DEV Community: Vishnu N

Collections in Java

Vishnu N — Tue, 24 Feb 2026 04:29:07 +0000

What are collections?
-Collections in Java is a framework that provides classes and interfaces to store and manipulate groups of objects dynamically.
-It is part of java.util package.

Why do we use collections?

Before collections:
-We used arrays.
-Arrays are fixed size.
-Cannot easily insert/delete elements.
**
After collections:**
-Dynamic size.
-Built-in methods.
-Better performance handling.

What is a collection? (Java Collection Framework)

Collection is an interface.
It is the root interface of List, Set, and Queue.
Map is NOT a child of Collection.

Main Interfaces in collection:

List.
Set.
Queue.
Map.

List in Java

Vishnu N — Thu, 19 Feb 2026 23:21:42 +0000

What is a List?

List is an interface in the Java Collection Framework that stores an ordered collection of elements and allows duplicates, and elements can be accessed by their index. *Maintains insertion order. *Allows duplicate elements. *Supports index-based access.

Why List?

-1. Order is Important

Data should maintain insertion order.

Duplicates Are Allowed

Example: Same product added twice in the cart.

Index-Based Access Needed

You can access elements using an index:

When List?

When the number of elements is unknown
When duplicates are allowed
When we need ordered data
When we need index-based operations

*** Real-Time Examples

E-commerce Cart

Use List → Products in cart (order matters)

Student Marks

Store multiple marks (duplicates allowed)

Log History

Maintain insertion order

Encapsulation in Java

Vishnu N — Wed, 18 Feb 2026 05:35:03 +0000

(Data Hiding + Controlled access)

private variables.
public getter and setter methods.

What is Encapsulation?

Encapsulation is wrapping data and methods into a single class and restricting direct access using private variables.

why:

It provides security, data control and better code organisation.

when:

It is used when data needs protection and controlled access in large applications.

examples:

class Student {

    private int age;     // private variable (hidden)
    private String name;

    // Getter
    public int getAge() {
        return age;
    }

    // Setter
    public void setAge(int age) {
        if(age > 0) {
            this.age = age;
        }
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

public class Test {
    public static void main(String[] args) {

        Student s = new Student();

        s.setAge(22);
        s.setName("Vishnu");

        System.out.println(s.getName());
        System.out.println(s.getAge());
    }
}

real-time example;

class BankAccount {

    private double balance;

    public void deposit(double amount) {
        if(amount > 0) {
            balance += amount;
            System.out.println("Deposited: " + amount);
        }
    }

    public void withdraw(double amount) {
        if(amount <= balance) {
            balance -= amount;
            System.out.println("Withdrawn: " + amount);
        } else {
            System.out.println("Insufficient balance");
        }
    }

    public double getBalance() {
        return balance;
    }
}

public class Main {
    public static void main(String[] args) {

        BankAccount acc = new BankAccount();

        acc.deposit(5000);
        acc.withdraw(2000);

        System.out.println("Balance: " + acc.getBalance());
    }
}

encapsulation with validation:

class Employee {

    private double salary;

    public void setSalary(double salary) {
        if(salary >= 10000) {
            this.salary = salary;
        } else {
            System.out.println("Salary too low!");
        }
    }

    public double getSalary() {
        return salary;
    }
}

Runtime Polymorphism (Method Overriding) in Java

Vishnu N — Thu, 18 Dec 2025 18:53:05 +0000

What is polymorphism?

Polymorphism allows one method to perform different actions based on the object.

What is method overriding?

Method overriding in the child class gives its own implementation of the method that already exists in the parent class.

why use

To achieve runtime polymorphism.
To change the parent class behaviour.

Rules

Method and parameters must have the same name.
static, final and private cannot be overridden.
Access modifiers cannot be weaker.

//parent class
public class MethodOverriding{

protected void display(){
    System.out.println("Hello..");
}


}

//child class
public class Overriding extends MethodOverriding{

 public void display(){
    System.out.println("Hii...");  //child class overrides the parent class method.
 }

 public static void main(String[] args){
    MethodOverriding m1=new Overriding();
    m1.display();
 }
}

D/B method overriding and Runtime polymorphism :

MO- child class changes parent class method.
RTP- JVM decides which method to call at runtime.

What is Compile-Time Polymorphism(Method Overloading) in Java

Vishnu N — Wed, 26 Nov 2025 06:58:06 +0000

What is compile-time polymorphism?

Compile-time polymorphism means the method is selected at compile time, not at runtime.

What is Method Overloading?

Method Overloading means having multiple methods with the same name but different parameters in the same class.
It is a type of Compile-Time Polymorphism.

