Java 执行器：当任务完成时，如何在不阻塞的情况下收到通知

Java 执行器：当任务完成时，如何在不阻塞的情况下收到通知？

java
import java.util.concurrent.*;
public class ExecutorExample {
    public static void main(String[] args) throws InterruptedException, ExecutionException {
        ExecutorService executor = Executors.newSingleThreadExecutor();
        Future future = executor.submit(() -> {
            // 执行一些耗时的操作
            Thread.sleep(2000);
            return 42;
        });
        // 检查任务是否完成
        while (!future.isDone()) {
            System.out.println("任务尚未完成...");
            Thread.sleep(500);
        }
        // 获取任务的结果
        int result = future.get();
        System.out.println("任务完成，结果为：" + result);
        executor.shutdown();
    }
}

java
import java.util.concurrent.*;
public class ExecutorExample {
    public static void main(String[] args) throws InterruptedException, ExecutionException {
        ExecutorService executor = Executors.newFixedThreadPool(5);
        CompletionService completionService = new ExecutorCompletionService<>(executor);
        for (int i = 0; i < 10; i++) {
            final int taskId = i;
            completionService.submit(() -> {
                // 执行一些耗时的操作
                Thread.sleep(2000);
                return taskId;
            });
        }
        for (int i = 0; i < 10; i++) {
            Future future = completionService.take();
            int result = future.get();
            System.out.println("任务 " + result + " 完成");
        }
        executor.shutdown();
    }
}