java - Using new Date() as unique identifier -

imagine have proccess creates 1000 entities each second. each of these entities call setter :

newentity.setdate(new date()); 

1) possible 2 entities recieve same date? or safe assume unique identifier effect date field?

2) if answer question #1 :"yes" - let's make minor tweak: lets create function:

public static synchronized date getdate() {      return new date(); } 

will work now?

newentity.setdate(getdate()); 

3)

system.nanotime()? 

edit 4) :

public static synchronized date getdate() {      thread.sleep(1000);      return new date(); } 

thanks.

a simple test shows 2 consecutive calls new date() can return same date. making method synchronized won't make difference.

if need unique id, use atomicinteger counter , return counter.getandincrement(); new ids.

ps: using system.nanotime() won't either resolution os , processor dependent , low enough 2 consecutive calls can return same result too.

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edit

your 4th proposal sleep second in synchronized method solve unicity issue (although pointed out yshavit, nothing in javadoc guarantees it). note using date unique id bad idea in itself: dates mutable calling code change id settime method (by mistake or on purpose).

finally, if want id date related, use long representing milliseconds since epoch , keep track of existing ids - this:

private static final set<long> usedids = new hashset<> (); public static synchronized long getuniqueid() {     long millis;     {         millis = system.currenttimemillis();     } while (!usedids.add(millis));     return millis; }