DEV Community: Kavya S

Features of Java

Kavya S — Thu, 16 Oct 2025 07:08:45 +0000

Features of Java

1.Simple Syntax
Java's syntax is clean and easy to understand and remove complex features

2.Object Oriented
It focus on the concept of object and the concepts of oops like Abstraction,Encapsulation,Inheritance and Polymorphism

3.Platform Independent
Java code is compiled not into native machine code, but into an intermediate format called bytecode.This byte code can run on any platform that has a JVM.
The JVM interprets the bytecode into native machine instructions for the specific platform.
we can write it once,run anywhere if JVM is installed.

4.Interpreted and Compiled
It acts like compile during .java file to .class bytecode and interpreter during .class bytecode to machine code

5.Multithread
This allows a program to perform multiple tasks simultaneously, leading to better performance.

6.Portable
There are no implementation-dependent aspects, compiled Java code (bytecode) is highly portable. You can carry the bytecode and run it on any machine with a JVM.

7.High Performance
JIT compilers optimize bytecode to native code.so,It provides fast execution for modern applications.

8.Rich Standard Library
provides pre-built tools and libraries known as API.
With the help of these libraries developers save a lot of time.

9.Secured and Robust
It can catch mistakes early while writing the code and also keeps checking for errors when the program is running. It also has a feature called exception handling that helps deal with unexpected problems smoothly.

10.Memory Management

Memory management in java is handled by Java Virtual Machine.
Memory for objects are stored in Heap
Methods and local variables are stored in stack

Common Errors in Java Program

Kavya S — Thu, 16 Oct 2025 02:50:28 +0000

Hello World Program

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

Common Errors

Class name should match Filename

// File named: HelloWorld.java
public class HelloWorld {  // CORRECT: Class name matches filename
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Java is Case Sensitive (eg., 'system should be System')

System.out.println("Hello, World!");

Class name must start with Uppercase

public class HelloWorld

Every end of statements must have semicolons

System.out.print("Hello");
System.out.println("World!");

To print a string, use double quotes

System.out.print("Hello");

To print a single character,use single quotes

System.out.print('c');

Use Proper Braces

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }  // CORRECT: Braces properly placed
}

Java Variable and Data type

Kavya S — Tue, 14 Oct 2025 07:25:50 +0000

What is Variable?
-Variable is a container that can hold value
In java,declaring a varible should be follows like

//dataType variablename=value;
int number=10;

datatype : This defines what kind of data the variable can hold(eg:numbers,text,true/false)
variablename : This is a unique identifier you give to the variable so you can refer it later
= : this is assignment operator.It assigns the value to the variable on its left
value : the actual data you want to store

Variable Rules

Can contain letters, digits, underscores (_), and dollar signs ($).
Cannot start with a digit. (7days is invalid, but days7 is valid).
Cannot be a Java keyword (like int, class, public, if).
Case-sensitive (myVar and myvar are different variables).

DataType

as discussed,it defines the type of value
There are 2 types of datatype
primitive datatype
non-primitive datatype

Primitive Datatype
There are 8 primitive datatypes

byte
short
int
long
float
double
boolean

Java Introduction

Kavya S — Mon, 13 Oct 2025 07:01:05 +0000

What is Java?

Java is a high-level,object oriented programming language developed by sun microsystems.
It is mostly used for building web applications.
It is platform independent,because we can write it once,it will run on any device if jvm is installed

Why object-oriented?

Java is object oriented because it focuses on the concept of object and supports encapsulation,inheritance,polymorphism and abstraction.

Core concepts of Java Ecosystems
JDK = JRE + Development Tools
JRE = JVM + Libraries

Compiler translates the human readable code to machine readable code.
That compiler consists of multiple set of software known as Java Development KIT.
We save that java file using .java after that byte code will save that file as .class
Java virtual machine,converts Java bytecode (compiled code) into machine code.
It is the intermediate between java code and hardware.
The JIT or Just-In-Time compiler converts bytecode into native machine code at runtime.

Example Java Code

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

React Question & Answer

Kavya S — Tue, 07 Oct 2025 01:55:56 +0000

1. What is the difference between a functional component and a class component in React?

Functional component is a javascript function that takes props and returns a react element(jsx) while class component use render() method, which returns the JSX
Implements hooks easily within the function to handle state and effects but in class component,states are handled through class methods
Hooks handle state initialization but in class component requires a constructor for initializing state

2. How does JSX work internally? Why do we need it instead of plain JavaScript?

JSX is like a shortcut that gets converted to regular JavaScript. When you write JSX like <h1>Hello</h1>, it gets turned into React.createElement('h1', {}, 'Hello') behind the scenes.

why we need?
JSX makes writing React code much easier and cleaner. Without JSX, you'd have to write long, complicated JavaScript code to create simple HTML elements. JSX looks like HTML so it's familiar and easy to read.

3. What is Virtual DOM and how does React use it for rendering?

Virtual DOM acts as a bridge between UI and real DOM.
It updates only the specific part of the page we need to change.
If we update any components in a web page,it first update the changes in virtual DOM and it compare it with Real DOM.
If it updates in actual DOM,it takes more time to update but virtual DOM makes it faster.

4. Explain props vs state with an example.

Props are properties that is passed from a parent component to a child component
but in state,it can change over time based on user interactions or API responses.
Props can be used with state and functional components and The state can be used only with the state components/class component
Props are read-only,State can be updated with setState

Example for props

// Parent Component
function App() {
  return <User name="John" age={25} />;
}

// Child Component
function User(props) {
  return (
    <div>
      <h1>Name: {props.name}</h1>
      <p>Age: {props.age}</p>
    </div>
  );
}

Example for State

function Counter() {
  const [count, setCount] = useState(0); // STATE

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => setCount(count + 1)}>
        Increase
      </button>
    </div>
  );
}

5) What is lifting state up in React? Give an example.

