Exceptions, Assertions, and Threads - Java 6 - page 201

object as an argument. You could create a threaded StockTicker object with the follow-
ing statement:

StockTicker tix = new StockTicker();
Thread tickerThread = new Thread(tix);

Two good places to create threads are the constructor for an application and the construc-
tor for a component (such as a panel).

A thread is begun by calling its start() method, as in the following statement:

tickerThread.start();

The following statements can be used in a thread class to start the thread:

Thread runner;
if (runner == null) {
runner = new Thread(this);
runner.start();

}

The this keyword used in the Thread() constructor refers to the object in which these
statements are contained. The runner variable has a value of null before any object is
assigned to it, so the if statement is used to make sure that the thread is not started more
than once.

To run a thread, its start() method is called, as in this statement from the preceding
example:

runner.start();

Calling a thread's start() method causes another method to be called—namely, the
run() method that must be present in all threaded objects.

The run() method is the engine of a threaded class. In the introduction to threads, they
were described as a means of segregating processor-intensive work so that it ran sepa-
rately from the rest of a class. This kind of behavior would be contained within a
thread's run() method and the methods that it calls.

A Threaded Application
Threaded programming requires a lot of interaction among different objects, so it should
become clearer when you see it in action.

7

Listing 7.3 contains a class that finds a specific prime number in a sequence, such as the
10th prime, 100th prime, or 1,000th prime. This can take some time, especially for num-
bers beyond 100,000, so the search for the right prime takes place in its own thread.