Custom countdown second timer

Question

I'm making a card game and I found useful to include a 60 second countdown timer. Here is my approach:

import java.util.Timer;
import java.util.TimerTask;
public class SecondTimer {
 private Timer timer;
 private int countDown;
 private int secondsLeft;
 public SecondTimer() {
 timer = new Timer();
 }
 public void reset() {
 secondsLeft = countDown;
 // Decrease seconds left every 1 second.
 timer.schedule(new TimerTask() {
 @Override
 public void run() {
 secondsLeft--;
 if (secondsLeft == 0) {
 timer.cancel();
 }
 }
 }, 0, 1000);
 }
 public void setCountDown(int seconds) {
 this.countDown = seconds;
 }
 public int getSecondsLeft() {
 return secondsLeft;
 }
}

Is this considered clean? How can I test such classes?

• 200_success: What is hooked up to this code? How is the remaining time displayed? Is it supposed to trigger some action at the end of 60 seconds?

Answer 1

• Avoid using java.util.Timer. See Checking if a Java Timer is cancelled and java.util.Timer: Is it deprecated? Instead use a ScheduledExecutorService.
• When changing to a ScheduledExecutorService, don't cancel or shutdown your ScheduledExecutorService, instead cancel the FutureTask that you will get when scheduling a task.
• Don't decrease a counter once a second. Nothing guarantees that it will be called with exactly 1000 ms periodicity.

In your reset method, use System.nanoTime() (not System.currentTimeMillis) to calculate when the time is up, such as:

this.targetTime = System.nanoTime() + seconds * 1_000_000_000;

Then calculate in getSecondsLeft, by using System.nanoTime() again, how many seconds remain until the target nanosecond value has been reached.