Java Reference
In-Depth Information
As a final example before moving on to a different subject, let's take a look at how we could
set up the fetching of a team roster on a regular basis, so we could be sure of always having
the most recent lineup. To do this, we could just change our run() method so that it is an
infinite loop that would end with a wait() on completing each iteration. But this means that
the thread that runs the RosterRetriever is around all the time, which wastes resources. A
better way is to use a Timer object, which can be used to schedule any number of recurring
tasks like this using a single thread.
To do this, we first have to change our RosterRetriever class to be a particular kind of
Runnable , the TimerTask . Once again, this just requires a change in the declaration of the
RosterRetriever class, since the all-important run() method is common to Thread , Run-
nable , and TimerTask objects. So now our RosterRetriever is declared as:
private class RosterRetriever extends TimerTask {
We also add a Timer to our local state in the StatReporterImpl , something like:
private Timer taskTimer = new Timer(true);
Now we can use the taskTimer to schedule recurring runs of our RosterRetriever objects.
To schedule a task, we could use a method like:
void setRetrieverUpdate(long hours, RosterRetriever rr){
long millis = TimeUnit.HOURS.convert(hours, TimeUnit.MILLISECONDS);
taskTimer.schedule(rr, System.currentTimeMillis(), millis);
This method will take a RosterRetriever object and a number of hours indicating how often
we want to get an update on that object. Each RosterRetriever will initially be run when
added to the taskTimer , and then will run again every hours hours. Note that we have to
convert the interval from hours to milliseconds, which are the units used throughout Java; this
is made somewhat easier by using the TimeUnit conversion functions.
There are lots of other ways to get multiple threads running in a program, as well as ways of
querying and manipulating those threads. This is just meant to give a flavor of what can be
done. By generating lots of threads, you can have your programming doing lots of different
things at the same time, thus making better use of the computing resources that are available
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