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Java Newcomers Guide (Interview & Practice Edition)

Welcome to the Java side of this monorepo! This guide is designed for both beginners and those preparing for interviews, with a focus on hands-on learning and real-world application.

1. Key Directories & What You'll Find

  • src/main/java/com/: Business logic for the e-commerce and loan management system (Spring Boot based)
  • src/main/java/dsa/: Data structures and algorithms—great for interview prep and Java fundamentals
  • src/main/java/leetcode/: LeetCode and coding challenge solutions
  • test/java/: Unit and integration tests for both business and DSA code

2. Core Java Concepts to Master (with Examples)

  • OOP Principles: Classes, objects, inheritance, polymorphism, encapsulation, abstraction
    • See: ParentChildTest.java, ParentChildTest2.java, BuilderPatternOrder.java
  • Collections Framework: Lists, Sets, Maps, Queues, Stacks
    • See: ArrayListBST.java, MapsExample.java, CustomLinkedList.java
  • Exception Handling: try-catch, custom exceptions, checked vs unchecked
    • See: exception/ package in business logic, and DSA examples
  • Threads & Concurrency: Thread creation, synchronization, deadlocks
    • See: ThreadingExample.java, DeadlockExample.java, LocksExample.java
  • Streams & Lambdas: Functional programming in Java 8+
    • See: StreamExample.java, StreamExamples.java
  • String Manipulation: String methods, immutability, performance
    • See: StringMethodsExample.java

3. Interview-Oriented Practice

  • DSA Folder: Practice classic data structures (linked lists, trees, stacks, queues) and algorithms (sorting, searching, recursion)
  • LeetCode Folder: Real-world coding problems, often asked in interviews
  • Patterns: Builder, Singleton, Factory, etc. (see BuilderPatternOrder.java)
  • Java Language Features: Practice with generics, enums, annotations, and inner classes

4. Best Practices for Java Development

  • Follow Java naming conventions (CamelCase for classes, camelCase for variables/methods)
  • Keep classes focused and methods short
  • Use interfaces and abstract classes for extensibility
  • Prefer immutability where possible (use final)
  • Avoid magic numbers/strings—use constants
  • Write JavaDocs for public classes and methods
  • Use unit tests to verify logic (see test/java/)
  • Clean up unused code and imports before committing

5. Getting Started & Workflow

  1. Setup: Install JDK 11+ and an IDE (IntelliJ IDEA or Eclipse recommended)
  2. Build: Use Maven wrapper (mvnw.cmd clean install)
  3. Run Tests: mvnw.cmd test
  4. Explore: Start with simple DSA classes, then move to business logic
  5. Practice: Try modifying DSA/LeetCode examples or add your own

6. Interview Tips

  • Be able to explain OOP concepts with code examples
  • Practice writing and debugging code without an IDE (for whiteboard interviews)
  • Know the time/space complexity of your solutions
  • Be comfortable with Java 8+ features (lambdas, streams, Optionals)
  • Review exception handling and custom exceptions
  • Practice multi-threading basics and common pitfalls (deadlocks, race conditions)

For more details, see .github/copilot-instructions.md and the Spring Boot Newcomers Guide in .github/newcomers-spring-boot.md.