DEV Community: swetha palani

Java Architecture

swetha palani — Fri, 24 Oct 2025 04:48:55 +0000

Java Architecture defines how the Java programming language works internally — from writing code to running it on any device.
It explains how Java achieves its famous feature:

“Write Once, Run Anywhere” (WORA)

2. Main Components of Java Architecture

Java Architecture mainly consists of three key parts:

A. Java Virtual Machine (JVM)

JVM is the engine that runs Java programs.
It converts bytecode (intermediate code) into machine code for the current operating system.
It makes Java platform-independent.

Functions of JVM:

Loads code
Verifies code
Executes code
Manages memory (Garbage Collection)

B. Java Runtime Environment (JRE)

JRE = JVM + Libraries + Other components to run applications.
It provides all the necessary runtime environments for Java programs.

Think of JRE as:
The setup needed to run a Java program (but not to develop one).

C. Java Development Kit (JDK)

JDK = JRE + Development tools.
It’s used by developers to write, compile, and run Java programs.

Includes:

Compiler (javac)
Debugger
JavaDoc tool
JRE

Think of JDK as:
The complete toolkit for Java developers.

3. Flow of Execution in Java

Here’s how a Java program runs step-by-step:

You write code → MyProgram.java
Compiler (javac) → converts code to Bytecode → MyProgram.class
Classloader → loads .class files into JVM
Bytecode Verifier → checks code safety
JIT Compiler (Just-In-Time) → converts bytecode to native machine code
JVM executes the program

4. Diagram: Java Architecture

          ┌──────────────────────────────┐
          │       Java Application       │
          └──────────────┬───────────────┘
                         │
                (1) Compiled by javac
                         │
          ┌──────────────▼───────────────┐
          │        Bytecode (.class)     │
          └──────────────┬───────────────┘
                         │
                (2) Loaded by Classloader
                         │
          ┌──────────────▼───────────────┐
          │             JVM              │
          │  ┌────────────────────────┐  │
          │  │ Class Loader Subsystem │  │
          │  │ Bytecode Verifier      │  │
          │  │ Interpreter/JIT        │  │
          │  │ Garbage Collector      │  │
          │  └────────────────────────┘  │
          └──────────────┬───────────────┘
                         │
               (3) Machine Code Executed

Logical probelms

swetha palani — Fri, 10 Oct 2025 06:49:35 +0000

🧠 50 Python Logical Coding Questions (Zoho-Style)

(Focus on loops, strings, arrays, logic, and real test patterns)

🔹 Basic Level (1–15)

Print numbers from 1 to 100 without using loops.
Print the Fibonacci series up to n terms.
Find the factorial of a given number.
Check if a number is prime.
Reverse a number using while loop.
Check if a string is a palindrome.
Count vowels and consonants in a string.
Find the sum of digits of a number.
Swap two numbers without using a third variable.
Print all even numbers in a given range.
Print multiplication table of a given number.
Find the greatest of three numbers using if-else.
Check if a number is an Armstrong number.
Print all prime numbers between 1 to 100.
Find the average of numbers in a list.

🔹 Intermediate Level (16–35)

Find 2nd largest element in a list.
Remove duplicates from a list.
Sort a list without using sort() or sorted().
Find common elements between two lists.
Count frequency of elements in a list.
Merge two sorted lists.
Reverse a string without using slicing.
Check if two strings are anagrams.
Count words in a given sentence.
Find character frequency in a string.
Replace all vowels in a string with *.
Remove special characters from a string.
Find missing number in 1 to n series.
Find sum of even and odd numbers in a list.
Print pattern:
```
*
**
***
****
```
Print pattern:
```
1
12
123
1234
```
Print pattern:
```
A
BB
CCC
DDDD
```
Find the intersection and union of two sets.
Count capital and small letters in a string.
Print all unique elements in a list.

🔹 Advanced / Zoho Test Level (36–50)

Implement a program to check for balanced parentheses.
Find all pairs in a list whose sum equals a given number.
Rotate array elements to left/right by k steps.
Implement a simple calculator using functions.
Find the longest word in a given sentence.
Convert string "a3b2c1" → "aaabbc".
Convert a decimal number to binary manually.
Print frequency of each word in a paragraph.
Reverse words in a sentence but not characters.
Find the first non-repeating character in a string.
Remove duplicates from string while maintaining order.
Find if a number is “strong number” (sum of factorial of digits = number).
Find sum of all prime digits in a number.
Find maximum occurring character in a string.
Given matrix → print its transpose.

