DEV Community: Arun

Display flex Display inline Display block

Arun — Wed, 24 Sep 2025 17:24:55 +0000

display: flex

Turns a container into a flex container.

The direct child elements inside it become flex items.

Items can be easily aligned horizontally or vertically.

👉 Example:

.container {
display: flex;
}

This arranges items inside .container in a row by default.

display: inline

Makes the element behave inline, meaning it flows with text, doesn’t start on a new line, and only takes as much width as needed.

You cannot set width/height properly on inline elements.

👉 Example:

span {
display: inline;
}

display: block

Makes the element a block-level element.

Always starts on a new line and takes full available width by default.

You can set width, height, padding, and margin.

👉 Example:

div {
display: block;
}

flex-wrap (wrap)

Works only with display: flex.

Controls whether flex items stay in one line or move (wrap) to the next line if there’s not enough space.

👉 Example:

.container {
display: flex;
flex-wrap: wrap;
}

nowrap → (default) all items in one line, shrink if needed.

wrap → items move to the next line.

wrap-reverse → items wrap but in reverse order.

BASICS OF HTML CSS JAVASCRIPT

Arun — Fri, 19 Sep 2025 19:26:02 +0000

**1. What is HTML?

Definition: HTML (HyperText Markup Language) is the standard language used to structure content on the web.

Purpose: It defines the skeleton of a webpage (headings, paragraphs, images, links, forms, etc.).

Nature: It is a markup language, not a programming language.

Tag vs Element

Tag: The keyword enclosed in angle brackets (< >) like

, .

Element: The complete structure, including the start tag, content, and end tag. Example:

Hello

Difference: A tag is just the marker, but an element is the full unit (tag + content).

Framework vs Library

Library: A collection of reusable functions you can call when needed (e.g., jQuery, Lodash).

Framework: Provides a structured environment where it often calls your code (e.g., React, Angular).

Key Difference: With a library, you control the flow. With a framework, it controls the flow (Inversion of Control).

What is CSS?

Definition: CSS (Cascading Style Sheets) styles the HTML content.

Purpose: It controls design, layout, and appearance (colors, fonts, spacing, animations).

Nature: It separates structure (HTML) from presentation (CSS).

What is JavaScript (JS)?

Definition: JS is a programming language that makes web pages interactive and dynamic.

Purpose: It enables things like form validation, sliders, dropdowns, and real-time updates.

Nature: Runs in the browser (client-side), but can also run on servers (e.g., Node.js).

What is a List?

A list in HTML is used to group related items together in a structured way.

Lists help in organizing content (like menus, steps, or collections).

HTML supports different types of lists depending on the need.

Types of list

Types of Lists

A. Ordered List (

Items are displayed in a specific order (numbers, roman numerals, letters).

Each item is wrapped in

(list item).
Example: Steps in a recipe or procedure.
1. Wake up
2. Brush teeth
3. Have breakfast
Output (Ordered List)
1. Wake up
2. Brush teeth
3. Have breakfast
B. Unordered List (

This and Super keyword

Arun — Wed, 10 Sep 2025 16:45:02 +0000

****👉 What is this keyword in Java?

✓✓ this is a reference variable in Java.

✓✓ It always refers to the current object of the class.

✓✓ Used to avoid confusion and to make code clear.

✓✓ this can be used to call constructors or methods of the same class.

✓✓ this represents the object through which the method or constructor is called.

,👉 Why we use this keyword?

Differentiate instance variables and local variables when they have the same name.
Call another constructor in the same class (constructor chaining).
Pass the current object as a parameter to another method or constructor.
Return the current object from a method.
To call current class method
To call current class constructor

🔹👉 When we use this keyword?

✓✓ When local variables and instance variables have the same name.

✓✓ When we want to call another constructor inside the same class.

✓✓ When we need to refer to the current object inside a method or constructor.

🔹 Example Program (using this keyword to differentiate variables)

class Student {
int rollno;
String name;

// Constructor with local variables having same names as instance variables
Student(int rollno, String name) {
    this.rollno = rollno;   // 'this' refers to instance variable
    this.name = name;       // differentiates instance variable from local variable
}

void display() {
    System.out.println("Roll No: " + this.rollno);
    System.out.println("Name: " + this.name);
}

}

public class Main {
public static void main(String[] args) {
Student s1 = new Student(101, "Arun");
Student s2 = new Student(102, "Kumar");

    s1.display();
    s2.display();
}

}

Output
Roll No: 101
Name: Arun
Roll No: 102
Name: Kumar

👉 What is super keyword?

