.getTime() on both and subtract ?

Arne

import java.util.Date;
import java.util.concurrent.TimeUnit;

/**
* Computes the time difference between two dates, as a-b.
* @param units the desired units of the result. Units larger than
*   MILLISECONDS may cause truncation
*/
public long getDifference(Date a, Date b, TimeUnit units) {
  return units.convert(a.getTime()-b.getTime(), TimeUnit.MILLISECONDS);
}

Date is appropriate if you are echoing the Date information to a log,  
console, or are otherwise presenting the "time of occurence" somewhere in  
a human readable format. It uses System.currentTimeMillis under the hood.

System.currentTimeMillis is appropriate for exchanging time between two  
remote machines, or for saving a timestamp to be read back in a later  
session. But, for 2 or more machines, keep in mind that those machines may  
have the clock set slightly differently. System.currentTimeMillis is also  
dependant on the OS clock granularity, and on Windows this value only  
changes every 10ms or so. Lastly, if the system clock changes between  
calculations, then you don't get a measurement of the timelapse between  
said events. While it may be uncommon for a user to change the clock  
between events, many modern systems do have the option for network time  
syncs, which can automatically adjust the clock in the background.

System.nanoTime is appropriate for measuring elapsed time within a single  
VM session. If you just call System.nanoTime(), the result doesn't have  
any meaning that you can display. But differences between calls will give  
you a good measure of elapsed time. Of course, differences between  
System.nanoTime taken on one host vs another host aren't going to have  
much value or meaning, and the same goes for taking differences between  
the current VM session and a previous session. However, System.nanoTime is  
immune from clock changes, and will give you correct elapsed time results,  
and with much greater precision than System.currentTimeMillis.

Hope that helps to answer your question.

-Zig

see http://mindprod.com/jgloss/time.html