DEV Community: RADHAKRISHNAN S

JAVA

RADHAKRISHNAN S — Tue, 22 Sep 2026 02:22:34 +0000

JAVA

Java is a popular and powerful programming language, created in 1995.

It is owned by Oracle, and more than 3 billion devices run Java.

It is high level programming language.

It also statically type programming language.

It is used for develop web applications desktop applications and games etc..,

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Why Use Java?

Java works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc.)
It is one of the most popular programming languages in the world
It has a large demand in the current job market
It is easy to learn and simple to use
It is open-source and free
It is secure, fast and powerful

What is JDK?

JDK stand for java development kit

It is used to build and develop the java program

It internally contains JRE

It contains the compiler and debugger

It contains all the related set of libraries and files to build and compile the java program

Without JDK we cant build any java program

What is JRE?

JRE stands for Java Runtime environment

JRE is the responsible unit to run the java program

Without JRE we cant run java program (JDK is used to build java program, where as JRE is used to run java program. Such that without JDK, I mean with only JRE we can run the java program even without JDK)

JRE contains JVM

JRE contains all the inbuilt packages and library files (lang, io, util etc all packages are present in JRE)

What is JVM?

JVM stands for Java Virtual Machine

JVM is platform dependent

JVM takes .class files and executes it by managing the memory (JVM architecture is attached in other slide, for more reference)

JVM contains JIT

JVM loads, verifies and executes the code and provides the runtime environment

JVM plays a major role in java memory management

What is JIT?

JIT stands for Just In Time compiler

Java was a interpreted programming language, but after introducing JIT it was called as interpreted-compiled programming language

JIT increased the speed of execution

JIT helps the JVM to find the active OS

JIT was introduced from 1.2 JDK

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REACT JAVASCRIPT

RADHAKRISHNAN S — Tue, 22 Sep 2026 01:54:09 +0000

What is REACT ?
React is a JavaScript library for building user interfaces.

React is used to build single-page applications.(SPA)

React allows us to create reusable UI components

REACT Invented by Facebook now they were changed the name Meta.

Current version of react is 19.2

DOM-TASK1

RADHAKRISHNAN S — Sat, 01 Aug 2026 03:31:21 +0000

LIVE CLOCK

<!DOCTYPE html>
<html>
<head>
    <title>Document</title>
</head>
<body>
    <h1 id="clock">00:00:00</h1> 

    <script>
const clockNew=document.getElementById("clock");
function updateClock() {
    const time = new Date();
    const h = String(time.getHours()).padStart(2, '0');
    const m = String(time.getMinutes()).padStart(2, '0');
    const s = String(time.getSeconds()).padStart(2, '0');

    clockNew.innerText = h + ":" + m + ":" + s;
}
updateClock();
setInterval(updateclock, 1000); 
    </script>
</body>
</html>

Syntax:The padStart() method in JavaScript is used to pad a string with another string until it reaches the given length. The padding is applied from the left end of the string.

javascript string.padStart(targetLength, padString)

DYNAMIC FONT SIZE CHANGER

<!DOCTYPE html>
<html>
<head>
    <title>Document</title>
</head>

<body>
    <div style="height: 100px; text-align: center;">
        <h1 id="word">Hi Hello</h1>
    </div>

    <div style="text-align: center;">
        <input type="range" min="10" max="48" value="22" id="size">
    </div>

    <script>
        const word = document.getElementById('word');
        const size = document.getElementById('size');

        size.addEventListener('input', () => {
            // Appending 'px' ensures the CSS property applies correctly
            word.style.fontSize = size.value + 'px';
        });
    </script>
</body>

</html>

The addEventListener() method attaches an event handler function to a specified HTML element without overwriting existing event handlers.

ENABLE AND DISABLE SUBMIT BUTTON

<!DOCTYPE html>
<html>
<head>
    <title>Document</title>
</head>
<body>
   <input onclick="mysubmit()" type="checkbox" id="check" >
    <button id="btn" disabled>submit</button> 
    <script>
        const box =  document.getElementById("check");
        console.log(box);

        const button =   document.getElementById("btn");
        function mysubmit(){
            if (box.checked == true ){   //checked means enter (tick)
                button.disabled = false;
            }else{
                button.disabled = true;   //not clicked  disabled
            }
        }
    </script>  
</body>
</html>

UPPERCASE

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- <h1 id="h1" oninput="convert()"></h1> -->
    <input type="text"  id="h1" > 
    <button id="btn" onclick="convert()">convert</button>



</body>
<script>


    function convert()
    {
        document.getElementById("h1").value = document.getElementById("h1").value.toUpperCase();
    }


    // btn.addEventListener("click",()=>{document.getElementById("h1").value = document.getElementById("h1").value.toUpperCase();})
</script>
</html>

PYTHON-FUNCTIONS

RADHAKRISHNAN S — Fri, 31 Jul 2026 03:17:06 +0000

What is runtime?

