有时侯，自己只需要简单写代码就可以证实的东西，可以自己先实验下，避免部分不正确的言论误导自己

import java.util.Date;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
public class Test {
    public static void main(String[] args) {
        ScheduledExecutorService executorServiceRate = Executors.newSingleThreadScheduledExecutor();
        ScheduledExecutorService executorServiceDelay = Executors.newScheduledThreadPool(2);
        executorServiceRate.scheduleAtFixedRate(new Task("fixed-rate"), 0, 1, TimeUnit.SECONDS);
        executorServiceDelay.scheduleWithFixedDelay(new Task("fixed-delay"), 0, 1, TimeUnit.SECONDS);
    }
}
class Task implements Runnable {
    private String name;
    public Task(String name) {
        this.name = name;
    }
    @Override
    public void run() {
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("name = " + name + ", now = " + new Date());
    }
}

控制台输出

name = fixed-rate, now = Wed Nov 29 18:48:06 CST 2017
name = fixed-delay, now = Wed Nov 29 18:48:06 CST 2017
name = fixed-rate, now = Wed Nov 29 18:48:08 CST 2017
name = fixed-delay, now = Wed Nov 29 18:48:09 CST 2017
name = fixed-rate, now = Wed Nov 29 18:48:10 CST 2017
name = fixed-rate, now = Wed Nov 29 18:48:12 CST 2017
name = fixed-delay, now = Wed Nov 29 18:48:12 CST 2017
name = fixed-rate, now = Wed Nov 29 18:48:14 CST 2017
name = fixed-delay, now = Wed Nov 29 18:48:15 CST 2017
name = fixed-rate, now = Wed Nov 29 18:48:16 CST 2017
name = fixed-delay, now = Wed Nov 29 18:48:18 CST 2017

总结

• 无论是 scheduleAtFixedRate 还是 scheduleWithFixedDelay 都会是在上一次任务执行完才执行（及同一个时间点，不会有2个task都在运行）
• 区别在于， FixedRate 执行完后，如果已经到了（超过）下一个的执行时间点的情况，会直接执行，而FixedDelay，会顺着当前的时间点延到下一个周期再开始执行