Question

Why javax.xml.datatype.Duration.getMinutes() always returns 0 although the duration is incremented? If you run the code below longer than a minute you will see the output like this:

minutes: 0 , seconds: 61

I have never used this class before. Do I miss some basic knowledge about it?
Here is the code:

import java.util.Timer;
import java.util.TimerTask;

import javax.xml.datatype.DatatypeConfigurationException;
import javax.xml.datatype.DatatypeFactory;
import javax.xml.datatype.Duration;

public class TestDuration {

    class MyTimerTask extends TimerTask {
        DatatypeFactory df;
        long delay;
        Duration duration;

        public MyTimerTask(DatatypeFactory df, long delay) {
            this.df = df;
            this.delay = delay;
            duration = df.newDuration(0);
        }

        @Override
        public void run() {
            duration = duration.add(df.newDuration(delay));
            System.out.println("minutes: " + duration.getMinutes() + " , seconds: " + duration.getSeconds());
        }
    }

    public static void main(String[] args) {
        Timer timer = new Timer();
        final long delay = 1 * 1000;
        DatatypeFactory df = null;

        try {
            df = DatatypeFactory.newInstance();
        } catch (DatatypeConfigurationException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }

        MyTimerTask task = new TestDuration().new MyTimerTask(df, delay);
        timer.schedule(task, 0, delay);
    }
}

Answer 1

This is by design it seems. Take a look at the JavaDoc for Duration.add():

Computes a new duration whose value is this+rhs.

For example,

"1 day" + "-3 days" = "-2 days"
"1 year" + "1 day" = "1 year and 1 day"
"-(1 hour,50 minutes)" + "-20 minutes" = "-(1 hours,70 minutes)"
"15 hours" + "-3 days" = "-(2 days,9 hours)"
"1 year" + "-1 day" = IllegalStateException

I’ve emboldened the line that matters here. Clearly this class is only concerned with correctly representing the interval, rather than worrying about what makes sense from a "human" perspective.

Depending upon your use case, you can either continue to work with Duration, but understand that you will need to perform formatting calculations before displaying the value to a user, or you should move to a different class that does what you expect when you perform addition/subtraction. An example might be the Duration and Period classes from the Yoda Time project.