DEV Community: SILAMBARASAN A

Java Packages

SILAMBARASAN A — Tue, 21 Apr 2026 06:32:08 +0000

A package in Java is used to group related classes. Think of it as a folder in a file directory. We use packages to avoid name conflicts, and to write a better maintainable code. Packages are divided into two categories.

Built-in Packages (packages from the Java API)
User-defined Packages (create your own packages) The Java API is a library of prewritten classes, that are free to use, included in the Java Development Environment.

Built-in Packages

The library contains components for managing input, database programming, and much much more. The complete list can be found at Oracles website: https://docs.oracle.com/javase/8/docs/api/.

User-defined Packages

To create your own package, you need to understand that Java uses a file system directory to store them. Just like folders on your computer.

java.lang: This package holds the foundational classes.
java.io: It handles all sorts of input and output operations.
java.awt: This package provides the basic building blocks for creating graphical user interfaces (GUIs).
javax.swing: It is best for more advanced and richer desktop application GUIs due to its comprehensive toolkit.
java.net: It contains classes essential for developing network-aware applications.
java.util: It is a versatile package filled with utility classes, including the powerful Collections Framework.
java.applet: This package includes classes for building applets, which are small applications designed to run in web browsers (though less common now).
java.sql: Here you will find the classes for interacting with databases and processing relational data. above the all to be discussed.

User-defined packages

User-defined packages in Java are not readily available, as their name suggests. These are created by developers to define interfaces and classes according to the application requirements. It is defined using a unique syntax as shown below:


package packageName;

You can see the package keyword in its syntax, it defines the package name. It is important to declare the package just before any import statements of a Java class. It is also important to ensure that all the classes are public so that you can access them from both inside and outside the package.

Java basic program

SILAMBARASAN A — Mon, 20 Apr 2026 03:02:38 +0000

this program helps me to understand Object, method, constructor.

class Dmart{ 

String product_name;
int product_price;
int product_discountpercentage;
int product_discountprice;
int finalprice;


public Dmart(String name ,int price ,int discountpercentage){

this.product_name=name;
this.product_price=price;
this.product_discountpercentage=discountpercentage;
}


public static void main(String[] args){

Dmart product1=new Dmart("shop" , 50 , 8);
Dmart product2=new Dmart("chips" , 30 , 5);
Dmart product3=new Dmart("Choclate" , 200 , 2);
Dmart product4=new Dmart("Biscut"  ,  15 , 7);
Dmart product5=new Dmart("HotChips" , 25 , 12);

product1.buy();
product2.buy();
product3.buy();
product4.buy();
product5.buy();

}
public void buy(){

this.product_discountprice = (this.product_price * this.product_discountpercentage) / 100;
this.finalprice=this.product_price-this.product_discountprice;

System.out.println("productname => "+ this.product_name);
System.out.println("proprice => " + this.product_price);
System.out.println("prodiscountpercentage => " + this.product_discountpercentage);
System.out.println("discountprice => " + this.product_discountprice);
System.out.println("finalprice => " + this.finalprice);

}

}

Pincode validate

SILAMBARASAN A — Sat, 18 Apr 2026 07:03:24 +0000

too be disscused

        const regions = {
    1: "Delhi",
    2: "Uttar Pradesh & Uttarakhand",
    3: "Rajasthan & Gujarat",
    4: "Maharashtra",
    5: "Andhra Pradesh & Telangana",
    6: "Tamil Nadu & Kerala",
    7: "West Bengal & North East",
    8: "Bihar & Jharkhand",
    9: "Army Postal Service"
};

const sub_regions = {
    11: "Delhi Region",
    40: "Mumbai Region",
    60: "Chennai Region",
    70: "Kolkata Region"
};

const districts = {
    110: "Delhi",       111: "Delhi (North)",      112: "Delhi (South)",
    400: "Mumbai",      401: "Mumbai (Suburban)",   402: "Mumbai (West)",
    600: "Chennai",     601: "Tiruvallur",          602: "Kanchipuram",
    700: "Kolkata",     701: "Kolkata (North)",     702: "Kolkata (South)"
};

function getPincodeDetails(pincode) {
    if (!/^\d{6}$/.test(pincode)) {
        console.log("Invalid pincode. Enter exactly 6 digits.");
        return;
    }

    const num        = Number(pincode);
    const firstDigit = Math.floor(num / 100000);
    const firstTwo   = Math.floor(num / 10000);
    const firstThree = Math.floor(num / 1000);

    console.log("Region:     ", regions[firstDigit]   || "Unknown");
    console.log("Sub-region: ", sub_regions[firstTwo] || "Unknown");
    console.log("District:   ", districts[firstThree] || "Unknown");
}

getPincodeDetails(prompt("enter the number"))

Gmail Validation

SILAMBARASAN A — Sat, 18 Apr 2026 06:58:29 +0000

how i validate the given gmail is valid or invalid.