📘 50 Aptitude & Reasoning Practice Questions (Zoho-Style)

🔹 Quantitative Aptitude (1–25)

A train 120 m long passes a man walking at 6 km/hr in 10 sec. Find train speed.
The ratio of ages of A and B is 3:5. After 10 years, ratio becomes 4:6. Find their present ages.
If the cost price is ₹800 and gain is 20%, find selling price.
A can do a work in 10 days, B in 15 days. How long will they take together?
A person spends 40% on rent, 30% on food, saves ₹600. Find income.
Find the simple interest on ₹5000 at 8% per annum for 2 years.
Find compound interest on ₹4000 for 2 years at 10%.
Ratio of milk to water is 3:2. Add 10L water → new ratio 3:4. Find milk quantity.
Two pipes fill a tank in 12 and 15 mins. Together?
Speed of boat in still water = 10 km/hr, current = 3 km/hr. Find upstream speed.
If 20 men complete a work in 15 days, 10 men do it in how many days?
Selling price = ₹660, cost = ₹600. Find profit %.
A can finish a job in 12 days, B can do same in 8 days. Find ratio of their efficiency.
Find average of 23, 27, 31, 35, 39.
If 30% of x = 45, find x.
A car travels 120 km at 60 km/h. Time taken?
A number is increased by 20% and then decreased by 10%. Find net % change.
Find least number divisible by 8, 12, 15.
A man buys 10 pens at ₹15 each and sells them for ₹180 total. Find gain %.
The sum of first 20 natural numbers = ?
Two numbers are in ratio 4:5. Their LCM = 180. Find numbers.
Find the perimeter of a rectangle with l=12, b=8.
A can do 1/3 of work in 5 days. Whole work in?
Find HCF of 36 and 84.
20% of a number is 50. Find the number.

🔹 Logical Reasoning & Puzzles (26–50)

Arrange order:

Ramesh taller than Suresh
Mahesh shorter than Ramesh
Who is tallest?

If CAT = 3120, DOG = 4157 → BAT = ?
Series: 2, 6, 12, 20, 30, ?
Find the odd one: 3, 5, 7, 9, 11
If + means ×, − means ÷, × means −, ÷ means +, find: 6 + 3 × 2 − 4 ÷ 2
Arrange words in dictionary order: Mango, Apple, Orange, Banana
If 3x + 7 = 16, find x.
Fill series: A1, B2, C3, D4, ?
Which word can be made from “INFORMATION”?
In a row, Ram is 7th from left and 10th from right. How many students total?
3 persons A, B, C. A beats B, B beats C, C beats A. Who is best?
If 9 = 81, 8 = 64, 7 = 49, then 6 = ?
Statement: All dogs are animals. All cats are animals. Conclusion: ?
Odd one out: Square, Rectangle, Triangle, Circle
If North-East = 1, South-West = 3, North-West = ?, find logic.
Missing number:

3 5 8  
2 4 6  
1 ? 5

Mirror image of word “TEAM”?
If today is Wednesday, what day will it be after 45 days?
Rahul’s mother is sister of Rani’s father. How is Rahul related to Rani?
Which number replaces the question mark: 4 → 16, 5 → 25, 6 → ?
Spot the pattern: 1, 4, 9, 16, 25, ?
Arrange logic: Q → S, R → T, then U → ?
6 people sit in a circle. A is left of B, C is opposite D — who is right of A?
If in a code, A = 2, B = 4, C = 6, then ACE = ?
Find missing alphabet: AZ, BY, CX, ?

Would you like me to:

📄 Send these 100 questions as a PDF file (Zoho Crash Pack)
or 📚 Give answers + explanations for all coding and aptitude questions (for practice review)?

Which do you want next, da — PDF or with answers?

PROPS in React

swetha palani — Fri, 10 Oct 2025 06:45:49 +0000

Props (short for properties) are read-only data passed from a parent component to a child component.They help in reusing components and data sharing.

Props are arguments passed into React components, Props are passed to components via HTML attributes.

EXAMPLE:

**parent class(app.jsx)**

function App(){
return(
<Welcome 
name="swetha"
/>
)
}

**child class(Welcome.jsx)**

function Welcome(props){
return(
<div>
<h1>HELLO{props.name}</h1>

);
}

OUTPUT

HELLO swetha

Why are props used in React?