Lifting State Up is a pattern in React where you move the state from a child component to its parent component, allowing multiple child components to share and synchronize the same state data. [to be discussed]

Props in React

Kavya S — Wed, 01 Oct 2025 09:29:39 +0000

What is Props?

Props are properties that are used to pass information from one component to another.
The main purpose of props is to allow a parent component to send data to its child components.

Why props?

Pass data from parent to child components
Enable inter-component communication
Create clear data flow channels

Example

// Parent Component
function App() {
  return (
    <div>
      <Greeting name="Alice" />
      <Greeting name="Bob" />
      <Greeting name="Charlie" />
    </div>
  );
}

// Child Component receiving props
function Greeting(props) {
  return <h1>Hello, {props.name}!</h1>;
}

Output

Hello, Alice!
Hello, Bob!
Hello, Charlie!

Jsx,React DOM,Components

Kavya S — Mon, 15 Sep 2025 01:58:45 +0000

what is jsx?

It allows you to write HTML code directly inside the JS file.
Before jsx,developers had to use complex JS functions to create HTML.
with jsx,it makes HTML easier to visible

React DOM

Acts bridge between UI and actual DOM.
It update only the specific parts of the page we need to change.

Component

Components are independent and reusable bits of code
There are two common ways to write components:
Function components
Class components

Function component

When creating a React component, the component's name MUST start with an upper case letter.
React components returns HTML code.

Example
Create a Function component called Car

function Car() {
  return (
    <h2>Hi,I have a Car!</h2>
  );
}

Rendering a component

To use this component in your application, refer to it like this:

Example
Display the Car component in the "root" element:

createRoot(document.getElementById('root')).render(
  <Car />
)

React,CRA,Vite

Kavya S — Sat, 13 Sep 2025 03:26:57 +0000

What is React?

React is a javascript library to build user interface and single page application
It allows developers to create large web applications that can change data,without refreshing the page

What is CRA?

CRA stands for Create React App
It provides a pre-configured environment with default setup, including Webpack, Babel, and ESLint.
This allows developers to focus on writing code rather than dealing with complex build configurations.

What is Vite?

Vite is a frontend tool that is used for building fast and optimized web applications.
It uses a modern build system and a fast development server to provide a streamlined and efficient development experience.
It features rapid hot module replacement (HMR), so you can instantly see updates as you change your code.

Fetch,Axios in JavaScript

Kavya S — Sat, 13 Sep 2025 01:44:28 +0000

What is Fetch?

Fetch is a tool in Javascript that allows website to communicate to a server to get or send information

Why Fetch?

When you shop online,fetch retrieves product details or sends your order to server

Example

<script>
fetch("https://fakestoreapi.com/products")
.then ((res) => res.json())
.then (jsonresponse) => console.log(jsonresponse))
.catch ((rej) => rej.json())
</script>

What is Axios?

Axios is an external library
Axios is a promise-based HTTP Client for node.js and the browser

Example

axios.get("https://fakestoreapi.com/products")
.then (res => {
console.log(res);
})
.catch (err => {
console.error(err);
})

Promise in JavaScript

Kavya S — Fri, 12 Sep 2025 02:36:09 +0000

What is Promise?

Promise is an object that is used to handle asynchronous operation.
This will execute either resolve or reject
if resolve, it will execute then block
else, it will execute catch block

Why we use Promise?

1.Avoid Callback Hell
Promises allow you to chain asynchronous operations instead of nesting them. This is done using .then()

2.Error Handling
With callbacks, you had to check for errors at every single level of nesting. Promises provide a single .catch() method at the end of the chain.
so,it makes easy to check the error

When should we use Promise?

When Making Network Requests
When Working with Databases
When Reading or Writing Files
When Using Timers or Delays

Example

 function booking(){
            return new Promise((resolve,reject)=>{
                let bookingsuccess=true;
                if(bookingsuccess)
                resolve(850)
            else
            reject()
            })
        }
        booking().then(()=> console.log("booking success"))
        .then((amt)=> console.log('i have transfered ${amt}'))
        .catch(()=> console.log("try again"))

CallBack,CallBack Hell

Kavya S — Thu, 11 Sep 2025 01:26:42 +0000

What is CallBack?

It is a function that is passed as an argument to another function
callback allows another function to call
A function can accept another function as argument

function greet(name,callback) {
    console.log("Hello, " + name);
    callback();
    }

    function sayBye() {
    console.log("Goodbye!");
    }

    greet("Ajay", sayBye);

When to use callback?

when performing asynchronous operations such as network requests
It is used to handle events such as user input,mouse clicks

What is CallBack Hell?

Multiple nested callback functions make code more difficult to read and maintain so that we call it as callback hell.

 setTimeout(()=>{
           console.log("step1");
           setTimeout(()=>{
            console.log("step2");
            setTimeout(()=>{
                console.log("step3");
                setTimeout(()=>{
                    console.log("step4")
                },1000)
            },1000)
           },1000)
       },1000)

Problems with callback hell:

Readability
Error Handling
Maintaining

Solutions to avoid callback hell

Promises
Async/Await

Synchronous,Asynchronous in JavaScript

Kavya S — Thu, 11 Sep 2025 01:14:07 +0000

What is Synchronous?

In synchronous,each line of code executes line by line.
that means,each line of code waits for the previous one to execute

Example:

console.log("Hi")
console.log("Welcome")

Output
Hi
Welcome

What is Asynchronous?

In asynchronous,a task can be initiated and while waiting for it to complete, other task can be proceed.
It improves performance

Example:

console.log("Task1")
setTimeOut(()=>{
console.log("Task2")
},2000);
console.log("Task3")

Output
Task1
Task3
Task2