DEV Community: subash

How Java Compiles and Runs & Difference between Static and non Static variable.

subash — Fri, 03 Jul 2026 12:22:18 +0000

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

STEP 1 : We save it has Main.java
STEP 2 : we right click the folder screen then click terminal in terminal we enter -- javac Main.java , to compile the file . after that Main.class file will create.(main.class) -- this called byte code.

Main.java
│
▼
Java Compiler (javac)
│
▼
Main.class

STEP3 : JVM, Now run , java Main

Main.class
│
▼
JVM
│
▼
Machine Code
│
▼
CPU

Why not directly Machine Code?

Before JAVA,
C, C++, pascal these are only the programing language was used before java, then had some problem what is
1.Platform dependencies(software + hardware = plateform)
Here developer need to create separate version for different systems. this was taken time, cost and maintenance.

After java :
Write Once, Run Anywhere

Why should file name be Main.java?

The public class name and filename must be the same.
Main.java
public class Main

Hello.java
public class Main , this will cause error

Program for how use non static variable

class Product {

    String name;
    int price;

}

public class Index {

    public static void main(String[] args) {

        Product product1 = new Product();
        Product product2 = new Product();
        Product product3 = new Product();

        product1.name = "Laptop";
        product1.price = 50000;

        product2.name = "Mobile";
        product2.price = 20000;

        product3.name = "Headphone";
        product3.price = 3000;

        System.out.println(product1.name + " : " + product1.price);
        System.out.println(product2.name + " : " + product2.price);
        System.out.println(product3.name + " : " + product3.price);

    }

}

here java have two variable one is static variable and another one is non static variable , non static variable need object.

class Product {

    String name;
    int price;

}

This is not public class , this class name is Product , always the class name should be in start with caps, that class have two non static variable one is name and another one is price, i did not give any value , so in default string have null value in that variable and int have 0 value in default .

then we create Public class Index {,
In class Index have main method , if i want to create any static variable then should create it only outside of main method or inside Index class . in this case we did not created any static variable , so we will going to inside main method , already we know that we have two non static variable in product class, we need to use that, but before that we need to create object to allocate space to use that in diff object,

     Product product1 = new Product();
        Product product2 = new Product();
        Product product3 = new Product();

        product1.name = "Laptop";
        product1.price = 50000;

        product2.name = "Mobile";
        product2.price = 20000;

        product3.name = "Headphone";
        product3.price = 3000;

how to allocate space, class variable is the key thing to create , we two non static variable in product class right, so we can able to create multiple object to create multiple space ,

first class name ,

product product1 = new product()

product
product()-- these two are class names where we create non static variable ,

product1 is variable we can give any name

after that product 1 is the object to use non static variable

so create,

product1.name = "laptop"
 product1.price = 50000;

plaintext
Here we assigned a value for name and price only for product1,
now we can able to print


        System.out.println(product1.name + " : " + product1.price);

plaintext
we can able to create many object based on the needs.

In another same program

public class Index {
    String name;
    int price;
    public static void main(String[] args) {

        Index product1 = new Index();
        Index product2 = new Index();
        Index product3 = new Index();

        product1.name = "Laptop";
        product1.price = 50000;

        product2.name = "Mobile";
        product2.price = 20000;

        product3.name = "Headphone";
        product3.price = 3000;

        System.out.println(product1.name + " : " + product1.price);
        System.out.println(product2.name + " : " + product2.price);
        System.out.println(product3.name + " : " + product3.price);

    }

}

plaintext

what the diff is ?

class Product {

    String name;
    int price;

}

This only the main difference , here we create the non static variable in same class .

Differences between static and non static variables

Static	Non-static
One copy for the whole class	One copy per object
Shared	Not shared
Access using class name	Access using object

Object , Class , Inheritance

subash — Thu, 25 Jun 2026 16:17:14 +0000

OOPS

It is a programming paradigm that organizes code using object and classes.

First we will discuss about what is paradigms?

we can solve the problem using different programing way or diff programs solve the same problem. those things are collectively called paradigms.

