Time class without javadoc comments

import java.util.Date;
import java.util.Calendar;
import java.text.SimpleDateFormat;

/**
 * Time is the current local clock time at an airport
 * at which a flight arrives or departs.
 * @author Some Student
 */
public class Time
{
    private Date aTime;
    private SimpleDateFormat df = new SimpleDateFormat("HHmm");

    public Time()
    {
        try {
        aTime = df.parse("0000");
        } catch (java.text.ParseException ex)
        { ex.printStackTrace();
        }

    }

    public Time(String time)
    {
        try {
        aTime = df.parse(time);
        } catch (java.text.ParseException ex)
        { ex.printStackTrace();
        }
    }

    public int subtract(Time other)
    {
        Calendar cal = Calendar.getInstance();
        cal.setTime(aTime);
        long ms = cal.getTimeInMillis();
        cal.setTime(other.aTime);
        ms -= cal.getTimeInMillis();
        final long msPerMin = 1000L * 60L;
        return (int) (ms / msPerMin);
    }

    public void addOne()
    {
        Calendar cal = Calendar.getInstance();
        cal.setTime(aTime);
        cal.add(Calendar.MINUTE,1);
        aTime = cal.getTime();
    }

    public String toString()
    {
        return df.format(aTime);
    }

    public int compareTo(Time other)
    {
        return aTime.compareTo(other.aTime);
    }
}