DEV Community: Annapoorani Kadhiravan

One Commit at a Time ! Series - 9

Annapoorani Kadhiravan — Wed, 14 Oct 2026 18:14:01 +0000

JAVA

import java.util.Arrays;

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

        int [] source = {1, 2, 3, 4, 5, 6};
        int [] destination = new int[6];

        // iterate and copy elements from source to destination
        for (int i = 0; i < source.length; ++i) {
            destination[i] = source[i];
        }

         // converting array to string
        System.out.println(Arrays.toString(destination));
    }
}

Explanation :

import java.util.Arrays; Imports the built-in utility class Arrays from the standard java.util package, allowing access to helper methods like Arrays.toString() for array manipulation and display.
class Main { Declares a class named Main. In Java, all code must reside inside a class structure.
public static void main(String[] args) { Defines the entry point of the Java application:
public: Accessible from anywhere.
static: Can be invoked without creating an instance of Main.
void: Does not return any value.
main: Name of the standard startup method.
String[] args: Accepts optional command-line arguments as an array of strings.
int [] source = {1, 2, 3, 4, 5, 6}; Declares and initializes an integer array named source containing six elements: 1, 2, 3, 4, 5, 6.
int [] destination = new int[6]; Allocates a new integer array named destination of size 6. By default, Java initializes all its integer elements to 0.
// iterate and copy elements from source to destination A single-line comment explaining the purpose of the subsequent for loop (ignored by the compiler).
for (int i = 0; i < source.length; ++i) { Sets up a loop to iterate through each index of the array:
int i = 0: Initializes loop index i at 0 (the first element).
i < source.length: Condition to keep looping while i is less than 6 (indices 0 through 5).
++i: Pre-increments i by 1 after each loop cycle.
destination[i] = source[i]; Copies the element at index i of the source array into the matching index i of the destination array.
}Marks the end of the for loop body.
// converting array to string A single-line comment indicating that the array will be converted into a readable string format.
System.out.println(Arrays.toString(destination));
Arrays.toString(destination) converts the destination array into a readable string representation: "[1, 2, 3, 4, 5, 6]".
System.out.println(...) prints this string to the console followed by a newline.
} Closes the main method.
}Closes the Main class definition.

SQL

SELECT TOP Clause
The SELECT TOP clause is used to limit the number of records to return.

The SELECT TOP clause is useful on large tables with thousands of records. Returning a large number of records can impact performance.

The following SQL selects only the first 3 records of the "Customers" table:

#Select only the first 3 records of the Customers table:

SELECT TOP 3 * FROM Customers;

References :

https://www.programiz.com/java-programming/copy-arrays
https://www.w3schools.com/sql/sql_top.asp

One Commit at a Time ! Series - 8

Annapoorani Kadhiravan — Tue, 13 Oct 2026 17:56:39 +0000

JAVA

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

        int [] numbers = {1, 2, 3, 4, 5, 6};
        int [] positiveNumbers = numbers;    // copying arrays

        // change value of first array
        numbers[0] = -1;

        // printing the second array
        for (int number: positiveNumbers) {
            System.out.print(number + ", ");
        }
    }
}

Explanations

class Main {: Declares a public class named Main to serve as the structural framework for the application.
public static void main(String[] args) {: The entry point method where the Java Virtual Machine begins execution.
int [] numbers = {1, 2, 3, 4, 5, 6};: Declares and initializes an integer array named numbers containing six elements in memory.
int [] positiveNumbers = numbers;: Copies the reference (memory address) of the numbers array into a new array reference variable named positiveNumbers. This does not duplicate the underlying array data; both variables now point to the exact same array object in memory.
numbers[0] = -1;: Modifies the first element (index 0) of the array to -1. Because both numbers and positiveNumbers point to the same array object, this change will also be reflected when accessing the array through positiveNumbers.
for (int number: positiveNumbers) {: Starts an enhanced for-loop to iterate through each element stored in the positiveNumbers array reference.
System.out.print(number + ", ");: Prints each element of the array followed by a comma and a space on the same line (resulting in output where the first item is -1 instead of 1).
}: Closes the loop block.
}: Closes the main method block.
}: Closes the Main class block.

