DEV Community: Keerthiga P

Debugging

Keerthiga P — Mon, 30 Mar 2026 18:23:08 +0000

1. What is Debugging?

Debugging is the process of finding and fixing errors (bugs) in a program.

Bugs can be:

Syntax errors (code cannot run)
Logical errors (wrong output)
Runtime errors (program crashes while running)

2. Why Do We Use Debugging?

Debugging is important because:

✅ Helps find the cause of errors
✅ Makes programs run correctly
✅ Helps understand program flow
✅ Saves time instead of guessing what went wrong

3. How to Use Debugging?

There are several ways to debug:

a) Print Statements

Check variables and program flow using print() (optional for small programs).

b) Using Debugger in IDE

Most IDEs (VS Code, PyCharm, Eclipse) have built-in debuggers:

Set Breakpoints → pause execution at a line
Step Into / Step Over → go line by line
Watch Variables → check values while running
Call Stack → see which function called which

c) Dry Run (Manual)

Go line by line on paper with sample input to trace program flow.

4. Example: Debugging a Factorial Function in Python
Code with Error:

def factorial(n):
    return n * factorial(n - 1)  # Missing base case
print(factorial(5))

Problem: Infinite recursion → program crashes.

Fix by Adding Base Case:

def factorial(n):
    if n == 0:        # Base case added
        return 1
    return n * factorial(n - 1)
print(factorial(5))

Output:

Explanation:

Base case stops recursion at n = 0
Recursive call now reduces n each time
Program works correctly without crashing

Features of java

Keerthiga P — Mon, 30 Mar 2026 18:09:14 +0000

Features of Java

Java is one of the most popular programming languages in the world. It is widely used for web applications, mobile apps, and enterprise software because of its powerful and flexible features.

1. Simple Syntax

Java is easy to learn and understand.

Clean and readable syntax
No pointers (unlike C/C++)
Beginner-friendly

👉 Example:

class Main {
public static void main(String[] args) {
System.out.println("Hello Java!");
}
}

👉 Execution starts from the main() method.

2. Object-Oriented Programming (OOP)

Java follows OOP concepts:

Class
Object
Inheritance
Encapsulation
Abstraction
Polymorphism

👉 This helps in writing reusable and organized code.

3.Platform Independent

Java follows:

👉 Write Once, Run Anywhere

Code → Compiled → Bytecode
Bytecode runs on JVM

👉 Works on any OS (Windows, Linux, Mac)

4. Interpreted + Compiled

Java is both:

Compiled (to bytecode)
Interpreted (by JVM)

👉 Makes Java flexible and portable.

5. Scalable

Java supports:

Small applications
Large enterprise systems

👉 Used in banking, e-commerce, and large platforms.

6. Portable

Java programs can run on any system with JVM.

👉 No need to rewrite code for different platforms.

7. Secure & Robust

No pointers → safer
Exception handling
Strong memory checking

👉 Reduces crashes and errors.

8.Automatic Memory Management

Java handles memory automatically.

Heap → Objects
Stack → Methods
Garbage Collector → Removes unused objects

👉 Developer doesn’t need to manage memory manually.

9.High Performance

Uses JIT (Just-In-Time Compiler)
Faster than many interpreted languages

👉 Slightly slower than C++, but still powerful.

10.Multithreading

Java allows multiple tasks at the same time.

👉 Improves performance in:

Games
Real-time apps
Web servers

11.Rich Standard Library

Java provides built-in libraries for:

File handling
Networking
Database (JDBC)
Security 👉 Saves development time.

12.Functional Programming Features

Introduced in Java 8.

Lambda expressions
Stream API
Functional interfaces

👉 Makes code shorter and cleaner.

13.Integration with Other Technologies

Java works with:

C/C++ (JNI)
Databases (JDBC)
Web services (REST, SOAP)
Frameworks (Spring, Spring Boot)

14.Support for Web & Mobile

👉 Web:

JSP, Servlets
Spring Boot

👉 Mobile:

Android apps (Java-based)

15.Documentation & Community Support

Strong official documentation
Huge developer community
Many tutorials and forums 👉 Easy to learn and solve problems.

