topics.txt

✅ MASTER STRUCTURE FOR YOUR JAVA REFERENCE REPO



1. Java Fundamentals

1.1 Syntax & Basics
- Variables, Data Types
- Operators
- Input/Output
- Control Flow (if/else, loops, switch)
- Type Casting (implicit, explicit)

1.2 Key Concepts
- Pass-by-value in Java
- Immutability
- Wrapper Classes & Autoboxing/Unboxing
- String, StringBuilder, StringBuffer

README.md 



2. OOP (Object-Oriented Programming)


2.1 Core OOP

- Classes & Objects
- Constructors
- this & super
- Encapsulation


2.2 Inheritance

-Types of inheritance
-Method Overriding
-final keyword


2.3 Polymorphism

-Compile-time polymorphism
-Runtime polymorphism

2.4 Abstraction

-Abstract classes
-Interfaces
-Multiple inheritance via interfaces

2.5 Object Class

-toString()
-equals()
-hashCode()
-clone()

3. Java Memory Model + JVM Internals
3.1 JVM Architecture

ClassLoader subsystem

Runtime Data Areas

Execution Engine

3.2 JMM (Java Memory Model)

Stack vs Heap

Method Area

Thread Stack behavior

Escape Analysis

TLAB

3.3 Garbage Collection

GC Types: Serial, Parallel, CMS, G1, ZGC

How GC works internally

GC Roots

Stop-the-world events

3.4 JIT & Performance

JIT compiler

Hotspot optimizations

4. Java Collections Framework
4.1 Core Interfaces

Collection

List

Set

Map

Queue/Deque

4.2 List Implementations

ArrayList

LinkedList

Vector/Stack

4.3 Set Implementations

HashSet

LinkedHashSet

TreeSet

4.4 Map Implementations

HashMap (with hashing demo)

LinkedHashMap

TreeMap

ConcurrentHashMap (advanced)

4.5 Queue/Deque

PriorityQueue

ArrayDeque

4.6 Under the Hood

Hashing

Load factors

Collisions (chaining, probing)

Fail-fast vs fail-safe iterators

5. Generics

Type parameters

Wildcards (? extends, ? super)

Bounded Types

Generic Methods

Type Erasure (under the hood)

6. Java 8+ Functional Programming
6.1 Lambda Expressions
6.2 Functional Interfaces

Predicate

Function

Consumer

Supplier

Custom functional interfaces

6.3 Streams

Stream operations

Intermediate vs Terminal ops

Collectors

Parallel Streams

6.4 Optional
7. Exception Handling
7.1 Basics

Exception hierarchy

Checked vs Unchecked

7.2 Best Practices

Custom exceptions

try-with-resources

Finally blocks

7.3 Under the Hood

Throwable internals

Stack traces

8. Multithreading + Concurrency
8.1 Basics

Thread class

Runnable

Executors

8.2 Concurrency Utilities

ExecutorService

Future, Callable

Thread pools

ScheduledExecutorService

8.3 Synchronization

Locks

synchronized

Volatile

Atomic classes

8.4 Advanced Concurrency

CountDownLatch

CyclicBarrier

Semaphore

Phaser

BlockingQueues

8.5 Fork/Join Framework
8.6 Under the Hood

Happens-before

Memory barriers

Thread lifecycle

9. File I/O & Serialization
9.1 Java I/O

Streams

Readers/Writers

9.2 NIO.2

Paths

Files

Channels

WatchService

9.3 Serialization

Serializable

Externalizable

SerialVersionUID

10. Java Networking

Sockets

ServerSocket

HTTP (basic)

URLConnection

11. Java Annotations

Built-in annotations

Custom annotations

Retention/Target policies

Annotation processing

12. Reflection & Dynamic Programming

Reflection basics

Accessing fields/methods

Creating objects dynamically

Method handles

Why reflection is slow

13. Design Patterns (Java-Focused)
13.1 Creational

Singleton (thread-safe)

Factory

Abstract Factory

Builder

Prototype

13.2 Structural

Adapter

Decorator

Facade

Composite

13.3 Behavioral

Strategy

Observer

Command

Template Method

14. Java Best Practices

Naming

Mutability

Defensive copying

ToString, equals, hashcode

Avoiding memory leaks

Effective Java principles

15. Advanced Topics
15.1 ClassLoaders

Parent delegation model

Custom class loaders

15.2 Modules (Java 9+)

module-info.java

Modular JARs

15.3 Records

Value-based classes

15.4 Sealed Classes
16. Build Tools

Maven

Gradle

How dependencies are resolved

Multi-module projects

17. Unit Testing

JUnit 5

Mockito

Testcontainers (optional but nice)

18. Java + Microservices (Optional Section)

Spring Boot basics

REST

Config

Filters, Interceptors

JPA

Hibernate internals