✓✓ super is a reference variable in Java.

✓✓ It is used to refer to the immediate parent class object.

👉 Why super keyword is used?

We use super mainly for three purposes:

To call parent class constructor
→ super() is used inside a child class constructor to call the parent’s constructor.
To access parent class variables
→ If child and parent have same variable names, we can use super.variableName to access the parent’s variable.
To access parent class methods
→ If child overrides a parent method, we can call the parent’s method using super.methodName().

👉 When super is used?

✓✓ Inside a constructor (to call parent’s constructor).

✓✓ Inside a method (to call parent’s variable or parent’s method).

✓✓ When there is overriding or same variable names in parent and child.

Example Program

class Parent {
int value = 100;

Parent() {
    System.out.println("Parent Constructor Called");
}

void display() {
    System.out.println("Parent display() method");
}

}

class Child extends Parent {
int value = 200;

Child() {
    super(); // calls Parent constructor
    System.out.println("Child Constructor Called");
}

void display() {
    super.display(); // calls Parent method
    System.out.println("Child display() method");
}

void showValues() {
    System.out.println("Child value: " + value);        // child variable
    System.out.println("Parent value: " + super.value); // parent variable
}

}

public class SuperDemo {
public static void main(String[] args) {
Child c = new Child();
c.display();
c.showValues();
}
}

Output

Parent Constructor Called
Child Constructor Called
Parent display() method
Child display() method
Child value: 200
Parent value: 100

CONSTRUCTOR IN OOPS

Arun — Wed, 03 Sep 2025 17:50:05 +0000

In OOPs (Object-Oriented Programming System), a constructor is a special method that is automatically called when an object of a class is created.

👉 It is mainly used to initialize objects (assign values to variables when the object is created).

Key Points about Constructor:

Name same as class → A constructor must have the same name as the class.
No return type → Not even void.
Called automatically → Executes when an object is created using new.
Used for initialization → Sets initial values for object variables.

Program
class Student {
int age;
String name;

// Constructor
Student(int a, String n) {
    age = a;
    name = n;
}

void display() {
    System.out.println("Name: " + name + ", Age: " + age);
}

}

public class Main {
public static void main(String[] args) {
// Object creation calls constructor
Student s1 = new Student(20, "Arun");
Student s2 = new Student(22, "Kumar");

    s1.display();
    s2.display();
}

}
Output
Name: Arun, Age: 20
Name: Kumar, Age: 22

Why we need constructors in OOPs?

Automatic Initialization

When you create an object, its variables get values immediately without calling any extra method.

Student s = new Student(20, "Arun"); // values set automatically

Code Simplicity

Without constructors, you would write a method like setData() and call it manually after creating the object.

Constructors remove this extra step.

Encapsulation Support

They help keep variables private and still allow controlled initialization.

Different Ways of Object Creation

With overloaded constructors (same name, different parameters), we can create objects in different ways.

Student s1 = new Student(); // default constructor
Student s2 = new Student(20, "Arun"); // parameterized constructor

Readability & Maintainability Code becomes more organized because initialization is tied to object creation.

Example without constructor
class Student {
int age;
String name;

void setData(int a, String n) {
    age = a;
    name = n;
}

}

public class Main {
public static void main(String[] args) {
Student s = new Student();
s.setData(20, "Arun"); // must call method separately
}
}

Example With Constructor

class Student {
int age;
String name;

Student(int a, String n) {
    age = a;
    name = n;
}

}

public class Main {
public static void main(String[] args) {
Student s = new Student(20, "Arun"); // initialized automatically
}
}

Polymorphism in OOPS

Arun — Mon, 01 Sep 2025 18:12:01 +0000

✓✓Polymorphism means “many forms”.
✓✓In OOP, it allows one entity (method or object) to perform different tasks in different scenarios.

🔹 Types of Polymorphism in Java:

Compile-time Polymorphism (Method Overloading)

✓✓Same method name but different parameter list.

✓✓Decided at compile time.

Runtime Polymorphism (Method Overriding)

✓✓Same method name, same parameters, but defined in parent and child classes.

✓✓Decided at runtime using dynamic method dispatch. at runtime using dynamic method dispatch.