Debugging in Java

Keerthiga P — Mon, 30 Mar 2026 03:26:05 +0000

❌ Error 1: Semicolon after Class

public class Home;
{
    public static void main(String[] args) {
        System.out.println("Hello World");
    }
}

❌ Error 2: Wrong { Position

public class Home;
{
    public static void main(String[] args) {
        System.out.println("Hello World");
    }
}

❌ Error 3: string instead of String

public class Home {
    public static void main(string[] args) {
        System.out.println("Hello World");
    }
}

❌ Error 4: Wrong Array Syntax

public class Home {
    public static void main(String() args) {
        System.out.println("Hello World");
    }
}

❌ Error 5: Semicolon after main

public class Home {
    public static void main(String[] args);
    {
        System.out.println("Hello World");
    }
}

❌ Error 6: System.Out

public class Home {
    public static void main(String[] args) {
        System.Out.println("Hello World");
    }
}

❌ Error 7: PrintLn

public class Home {
    public static void main(String[] args) {
        System.out.PrintLn("Hello World");
    }
}

❌ Error 8: Missing Quotes

public class Home {
    public static void main(String[] args) {
        System.out.println("Hello World);
    }
}

❌ Error 9: Missing Semicolon

public class Home {
    public static void main(String[] args) {
        System.out.println("Hello World")
    }
}

❌ Error 10: Missing }

public class Home {
    public static void main(String[] args) {
        System.out.println("Hello World");
}

Recursion

Keerthiga P — Mon, 30 Mar 2026 02:38:02 +0000

What is Recursion?

Recursion means a function calls itself to solve a problem.

Every recursive function has two main parts:

Base Case → stops the function
Recursive Call → calls the function again

1) 1 1 1 1 1

Flowchart

Python

def display(num):
    if num <= 5:
        print(1, end=" ")
        display(num + 1)
display(1)

Output:

JavaScript

function display(num) {
    if (num <= 5) {
        console.log("1 ");
        display(num + 1);
    }
}
display(1);

Java

public class Main {
    public static void main(String[] args) {
        display(1);
    }
    public static void display(int num) {
        if (num <= 5) {
            System.out.print(1 + " ");
            display(num + 1);
        }
    }   
}

2. 1 2 3 4 5

Flowchart

Python

def display(num):
    if num <= 5:
        print(num, end=" ")   
        display(num + 1)
display(1)

Output

JavaScript

function display(num) {
    if (num <= 5) {
        console.log(num + " "); 
        display(num + 1);
    }
}
display(1);

Java

public class Main {
    public static void main(String[] args) {
        display(1);
    }
    public static void display(int num) {
        if (num <= 5) {
            System.out.print(num + " ");  
            display(num + 1);
        }
    }
}

3) 1 3 5 7 9

Flowchart

Python

def display(num):
    if num <= 9:
        print(num, end=" ")
        display(num + 2)   
display(1)

Output

JavaScript

function display(num) {
    if (num <= 9) {
        console.log(num + " ");
        display(num + 2);   
    }
}
display(1);

Java

public class Main {
    public static void main(String[] args) {
        display(1);
    }

    public static void display(int num) {
        if (num <= 9) {
            System.out.print(num + " ");
            display(num + 2);   
        }
    }
}

4. 5 10 15 20 25

Flowchart

Python

def display(num):
    if num <= 25:
        print(num, end=" ")
        display(num + 5)   
display(5)

Output

JavaScript

function display(num) {
    if (num <= 25) {
        process.stdout.write(num + " ");
        display(num + 5);   
    }
}
display(5);

Java

public class Main {
    public static void main(String[] args) {
        display(5);
    }
    public static void display(int num) {
        if (num <= 25) {
            System.out.print(num + " ");
            display(num + 5);   
        }
    }
}

5. Factorial

Python

def factorial(n):
    if n == 1:
        return 1
    return n * factorial(n - 1)
print(factorial(5))

Output

JavaScript

function factorial(n) {
    if (n === 1) {
        return 1;
    }
    return n * factorial(n - 1);
}
console.log(factorial(5));

Java

public class Main {
    public static void main(String[] args) {
        System.out.println(factorial(5));
    }
    public static int factorial(int n) {
        if (n == 1)
            return 1;
        return n * factorial(n - 1);
    }
}

6. Sum of first n numbers

Python

def sum_n(n):
    if n == 1:
        return 1
    return n + sum_n(n - 1)
print(sum_n(5))

Output

JavaScript

function sum(n) {
    if (n === 1) {
        return 1;
    }
    return n + sum(n - 1);
}
console.log(sum(5));

Java

public class Main {
    public static void main(String[] args) {
        System.out.println(sum(5));
    }
    public static int sum(int n) {
        if (n == 1)
            return 1;
        return n + sum(n - 1);
    }
}

History of Java,Architecture of Java and Java Server Provider Companies

Keerthiga P — Fri, 27 Mar 2026 17:34:42 +0000

1.The History of Java:

🌱 Beginning

Java was created in 1991 by James Gosling at Sun Microsystems.

