Concurrency - SCJP Sun Certified Programmer for Java Platform SE6 - page 352

Threads that have the same priority execute in a round-robin fashion, meaning that the
currently executing thread runs until it either terminates or transitions into a waiting state.
Use the static yield or sleep method of the Thread class if you are concerned a thread is
hogging the CPU. The sleep method causes a thread to transition into the TIMED_WAITING
state until the specifi ed amount of time elapses. The yield method causes the currently
running thread to give up the CPU, allowing another thread to be scheduled. Figure 5.3
shows the transitions for sleep and yield .

FIGURE 5.3 The thread state transition of the sleep and yield methods

TIMED_WAITING

timeout

sleep()

yield()

RUNNABLE CPU

scheduled

Notice that invoking yield does not change the state of a thread; it just pushes the
thread to the back of the line of other runnable threads. The sleep method actually
transitions a thread from RUNNABLE to TIMED_WAITING . When the specifi ed time elapses, the
thread becomes RUNNABLE and goes to the back of the line of runnable threads.
To demonstrate the yield method, I added a call to yield in the run method of the
SayHello class from the previous section:
public void run() {

for(int i = 1; i <= 10; i++) {
System.out.print(greeting);
Thread.yield();
}
System.out.println(“End of run”);
}

Similarly, I added a call to yield in the CountToTen program, which now yields after
printing each int :

for(int k = 1; k <= 10; k++) {
System.out.print(k);
Thread.yield();
}

Running the program again results in an entirely different output than before the yields
were added:

1Hi2Hi3Hi4Hi5Hi6Hi7Hi8Hi9Hi10HiEnd of main
End of run