Before learning advanced Java concepts such as polymorphism and abstraction, it is essential to understand three fundamental concepts:
Class
Object
Inheritance

What is class ?

we let's imagine class is a design of the bike , object is real bike , there is no bike without design and there is no object without class, but class is avail without object. class will determine what the behaviors of object.

object

An object is a actual things created from the class, class is a blueprint

inheritances

If one class have some code that code access by another class that we called inheritances.

Remove unwanted space in through forloop in python

subash — Thu, 25 Jun 2026 15:16:27 +0000

How to remove extraspace between the word

sentence = 'how           are           you'
result = ""
first_space = True
for letter in sentence:
    if letter !=" ":
        result +=letter 
        first_space = True
    elif first_space==True:
        result += " "
        first_space = False
print(result)

OUTPUT:

Explanation :

First we create sentence variable that have the content "how are you" with extra space , we want to remove extra space , that's the purpose of this program,
we create another variable that's called result that have empty string to store correct sentences without extra space.
we need to create one more variable to store boolean value

We create for loop :

for letter in sentence:

Here sentence we already know that is variable what we created , here what will happen is each letter in sentence variable also include space store store in letter variable , like first store 'h' and then second 'o' and then 'w', this loop will run until finish the character of sentences.

 if letter !=" ":
        result +=letter 
        first_space = True

here what was happened is letter have the first character of sentences that is h, now this condition will letter not equal to space(" "), if true result variable keep that character and this condtion last we gave first_space we put again true this will help to store the first empty space inbetween the word , until w it will collect , and then first space will come in letter then if condition will false , program will enter the elif part,

    elif first_space==True:
        result += " "
        first_space = False

here first space is true so space will store the result , and we gave firs_space = false , here after this not store space again , because if and elif both conditions will false, when letter variable return any spelling then again if condition is true and then first_space will true , again store first space , and first_space will false etc

this program will remove all the extra space,

JAVA Histories

subash — Wed, 24 Jun 2026 07:02:58 +0000

Before JAVA

C, C++, pascal these are only the programing language was used before java, then had some problem what is
1.Platform dependencies(software + hardware = plateform)
Here developer need to create separate version for different systems. this was taken time, cost and maintenance.
2.Memory Management
language like c, c++ required programmers to manually manage memory.
if programmer forgot to free memory then
1.memory leack accurred
2.Program crashed
3.system become slow

3.Security Issue:
c, c++ allows direct memory access.
This could cause
1.Buffer overflows
2.Crashes
3.Security vulnerabilities

4.Internet was Growing
Around 1990s,, the internet started growing so developer need a language like without plateform dependencies so.

Who created java?

Java was created by james gosling, in 1991 at sunmicrosystem.
In early stage we called oak , instead of java

How java solved the program

In traditional language;

C Code
↓
Windows Compiler
↓
Windows Program

but in java :

Java Code
↓
Java Compiler
↓
Bytecode (.class)
↓
JVM(Java Virtual Machine)
↓
Any Operating System

Problem Before Java	Java Solution
Platform dependent	JVM made it portable
Manual memory management	Garbage Collector
Security issues	No direct memory access
Internet applications difficult	Built-in networking support
Complex development	Simpler than C++

why java became popular:

because that is object oriented program

java support :
1.class
2.object
3.inheritance
4.Polymorphism

Strong Security

Java programs run inside the JVM.

advantages:
Memory safety
Better security
Fewer crashes

Rich Libraries

Java comes with libraries for:

Networking
File handling
Collections
Database access
GUI development

Java Impact

Java became one of the most successful languages in history.

Enterprise applications
Banking systems
Android apps (historically)
Web applications
Backend servers
Cloud systems
Big Data tools

Examples:

Amazon
Netflix
LinkedIn

java flow

English --[JDK(compiler)]-- byte code --(JIT compilar)--->0,1(binary)

JDK -- stands for Java Development Kit , which is used to find out syntax error and exception ,

JDK is Platform independent

after byte code all are consider as Java Runtime Environment

Java Runtime Environmen have Java Virtual Machine(jvm)