Program
Method Overloading (Compile-time)

class Calculator {
// Method with 2 parameters
int add(int a, int b) {
return a + b;
}

// Method with 3 parameters
int add(int a, int b, int c) {
    return a + b + c;
}

}

public class Main {
public static void main(String[] args) {
Calculator calc = new Calculator();

    System.out.println("Sum of 2 numbers: " + calc.add(10, 20));
    System.out.println("Sum of 3 numbers: " + calc.add(10, 20, 30));
}

}

🔹 Output:

Sum of 2 numbers: 30
Sum of 3 numbers: 60

Example 2: Method Overriding (Runtime Polymorphism)

class Animal {
void sound() {
System.out.println("Animal makes a sound");
}
}

class Dog extends Animal {

void sound() {
    System.out.println("Dog barks");
}

}

class Cat extends Animal {

void sound() {
    System.out.println("Cat meows");
}

}

public class Main {
public static void main(String[] args) {
Animal a1 = new Animal();
a1 = newDog();
a1.sound();

   a1 = newCat();
   a1.sound();
}

}

🔹 Output:

Dog barks
Cat meows

Test in java

Arun — Sun, 31 Aug 2025 08:05:11 +0000

**Rules for identifiers in java

✓ In Java, an identifier is the name you give to classes, methods, variables, interfaces, etc.
✅ Rules for Identifiers in Java:

Allowed characters Letters (A-Z, a-z) Digits (0-9) Underscore (_) Dollar sign ($) 👉 Example: myVar, student_name, $_count
Must not begin with a digit
Invalid - 1number
Valid - number1
No special characters or spaces (except _ and $)
Invalid - my-name, first name
Valid - myName, first_name
Cannot be a reserved keyword (like int, class, static, if)
Invalid: class
Valid: className
Case-sensitive
Student and student are different identifiers
No length limit:
✓ You can make identifiers very long, but short and meaningful names are recommended.
Convention rules (not enforced by compiler but recommended):

✓ Variables & methods → start with a lowercase letter (studentAge, calculateSum())

✓ Classes & interfaces → start with an uppercase letter (Student, CarDetails)

✓ Constants → written in UPPERCASE with underscores (MAX_VALUE, PI)

**Example Program
class StudentDetails {
int studentAge;

String studentName;

void displayInfo() 
{
 System.out.println(studentName + " is " + studentAge + " years old.");
}

}

Declaration (Declarisation) ✓✓ Declaration is the process of introducing a variable in a program by specifying its data type and name. At this point, memory is reserved for the variable, but it does not yet have a value (unless given a default).

📌 Syntax:
datatype variableName;
📌 Example:
int age; // declaration
String name; // declaration
Here, age is declared as an integer, name as a string.

Initialization ✓✓ Initialization means assigning an initial value to a declared variable. ✓✓ It can happen at the time of declaration or later in the code.

📌 Syntax:
datatype variableName = value;
📌 Example:
int age = 20; // declaration + initialization
String name = "Arun"; // initialized with value
Here, age is initialized with 20, name with "Arun".

Compiler and Interpreter

Compiler

Translates the entire program (source code) into machine code at once.

Execution is faster.

Example: C, C++ use compilers.

Interpreter

Translates the program line by line and executes it immediately.

Execution is slower.

Example: Python, Java (partly) use interpreters.

👉 Java uses both:

Java code is compiled by javac (compiler) into bytecode.

Then the JVM (Java Virtual Machine) interprets/executes the bytecode.

Class and Object

Class → A blueprint/template that defines properties and behaviors.

Object → A real-world entity created from the class.

✅ Example:

class Car {
String color;
void drive() {
System.out.println("Car is driving");
}
}

public class Main {
public static void main(String[] args) {
Car myCar = new Car(); // Object creation
myCar.color = "Red";
myCar.drive();
}
}

ASCII and Unicode

ASCII (American Standard Code for Information Interchange)

7-bit code (128 characters).

Covers English letters, digits, symbols.

Example: ‘A’ = 65, ‘a’ = 97.

Unicode

16-bit or more (65,536+ characters).

Supports all languages (English, Tamil, Hindi, Chinese, etc.).

Java uses Unicode for characters.

Basics of java

Arun — Fri, 29 Aug 2025 18:21:20 +0000

Declaration (Declarisation) ✓✓ Declaration is the process of introducing a variable in a program by specifying its data type and name. At this point, memory is reserved for the variable, but it does not yet have a value (unless given a default).

📌 Syntax:
datatype variableName;
📌 Example:
int age; // declaration
String name; // declaration
Here, age is declared as an integer, name as a string.

Initialization ✓✓ Initialization means assigning an initial value to a declared variable. ✓✓ It can happen at the time of declaration or later in the code.

