README.md

Java Beginner to Developer

This repository documents my daily journey from Java basics to developer-level problem solving and system thinking.

Goals

• Build strong fundamentals
• Practice daily coding
• Prepare for backend & full-stack interviews

Structure

• Day-wise problems
• Clean and readable code
• Interview-oriented solutions

Day 1 – Java Basics & Setup

Topics covered:

• How Java works (JVM, bytecode, platform independence)
• Java program structure
• main method as JVM entry point
• Printing output using System.out.println
• Variables and basic data types

Code location:

• src/day01_basics/

Day 2 – Control Flow & Decision Making

Topics covered:

• if / else conditions
• Logical operators (AND, OR)
• switch statement
• Real-world business logic examples

Code location:

• src/day02_control_flow/

Day 3 – Loops & Iteration

Topics covered:

• for loop
• while loop
• do-while loop
• Loop-based logic problems

Code location:

• src/day03_loops/

Day 4 – Methods & Code Reusability

Topics covered:

• Creating custom methods
• Parameters and return types
• Writing reusable business logic

Code location:

• src/day04_methods/

Day 5 – Arrays & Iteration

Topics covered:

• Array declaration and initialization
• Accessing array elements
• Iterating through arrays
• Multi-dimensional arrays
• Common array operations

Code location:

• src/day05_arrays/

Day 6 – OOP Basics (Classes & Objects)

Topics covered:

• Class and object creation
• Constructors
• Instance variables
• Basic object behavior modeling

Code location:

• src/day06_oop_basics/

Day 7 – Encapsulation & Access Modifiers

Topics covered:

• Data hiding using private variables
• Getters and setters
• Controlled access to object state
• Access modifiers (private, public)

Code location:

• src/day07_encapsulation/

Day 8 – Inheritance

Topics covered:

• extends keyword
• super constructor
• Method overriding
• Code reuse through class hierarchy

Code location:

• src/day08_inheritance/

Day 9 – Polymorphism

Topics covered:

• Method overloading
• Method overriding with polymorphic behavior
• Runtime polymorphism using interfaces
• Upcasting and downcasting
• Polymorphic method calls

Code location:

• src/day09_polymorphism/

Day 10 – Abstraction

Topics covered:

• Abstract classes and abstract methods
• Difference between abstraction and inheritance
• Method overriding in abstract classes
• Runtime polymorphism using abstract classes
• Concrete methods inside abstract classes
• Real-world abstraction example (Bank system)

Code location:

• src/day10_abstraction/

Day 11 – Interfaces

Topics covered:

• Introduction to interfaces
• Implementing interfaces using implements
• Runtime polymorphism with interfaces
• Multiple inheritance using interfaces
• Real-world payment system example

Code location:

• src/day11_interfaces/

Day 12 – Exception Handling

Topics covered:

• try, catch, and finally blocks
• Handling multiple exceptions
• Understanding exception hierarchy
• Creating custom exceptions
• Using throw and throws
• Real-world bank withdrawal example

Code location:

• src/day12_exceptionhandling/

Day 13 – Collections Framework (Part 1)

Topics covered:

• Introduction to Java Collections Framework
• Working with ArrayList
• Working with LinkedList
• Using HashSet for unique elements
• Using HashMap for key-value storage
• Storing custom objects in collections

Code location:

• src/day13_collections/

Day 14 – Collections Framework (Advanced)

Topics covered:

• Using Iterator for traversal
• Implementing Comparable for natural sorting
• Using Comparator for custom sorting
• Sorting collections with Collections.sort()
• Working with TreeSet for automatic sorting

Code location:

• src/day14_collections_advanced/

Day 15 – File Handling (I/O)

Topics covered:

• Creating files using File class
• Writing data using FileWriter
• Reading data using FileReader
• BufferedReader and BufferedWriter usage
• Reading files line by line
• Appending logs to a file

Code location:

-src/day15_filehandling/

Day 16 – Multithreading (Basics)

Topics covered:

• Creating threads using Thread class
• Creating threads using Runnable interface
• Using sleep() method
• Understanding thread lifecycle basics
• Synchronization using synchronized keyword
• Preventing race conditions
• Using join() method

Code location:

• src/day16_multithreading/

Day 17 – Java 8 Features (Lambda & Streams)

Topics covered:

• Lambda expressions
• Functional interfaces
• Method references
• Streams API
• Filtering and mapping collections
• Using forEach with streams

Code location:

• src/day17_java8_features/

Day 18 – JDBC (Database Connectivity)

Topics covered:

• Connecting to MySQL using JDBC
• Creating tables using Statement
• Inserting data using PreparedStatement
• Retrieving data using ResultSet
• Updating records in database
• Using try-with-resources for resource management

Code location:

• src/day18_jdbc/

Day 19 – JDBC Mini CRUD Project

Topics covered:

• Building a console-based CRUD application
• Implementing DAO pattern
• Performing Insert, Select, Update, and Delete operations
• Using PreparedStatement for secure queries
• Structuring a real backend-style project

Code location:

• src/day19_jdbc_crud/

Day 20 – Introduction to Spring Boot

Topics covered:

• Understanding Spring Boot architecture
• Creating a Spring Boot project using Spring Initializr
• Building a REST controller
• Creating GET endpoints
• Running embedded Tomcat server
• Testing REST APIs in browser

Code location:

• day20_springboot/

##Day 21 – Spring Boot CRUD API

Topics covered:

• Creating a Spring Boot CRUD application
• Connecting Spring Boot with MySQL
• Using Spring Data JPA
• Implementing layered architecture (Controller, Service, Repository)
• Building RESTful endpoints

Code location:

-src/day21_springboot_crud/