Pass data from parent to child component, Make components dynamic and reusable, Maintain one-way data flow

Can you modify props inside a component?

Props are immutable (cannot be changed).
If you try to modify them, React will throw a warning or behave unexpectedly.

How to pass multiple props to a component?

You can pass multiple props as key-value pairs.

App.jsx

Are props read-only or mutable?

Props are read-only.
You cannot modify props inside the child component.
If data needs to change, use state instead

What happens if a prop is not passed?

If a prop is missing, it will be undefined unless you use default props.

Components in react

swetha palani — Thu, 09 Oct 2025 12:55:31 +0000

Components are independent and reusable bits of code. They serve the same purpose as JavaScript functions, but work in isolation and return HTML.
components come in two types, Class components and Function components
If it react component can start captial Letter, all react component "JavaScript functions" but JavaScript functions not a react components.
An react component to return HTML tags

TYPES OF COMPONENTS

1.Functional Components

Simple JavaScript functions that return JSX.
Use React Hooks (useState, useEffect, etc.).

Example:

function Hello(){
return (
<h1>React Components</h1>
);
}
export default Hello;

Class components

Use ES6 classes and render() method.
Support lifecycle methods.

useEffect in React

swetha palani — Tue, 07 Oct 2025 05:13:07 +0000

What is `useEffect`?

useEffect is a React hook that lets you perform side effects in your components.
Side effects are things like:

Fetching data from an API
Updating the DOM manually
Setting up a timer
Logging data

It runs after the component renders.

syntax useEffect

Basic Syntax

useEffect(() => {
  // code to run (side effect)
});

Runs after every render by default.

Run only once (on mount)

useEffect(() => {
  // code to run once
}, []);

Empty dependency array [] → runs only when component mounts.

Run on specific state or prop change

useEffect(() => {
  // code to run when `variable` changes
}, [variable]);

variable → dependency, runs only when this changes.

Cleanup function (optional)

useEffect(() => {
  // setup code
  return () => {
    // cleanup code (like unsubscribing, clearing timers)
  };
}, [dependencies]);

When to use `useEffect`

When you want something to happen after render.
When you want to watch for changes in a variable (state or props).
When you want to clean up resources (like timers, subscriptions) when a component unmounts.

Where to use

Inside a functional component.

Simple Code Example

import React, { useState, useEffect } from "react";

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

  // useEffect runs after every render by default
  useEffect(() => {
    console.log("Count changed:", count);
  }, [count]); // dependency array

  return (
    <div>
      <h1>{count}</h1>
      <button onClick={() => setCount(count + 1)}>Increase</button>
    </div>
  );
}

export default Counter;

Explanation:

useEffect(() => {...}, [count]) → Runs only when count changes.
Without [count], it runs after every render.
With [] (empty array), it runs only once when the component mounts.

Useref in react theory question

swetha palani — Fri, 03 Oct 2025 06:54:27 +0000

What is useRef in React?

Answer: useRef is a React hook that returns a mutable object (.current) whose value persists across re-renders.
Example: const myRef = useRef(null);

What’s the difference between useRef and useState?

useState triggers re-renders when updated.
useRef does not trigger re-renders when .current changes.

When should you use useRef instead of useState?

When you want to store values that:
- Don’t affect rendering.
- Should persist between renders (like timers, previous values, DOM references).

How does useRef help in accessing the DOM?

useRef stores a reference to a DOM element that you can access directly.
Example: myRef.current.focus() to focus an input.

What happens if you update a useRef value? Does the component re-render?

No. Updating .current does not cause re-render.

Difference between useRef and createRef?

createRef is re-created on each render (used in class components).
useRef persists the same object between renders.

Can useRef be used to store previous state values?

Yes, by manually updating .current inside useEffect.

Can you pass useRef between components?

Yes, but usually with forwardRef to expose refs from child to parent.

What is the initial value of a useRef object?

Whatever you pass inside useRef(initialValue) → stored in .current.

Why is useRef called a “box” object in React docs?

* Because `.current` acts like a box where you put a value and retrieve it without triggering re-renders.

Useref in react interview question

swetha palani — Fri, 03 Oct 2025 06:50:57 +0000

1.What is useRef in React?