Originally, it was called Oak and was designed for small devices.

🔄 Name Change

In 1995, Oak was renamed to Java.
At the same time, the internet was growing, and Java became perfect for web development.

🌐 Why Java Became Popular?

Java introduced the idea:

👉 “Write Once, Run Anywhere”

This means Java code can run on any system using JVM (Java Virtual Machine).

🏢 Big Change

In 2010, Oracle Corporation bought Sun Microsystems and took control of Java.

🚀Today, Java is used in:

Web development
Android apps
Enterprise applications

2.Architecture of Java:
_
🧱 What is Java Architecture?_

Java architecture is the process that explains how a Java program is compiled and executed. It is designed to follow the concept:

👉 “Write Once, Run Anywhere”

This means Java code can run on any system without changing the program.

🔄 How Java Works?

The working process of Java is simple:

You write code in a .java file
The compiler (javac) converts it into bytecode (.class)
The JVM (Java Virtual Machine) runs the bytecode
Output is generated

⚙️ Main Components of Java Architecture

🔹 JDK (Java Development Kit)

JDK is used by developers to write and compile Java programs. It includes tools like the compiler.

🔹 JRE (Java Runtime Environment)

JRE provides the environment to run Java programs. It includes JVM and necessary libraries.

🔹 JVM (Java Virtual Machine)

JVM is the heart of Java. It converts bytecode into machine code and executes it.

🧩 Inside JVM

JVM has important parts:

Class Loader – Loads the class files
Memory Area – Stores data (Heap, Stack)
Execution Engine – Runs the program
Garbage Collector – Removes unused memory

✨ Why Java Architecture is Important?

Platform independent
Secure and reliable
Automatic memory management
Better performance using JIT

3.Java Server Provider Companies:

🌍 Cloud & Hosting Providers

🔹 Hostinger

 Hostinger is a popular hosting provider. It offers VPS hosting that supports Java applications like JSP and Servlets. It is beginner-friendly and affordable.

🔹 Jelastic

Jelastic is a cloud platform specially designed for Java developers. It supports modern technologies like Docker and Kubernetes.

🔹 RackBank

RackBank is an Indian hosting provider. It offers reliable Java hosting with good support and performance.

🔹 Javapipe

Javapipe provides dedicated Java hosting. It supports frameworks like Spring and Hibernate.

🖥️ Java Application Servers

🔹 Apache Tomcat

Apache Tomcat is the most widely used Java server. It is mainly used to run web applications.

🔹 JBoss (WildFly)

JBoss is an enterprise-level server used for large-scale applications.

🔹 GlassFish

GlassFish is a Java EE server used for developing and testing applications.

🧠 Why Do You Need a Java Server?

To run Java web applications
To host websites and APIs
To manage backend services

Sum of Numbers,Factorial,LCM

Keerthiga P — Fri, 27 Mar 2026 12:54:28 +0000

1.Sum of n numbers:

FlowChart:

JavaScript:

let sum = 0;
let num = 1;
while (num <= 10) {
    sum = sum + num;
    num = num + 1;
}
console.log("Sum =", sum);

Output:

Java:

public class Main {
    public static void main(String[] args) {
        int sum = 0;
        int num = 1;
        while (num <= 10) {
            sum = sum + num;
            num = num + 1;
        }
        System.out.println("Sum = " + sum);
    }
}

Python:

sum = 0
num = 1
while num <= 10:
    sum = sum + num
    num = num + 1
print("Sum =", sum)

2.Factorial of n Numbers:

FlowChart:

Javascript:

let fac = 1;
let no = 1;
while (no <= 10) {
    fac = fac * no;
    no = no + 1;
}
console.log("Factorial =", fac);

Output:

Java:

public class Main {
    public static void main(String[] args) {
        int fac = 1;
        int no = 1;
        while (no <= 10) {
            fac = fac * no;
            no = no + 1;
        }
        System.out.println("Factorial = " + fac);
    }
}