Runtime refers to the period when a program is actively running and performing operations.

What is compile time?

Compile time is the stage where Python checks your code and converts it into bytecode before executing it.

System language: o's and 1's (signals)

Python User Input:

Python allows for user input.
That means we are able to ask the user for input.
Example:Your name,age,gender collects the data and printed the screen.

name = input("Enter your name: ")
print("Hello,", name)

O/P:
Enter your name: Rohit
Hello, Rohit

Function overloading:

Same method name with difference number of parameters.
Ex; withdraw(pin);
withdraw(otp);

FUNCTION:

*Set of instructions with a name
*Function must have () & english verb forms.
*A function is a block of code which only runs when it is called.
*A function can return data as a result.
Ex: (),parameters(inputs)

Function names:

A function name must start with a letter or underscore
A function name can only contain letters, numbers, and underscores
Function names are case-sensitive (myFunction and myfunction are different)

Creating a Function:

In Python, a function is defined using the def keyword, followed by a function name and parentheses().

def my_function():
  print("Hello from a function")

Calling a Function:

To call a function, write its name followed by parentheses:

def walking():
  print("Go to home")

walking()

O/P:
Go to home

We can call the same function multiple times:

walking()
walking()
walking()

Return Values:

Functions can send data back to the code that called them using the return statement.

Sometime function has no return values.

def get_greeting():
  return "Hello from a function"

message = get_greeting()
print(message)

O/P:
Hello from a function

DOM-ELEMENT SELECTOR

RADHAKRISHNAN S — Thu, 30 Jul 2026 12:11:32 +0000

Selecting Elements:

*Finding HTML elements by id
*Finding HTML elements by tag name
*Finding HTML elements by class name
*Finding HTML elements by CSS selectors
     i)The querySelector() Method
     ii)The querySelectorAll() Method
*Finding HTML elements by HTML object collections

Finding HTML Element by Id:

The easiest way to find an HTML element in the DOM, is by using the element id.

id="user":
const element=document.getElementById("user")

Finding HTML elements by tag name:

Select from the Tag name

 <P>,<span>and<a>,<h1>-<h6>etc..,


<h2>HTML</h2>
const element=document.getElementsByTagName("h2");

Finding HTML elements by class name:

Selects all elements with the same class name.

<p class="text">Apple</p>
<p class="text">Banana</p>
<script>
let element=document.getElementsByClassName("text");
<script>

The querySelector() Method:

Selects only the first element that matches a CSS selector.

<!DOCTYPE html>
<html>
<body>
<h1>JavaScript HTML DOM</h1>
<h2>The querySelector() Method</h2>

<p class="demo"></p>

<script>
// Access a paragraph Element
const myPara = document.querySelector(".demo");

// Change the content of the Element
myPara.innerHTML = "Hello World!";
</script>

</body>
</html>

We can use

document.querySelector("#title"); // id
document.querySelector(".text"); // class name
document.querySelector("p"); // tag name

The querySelectorAll() Method:

Selects all elements that match a CSS selector.

<!DOCTYPE html>
<html>
<body>
<h1>JavaScript HTML DOM</h1>
<h2>The querySelectorAll() Method</h2>

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

<script>
// Access a paragraph Element
const myItems = document.querySelectorAll(".demo");

// Change the content of the Element
myItems[0].innerHTML = "First";
</script>

</body>
</html>

We think of a classroom:

querySelector() = Calls one student (the first one who matches).
querySelectorAll() = Calls all students who match the condition.

PYTHON - DATATYPES

RADHAKRISHNAN S — Wed, 29 Jul 2026 13:11:29 +0000

DATA TYPES:

Variables can store data of different types, and different types can do different things

Numeric Data Types:

Numeric data types are used to store numeric values. It can be an integer, floating number or even a complex number.

*int - positive or negative numbers
*float - numbers with a *floating decimal points
*complex - Numbers with a real and an imaginary part

Sequence Data Types:

A sequence is an ordered collection of items, which can be of similar or different data types. Elements in a sequence can be accessed using indexing.

