从时代开始经过的显示时间

Question

I am working on creating a time app that calculates both the current time and the time elapsed since midnight, January 1, 1970, in milliseconds. I went ahead and used Calendar and was able to successfully return the current time but for some reason the elapsed time returns 0. Not sure why that would be.

Here is my current code:

import java.util.Calendar;
import java.util.TimeZone;

public class TimeApp {
  public static void main(String[] args) {
     Time time1 = new Time();
     System.out.println("Hour: " + time1.getHour() + " Minute: " +
                   time1.getMinute() + " Second: " + time1.getSecond());

     Time time2 = new Time();
     System.out.println("Elapsed time since epoch: " + time2.getElapsedTime());
  }
}

final class Time {
  private int hour;
  private int minute;
  private int second;
  private long secondsSinceEpoch;

  public Time() {
    Calendar calendar = Calendar.getInstance();
    this.second = calendar.get(Calendar.SECOND);
    this.minute = calendar.get(Calendar.MINUTE);
    this.hour = calendar.get(Calendar.HOUR_OF_DAY);
  }

  public Time(long elapsedTime) {
    Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
    calendar.clear();
    calendar.set(2016, Calendar.SEPTEMBER, 9);
    secondsSinceEpoch = calendar.getTimeInMillis() / 1000L;
  }

@Override
   public String toString() {
     return hour + ":" + minute + ":" + second;
  }

  public int getHour() {
     return hour;
  }

  public int getMinute() {
     return minute;
  }

  public int getSecond() {
     return second;    
  }

  public long getElapsedTime() {
   return secondsSinceEpoch;
  }
}

Answer 1

You aren't setting elapsedTime for time2 . I think you wanted

Time time2 = new Time(System.currentTimeMillis());

And as pointed out in the comments, you aren't using elapsedTime in your constructor. Something like

public Time(long elapsedTime) {
    secondsSinceEpoch = elapsedTime / 1000;
}

Answer 2

I think you are using the wrong constructor for time2 since you called Time() and this version does not set secondsSinceEpoch . Try using your other constructor Time(long elapsedTime) with any long value and see if it works. Like this ..

Time time2 = new Time(10000);

Then re-write this constructor since you never use elapsedTime anyway, or delete it completely and re-write the first constructor to assign a value to secondsSinceEpoch .

public Time() {
    Calendar calendar = Calendar.getInstance();
    this.second = calendar.get(Calendar.SECOND);
    this.minute = calendar.get(Calendar.MINUTE);
    this.hour = calendar.get(Calendar.HOUR_OF_DAY);
    secondsSinceEpoch = calendar.getTimeInMillis() / 1000L;
  }