Condition :
Gmail end should end like this "@gmail.com"
so, I first checked last 10 character from given gamil.

If condition is false return"gmail end should end like @gmail.com"

If condition is True, checks the next condition

next take the gmail copy except "@gmail.com"
the gmail copy is only have charactors and numbers and plus and dot.
the condition is true return "valid"
the condition is false return "special charector not allow"

def verify_Gmail(Gmail):
    if Gmail[-10:]=="@gmail.com":
        i=0
        gmailcopy=Gmail[0:len(Gmail)-10]
        while i<len(gmailcopy):
            current=gmailcopy[i]
            i+=1
            if current>="a" and current<="z":
                continue;
            elif current>="A" and current<="Z":
                continue;
            elif current>="0" and current<="9":
                continue;
            elif current=="." or current=="_":
                continue;
            else:
                return "special charector not allow"
        return "valid"
    else:
        return "gmail end like this @gmail.com "

print(verify_Gmail(input("Enter Your Gmail :")))

Constructors in Java

SILAMBARASAN A — Sat, 18 Apr 2026 03:05:54 +0000

constructor in java is a spacial method, that is called when object is created. Its main purpose is to initialize the object. It is used to set default or user-defined values for the object's attributes.

A constructor has the same name as the class.
It does not have a return type, not even void.
It can accept parameters to initialize object properties

Rules of Constructor

Constructor name must be the same as the class name.
Constructors do not have a return type (not even void).
If you add a return type, it becomes a method, not a constructor.
A constructor is called once per object creation (when using new).
If no constructor is defined, Java provides a default no-arg constructor.
If you define any constructor, the default is con't provided.

Default Constructor :

Java provides this automatically if you don’t define any constructor

public class Constructor{
int age=10;
public static void main(String[] args){
Constructor obj = new Constructor();
System.out.println(obj.age);
}
}

No-Argument Constructor

You write it yourself, no parameters.

public class Constructor{
int age=10;
public Constructor(){
System.out.println("no agru constructor");
}
public static void main(String[] args){
Constructor obj = new Constructor();
System.out.println(obj.age);
}
}

Parameterized Constructor

Used to pass values at object creation and set value for arttibutes.

public class Constructor{
int age;
public Constructor(int a){
age=a;
}
public static void main(String[] args){
Constructor obj = new Constructor(19);
System.out.println(obj.age);
}
}

Mobile Number Verify

SILAMBARASAN A — Fri, 17 Apr 2026 19:49:24 +0000

Now my code is 100% Right way to verify mobile number exactly.

I checked some condition to confirm given number is mobile number.

condition 1 :
given numbers must be only 0 to 9 or + or empty space .

above the condition is true, then only checks the next conditions.
otherwise return characters and characters spl are not allow.

i created one function the name of verify. that function checks given given argument is only have 0 To 9.

condition 2 :
my second condition is checks the length of the given numbers, the length should be 10, then only enter in condition 2. else goes the next condition3.

okay, let come's to the condition 2

condition 2 is checks, Given numbers in first number must be greater than or equal to 6 and less than or equal to 9 and calling the verify function and argument is given number.

above the both condition is true, return "Valid Mobile Number"
above the both condition is false, return "check the first digit and space and plush not allowed".

Condition 3 :
condition 3 also checks the length of the given numbers, the length is must be 13, then only enter in condition 3. else goes the next condition 4.

let come's to the condition 3

condition 3 is checks the given first three numbers is == "+91"

Above the condition is False, return "First three number should like +91"
above the condition is true, checks the next condition, next condition is checks the fourth digit is must be greater than or equal to 6 and less than or equal to 9 and calling the verify function and argument is given number except first three index.
- the both condition is true, return "Valid Mobile Number"
- the condition is false, return "check the fourth digit and plus and space not allow between the number"

condition 4 :
condition 4 is similar to condition 3, extra checks space.
condition 4 checks the length of the given numbers, the length is must be 14, then only enter in condition 4. else goes next .

condition 4,
checks the given first four ind is == "+91 "

Above the condition is False, return "First four number should like +91 "
above the condition is true, checks the next condition, next condition is checks the fifth number is must be greater than or equal to 6 and less than or equal to 9 and calling the verify function and argument is given number except first four index.
- the both condition is true, return "Valid Mobile Number"
- the condition is false, return "check the fifth digit and, plus and space not allowed

