If there's only one thread running(main) and sleep(1000) is invoked, will the thread sleep for exactly 1 second or atleast 1 second?

Question

In the below code:

 class Test {
      public static void main(String [] args) {
           printAll(args);
      }
      public static void printAll(String[] lines) {
           for(int i=0;i<lines.length;i++){
                System.out.println(lines[i]);
                Thread.currentThread().sleep(1000);
           }
      }
 }

Will each String in the array lines output:

1. With exactly 1-second pause between lines?
2. With at least 1-second pause between lines?

Answer 1

Approximately 1-second pause. The thread can be woken up beforehand and you'll get an InterruptedException, or the thread can sleep for 1000ms and then not get to run immediately, so it will be 1000ms + microseconds (or more, if there are higher priority threads hogging the CPU).

You're also calling it wrong. It's Thread.sleep(1000);, as a static method it always acts on the current thread and you can't make other threads sleep with it.

Answer 2

So it will sleep for exactly 1 second to the best of it's knowledge. The thread.sleep method is not perfect. See this and other related questions:

https://stackoverflow.com/a/18737109/4615177