Program Execution Life Cycle in Java

Write the Code
✓✓ You write the Java program in a .java file using an editor or IDE.
**Example: Hello.java
Compile the Code
✓✓ The Java compiler (javac) compiles the .java file into bytecode.

Output : A . class file is created.
**Example: Hello.class

Class Loader
✓✓ When you run the program, the Class Loader loads the .class file into JVM memory.
✓✓ It handles loading, linking, and initialization of classes.
Bytecode Verification
✓✓ JVM’s Bytecode Verifier checks the .class file for security and correctness (e.g., no illegal code, stack overflow issues
JVM Execution
✓✓ The Interpreter reads bytecode instructions one by one and executes them.
✓✓The JIT Compiler (Just-In-Time) may also compile frequently used bytecode into native machine code for better performance.
Execution in OS
✓✓ The translated code finally executes as native instructions on the operating system and hardware.
Program Output
✓✓The program produces the result/output on the console.

What is methods and types of methods in java ?

✓ A method in Java is a block of code that performs a specific task, executes when it is called, and can return a value or be void.

👉 In simple words: A method is like a function in other languages, used for code reusability and modularity.

***Syntax of a Method
returnType methodName(parameters) {
// method body
// statements
return value; // if returnType is not void
}
Types of Methods in Java

Built-in Methods (Predefined methods) ✓✓ Provided by Java libraries (inbuilt).
User-defined Methods ✓✓ Created by the programmer to perform custom tasks.

Rules for identifiers in java

✓ In Java, an identifier is the name you give to classes, methods, variables, interfaces, etc.
✅ Rules for Identifiers in Java:

Allowed characters Letters (A-Z, a-z) Digits (0-9) Underscore (_) Dollar sign ($) 👉 Example: myVar, student_name, $_count
Must not begin with a digit
Invalid - 1number
Valid - number1
No special characters or spaces (except _ and $)
Invalid - my-name, first name
Valid - myName, first_name
Cannot be a reserved keyword (like int, class, static, if)
Invalid: class
Valid: className
Case-sensitive
Student and student are different identifiers
No length limit:
✓ You can make identifiers very long, but short and meaningful names are recommended.
Convention rules (not enforced by compiler but recommended):

✓ Variables & methods → start with a lowercase letter (studentAge, calculateSum())

✓ Classes & interfaces → start with an uppercase letter (Student, CarDetails)

✓ Constants → written in UPPERCASE with underscores (MAX_VALUE, PI)

**Example Program
class StudentDetails {
int studentAge;

String studentName;

void displayInfo() 
{
 System.out.println(studentName + " is " + studentAge + " years old.");
}

}

What is Datatypes in java ?

✓ A data type in Java is a classification that specifies which type of value a variable can hold and what kind of operations can be performed on it.

In simple words:
👉 Data type tells the compiler and JVM what kind of data (numbers, characters, text, true/false, etc.) is stored in a variable.

**Example Program
int age = 25; // int → stores integer values
double salary = 4500.50; // double → stores decimal values
char grade = 'A'; // char → stores a single character
boolean flag = true; // boolean → stores true/false

Types of datatypes

Primitive Data Types
Non primitive Data Types

What I learned today ?

Arun — Thu, 28 Aug 2025 16:23:59 +0000

***** 1. What is parameter and non - parameter in java?
Parameter
✓ parameter in Java is a variable that is declared inside the parentheses of a method or constructor
✓ It is used to receive values (called arguments) when the method or constructor is invoked.
✓ Parameters allow methods to be dynamic and reusable, because they can accept different input values at runtime.
Examples:
void add(int a, int b)
{ // a and b are parameters.

System.out.println(a + b);
}
Non - Parameter
✓ Non-parameter method or constructor in Java is one that does not take any input values.
✓ It has empty parentheses and performs its task using fixed logic or by accessing instance variables directly.
✓ Non-parameter methods are useful when no external input is required.
Example:
void showMessage()
{ // no parameters
System.out.println("Welcome to Java!");
}
**

Parameters and Non Parameters

Arun — Wed, 27 Aug 2025 12:06:17 +0000

A Parameterized method takes input values when called, while a non - parameterized method does not takes input values.

class Example {
void greet() {
System.out.println("Hello!");
void greet(String name) {
System.out.println("Hello " + ALEX);
}
}

GREET -> No parameters
GREET("ALEX") -> With Parameters
**
**Prithiv sir assigned some tasks which I completed successfully and uploaded to Gitlab.Through these tasks,I learned new concepts, applied them in practical coding and improved my problem solving skills.I maintained clean code with proper documentation and shared my updates consistently.Looking forward to taking on more challening tasks and growing futher.

