Java计时器

Question

我正在尝试使用计时器来安排应用程序中的重复事件.但是,我希望能够实时调整事件触发的时间段(根据用户输入).

例如:

public class HelperTimer extends TimerTask
{
    private Timer timer;
    //Default of 15 second between updates
    private int secondsToDelay = 15;

    public void setPeriod(int seconds)
    {
        this.secondsToDelay = seconds;
        long delay = 1000; // 1 second
        long period = 1000*secondsToDelay; // seconds
        if (timer != null) 
        {
            timer.cancel();
        }
        System.out.println(timer);
        timer = new Timer();
        System.out.println(timer);
        timer.schedule(this, delay, period);
    }
    public int getPeriod()
    {
        return this.secondsToDelay;
    }
}

然后我启动这个类的新实例并调用它的set period函数.但是,当我这样做时,我得到一个非法状态异常.你可以看到System.out.println(计时器); 在那里,因为我正在检查,并且确实,他们是两个不同的计时器...所以当我尝试在一个全新的Timer实例上运行计划调用时,为什么我会收到IllegalStateException!？!？!？!

java.util.Timer@c55e36
java.util.Timer@9664a1
Exception in thread "AWT-EventQueue-0" java.lang.IllegalStateException: Task already scheduled or cancelled
    at java.util.Timer.sched(Unknown Source)
    at java.util.Timer.schedule(Unknown Source)
    at HelperTimer.setPeriod(HelperTimer.java:38)

Answer 1

你不能像在这里那样重复使用TimerTask.

计时器的相关部分:

private void sched(TimerTask task, long time, long period) {
    if (time < 0)
        throw new IllegalArgumentException("Illegal execution time.");

    synchronized(queue) {
        if (!thread.newTasksMayBeScheduled)
            throw new IllegalStateException("Timer already cancelled.");

        synchronized(task.lock) {
            //Right here's your problem.
            //  state is package-private, declared in TimerTask
            if (task.state != TimerTask.VIRGIN)
                throw new IllegalStateException(
                    "Task already scheduled or cancelled");
            task.nextExecutionTime = time;
            task.period = period;
            task.state = TimerTask.SCHEDULED;
        }

        queue.add(task);
        if (queue.getMin() == task)
            queue.notify();
    }
}

您需要重构代码,以便创建新的TimerTask,而不是重新使用它.