Core Java Fundamentals for Interviews (Beginner to Advanced)

🟢 SECTION 1: Introduction to Java & Setup

1. What is Java? Why Java is still relevant
2. Features of Java (Platform Independent, OOP, etc.)
3. JDK vs JRE vs JVM (Overview)
4. How Java Code Executes (Compilation → Bytecode → JVM)
5. Setting up Java Environment (JDK installation)
6. Writing Your First Java Program
7. Java Program Structure Explained

🟢 SECTION 2: Java Fundamentals (Core Concepts)

🔹 OOP Concepts

1. What is OOP?
2. Encapsulation (with real-world example)
3. Inheritance (Types + use cases)
4. Polymorphism (Compile-time vs Runtime)
5. Abstraction (Interface vs Abstract Class)
6. SOLID principles (basic intro)

🔹 Data Types & Variables

7. Primitive Data Types
8. Non-Primitive Data Types
9. Type Casting (Implicit vs Explicit)
10. Wrapper Classes
11. Final, Static keywords

🔹 Control Flow

12. If-Else, Switch Case
13. Loops (for, while, do-while)
14. Break & Continue

🔹 Arrays

15. Introduction to Arrays
16. Single vs Multi-dimensional arrays
17. Array vs ArrayList

🔹 Introduction to Collections & Streams

18. What is Collection Framework?
19. Intro to List, Set, Map
20. Introduction to Stream API
21. Lambda Expressions Basics

🟣 SECTION 3: String Handling (Interview Critical)

1. What is String in Java?
2. String Immutability (Why & Benefits)
3. String Pool (Memory Concept)
4. String Interning Explained
5. String vs StringBuilder vs StringBuffer
6. == vs equals() method
7. Important String Methods (substring, replace, etc.)
8. String Performance & Best Practices
9. Top String Interview Questions

🔵 SECTION 4: Collection Framework (Deep Dive) ⭐

🔹 List

1. List Interface Overview
2. ArrayList (Internal working + resizing)
3. LinkedList (Doubly Linked structure)
4. ArrayList vs LinkedList

🔹 Set

5. Set Interface Overview
6. HashSet (Internal working)
7. LinkedHashSet
8. TreeSet (Sorting + Red-Black Tree)

🔹 Map

9. Map Interface Overview
10. HashMap Internal Working (Bucket, Hashing) 🔥
11. HashMap vs Hashtable
12. LinkedHashMap
13. TreeMap

🔹 Advanced Concepts

14. Comparable vs Comparator
15. Iterator vs ListIterator
16. Fail-fast vs Fail-safe
17. Collections Utility Class
18. Time Complexity of Collections

🔹 Concurrency Collections

19. ConcurrentHashMap
20. CopyOnWriteArrayList

🟠 SECTION 5: Java Threads & Concurrency

1. What is Multithreading?
2. Thread Lifecycle
3. Creating Threads (Thread vs Runnable)
4. Callable & Future
5. Synchronization Basics
6. synchronized keyword
7. Deadlock (with example)
8. Inter-thread communication (wait, notify)
9. Executor Framework
10. Thread Pool (Fixed, Cached)
11. CompletableFuture (modern concurrency)
12. Real-world use cases

🔴 SECTION 6: Exception Handling

1. What is Exception?
2. Checked vs Unchecked Exceptions
3. try-catch-finally block
4. throw vs throws
5. Custom (User Defined) Exceptions
6. Best Practices for Exception Handling

🟡 SECTION 7: Java Memory Management (JVM Internals)

1. Stack vs Heap Memory
2. Method Area & Metaspace
3. Object Creation Flow
4. Garbage Collection Basics
5. Types of Garbage Collectors
6. Memory Leaks in Java
7. OutOfMemoryError
8. JVM Tuning Basics (Intro level)

⚫ SECTION 8: JVM, JDK, JRE Deep Dive

1. JDK vs JRE vs JVM (Detailed)
2. ClassLoader (Bootstrap, Extension, Application)
3. Java Execution Flow (Step-by-step)
4. Bytecode & JVM role
5. JIT Compiler (Just-In-Time Compilation)

🟤 SECTION 9: Serialization

1. What is Serialization?
2. Serializable Interface
3. Externalizable Interface
4. transient keyword
5. SerialVersionUID
6. Real-world use cases
7. Security concerns

⚪ SECTION 10: Cloning in Java

1. What is Object Cloning?
2. Cloneable Interface
3. Shallow Copy vs Deep Copy
4. Cloning limitations
5. Best practices & alternatives

🧠 SECTION 11: Interview Preparation Module (BONUS)

1. Top 50 Java Interview Questions
2. Scenario-based Questions
3. Coding + Concept Mix Questions
4. Common Mistakes Candidates Make
5. How to Explain Answers in Interviews