JVM have JIT Compiler

Python Beginner Practise

subash — Sun, 07 Jun 2026 12:41:30 +0000

count = 0
while count < 5:
    print("1", end=" ")
    count+=1

OUTPUT;

count = 1
while count <= 5:
    print(count, end=" ")
    count+=1

OUTPUT;

while count <= 9:
    print(count, end=" ")
    count+=2

OUTPUT;

count = 3
while count <= 15:
    print(count, end=" ")
    count+=3

OUTPUT;

count = 15
while count >= 3:
    print(count, end=" ")
    count-=3

OUTPUT;

count = 10
while count >= 2:
    print(count, end=" ")
    count-=2

OUTPUT;


count = 9
while count >= 1:
    print(count, end=" ")
    count-=2

OUTPUT;

count = 1
while count <= 100:
    if count % 3 == 0 and count % 5 == 0:
        print(count)
    count+=1

OUTPUT;


count = 1
while count <= 100:
    if count % 3 == 0 or count % 5 == 0:
        print(count)
    count+=1

OUTPUT;

10.

givennumber = 15
count = 1
while count <= givennumber:
    if givennumber % count == 0:
        print(count)
    count+=1

OUTPUT;

11.

givennumber = 15
count = 1
total = 0
while count <= givennumber:
    if givennumber % count == 0:
        print(count)
        total+=count
    count+=1    

print("total :",total)

OUTPUT;

12.



givennumber = 15
count = 1
total = 0
while count <= givennumber/2:
    if givennumber % count == 0:
        print(count)
        total+=count
    count+=1    
if total == givennumber:
    print("perfect number because total and givennumber are same")
else:
     print(" not a perfect number,because total and givennumber are not same")

output;

13.

givennumber = 37

if givennumber < 2:
    print("not a prime number")
else:
    count = 2

    while count <= givennumber//2:
        if givennumber % count == 0:
            print("not a prime number")
            break
        count += 1
    else:
        print("prime number")

OUTPUT;

14.







references
https://dev.to/sivakumar_mathiyalagan_/python-exercise-37cg

React project using useState, useContext , useNavigate and browser Router

subash — Fri, 29 May 2026 14:49:12 +0000


import { createContext, useState } from "react";
import {BrowserRouter, Route, Routes, Link} from "react-router-dom"
import Dashboard from "./dashboard";
import Loginpage from "./loginpage";
import Profilepage from "./Profilepage";

export const userContext = createContext();
function App(){
const [name, setName] = useState("")
return(
    <>
    <userContext.Provider value = {{name, setName}}>
        <BrowserRouter>
        <Link to="/">profilepage</Link>
        <Link to="/dashboard">Dashboard</Link>

        <Link to="/loginpage">Loginpage</Link>
        <Routes>
            <Route path="/" element={<Profilepage/>}/>
            <Route path="/dashboard" element={<Dashboard/>}/>
            <Route path="/loginpage" element={<Loginpage/>}/>   
        </Routes>
        </BrowserRouter>
    </userContext.Provider>
    </>
)
}

export default App;

This is App component connect here we will assign the path through the route and create Link, to go another component, it is the replacement of tag, userContext is used to share the data components together easily, it is the solution of props drilling also,

First we create use navigate and we put it that in variable , that variable is userContext at the same time we should export it, then we create a function App() after that function we should export that function, because after export only we can able to connect component together,
Link only present in inside the BrowserRouter.

then create variable through the useState inside the App function

then we write return () , return only able to keep only one div, so w should create one div and we put these in it. inside return we should provide .

import { useContext } from "react";
import { userContext } from "./App";
import { useNavigate } from "react-router-dom";

function Loginpage(){
     const {setName} = useContext(userContext);
     const navigate = useNavigate();

     function handleClick(){
        navigate("/dashboard")
     }

     return(

     <>
     <h1>Login page</h1>
     <input type="text" placeholder="entername" onChange={(e) => setName(e.target.value )} />

     <button onClick={handleClick}>login</button>

     </>)



}

export default Loginpage;

import { useContext } from "react";
import { userContext } from "./App";
import { useNavigate } from "react-router-dom";
import Profilepage from "./Profilepage";

function Dashboard(){
    const {name} = useContext(userContext);
     const navigate = useNavigate();

     function logout(){
        navigate("/")

     }

     return(

     <>
     <h1>Dash Board</h1>

     <h2>welcome {name}</h2>


     <button onClick={logout}>logout</button>

     </>
     );



}

export default Dashboard;

import { useContext } from "react";
import { userContext } from "./App";
function Profilepage(){
  const { name } = useContext(userContext);
    return (
    <div>