Python:

fac = 1
no = 1
while no <= 5:
    fac = fac * no
    no = no + 1
print("Factorial =", fac)

3.LCM(Least Common Multiple):

Flowchart:

Javascript:

let no1 = 3;
let no2 = 10;
let big = no1 > no2 ? no1 : no2;
let big2 = big;
while (true) {
    if (big % no1 === 0 && big % no2 === 0) {
        console.log("LCM =", big);
        break;
    }
    big += big2;
}

Output:

Java:

public class LCMExample {
    public static void main(String[] args) {
        int no1 = 3;
        int no2 = 10;
        int big = (no1 > no2) ? no1 : no2;
        int big2 = big;

        while (true) {
            if (big % no1 == 0 && big % no2 == 0) {
                System.out.println("LCM = " + big);
                break;
            }
            big += big2;
        }
    }
}

Python:

no1 = 3
no2 = 10
big = no1 if no1 > no2 else no2
big2 = big
while True:
    if big % no1 == 0 and big % no2 == 0:
        print("LCM =", big)
        break
    big += big2

Ternary Operator,Prime Number,GCD

Keerthiga P — Thu, 26 Mar 2026 12:53:02 +0000

Ternary Operator for 3 numbers :

Java:

class Main {
    public static void main(String[] args) {
        int a = 10, b = 5, c = 8;

        int smallest = (a < b) 
                        ? (a < c ? a : c) 
                        : (b < c ? b : c);

        System.out.println(smallest);
    }
}

Output:

Javascript:

let a = 10, b = 55, c = 80;
let smallest = (a < b) 
                ? (a < c ? a : c) 
                : (b < c ? b : c);

console.log(smallest);

Output:

Python:

a = 100
b = 53
c = 18
smallest = a if (a < b and a < c) else (b if b < c else c)
print(smallest)

Output:

Range of prime numbers :

FlowChart:

Python:

no1 = 10
while no1 <= 50:
    div = 2
    flag = True
    while div <= no1 // 2:
        if no1 % div == 0:
            flag = False
            break
        div = div + 1
    if flag:
        print(no1, "is prime")
    no1 = no1 + 1

Output:

JavaScript:

let no1 = 10;
while (no1 <= 50) {
    let div = 2;
    let flag = true;
    while (div * div <= no1) {
        if (no1 % div === 0) {
            flag = false;
            break;
        }
        div++;
    }
    if (flag && no1 > 1) {
        console.log(no1 + " is prime");
    } 
    no1++;
}

Output:

Java:

public class PrimeCheck {
    public static void main(String[] args) {
        int no1 = 10;
        while (no1 <= 50) {
            int div = 2;
            boolean flag = true;
            while (div * div <= no1) {
                if (no1 % div == 0) {
                    flag = false;
                    break;
                }
                div++;
            }
            if (flag && no1 > 1) {
                System.out.println(no1 + " is prime");
            } 
            no1++;
        }
    }
}

Output:

Find the Greatest of Common Divisor:

FlowChart:

python:

a = 10
b = 5
c = 8
small = a if a < b and a < c else (b if b < c else c)
print("Smallest =", small)

Output:

Javascript:

let a = 10;
let b = 5;
let c = 8;
let small = (a < b && a < c) ? a : (b < c ? b : c);
console.log("Smallest =", small);

Java:

public class Smallest {
public static void main(String[] args) {
    int a = 10;
    int b = 5;
    int c = 8;
    int small = (a < b && a < c) ? a : (b < c ? b : c);
    System.out.println("Smallest = " + small);
}
}

Divisor and Prime Number Programs

Keerthiga P — Wed, 25 Mar 2026 17:40:32 +0000

1.Prime Number
A Prime Number is a number that has only two factors 1 and itself.
Flow Chart:

Python:

JavaScript:

Java:

2.Divisor:
A Divisor is a number that divides another number exactly (remainder = 0).

Example:
20 → divisors are:
1, 2, 4, 5, 10, 20

Flow Chart:

JavaScript:

Python:

Java:

3.Count Divisor:

Count how many numbers divide the given number exactly.

Example:
20 → divisors: 1, 2, 4, 5, 10, 20
Count = 6

Flow Chart:

JavaScript:

Python:

Java:

Why react is single page application?

