DEV Community: Divya Divya

Java Constructor Program

Divya Divya — Sun, 19 Apr 2026 18:49:20 +0000

Product Program

class Dmart{ 

String productname;
int proprice;
boolean prodiscount;
int prodiscountpercentage;
int discountprice;
int finalprice;


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

this.productname=name;
this.proprice=price;
this.prodiscount=discount;
this.prodiscountpercentage=discountpercentage;
}


public static void main(String[] args){

Dmart product1=new Dmart("Mobile" , 70000 ,true , 8);
Dmart product2=new Dmart("Watch" , 300 , true , 5);
Dmart product3=new Dmart("Choclate" , 450 , true , 2);
Dmart product4=new Dmart("Biscut"  ,  30 , true , 7);
Dmart product5=new Dmart("HotChips" , 25 , true ,12);

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

}
public void buy(){

this.discountprice = (this.proprice * this.prodiscountpercentage) / 100;
this.finalprice=this.proprice-this.discountprice;

System.out.println("productname => "+ this.productname);
System.out.println("proprice => " + this.proprice);
System.out.println("prodiscount => "  + this. prodiscount);
System.out.println("prodiscountpercentage => " + this.prodiscountpercentage);
System.out.println("discountprice => " + this.discountprice);
System.out.println("finalprice => " + this.finalprice);

}

}

Output:

Mobile Number , G-mail , Pin Code Validation

Divya Divya — Sat, 18 Apr 2026 03:35:09 +0000

Mobile Number Validation

def verify(mobnum):
    index=0
    while index<len(mobnum):
        if mobnum[index]>="0" and mobnum[index]<="9":
            index+=1
            continue;
        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 : ")));

Output:

Gmail Validation

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 False
        return True
    else:
        return False

if verify_Gmail(input("Enter Your Gmail :")):
    print("valid")
else:
    print("invalid")

Output:

Pin code Validation

const tamilNaduPincode = {
            region: {
                6: "Tamil Nadu & Kerala"
            },

            subRegion: {
                60: "Chennai Region",
                61: "Northern Tamil Nadu Region",
                62: "Southern Tamil Nadu Region",
                63: "Central Tamil Nadu Region",
                64: "Western Tamil Nadu Region"
            },

            district: {
                600: "Chennai",
                601: "Tiruvallur",
                602: "Kanchipuram",
                603: "Chengalpattu",
                604: "Villupuram",
                605: "Cuddalore",
                606: "Tiruvannamalai",
                607: "Cuddalore (Rural)",
                608: "Nagapattinam",
                609: "Mayiladuthurai",

                610: "Tiruvarur",
                611: "Nagapattinam",
                612: "Thanjavur",
                613: "Thanjavur",
                614: "Thiruvarur",
                615: "Ariyalur",
                616: "Perambalur",
                617: "Karur",
                618: "Karur",
                619: "Nagapattinam",

                620: "Tiruchirappalli",
                621: "Perambalur",
                622: "Pudukkottai",
                623: "Ramanathapuram",
                624: "Dindigul",
                625: "Madurai",
                626: "Virudhunagar",
                627: "Tirunelveli",
                628: "Thoothukudi",
                629: "Kanyakumari",

                630: "Sivagangai",
                631: "Kanchipuram",
                632: "Vellore",
                633: "Vellore",
                634: "Krishnagiri",
                635: "Dharmapuri",
                636: "Salem",
                637: "Namakkal",
                638: "Erode",
                639: "Karur",

                640: "Coimbatore",
                641: "Coimbatore",
                642: "Coimbatore (Pollachi)",
                643: "Nilgiris"
            }
        };
        function getPincodeDetails(pincode) {
            let firstDigit = Math.floor(pincode / 100000);
            let firstTwo = Math.floor(pincode / 10000);
            let firstThree = Math.floor(pincode / 1000);

            console.log("Region: ", tamilNaduPincode.region[firstDigit]);
            console.log("Sub-region: ", tamilNaduPincode.subRegion[firstTwo]);
            console.log("District:", tamilNaduPincode.district[firstThree]);
        }

        getPincodeDetails(606902);

Output:

To be discussed...

