[]) {
        System.out.println("HELLO WORLD!!!");
    }
}

o/p:
ERROR!
/tmp/UMTKDZ87fM/Main.java:5: error: <identifier> expected
    public static void main(String[]) {
                                    ^
1 error
ERROR!
error: compilation failed

class Sample {
    public static void main(String args) {
        System.out.println("HELLO WORLD!!!");
    }
}
o/p:
ERROR!
error: can't find main(String[]) method in class: Sample

class Sample {
    public static void main(String[] args) {
        System.out.println("HELLO WORLD!!!");

}
o/p:
ERROR!
/tmp/dDrMpwFDDr/Main.java:8: error: reached end of file while parsing
}
 ^
1 error
ERROR!
error: compilation failed

Sample {
    public static void main(String[] args) {
        System.out.println("HELLO WORLD!!!");
    }
}
o/p:
ERROR!
/tmp/51yfKuJfaN/Main.java:4: error: class, interface, enum, or record expected
Sample {
^
ERROR!
/tmp/51yfKuJfaN/Main.java:5: error: unnamed classes are a preview feature and are disabled by default.
    public static void main(String[] args) {
                  ^
  (use --enable-preview to enable unnamed classes)
ERROR!
/tmp/51yfKuJfaN/Main.java:8: error: class, interface, enum, or record expected
}
^
3 errors
ERROR!
error: compilation failed

HOW TO START A PROJECT IN REACT?

R.Shobika CSE — Thu, 27 Aug 2026 14:20:22 +0000

How to start a project in a react

1st we have to type the comment and create the react project
the comments are:

npm create vite@latest [npm is a node package manager]
|
project name 
|
framework selection
|
variant selection
|
it will ask you want to install the npm if you want means click yes otherwise no
|
the project folder is created successfully

In React only it install the some of the packages and inbuild main.jsx,app.jsx,index.html,app.css,index.css files are having
We can modify them for our proposed project.

WHAT IS JSX?

JSX is a JavaScript XML
In JSX we can write HTML inside of the JavaScript code

DIFFERENCE BETWEEN HTML AND XML

COUNTER PROJECT

Counter.jsx

import {useState} from "react"
function Counter(){
    const [count,setCount]=useState(0)
    function incre(){
        setCount(count+1)
    }
    function decre(){
        setCount(count-1)
    }
    function reset(){
        setCount(0)
    }

    return(
        <div>
            <h1>Counter:{count}</h1>
            <button onClick={incre}>+</button>
            <button onClick={decre}>-</button>
            <button onClick={reset}>reset</button>
        </div>
    )
}
export default Counter

App.jsx

In App.jsx i just call the Counter.jsx file


import './App.css'
import Counter from './Counter'

function App() {


  return (
   <Counter/>
  )
}

export default App

Main.jsx:

In Main.jsx i call the App.jsx file

import { StrictMode } from 'react'
import { createRoot } from 'react-dom/client'
import './index.css'
import App from './App.jsx'

createRoot(document.getElementById('root')).render(
  <StrictMode>
    <App />
  </StrictMode>,
)

In all the react project there is only one html file only

output:

REACT.JS INTRO

R.Shobika CSE — Thu, 27 Aug 2026 13:47:24 +0000

REACT.JS

React is a JavaScript Library
It is a Single Page Application
Its is a component based architecture
It was created by Facebook
And main advantage is reusable ui

DIFFRENCE BETWEEN LIBRARY AND FRAMEWORK:

Why Node.js in React?

Node.js is used for React primarily to power the development environment and build tools on your computer, not to run the React app in the browser.
Because web browsers cannot directly understand modern React code (like JSX or ES6 modules), Node.js acts as the engine that transforms, bundles, and prepares your code for the web.

