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Is println() always executed as an 'atomic unit' by a thread?

 
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When experimenting with threads, it seems as though when a given thread executes a println() statement, no other thread can 'but-in' and insert any of its own printout in the middle.

For example.


The screen output always consists of entire lines of As or entire lines of Bs, even if I make the two strings much much longer.

Is that just luck, or behind the scenes, is each thread acquiring a lock on say System.console() for the duration of the activity required for each println() statement?
 
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System.out is an instance of java.io.PrintStream.

I checked its sources (JDK 1.8_60) and it looks like the println(String) method uses synchronization.
 
Richard Hayward
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Thank you Pawel.

I'd not realized that source code came as part of the java distribution.
 
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