SQL

IN Operator

The IN operator is used in the WHERE clause to check if a specified column's value matches any value within a provided list.

The IN operator functions as a shorthand for multiple OR conditions, making queries shorter and more readable.

Syntax :
SELECT column_name(s)
FROM table_name
WHERE column_name IN (value1, value2, ...);

SELECT * FROM Customers
WHERE Country IN ('Germany', 'France', 'UK');

Reference :
https://www.w3schools.com/sql/sql_in.asp
https://www.programiz.com/java-programming/copy-arrays

One Commit at a Time ! Series - 7

Annapoorani Kadhiravan — Mon, 12 Oct 2026 04:40:00 +0000

JAVA

# Create objects inside the same class

class Lamp {

  // stores the value for light
  // true if light is on
  // false if light is off
  boolean isOn;

  // method to turn on the light
  void turnOn() {
    isOn = true;
    System.out.println("Light on? " + isOn);

  }

  public static void main(String[] args) {

    // create an object of Lamp
    Lamp led = new Lamp();

    // access method using object
    led.turnOn();
  }
}

OUTPUT :
Light on? true

SQL

The SELECT DISTINCT statement is used to return only distinct (unique) values.

In a table, a column may contain several duplicate values - and sometimes you want to list only the unique values.

SELECT DISTINCT Syntax
SELECT DISTINCT column1, column2, ...
FROM table_name;

SELECT DISTINCT Country FROM Customers;

Count Distinct Values
By using the COUNT() function with the DISTINCT keyword, we can count the number of unique countries.

SELECT COUNT(DISTINCT Country) FROM Customers;

References :
https://www.w3schools.com/sql/sql_distinct.asp
https://www.programiz.com/java-programming/class-objects

One Commit at a Time ! Series - 6

Annapoorani Kadhiravan — Sun, 11 Oct 2026 13:38:41 +0000

JAVA

class Lamp {

  // stores the value for light
  // true if light is on
  // false if light is off
  boolean isOn;

  // method to turn on the light
  void turnOn() {
    isOn = true;
    System.out.println("Light on? " + isOn);

  }

  // method to turnoff the light
  void turnOff() {
    isOn = false;
    System.out.println("Light on? " + isOn);
  }
}

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

    // create objects led and halogen
    Lamp led = new Lamp();
    Lamp halogen = new Lamp();

    // turn on the light by
    // calling method turnOn()
    led.turnOn();

    // turn off the light by
    // calling method turnOff()
    halogen.turnOff();
  }
}

SQL

SELECT - extracts data from a database
UPDATE - updates data in a database
DELETE - deletes data from a database
INSERT INTO - inserts new data into a database
CREATE DATABASE - creates a new database
ALTER DATABASE - modifies a database
CREATE TABLE - creates a new table
ALTER TABLE - modifies a table
DROP TABLE - deletes a table
CREATE INDEX - creates an index (search key)
DROP INDEX - deletes an index

The most commonly used SQL aggregate functions are:

MIN() - returns the smallest value of a column
MAX() - returns the largest value of a column
COUNT() - returns the number of rows in a set
SUM() - returns the sum of a numerical column
AVG() - returns the average value of a numerical column
Aggregate functions ignore null values (except for COUNT(*)).

References :

https://www.programiz.com/java-programming/class-objects
https://www.w3schools.com/sql/sql_aggregate_functions.asp

One Commit at a Time Series - 5

Annapoorani Kadhiravan — Sat, 10 Oct 2026 18:15:19 +0000

JAVA

### Check if an array contains the given value using Stream

import java.util.stream.IntStream;

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

    int[] num = {1, 2, 3, 4, 5};
    int toFind = 7;

    boolean found = IntStream.of(num).anyMatch(n -> n == toFind);

    if(found)
      System.out.println(toFind + " is found.");
    else
      System.out.println(toFind + " is not found.");