Gitlab link - https://gitlab.com/Gitlab202515/rohit/-/tree/ec87c17c629a679d380e5fecb07b25e5cb2bb7f5/

JAVA Notes

Arun — Tue, 26 Aug 2025 12:08:10 +0000

Toady at payilagam Institute, I revised and practiced multiple programming concepts in java. I also pushed my programs to Gitlab* and shared the updates with prithiv sir for feedback. This give me more clarity on the basics of java and improved my coding confidence.

The Topics I have covered so far are:

Keywords - Reserved words in java with predefined meaning
Example - class,pubic.
Tokens - Smallest elements of a program
Example - Keywords, Identifiers,Literals.

3.Identifiers - Names for variables,classes,method,etc.

4.Rules for Identifiers - Cannot start with digits.
- No keywords , case-sensitive and $ allowed.

5.Literals - Fixed values like numbers,strings,characters,and
booleans.

6.Declaration and Initialization - Declaration creates a variable.
- Initialization assigns value.

7.Features of java - Platform - independent,Object-oreinted,
secure and protable.

8.History of java -Created by James Gosling (1991),released in 1995

by Sun Microsystems

9.Operators - Used to perform operations (Arithmetric ,Relational,
Logical,Assignment).

10.Datatypes - Datatypes are diveded into types
1.primitivedatatypes[int,float,double,boolean,etc]
2.Non - primitive datatypes.

11.Class - Blueprint or template for creating objects.

12.Object - Instance of class with state (variables) and

Behaviour(Method)

13.Methods and types - Block of code performing tasks.
types - Predefined and user defined.

Number system and conversions-Binary,Octal,Decimal,Hexadecimal.

15.Local and Instance variables - Local - Inside methods.
Instance - inside class but outside methods.

16.Compiler - compiler converts source code into bytecode
.
17.Interpreter - java visual machine interprets bytecode line by
line.

18.Installing and Running java - Install JDK,set path,write program,
compile with javac,run with java.

19.Program Excetion life Cycle - Source code -> Compilation->Bytecode
-> JVM -> Output.

I have uploaded all the programs I practised here :

Gitlab Repository Link : https://gitlab.com/Gitlab202515/rohit/-/tree/beff5b6624527f1310d35d61ecc53eb37908a09d/

Overall,Today's session helped me strengthen my basics,gain practical coding knowledge, and pick up useful shortcuts for number stytem conversions.I fell more confident in moving towards the next level of programming.

DAY 6 OF PAYILAGAM INSTITUTE

Arun — Tue, 19 Aug 2025 03:22:02 +0000

Morning session - Java class

what is datatypes?
The type of data a variable can store in java

Types of datatypes

1.Primitive datatypes.
2.Non - Primitive datatypes.

What is operator?
Operator is a symbol that performs a specific operation on variables and values.

Types of operators in java:

1.Arithmetric operators
2.Relational operators
3.Logical operators
4.Assignment operators
5.Unary operators
6.Bitwise operators
7.Ternary operators

Evening session - Communication Class

1.Communication is not just speaking-it includes listening,body language, and clarity.
2.Good communication builds confidence and creates a positive impression.
3.Practicing communication daily improves fluency and confidence.

DAY 4 OF PAYILAGAM INSTITUTE

Arun — Fri, 15 Aug 2025 02:42:05 +0000

OPENING :
"Hey everyone! yesterday at payilagam institute,we had an amazing learning session all about Gitlab on Linux. it was super useful for our developer journey!"

CONTENT :
'Gitlab is a platform where we store,manage and track our code.we use it because it keeps our projects safe,allows teamwork,and shows the full history of changes.

Why we use Gitlab? - To collaborate,version control, and manage projects.

When we use Gitlab? - when working in terms,managing large codebases, or tracking code changes

Where we use Gitlab? - In software companies, open-source projects,and personal coding work.

How we use Gitlab? - Install Git on linux,clone,add the text file, commit the main and push projects, manage code via Gitlab's web or terminal commands

DEV Community: Arun

Display flex Display inline Display block

BASICS OF HTML CSS JAVASCRIPT

, .

My Website

About Me

This and Super keyword

CONSTRUCTOR IN OOPS

Polymorphism in OOPS

Test in java

Basics of java

What I learned today ?

Parameters and Non Parameters

JAVA Notes

DAY 6 OF PAYILAGAM INSTITUTE

DAY 4 OF PAYILAGAM INSTITUTE