DEV Community: Kiruthiga S

Java

Kiruthiga S — Wed, 07 Oct 2026 13:57:38 +0000

Inheritance
Allows one class to acquire properties and methods of 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

class Animal {
    void eat() {
        System.out.println("Animal eats");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("Dog barks");
    }
    public static void main(String[] args) {
        Dog d = new Dog();
        d.eat();
        d.bark();
    }
}

Output:
Animal eats
Dog barks

Java

Kiruthiga S — Fri, 25 Sep 2026 15:36:25 +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

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(){
---
---
}

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

Polymorphism
Method overloading is also called as compile-time polymorphism
Method overriding is also called as run-time polymorphism

Java

Kiruthiga S — Thu, 24 Sep 2026 15:17:16 +0000

Constructor
- Constructor will called automatically when object is created
- Initializing object specific values
- Constructor name will be same as the class name
- Constructors can have parameters and can be overloaded

Default Constructor
A default constructor has no parameters. It’s used to assign default values to an object.

Argument Constructor
A constructor with arguments (parameters) is called parameterized constructor.
It is used to give values to an object when the object is created.

Zero Argument Constructor
Non-zero argument constructor means a constructor that receives one or more arguments.

Constructor Overloading
Allows a class to have multiple constructors with different parameter lists
provides different ways to initialize objects based on the values available at the time of object creation

public class SuperMarket {
   String prod_name;
   int price;

   public SuperMarket(String str,int i)
   {
      this.prod_name=str;
      this.price=i;
      System.out.println("Constructor called");
   }
   public SuperMarket()
   {
      System.out.println("Zero Constructor called"); 
    }

    public static void main(String[] args)
    {
        SuperMarket product1=new SuperMarket("boost",250);
        SuperMarket product2=new SuperMarket("Horlicks",300);
        SuperMarket product3=new SuperMarket();
    }
}

Output:
Constructor called
Constructor called
Zero Constructor called

Java

Kiruthiga S — Wed, 23 Sep 2026 17:05:41 +0000

OBJECT
Object is an instance of a class that represents a real-world entity
Used to access the variables and methods defined inside a class

Variable
1.Local
2.Global
-Static
-Non-Static

Static
- Class
- Static will create only one memory

Non-Static
- Object,instance
- Non-Static will depends on the according to the number of products

public class SuperMarket {
   String prod_name="boost";
   int price=250;
    public static void main(String[] args)
    {
        SuperMarket product=new SuperMarket();
        System.out.println(product.prod_name);
        System.out.println(product.price);
    }
}

Output:
boost
250

public class SuperMarket {
   String prod_name1="boost";
   int price1=250;
   String prod_name2="Horlicks";
   int price2=300;
    public static void main(String[] args)
    {
        SuperMarket product1=new SuperMarket();
        System.out.println(product1.prod_name1);
        System.out.println(product1.price1);
        SuperMarket product2=new SuperMarket();
        System.out.println(product2.prod_name2);
        System.out.println(product2.price2);

    }
}

Output:
boost
250
Horlicks
300

Java

Kiruthiga S — Tue, 22 Sep 2026 16:57:21 +0000

OOP (Object Oriented Programming)
OOP is idea
Object-Oriented Programming (OOP) is a programming paradigm based on the concept of objects that contain data (fields) and behavior (methods). It focuses on designing software that closely represents real-world entities.

Class
- Blueprint or template
- Starts with uppercase
- The letter starts with capital letter is always class
- No space allowed and no special characters except _ and $

Data Types in Java
1.Primitive datatype
byte - 1byte
small - 2byte
int - 4byte
long - 8byte
float - 4byte
double - 8byte
char - 2byte
boolean - 1byte

2.Non-primitive datatype
String
Array

public class Home{
static String name="Kiruthiga";
static int age=21;
public static void main(String[] args)
{
    System.out.println(Home.name);
    System.out.println(Home.age);
    // system.out.println("Hello World!");
}
}

