[WIP] Add comprehensive learning guide for Java concepts

[Copilot]

• Create JAVA_CONCEPTS.md with the following sections:
  • SOLID Design Principles (S, O, L, I, D with code examples)
  • Multithreading (Thread creation, ExecutorService, Synchronization, CompletableFuture)
  • Immutability (concepts, implementation, benefits, Java Records)
  • Streaming & Messaging (Java Streams API, parallel streams, Kafka/RabbitMQ basics)
  • Caching (strategies, implementations, Redis, Spring Cache)
  • Security (SSL/TLS, JWT, OAuth 2.0, Spring Security)
  • Design Patterns (Factory, Decorator, Singleton, Observer)
  • Test-Driven Development (TDD cycle, JUnit 5, Mockito)
• Ensure all code examples are well-documented and beginner-friendly
• Use proper Markdown formatting with syntax highlighting

Original prompt

Create a detailed Markdown file (JAVA_CONCEPTS.md) that serves as a comprehensive learning guide for the following Java topics with detailed explanations and code examples:

Topics to Cover:

1. SOLID Design Principles

• Single Responsibility Principle (SRP)
• Open/Closed Principle (OCP)
• Liskov Substitution Principle (LSP)
• Interface Segregation Principle (ISP)
• Dependency Inversion Principle (DIP)
• Include Java code examples for each principle

2. Multithreading

• Thread creation (Thread class, Runnable, Callable)
• ExecutorService and Thread Pools
• Synchronization and Locks
• Concurrent collections
• CompletableFuture
• Include practical examples

3. Immutability

• What is immutability and why it matters
• How to create immutable classes in Java
• Benefits in multithreaded environments
• Java Records (modern approach)
• Include examples

4. Streaming & Messaging

• Java Streams API (map, filter, reduce, collect)
• Parallel streams
• Messaging concepts (Kafka, RabbitMQ basics)
• Include stream operation examples

5. Caching

• Caching strategies (LRU, TTL, etc.)
• In-memory caching
• Redis/distributed caching concepts
• Spring Cache abstraction
• Include implementation examples

6. Security

• SSL/TLS concepts and implementation
• JWT (JSON Web Tokens) - creation, validation, structure
• OAuth 2.0 flows and implementation
• Spring Security basics
• Include code examples

7. Design Patterns

• Factory Pattern - with Java example
• Decorator Pattern - with Java example
• Singleton Pattern - thread-safe implementations
• Observer Pattern - with Java example
• When to use each pattern

8. Test-Driven Development (TDD)

• TDD cycle (Red-Green-Refactor)
• JUnit 5 basics
• Mockito for mocking
• Writing testable code
• Include test examples

Requirements:

• Create the file at the root level of the repository as JAVA_CONCEPTS.md
• Use clear headings and subheadings
• Include detailed code examples for each topic
• Add explanatory comments in the code
• Make it beginner-friendly but comprehensive
• Use proper Markdown formatting with syntax highlighting for Java code blocks

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