*String - used to stored text data.represent str cls and used single , double and triple .

*List - Ordered and mutable collections used to store multiple variable.In diff data types and accessed using index

Tuple- Ordered and immutable collection used to store multiple values in **single* Cannot be modified

Boolean Data Type:

Boolean data type represents one of two values: True or False. It is mainly used in conditions and comparisons and is represented by the bool class.

Set Data Type:

Sets are unordered and mutable collections used to store unique elements. Since sets are unordered, elements cannot be accessed using indexing.

Dictionary Data Type:

Dictionaries are used to store data in key:value pairs. Each key in a dictionary must be unique and values are accessed using their keys with square brackets [] or get() method.

KEYWORDS IN PYTHON:

Python has a set of keywords that are reserved words that cannot be used as variable names, function names, or any other identifiers.

Go to the linux terminal
to list the python keywords in idle use this command:

import keyword keyword.kwlist

['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']

DOM - ALERT

RADHAKRISHNAN S — Wed, 29 Jul 2026 13:04:46 +0000

<!DOCTYPE html>
<html>
<style>
body{
    display:flex;
    align-items: center;
    justify-content: center;
}
</style>
<body>

<input type="text" id="name">

<button onclick="greet()">Greet</button>

<h4 id="message"></h4>

<script>
function greet() {

    const input = document.getElementById("name");
    const name = input.value;
    const message = document.getElementById("message");

    if (name == "") {
       message.innerText="Please enter text!"
    }
    else {
         message.innerHTML = '<img src="https://pbs.twimg.com/media/FgOkmTFaYAAGzYY.jpg" width="250">';
    }

}
</script>

</body>
</html>

DOM(ON-OFF)

RADHAKRISHNAN S — Tue, 28 Jul 2026 02:32:25 +0000

html
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button id="btn" onclick="greetbtn()">ON</button>
    <script>
        function greetbtn(){
            const inside=document.getElementById("btn");
            console.log(inside.innerText);
            if(inside.innerText=="ON"){
                inside.innerText="OFF";
            }else{
                inside.innerText="ON"
            }
            // inside.innerText="OFF"

        }
    </script>



</body>

</html>

TOSSCONF 26 II

RADHAKRISHNAN S — Sun, 26 Jul 2026 13:27:08 +0000

We put the stall in ST.JOSEPH engineering college.The title is GITLAB.It is an open source meeting so we choose this platform.
The meeting was arranged by SYED and SALMAN bro's. They are the organizer of TOSSCONF. We communicate with the students and well experienced IT employees.They are giving spark of the open source speech.It was inspired to me.I know the operating system only WINDOWS then i came to payilagam they were told that LINUX os .
There was the initial part of open source in my local machine.
Then i tried to install the BOSS LINUX version.I feel the difference between windows and linux.SO i decided linux is the best os .

Overall the meeting we get more informations and knowledge about open source. Toatally 31 stalls inside the room.Every team content was very useful for us.I visted to everystalls and gathered the was different.Also they gave the related STICKERS for promotion and i cellected it all.Eventually that TOSSCONF was ended with superb.We are enjoing well.

                        THANK YOU

PYTHON INTRO

RADHAKRISHNAN S — Sun, 26 Jul 2026 12:39:42 +0000

What is python?

It is a general purpose high level programming language.
It was created by Guido van Rossum, and released in 1991.
The latest version of python 3.14.6 .
It is used for web development (server-side), software development,mathematics and system scripting.

What is high level programming language?

A high-level programming language is a language designed to be easy for humans to read, write, and understand.(human language)

Examples: python,java,c,c++,c#,javascript.

TOSSCONFO

RADHAKRISHNAN S — Wed, 22 Jul 2026 16:34:52 +0000

I have to share about this TOSSCONFO meeting. In payilagam institution teammates are participate the meeting. The meeting will conduct in next three days.
First day we have Hackathon , second day Workshopand Third day STALL.

Me and my team(Vinoth&Kiruthiga) are put the stall in Tossconfo meeting. The title is GITLAB .
We install the Gitlab to students and also explain how to works it , that's purpose and features.

DOM

RADHAKRISHNAN S — Wed, 22 Jul 2026 01:24:56 +0000

What is DOM?

The HTML DOM (HTML Document Object Model) is an Object Model for HTML Documents.

The DOM Tree
When a web page loads, the browser creates a tree-like representation of the HTML document.

Each part of the document are nodes in the tree: