Java定时器 [英] Java Timer

问题描述

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).

I'm trying to use a timer to schedule a recurring event in an application. However, I want to be able to adjust the period at which the event fires in real time (according to the users input).

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;
    }
}

然后我开始这个类的一个新实例并调用它的设置周期函数.但是，当我这样做时，我会收到非法状态异常.你可以看到 System.out.println(timer);在那里，因为我正在检查，是的，确实，它们是两个不同的计时器......那么当我尝试在全新的 Timer 实例上运行调度调用时，为什么会收到 IllegalStateException ！?！?！?！

I then start a new instance of this class and call its set period function. However, when I do that, I get an Illegal state exception. You can see the System.out.println(timer); in there because I'm checking, and yep sure enough, they are two different timers... so why am I getting an IllegalStateException when I try to run a schedule call on a brand new Timer instance!?!?!?!

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)

推荐答案

您不能像这里那样重复使用 TimerTask.

You can't reuse a TimerTask as you're doing here.

Timer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，以便创建一个新的 TimerTask，而不是重复使用一个.

You'll need to refactor your code so that you create a new TimerTask, rather than re-using one.

这篇关于Java定时器的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！