Output
Kiruthiga
21

Python

Kiruthiga S — Mon, 21 Sep 2026 10:15:27 +0000

To print A

for row in range (1,8):
    for col in range(1,8):
        if  col==1 or col== 7 or row == 1 or row == 4  :
            if (row==1 and(col==1 or col==7)) or (row==7 and (col==1 or col==7)):
                print(" ", end=' ')
            else:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print B

for row in range (1,8):
    for col in range(1,8):
        if  row==1 or row== 7 or row==4 or col == 1 or col == 7  :
            if (row==1 and  col==7) or (row==7 and  col==7):
                print(" ", end=' ')
            else:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print C

for row in range (1,8):
    for col in range(1,8):
        if  row==1 or row == 7 or col == 1:
            if (row==1 and(col==1 or col==7)) or (row==7 and (col==1 or col==7)):
                print(" ", end=' ')
            else:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print D

for row in range (1,8):
    for col in range(1,8):
        if  row==1 or row== 7 or col == 3 or col == 7  :
            if (row==1 and(col==1 or col==7)) or (row==7 and (col==1 or col==7)):
                print(" ", end=' ')
            else:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print E

for row in range (1,8):
    for col in range(1,8):
        if  row==1 or row== 7 or row==4 or col == 1:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print F

for row in range (1,8):
    for col in range(1,8):
        if  row==1 or row==4 or col == 1:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print H

for row in range (1,8):
    for col in range(1,8):
        if   row==4 or col == 1 or col == 7:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print I

for row in range (1,8):
    for col in range(1,8):
        if   col==4 or row == 1 or row == 7:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print J

for row in range (1,8):
    for col in range(1,8):
        if   col==4 or row == 1 or row == 7:
             if   (col==4 and row == 7) or(row==7 and col==5) or (row==7 and col==6 ) or (row==7 and col==7):
                print(" ", end=' ')
             else:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print L

for row in range (1,8):
    for col in range(1,8):
        if   col==1 or row == 7 :
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

To print T

for row in range (1,8):
    for col in range(1,8):
        if   col==4 or row == 1 :
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

Python

Kiruthiga S — Mon, 21 Sep 2026 10:07:15 +0000

for row in range (1,8):
    for col in range(1,8):
        if  row == 1 or row == 7 :
            print(" *", end=' ') 
        else:
            print(" ", end=' ')
    print()

for row in range (1,8):
    for col in range(1,8):
        if  col == 1 or col == 7 :
            print(" *", end=' ') 
        else:
            print(" ", end=' ')
    print()

for row in range (1,8):
    for col in range(1,8):
        if  row == 1 or row == 7 or col == 1 or col == 7 :
            print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

for row in range (1,8):
    for col in range(1,8):
        if  row == 1 or row == 7 or col == 1  :
            print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

for row in range (1,8):
    for col in range(1,8):
        if  row == 1 or row == 7 or col == 7  :
            print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

for row in range (1,8):
    for col in range(1,8):
        if  row == 1 or col == 1 or col == 7  :
            print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

for row in range (1,8):
    for col in range(1,8):
        if  row == 7 or col == 1 or col == 7  :
            print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

for row in range (1,8):
    for col in range(1,8):
        if  row==1 or row == 7 or col == 1 or col == 7  :
            if row==1 and col==7 or row==7 and col==1:
                print(" ", end=' ')
            else:
                print("*", end=' ') 
        else:
            print(" ", end=' ')
    print()

Java

Kiruthiga S — Mon, 21 Sep 2026 09:53:30 +0000

JAVA
- Java is a high-level Programming Language
- Used to develop web, desktop, enterprise and mobile application
- Simple, secure, portable and platform independent
- Follows the principle of OOPs

Java Features
- Mobile Applications(Android)
- Web and Desktop Applications
- Scientific Application
- Database connections
- Banking and Finance Systems

History of Java
- Java was developed by James Gosling at Sun Microsystems in 1995
- Originally it was called "Oak"
- Later the name was changed to "Java"
- In 2009, Oracle acquired Sun Microsystems
- Java is the most popular language in the world

JVM (Java Virtual Machine)
- JVM is the heart of java
- Virtual Machine that runs the Java bytecode
- Provides Platform independence
- Performs class loading ,bytecode verification, code execution, memory management, ect

JRE (Java Runtime Environment)
- JRE is the implementation of JVM
- Includes everything required to run a java program
- Contains JVM + core libraries + other supporting files

JDK (Java Development Kit)
- JDK is a complete package
- Used by developers to develop, compile, debug and run java programs
- It contains JRE + development tools

JVM - Runs the java code
JRE - Runs the java program
JDK - Develops + Runs the java program

How Java Program Executes?