  }
}

Explanations

import java.util.stream.IntStream;: Imports the IntStream class from the java.util.stream package, which provides methods for processing sequences of primitive integer values using functional-style operations.
class Main {: Declares a public class named Main to house the Java application.
public static void main(String[] args) {: The standard entry point method where the Java Virtual Machine begins program execution.
int[] num = {1, 2, 3, 4, 5};: Declares and initializes an integer array containing the sequence of numbers from 1 to 5.
int toFind = 7;: Defines the target integer value (7) that we want to search for in the array.
boolean found = IntStream.of(num).anyMatch(n -> n == toFind);: Converts the array into a sequential stream using IntStream.of(num), then uses the terminal operation anyMatch() with a lambda expression (n -> n == toFind) to check if any element in the stream matches the target value, storing the resulting boolean (true or false) in the found variable.
if(found): Evaluates whether the boolean flag found is true.
System.out.println(toFind + " is found.");: Executes if found is true, printing a confirmation message.
else: Executes if the match condition evaluates to false.
System.out.println(toFind + " is not found.");: Prints a message stating that the target value does not exist in the array (which executes in this example since 7 is not in the array).

SQL

DQL – Data Query Language - Focused on retrieving data.

SELECT → Fetch data from tables.

Clauses like WHERE, GROUP BY, HAVING, ORDER BY refine queries.

Example:

SELECT Name, Age FROM Students WHERE Age > 20;

Reference :
https://www.programiz.com/java-programming/examples/array-contains-value

One Commit at a Time Series - 4

Annapoorani Kadhiravan — Fri, 09 Oct 2026 18:29:43 +0000

LINUX

man - is used to display command manuals grep - is used to search text patters [case sensitive] echo - is used to display text in terminal wget - is used to download files from internet using URL whoami - is used to display the current user sort - is used to sort file contents cal - is used to display the calendar whereis - is used to locate command files df - is used to display disk space usage wc - is used to display number of lines, words and bytes in the file

JAVA

# Check if Int Array contains a given value

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

    int[] num = {1, 2, 3, 4, 5};
    int toFind = 3;
    boolean found = false;

    for (int n : num) {
      if (n == toFind) {
        found = true;
        break;
      }
    }

    if(found)
      System.out.println(toFind + " is found.");
    else
      System.out.println(toFind + " is not found.");
  }
}

Explanations

class Main: Declares a public class named Main, which serves as the container for the Java program.
public static void main(String[] args): The main entry point of any Java application where execution begins.
int[] num = {1, 2, 3, 4, 5};: Declares and initializes an integer array containing elements 1 through 5.
int toFind = 3;: Defines the specific integer value we want to check for in the array.
boolean found = false;: Initializes a boolean flag to track whether the target value has been located.
for (int n : num): Iterates sequentially through each element in the array.
if (n == toFind): Checks if the current array element matches the target value.
found = true;: Updates the flag to true since the value has been matched.
break;: Exits the loop immediately once the value is found to save processing time.
if(found): Evaluates whether the flag remains true after the loop completes.
System.out.println(toFind + " is found.");: Prints a confirmation message if the value exists in the array.
System.out.println(toFind + " is not found.");: Prints a message if the loop completed without finding the value.

SQL

DML – Data Manipulation Language
Used to manipulate data stored in tables.

INSERT → Add new records.

UPDATE → Modify existing records.

DELETE → Remove records.

MERGE → Combine data from multiple sources.

Example:

INSERT INTO Students (StudentID, Name, Age)
VALUES (1, 'Annapoorani', 22);

References :

https://www.geeksforgeeks.org/linux-unix/basic-linux-commands/

One Commit at a Time Series - 3

Annapoorani Kadhiravan — Thu, 08 Oct 2026 18:24:50 +0000

LINUX

mv - is used to move or rename files and directories rm - is used to delete files permanently uname - is used to display system information locate - is used to find files using a database touch - is used to create empty files and updates file timestamps ln - is used to create links between files clear - is used to clear the terminal screen ps - is used to display running processes

JAVA

Java is platform independent Language
Java stores file as bytecode, which helps to run the same file in different OS, make it platform independent
JDK converts into bytecode (.class files) and JIT converts it into Binary code for machine understandable language, after conversion its handled by JVM.
All these process runs in JRE [ Java Runtime Environment ]
toString() is a method used to convert objects into that data type.

