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Concurrency
Pausing Execution with Sleep
Thread.sleep causes the current thread to suspend
execution for a specified period. This is an efficient means of
making processor time available to the other threads of an application
or other applications that might be running on a computer system. The
sleep method can also be used for pacing, as shown in the
example that follows, and waiting for another thread with duties that are
understood to have time requirements, as with the
SimpleThreads example in a later section.
Two overloaded versions of sleep are provided: one
that specifies the sleep time to the millisecond and one that
specifies the sleep time to the nanosecond. However, these sleep times
are not guaranteed to be precise, because they are limited by the
facilities provided by the underlying OS. Also, the sleep period can
be terminated by interrupts, as we'll see in a later section.
In any case, you cannot assume that invoking sleep will
suspend the thread for precisely the time period specified.
The
SleepMessagessleep to print messages at four-second
intervals:
public class SleepMessages {
public static void main(String args[]) throws InterruptedException {
String importantInfo[] = {
"Mares eat oats",
"Does eat oats",
"Little lambs eat ivy",
"A kid will eat ivy too"
};
for (int i = 0; i < importantInfo.length; i++) {
//Pause for 4 seconds
Thread.sleep(4000);
//Print a message
System.out.println(importantInfo[i]);
}
}
}
Notice that
main declares that it
throws
InterruptedException. This is an exception that
sleep throws when another thread interrupts the current
thread while
sleep is active. Since this application has
not defined another thread to cause the interrupt, it doesn't bother
to catch
InterruptedException.