FINAL :
given number is can't enter in any condition 2,3,4.
return "given number is invalid"

the function is return a string, So function must be call in print.
**
**and this is my code :

def verify(mobnum):
    index=0
    while index<len(mobnum):
        if mobnum[index]>="0" and mobnum[index]<="9":
            index+=1
        else:
            return False
    return True



def mobile(n):
    i=0
    while i<len(n):
        if(n[i]>="0" and n[i]<="9") or (n[i]=="+") or (n[i]==" "):
            i+=1
        else:
            return "characters and special charactors not allowed"

    if len(n)==10:
        if n[0]>="6" and n[0]<="9" and verify(n):
            return "valid";
        else:
            return "incorrect"

    if len(n)==13:
        if n[0:3]=="+91":
            if n[3]>="6" and n[3]<="9" and verify(n[3:]):
                return "valid"
            else:
                return "incorrect"
        return "First three number should like +91"

    if len(n)==14:
        if n[0:4]=="+91 ":
            if n[4]>="6" and n[4]<="9" and verify(n[4:]):
                return "valid"
            else:
                return "incorrect"
        return "First four number should like +91 "
    return "Please Enter Your valid Mobile Number"      
print(mobile(input("Enter Your Mobile  Number : ")));

drop your ideas in comments

Client Server Architechture

SILAMBARASAN A — Mon, 13 Apr 2026 04:53:35 +0000

The main idea — Clients ask. Servers give. They each have one job.
Client — your phone, laptop, or app. It asks for things — like when you tap a link or open Instagram. It doesn't store anything big. It just shows you what the server sends back.
Server — a big, always-on computer somewhere. It listens for requests, does the work, and sends back the answer. It talks to hundreds of people at the same time.
How it works, step by step:

You click a link → your browser asks the server "give me this page"
The server gets the request, looks up the data it needs
The server sends the page back to you
Your browser shows it on screen

Why it's a good system:

One place for data — everything is saved on the server, not scattered across everyone's devices. Easy to keep safe and up to date.
Can grow easily — if too many people use it at once, you just add more servers.
Each side does its own thing — your device handles what you see, the server handles what happens behind the scenes.

User side is everything that runs on your device — your browser or app, the screen you see, and a tiny bit of temporary storage (like saved passwords or cookies). It sends requests and displays whatever the server sends back. It does not make big decisions or store important data.

Server side is everything running on a remote computer — it receives your request, checks who you are (authentication), runs the rules (business logic), talks to the database, and sends back a clean response.

System Software and Application Software

SILAMBARASAN A — Sun, 12 Apr 2026 02:38:10 +0000

SYSTEM SOFTWARE :

System software is software that helps to operate and control a computer.

system software is helps to the computer (CPU, RAM, etc.) to work properly.

system software is providing a platform for application software to run on.

Types of System Software

Operating system(os) --> the core system software (e.g., Windows, macOS, Linux, Android). It manages the CPU, memory, storage, and input/output devices, and provides a user interface.

Device Drivers --> small programs that allow the OS to communicate with hardware components like printers, graphics cards, and keyboards.

Utility Software --> tools that help maintain, optimize, or protect the system. Examples include antivirus programs, disk cleanup tools, and file managers.

Firmware --> low-level software permanently embedded in hardware (e.g., BIOS/UEFI in a motherboard), responsible for booting the system.

Language Translators --> compilers, interpreters, and assemblers that convert programming code into machine-readable instructions.

APPLICATION SOFTWARE :

Application software (also called apps or programs) is software designed to help users perform specific tasks. It runs on top of system software (the OS) and directly interacts with the user.

Types of Application Software

Word Processing Software
Used to create and edit documents.
Examples: Microsoft Word, Google Docs, LibreOffice Writer
Presentation Software
Used to create slideshows and visual presentations.
Examples: Microsoft PowerPoint, Google Slides, Canva
Database Software
Used to store, manage, and retrieve data.
Examples: MySQL, Microsoft Access, Oracle
Web Browsers
Used to access and browse the internet.
Examples: Google Chrome, Firefox, Safari
Communication Software
Used for messaging, email, and video calls.
Examples: Gmail, WhatsApp, Zoom, Microsoft Teams

About Me

SILAMBARASAN A — Thu, 09 Apr 2026 17:58:57 +0000

myself silambarasan, from guindy, and my native is thiruvannamalai,
I have completed my BSC computer science at kgc chennai in 2025.

I am a quick learner and highly interested in learning new technologies, especially in programming. I have knowledge in HTML, CSS, JavaScript, and React.

