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?

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.