Constructor in Java

Divya Divya — Sat, 18 Apr 2026 03:03:13 +0000

What is Constructor:

Constructor is a Special method in Java.
When object is create , it's automatically called.
Constructor it helps to object set the initial value.
Giving an initial value to a variable when it is created.

Default Constructor:

Default Constructor is no arguments in the constructor.
You don't define the constructor , Java is given the default constructor.
If you do NOT write any constructor → the compiler will automatically create a default (no-argument) constructor.
Purpose of constructor provides default values (0,null).

Example:

 class Person{
     String name;
     int age;

public static void main(String[] args){
    Person s1=new Person();

System.out.println(s1.name);
System.out.println(s1.age);
}
 }

Output:

Parameterized Constructor

A parameterized constructor is a special method in Java.
It is used to set values when an object is created.
Unlike a default constructor (which gives common values like 0 or null).
a parameterized constructor lets you pass your own values.
You can give values while creating the object.
It sets those values to the object’s variables (fields)

Output

 class Person{
     String name;
     int age;



public Person(String a , int b){
    name=a;
    age=b;
}

public static void main(String[] args){
    Person s1=new Person("Divya" , 21);

System.out.println(s1.name);
System.out.println(s1.age);
}
 }

Output

No-Arguments Constructor

This Constructor created by programmer
It has a no parameters
It helps to some specific code run , at the time of object creation
It is used to set a common values and message print.
Purpose of Zero argument constructor , assigns custom starting values.

Example

public class Person {

    public Person() {
        System.out.println("No-argument");
    }

    public static void main(String[] args) {
        Person s1 = new Person();
    }
}

Output

Test Case

Divya Divya — Thu, 16 Apr 2026 03:32:12 +0000

What is TestCase?

A Test Case is a step-by-step guide used to check if a specific part of a software application works correctly as expected.
It defines the actions to be taken, the required data, and the expected result to validate that a feature functions as per the requirements.

Why TestCase is Important?
Test cases are crucial for ensuring software quality by defining specific steps, inputs, and expected outcomes to validate functionality, verify requirements, and catch bugs early.

Reason:

Validate Requirements and Functionality.
Early Defect Identification.
Consistency and Repeatability.
Regression Testing & Risk Management.
Documentation and Knowledge Transfer.
Foundation for Automation.

Components of a Test Case:

A standard test case includes:

Test Case ID
Test Scenario / Name
Test Case
Preconditions
Test Steps
Expected Result
Status (Pass/Fail)

TestCase Format:

What is URL?

Divya Divya — Sun, 12 Apr 2026 02:54:39 +0000

URL(Uniform Resource Location):

URL is full address used to find something on the internet, like a webpage or file.
It tells your browser where to go and how to get the data.

Part of URL:

Protocol: (http , https) => How to access the resource. It tells how to fetch data.

Data Fetch means:Getting data from a server or API and using it.

Explain:
When you open a website (like Instagram or YouTube), the data shown on your screen (posts, videos, users) is not stored locally. It is stored on a server. We fetch that data from the server and bring it to the browser. This process is called fetching.

Domain: tells which website.

Explain:
A computer actually has an IP address (like 142.250.190.78), but it is difficult to remember. So, for easy to use, we use a domain name instead of the IP address.”

Example: YouTube.com ,Google.com , amazon.in.

Path: Tells which page.

Explain:

https://example.com/about
example.com → website
/about → path
Go to the About page.

Why good URLs important:

Easy to understand
Easy to Share
Helps search engines understand your site.

SEO (Search Engine Optimization)means: Make your website for search engine to find , understand , and recomend to user

So, a clean and clear URL makes ypur website better.

URL Structure

A URL (Uniform Resource Locator) consists of several parts that pinpoint a specific web resource's location.

https:// Scheme:
Defines the protocol used to access the resource.

www. Subdomain:
Specifies a subdivision of the main domain .

example. Domain:
Identifies the main website name.

com Top-Level Domain:
Indicates the domain extension.

:443 Port Number:
Specifies the server port.

/blog/article/search Path:
Points to the resource location on the server.