COMMENTS FOR REACT PROJECT CREATION:

npm create vite@latest [npm is a node package manager]
|
project name 
|
framework selection
|
variant selection
|
it will ask you want to install the npm if you want means click yes otherwise no
|
the project folder is created successfully

JS - Closure

R.Shobika CSE — Mon, 24 Aug 2026 15:24:58 +0000

Closure:
A closure is created when a function remembers the variables from its outer scope, even after the outer function has finished executing.

function bank(){
let min_bal=500;
function deposit(amt){
min_bal=min_bal+amt;
console.log(min_bal)
}
return deposit
}
const customer1=bank();
customer1(1500);
customer1(500);

ouput:
2000
2500

How can return more than one function ?

we can store the function in a objects. In object we can store functions and properties , we can access them in key value pair.

function bank(){
let min_bal=500
const admin={
deposit:function(amt){
min_bal = min_bal+amt;
}
withdraw:function(amt){
min_bal=min_bal-amt;
}
checkbal:function(){
console.log(min_bal)
}
}
return admin;
}
const cus1=bank();
cus1.withdraw(100);
cus1.deposit(5000);
const cus2=bank();
cus2.withdraw(100);

output:
400
5400
400

PYHTON TASK 7

R.Shobika CSE — Sat, 22 Aug 2026 15:53:11 +0000

TASK
1. NEON NUMBER:

A neon number is a number where the sum of the digits of its square is equal to the number itself

eg:
9^2=>81
8+1=>9 (neon number)

12^2=>144
1+4+4=>9 (not a neon number)

def sum_of_digit(no):
    sum=0
    a=0
    while no>0:
        a=no%10
        sum=sum+a
        no=no//10
    return sum

no=int(input("enter a number"))
sq=no**2
result=sum_of_digit(sq)
if no==result:
    print(f'{no} this is neon number')
else:
    print(f' {no} this is not a neon number')

output:

enter a number9
9 this is neon number

2. Strong number:

A Strong number is a number equal to the sum of the factorials of its digits and its equal to the number itself

eg: number = 145
1!+4!+5!
1+24+120=145

def fact(no):
    facto=1
    while no>0:
        facto=facto*no
        no=no-1
    return facto

def sum_digit(no):
    sum=0
    a=0
    while no>0:
        a=no%10
        factorial=fact(a)
        sum=sum+factorial
        no=no//10
    return sum

no=int(input("enter a number:"))
result= sum_digit(no)
if result==no:
    print(f'{result} is a strong number')
else:
    print(f'{result} is not a strong number')

output:

enter a number:145
145 is a strong number

enter a number:123
9 is not a strong number

3. Duck number

A number should not start with 0 and a number atleast contain a one 0

no=input("enter a number")
if no[0]=='0':
    print(f'{no} is not a duck number')
else:
    print(f'{no} is a duck nunber')

output:

enter a number0134
0134 is not a duck number

enter a number10234
10234 is a duck nunber

4. Spy number:

A Spy Number is a number where the sum of its digits equals the product of its digits.

def sum_of_digit(no):
    sum=0
    a=0
    while no>0:
        a=no%10
        sum=sum+a
        no=no//10
    return sum
def mul_of_digit(no):
    mul=1
    a=0
    while no>0:
        a=no%10
        mul=mul*a
        no=no//10
    return mul    

no=int(input("enter a number: "))
sum=sum_of_digit(no)
mul=mul_of_digit(no)
if sum==mul:
    print(f'{sum} and {mul} are spy number')
else:
    print(f'{sum} and {mul} are not spy number')

output:

enter a number: 123
6 and 6 are spy number

enter a number: 456
15 and 120 are not spy number

PYTHON TASK6

R.Shobika CSE — Fri, 21 Aug 2026 14:13:05 +0000

TASK:

Count of a digit

no=int(input("enter a number: "))
count=0
while(no>0):
    count+=1
    no=no//10
print(f'count of a digit is : {count}')

output:

enter a number: 12365
count of a digit is : 5

Sum of Digit:

no=int(input("enter a number: "))
sum=0
while no>0:
    sum=sum+(no%10)
    no=no//10
print(f'sum of digit: {sum}')

output:

enter a number: 123
sum of digit: 6

Reverse of a number

no=int(input("enter a number: "))
rev=0
while no>0:
    rev=rev*10+(no%10)
    no=no//10
print(f'rev of digit: {rev}')

output:

enter a number: 123
rev of digit: 321

Palindrome of a number

no=int(input("enter a number:"))
temp=no
rev=0
a=0
while no>0:
    a=no%10
    rev=rev*10+a
    no=no//10
if(rev==temp):
    print(f'This number is a palindrome {rev}')
else:
        print(f'This number is not a palindrome {rev}')

output:

enter a number:121
This number is a palindrome 121

enter a number:1234
This number is not a palindrome 4321