I have worked on small projects using React, such as a portfolio website, a quiz application, and a simple e-commerce application. These projects helped me improve my front-end development and problem-solving skills.

I am currently working every day to improve my technical skills, and my goal is to start my career as a software developer where I can apply my knowledge and grow professionally.

What is ASCII Code?

SILAMBARASAN A — Thu, 09 Apr 2026 03:42:00 +0000

ASCII means American Standard Code for Information Interchange.

It is a system that changes letters, numbers, and symbols into numbers, so computers can understand them.

Examples:

A → 65
a → 97
0 → 48
@ → 64

Computers cannot understand text directly
They understand only numbers

So, ASCII helps convert characters into numbers.

Why was ASCII introduced?

Before ASCII, each computer had its own way of storing characters

This created problems when sharing data between computers.

Problems before ASCII:

Different systems used different codes
Same character had different meanings
Data sharing was difficult

Solution: ASCII

ASCII was introduced to:

Standardize characters
- Same number for same character everywhere
Make data sharing easy
- Files can be opened in different systems
Improve communication
- Helpful in early internet and networking

ASCII range = 0 to 127

0–31 → Control characters
32–126 → Printable characters
127 → Delete

Printable Characters (32–126)

These are visible characters:

32 → Space
48–57 → Numbers (0–9)
65–90 → Uppercase letters (A–Z)
97–122 → Lowercase letters (a–z)
Others → Symbols (!, @, #, etc.)

ASCII PROGRAM :

name="silambu9391a@gmail.com"
index=0
while (index < name.length) {
    console.log(name[index]+ " = " + name.charCodeAt(index));
    index+=1
}

OUTPUT :

Method Overloading in Java

SILAMBARASAN A — Wed, 08 Apr 2026 19:04:08 +0000

Introduction

In Java, method overloading is a concept where you can define multiple methods with the same name but different parameters in the same class.

It is one of the important features of compile-time polymorphism.

Method overloading means creating multiple methods with the same name but different parameter lists and diffrent data type.

Why Do We Need Method Overloading?

Imagine you want to perform the same operation (like addition) with different inputs:

Add 2 numbers
Add 3 numbers
Add decimal numbers

Instead of using different method names, we can use one method name.

class Calculator {

    // Method 1
    int add(int a, int b) {
        return a + b;
    }

    // Method 2
    int add(int a, int b, int c) {
        return a + b + c;
    }

    // Method 3
    double add(double a, double b) {
        return a + b;
    }
}

public class Main {
    public static void main(String[] args) {
        Calculator obj = new Calculator();

        System.out.println(obj.add(10, 20));        // 30
        System.out.println(obj.add(10, 20, 30));    // 60
        System.out.println(obj.add(5.5, 2.5));      // 8.0
    }
}

How Java Decides Which Method to Call

Java checks based on:

Number of parameters
Type of parameters
Order of parameters

This happens at compile time.

Rules of Method Overloading

✔ Method name must be same
✔ Parameters must be different (type / number / order)

Return type alone is NOT enough

int add(int a, int b)
double add(int a, int b) // Not allowed

Real-Life Example

Think like a remote control

Same button → "Volume"
But action changes:
- Press once → increase little
- Hold → increase continuously

Same name, different behavior = Overloading

What is a Constructor ?

SILAMBARASAN A — Wed, 08 Apr 2026 18:15:30 +0000

Introduction

In JavaScript, a constructor is a special function or method used to create and initialize objects. Whenever you want to create multiple objects with similar structure, constructors help you do it easily and efficiently.

Why Do We Need Constructors?

Without constructors, you would have to manually create objects like this:

let student1 = { name: "Silambu", age: 21 };
let student2 = { name: "sanjay", age: 22 };

This becomes repetitive and messy when creating many objects.

Constructors solve this problem by providing a template (blueprint).

Constructor Using Class (Modern Way)

class Student {
    constructor(name, age) {
        this.name = name;
        this.age = age;
    }
}

let s1 = new Student("Silambu", 21);
console.log(s1);

Output:

{ name: "Silambu", age: 21 }

How It Works Internally

When you write:

let s1 = new Student("Silambu", 21);

JavaScript does the following steps:

Creates an empty object { }
Sets this to point to that object
Calls the constructor function
Assigns values (name, age)
Returns the object

Concepts

constructor()

Special method inside a class
Runs automatically when object is created

this

Refers to the current object
Used to assign values

new keyword

Creates object
Calls constructor

Constructor Function (Old Way)

Before ES6, constructors were written like this:

function Student(name, age) { 
    this.name = name; 
    this.age = age; 
} 

let s1 = new Student("Silambu", 21);

This still works, but modern JS prefers class syntax.