      <h1>Profile Page</h1>

      <h2>User Name : {name}</h2>

    </div>
  );
}

export default Profilepage;

Logical while loop for beginner through the story

subash — Thu, 28 May 2026 13:46:35 +0000

1.train1 is stop every 3rd station and train2 is stop every fifth station , we should print train 1 ,every 3rd station and train 2 every 5th station , if two trains meet same station then we print both ?

train = 0
while train < 30:
    train = train + 1 

    if train % 3 == 0 and train % 5 == 0:
        print("both")

    elif train % 3 == 0:
        print("Train1")
    elif train % 5 == 0:
        print("Train2")

output:

Here train is count of station , and while loop condition is train less than 30 , then train will increase by one in inside the while loop,
then we do if and elif , first if, if train divisible by 3 and 5 then i print "both", elif train divisible by 3 then we will print train1 and elif train divisible by 5 then train2 what we print.

Here we should put the (and) condition first why because if we put 3 or 5 of instead of both , then what will happen is incase if condition get true then elif not working. we also want to both divisible of 3 and 5 right.in case 3 and 5 also get divisible at that time if we put 3 divisible in if condition incase that will true then elif condition will not work , so we missed the both train meeting station.

2.Train1 will stop everry 3rd station , train 2 will stop every 8th station , we should print the station no and station count and which is last station number?


train = 0
count = 0
while train < 300:
    train = train + 1 

    if train % 3 == 0 and train % 8 == 0:
        count+=1
        print("station no :",train)
print("totalstation is ",count)

Output:

same concept like except some condition,
here we create count variable to print total count station where is two train will meet, and we print all stations numbers.

we have to duscuss about how to print last station .

while loop through the story

subash — Wed, 27 May 2026 12:15:44 +0000

In this story one thief and one police , there is 40feet distance between them, thief try to escape from police , but he to cover only 2 feet in a step, but police cover 5 feet in a single step, police how many feets needs to catch thief ?

theif = 40
police = 0

while theif > police:
    theif += 2
    police += 5
print(theif)

OUTPUT;
68

First we create variable for thief and police , police is 0 and thief is 40 , because 40 is the distances of them , then we create while loop when police greater than thief , this while loop is stop, inside the while loop increase by 2 and police increase by 5 feet after while loop end , i was printed thief.
now we understand police needs 68 feet to catch thief

In this story there are two trains , train1 is stop every third station , and train2 is stop every 5th station , Question is which station these two trains will meet.

train = 0

while train < 30:
    train = train + 1 

    if train % 3 == 0 and train % 5 == 0:
        print("train will meet in ", train)

OUTPUT:
train will meet in 15
train will meet in 30

First i created one variable commonly train and it's value is 0 , i set while loop condition with in 30 that's mean until 29 this while will run , then inside while loop have train = train + 1,
and if condition , what the if condition is if train count is divisible by 3 and 5 then this condition will true , then execute what inside the condition , now print
train will meet in 15
train will meet in 30

we have confusion in 30 , like how it run because while loop condition is < 30 , after that in inside of while loop 29 +1 , then only we did if condition so it will print (30).

While loop and factorial

subash — Tue, 26 May 2026 14:15:15 +0000

Frog is fallen 50 feet borewell, each day that will go up 2 feet and return down 1.25 feet , question is how days needs to frag come out of the borewell, we have to create code for this senario.


feet = 50
up = 2
down = 1.25
day = 0
while feet>0:
    feet = feet - up + down
    day = day + 1
print(day);

OUTPUT;
67

Here what was happened is we create variable and value for feet, up , down and day,
then we create while loop , while loop condition is when feet is greater than 0 then the loop will run,
what inside the loop have is feet = feet - up + down
frag jump 2 feet per day and again down 1.25 feet so we add that,
each time while running day one increase when the while condition false then print day will work because this print is present outside of the loop.

#Additive Identity
0 is additive identity
because all number are return same value while addition with anynumber that same number will return

Multiplicative Identity

1 is multiplicative identity
because all number are return same value while multiple with anynumber that same number will return

Factorial

Factorial means multiplying from 1 to n.

