How do I say 5 seconds from now in Java?

Question

I am looking at the Date documentation and trying to figure out how I can express NOW + 5 seconds. Here's some pseudocode:

import java.util.Date
public class Main {

    public static void main(String args[]) {
         Date now = new Date();
         now.setSeconds(now.getSeconds() + 5);
    }
}

Answer 1

You can use:

now.setTime(now.getTime() + 5000);

Date.getTime() and setTime() always refer to milliseconds since January 1st 1970 12am UTC.

However, I would strongly advise you to use Joda Time if you're doing anything more than the very simplest of date/time handling. It's a much more capable and friendly library than the built-in support in Java.

Answer 2

I just found this from java docs

import java.util.Calendar;

public class Main {

  public static void main(String[] args) {
    Calendar now = Calendar.getInstance();
    System.out.println("Current time : " + now.get(Calendar.HOUR_OF_DAY) + ":"
        + now.get(Calendar.MINUTE) + ":" + now.get(Calendar.SECOND));

    now.add(Calendar.SECOND, 100);
    System.out.println("New time after adding 100 seconds : " + now.get(Calendar.HOUR_OF_DAY) + ":"
        + now.get(Calendar.MINUTE) + ":" + now.get(Calendar.SECOND));
  }
}

Is there a convention I should be aware of?

Answer 3

Date is almost entirely deprecated and is still there for backward compatibility reasons. If you need to set particular dates or do date arithmetic, use a Calendar:

Calendar calendar = Calendar.getInstance(); // gets a calendar using the default time zone and locale.
calendar.add(Calendar.SECOND, 5);
System.out.println(calendar.getTime());

Answer 4

From the one-liner-hacky dep.:

new Date( System.currentTimeMillis() + 5000L)

As I understand it from your example, 'now' is really 'now', and "System.currentTimeMillis()' happens to represent that same 'now' concept :-)

But, yup, for everything more complicated than that the Joda time API rocks.

Answer 5

As others have pointed out, in Joda it's much easier:

DateTime dt = new DateTime();
DateTime added = dt.plusSeconds(5);

I would strongly recommend you migrate to Joda. Almost any Java date-related question on SO resolves to a Joda recommendation :-) The Joda API is supposed to be the basis of the new standard Java date API (JSR310), so you'll be migrating towards a new standard.