Chapter 21
Digging Deeper into Concurrent Execution
Even in such a concise tutorial as this one, Java threads deserve two dedicated lessons. Let’s continue delving deeper into the world of multi-threaded applications.
Joining Threads
In Lesson 20 you learned that a thread can wait for a fixed period or for a notification on some event. Now let’s consider a scenario in which you need to start multiple threads and continue program execution only when all threads are complete. The Thread class has a method, join(), that you can use in this case.
Revisit the TestThreads3 program shown in Listing 20-9. If you run this program the system console will show the message “The main method of TestThreads3 is finished”; after that will it show the output of the portfolio and market news threads, which keep running for a while. If you want to make sure that the main method is waiting until the other two threads are finished, you can use the method join(), as shown in Listing 21-1.
Listing 21-1: Joining threads
public class TestThreadJoin { public static void main(String args[]){ MarketNews3 mn = new MarketNews3("Market News"); mn.start(); Portfolio3 p = new Portfolio3("Portfolio data"); p.start(); try{ mn.join(); p.join(); }catch (InterruptedException e){ e.printStackTrace(); } ...