Execution flow of a java program
- we writes code as .java file
- compiler (javac) converts it into bytecode(.class file)
- JVM loads .class file and executes the code
- JVM converts bytecode into machine specific code
- Then the output is displayed

Python

Kiruthiga S — Fri, 04 Sep 2026 14:45:42 +0000

For Loop
used to iterate over sequences such as lists, tuples, strings and ranges

s = "Geeks"
for i in s:
    print(i)

Output:
G
e
e
k
s

for i in range(0, 10, 2):
    print(i)

Output:
0
2
4
6
8

for i in range(1, 4):
    print(i)
else:  
    print("No Break\n")

Output:
1
2
3
No Break

React JS

Kiruthiga S — Fri, 04 Sep 2026 14:33:42 +0000

useEffect
useEffect is the one of the commonly used hook in ReactJS
Used to handle side effects in functional components

Syntax

useEffect(effectFn,[])

useEffect(()=>{
console.log("API Calling");
},[]);

useEffect(()=>console.log("API Calling"),[]);

Components lifecycle
Mounting-first time call
Update-to execute again and again
Unmounting-change to another

Types of useEffect
1.empty dependency array-mounting

useEffect(() => {
  //Runs only on the first render
}, []);

2.dependency array-update

useEffect(() => {
  //Runs on the first render
  //And any time any dependency value changes
}, [prop, state]);

3.no dependency array-unmounting

useEffect(() => {
  //Runs on every render
});

setInterval
The setInterval() method executes a function repeatedly at a specified interval. We can use the setInterval method in a React component to update the component's state or perform other actions.

Strict Mode
StrictMode is a react component used to identify the potential issues and bug in the react code
If strictmode is ON,the output will execute two times

React JS

Kiruthiga S — Thu, 03 Sep 2026 05:21:47 +0000

Props
Props are used to pass data from a parent component to a child component

function Parent(props) {
  return <h1>Hello, {props.name}!</h1>;
}
function Child() {
  return <Parent name="John" />;
}

Destructuring props

function Greeting({ name, age }) {
  return (
    <div>
      <h1>Hello,I'm {name}!</h1>
      <p>I am {age} years old.</p>
    </div>
  );
}

function App() {
  return <Greeting name="Kiruthiga" age={21} />;
}

What are the ways to use props

Passing Strings

function Welcome(props) {
  return <h1>Hello, {props.name}</h1>;
}

function App() {
  return <Welcome name="Alice" />;
}

Passing Numbers

function Student({ marks }) {
  return <p>Marks: {marks}</p>;
}

function App() {
  return <Student marks={95} />;
}

Passing Boolean Values

function User({ isLoggedIn }) {
  return (
    <h1>{isLoggedIn ? "Welcome!" : "Please Login"}</h1>
  );
}

function App() {
  return <User isLoggedIn={true} />;
}

Passing Arrays

function Fruits({ items }) {
  return (
    <ul>
      {items.map((fruit) => (
        <li key={fruit}>{fruit}</li>
      ))}
    </ul>
  );
}

function App() {
  return <Fruits items={["Apple", "Banana", "Orange"]} />;
}

Passing Objects

function Employee({ emp }) {
  return (
    <div>
      <h2>{emp.name}</h2>
      <p>{emp.role}</p>
    </div>
  );
}

function App() {
  const employee = {
    name: "John",
    role: "Developer",
  };

  return <Employee emp={employee} />;
}

Passing Functions

function Button({ handleClick }) {
  return <button onClick={handleClick}>Click Me</button>;
}

function App() {
  function greet() {
    alert("Hello!");
  }

  return <Button handleClick={greet} />;
}

React JS

Kiruthiga S — Wed, 02 Sep 2026 04:36:17 +0000

Arrow Function

without arrow function

function greet() {
    return "Hello";
}

with arrow function

const greet = () => {
    return "Hello";
}

const greet = () => "Hello";

with parameters

function add(a,b){
    return a+b;
}

const add = (a,b) => a+b;

Why React uses Arrow Functions?

const Home = () => {
    return <h1>Home Page</h1>;
}

Destructuring
Taking values out of an object or array easily

Object Destructuring

const student = {
    name: "Alice",
    age: 22,
    city: "Chennai"
};

without destructuring

console.log(student.name);
console.log(student.age);

with destructuring

const { name, age } = student;

console.log(name);
console.log(age);

Array Destructuring

const colors = ["Red","Blue","Green"];

without destructuring

const first = colors[0];
const second = colors[1];

with destructuring

const [first, second] = colors;