Example:

public class MethodOverloading{

public void add(int i, int j){
    System.out.println(i+j);
}

public void add(int i, String j){
    System.out.println(i+j);
}

public void add(int i, int j, String b){
    System.out.println(i+j+b);
} 

public void add(int i, String j, int k, String l){
    System.out.println(i+k+j+l);
}
public void add(String l){
    System.out.println(l);
}

public static void main(String[] args){
    MethodOverloading  sp= new MethodOverloading();
    sp.add(8, 10);
    sp.add(8,"Virat");
    sp.add(8, 10, "Virat");
    sp.add(8, "Virat", 10, "Kohli");
    sp.add(8 + 10 + "Virat");
}
}

Why do we go to Method Overloading?

Improves code readability.
Avoids creating multiple method names.
To perform the same task in different ways.

Class and Object in java

Vishnu N — Wed, 26 Nov 2025 01:23:12 +0000

What is class?

A class in Java is a Blueprint or template from which an object is created. The object is defined by the Structure and behaviour(methods) that objects of that class will possess.
It is a logical entity.
No memory is allocated when a class is defined.
All classes are non-primitive datatypes.

How to create a class?

**
BASIC SYNTAX for creating a class:**

public class Car
{
    // Data members (fields)- hold  the actual value

String brand;
int speed;
    //Behaviour (method)
void drive()

{
System.out.println("driving a car");
}


}
//But it’s not a real car yet. It’s just the plan.

Class Name Rules:

Must start with an Uppercase first letter or (_) underscore or dollar sign ($).
can not start with a number
cannot contain spaces or special characters
Use Pascal-case for naming

What is an Object?

An object is an instance of a class, and it has its own memory copy. It is a physical entity. An object is created with the new keyword.
When a class is created, no memory is used. Memory is allocated only when an object is created from that class.

Creating an Object :
classname, reference var,assignment operator,new keyword,classname();

Student id = new Student();

class in java

Vishnu N — Mon, 24 Nov 2025 06:33:02 +0000

"June Ponal, July Kaatre" - Tech Meetup.

Vishnu N — Mon, 14 Jul 2025 14:55:12 +0000

Hello Friends,

The JAVA tech meetup "Code ON JVM" at YuniQ Technologies, TICEL Bio Park, Tharamani. So, this is my second meetup. I have shared my experience on this blog.

Session 1:
Speaker - Jenifar
Topic - Concurrency and Multithreading.
Concurrency - The ability of a program to execute multiple tasks at the same time.
Multithreading - It enables the concurrent execution of multiple parts of a program, known as threads, within a single process.

A short break with Tea:
A cup of Tea with biscuits. It is ginger tea that was very tasty.
After the break.

Session 2:
Speaker - Karthick
Topic - Garbage Collection.
Garbage Collection - GC is the automatic process of reclaiming memory used by unreachable objects. It improves Application Stability.

Thank you.

JavaScript Operators : Types of Operators in JS

Vishnu N — Wed, 09 Jul 2025 15:50:53 +0000

Hello friends,

Today will learn the Operators in JavaScript. Yesterday i will discuss the arithmetic operators. so, today will discuss the other operators in JavaScript.

JavaScript Operators are used to perform specific mathematical and logical computations on operands. In other words, an operator operates the operands.

example: Types of mathematical and logical computations .

The Assignment Operator (=) is used to assigns values.
The Addition Operator (+) is used to adds values.
The Multiplication Operator (*) is used to multiplies values.
The Comparison Operator (>) is used to compares values.

Types of Operators :

There are different types of Operators in JS are;


-Arithmetic Operators
-Assignment Operators
-comparison Operators
-String Operators
-Logical Operators
-Bitwise Operators
-Ternary Operators
-Typeof Operators

Arithmetic Operators : These are the operators that work on numerical values and then return a number. These are basically used to perform mathematical operations.
Assignment Operators : Assignment operators assign values to JavaScript variables.
Comparison Operator : These are the operators that are used to perform equality or difference comparisons between the values. It checks whether an element is greater, smaller equal, or unequal to the other element.
String Operators : All the comparison operators above can also be used on strings.

example: "hello" .

-Logical Operators : These are the operators which allow us to compare variables or values. The logical operator is mostly used to make decisions based on conditions specified for the statements.

-Bitwise Operators : These operators convert the number to a 32-bit binary number and perform the bitwise operation. The number is converted back to the 64-bit number after the result.

-Ternary Operators : The Ternary Operator in JavaScript is a shortcut for writing simple if-else statements. It’s also known as the Conditional Operator because it works based on a condition. The ternary operator allows you to quickly decide between two values depending on whether a condition is true or false.

-Typeof Operator : The typeof operator in JavaScript is used to determine the data type of a value or variable. It returns a string indicating the type, such as "string", "number", "boolean", "object", etc.

This is the Operators in JavaScript and i'll research from w3 schools and geeksforgeeks. Then, i will pin the link to you.

reference:
w3 schools - [https://www.w3schools.com/js/default.asp]
geeksforgeeks - [https://www.geeksforgeeks.org/javascript/javascript-operators-reference/].