? Query:
The ? symbol that starts query parameters.

docid=720&hl=enParameters:
Passes data as key-value pairs using &.

#dayone Fragment:
Refers to a specific section within the resource using #.

Self-Introduction

Divya Divya — Thu, 09 Apr 2026 18:18:41 +0000

I'm Divya. I am from Velachery.

I have completed my Bachelor of Computer Applications (BCA) from Sri Saradha College for Women’s, Perambalur.

I am passionate about learning new technologies and continuously improving my skills. I have knowledge of HTML, CSS, and JavaScript, and I can build interactive and user-friendly websites.

I have worked on small projects such as a YouTube clone, a Google homepage clone, and a login page using HTML, CSS, and JavaScript. These projects helped me strengthen my front-end development skills.

I am looking for an opportunity where I can start my career, enhance my skills, and contribute to the organization.

Thank you for this opportunity.

Self-Introduction

Divya Divya — Thu, 09 Apr 2026 18:06:42 +0000

I'm Divya , I'm From Velachery,I have completed my degree BCA (Computer Applications) at Sri Saradha College for Women's in Perambalur.

I'm Passionate about learning new technologies and improving my skills.I have knowledge of HTML , CSS and JavaScript , and I can build interactive websites.

I have done small projcets like a Youtube clone , Google homepage clone and a login page using HTML , CSS and JavaScript.

I'm looking for this opportunity will help me build my career and enhance my skills. Thank you for giving me this opportunity.

ASCII

Divya Divya — Thu, 09 Apr 2026 11:16:18 +0000

ASCII (American Standard Code for Information Interchange) is one of the earliest character encoding systems. It assigns numeric values to characters so computers can process text.

Example:
A → 65
a → 97
0 → 48

Why is ASCII Used?

ASCII is used for:

Representing basic English characters
Simple text processing
Early computer systems

Limitations of ASCII:

Supports only 128 characters
Cannot represent other languages like Tamil, Hindi, or Chinese

What is Unicode?

Unicode is a modern character encoding system that supports characters from all languages.

Example:

A → U+0041
₹ → U+20B9
அ → U+0B85

Why is Unicode Used?

Unicode is used for:

Supporting multiple languages
Handling global applications and websites
Representing symbols and emojis

Why Do We Need Both?

ASCII is simple and efficient for basic English text. Unicode is necessary for modern applications that require multiple languages and symbols.
In fact, Unicode includes ASCII as a subset, meaning all ASCII characters are also part of Unicode.

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

Output

What is ASCII?

Divya Divya — Thu, 09 Apr 2026 03:29:11 +0000

ASCII (American Standard Code for Information Interchange) is one of the earliest character encoding systems. It assigns numeric values to characters so computers can process text.

Example:
A → 65
a → 97
0 → 48

Why is ASCII Used?

ASCII is used for:

Representing basic English characters
Simple text processing
Early computer systems

Limitations of ASCII:

Supports only 128 characters
Cannot represent other languages like Tamil, Hindi, or Chinese

What is Unicode?

Unicode is a modern character encoding system that supports characters from all languages.

Example:

A → U+0041
₹ → U+20B9
அ → U+0B85

Why is Unicode Used?

Unicode is used for:

Supporting multiple languages
Handling global applications and websites
Representing symbols and emojis

Why Do We Need Both?

ASCII is simple and efficient for basic English text.
Unicode is necessary for modern applications that require multiple languages and symbols.
In fact, Unicode includes ASCII as a subset, meaning all ASCII characters are also part of Unicode.

ASCII Program

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

Output

What is Constructor?

Divya Divya — Wed, 08 Apr 2026 18:05:14 +0000

Constructor

A constructor is a special function/method used to initialize an object when it is created.

Function Constructor
A function constructor is a normal function used with the newkeyword to create and initialize objects.

