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/