java-concurrency

# Java Concurrency

Master Java's concurrency utilities including ExecutorService,
CompletableFuture, locks, and modern virtual threads for building
high-performance concurrent applications.

## Thread Basics

Understanding Java threads is fundamental to concurrency.

**Creating and running threads:**

```java
public class ThreadBasics {
    public static void main(String[] args) {
        // Using Thread class
        Thread thread1 = new Thread(() -> {
            System.out.println("Running in thread: " +
                Thread.currentThread().getName());
        });
        thread1.start();

        // Using Runnable
        Runnable task = () -> {
            for (int i = 0; i < 5; i++) {
                System.out.println("Task iteration: " + i);
            }
        };
        Thread thread2 = new Thread(task);
        thread2.start();

        // Join threads
        try {
            thread1.join();
            thread2.join();
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }
}
```

## ExecutorService

ExecutorService provides thread pool management and task scheduling.

**Basic executor usage:**

```java
import java.util.concurrent.*;

public class ExecutorBasics {
    public static void main(String[] args) {
        // Fixed thread pool
        ExecutorService executor = Executors.newFixedThreadPool(3);

        // Submit tasks
        for (int i = 0; i < 5; i++) {
            final int taskId = i;
            executor.submit(() -> {
                System.out.println("Task " + taskId + " on " +
                    Thread.currentThread().getName());
                return taskId * 2;
            });
        }

        // Shutdown executor
        executor.shutdown();
        try {
            if (!executor.awaitTermination(60, TimeUnit.SECONDS)) {
                executor.shutdownNow();
            }
        } catch (InterruptedException e) {
            executor.shutdownNow();
            Thread.c