Creating a unique timestamp in Java

Question

I need to create a timestamp (in milliseconds) in Java that is guaranteed to be unique in that particular VM-instance. I.e. need some way to throttle the throughput of System.cu

Answer 1

You could use System.nanoTime(), which is the most precise available system timer, and divide that by million to get milliseconds. While there are no formal guarantees on how often it's updated, I believe it's reasonable to assume that it updates way more (order(s) of magnitude) frequently than once per millisecond. Of course, if you create integer timestamps by less than millisecond interval, then they can't all be unique.

Note that the absolute value nanoTime() is arbitrary. If you want absolute time, calibrate it somehow, i.e. compare it to currentTimeMillis() when starting.