Answer: useRef is a React hook that returns a mutable object (.current) whose value persists across re-renders.

Example: const myRef = useRef(null);

2.What’s the difference between useRef and useState?

useState triggers re-renders when updated.

useRef does not trigger re-renders when .current changes.

3.When should you use useRef instead of useState?

When you want to store values that:

Don’t affect rendering.

Should persist between renders (like timers, previous values, DOM references).

4.How does useRef help in accessing the DOM?

useRef stores a reference to a DOM element that you can access directly.

Example: myRef.current.focus() to focus an input.

5.What happens if you update a useRef value? Does the component re-render?

No. Updating .current does not cause re-render.

6.Difference between useRef and createRef?

createRef is re-created on each render (used in class components).

useRef persists the same object between renders.

7.Can useRef be used to store previous state values?

Yes, by manually updating .current inside useEffect.

8.Can you pass useRef between components?

Yes, but usually with forwardRef to expose refs from child to parent.

9.What is the initial value of a useRef object?

Whatever you pass inside useRef(initialValue) → stored in .current.

10.Why is useRef called a “box” object in React docs?

Because .current acts like a box where you put a value and retrieve it without triggering re-renders.

CODEONJVM for JavaCraft

swetha palani — Tue, 30 Sep 2025 06:04:20 +0000

✨ Had an incredible learning experience today at JavaCraft: Coding Possibilities, hosted by Code on JVM Chennai at Entrans Inc. Technologies Private Limited, Chennai 🚀☕
The workshop was a perfect blend of knowledge, hands-on practice, and insights from industry professionals:
🔹 Sri Santhosh Natarajan (Senior Software Engineer, Pearson India) – Reactive Java 101
We delved into moving from blocking to non-blocking APIs, exploring Spring WebFlux, FastAPI, and databases like MongoDB & PostgreSQL. The session offered a clear understanding of building scalable, reactive applications ⚡.
🔹 Yagapriyan G (Software Engineer II, Arcadia) – JDBC Made Easy with PL/SQL
An in-depth session on JDBC connectivity and database operations, explained with practical examples and real-time scenarios 🔗.
Both sessions were highly interactive and beginner-friendly, making it easy to grasp not just how things work, but also why they work that way 🙌.
A huge thank you to the organizers for providing such an amazing platform for developers to learn, connect, and grow! 💻✨

JSON in react

swetha palani — Fri, 26 Sep 2025 09:49:52 +0000

What is JSON?

JSON stands for JavaScript Object Notation.
It is a lightweight data format used for storing and exchanging data.
It looks like JavaScript objects, but it’s just text (a string).

Why JSON is used?

Easy to read and write (human-friendly).
Easy for machines to parse and generate.
Commonly used in APIs to send data between a server and a client (like React, mobile apps, etc.).

Example of JSON

{
  "name": "Swetha",
  "age": 22,
  "isStudent": true,
  "skills": ["JavaScript", "React", "Python"]
}

This is just data in key-value pairs.

JSON Rules

Data is in key-value pairs → "key": "value"
Keys must be in double quotes → "name", not name.
Values can be:

String → "Swetha"
Number → 22
Boolean → true / false
Null → null
Array → [1,2,3]
Object → { "city": "Chennai" }

🔹 JSON vs JavaScript Object

JSON:

  { "name": "Swetha", "age": 22 }

JS Object:

  { name: "Swetha", age: 22 }

Difference: In JSON, keys must be in double quotes, and it’s only text, not an actual object.

In simple words:
JSON is a text-based format to store and share data between different systems, especially in web development.

How JSON is used in React

A backend/server sends data in JSON format.
React fetches it using fetch() or axios.
JSON is converted into a JavaScript object using .json().
React renders that data inside components.

Step-by-step

fetch() → calls API.
.json() → parses JSON string into JS object.
setUsers(data) → saves data into state.
map() → displays the data dynamically.

Interview 1-Minute Answer

“JSON is mainly used in React when fetching data from APIs. The server usually returns a JSON response, which we parse using .json(). Then we store it in state and render it inside components using methods like .map().”

Props types in raect

swetha palani — Fri, 26 Sep 2025 09:20:13 +0000

In React, PropTypes is a way to check the data types of props that a component receives.
It helps you catch bugs by warning you if the wrong type of data is passed to a component.

Why use PropTypes?

Ensures components get the right type of data.
Provides documentation for other developers.
Helps in debugging unexpected prop values.

