Decrement at Regular Intervals in Java

Question

I'm writing an application in Java, but need to know how to subtract from a variable once every second. What's the easiest way to do this? Thanks!

Answer 1

Use a java.util.Timer to create a TimerTask.

Answer 2

The name of the very Java class you need to use to do repeating operations is already sitting there in one of your tags! ;)

Answer 3

class YourTimer extends TimerTask
{
  public volatile int sharedVar = INITIAL_VALUE;

  public void run()
  {
    --sharedVar;
  }

  public static void main(String[] args)
  {
     Timer timer = new Timer();

     timer.schedule(new YourTimer(), 0, 1000);
     // second parameter is initial delay, third is period of execution in msec
  }
}

Remeber that Timer class is not guaranteed to be real-time (as almost everything in Java..)

Answer 4

While the Timer class will work, I recommend using a ScheduledExecutorService instead.

While their usage is extremely similar, ScheduledExecutorService is newer, more likely to receive ongoing maintenance, fits in nicely with other concurrent utilities, and might offer better performance.

Answer 5

What are you trying to achieve? I would not try relying on the timer to properly fire exactly once per second. I would simply record the start time, and whenever a timer fires, recalculate what the value of the variable should be. Here's how I would do it...

class CountdownValue {
  private long startTime;
  private int startVal;

  public CountdownValue(int startVal)
  {
     startTime = System.currentTimeMillis();
  }

  public int getValue()
  {
     return startVal - (int)((System.currentTimeMillis() - startTime)/1000);
  }
}