Java util.timer fixed delay not working?

问题:

I tried to see how a timer's fixed delay method (schedule) works but looks like i failed.

This is my code :

public class Timer_Test {    
  static Timer _a_timer;
  static int num_o_proc = 0;
  static int timer_call = 0;
  static double prog_begin_time;

public static void main(String[] args) {
    prog_begin_time = System.currentTimeMillis();

    _a_timer = new Timer();

    _a_timer.schedule(new TimerTask() {
        @Override
        public void run() {
            timer_call++;
            System.out.println(timer_call + " timer start   at " + (System.currentTimeMillis() - prog_begin_time));
            process();


            System.out.println(timer_call + " timer end   at " + (System.currentTimeMillis() - prog_begin_time));
            if (timer_call >= 5) {
                System.exit(0);
            }
        }
    }, 1000, 2000);
}

public static void process() {
    num_o_proc++;
    int local_num_o_proc = num_o_proc;
    System.out.println(local_num_o_proc + " process start   at " + (System.currentTimeMillis() - prog_begin_time));

    double _a_ = 0;
    for(int x=0; x<Integer.MAX_VALUE/2; x++) {
        _a_++;
    }
    System.out.println(local_num_o_proc + " process end   at " + (System.currentTimeMillis() - prog_begin_time));
  }
}

This is what I get :

1 timer start at 1000.0

1 process start at 1000.0

1 process end at 2109.0

1 timer end at 2109.0

2 timer start at 3000.0

2 process start at 3000.0

2 process end at 4109.0

2 timer end at 4109.0

3 timer start at 5000.0

3 process start at 5000.0

3 process end at 6109.0 .....

Shouldn't timer 2 start at 4109 (instead of 3000) since the first timer task ended at 2109 (2109 + 2000)? I tried using 'scheduleAtFixedRate' and it gave me exact same result. Did I do something wrong? Or is there some concept I fail to understand?

回答1:

Nope, that's how it is intended to work. The period is the period between start times, not the period between an end time and the next start time.

Basically you're telling it in plain english "start at 1 second and execute every two seconds after that" so 1, 3, 5, 7, etc is the logical interpretation.