Thread

// Java Thread 예제 - 다양한 스레드 생성 및 동기화

import java.util.concurrent.*;
import java.util.concurrent.locks.*;

public class ThreadExample {

    // 1. Thread 클래스 상속
    static class MyThread extends Thread {
        private String name;

        public MyThread(String name) {
            this.name = name;
        }

        @Override
        public void run() {
            for (int i = 0; i < 5; i++) {
                System.out.println(name + ": " + i);
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            }
        }
    }

    // 2. Runnable 인터페이스 구현 (권장)
    static class MyRunnable implements Runnable {
        private String name;

        public MyRunnable(String name) {
            this.name = name;
        }

        @Override
        public void run() {
            System.out.println(name + " 실행 중 - " +
                Thread.currentThread().getName());
        }
    }

    // 3. 동기화 예제 - synchronized
    static class Counter {
        private int count = 0;

        // synchronized 메서드
        public synchronized void increment() {
            count++;
        }

        // synchronized 블록
        public void incrementWithBlock() {
            synchronized(this) {
                count++;
            }
        }

        public int getCount() {
            return count;
        }
    }

    // 4. ReentrantLock 사용
    static class SafeCounter {
        private int count = 0;
        private final ReentrantLock lock = new ReentrantLock();

        public void increment() {
            lock.lock();
            try {
                count++;
            } finally {
                lock.unlock();  // 반드시 finally에서 해제
            }
        }

        public int getCount() {
            return count;
        }
    }

    public static void main(String[] args) throws Exception {
        // Thread 클래스 사용
        MyThread t1 = new MyThread("Thread-1");
        t1.start();

        // Runnable 사용
        Thread t2 = new Thread(new MyRunnable("Runnable-1"));
        t2.start();

        // Lambda 표현식 (Java 8+)
        Thread t3 = new Thread(() -> {
            System.out.println("Lambda Thread 실행");
        });
        t3.start();

        // ExecutorService - 스레드 풀 (권장)
        ExecutorService executor = Executors.newFixedThreadPool(4);

        for (int i = 0; i < 10; i++) {
            final int taskId = i;
            executor.submit(() -> {
                System.out.println("Task " + taskId + " - " +
                    Thread.currentThread().getName());
            });
        }

        // Future를 통한 결과 받기
        Future future = executor.submit(() -> {
            Thread.sleep(1000);
            return 42;
        });

        System.out.println("결과: " + future.get());  // 블로킹

        executor.shutdown();
        executor.awaitTermination(5, TimeUnit.SECONDS);

        // CompletableFuture (Java 8+, 비동기 체이닝)
        CompletableFuture.supplyAsync(() -> "Hello")
            .thenApply(s -> s + " World")
            .thenAccept(System.out::println)
            .join();
    }
}