🧠 Java Training Hub – Problem Solving Sheets (1 to ∞)

🚀 A comprehensive and ever-growing repository for mastering Java programming through structured problem-solving sheets and backend-focused exercises.
This is part of my continuous journey to become a highly capable Backend Java Developer, building strong mental foundations in:

• Java Syntax & Core Principles
• OOP & Design Patterns
• Data Structures & Algorithms
• Multithreading & Concurrency
• Clean Code, SOLID, and Software Craftsmanship

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📘 Overview

This repository is structured into a series of progressive Java Problem Solving Sheets, starting from basic syntax and gradually advancing toward complex backend logic and real-world systems.

Each problem is solved using clean, modular, testable Java code, written in a way that promotes deep understanding, reusability, and engineering discipline.

🧠 Think of each sheet as a level in your mental gym – and the gym never closes.

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🚀 Topics & Skills Covered

• ✅ Basic Syntax & Variables – Java fundamentals, data types, operators
• ✅ Control Flow – if/else, loops, switch-case
• ✅ Functions & Recursion – Modular programming and recursive strategies
• ✅ Arrays & Data Structures – Arrays, Lists, Stacks, Queues, HashMaps, Sets
• ✅ Object-Oriented Programming (OOP) – Encapsulation, Inheritance, Polymorphism, Abstraction
• ✅ Design Patterns – Singleton, Factory, Strategy, and more
• ✅ Exception Handling – Robust error management & custom exceptions
• ✅ Algorithms – Searching, Sorting, Problem Solving
• ✅ Multithreading – Concurrency models and real-world thread use
• ✅ Clean Code & SOLID Principles – Write for humans, not just machines
• ✅ Modularization – Reusable components with separation of concerns

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📁 Folder Structure

The structure is open-ended and infinitely extensible:

src/ ├─ sheet1/ │ ├─ Sh1Pr1.java │ ├─ Sh1Pr2.java │ └─ ... ├─ sheet2/ │ └─ ... └─ sheetN/

Each sheet includes:

• 📄 Well-named Java classes (e.g., Sh5Pr2.java)
• 🧠 Inline problem descriptions where applicable
• 🧪 Testable & clean implementations with modular design
• 🧱 Built to reflect real backend workflows and encourage scalability

♾️ The sheet count keeps growing as learning continues.

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🧩 Sample Problems

🔸 Basic Syntax & Logic

• Hello World
• Swap Without Temp
• Even or Odd
• Find Largest of 3
• Sum of Digits

🔸 Control Flow

• Factorial with Loops
• Prime Number Detection
• Reverse Digits
• Fibonacci Sequence
• Armstrong Number Check

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📊 Infinite Progress Tracker

Sheet	Status	Focus Area
Sheet 1	✅ Completed	Java basics & intro problems
Sheet 2	✅ Completed	Arrays & simple data structure use
Sheet 3	✅ Completed	Strings & char manipulation
Sheet 4	✅ Completed	Patterns, nested loops
Sheet 5	✅ Completed	2D Arrays, matrices
Sheet 6	🟡 In Progress	Matrix logic & deeper conditions
Sheet 7	⏳ Upcoming	Intermediate structures & sorting
Sheet 8	⏳ Upcoming	Recursion & OOP combinations
Sheet 9	⏳ Upcoming	Dynamic programming & analysis
Sheet 10+	♾️ Endless	Real-world backend & architecture

🔁 The tracker reflects continuous improvement — not a final destination.

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🔮 What's Next?

This hub will keep expanding with:

• ✨ Recursive Problem Solving & Memoization
• ✨ Data Structures from Scratch – Linked Lists, Trees, HashMaps
• ✨ Multithreading Challenges – Runnable, Threads, Sync
• ✨ File Handling & Stream APIs
• ✨ JUnit & Integration Testing
• ✨ Mini Backend Systems – CLI projects, service layers, modular logic
• ✨ Controller-based Architecture – Preparing for scalable backend design

🎯 Goal: Build the mindset and codebase of a real software engineer — not just a student.

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🛠 Getting Started

1. Clone the Repository

git clone https://github.com/ehab-elshimi-developer/java-problem-solving-sheets.git

2. Open in Your Preferred Java IDE

💡 Recommended: IntelliJ IDEA or VS Code with Java Extension Pack

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3. Explore & Run

This repository follows a modular, auto-scalable structure powered by Generator.java.

Each set of problems is organized into folders:

src/
 ├─ sheet1/
 │   ├─ Sh1Pr1.java
 │   ├─ Sh1Pr2.java
 │   └─ ...
 ├─ sheet2/
 │   └─ ...
 └─ ...

✅ Naming Convention
ShXPrY.java → where X = sheet number, Y = problem number

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🔁 Run a Specific Problem

Update Main.java:

runProblem(6, 4); // Executes sheet6.Sh6Pr4

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🔄 Run a Full Sheet

testGeneratedSheet(6); // Executes Sh6Pr1 to Sh6Pr10

🧪 Reflection is used to dynamically load and invoke the .run() method of each class.

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⚙️ Use the Generator

Run Generator.java to:

• 🔍 Detect the latest existing sheet
• 🆕 Create the next sheet automatically (e.g., sheet7/)
• 🧱 Generate files like Sh7Pr1.java to Sh7Pr6.java
• 🛠️ Update Main.java for immediate execution

🧭 Whether you're starting with syntax or diving into algorithms — just generate and go.

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🏷️ Tags

Java Problem Solving Backend Development OOP
Data Structures Algorithms Multithreading Design Patterns
SOLID Principles Clean Code Modularization Exception Handling Reflection

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🤝 Contributing

This repo is part of a personal learning journey — but open to evolution.

If you’d like to:

• 💡 Suggest a new challenge
• 🛠 Improve an existing solution
• 🐞 Fix a bug
• ✨ Refactor structure or readability

Feel free to:

• 📥 Open an Issue
• 🔁 Submit a Pull Request

🙌 All contributions are welcome!

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👨‍💻 Author

Ehab Elshimi
🎯 Aspiring Backend Java Developer
📍 Egypt – Preparing for European opportunities
💡 Passionate about clean architecture & scalable systems
📬 ehabelshimi.dev@gmail.com
🌐 @ehab-elshimi-developer

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🧠 "Train your mind to solve problems like an engineer. Write code like you’re building a system, not just passing a test."
— Ehab Elshimi 🚀