Pausing/stopping and starting/resuming Java TimerTask continuously?

Question

I have one simple question regarding Java TimerTask. How do I pause/resume two TimerTask tasks based on a certain condition? For example I have two timers that run between each other. When a certain condition has been met inside the task of first timer, the first timer stops and starts the second timer, and the same thing happens when a certain condition has been met inside the task of second timer. The class below shows exactly what I mean: ``` public class TimerTest { Timer timer1; Timer timer2; volatile boolean a = false; public TimerTest() { timer1 = new Timer(); timer2 = new Timer(); } public void runStart() { timer1.scheduleAtFixedRate(new Task1(), 0, 1000); } class Task1 extends TimerTask { public void run() { System.out.println("Checking a"); a = SomeClass.getSomeStaticValue(); if (a) { // Pause/stop timer1, start/resume timer2 for 5 seconds timer2.schedule(new Task2(), 5000); } } } class Task2 extends TimerTask{ public void run() { System.out.println("Checking a"); a = SomeCl…

Accepted Answer

From `TimerTask.cancel()`:

Note that calling this method from within the run method of a repeating timer task absolutely guarantees that the timer task will not run again.

So once cancelled, it won't ever run again. You'd be better off instead using the more modern `ScheduledExecutorService` (from Java 5+).

Edit: The basic construct is:

```
ScheduledExecutorService exec = Executors.newSingleThreadScheduledExecutor();
exec.scheduleAtFixedRate(runnable, 0, 1000, TimeUnit.MILLISECONDS);
```

but looking into it there's no way of cancelling that task once its started without shutting down the service, which is a bit odd.

`TimerTask` might be easier in this case but you'll need to create a new instance when you start one up. It can't be reused.

Alternatively you could encapsulate each task as a separate transient service:

```
final ScheduledExecutorService exec = Executors.newSingleThreadScheduledExecutor();
Runnable task1 = new Runnable() {
  public void run() {
    a++;
    if (a == 3) {
      exec.shutdown();
      exec = Executors.newSingleThreadScheduledExecutor();
      exec.scheduleAtFixedRate(task2, 0, 1000, TimeUnit.MILLISECONDS)
    }
  }
};
exec.scheduleAtFixedRate(task1, 0, 1000, TimeUnit.MILLISECONDS);
```

Pausing/stopping and starting/resuming Java TimerTask continuously?

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