Java 并发编程

线程基础

// 方式一：继承 Thread
Thread t = new Thread(() -> System.out.println("Hello from thread"));
t.start();

// 方式二：ExecutorService
ExecutorService executor = Executors.newFixedThreadPool(4);
executor.submit(() -> System.out.println("Task 1"));
executor.submit(() -> System.out.println("Task 2"));
executor.shutdown();

synchronized 与锁

// 同步方法
public synchronized void increment() {
    count++;
}

// 同步代码块
synchronized (lock) {
    // 临界区
}

// ReentrantLock（更灵活）
private final ReentrantLock lock = new ReentrantLock();

public void transfer() {
    lock.lock();
    try {
        // 业务逻辑
    } finally {
        lock.unlock();
    }
}

并发集合

集合	特点
`ConcurrentHashMap`	高并发哈希表，分段锁
`CopyOnWriteArrayList`	读无锁，写时复制
`BlockingQueue`	生产者-消费者模式
`ConcurrentLinkedQueue`	无锁并发队列

BlockingQueue<String> queue = new ArrayBlockingQueue<>(10);

// 生产者
queue.put("item");

// 消费者
String item = queue.take();

CompletableFuture

Java 8 引入的异步编程工具：

CompletableFuture<String> future = CompletableFuture
    .supplyAsync(() -> fetchData())
    .thenApply(data -> processData(data))
    .thenApply(result -> formatResult(result))
    .exceptionally(ex -> "Error: " + ex.getMessage());

String result = future.get();

虚拟线程（Java 21）

轻量级线程，百万级并发不再是梦想：

// 创建虚拟线程
Thread.ofVirtual().start(() -> {
    System.out.println("Virtual thread: " + Thread.currentThread());
});

// 虚拟线程 ExecutorService
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    IntStream.range(0, 100_000).forEach(i -> {
        executor.submit(() -> {
            Thread.sleep(Duration.ofSeconds(1));
            return i;
        });
    });
} // 10 万个任务，每个睡 1 秒，约 1 秒全部完成