3!=1×2×3=6

3!=3×2×1=6

because multiple order is not change the result

First N Numbers Sum

Standard way:

1+2+3=6

It can also be:

3+2+1=6

Both are correct

Formula for first n number:

n * (n+1)/2

Python Basics for Begginer

subash — Mon, 25 May 2026 14:50:39 +0000

Python is one of the most easiest language, why because,It allows humans to think naturally and write code almost like English. That is the real reason Python became powerful also it removes unnecessary complexity.

Today, Python is used in:

Artificial Intelligence
Cybersecurity
NASA projects
Automation
Data Science
Web Development
Robotics

Condition statement;

Conditional statements help Python decide which code should execute and which code should not execute.

#1. conditional statements:

Programs cannot make decisions

Every line of code would execute in the same order

Applications would not become interactive or smart

2.Conditional statements make programs:

Intelligent

Dynamic

Interactive

Flexible

Loop Statement

Looping statements are used in Python to execute a block of code repeatedly without writing the same code again and again.
Without loops, programmers would need to write repetitive code manually, which makes programs lengthy.

program:

EXAMPLE 1;

count = 1
while count<=5:
    print(count*2, end=' ')      
    count=count+1
print(count)
print(count*2)

end is parameter

In default python put \n in end parameter ,

\n - this means print next line.
Here remove that default \n that's why output is like sequences but 8 have \n so 10 was added that sequences but 10 in default end='\n' that why 12 was gone to next line.

OUTPUT;
2 4 6 8 10 6
12

EXAMPLE -2

count = 1
while count<=5:
    print(count*2 )       #print(1, end='\n')
    count=count+1
print(count)
print(count*2)

I already told you in default end = '\n"

OUTPUT:
2
4
6
8
10
6
12

sep(separate parameter):

print(1, 2, 3, sep='-')

OUTPUT;
1-2-3

Refferal link;

https://dev.to/hariharan_sj_2003/the-backbone-of-python-conditions-and-loops-182j

what is useSate and useEffect

subash — Mon, 25 May 2026 11:24:16 +0000

useState;

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

count - is the variable
[count, setCount] - Array Destructuring
useState(0)- function call with arugument 0
this 0 will store in count variable , we can not able to change the variable directly so we should call the setCount function to change the variable value through the arugument.

what is the purpose of useState is , if we put normal variable like
let count = 0 ; then if there is any need to make variable dynamic through the loop, then it will not work because , here we write code in components right, we should call the function name what inside the components , first time only appear the variable value in UI , because we call only one time to render that function, so if we use useState then the component will automatically rerender when the changes will happen.

useEffect

What is a Side Effect?

import { useEffect, useState } from "react";

function App() {

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

  useEffect(() => {
    console.log("Count Updated");
  }, [count]);

  return (
    <>
      <h1>{count}</h1>

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

export default App;

A side effect means:

Fetching data from API
Updating DOM
Setting timers
Using local storage
Running code after rendering

Easy Real-Life Example

Imagine:

Your main job = Cooking food

While cooking:

answering phone
setting timer
opening fridge

These are not the main cooking task.

They are “side tasks”.

Similarly in React:

Rendering UI = Main work
API calls / timers = Side effects

concept

useEffect(() => { console.log("Count Updated"); }, [count]);

React watches count
Whenever count changes, useEffect runs

2.useEffect(() => {
console.log("Count Updated");
}, []);
It will NOT run again

3.useEffect(() => {
console.log("Count Updated");
});

every rerender it will work

Code	Runs When
`[count]`	When `count` changes
`[]`	Only once
No array	Every render

StrictMode

It helps developers:
find errors
detect unsafe code
identify deprecated features
improve React applications

CONTROL FLOW STATEMENT

subash — Fri, 22 May 2026 16:08:26 +0000

Programming Rules:
1) Don't say I don't know
2) Let me Try
3) Known To Unknown
4) Don't Think about entire output
5) Think about very next step
6) Introduce variable if you feel it is necessary
7) Micro To Macro

BOX is memory to store,

a=10

a is references variable

now we change

a = a+5

now a value is 15 but , that box is not changed , the value will modify in the same box or memory.

count = 1
while count<=5:
print(1, end=' hi ')
count=count+1

indefault /n in end , that means print next line