java中的方法优化

Question

我是 Java 新手。我正在尝试优化以下方法：public void myLongRunningMethod(){LongRunningOperation1();LongRunningOperation2();LongRunningOperation3();Log.Info("completion message goes here.")}LongRunningOperation1()、LongRunningOperation2() 和 LongRunningOperation3() 相互独立，它们的完成顺序无关紧要。但是只有在所有这些方法调用成功完成后才应该打印日志语句。如果我采用以下方法，由于它使用新线程，我相信方法的完成顺序不会得到保证。public String myMethod(){Thread thread1 = new Thread(() -> {    LongRunningOperation1();}).start();Thread thread2 = new Thread(() -> {    LongRunningOperation2();}).start();Thread thread3 = new Thread(() -> {    LongRunningOperation3();}).start();Log.Info("completion message goes here.")}

Answer 1

正如评论所提到的，最简单的方法是在 3 个线程中的每一个上调用 join() ：thread1.join(); thread2.join(); thread3.join();

或者使用 aCountDownLatch虽然它涉及更多（但在概念上可能更“正确”）：

• latch = new CountDownLatch(3)

• 在完成任务latch.countDown() 后让每个线程去做。

• 让主线程latch.await()- 瞧。

Answer 2

与其手动创建Threads ，不如使用ExecutorService API. 使用ExecutorService您可以提交长时间运行的操作，结果您将收到Future实例，让您等到操作完成。

请参阅下面的示例，该示例显示了该想法：

import java.util.ArrayList;

import java.util.List;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.Future;

import java.util.concurrent.TimeUnit;

public class Threads {

    public static void main(String[] args) {

        new Threads().myMethod();

    }

    private String myMethod() {

        ExecutorService executor = Executors.newFixedThreadPool(3);

        List<Future<?>> futures = new ArrayList<>(3);

        futures.add(executor.submit(this::LongRunningOperation1));

        futures.add(executor.submit(this::LongRunningOperation2));

        futures.add(executor.submit(this::LongRunningOperation3));

        for (Future<?> future : futures) {

            try {

                future.get();

            } catch (Exception e) {

                e.printStackTrace();

            }

        }

        System.out.println("All operations are finished!");

        return "Done";

    }

    private void LongRunningOperation1() {

        sleep(TimeUnit.SECONDS.toMillis(1));

        System.out.println("LongRunningOperation1 is finished!");

    }

    private void LongRunningOperation2() {

        sleep(TimeUnit.SECONDS.toMillis(2));

        System.out.println("LongRunningOperation2 is finished!");

    }

    private void LongRunningOperation3() {

        sleep(TimeUnit.SECONDS.toMillis(3));

        System.out.println("LongRunningOperation3 is finished!");

    }

    private void sleep(long millis) {

        try {

            Thread.sleep(millis);

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

    }

}

上面的代码打印：

LongRunningOperation1 is finished!

LongRunningOperation2 is finished!

LongRunningOperation3 is finished!

All operations are finished!