Java 并发（多线程）超详细

Java 中处理并发通常涉及到 Thread 类和其他并发工具类，如 Runnable, Callable, Future, FutureTask, Executor, ExecutorService, Semaphore, CountDownLatch, CyclicBarrier 等。以下是一个简单的例子，展示了如何使用这些工具来处理并发。

import java.util.concurrent.*;
 
public class ConcurrencyExample {
    public static void main(String[] args) {
        ExecutorService executor = Executors.newFixedThreadPool(4);
        CountDownLatch latch = new CountDownLatch(4);
 
        for (int i = 0; i < 4; i++) {
            final int taskId = i;
            executor.submit(new Runnable() {
                public void run() {
                    try {
                        System.out.println("Task " + taskId + " is running.");
                        Thread.sleep(2000);
                        System.out.println("Task " + taskId + " is done.");
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    } finally {
                        latch.countDown();
                    }
                }
            });
        }
 
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            executor.shutdown();
        }
 
        System.out.println("All tasks are completed.");
    }
}

这段代码创建了一个固定大小的线程池，然后提交了四个简单的任务。每个任务在运行前后打印一条消息，并休眠2秒钟。使用 CountDownLatch 来确保主线程等待所有任务完成后再继续执行。最后关闭线程池。这是一个并发编程的基本例子，展示了如何在Java中使用并发工具来提高程序的性能和响应性。