# Print an Array using For loop
public class Array {

    public static void main(String[] args) {
        int[] array = {1, 2, 3, 4, 5};

        for (int element: array) {
            System.out.println(element);
        }
    }
}

# Print an Array using standard library Arrays
import java.util.Arrays;

public class Array {

    public static void main(String[] args) {
        int[] array = {1, 2, 3, 4, 5};

        System.out.println(Arrays.toString(array));
    }
}

SPRINGBOOT

SQL

DDL – Data Definition Language

Used to define and modify database structures.

CREATE → Create tables, databases, indexes, views.

ALTER → Modify existing database objects.

DROP → Delete database objects.

TRUNCATE → Remove all records from a table (faster than DELETE).

RENAME → Change the name of a database object.

👉 Example:

CREATE TABLE Students (
   StudentID INT PRIMARY KEY,
   Name VARCHAR(50),
   Age INT
);

Reference

https://www.programiz.com/java-programming/examples/print-array
https://www.geeksforgeeks.org/java/difference-between-spring-and-spring-boot/
https://www.w3schools.com/JAVA/ref_string_tostring.asp

One Commit at a Time Series - 2

Annapoorani Kadhiravan — Wed, 07 Oct 2026 17:08:01 +0000

Linux

cp → copy files

mv → move or rename files

cat → view file contents

locate → quickly find files by name

SPRING vs SPRINGBOOT

JAVA

#Find ASCII value of a character
public class AsciiValue {

    public static void main(String[] args) {

        char ch = 'a';
        int ascii = ch;
        // You can also cast char to int
        int castAscii = (int) ch;

        System.out.println("The ASCII value of " + ch + " is: " + ascii);
        System.out.println("The ASCII value of " + ch + " is: " + castAscii);
    }
}

Output

The ASCII value of a is: 97
The ASCII value of a is: 97

SQL

Type	Full Form	Common Commands	Purpose
DDL	Data Definition Language	CREATE, ALTER, DROP, TRUNCATE	Define/modify database structure
DML	Data Manipulation Language	INSERT, UPDATE, DELETE, MERGE	Manage data inside tables
DQL	Data Query Language	SELECT	Retrieve data
DCL	Data Control Language	GRANT, REVOKE	Manage user permissions
TCL	Transaction Control Language	COMMIT, ROLLBACK, SAVEPOINT	Control transactions

Reference :

https://www.geeksforgeeks.org/sql/sql-ddl-dql-dml-dcl-tcl-commands/?utm_source=copilot.com
https://www.geeksforgeeks.org/linux-unix/basic-linux-commands/

One Commit at a Time Series - 1

Annapoorani Kadhiravan — Tue, 06 Oct 2026 18:22:30 +0000

Sharing my journey of One Commit at a time series, where I learn and share it here. Hoping to bring a huge impact at the end of this series. Starting with Day - 1 :

LINUX

Commands and its usage :

ls - list the files cd - change directory pwd - present working directory mkdir [dirname] - make a directory rmdir [dirname] - remove a directory cd / cd ~ / cd $HOME - move to home cat >filename - create a file in directory with write mode touch filename - create a file in directory echo "content" >>filename - write content in the respective file cat filename - to view the content inside the file

JAVA

# Program to find odd or even

import java.util.Scanner;

public class OddOrEven {
 public static void main (String args[]){
Scanner sc = new Scanner(System.in);
System.out.println("Enter the number:");
int num = sc.nextInt();
if(num%2 == 0)
{
System.out.println("The given number is Even : "+ num);
}
else
{
System.out.println("The given number is Odd : "+ num);
} 
sc.close();
}
}

SPRINGBOOT

Spring is a framework, which is used in building enterprise level applications.
Spring will take care of object creation, we don't have to create any objects.
It helps in creating loosely coupled application and also can integrate other frameworks easily.
SpringBoot is the first project created by spring, hence it closely resembles spring.
SpringBoot is famous for its conventions over configurations.
It also have embedded server (Tomcat) available with it. Without server, it will show as "This site can't be reached".
Using SpringBoot, APIs can be built in minutes. [ HTTP Methods : GET, POST, PUT, DELETE ]
SpringBoot is a standalone application where output can be seen in IDE terminal rather than running it in a web browser.