Example

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

const s1 = new Student("Divya", 20);
const s2 = new Student("Aruna", 22);

console.log(s1.name); // Divya
console.log(s2.age);  // 22

Keywords Points

Function name usually starts with a capital letter
new keyword is mandatory
this refers to the new object

How it Works

const user = new Person("Divya", 22);

Creates an empty object {}
Sets this to that object
Assigns values (this.name, this.age)
Returns the object

Constructor in Class

A constructor is a method inside a class that:

Runs automatically when an object is created
Is used to set initial values (properties)

Example

class Person {
  constructor(name, age) {
    this.name = name;   // assign value
    this.age = age;
  }
}

const p1 = new Person("Divya", 22);

console.log(p1.name); // Divya
console.log(p1.age);  // 22

How it works (Step-by-step)

new Person("Divya", 22) is called
A new empty object is created
constructor() runs automatically
this.name = "Divya"
this.age = 22
Object is returned

Method in Java

Divya Divya — Wed, 08 Apr 2026 15:29:55 +0000

A method is a block of code designed to perform a specific task. Methods are executed only when they are called, making programs more structured, reusable, and easier to maintain.

What is a Method?

A method is similar to a function in other programming languages. It groups a set of statements together to perform an operation.

class Test {

    static void greet() {
        System.out.println("Hello, Java!");
    }

    public static void main(String[] args) {
        greet();  // method call
    }
}

Execution Flow

The program starts from the main() method
greet() method is called
The message is printed

Method Overloading

Method Overloading is a feature in Java where multiple methods share the same name but differ in their parameters. It is an example of compile-time polymorphism.

Method overloading means:

Same method name
Different parameter list (type, number, or order)

Different Number of Parameters

class Test {

    static int add(int a, int b) {
        return a + b;
    }

    static int add(int a, int b, int c) {
        return a + b + c;
    }

    public static void main(String[] args) {
        System.out.println(add(2, 3));      // 2 params
        System.out.println(add(2, 3, 4));   // 3 params
    }
}

Different Data Types

class Test {

    static int add(int a, int b) {
        return a + b;
    }

    static double add(double a, double b) {
        return a + b;
    }

    public static void main(String[] args) {
        System.out.println(add(5, 10));        // int
        System.out.println(add(5.5, 2.5));     // double
    }
}

Different Order of Parameters

class Test {

    static void display(int a, String b) {
        System.out.println(a + " " + b);
    }

    static void display(String b, int a) {
        System.out.println(b + " " + a);
    }
}

Important Rules

✔ Must Change Parameter List
Overloading works only if parameters differ in:

Number
Data type
Order

Same name + same parameters + different return → ERROR

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

//  Error (same parameters)
double add(int a, int b) { return a + b; }

Why Use Method Overloading?

Improves code readability
Reduces method name complexity
Reuse same method name for similar operations

Example

System.out.println(10);
System.out.println("Hello");
System.out.println(3.14);

println() is overloaded to handle different data types.

At compile time, Java decides:

Which method to call based on arguments
This is called compile-time polymorphism

Summary

Same method name
Different parameters
Compile-time decision
Improves flexibility and readability

Return types in Java

Divya Divya — Wed, 08 Apr 2026 05:38:34 +0000

In Java, every method must specify a return type, which defines the type of value the method will return after execution. Understanding return types is essential for writing correct and efficient programs.

Method with Return Type

Example

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

Explanation

int → return type
Method returns the sum of a and b
Returned value must be an integer

Void Return Type

Sometimes, a method performs an action but does not return any value. In such cases, we use void.

Example

void displayMessage() 
{ 
System.out.println("Welcome to Java");
 }

Key Point

No value is returned
return statement is optional

Common Return Types in Java

In Java, every method must specify a return type, which defines the type of value the method sends back after execution. Understanding return types is essential for writing clear and functional programs.

class Test 
{
    static int square(int x) {
       return x * x; 
    } 
    public static void main(String[] args) { 
       int result = square(4); 
       System.out.println(result);
    }
 }

Step-by-Step Flow

square(4) is called
x * x = 16
Method returns 16
Value stored in result
Output: 16

Multiple Return Statements

A method can have multiple return statements based on conditions.

Example

boolean isEven(int n) {
     if (n % 2 == 0) 
         return true; 
     else 
         return false; 
}

Important Rules

A method must return a value if the return type is not void
The returned value must match the declared return type
return statement ends the method execution immediately
You cannot return multiple values directly (use arrays or objects instead)