Arithmetic Operators in Java Script.

Vishnu N — Tue, 08 Jul 2025 18:27:51 +0000

Hi guys,

Today i learned Java Script Arithmetic Operators.
The topic is very interesting, so i'll discuss the Arithmetic Operators.

what is arithmetic operators ?

In JavaScript, arithmetic operators are symbols used to perform basic mathematical operations on numeric values.

classification of the Arithmetic Operators:

operators :        


+               Addition/concatenation       
-               Subtraction
*               Multiplication
/               Division
%               Modules(remainder)
**              Exponentiation(power)
++              Increment by 1
--              Decrement by 1

what is concatenation ?

String concatenation in JavaScript refers to the process of combining two or more strings into a single string.

example:


**input:**
let i="200"+6;
let i++:
console.log(i);

**output:**
2006

- Increment and Decrement

There are two types,

prefix form (First increments and decrement of the variable. Then the updated value)

[eg; increment
let x=7;
++x;
console.log(x); ] // 7 // 8

[decrement
let x=7;
--x;
console.log(x); ] //7 //6

postfix form (Returns the original value first. Then the modified the variable)

`[eg;increment
let x=7;
x++;
console.log(x);]   //7  //8]

decrement
let x=7;
x--;
console.log(x); ]  //7 //6`

I Hope, this blog is helpfull for anyone and helpfull myself.

Thankyou.

Java Script: Basics of Data Types, Variables, Objects and Properties.

Vishnu N — Mon, 07 Jul 2025 18:07:42 +0000

Hello Everyone,

Today we will learn the basics of data types, variables, objects and the properties in Java Script.

what is java script?

Java Script is the programming language of the web development and the use of update and change the HTML and CSS. It can be calculate, manipulate and validate the data.

why java script?

It you can use the java script to program the behavior of the web pages.

data

Data Types:

String (if you declare letters inside the double course, [example: "java script"]).
Number (Any numbers, example: int[95] or float[8.34] ).
Bigint (Large int in number list [eg: 234567894352356] ).
Boolean (Logical values [True or False] ).
Undefined ( some variales is declared but not defined the values).
Null ( developers intentional is empty value for the input null).
symbol (it is a Unique Identifiers).

let name = "Vishnu";     
let age = 25; 
let bigNumber = 3456789098765483553;             
let isStudent = true;      
let score;                
let emptyValue = null;    
let uniqueId = Symbol("id");

IDENTIFIERS AND VARIABLES IN JAVA SCRIPT:

An identifier is the name used to identify variables, functions, arrays, objects [ex: city, age, state, country]
In the Keyword of the variables is { var, let, const}.
var - In the function is scoped the older way.
let - If you assign one value, you can change the other value.
const - If you assign one value is constant, you can't change the value.

example: [var, let, const]

OBJECTS AND PROPERTIES IN JS:

The object are called the things. [eg; bike, house, person].

The name of the values in java script object are called properties.
eg: [name, age, gender, qualification, height, weight] .

create on object:

// Create an Object:
person = {



            //property            // values

            firstName:              "John",
            lastName:               "Doe",
            age:                     50,
            eyeColor:               "blue"
};

PROGRAMMING LANGUAGE:

Programming languages are two types these;

Compiled Programming language: The compiled program are like java and c, c++. It is statically type.
Interpreter Programming language: Java Script and python etc.,
Java Script is dynamically type.

Thus the above concepts today i learned my class. The java script basics are very helpful for me and learners.

HOW I LEARN LINUX MINT INSTALLATION : MY EXPERIENCE

Vishnu N — Wed, 18 Jun 2025 12:50:03 +0000

Hi everyone,
How's my linux mint installation process:

My trainee is refer to LINUX MINT(cinnaman) operating system, so I'll try to use LINUX MINT.
SO, I'll INSTALL LINUX OPERATING SYSTEM.

STEP 1:DOWNLOAD FILE.

Download the LINUX file from web browser and then download rufus Tool for booting process.

STEP 2:EXTRACT AND FLASH PENDRIVE.

Insert the empty Pendrive in your disk.

Extract the rufus tool and select the LINUX download file in filemanager,and the other option to select your pendrive.

Then you starting flash the pendriver, and will be finish the flashing process and eject the pendrive in your disk.

STEP 3:BOOTING PROCESS.

The flashing pendriver is ready to boot your system.
Insert the bootable pendrive in the system and switch on the system and continue pressing the bootkey on your booting device and select your pendrive then tap to start.

STEP 4: INSTALLATION PROCESS.

Select the LINUX MINT(cinnaman) Press enter to Start.
open the install option in your desktop, then select english, english(US) to press enter to continue and select the map in country(INDIA) to continue and will be fished your installation process.

Successfully installed LINUX Mint in your system, so ready to use.

THANKYOU.