How to use `PropTypes`

Import prop-types package:

npm install prop-types

Example in a component:

import React from "react";
import PropTypes from "prop-types";

function Student(props) {
  return (
    <div>
      <p>Name: {props.name}</p>
      <p>Age: {props.age}</p>
      <p>Student: {props.isStudent ? "Yes" : "No"}</p>
    </div>
  );
}

//  Setting PropTypes
Student.propTypes = {
  name: PropTypes.string.isRequired,   // must be a string
  age: PropTypes.number,              // must be a number
  isStudent: PropTypes.bool           // must be true/false
};

// Default props
Student.defaultProps = {
  age: 18,
  isStudent: false
};

export default Student;

Common PropTypes

PropTypes.string → string
PropTypes.number → number
PropTypes.bool → true/false
PropTypes.array → array
PropTypes.object → object
PropTypes.func → function
PropTypes.node → anything that can be rendered (elements, strings, numbers)
PropTypes.element → React element
PropTypes.oneOf(["a", "b"]) → one specific value
PropTypes.arrayOf(PropTypes.number) → array of numbers
PropTypes.shape({ key: PropTypes.string }) → object with specific structure

PropTypes vs TypeScript in React

Feature	PropTypes	TypeScript
What it is	A separate library (`prop-types`) for runtime type checking	A superset of JavaScript that adds static typing
Type Checking	Happens at runtime → shows warnings in the console when props are invalid	Happens at compile-time → errors before running the code
Scope	Only checks props in React components	Checks props + state + functions + variables + entire codebase
Installation	`npm install prop-types`	`npm install typescript`
Ease of Use	Lightweight, simple, no extra setup	More setup (tsconfig.json, type definitions)
Best For	Small projects, quick prop validation	Large projects, full-scale type safety

Interview-Friendly Answer (30 sec)

“PropTypes is a library in React for runtime type checking of props, whereas TypeScript provides compile-time type safety for the entire codebase, not just props. PropTypes is simpler and useful in small projects, but TypeScript is preferred in modern large-scale applications because it prevents errors before running the code.”

Function compound & class compound in react

swetha palani — Fri, 26 Sep 2025 04:51:05 +0000

Function Component in React
A function component is a plain JavaScript function that returns JSX and can use React Hooks like useState and useEffect to manage state and lifecycle. It’s simpler and more efficient than class components.

Compound Component Pattern
The compound component pattern lets multiple related components work together, sharing state via React context instead of passing many props. Example: Tabs with Tab, TabList, and TabPanel. It provides a clean, flexible, and reusable API.

Simple :
“Function components are the modern way of building React components using hooks, and the compound component pattern helps create reusable, flexible UIs by allowing components to communicate implicitly.”

Class components:

“A class component in React is an ES6 class that extends React.Component. It must have a render() method that returns JSX. Unlike function components, class components can manage state using this.state, update it with this.setState(), and use lifecycle methods like componentDidMount and componentWillUnmount. However, in modern React, class components are less common because function components with hooks provide the same features in a simpler way.”

USESTATE IN REACT

swetha palani — Tue, 23 Sep 2025 05:44:36 +0000

What is useState?

useState is a Hook in React, It allows functional components to have state (something only class components could do earlier with this.state).

SYNTAX:

const [state, setState] = useState(initialValue);

state → current value of the state.
setState → function to update the state.
initialValue → the value you want the state to start with.

Alright! Let’s make React Hook super clear, especially from an interview perspective.

1. What is a React Hook?

Hooks are special functions in React that let you “hook into” React features like state and lifecycle methods in functional components.
They were introduced in React 16.8 to avoid using class components for stateful logic.

Key idea: Hooks allow functional components to have state, side effects, and more without writing a class.

2. Common React Hooks

useState → for state management
useEffect → for side effects like API calls, timers
useContext → for consuming context
useReducer → for complex state management
useRef → to access DOM elements or persist values

3. Why Hooks? (Advantages)

No need for class components → simpler, cleaner code.
Reuse stateful logic across components (custom hooks).
Better separation of concerns in components.
Avoids confusion with this keyword in classes.

4. Where to use Hooks?

Only inside functional components or custom hooks.
Not in loops, conditions, or nested functions → must be top-level.

5. How to use a Hook?

Example with useState:

import { useState } from 'react';

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

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