SQL

1. To select Customer name starts with 'M' :

SELECT * FROM Customers  WHERE name LIKE '%M'

2. To select customer name ends with 'n' :

SELECT * FROM Customers WHERE name LIKE '%n'

3. To Select Customer name which contains 'r' in their name :

SELECT * FROM Customer WHERE name LIKE '%r%'

4. To Select Customer name whose name has 'r' in 3rd position :

SELECT * FROM Customer WHERE name LIKE '__r%'

References :

https://www.geeksforgeeks.org/linux-unix/basic-linux-commands/
https://www.geeksforgeeks.org/linux-unix/different-ways-to-create-file-in-linux/
https://www.youtube.com/watch?v=SSKVgrwhzus&list=PLNcg_FV9n7qZY_2eAtUzEUulNjTJREhQe&index=1
https://www.youtube.com/watch?v=7d0c_CaHgEc
https://www.w3schools.com/JAVA/java_practice.php

Understanding VMware and Virtualization - Part 2

Annapoorani Kadhiravan — Mon, 14 Sep 2026 16:02:18 +0000

What Is VMware ESXi?

VMware ESXi is a Type 1, or bare-metal, hypervisor.

It is installed directly on a physical server.

Physical Server
↓
ESXi
↓
┌────┼────┐
↓ ↓ ↓
VM1 VM2 VM3

ESXi provides the virtualization layer.

It allows multiple VMs to share the physical resources of the server.

For example, imagine a physical server has:

CPU: 32 cores
RAM: 128 GB
Storage: 2 TB

ESXi can host multiple VMs on that server.

Each VM can be assigned a certain amount of CPU, memory, storage, and network connectivity.

How Does VMware Virtualization Work?

Let's understand the complete flow.

Step 1: Physical Server

First, we have a physical server containing hardware resources.

CPU
RAM
Storage
Network
Step 2: Install ESXi

ESXi is installed directly on the physical server.

Physical Hardware
↓
ESXi
Step 3: Create Virtual Machines

The administrator creates VMs on the ESXi host.

ESXi
├── VM1
├── VM2
└── VM3
Step 4: Assign Resources

Each VM receives virtual resources.

For example:

VM1 → 4 vCPU + 8 GB RAM
VM2 → 2 vCPU + 4 GB RAM
VM3 → 4 vCPU + 16 GB RAM
Step 5: Install Operating Systems

Each VM can have a supported operating system.

VM1 → Windows
VM2 → Linux
VM3 → Linux
Step 6: Run Applications

Applications are installed inside the guest operating systems.

The result is multiple independent workloads running on the same physical server.

What Is a VMware Host?

A host is a physical server running ESXi.

For example:

Physical Server
↓
ESXi
↓
Host
↓
VMs

A large enterprise environment may contain many ESXi hosts.

For example:

ESXi Host 1
ESXi Host 2
ESXi Host 3
ESXi Host 4

These hosts can be managed together.

What Is vCenter Server?

When an organization has many ESXi hosts, managing each host individually can become difficult.

This is where vCenter Server is used.

vCenter provides centralized management for VMware infrastructure.

            vCenter
               ↓
    ┌──────────┼──────────┐
    ↓          ↓          ↓
 ESXi 1     ESXi 2     ESXi 3
    ↓          ↓          ↓
   VMs        VMs        VMs

Through vCenter, administrators can manage resources and perform operations across supported VMware infrastructure.

For a beginner, remember:

ESXi runs the VMs. vCenter manages the VMware environment centrally.

What Is VMware vSphere?

vSphere is VMware's server virtualization platform.

It brings together the technologies used to create and manage virtualized infrastructure.

A simplified view is:

vSphere
│
├── ESXi
│
└── vCenter

It is important not to confuse these terms.

ESXi is the hypervisor.

vCenter provides centralized management.

vSphere refers broadly to the VMware virtualization platform.

Exact product packaging and licensing can vary by VMware/Broadcom product version, so beginners should always check the documentation for the specific version they are learning.

