java - 在此示例代码中怎么可能实例化接口(interface)？

Question

我正在阅读的手册包含此示例，其中 ScheduledExecutorService正在创建中。但是，API 显示 ScheduledExecutorService是一个接口(interface)，而不是一个类。那么它怎么可能被实例化呢？

下面是示例代码:

import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledFuture;
import static java.util.concurrent.TimeUnit.*;

class BeeperControl {
    private final ScheduledExecutorService scheduler =
            Executors.newScheduledThreadPool(1);

    public void beepForAMinute() {
        final Runnable beeper = new Runnable() {
            public void run() {
                System.out.println("beep");
            }
        };

        final ScheduledFuture<?> future =
                scheduler.scheduleAtFixedRate(beeper, 250, 250, MILLISECONDS);
        scheduler.schedule(
                new Runnable() {
                    public void run() {
                        future.cancel(true);
                    }
                }, 3, SECONDS);
        while (!future.isDone()) {
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
            }
        }
        scheduler.shutdown();
    }

    public static void main(String[] args) {
        BeeperControl bc = new BeeperControl();
        bc.beepForAMinute();
    }
}

Answer 1

Executors.newSceduledThreadPool(int)是一个工厂方法，它返回一个实现 ScheduledExecutorService 接口(interface)的类。

根据 GrepCode:

public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize, ThreadFactory threadFactory) {
    return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
}

所以这里它返回实现 ScheduledExecutorService 接口(interface)的 ScheduledThreadPoolExecutor 的新实例。