Timer scheduleAtFixedRate与schedule的区别_JAVA_编程开发_程序员俱乐部

scheduleAtFixedRate与schedule的区别主要是基准时间点以及第一次执行时执行的次数

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?timer.scheduleAtFixedRate(TimerTask, startTime, period): 如果执行时间executeTime>startTime，则一执行就会从startTime开始，每隔peroid跑TimerTask。以startTime为起点

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class="java">public class TimerTest {
    public static void main(String args[]) throws ParseException {
        SimpleDateFormat f = new SimpleDateFormat(
                "yyyy-MM-dd HH:mm:ss");
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                System.out.println("do task at "+new Date());
            }
        }, f.parse("2014-04-15 17:20:00"), 10 * 1000);
    }
}

?执行时间是17:28:01，执行结果是

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do task at Tue Apr 15 17:28:01 CST 2014
do task at Tue Apr 15 17:28:01 CST 2014
do task at Tue Apr 15 17:28:01 CST 2014
do task at Tue Apr 15 17:28:01 CST 2014
do task at Tue Apr 15 17:28:01 CST 2014
do task at Tue Apr 15 17:28:01 CST 2014
do task at Tue Apr 15 17:28:01 CST 2014
//以上是开始执行时立刻执行了X次，X是从startTime开始每隔peroid时间执行一次直到executeTime.
//以下是以startTime开始每隔peroid执行一次
do task at Tue Apr 15 17:28:10 CST 2014
do task at Tue Apr 15 17:28:20 CST 2014

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timer.schedule(TimerTask, startTime, period): 如果执行时间executeTime>startTime，其实基准时间已经变成executeTime，每隔peroid跑TimerTask。以executeTime为起点。(如果executeTime<startTime，则基准时间还是startTime)

同样的例子，结果是

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do task at Tue Apr 15 17:28:01 CST 2014
do task at Tue Apr 15 17:28:11 CST 2014
do task at Tue Apr 15 17:28:21 CST 2014

?就在executeTime执行一次，然后以executeTime为基准点每隔peroid执行一次

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?scheduleAtFixedRate与schedule的下一次执行时间都是上一次执行完成时间+间隔时间，只是由于第一次执行时executeTime>startTime时造成的基准时间不一致而造成的的。

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另外，如果task的执行时长>间隔时长peroid, 则下一次执行时间是上一次完成时间，?scheduleAtFixedRate与schedule和都是一样的。

public class TimerTest {
    public static void main(String args[]) throws ParseException {
        SimpleDateFormat f = new SimpleDateFormat(
                "yyyy-MM-dd HH:mm:ss");
        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("start do task at "+new Date());
                try{
                    Thread.sleep(11000);
                }catch(Exception e){
                    e.printStackTrace();
                }
                System.out.println("end do task at "+new Date());
            }
        }, f.parse("2014-04-15 18:01:00"), 10 * 1000);
    }
}

?执行时间是18:01:25, 执行结果

start do task at Tue Apr 15 18:01:25 CST 2014
end do task at Tue Apr 15 18:01:36 CST 2014
//这里可以看出下次执行时间就是上次完成时间
start do task at Tue Apr 15 18:01:36 CST 2014
end do task at Tue Apr 15 18:01:47 CST 2014
start do task at Tue Apr 15 18:01:47 CST 2014
end do task at Tue Apr 15 18:01:58 CST 2014

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scheduleAtFixedRate结果也是一样的