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在Java中实现并发执行可以通过多种方式，最常见的方式包括使用线程、ExecutorService、ForkJoinPool等。以下是几种常用并发执行的示例：

1. 使用Thread类

这是Java中最基础的并发实现，通过创建一个继承自Thread的类或实现Runnable接口来定义任务，并启动线程。

class MyTask extends Thread {@Overridepublic void run() {System.out.println(Thread.currentThread().getName() + " is executing task.");}
}public class Main {public static void main(String[] args) {MyTask task1 = new MyTask();MyTask task2 = new MyTask();task1.start();task2.start();}
}

2. 使用Runnable接口

Runnable接口更灵活，因为可以让任务类继承其他类，同时实现并发任务。

class MyRunnableTask implements Runnable {@Overridepublic void run() {System.out.println(Thread.currentThread().getName() + " is executing task.");}
}public class Main {public static void main(String[] args) {Thread thread1 = new Thread(new MyRunnableTask());Thread thread2 = new Thread(new MyRunnableTask());thread1.start();thread2.start();}
}

3. 使用ExecutorService

ExecutorService是Java中用于管理线程池的接口，能够更高效地执行并发任务，适合管理大量并发任务。

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;public class Main {public static void main(String[] args) {ExecutorService executor = Executors.newFixedThreadPool(2);Runnable task1 = () -> {System.out.println(Thread.currentThread().getName() + " is executing task 1.");};Runnable task2 = () -> {System.out.println(Thread.currentThread().getName() + " is executing task 2.");};executor.submit(task1);executor.submit(task2);executor.shutdown(); // 关闭线程池}
}

4. 使用Callable和Future

Callable接口允许任务返回结果，而Future可以用于获取结果或控制任务的执行状态。

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;public class Main {public static void main(String[] args) throws Exception {ExecutorService executor = Executors.newSingleThreadExecutor();Callable<Integer> task = () -> {System.out.println(Thread.currentThread().getName() + " is executing task.");return 123;};Future<Integer> future = executor.submit(task);// 阻塞等待结果Integer result = future.get();System.out.println("Task result: " + result);executor.shutdown();}
}

5. 使用ForkJoinPool

ForkJoinPool是专门用于并行处理任务的线程池，特别适合用于递归任务。

import java.util.concurrent.RecursiveTask;
import java.util.concurrent.ForkJoinPool;class FibonacciTask extends RecursiveTask<Integer> {private final int n;public FibonacciTask(int n) {this.n = n;}@Overrideprotected Integer compute() {if (n <= 1) {return n;}FibonacciTask f1 = new FibonacciTask(n - 1);FibonacciTask f2 = new FibonacciTask(n - 2);f1.fork();return f2.compute() + f1.join();}
}public class Main {public static void main(String[] args) {ForkJoinPool pool = new ForkJoinPool();FibonacciTask task = new FibonacciTask(10);Integer result = pool.invoke(task);System.out.println("Fibonacci result: " + result);}
}

这些例子展示了不同的Java并发编程方式，使用场景可以根据实际需求选择合适的实现方式。例如，对于简单的并发任务，Thread和Runnable就足够了；而对于复杂的任务，ExecutorService或ForkJoinPool可能会更高效。