Understanding VMware and Virtualization - Part 1

Annapoorani Kadhiravan — Wed, 09 Sep 2026 18:24:41 +0000

Introduction

Modern IT infrastructure has changed significantly over the last few decades. Earlier, organizations often needed a separate physical server for every application or workload. As the number of applications increased, this approach became expensive, difficult to maintain, and inefficient.

This is where virtualization became important.

Virtualization allows a single physical server to run multiple virtual machines (VMs). Each virtual machine behaves like an independent computer with its own operating system, CPU, memory, storage, and network connection.

One of the most widely known technologies in enterprise virtualization is VMware.

But what exactly is virtualization? What is VMware? Where are these technologies used? And how do they actually work?

This blog answers these questions in a simple way.

1. What Is Virtualization?

Virtualization is the process of creating a virtual version of a physical computing resource.

The most common example is server virtualization.

Imagine a physical server with:

16 CPU cores
64 GB RAM
1 TB storage

Without virtualization, the organization might install one operating system directly on the server and run its applications there.

Physical Server
      ↓
Operating System
      ↓
Application

The problem is that the server may not use all of its CPU and memory all the time.

Virtualization allows the same physical server to run multiple virtual machines.

             Physical Server
                    ↓
               Hypervisor
          ┌─────────┼─────────┐
          ↓         ↓         ↓
         VM1       VM2       VM3
          ↓         ↓         ↓
       Windows     Linux     Linux

Each VM can run its own operating system and applications.

Therefore, virtualization helps organizations use physical hardware more efficiently.

2. What Is a Virtual Machine?

A Virtual Machine, or VM, is a software-based computer running on a physical server.

Although a VM is not a physical computer, it behaves like one.

A VM can have:

Virtual CPU
Virtual memory
Virtual hard disk
Virtual network adapter
Operating system
Applications

For example:

VM
├── 4 vCPU
├── 8 GB RAM
├── 100 GB Virtual Disk
├── Virtual Network Adapter
└── Windows/Linux

From the perspective of the operating system installed inside the VM, it behaves much like a normal computer.

The important difference is that its hardware resources are virtualized.

3. What Is a Hypervisor?

The technology that makes virtualization possible is called a hypervisor.

A hypervisor is software that creates and manages virtual machines.

It sits between the physical hardware and the VMs.

Physical Hardware
       ↓
    Hypervisor
       ↓
 ┌─────┼─────┐
 ↓     ↓     ↓
VM1   VM2   VM3

The hypervisor manages resources such as:

CPU
Memory
Storage
Networking

It allocates these resources to virtual machines according to their configuration and the requirements of the environment.

4. Where Does Virtualization Take Place?

Virtualization normally takes place on a physical server, commonly located in a data center.

For example, a company's data center might contain:

Data Center
│
├── Physical Server 1
├── Physical Server 2
├── Physical Server 3
├── Storage
└── Network Devices

A hypervisor can be installed on these physical servers.

The hypervisor then allows multiple VMs to run on each server.

Physical Server
      ↓
   Hypervisor
      ↓
 ┌────┼────┐
VM1  VM2   VM3

Virtualization is widely used in:

Enterprise data centers
Private clouds
Hybrid cloud environments
Development and testing environments
Virtual desktop infrastructure
Disaster recovery environments
Application hosting

5. What Is VMware?

VMware is a technology company known for virtualization and enterprise infrastructure software.

VMware became one of the major names in server virtualization by providing technologies that allow organizations to create, manage, and operate virtual machines at scale.

Today, VMware is part of Broadcom following Broadcom's acquisition of VMware.

For a beginner, VMware should not be viewed as just one software product.

It is better to think of VMware as an ecosystem of technologies used to build and manage virtualized infrastructure.

Some important VMware terms are:

ESXi
vSphere
vCenter Server
Virtual Machines
Hosts
Clusters
Datastores
Virtual Networks
vMotion
High Availability
DRS

Calculating Subnetting

Annapoorani Kadhiravan — Thu, 03 Sep 2026 17:48:45 +0000

network
subnet
host name