Keerthiga P — Wed, 25 Mar 2026 06:19:42 +0000

React applications are inherently structured as Single Page Applications (SPAs) because
they load a single HTML page and then dynamically update the content using JavaScript, without requiring full page reloads. This provides a faster, smoother, and more app-like user experience compared to traditional multi-page applications (MPAs).

REACT

Keerthiga P — Wed, 25 Mar 2026 06:13:21 +0000

What is React?
React is a JavaScript library used to build user interfaces (UI) — mainly single-page web applications.
It is used to create fast, interactive, and reusable UI components.

Why we use React?
React is a popular JavaScript library used to build fast, dynamic, and interactive user interfaces for web and mobile apps, primarily through its component-based architecture and Virtual DOM.

1️⃣ Component-Based
React splits the UI into small reusable parts called components.
1.Example: Header, Button, Login Form
2.Write once → use many times
3.Code neat & easy

2️⃣ Faster Performance (Virtual DOM)
React uses a Virtual DOM.
1.Page full-aa reload aagathu
2.Change aana part mattum update aagum
3.So app fast-aa work aagum

3️⃣ Single Page Application (SPA)
React apps are SPA.
1.Page refresh illa
2.Smooth navigation
3.Mobile app maari feel

4️⃣ Easy to Maintain
Reusable components
1. Clear code structure
2. Easy debugging
3. Big projects-ku perfect

React Concepts

Keerthiga P — Wed, 25 Mar 2026 06:13:05 +0000

Default export?
Default export is a JavaScript feature that allows a file to export one main value (function, component, or variable) so it can be imported without curly braces in another file.

What is components?
Component is a function or class that returns JSX and represents a part of the UI.
Types of Components:

Class Component
Function Component

Class Component
A class component is created using a JavaScript class and must have a render() method.
Example:

class Hello extends React.Component {
  render() {
    return <h1>Hello</h1>;
  }
}

Function Component
A function component is a normal JavaScript function that returns JSX.
Example

function Hello() {
  return <h1>Hello</h1>;
}

JavaScript (JS):
JavaScript is a programming language used to create logic, behavior, and interactivity in web applications.

JSX:
JSX is a JavaScript syntax extension used in React that allows writing HTML-like code inside JavaScript to define UI.

XML:
XML (eXtensible Markup Language) is a markup language used to store and transport data in a structured format.

DOM IN JAVASCRIPT

Keerthiga P — Thu, 22 Jan 2026 06:01:55 +0000

1.DOM - Document Object Model
It is a programming interface for web documents that allow javascript to access and manipulate the structure,style,and content of a webpage.
(One line answer:allows javascript to access and manipulate HTML elements)

2.why we use DOM?

change text on a webpage
change styles(color,size)
get user input values
add or remove elements
Respond to events(click,input)

3.How do you select an element using id?
document.getElementById("id")

4.Difference between innerText and innerHTML?**
innerText = "Text"
innerHTML = "Bold"

5.How do you change text color using DOM?
element.style.color = "red";

6.How to create a new element?
document.createElement("p");

7.how to add an element to the page?
parent.appendchild(child);

8.what is an event in javascript?
An event is an action like click,keypress,or mouse movement

9.HTML Events?

onclick
onsubmit
onchange
onfocus
onblur
onload
onkeydown

10.Dom Methods:
document.getElementById("id")
document.getElementsByClassName("class")
document.getElementsByTagName("p")
document.querySelector("class")
document.querySelectorAll("p")

11.document.getElementById("id")

<h1 id="title">hello</h1>
  <script>
        function changeText(){
            const p =document.getElementById("title");
         console.log(p)
        }
    </script>

output:<h1 id="title">hello</h1>

12.document.getElementsByClassName("class")

<p>class="text">One</p>
<p>class="text">Two</p>

<script>
  const p = document.getElementsByClassName("text");
  console.log(p)
</script>

output: HTMLCollection(2)
0: One 1: Two

11.document.getElementsByTagName("p")

<p>A</p>
<p>B</p>
<script>
  let p = document.getElementsByTagName("p");
  console.log(p[0])
</script>

output:A

12.document.querySelector("class")

<p class="text">A</p>
<p class="text">B</p>
<script>
  let p = document.querySelector(".text");
  console.log(p);
</script>

output:A

13.document.querySelectorAll("p")

<p class="text">A</p>
<p class="text">B</p>
<script>
  let p = document.querySelectorAll(".text");
  console.log(p);
</script>

output:NodeList(2)
0: A 1: B