Miscellaneous Utilities - The Java Programming Language - page 968

22.7. Timer and TimerTask
The Timer class helps you set up tasks that will happen at some future
point, including repeating events. Each Timer object has an associated
thread that wakes up when one of its TimerTask objects is destined to run.
For example, the following code will set up a task that prints the virtual
machine's memory usage approximately once a second:
Timer timer = new Timer(true);
timer.scheduleAtFixedRate(new MemoryWatchTask(), 0, 1000);
This code creates a new Timer object that will be responsible for schedul-
ing and executing a MemoryWatchTask (which you will see shortly). The TRue
passed to the Timer constructor tells Timer to use a daemon thread (see
page 369 ) so that the memory tracing activity will not keep the virtual
machine alive when other threads are complete.
The scheduleAtFixedRate invocation shown tells timer to schedule the task
starting with no delay (the 0 that is the second argument) and re-
peat it every thousand milliseconds (the 1000 that is the third argu-
ment). So starting immediately, timer will invoke the run method of a
MemoryWatchTask :
import java.util.TimerTask;
import java.util.Date;
public class MemoryWatchTask extends TimerTask {
public void run() {
System.out.print(new Date() + ": " );
Runtime rt = Runtime.getRuntime();
System.out.print(rt.freeMemory() + " free, ");
System.out.print(rt.totalMemory() + " total");
System.out.println();
}
}