（原创）定时线程池中scheduleWithFixedDelay和scheduleAtFixedRate的区别

scheduleAtFixedRate 没有什么歧义，很容易理解，就是每隔多少时间，固定执行任务。

scheduleWithFixedDelay 比较容易有歧义

貌似也是推迟一段时间执行任务，但Oracle的解释如下,delay 的意思是当结束前一个执行后延迟的时间

scheduleWithFixedDelay Parameters:

command - the task to execute

initialDelay - the time to delay first execution

delay - the delay between the termination of one execution and the commencement of the next

unit - the time unit of the initialDelay and delay parameters

scheduleWithFixedDelay 比如当前一个任务结束的时刻，开始结算间隔时间，如0秒开始执行第一次任务，任务耗时5秒，任务间隔时间3秒，那么第二次任务执行的时间是在第8秒开始。

import java.util.Date;

public class WorkerThread implements Runnable{

private String command;

    public WorkerThread(String s){
        this.command=s;
    }

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+" Start. Time = "+new Date());
        processCommand();
        System.out.println(Thread.currentThread().getName()+" End. Time = "+new Date());
    }

    private void processCommand() {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    @Override
    public String toString(){
        return this.command;
    }
}

import java.util.Date;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class ScheduledThreadPool {

    public static void main(String[] args) throws InterruptedException {
        ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);

        System.out.println("Current Time = "+new Date());
        for(int i=0; i<10; i++){
            Thread.sleep(1000);
            WorkerThread worker = new WorkerThread("do heavy processing");
            //scheduledThreadPool.schedule(worker, 3, TimeUnit.SECONDS);
            //scheduledThreadPool.scheduleAtFixedRate(worker, 5, 5, TimeUnit.SECONDS);
            scheduledThreadPool.scheduleWithFixedDelay(worker, 5, 3, TimeUnit.SECONDS);
        }
        Thread.sleep(300000);

        scheduledThreadPool.shutdown();
        while(!scheduledThreadPool.isTerminated()){
        }
        System.out.println("Finished all threads");
    }

}