🧵 Java Concurrency Playground

This repository is a pure Java learning project created to understand and experiment with the core concepts of Java concurrency using the java.util.concurrent package.

Each concurrency concept is implemented as a separate Java class with its own main() method, making it easy to run, observe, and modify behavior independently.

📚 Reference
This project is based on and inspired by Baeldung’s excellent guide:
https://www.baeldung.com/java-util-concurrent

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🎯 Objectives

• Understand why Java concurrency utilities exist
• Learn how different concurrency tools behave
• Observe real multithreaded execution
• Build a strong foundation before moving to:
  • CompletableFuture
  • Reactive programming
  • Virtual Threads (Java 21+)

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🗂 Project Structure

com.example.concurrency
 ├── ExecutorDemo.java
 ├── ExecutorServiceDemo.java
 ├── ScheduledExecutorDemo.java
 ├── FutureDemo.java
 ├── CountDownLatchDemo.java
 ├── CyclicBarrierDemo.java
 ├── SemaphoreDemo.java
 ├── ThreadFactoryDemo.java
 ├── BlockingQueueDemo.java
 ├── DelayQueueDemo.java
 ├── LockDemo.java
 └── PhaserDemo.java

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🔹 2.1 Executor

Executor represents a strategy for executing tasks.
It does not guarantee asynchronous execution.

Key takeaway:

Decouples task submission from execution strategy.

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🔹 2.2 ExecutorService

Provides a complete asynchronous execution framework with thread pooling and lifecycle management.

Key takeaway:

Backbone of async execution in Java.

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🔹 2.3 ScheduledExecutorService

Used for delayed and periodic tasks such as polling and heartbeats.

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🔹 2.4 Future

Represents the result of an asynchronous computation.

Limitation: blocking-only (get()).

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🔹 2.5 CountDownLatch

Allows one or more threads to wait until N operations complete.

Mental model:

Wait until all tasks finish.

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🔹 2.6 CyclicBarrier

Allows multiple threads to wait for each other at a common point.

Mental model:

All workers must arrive before proceeding.

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🔹 2.7 Semaphore

Controls how many threads access a resource simultaneously.

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🔹 2.8 ThreadFactory

Customizes thread creation (naming, daemon status, handlers).

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🔹 2.9 BlockingQueue

Designed for producer–consumer scenarios with built-in blocking.

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🔹 2.10 DelayQueue

Elements become available only after a delay expires.

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🔹 2.11 Lock (ReentrantLock)

Explicit locking with more control than synchronized.

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🔹 2.12 Phaser

Advanced synchronization barrier supporting:

• Multiple phases
• Dynamic registration
• Reusability

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▶️ How to Run

Each class contains a main() method.

javac ClassName.java
java com.example.concurrency.ClassName

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📚 Reference

https://www.baeldung.com/java-util-concurrent

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✅ Final Note

This project focuses on understanding:

• why concurrency tools exist
• what problems they solve
• when to use which

Building this intuition is key to mastering Java concurrency.