setPriority not working as expected

[Jason Anderson]

I'm trying to teach myself about threads for the certification exam. I wrote the following sample code:

public class PrintThread
{
  public static void main(String[] args)
  {
    ThreadMaker thread1 = new ThreadMaker("Thread1", 1);
    ThreadMaker thread2 = new ThreadMaker("Thread2", 2);
    ThreadMaker thread3 = new ThreadMaker("Thread3", 3);
    ThreadMaker thread4 = new ThreadMaker("Thread4", 4);
    ThreadMaker thread5 = new ThreadMaker("Thread5", 5);
    thread1.start();
    thread2.start();
    thread3.start();
    thread4.start();
    thread5.start();
  }
}
class ThreadMaker extends Thread
{
    public ThreadMaker (String name, int priority)
    {
      super (name);
      setPriority (priority);
    }
    public void run ()
    {
          System.err.println(getName() + " with priority " + getPriority() + " executing.");
    }
}  

I would expect this to output:
Thread5
Thread4
Thread3
Thread2
Thread1
However, it prints:
Thread5
Thread3
Thread4
Thread1
Thread2
Can anyone tell me why this isn't running the threads in order of priority?
Thanks,
Jason

[Rob Ross]

Thread scheduling is always up to the specific underlying implementation. You don't really have control in java to affect this. You can make *suggestions* to the Thread scheduler, such as calling Thread.yield() or setting a thread's priority, but there's no guarantee that these calls will be used for anything.

[Jason Anderson]

Thank you, Rob. I appreciate the help.

[Peter Haggar]

This creates problems when you want to control the order of execution of waiting threads. You can't rely on priority, or on which thread has been waiting the longest, even on the same JVM. To control the order of waiting threads you can use the specific notification pattern. Details and programming examples are here.
Peter Haggar