as you can see at Java 5 API Doc the method only sets a new priority in the thread group. That won't invoke a thread termination! I've never tested if it works, but as I understand this the thread will run with lower prio, so that other threads get more CPU time.
Not, it only configures the priopridade of one thread. The value passing must be enters 1 to the 10. However some JVM not to implement of 1 to the 10 and yes of 1 to the 5. But if voc� to pass 10 jvm goes to adopt 5 as the maximum priority, you nao can pass a value is of this interval, therefore in execution time an exception occurs.