How do I calculate the elapsed time of an event in Java?

I would avoid using System.currentTimeMillis() for measuring elapsed time. currentTimeMillis() returns the 'wall-clock' time, which may change (eg: daylight savings, admin user changing the clock) and skew your interval measurements.

System.nanoTime(), on the other hand, returns the number of nanoseconds since 'some reference point' (eg, JVM start up), and would therefore not be susceptible to system clock changes.

This is some sample code.

long startTime = System.currentTimeMillis();
// Run some code;
long stopTime = System.currentTimeMillis();

System.out.println("Elapsed time was " + (stopTime - startTime) + " miliseconds.");

Apache Commons-Lang also has the StopWatch class suited just for your purpose. It uses System.currentTimeMillis(), so you'll still have resolution problems, but you can pause and do lap times and such. I use it as standard now for event stats.

http://commons.apache.org/lang/api-release/org/apache/commons/lang/time/StopWatch.html

java.lang.System.currentTimeMillis() or java.lang.System.nanoTime() ought to work to measure elapsed time.